Ankush Verma

IR/3/10H3/27/2017

3D PRINTED PROSTHETICS: A NEW GENERATION

ABSTRACT

3D Printing and Robotics have the ability to revolutionize the medical industry if they are

combined together. A foot prosthetic that combines both 3D printing and Targeted

Muscle Reinnervation is the pivoting point for this idea to occur. Indubitably, this

prosthetic can be used to solve issues in low-income areas, as it would be relatively

inexpensive. The robotics portion of the prosthetic is able to develop with a child, similar

to how a normal foot would. This eliminates the issue of multiple prosthetics over the

course of multiple years, as limbs change. This would be done through a simple Java

program that automatically extends a metal piece out, expanding the length and width of

the foot.

MAIN BODY

Robotics has made a huge impact in the medical industry. There have been

major breakthroughs within this industry, for example, surgery with robotics as well as

robotic prosthetics, 3D printing, 3D printed prosthetics, which has been around for quite

a long time. Many prosthetists have created expensive robotic arms that have movable

fingers and others have created cheaper, 3D printed arms which have movable fingers.

The issue is the integration of both ideas, as many issues can branch off based on the

price of the prosthetic or whether the prosthetic would work or not. A innovative solution

would be to create a prosthetic for the foot, as that is an area that is currently not being

extensively researched upon, which can move around; develop along with the child,

effectively lowering the cost; and combine both 3D printing and robotics.

There has been an issue regarding the price of the prosthetic for a foot. This has

been solved for the hand. A few years ago, a group of college students set out to create

a robotic arm, formally named the “Cyborg Beast,” for those who lacked a prosthetic.

The contraption created was inexpensive and could perform the assigned job of a hand,

as that is what prosthetics are made for. Two mechanisms that were used were ones

that would easily move the fingers and the 3D printed parts. The prosthetic was created

in a Computer Aided Design (CAD) program and printed on a MakerBot. The students

also described how the Targeted Muscle Reinnervation functions were high on

maintenance, as it is a robotic piece and can be destroyed easily, especially in a low-

income area where the conditions are not well. This resulted in the exclusion of it from

the project (Zuniga et. Al. 2015).

The mechanism for the fingers were an elastic cord. They are low-cost and easy

to manage, as well as they can sustain longer than a rubber band. This user-friendly

design makes it an indispensable apparatus to be included in any cheap prosthetic. An

example of the cord is shown in FIG 1. The prosthetic had the ability to switch parts at

ease if one were to break.

FIG 1: E-NABLE created a 3D prosthetic hand that is very much comparable to

the prosthetic created by the students.

For the finger mechanisms to function, there must be rubber bands that connect

to the separate fingers, allowing for their movement. The CAD program used to design

the prosthetic was called Blender. It is quite difficult to use for CAD purposes, as the

interface is not as straightforward compared to traditional programs and it is generally

used for animations. A better alternative would be an open-source program named

Libre-CAD. Libre-CAD is a straightforward conceptual designer used to design 3D parts,

as well as it is designed for CAD creation only. The limiting factor of the CAD program is

that the creation of any corporeality in the program must be able to convert to a .STL

file, which is the most common file for 3D printers. (Zuniga et. Al. 2015)

The students who created this project chose to exclude the Targeted Muscle

Reinnervation, which deals with the rerouting of nerve cells to allow for movement of the

limbs (See page 4), idea completely as it would be difficult to manage, as the living

conditions are low-end. These types of prosthetics do not have anything protecting it,

causing the item to be destroyed easily if not managed properly, as the conditions in

poor areas are not great. A strong 3D printed carbon fiber prosthetic casing must be

used for greater durability. Another issue would be the high cost of a replacement as

certain parts cannot be taken apart, rather the whole conceptually designed article must

be removed. The solution to this would be to minimize the TMR idea to a small space

and make most of the prosthetic out of 3D printing. This allows for the ease of

modularity, which makes the prosthetic significantly, or eloquently, cheaper.

The problem with prosthetics, including the Cyborg Beast, is that they cannot

develop, or grow the way a human foot grows. For this to happen, the prosthetic must

be able integrate Targeted Muscle Reinnervation and an array that is to be attached,

which would be coded with a coding language called Java. Java is a field that scientists

argue should be well-taught and generalized in this current era (Vee). It is important to

implement it into such an article for outcome of teaching people Java and coding

overall. Since the focus of the research deals with the foot, not the hand, at ages 5-10, it

will be required that there is a mathematical formula in the code that can determine how

much the prosthetic foot should extend over a certain period. For example, at the age of

5, the foot “will grow rapidly” and there will be a ½ size increase every 4 months.

Afterward, there will be a difference in the growth, either growing at a faster or slower

rate. This would require the formula to determine the certain length based on the age,

gender, and current size. It will be straightforward in the implication that the width will

stay proportional to the length. Essentially, the Java code will be setup and the numbers

must be plugged in. A more visual aspect of the growth and proportionality is shown in

FIG 2. The formula would be created using the chart mentioned below.

