masters thesis

Delivery System Handle Platform

Kevin O’Toole BSc (Hons)

Submitted as part requirement for Master of Science Degree in Medical Device Design,

Faculty of Design,

The National College of Art and Design,

A Recognized College of the National University of Ireland

Supervisor: Paul Fortune

31st August 2012

National College of Art and Design

Declaration on Plagiarism

Name: Kevin O’Toole

Student ID Number: 11100591

Course: MSc Medical Device Design

I hereby declare that this dissertation is entirely my own work and that it has not been

submitted as an exercise for a diploma or a degree in any other college or university. I agree

that the Library may lend or copy the dissertation upon request from the date deposit of the

dissertation.

Signed: ____________________________________________________________

Dated: ________________________________________

Word Count: 11,476

Acknowledgements

I would like to thank my course director Paul Fortune for all the advice and feedback received

throughout the duration of the project. Also, Caroline Kinsella for all her efforts in helping me

with workshop facilities.

I would also like to thank all of the staff members at Medtronic Cardiovascular Ltd Galway, in

particular Patrick Griffon, John Gallagher, and Caoimhin O’Donnellan for all of they’re help

throughout the design project.

Abstract

The goal of this project is to design a handle which can manually deliver a replacement heart

valve through the body’s cardiovascular system and into a patient’s diseased native valve. The

proposed design within this report offers effective controllability which requires a sequence of

rotary and linear operations for the deployment and release of the prosthetic replacement

heart valve.

This report details the importance of Trans-catheter Valve Technology in the medical field.

Research into current handle designs is explored, highlighting the necessary mechanical

operations involved.

Concepts are generated in accordance with a devised design brief, and development of a single

concept is carried out. A three-dimensional computer-aided design model is drawn up, and a

further testing and evaluation phase is conducted to ensure maximum design efficacy.

The evaluation of the final design is explained and the project concludes with recommendations

for further development.

Contents

Table of Contents Acknowledgements ............................................................................................................... 3

Abstract ................................................................................................................................ 4

Contents ............................................................................................................................... 6

1. Introduction ................................................................................................................... 6

1.1 Project Overview ................................................................................................................... 6

1.2 Project Aims .......................................................................................................................... 7

1.3 Project Objectives ................................................................................................................. 8

2. Research ......................................................................................................................... 9

2.1 Research Aims and Objectives .............................................................................................. 9

2.1.1 Area Background: ........................................................................................................... 9

2.1.2 User Identification: ........................................................................................................ 9

2.1.3 Product Research: ........................................................................................................ 10

2.2 Research Methods .............................................................................................................. 10

2.2.1 Literature Review: ........................................................................................................ 10

2.2.2 Observation: ................................................................................................................. 10

2.2.3 Expert Users: ................................................................................................................ 10

2.2.4 Photographic study: ..................................................................................................... 11

2.3 Results ................................................................................................................................. 11

2.3.1 Treatment for Heart Disease: ...................................................................................... 11

2.3.2 Anatomy of the Heart: ................................................................................................. 11

2.3.3 Trans-catheter Procedure: ........................................................................................... 14

2.3.4 Additional Findings ...................................................................................................... 15

2.5 Discussion and Design Specifications ............................................................................. 16

3 Design and Development .............................................................................................. 18

3.1 Introduction ........................................................................................................................ 18

3.2 Proposed Concept Design ................................................................................................... 18

3.2.1 Process: ........................................................................................................................ 19

3.2.2 Micro Retraction Mechanism: ..................................................................................... 21

3.2.3 Macro Retraction: ........................................................................................................ 22

3.2.4 Ergonomics Input: ........................................................................................................ 23

3.3 Further Development ......................................................................................................... 25

4 Phase 2 Development ................................................................................................... 27

4.1 Background ......................................................................................................................... 27

4.2 Further Design Specifications ............................................................................................. 27

4.3 Phase 2 Scheduling ............................................................................................................. 28

4.4 Phase 2 Objectives .............................................................................................................. 29

5 Design Modifications .................................................................................................... 30

5.1 Shaft Guides ........................................................................................................................ 30

5.1.1 Design Analysis:............................................................................................................ 31

5.1.2 Component to Shaft Bonding: ..................................................................................... 34

5.1.3 Conclusion: ................................................................................................................... 37

5.2 Shafts ................................................................................................................................... 39

5.2.1 Catheter Shaft Sizing: ................................................................................................... 39

5.2.2 Shaft Reinforcement: ................................................................................................... 41

5.2.3 Conclusion: ................................................................................................................... 43

5.3 Shaft Manipulation ............................................................................................................. 44

5.3.1 Guide Extrusion Length: ............................................................................................... 45

5.3.2 Conclusion: ................................................................................................................... 47

5.4 Micro Precision ................................................................................................................... 48

5.4.1 Worm Drive Dimensions: ............................................................................................. 50

5.4.2 Safety Feature: ............................................................................................................. 51

5.4.3 Conclusion: ................................................................................................................... 51

5.5 Human Factors .................................................................................................................... 52

5.5.1 Macro Movement: ....................................................................................................... 52

5.5.2 Usability Testing: .......................................................................................................... 54

5.5.3 Conclusion: ................................................................................................................... 55

5.6 Concept Refinement ........................................................................................................... 57

6 Prototype Construction................................................................................................. 59

6.1 Shaft Movement ................................................................................................................. 59

6.2 Worm Drive ......................................................................................................................... 64

6.2.1 Worm Drive Screws: .................................................................................................... 65

6.2.2 Rotary Knob: ................................................................................................................ 67

6.2.3 Platforms: ..................................................................................................................... 67

6.2.4 Assembly: ..................................................................................................................... 68

7 Proof of Principle .......................................................................................................... 69

7.1 Range of Travel: .................................................................................................................. 69

7.2 Micro Precision: .................................................................................................................. 71

7.3 Pulling Force ........................................................................................................................ 73

8 Final Design .................................................................................................................. 74

8.1 Aesthetics and Branding ..................................................................................................... 74

8.2 Dimensions .......................................................................................................................... 75

8.3 Manufacturing and Assembly Processes ............................................................................ 76

8.3.1 Shaft Guides: ................................................................................................................ 76

8.3.2 Inner Central Casing: .................................................................................................... 77

8.3.3 Guide Covers: ............................................................................................................... 78

8.3.4 Macro Button: .............................................................................................................. 79

8.3.5 Isolation Sheath: .......................................................................................................... 79

8.3.6 Outer Casing: ................................................................................................................ 80

8.3.7 Worm Drives: ............................................................................................................... 80

8.3.8 Rotary Knob: ................................................................................................................ 81

8.3.9 Guidewire Entry: .......................................................................................................... 82

8.3.10 Bill of Materials: ......................................................................................................... 83

8.4 Conclusion and Evaluation .................................................................................................. 83

8.4.1 Recommended for Use: ............................................................................................... 83

8.4.2 Further Development: ................................................................................................. 84

References .......................................................................................................................... 85

Bibliography ........................................................................................................................ 87

Appendices ......................................................................................................................... 88

List of Figures

Figure 1 – Heart Anatomy [2] ....................................................................................................... 12

Figure 2 – Heart Blood Circulation ................................................................................................ 12

Figure 3 – Replacement Heart Valves ........................................................................................... 13

Figure 4 – Trans-catheter Access Routes [2] ................................................................................ 14

Figure 5 – Initial Proposed Concept Design .................................................................................. 19

Figure 6 – Split Shaft Movement .................................................................................................. 19

Figure 7 – Rigid Shaft Reinforcement ........................................................................................... 20

Figure 8 – Universal Aspect ........................................................................................................... 21

Figure 9 – Micro Retraction .......................................................................................................... 21

Figure 10 – Micro Retraction Mechanism .................................................................................... 22

Figure 11 – Macro Retraction Mechanism ................................................................................... 22

Figure 12 – Inner Shafts Movement ............................................................................................. 23

Figure 13 – Ergonomics Input ....................................................................................................... 23

Figure 14 – Human Factors Input.................................................................................................. 24

Figure 15 – 1:1 Scale Model .......................................................................................................... 24

Figure 16 – Model Interaction ...................................................................................................... 25

Figure 17 – Further Design Recommendations ............................................................................ 26

Figure 18 – Phase 2 Scheduling .................................................................................................... 28

Figure 19 – Initial Shaft Guides Design ......................................................................................... 30

Figure 20 – Insert Molding Guides ................................................................................................ 31

Figure 21 – Guide Design FEA Test ............................................................................................... 32

Figure 22 – Guide Design Material Test ........................................................................................ 33

Figure 23 – Guide Redesign FEA Test ............................................................................................ 34

Figure 24 – Single Slot Bonding ..................................................................................................... 35

Figure 25 – Two Halves Bonding ................................................................................................... 36

