Design of a Mechanical Device to Design of a Mechanical Device to Influence Skin Wound Healing and Influence Skin Wound Healing and

Scar FormationScar Formation

Team:Team: JILL D. PINKSTAFFJILL D. PINKSTAFF11

ERIC N. HETTINGERERIC N. HETTINGER11

MICHELLE L. KLEINEMICHELLE L. KLEINE11

Advisor:Advisor:DR. SEAN S. KOHLESDR. SEAN S. KOHLES1,21,2

Sponsor:Sponsor:DR. SHELLEY R. WINNDR. SHELLEY R. WINN22

11Mechanical and Materials Engineering, PSU Mechanical and Materials Engineering, PSU 22Plastic and Reconstructive Surgery, OHSUPlastic and Reconstructive Surgery, OHSU

22

IntroductionIntroduction

During skin wound healing, excessive scar During skin wound healing, excessive scar material often protrudes beyond the material often protrudes beyond the boundaries of the woundboundaries of the wound

These abnormalities are known as These abnormalities are known as hypertrophic scars or keloidshypertrophic scars or keloids Affect up to 16% of the world’s population Affect up to 16% of the world’s population May lead to serious functional and cosmetic May lead to serious functional and cosmetic

problems for the patient problems for the patient

Current research has yet to determine the Current research has yet to determine the exact biological or mechanical exact biological or mechanical mechanisms behind their formationmechanisms behind their formation

33

State of the Art:State of the Art:Investigating Excessive Scar FormationInvestigating Excessive Scar Formation

Recent application of a published scar Recent application of a published scar wound model wound model A constant biological irritation was appliedA constant biological irritation was applied Used a Used a in vivoin vivo guinea pig model guinea pig model Extensive animal care was requiredExtensive animal care was required Approach was determined to be unsuccessfulApproach was determined to be unsuccessful

Alternative approach proposedAlternative approach proposed A constant mechanical stimulus is appliedA constant mechanical stimulus is applied Use an Use an in vivoin vivo guinea pig model guinea pig model Significantly reduce required careSignificantly reduce required care

The objective of this project is to design a The objective of this project is to design a device which can mechanically device which can mechanically manipulate an artificial open wound manipulate an artificial open wound modelmodel

44

Design SpecificationsDesign Specifications Defined as a device which can apply Defined as a device which can apply

controlled tensile and shear loads to a controlled tensile and shear loads to a guinea pig surrogate in preparation for a guinea pig surrogate in preparation for a living subject wound modelliving subject wound model

Design criteria includeDesign criteria include Have a reliable/repeatable functionHave a reliable/repeatable function Perform for a period of 30 daysPerform for a period of 30 days No excessive supervision or maintenance is requiredNo excessive supervision or maintenance is required No unnecessary harm is inflicted on the guinea pigNo unnecessary harm is inflicted on the guinea pig

Upon satisfying the design objective, this Upon satisfying the design objective, this technology will enable researchers to gather technology will enable researchers to gather information that may help prevent excessive information that may help prevent excessive scaring and develop new therapies for skin scaring and develop new therapies for skin wound healingwound healing

55

Concept Design ProcessConcept Design ProcessDESIGN CONFIGURATIONEXTERNAL FRAMES

LOAD APPLICATORS CONTROL SYSTEM

Secure mechanical stimulus to model

Configure load applicators to apply tension and shear to wound

Apply load via stepper motor and linear actuator

Control load applicators through LabView interface

66

Analysis Methods and Results:Analysis Methods and Results:Synthetic Skin TestingSynthetic Skin Testing

An experiment was An experiment was developed to quantify developed to quantify the effect of shear the effect of shear loading on a wound loading on a wound modelmodel Opposing forces were Opposing forces were

applied to a polymeric applied to a polymeric compositecomposite

Displacement was Displacement was recorded through digital recorded through digital image correlationimage correlation

The results yielded The results yielded initial load-initial load-displacement displacement parameters which have parameters which have been implemented into been implemented into the design process the design process

77

Analysis Methods and Results:Analysis Methods and Results:Finite Element AnalysisFinite Element Analysis

FEA model performed FEA model performed using ANSYS softwareusing ANSYS software

Analysis parametersAnalysis parameters Linear elastic, isotropic, Linear elastic, isotropic,

homogeneous materialhomogeneous material μμ = 0.45 and E = 1.6 MPa = 0.45 and E = 1.6 MPa Shear loading of 1 N on Shear loading of 1 N on

wound edges wound edges

Force yielded less than Force yielded less than 1 mm of displacement1 mm of displacement

Initial analysis shows Initial analysis shows the significance of the the significance of the skin-tissue composition skin-tissue composition in the model resultsin the model results

88

Device ConfigurationDevice Configuration

FRONT VIEW OF DEVICE

SP

INE

C

CB

B

A

A

TOP VIEW OF WOUND

Guinea Pig Surrogate

FORCE TRANSMISSION

WOUND

A A

A-A = Tension, B-B & C-C = Shear

For a 2 mm stroke, the actuator delivers a maximum load of 150 g

75 g

150 g

75 g

Tethered to control system

99

Unique Design InnovationsUnique Design Innovations

Stationary leg retainerStationary leg retainer Small and compactSmall and compact Multiple orientationsMultiple orientations Allows translation of Allows translation of

vertical motion to vertical motion to horizontal motionhorizontal motion

Control systemControl system LabVIEW allows complete

control over the system System enables user to

Orient the loading condition

Adjust motor/linear actuator speed

Alter dynamic loading cycle

15 mm

4 mm

1010

1111

SummarySummary Ongoing design, Ongoing design,

research and research and evaluation effortevaluation effort

Future applications Future applications includeinclude IACUC approval for IACUC approval for

future studiesfuture studies Hypothesis testing of Hypothesis testing of

scar formation scar formation mechanismsmechanisms

Test association with Test association with natural 'tension lines' natural 'tension lines' which currently guide which currently guide surgical techniquesurgical technique

1212

Special Thanks toSpecial Thanks to Bernie Bernie (Machinist)(Machinist) Clyde Clyde (Mobile Frame)(Mobile Frame) Meagan (Meagan (Synthetic Skin ExperimentSynthetic Skin Experiment)) Dr. Gong (Dr. Gong (Animal SpecialistAnimal Specialist)) Dr. Meekisho Dr. Meekisho (FEA)(FEA) Dr. Wern Dr. Wern (Control System)(Control System)

Funding provided by Funding provided by Division of Plastic and Reconstructive Division of Plastic and Reconstructive

Surgery (Surgery (OHSUOHSU))

Questions?Questions?