FIG 2: The CDC released a graph of child growth from ages 2-20, where the

focus would be from 5-10 years of age.

From thereon, the code will be installed on an array. The “experimental field

programmable analog array” (Toreyin and Bhatti 2013) would be installed within the

Targeted Muscle Innervated part itself. This portion will be both 3D printed and metal,

as the TMR requires metal, to make it both cheap and effective. The array would

process the information and move the motors, to indispensably create a real-life

situation of a growing foot in a robotic format.

It is a stipulation that such a code and array would be added. The child needs to

initiate and instigate the prosthetic at age 5 as that is when the foot begins growing

expeditiously. The prosthetic can also maintain a cheap functioning motor for a long

interval, therefore saving the prosthetic and making it last.

The part that the array for coding purposes would be attached to is the TMR. The

Prosthetic will be split up into two different parts, one for the TMR portion which allows

for coding to be possible and plausible, and the other being the 3D printed part, which

makes the prosthetic cheaper compared to metal.

Targeted Muscle Reinnervation, created by Dr. Todd Kuiken in the early 2000s,

is a relatively new way to create advanced prosthetics. It deals with rerouting a nerve

cell of an amputated limb, which has been dysfunctional, to another spot. The nerve

cells would be fired thereafter and it would be sent to the TMR prosthetic. The process

can be summed as the “[transferring of] residual arm nerves to alternative muscle sites”

(Kuiken et. Al. 2009). This part of the prosthetic would allow for the child to move their

foot and toes. To make the prosthetic grow, it must be programmed. Programming will

be achieved through an array installed within the Targeted Muscle Reinnervation portion

of the foot. An experimental field programmable analog array must be installed to make

this work. There would be a “signal processing circuitry [which] generates a non-linear

signal that codes angular velocity into a pulse rate for a single SCC” (Toreyin and Bhatti

2013).

One of the 3D printed portions is the socket for the prosthetic itself. For this to

occur, the residual ankle muscle must be scanned using “3D laser scanning…combined

with rapid prototyping” (Mavriodis et. Al 2011). The 3D scanner scans and creates a

socket for the residual ankle for the Prosthetic to be attached to, with space for the TMR

part to be attached. Through this, the child can seem comparably normal when walking.

This idea would be important as prosthetic hooks “have a high rejection rate, in part due

to an unacceptable cosmetic appearance” (Zuniga et. Al. 2015).

Unequivocally, 3D printing must be integrated into another portion of the TMR

prosthetic, rather than the socket part itself. Through this, the price can effectively be

decreased. If the two parts are kept separate, the price will be much higher than before.

An example to support this is if the 3D Printed Part costs $40 and the TMR part costs

$40 by themselves rather than half and half of both parts. Past prosthetic models have

chosen to either be 3D printed or made from metal. The prosthetic should be

inexpensive as well as develop, include the TMR and the array attached to it. This is

where the 3D printing and TMR combination arises, as the example above details that

the price would significantly decrease.

How the Prosthetic Functions ( See FIG 2 for CAD Example)

This Prosthetic will function differently compared to traditional prosthetic, as there is the

combination of both 3D printing and TMR included within this part itself, the amputated

area will be scanned and measured to find the right size for the socket. The socket of

the prosthetic is where the prosthetic itself can easily be attached and changed in case

something was to happen to the part overall. The Prosthetic will have a socket, the part

that attaches to the socket, and the ankle as 3D printed. The rest of the part, from the

ankle to the toes, will be a combination of 3D printing and Targeted Muscle

Reinnervation. The toes, for example, would be 3D printed as it would cost a great

amount of money to apply a motor for each.

FIG 2: 3D CAD Example (Created in Microsoft 3D Builder)

Conclusion (as if there were an Experimental Procedure already completed)

The results were impeccable: the prosthetic could withstand around 50 lbs. of

weight, the simulation moved the foot and toes, and the prosthetic could develop. This

is a necessary objective since the child must keep the prosthetic for quite an

approximate amount of time. With the future in 3D printing and robotics, such a

prototype would be a huge breakthrough in the prosthetics industry. Although this

product may take some time, this would be a life-long investment for parents and the

betterment of those less fortunate children at a young age. This idea requires support

from workers in the biomedical field to achieve, as it may be costly timewise.

REFERENCES (APA)

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Zuniga, Jorge, Dimitrios Katsavelis, Jean Peck, John Stollberg, Marc Petrykowski, Adam Carson, and Cristina Fernandez. “Cyborg Beast: A Low-Cost 3d-Printed Prosthetic Hand for Children with Upper-Limb Differences.” BMC Research Notes 8 (2015): 10. doi:10.1186/s13104-015-0971-9. Accessed January 29th 2017

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