Figure 26 – Split Shaft Bonding ..................................................................................................... 37

Figure 27 – Ideal Guide Design FEA Test ....................................................................................... 38

Figure 28 – Guide Including Clearance for Split ............................................................................ 39

Figure 29 – Shaft Resistance at a Straight .................................................................................... 40

Figure 30 – Shaft Resistance at an Arch ........................................................................................ 41

Figure 31 – Supporting Shaft FEA Plastic Test .............................................................................. 41

Figure 32 – Supporting Shaft FEA Steel Test ................................................................................. 42

Figure 33 – Minimum Shaft Sizes .................................................................................................. 43

Figure 34 – Central Shaft Positioning ............................................................................................ 44

Figure 35 – Central Shaft Positioning Method .............................................................................. 45

Figure 36 – ANSI Screw Standards [10] ......................................................................................... 46

Figure 37 – Guide Extrusion Length FEA Test ............................................................................... 47

Figure 38 – Shaft Guides Extrusion Length ................................................................................... 48

Figure 39 – Rotary to Linear Motion Principle .............................................................................. 49

Figure 40 – Single Actuation Principle .......................................................................................... 49

Figure 41 – ASTM Screw Tension & Torque Standards [10] ......................................................... 50

Figure 42 – Worm Drive Dimensions ............................................................................................ 50

Figure 43 – New Macro Approach ................................................................................................ 53

Figure 44 – Macro Assembly Approach ........................................................................................ 53

Figure 45 – Original Design Usability ............................................................................................ 54

Figure 46 – Macro Release Shape ................................................................................................. 55

Figure 47 – Product Semantic Approach ...................................................................................... 56

Figure 48 – Anthropometric Grip Data [13] .................................................................................. 56

Figure 49 – Anthropometric Hand Data [14] ................................................................................ 57

Figure 50 – Shafts Used................................................................................................................. 59

Figure 51 – Tools and Machining Processes ................................................................................. 60

Figure 52 – Outermost Shaft Construction ................................................................................... 61

Figure 53 – 3D Model Dimensions ................................................................................................ 61

Figure 54 – Inner Shaft Construction ............................................................................................ 62

Figure 55 – Innermost Shaft Construction .................................................................................... 63

Figure 56 – Shaft Movement Test Rig Assembly .......................................................................... 63

Figure 57 – Shaft Test Rig Structure.............................................................................................. 64

Figure 58 – Machining Processes 2 ............................................................................................... 65

Figure 59 – Cogs Used ................................................................................................................... 65

Figure 60 – Bonding Rig ................................................................................................................ 66

Figure 61 – Worm Drive Dimensions ............................................................................................ 66

Figure 62 – Rotary Knob Dimensions ............................................................................................ 67

Figure 63 – Platforms .................................................................................................................... 68

Figure 64 – Worm Drive Test Rig Assembly .................................................................................. 68

Figure 65 – Outermost Shaft Travel .............................................................................................. 69

Figure 66 – Inner Shaft Travel ....................................................................................................... 70

Figure 67 – Innermost Shaft Travel ............................................................................................... 70

Figure 68 – Micro Precision Test Rig ............................................................................................. 71

Figure 69 – Retract Vertical Platform ........................................................................................... 72

Figure 70 – Retract Horizontal Platform ....................................................................................... 72

Figure 71 – Shaft Guide Test ......................................................................................................... 73

Figure 72 – Newton Force ............................................................................................................. 73

Figure 73 – Refined Handle Design ............................................................................................... 74

Figure 74 – Refined Design Dimensions........................................................................................ 75

Figure 75 – Molded Shaft Guides .................................................................................................. 76

Figure 76 – Bond Guides to Shafts ................................................................................................ 77

Figure 77 – Inner Central Casing ................................................................................................... 77

Figure 78 – Attach Guide Covers .................................................................................................. 78

Figure 79 – Insert Threaded Cap ................................................................................................... 78

Figure 80 – Macro Release Button ................................................................................................ 79

Figure 81 – Attach Isolation Sheath .............................................................................................. 79

Figure 82 – Attach Outer Casing ................................................................................................... 80

Figure 83 – Insert Worm Drives .................................................................................................... 81

Figure 84 – Attach Rotary Knob .................................................................................................... 81

Figure 85 – Attach Stopper ........................................................................................................... 82

Figure 86 – Attach Guidewire Entry Point .................................................................................... 82

List of tables

Table 1 – Proposed Design Advantages and Disadvantages ........................................................ 25

Table 2 – Guide Design FEA Analyses ........................................................................................... 32

Table 3 – Guide Design Material Analyses .................................................................................... 33

Table 4 – Guide Redesign FEA Analysis ......................................................................................... 34

Table 5 – Ideal Guide Design FEA Analysis .................................................................................... 38

Table 6 – Supporting Shaft FEA Plastic Analysis ........................................................................... 42

Table 7 – Supporting Shaft FEA Steel Analysis .............................................................................. 42

Table 8 – Guide Extrusion Length FEA Analysis ............................................................................ 47

Table 9 – Bill of Materials ............................................................................................................. 83

[PHASE 1] 1. Introduction

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1. Introduction

1.1 Project Overview

The scope of this project is inspired by a design brief proposing the generation of a suitable

concept for a ‘modular handle platform for a delivery system’ to be used during Trans-catheter

Valve Deployment procedures. The design brief was devised by the Research and Development

Department at Medtronic Cardiovascular Galway Ltd. The degree of work on this project was

undertaken over two distinct phases of time:

Phase 1

November 2011 – February 2012

The initial phase originated from the proposed design brief which stated the aims and

objectives. A thorough research stage was explored and interpretations from the research

findings enabled the generation of early concepts. A single concept was chosen for

development whilst integrating certain aspects from an additional concept. After extensive

concept refinement, the single concept was presented to staff at the Research and

Development Department at Medtronic Cardiovascular Galway Ltd.

Phase 2

June 2012 – September 2012

The second phase of the project began when a request was made to further develop the

presented concept as the final project for the MSc in Medical Device Design. Additional design

features were implemented into the original design brief, and new objectives were defined. The

primary focus for phase two involved testing the feasibility of the more refined concept design.

This design report documents the project over both of these periods and sets out this work in a

structured and chronological fashion.


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1.2 Project Aims

Detailed below shows the design brief which created the framework for the design project:

Project Title:

The development of a common, modular, delivery system handle platform

Aim:

The handle is to feature:

- A common ‘Medtronic’ design theme

- Human factors input

- Scalability

- Multi-control expandability

Design Parameters:

- Accommodate up to 4 shafts (3 shafts actuating linearly)

- X = travel of each shaft (30 – 120mm), with the ability to restrict this travel

- Minimum hollow inner diameter of 0.035in (0.889mm) to allow travel over a guidewire

- Shaft diameter ranging from 16fr (5.3mm) to 32fr (10.7mm)

- Micro and macro mechanisms to allow independent movement of each shaft


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1.3 Project Objectives

The necessary tasks required to complete the design brief have been outlined below. These

identify the tasks that have been undertaken over both phases of the project to facilitate the

development of the final design of the product.

- Construct an in-depth research phase to gain an understanding of trans-catheter valve

technology, and how the current delivery system handles operate

- Generate a wide range of concepts in response to the design brief

- Undertake the development of a single concept

- Modify the concept to meet additional requirements

- Document a variety of experiments and tests to ensure maximum design efficacy

- Fabricate multiple test rigs to prove the mechanical feasibility of the refined design

[PHASE 1] 2. Research

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2. Research

As detailed in the project overview, this project was progressed over two time periods. This

section will discuss the basis for the design project by elaborating the importance of Trans-

catheter Valve Technology as a treatment for heart valve disease. Existing products will be

explored, detailing the mechanical principles and also the means for user interaction. Aims and

objectives will be constructed to provide a more extended investigation into the field of study,

consequently forming the framework for the design project.

2.1 Research Aims and Objectives

The areas of study can be sub-categorized under three main headings:

2.1.1 Area Background:

Research of the relevant anatomy involving trans-catheter valve therapy will provide the

understanding to the background of the design brief. Queries to resolve will include:

- What is trans-catheter valve therapy?

- How does the human heart function?

- What is the required trans-catheter valve procedure?

2.1.2 User Identification:

Research of the user will play an integral role in the development of the handle design. This

study will answer questions such as:

- Who are the users?

- How do the users interact with the handle controls on existing products?

- What problems arise while performing a procedure?


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2.1.3 Product Research:

Research of existing handle designs will provide an insight to the current market trends for

trans-catheter valve delivery systems. Areas examined will include:

- Established and emerging concepts

- Mechanical operations encased within handle designs

- Materials and manufacturing techniques

2.2 Research Methods

The research acquired for this project involved the use of a variety of mediums. Defined by the

aims and objectives, a broad spectrum of study was explored. However, resources on the

subject area were quite limited due to the confined area of specialty.

2.2.1 Literature Review:

Printed literature and medical journals were an excellent source for obtaining information on

the relative anatomy in accordance with the design brief. Practising surgeons released papers

documenting issues encountered while performing trans-catheter valve procedures. Internet

websites and existing patent applications were also a valuable resource for gathering

inspiration. They provided information on both, market competitors, and alternative products

with similar functions to that required for the design brief.

2.2.2 Observation:

As a relatively new and expensive field of study, access to trans-catheter valve procedures was

not a viable option. However, online videos and animations offered a practical solution.

Invaluable research was obtained with respect to the interaction between the user and the

handle delivery system.

2.2.3 Expert Users:

Discussions with industry experts enabled a more constructive view on the subject area.

Interviews were scheduled throughout the course of the project. With respect to the research


11

stage, it was a useful tool for resolving any related queries in terms of user preference,

materials and manufacturing techniques.

2.2.4 Photographic study:

A photographic study of three existing Medtronic products was constructed (see Appendix 1).

These included: the CoreValve; the Engager; and the Xcelerant. The theme and style of the

designs were recorded, along with the methods for user interaction. By dismantling the product

handles, it provided a more apparent understanding of the mechanical principles for

manipulating the catheter, deploying the valve, and also retracting the catheter.

2.3 Results

2.3.1 Treatment for Heart Disease:

Traditionally people with heart valve disease have been treated with open heart surgery,

although a high proportion of these patients are not eligible for surgery due to the high risk

factor. Trans-catheter valve therapy has emerged as an alternative to patients with valvular

heart disease who are not candidates for open heart surgery [1]. It provides a less invasive

method for delivering a replacement heart valve to the diseased native valve.

A prosthetic heart valve is mounted inside a delivery catheter. In order to deploy the valve in a

controlled manner, a handle is built onto the proximal end of the catheter. The user interacts

with the handle to manipulate the catheter into position, deploy the valve, and finally withdraw

the catheter from the patient’s body once the prosthesis is deployed.

Since the introduction of Trans-catheter Aortic Valve Implantation (TAVI) to the medical

community in 2002, there has been a constant rise in patients undergoing this procedure –

more than 10,000 to date [1].

2.3.2 Anatomy of the Heart:

The human heart consists of four valves which control the direction of blood flow throughout

the body. Each valve is shown in figure 1.


12

Figure 1 – Heart Anatomy [2]

A B C D

Aortic Valve Pulmonary Valve Tricuspid Valve Mitral Valve

Figure 2 – Heart Blood Circulation


13

There are two sets of pumping chambers shown in figure 2. The right atrium receives oxygen-

depleted blood from the body, which is pumped into the lungs through the right ventricle. The

left atrium receives aerated blood from the lungs, which is pumped out of the body through the

left ventricle. With each heartbeat, the ventricles contract together [3]. This causes the closure

of the valves, and it prevents backflow of blood from one chamber to the next [4].

When a heart valve fails, the following can occur [5]:

- Valve regurgitation – blood leaks back through the valve in the wrong direction

- Valve stenosis – blood flow is blocked due the inability of the valve to open wide enough

A valve repair or replacement is often a crucial remedy for valvular heart disease. Trans-

catheter valve therapy involves delivering a prosthetic heart valve replacement through the

body’s cardiovascular system. The prosthetic replacement valve consists of a nitinol frame

inside which a biologically derived tissue valve is mounted (see figure 3). The valves are either

bovine jugular vein valves or pericardial constructs [6], and act as a direct replacement for a

diseased native valve.

Figure 3 – Replacement Heart Valves


14

2.3.3 Trans-catheter Procedure:

The prosthetic valve is delivered to the native valve via a delivery catheter, which is primarily a

shaft with a protective sheath. The most common approach is to insert the catheter through

the transfemoral access point; however, where femoral access is not feasible in some patients;

the valve implantation may be successfully performed using the subclavian or axillar arterial

approach [1].

Figure 4 – Trans-catheter Access Routes [2]

Prior to the procedure, a pacemaker is inserted into the patient’s heart and is positioned in the

apex of the right ventricle to monitor the hearts activity [7]. The basic process for delivery is as

follows:

- A small incision is made at the insertion access point

- A guidewire is inserted and is fed up and into the heart’s native valve location

- The delivery catheter, containing the replacement valve, threads over the guidewire and

follows it to the failing valve. A fluoroscopic machine provides a visual of the catheter as

it navigates through the torturous anatomy inside the patients body


15

- When in position, the user interacts with the handle on the delivery catheter to retract

the outer sheath, thus exposing the prosthetic valve. Currently, trans-catheter valve

replacement stents can generally be classified as balloon-expandable or self-expanding

[6]. For self-expanding valves, as the outer sheath retracts, the mounted on stent forces

the valve to deploy. Others require the use of a balloon to deploy the valve

- The catheter and guidewire are removed from the body, leaving the fully operational

valve in position [8]

2.3.4 Additional Findings

After an in-depth study into the conclusive breakdown of the design brief, many findings were

taken into consideration. Each of these findings originated from the collection of mediums as

mentioned in the research methods. These include:

- Duration of the procedures can range from 1-2 hours [9]

- Both hands are required from the surgeon to perform the procedure. One hand feeds

the catheter through the patient’s body; the other operates the handle controls, whilst

concentrating on the screen for direction. An assistant is also present to aid in the

procedure

- The delivery catheter along with the handle is disposed of after the procedure

- When the prosthetic valve is fully deployed, it cannot be repositioned (the CoreValve

cannot be repositioned once it has surpassed two-thirds of its deployment)

- The surgeon is provided with minimal tactile feedback when the valve is in position

- The distal tip of the catheter can be quite stiff when forcing it through the anatomy,

especially when encountering the large bend at the aortic arch

- The CoreValve can be delivered to the aorta through either access route and requires

retraction movement of a single sheath. The macro mechanism is unpleasant to retract

and demands a great deal of force

- The Engager is delivered to the aorta by means of trans-apical approach, resulting in a

reduction in catheter length. It requires movement of two shafts: outer shaft moves

forward, inner shaft retracts. It also employs a safety feature which prohibits the inner


16

shaft from moving until the outer shaft has reached its destination. A visual of shaft

location is displayed on the handle platform

- The current products on the market require the movement of either one or two

catheter shafts. If more shafts were introduced, it would increase the overall length of

the handle

2.5 Discussion and Design Specifications

With respect to both the design brief and the research findings, design specifications were

formed. They are intended for a universal handle which is compatible for use with Medtronic

cardiovascular devices, ranging from replacement heart valves to stents. These specifications

created the framework of design parameters for generating early concepts. The main points

concluded that: The proposed design should be intuitive and easy to use and perform all of the

required tasks as set out in the design brief.

Travel Considerations:

It shall enable both a retraction and forward motion for each of the three catheter

shafts, with the integration of a micro precision mechanism on the outer-most shaft

Outer shaft must travel at a minimum of 120mm, whereas the inner-most shaft must

travel at a minimum of 30mm

Physical Considerations:

Inner-most shaft will conform to a size of 16fr, whereas the outer shaft will be 32fr

A comfortable grip shall be implemented into the proposed design to aid in user fatigue

due to long procedure hours

Easy access should be provided to the handle controls due to the surgeons focus being

directed at the fluoroscopic screen

Manufacturability Considerations:


17

The proposed handle design will be a single use device, therefore, it shall be low cost

allowing the employment of easy manufacturing methods

Parts should conform to a set standard size to enable a universal design

Aesthetic Considerations:

The handle shall be styled appropriately in relation to the ‘Medtronic’ design theme. It

shall be aesthetically pleasing and easily recognised as a medical device

[PHASE 1] 3. Design & Development

18

3 Design and Development

3.1 Introduction

Progressing forward from the initial research stage in Phase 1, and having defined a selection of

parameters as set out in the design specification, construction began on generating initial

concepts. A concept presentation was proposed to Medtronic early February 2012 involving

two very distinct concept ideas (please see Appendix 2). Based on their feedback, it was

understood that both concepts upheld interesting qualities, and a scope for development was

established. The next stage involved designing a single concept in response to the feedback

received.

This section will discuss the development and application of the final concept design which was

proposed to Medtronic at the end of February 2012.

3.2 Proposed Concept Design

Development revolved around an amalgamation of both concept ideas. The concluded design

can be seen in figure 5 and was presented to Medtronic Cardiovascular Ltd in Galway at the end

of February 2012.

It is a universal handle for trans-catheter delivery systems and is compatible for use with any of

Medtronic’s existing products (shown in Appendix 1).


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Figure 5 – Initial Proposed Concept Design

3.2.1 Process:

An appealing factor from the concept presentation was the application of a split shaft for

reducing the overall length of the handle. Figure 6 shows the more developed version.

Figure 6 – Split Shaft Movement


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The split section is present in the outer-most shaft. This allows retraction of the shaft without

affecting any of the inner shafts. An additional shaft is bonded to the inside of the outer-most

shaft (figure 7). This provides rigidity and prevents further tearing of the split section.

Figure 7 – Rigid Shaft Reinforcement

In order to manipulate shaft movement, guides are bonded to the end of each shaft. A central

casing is employed within the design to keep each of the shafts at the same level. The guides

extrude out past the casing and a cover is screwed over them. The casing simply acts as a cut-

off point (figure 8). A universal aspect of the design is that it conforms to a set size which can

accommodate any shaft size ranging from 16fr to 32fr.


21

Figure 8 – Universal Aspect

3.2.2 Micro Retraction Mechanism:

For precise retraction of the outer-most shaft, the guides on the shafts interact with a worm

drive mechanism. The user would simply rotate a knob at the base of the handle to perform

this action (figure 9).

Figure 9 – Micro Retraction


22

Both worm drives and the rotary knob have a cog built onto them. As the knob rotates, it forces

the cogs to rotate in the same direction, resulting in a linear movement of the shaft (figure 10).

Figure 10 – Micro Retraction Mechanism

3.2.3 Macro Retraction:

In order to retract quickly, the cover on the guides must disengage from the worm drive. This is

achieved with the aid of a spring. As the user presses down on the cover, it allows a quick

retraction of the shaft (figure 11).

Figure 11 – Macro Retraction Mechanism


23

The two inner shafts do not require micro precision; therefore, the user can simply slide the

covers to retract the shafts (figure 12).

Figure 12 – Inner Shafts Movement

3.2.4 Ergonomics Input:

The handle was designed with particular attention being focused on the user. A front grip on

the distal end of the handle enables a more comfortable operation. The shape on which the

user manipulates shaft movement is angled at 45 degrees to allow secure retraction (figure 13).

Figure 13 – Ergonomics Input


24

The overall diameter of the handle does not exceed 54mm, allowing the use of the whole hand

when utilizing the micro retraction mechanism. This provides a high degree of force. When

retracting the outer-most shaft with the macro approach, the user can pinch down with the

thumb and index finger (figure 14).

Figure 14 – Human Factors Input

A full scale physical model of the concept design was created to demonstrate user interaction

and the ease of access to the handle controls. This is shown in figures 15 and 16.

Figure 15 – 1:1 Scale Model


25

Figure 16 – Model Interaction

3.3 Further Development

In comparison to existing products on the market, the proposed concept idea offers both

advantages and disadvantages, as shown in Table 1:

Advantages: Disadvantages:

Access each shaft individually Bulky size

Capable of being used with multiple shafts

Reduction in length of the handle

Accommodate any shaft size (16fr to 32fr)

Standard parts for manufacturing

Table 1 – Proposed Design Advantages and Disadvantages

Possible recommendations which could be implemented into the design can be seen in figure

17.


26

Figure 17 – Further Design Recommendations

- Colour code each of the shafts to determine which shaft the user will be manipulating

- Insert a fourth moveable shaft and increase the length of the split shaft if required

- Attach a steering mechanism on the outer-most shaft. The pulling wire could be located

in between the outer-most and rigid shaft

[PHASE 2] 4. Phase 2 Development

27

4 Phase 2 Development

4.1 Background

Subsequent to the presentation of the refined design in the previous chapter, it was requested

that the project be further developed. This would require bringing the proposed concept to the

next stage of the design process. A meeting with Medtronic staff took place on the 28th June

2012 to discuss the project plan (see Appendix 3), and additional design specifications were

drawn up.

4.2 Further Design Specifications

The following specifications have been implemented into the initial design brief:

Implement the micro and macro mechanism on a second shaft

Enable a pulling force on the catheter shafts of at least 50 Newton’s

Reduce the overall size diameter of the handle without affecting its performance

Apply a more rigorous review on ‘Human Factors Input’

In addition to the design specifications, there will also be a need for further development on

the performance of the handle, and the feasibility of the refined design will need to be tested. A

more elaborate focus on design for manufacturing will also be an integral aspect into the design

development process.


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4.3 Phase 2 Scheduling

Prior to the beginning of phase two, it was clear that restraints on allocated time for the project

would be a deciding factor on whether each of the objectives could be accomplished. It was

important to set goals with subsequent deadlines to ensure all tasks received the required

amount of attention. Figure 18 shows the limited time period for the project and the amount of

time spent on each task.

Figure 18 – Phase 2 Scheduling

The numbers on the x axis represent the amount of weeks available for the project, beginning

28th June and ending 31st August, and also taking into account the final presentation on

September 4th. The list of tasks are displayed on the y axis.

1 2 3 4 5 6 7 8 9 10

Briefing

Design Refinement

Component Testing

General Review Meeting 1

Prototype Construction

General Review Meeting 2

Final Design

Project Completion

Presentation Preparation

NCAD Presentation


29

4.4 Phase 2 Objectives

The development work over this allocated period is summarised into the following objectives:

Refine the design of the handle to accommodate the need for additional requirements

Further develop the performance of each individual component within the design

Enable a working handle design for the smallest shaft size (16fr), so as to minimise the

overall size of the design

Research human factors design and implement the methodology into the handle design

Construct multiple test rigs to display proof of concept

Gain an insight into Medtronic’s current materials and manufacturing processes for

delivery system handles

[PHASE 2] 5. Design Modifications

30

5 Design Modifications

This chapter will explore the necessary requirements for meeting the project development

design specifications. Limited by the amount of resources, tests and experiments were

undertaken on each individual component of the design to ensure all criteria was met and that

the concept was refined to a more feasible design.

5.1 Shaft Guides

The shaft guides are bonded onto the ends of each catheter shaft, and allow the user to

manipulate shaft movement. Figure 19 shows a sectional view of the initial design of the

guides.

Figure 19 – Initial Shaft Guides Design

After an in depth discussion with a Medtronic representative, it was decided that the shaft

guides should be manufactured as a separate component, as opposed to the initial insert

moulding process (figure 20). This would provide a more accurate construction and a cheaper

means for mass production.


31

Figure 20 – Insert Molding Guides

The following tests will determine:

The most suitable materials from a manufacturing perspective

The most effective design for the shaft guides

The most appropriate means for bonding the guides onto the catheter shafts

5.1.1 Design Analysis:

A Finite Element Analysis (FEA) was used to determine the performance of the guides when

created as a separate component. A 3D model was drawn up to the required dimensions and

the material characteristics were defined.


32

Figure 21 – Guide Design FEA Test

Figure 21 shows the performance of a separate component with two cylindrical guides built

into it. Table 2 below shows the analysed report:

Material: Plastic Acrylic (medium-high impact)

Force Applied: 50 Newton’s

Max Stress Occurred: 3.32e +008 (N/m2)

Factor of Safety: 0.62

Table 2 – Guide Design FEA Analyses

As shown in figure 21, a deformity occurred on both guides. The selected design was unable to

withstand 50 Newton’s. The maximum stress that could be applied to the guides before

deformation occurred was 31 Newton’s.

Different materials were applied to the same design and the test was repeated (Figure 22):


33

Figure 22 – Guide Design Material Test

Material: Steel (1023 Carbon Steel Sheet) Aluminium (1060 Alloy)

Forces Applied: 50 (N) 50 (N)

Max Stress: 3.55e +008 (N/m2) 3.52e +008 (N/m2)

Factor of Safety: 0.80 0.078

Table 3 – Guide Design Material Analyses

Steel was the most effective material considering the size dimensions; however the design of

the component was still unable to withstand 50 Newton’s, with a maximum tolerance of 40

Newton’s before deformation occurred. The stress on each of the guides was too great, and

would eventually cause them to snap.


34

Figure 23 – Guide Redesign FEA Test




Factor of Safety: 12

Table 4 – Guide Redesign FEA Analysis

Figure 23 shows a redesign of the guides. When the same force was applied, the stress was

greatly reduced, even with a plastic material. From a manufacturing point of view, the ideal

material would be plastic. This type of design, with the given dimensions, can tolerate a

maximum of 600 Newton’s before it begins to deform, well above the target of 50 Newton’s.

5.1.2 Component to Shaft Bonding:

The purpose of this test was to analyse the most appropriate method for bonding the shaft

guides onto the catheter shafts for both ease of constructing the final prototype, and also ease

of assembly in a real working environment. Three physical models of the previous component

design were created using a 3d printer. Each model was created to accommodate different

shaft diameters, and the different types of bonding were tested:

Single Slot Bonding:


35

Figure 24 – Single Slot Bonding

Figure 24 shows the bonding of the component as a solid piece. The inner diameter of the

component was dimensioned so it could slot over the catheter shaft whilst keeping a tight fit,

as shown, and a glue adhesive was used to keep it in position.

This approach would only be suitable for the smaller shafts within the design. If it were

attached to the outer-most shaft, a side section would need to be cut-out to accommodate the

need for sliding over the inner shafts. This would lead to difficulties with correct sizing. In terms

of manufacturing in a working environment, electro welding could be utilised to ensure an

exact fitting without the need for an adhesive. However, an additional cutting process would be

required to form the side cut-out on the outer most shaft.

Bonding in Two Halves:


36

Figure 25 – Two Halves Bonding

Figure 25 shows the bonding of the component as two separate entities. The two parts were

pressed onto the end of the catheter shaft, as shown, and a glue adhesive was used to bond

them together.

The performance was just as effective as the previous method, ensuring an even tighter fitting.

This approach would be suitable for all shaft sizes and can provide allowance for split shafts if

necessary.

Bonding onto a Split Shaft:


37

Figure 26 – Split Shaft Bonding

Figure 26 shows the bonding of the component onto a split shaft. The two parts were bonded

onto the shaft, and a section of the shaft was cut-out.

The weight of the component had no effect on the shaft. However, results would vary

depending on the diameter and material of the shaft, and also the length of the cut-out.

5.1.3 Conclusion:

The most effective design for the shaft guides can be seen in figure 27. A further FEA study was

analysed on this design to determine the most suitable size. As shown, the size is reduced and is

able to withstand a maximum tolerance of 260 Newton’s before deformation occurs on the

guides.


38

Figure 27 – Ideal Guide Design FEA Test




Factor of Safety: 5.2

Table 5 – Ideal Guide Design FEA Analysis

The most appropriate means for bonding the guides to the catheter shaft would involve

creating the guides in two separate entities and then pressing them onto the shaft. This would

ensure a tight fitting and would also be suitable for all shaft ranges. For universal purposes,

each half should provide allowance for shafts with a cut-out section (figure 28). In terms of

manufacturing in a working environment, a single mould could be used to create the part,

allowing mould scalability for different shaft size ranges. Inserts could be placed within the

mould to create a cut-out section on the guides.


39

Figure 28 – Guide Including Clearance for Split

5.2 Shafts

The initial design of the handle involved the outer-most shaft sliding over the two inner shafts.

In relation to the further design specifications, it was intended to reduce the size of the handle

design, and the diameters of the shafts within the handle are a contributing factor to the

overall scale. The following tests will determine:

The minimum French size (French Catheter Scaling) for each individual catheter shaft

The effect that the shaft guides will have on shaft movement

A suitable size and material for reinforcing the outer most shaft

5.2.1 Catheter Shaft Sizing:

As mentioned previously, the initial design composed of three moving shafts and a fourth

additional shaft which is used primarily for keeping the outer-most shaft rigid during travel. The

purpose of this test is to measure any friction which may arise from using two consecutive shaft

sizes. A 13fr (4.3mm) and 14fr (4.7mm) catheter shaft was used for the demonstration, and a

Newton meter was able to obtain an approximate reading of resistance when in both a straight

and arched position.


40

The 14fr catheter was clamped in a straight position, and the 13fr catheter was retracted from

within it (figure 29). The maximum resistance the 13fr catheter experienced was approximately

1.2 Newton’s. However, when pushed forward it experienced slightly more resistance, rising to

1.5 Newton’s.

Figure 29 – Shaft Resistance at a Straight

A further study involved testing the friction at an arch, to accommodate the torturous anatomy

which it would encounter in a real case scenario (figure 30). When fully retracted, the maximum

resistance that the 13fr catheter experienced was approximately 4 Newton’s. When pushed

forward, it experienced approximately 5 Newton’s.


41

Figure 30 – Shaft Resistance at an Arch

5.2.2 Shaft Reinforcement:

An FEA study was performed on the supporting shaft, to test the feasibility of the concept with

the newly designed guide components attached. Two types of materials were tested.

Figure 31 – Supporting Shaft FEA Plastic Test


42



Max Stress Occurred: 3.10e + 007 (N/m2)

Max Displacement: 5.02e + 000 (mm)

Table 6 – Supporting Shaft FEA Plastic Analysis

The material proposed for the initial design was a rigid form of plastic. Figure 31 shows a

displacement result of over 5mm (Table 6).

Figure 32 – Supporting Shaft FEA Steel Test

Material: 1023 Carbon Steel



Max Displacement: 8.96e – 001 (mm)

Min Factor of Safety: 3.5

Table 7 – Supporting Shaft FEA Steel Analysis

The same test was conducted when a steel material was applied (figure 32). As shown, the

displacement was greatly reduced; however the shaft did experience compression at the


43

beginning of the split section (0.896 mm), almost completely pressing the two split shafts

together.

5.2.3 Conclusion:

Taking the wall thickness of each catheter shaft and also the attached shaft guides into

consideration, the minimum size of each shaft can be seen in figure 33.

Figure 33 – Minimum Shaft Sizes

According to the brief, the minimum shaft requires a 16fr (5.3mm) outer diameter. Due to little

friction between shafts, the second shaft can therefore be set at 17fr (5.7mm). This leaves a

minimum shaft outer diameter of 24fr (8mm) for the outer-most shaft.

Minimum length of travel for the outer-most shaft is 120mm; therefore, the minimum length of

the split in the shaft must be at least 130mm to accommodate the length of the attached guide

component. For this range of travel, steel would be the most rigid material for reinforcing the

outer shaft. However, if a longer version of the design were ever to be configured for use, the

increase in the split shaft would cause buckling under pressure, thus making travel over the

attached guides very difficult. As mentioned in the previous chapters, the original design of the

handle was able to tolerate this issue by screwing on a cover to act as a cut-off point.


44

5.3 Shaft Manipulation

To manipulate shaft movement, the user must interact with the shaft guides. With respect to

the given objectives and the newly refined shaft guides, a new design was required for user

manipulation. The following tests and data will determine:

- A refined approach for maintaining shaft positions

- A minimum extrusion length for the shaft guides

In relation to the feasibility of the original concept idea, a central shaft can still be a tangible

aspect for keeping the activated shafts at a level position. Figures 34 and 35 show a new

approach for achieving this.

Figure 34 – Central Shaft Positioning


45

Figure 35 – Central Shaft Positioning Method

A cover would simply slot over each guide, and the central casing could act as a cut-off point.

Each guide and cover would contain a cavity to allow a screw to pass through it, thus keeping it

in a fixed position.

5.3.1 Guide Extrusion Length:

A further FEA analysis was performed on the guides to determine the minimum extrusion

length. The cavity in each of the guides was also included in the test. According to the American

National Standards Institute (ANSI), the minimum thread diameter for a screw which should be

used with plastics is 0.060in (1.5mm), as shown in figure 36. Therefore, the diameter of the

cavity was tested in accordance with these standards.


46

Figure 36 – ANSI Screw Standards [10]

As tested previously, a 10mm extrusion length of the guides was able to withstand a tolerance

of up to 260 Newton’s. Taking the wall thickness of the central casing and shaft clearance into

account, only 8.65mm of this length extrudes past the casing, therefore only this amount of

contact would experience the force applied.

With respect to the materials and assembly techniques for the cover and guides, the cavity

placement should be positioned 3mm from the point it extrudes past the casing, to allow

sufficient space for the screw head once the cover is attached. This leaves a minimum length of

extrusion of 5.73mm. The feasibility of this size was tested (figure 37).


47

Figure 37 – Guide Extrusion Length FEA Test




Factor of Safety: 20

Table 8 – Guide Extrusion Length FEA Analysis

The employment of a central casing has a huge impact for reducing the amount of stress placed

on the guides. When 50 Newton’s of force was applied to the guides, they experienced very

minimal stress, resulting in a factor of safety of 20 (Table 8).

5.3.2 Conclusion:

The minimum length of the guides when extruding past the central casing is 5.73mm. All guides

should be uniform at this extrusion point to allow a standard size for the cover. The dimensions

for each of the three shaft guides are shown in figure 38 and can each tolerate up to 1000

Newton’s of force.


48

Figure 38 – Shaft Guides Extrusion Length

A grub screw would be the most suitable screw to combine the cover with the guides, as it

distributes the load evenly. It should be of carbon steel material and contain an AB type screw

point. This would be ideal for use with materials such as plastics due to the finer thread pitch

[10].

5.4 Micro Precision

After discussions with Medtronic staff members at the project briefing, it was requested that

the micro retraction mechanism be implemented on an additional shaft. A variety of concept

ideas were explored on how this could be achieved. The following tests will explain:

- The design adjustment for permitting micro retraction on two shafts

- A suitable size and material for each of the worm drives

- A safety measure for prohibiting movement of secondary shafts until primary shafts are

in position

The original design consisted of micro precision on a single shaft. A sketch model was

constructed to demonstrate this principle of rotary to linear movement (figure 39). Both worm


49

drives are fixed and consist of a cog bonded at their base. When a central cog is rotated, it

interacts with the worm drives, forcing the platform to move in a linear direction, as shown.

Figure 39 – Rotary to Linear Motion Principle

In order to minimise the amount of component parts, the ideal method would be to utilise a

single actuator which could interchange between both shafts. Unlike if two actuation knobs

were used, a single knob would reduce the risk of misleading the user on which knob to turn.

A sketch model was constructed to verify that the teeth on the cogs would engage with one

another when the rotary knob switches between them. This is demonstrated in figure 40.

Figure 40 – Single Actuation Principle


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5.4.1 Worm Drive Dimensions:

Each worm drive should consist of uniform screw threads with a 2A fitting. The platform which

travels over the worm drives would consist of a 2B fitting. This would enable a tight fitting and

prevent interference. Classes 2A and 2B offer optimum thread fit that balances fastener

performance, manufacturing economy and convenience. Almost 90% of all commercial and

industrial fasteners produced in North America contain this class of thread fit [10].

Figure 41 – ASTM Screw Tension & Torque Standards [10]

Figure 41 shows a standard of sizes which can be applied to the worm drive screws. Taking the

minimum size into account, the dimensions of the worm drive can be seen in figure 42.

Figure 42 – Worm Drive Dimensions


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According to the American Standards (figure 41), the minimum size diameter can be set at

0.250in (6.35mm) resulting in 20 threads per inch (20 per 25.4mm). Therefore:

= 1.27mm

Pitch diameter is the diameter of a theoretical cylinder that passes through the threads in such

a position that the widths of the thread ridges and thread grooves are equal. These widths, in a

perfect world, would each equal one-half of the thread pitch [10]. Therefore:

1.27 × 2 = 2.54mm

The angle of the threads has been set at 60°. Unified screw threads have a 30° flank angle and

are symmetrical. This is why they are commonly referred to as 60° threads [10].

5.4.2 Safety Feature:

A safety feature will need to be employed to prevent shafts from moving in conjunction with

one another. Restricting the amount of components being introduced into the assembly, the

ideal method would be to utilise components which are already within the assembly design.

The principle in which the single actuation knob operates can serve multiple functions. It can

also provide this safety measure.

The idea would involve a spring and a locking mechanism. When the actuation knob is engaged

with the first set of cogs, it is restricted to only those cogs until the operation has been

completed. The knob can then advance to the next set of cogs by acting on a spring. When in

position, a lock mechanism would simply catch the knob, thus preventing it from retracting.

Note: The knob will need to disengage from the catch and return to its original position to allow

reclosure of the catheter tip.

5.4.3 Conclusion:

The most suitable material for the worm drive screws would be plastic, similar to that of the

Medtronic ‘CoreValve’ product (see Appendix 1). If steel were to be used, it would add

considerable weight when the four drives are combined within an assembly. With plastic


52

screws, the centre could be hollowed out. This would reduce the weight of the handle and

require less material.

By harnessing a spring actuation mechanism, it would cause a high degree of recoil when the

knob disengages from the catch. The spring would force the knob back at a high speed.

5.5 Human Factors

A further review on human factors input has been explored so as to enhance the balance

between usability and performance. Research was gathered and the methodology was

implemented into the handle design.

5.5.1 Macro Movement:

The original approach for disengaging from the worm drive involved a platform with a spring

mechanism. However, due to the redesign of the guides and cover, the macro mechanism will

need to be adjusted.

For usability measures, the motion would need to involve a pinch action as this would provide

the highest degree of force. The threads on the worm drive do not need to engage with the

entire circumference of the drive, half threads would be sufficient. As mentioned previously,

the external threads on the worm drives would be a 2A fitting, therefore, the internal threads

on the moving platform need to be a 2B fitting. Figure 43 shows a new approach for

disengaging from the worm drive.


53

Figure 43 – New Macro Approach

An important factor when designing this approach was to design for manufacturing and

assembly. As shown, the springs do not affect the current method for assembling the cover

onto the guides. Also, the threaded platform should be manufactured as a separate attachment

for ease of manufacturing, resulting in a standard set of parts.

Figure 44 – Macro Assembly Approach


54

The method for assembly involves a spring with a hook (figure 44). Each cover would contain a

spring on either side, and each threaded cap contains a hook for the spring to latch into. The

spring keeps the cap in position, and is only disengaged when a force is applied.

5.5.2 Usability Testing:

Usability testing is a means to determine whether a given medical device will meet its intended

users’ needs and preferences [11]. According to Medtronic representatives, usability testing is

mainly evaluated through direct contact with physicians (Appendix 3). The main purpose for

this test is to interpret how the handle controls would be used in a real case scenario.

In terms of the original design, the order of sequence by which the handle is operated is shown

in figure 45.

Figure 45 – Original Design Usability

1. Handle is gripped with the left hand. The shape can accommodate both left and right

hand users. Due to long procedure hours, the wrist posture would tend to vary, possibly

resulting in wrist strain


55

2. Right hand interacts with the rotary knob to micro retract the outer-most shaft. This can

require a high degree of force. Due to the overall diameter of the original design, the

whole hand is used to rotate the knob

3. Right hand interacts with the macro mechanism by pinching down and sliding. This is

the ideal approach, as it provides the highest degree of force for the required action.

The thumb and index finger are used to achieve this as they can exert the most amount

of force

4. Rotate right hand to slide the inner shaft back

5. Right hand slides the inner-most shaft back

6. Rotate right hand to advance the outer-most shaft forward (reclosure of the tip) either

by micro or macro approach

5.5.3 Conclusion:

Judging by the list of actions involved for manipulating shaft movement, the most effective

shape which the user interacts with is shown in figure 46. This enables both effective forward

and retraction movement.

Figure 46 – Macro Release Shape


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Users are able to search more quickly for simple rather than complex shapes [12]. By

implementing product semantics, it also helps create a more comprehensive view on how they

should be interacted with.

Figure 47 – Product Semantic Approach

Figure 47 shows a top view of the macro release button. By integrating ridges in a linear

pattern, it helps create a psychological track for the user and communicates the mechanical

principle without the need for a description. Different size shapes will distinguish shafts from

one another.

The overall diameter of the handle front grip and rotary knob can be influenced by the

following data:

Figure 48 – Anthropometric Grip Data [13]


57

In terms of handle diameter and control dimensions, the most appropriate percentile statistic

to aim for would be the 5th percentile of the female population (43mm). This would assure that

all male and females above this category would be able to operate the proposed handle design.

However, the length of the front grip should be designed to target the 95th percentile of the

male population (100mm), as categorized in figure 49.

Figure 49 – Anthropometric Hand Data [14]

5.6 Concept Refinement

Plastic injection moulding should be used to create the shaft guide components, allowing

mould expandability to accommodate different shaft sizes. Inserts would placed inside the

mould to form a split shaft version of the component. Each guide would contain a cavity at a set

point of extrusion to allow the protrusion of a screw.

Handle design will revolve around an inner-most catheter shaft of 16fr (5.3mm). It will contain a

steel rigid shaft of 7.6mm (outer diameter), resulting in a minimum size for the outer-most

shaft could of 24fr (8mm). The handle will also consist of four equal plastic worm drives with a

6.350mm diameter and a central lumen.


58

There will be a standard size for each of the covers which the user interacts with. It would be

suitable for use with each of the three shafts. When micro adjustment is intended for use, a

threaded cap would be inserted. Springs would be attached to keep it in position.

Overall diameter of the front grip and rotary knob on the handle should not exceed 43mm. The

grip design should be shaped with respect to potential variations in wrist posture during a

procedure. It should also be suitable for right and left hand users. The rotary knob should

contain an arrow shape slightly extruding from the surface. This ‘Braille type’ effect would allow

the surgeon to feel the direction in which to rotate, as focus may be set on the fluoroscopic

screen.

[PHASE 2] 6. Prototype Construction

59

6 Prototype Construction

This chapter will explain the steps taken for constructing multiple test rigs to demonstrate the

working prototypes. With limited resources, the prototypes were created as accurately as

possible to resemble a working scale model.

6.1 Shaft Movement

The purpose for constructing this test rig is to demonstrate the individual movement of three

catheter shafts within the handle design. Restricted by available resources, the diameter of the

shafts were not of the exact size dimensions; however the required range of travel for each

shaft was incorporated.

Figure 50 – Shafts Used

Figure 50 shows the variety of hollow shafts prior to construction. The shaft diameters are as

follows:


60

Outer-Most Shaft Support Shaft Inner Shaft Inner-Most Shaft

Diameter (mm): 11 15 (od), 11 (id) 5 4

Each shaft was shaped and cut to a specified length in order to facilitate the assembly. Many

tools and machining processes were utilised to create this test rig (figure 51).

Figure 51 – Tools and Machining Processes

Outer-Most Shaft Construction:

Due to limitations with shaft diameters and materials, the support shaft needed to be bonded

to the outside of the outer-most shaft, whereas in the final design, it would be concealed within

it. The shaft was coated with a grey primer so as to resemble the final colour scheme of the

shaft. The specifications of the fully constructed support shaft can be seen in figure 52.


61

Figure 52 – Outermost Shaft Construction

A dimensioned 3d model was sent to Medtronic to be printed (see Appendix 3) and the outer

shaft was attached. The dimensions can be seen in figure 53:

Figure 53 – 3D Model Dimensions

Inner Shaft Construction:


62

A dimensioned 3d model was printed by Medtronic to accommodate the outer diameter of the

inner shaft, and the shaft was cut to length. The dimensions can be seen in figure 54.

Figure 54 – Inner Shaft Construction

Inner-Most Shaft Construction:

The same process was repeated to accommodate the outer diameter of the inner-most shaft.

The dimensions can be seen in figure 55. A stopper was also attached to the shaft to allow

easier shaft manipulation for the user.


63

Figure 55 – Innermost Shaft Construction

The constructed shafts were assembled in position, and the test rig was created (figure 56).

Figure 56 – Shaft Movement Test Rig Assembly


64

Figure 57 – Shaft Test Rig Structure

The employment of a transparent plastic casing was to maintain stability and prevent each

shaft from moving out of position. It also provides a visual of the mechanical operation,

enabling a more comprehensive view for the observer (figure 57). Additional stoppers were

inserted into the test rig to restrict travel of selected shafts. A copper wire was introduced

primarily to keep the inner shafts in a central position. It also represents the principle of a

guide-wire.

6.2 Worm Drive

The purpose for constructing this test rig is to demonstrate the micro retraction on two

separate shafts. A single actuator is used to manipulate movement on both shafts. Additional

machines used for constructing this test rig and can be seen in figure 58.


65

Figure 58 – Machining Processes 2

6.2.1 Worm Drive Screws:

Four screws of the same size were used to demonstrate linear movement. Each screw needed

to have a cog bonded to its base. With minimal resources, two cogs of the same size were

obtained. A CNC Milling Machine was used to create the other two cogs of equal dimensions as

the existing ones (figure 59). A 3D model was drawn up to achieve this.

Figure 59 – Cogs Used

In order to attach the cogs to the base of the worm drives, a rig was constructed to ensure they

were bonded accurately on their centre. Each worm drive was threaded through a frame


66

structure which kept them on a straight axis, and the cogs were bonded (figure 60). The final

dimensions of each worm drive can be seen in figure 61

Figure 60 – Bonding Rig

Figure 61 – Worm Drive Dimensions


67

6.2.2 Rotary Knob:

A CNC Milling Machine was used to create two cogs of different dimensions. Both have a

central lumen to fit over a wire shaft. An acrylic shaft was used to connect the two cogs

together to enable movement relative to one another. The final dimensions of the rotary knob

can be seen in figure 62.

Figure 62 – Rotary Knob Dimensions

6.2.3 Platforms:

The size of the platform was determined by the dimensions of the worm drives and the

attached cogs. All centre points were calculated prior to construction. Each platform consists of

two nuts which were bonded internally. Both nuts travel over the worm drives as shown in

figure 63.


68

Figure 63 – Platforms

6.2.4 Assembly:

The components were positioned in a wooden frame and the test rig was complete. Figure 64

shows the assembly of the worm drive test rig.

Figure 64 – Worm Drive Test Rig Assembly

[PHASE 2] 7. Proof of Principle

69

7 Proof of Principle

This chapter will demonstrate the mechanical feasibility of the refined design.

7.1 Range of Travel:

As outlined in the design brief, the range of travel for each shaft must be between 30mm and

120mm, with the ability to restrict this travel. The feasibility for the proposed concept to

reduce the overall length of the handle was tested, and a constructed test rig will demonstrate

the principle:

Figure 65 – Outermost Shaft Travel

As shown in figure 65 the split section in the outer-most shaft offers an effective technique for

reducing the overall length of the handle. It travels the full 120mm without affecting any shaft it

overlaps.


70

Figure 66 – Inner Shaft Travel

Figure 66 shows the travel of the inner shaft. It travels 45mm before a stopper prevents it from

proceeding.

Figure 67 – Innermost Shaft Travel


71

Figure 67 shows the travel of the inner-most shaft. It travels 30mm before it comes to a halt.

7.2 Micro Precision:

The integration of micro adjustment on two shafts resulted in a slight variation to the original

design approach. The single actuator must be able to engage with both sets of cogs to

manipulate the movement of both shafts. A constructed test rig will demonstrate this by

manipulating movement of platforms on a separate axis (figure 68).

Figure 68 – Micro Precision Test Rig

A = Worm Drive (engages with vertical platform)

B = Worm Drive (engages with horizontal platform)

C = Vertical Platform

D = Horizontal Platform

E = Cog (manipulates horizontal platform)

F = Cog (manipulates vertical platform)


72

Figure 69 – Retract Vertical Platform

Figure 69 shows the micro retraction of the vertical platform. The cogs are rotated which force

the platform to move in a linear direction.

Figure 70 – Retract Horizontal Platform

The rotary knob advances to the next set of gears, and retracts the horizontal platform (figure

70).


73

7.3 Pulling Force

The shaft guides need to withstand a tolerance of 50 Newton’s pulling force. With respect to

available resources, a 3D physical model of the two half design was printed, and the pulling

force was tested with this material. The model was bonded onto the end of a tube, and clamp

kept it in position. A Newton meter with a 30 Newton limit was used (figure 71).

Figure 71 – Shaft Guide Test

The Newton meter was pulled excessively, and as shown in figure 72, it was able to withstand

the maximum tolerance of 30 Newton’s.

Figure 72 – Newton Force

[PHASE 2] 8. Final Design

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8 Final Design

Figure 73 shows the refined design of the handle delivery system.

Figure 73 – Refined Handle Design

8.1 Aesthetics and Branding

Research was undertaken to gather knowledge on the ‘Medtronic theme and style. The colour

scheme implemented in the final design is a collaboration of Medtronic products (see Appendix

1). The basic principle is to resemble a clean and efficient medical device product.

In addition to theme and style, the colour scheme also plays a role in functionality of the

handle. The rotary knob is linked with the engaging shafts, which provides a comprehensive

view as to which shafts the user will be manipulating.


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8.2 Dimensions

Given the additional features devised from the project briefing, the handle is designed with the

minimum size dimensions in mind, without affecting the performance. In comparison to the

previous design, particular attention was aimed towards feasibility and realistic component size

standards. The dimensions can be seen in figure 74.

Figure 74 – Refined Design Dimensions

The initial design contained an outer diameter of 54mm for the rotary knob; however this

consisted of micro adjustment on only one shaft. The more refined design was reduced to

52mm, consisting of micro adjustment on two shafts.

The highest peak distance on the initial design was located in between the macro components,

with a spacing of 78.5mm. This was reduced to 54mm on the newly developed design. The front

grip was also greatly reduced from a high peak of 54mm down to 45mm, and a low peak of

38mm down to 23mm.


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8.3 Manufacturing and Assembly Processes

The trans-catheter handle delivery system is a single use device. The materials and

manufacturing processes for the proposed concept are low cost to accommodate for this issue.

The manufacturing and assembly processes for the handle design is as follows:

8.3.1 Shaft Guides:

Figure 75 – Molded Shaft Guides

Plastic injection moulding is used to create the guide components for set shaft French sizes and

each mould can be scaled appropriately. Figure 75 shows the two different types of component

guides. At (A), a single slot moulded part is formed; however, if a guide component is required

for a split shaft, inserts could be placed within the same mould to form this part (B). A plastic

adhesive is then used to bond the guides to the three individual catheter shafts (figure 76).


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Figure 76 – Bond Guides to Shafts

8.3.2 Inner Central Casing:

The inner central casing consists of two separate halves. The catheter shafts are aligned in

position and the casing closes over them (figure 77).

Figure 77 – Inner Central Casing


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8.3.3 Guide Covers:

As mentioned in the ‘design modifications’ chapter, the cover is manufactured as a standard

size, suitable for all shafts. It slots over each of the guides and a Grubb screw is inserted to

combine them (figure 78).

Figure 78 – Attach Guide Covers

When required to interact with the worm drive, a threaded cap is attached to the cover part, as

shown in figure 79.

Figure 79 – Insert Threaded Cap


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8.3.4 Macro Button:

The macro release button is added, and simply rests on top of each of the covers (figure 80).

Figure 80 – Macro Release Button

8.3.5 Isolation Sheath:

An isolation sheath is placed over the outer-most shaft at the distal end of the handle. This

prevents outside contamination, as it completely covers the split section on the shaft (figure

81). It also reduces any friction between the handle and the actuating sheath.

Figure 81 – Attach Isolation Sheath


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8.3.6 Outer Casing:

The outer casing consists of two halves and closes over the assembly. It keeps all component

parts in a compact position. Four screws are used to piece them together, as shown in figure

82. The screws also protrude through the inner central casing, keeping a secure assembly.

Figure 82 – Attach Outer Casing

8.3.7 Worm Drives:

Two sets of worm drives are inserted into the assembly. Each worm drive is fed through the

casing and component covers (figure 83).


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Figure 83 – Insert Worm Drives

8.3.8 Rotary Knob:

A compression spring slots over the central casing shaft, and the rotary knob is placed after it

(figure 84).

Figure 84 – Attach Rotary Knob


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A stopper is attached to keep the knob in position (figure 85).

Figure 85 – Attach Stopper

8.3.9 Guidewire Entry:

An entry point for a guidewire is attached (see figure 86). The dimensions and shape are taken

from an existing ‘Medtronic’ product – The Engager (see Appendix 1). A plastic adhesive is used

to bond the entry point to the central casing.

Figure 86 – Attach Guidewire Entry Point


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8.3.10 Bill of Materials:

Component Name: Quantity: Material: Manufacturing Process:

Shaft Guides 3 Plastic Injection Moulded

Rigid Shaft 1 Stainless Steel Cutting

Central Casing 2 Plastic Injection Moulded

Guide Covers 6 Plastic Injection Moulded

Threaded Caps 4 Plastic Injection Moulded

Grubb Screw 6 Carbon Steel N/A

Buttons 6 Plastic Injection Moulded

Outer Casing 2 Plastic Injection Moulded

Philips Screws 4 Carbon Steel N/A

Worm Drives (long) 2 Plastic Laser Cutting

Worm Drives (short) 2 Plastic Laser Cutting

Spring 1 Steel N/A

Rotary Knob 1 Plastic Injection Moulded

Guidewire Entrance 1 Polycarbonate Injection Moulding

Table 9 – Bill of Materials

8.4 Conclusion and Evaluation

8.4.1 Recommended for Use:

The concept of split shafts would only really be a beneficial option if a long range of travel on

the outer-most shaft was required. However, if the inner-most shaft (16fr) were to be scaled

up, it would have an impact on the anthropometric data of the handle, thus reducing the

amount of user percentiles which could operate it effectively.

With all features and components taken into consideration, the minimum grip diameter of the

proposed handle design is 52mm. Therefore, it is only really suitable for the 50th percentile

population or greater.


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8.4.2 Further Development:

As mentioned at the beginning of this project, the amount of development was determined by

the constraints in both limited resources and minimal timeframe. The primary focus was

meeting the design requirements as set out in the design brief. However, further development

is required:

- A user analysis will need to be conducted on physicians and surgeons, so as to gain

constructive feedback and comparisons

- A Failure Mode and Effect Analysis (FMEA) will identify any potential risks

- Material testing: heat; texture; hygiene

- A focus on packaging design will be important in terms of: storage, user interaction,

branding, and disposal

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References

[1] Medical Journal, Leon, Martin B., Nikolsky, Eugenia, October 10th, (2010), ‘The Next

Revolution: Percutaneous Aortic Valve Replacement’, Issue 2, Volume 1

[2] Human Anatomy Imaging, [online] https://www.biodigitalhuman.com/ (Accessed August

2012)

[3] Verdonck, Pascal, (2009), ‘Advances in Biomedical Engineering’, Amsterdam, the

Netherlands, Elsevier

[4] Dr. Iazzetti, Giovanni, Dr. Rigutti, Enrico, (2008), ‘Human Anatomy’, Surrey, Taj Books

International LLP

[5] NIH Library, [online] http://www.nlm.nih.gov/medlineplus/heartvalvediseases.html

(Accessed August 2012)

[6] Iaizzo, Paul A., (2009), ‘Handbook of Cardiac Anatomy, Physiology, and Devices’, Springer,

New York, Second Edition

[7] World Journal of Cardiology, June 26th, (2011), ‘Transcatheter Aortic Valve Implantation:

Current Status and Future Perspectives’, Issue 6, Volume 3

[8] Medtronic CoreValve, [online] http://www.medtronic.com/corevalve/ous/about.html

(Accessed November 2011)

[9] Medtronic Melody, [online] http://www.medtronic.com/melody/procedure.html (Accessed

November 2011)

[10] Standard Screw Sizes, ‘Fastenal Industrial Construction Guide’, [online]

http://www.fastenal.com/content/documents/FastenalTechnicalReferenceGuide.pdf (Accessed

August 2012)

https://www.biodigitalhuman.com/

http://www.nlm.nih.gov/medlineplus/heartvalvediseases.html

http://www.medtronic.com/corevalve/ous/about.html

http://www.medtronic.com/melody/procedure.html

http://www.fastenal.com/content/documents/FastenalTechnicalReferenceGuide.pdf

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[11] Wiklund et al, (2011), [online] ‘Usability Testing of Medical Devices’, USA, CRC Press

[12] Goebel et al, (2009), [online] ‘Engineering Psychology and Cognitive Ergonomics’, Berlin,

Springer

[13] Hand Anthropometry, [online] http://usability.gtri.gatech.edu/eou_info/hand_anthro.php

(Accessed August 2012)

[14] Science Journal, PDF [online], (2009) ‘Anthropometric Data of the Hand, Foot and Ear of

University Students in Nigeria’, (Accessed August 2012)

http://usability.gtri.gatech.edu/eou_info/hand_anthro.php

87

Bibliography

[1] Stanton, Neville et al, (2005), ‘Handbook of Human Factors and Ergonomic Methods’, USA,

CRC Press

[2] West, S.H., U.S. Patent 6 156 027, (2000)

[3] Bortlein, G., Pannek, E., U.S. Patent 2010/0100167 A1, (2010)

[4] Yeung et al, U.S. Patent 2011/0098804 A1, (2011)

[5] Dwork et al, U.S. Patent 2011/0098805 A1, (2011)

[6] Dwork, J., U.S. Patent 2011/0251675 A1, (2011)

[7] Tabor, C., U.S. Patent 2011/0251683 A1, (2011)

[8] Dwork et al, U.S. Patent 2011/0264203 A1, (2011)

[9] Magellan Robotic System, ‘Product Video’, [online video]

http://www.hansenmedical.com/eu/products/vascular/magellan.html (Accessed December

2011)

[10] Aortic Valve Replacement by femoral approach, ‘Percutaneous Aortic Valve Replacement’,

[online video] http://www.youtube.com/watch?v=1Bfheuz1SK4 (Accessed December 2011)

[11] Trans-catheter procedure, ‘Trans-catheter Aortic Valve Replacement’, [online video]

http://www.youtube.com/watch?v=zvQpJQHAwKk (Accessed December 2011)

[12] CoreValve delivery procedure, ‘CoreValve Aortic Valve Medtronic 201106’, [online video]

http://www.youtube.com/watch?v=Qg9Kvq-nTN4 (Accessed December 2011)

http://www.hansenmedical.com/eu/products/vascular/magellan.html

http://www.youtube.com/watch?v=1Bfheuz1SK4

http://www.youtube.com/watch?v=zvQpJQHAwKk

http://www.youtube.com/watch?v=Qg9Kvq-nTN4

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Appendices

Appendix 1

(Photographic Study)

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The CoreValve:

CoreValve Handle:

Single Sheet Retraction (Accutrak Stability Shaft attached):

Micro retraction mechanism:

90

Macro Retraction Mechanism:

91

The Engager:

Engager Handle:

Shaft 1/Blue Knob (forward shaft movement):

Shaft 2/Black Knob (retraction shaft movement):

92

Safety button:

Indication of Shaft Location:

93

The Xcelerant:

The Xcelerant doesn’t deliver valve replacements to the heart; it delivers a stent graft to the

abdomen. However, it involves similar mechanical principles and requires retraction movement

of two shafts.

Xcelerant Handle:

Shaft 1/Outer Shaft Micro mechanism:

94

Macro Mechanism:

Shaft 2/Inner Shaft (locking mechanism):

95

Appendix 2

(Concept Presentation)

99

Appendix 3

(Email Arrangements)

100

Briefing:

Review Meeting 1:

102

Tubing Samples:

103

Project Queries:

106

Review Meeting 2:

masters thesis

Documents

design project

design declaration

faculty of design

proposed design

final design

devised design brief

maximum design efficacy

msc medical device design