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

Design of a Mechanical Device to Influence Skin Wound Healing and Scar Formation. Team: JILL D. PINKSTAFF 1 ERIC N. HETTINGER 1 MICHELLE L. KLEINE 1 Advisor: DR. SEAN S. KOHLES 1,2 Sponsor: DR. SHELLEY R. WINN 2.

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

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  1. Design of a Mechanical Device to Influence Skin Wound Healing and Scar Formation Team: JILL D. PINKSTAFF1 ERIC N. HETTINGER1 MICHELLE L. KLEINE1 Advisor: DR. SEAN S. KOHLES1,2 Sponsor: DR. SHELLEY R. WINN2 1Mechanical and Materials Engineering, PSU 2Plastic and Reconstructive Surgery, OHSU

  2. Introduction • During skin wound healing, excessive scar material often protrudes beyond the boundaries of the wound • These abnormalities are known as hypertrophic scars or keloids • Affect up to 16% of the world’s population • May lead to serious functional and cosmetic problems for the patient • Current research has yet to determine the exact biological or mechanical mechanisms behind their formation

  3. State of the Art:Investigating Excessive Scar Formation • Recent application of a published scar wound model • A constant biological irritation was applied • Used a in vivo guinea pig model • Extensive animal care was required • Approach was determined to be unsuccessful • Alternative approach proposed • A constant mechanical stimulus is applied • Use an in vivo guinea pig model • Significantly reduce required care • The objective of this project is to design a device which can mechanically manipulate an artificial open wound model

  4. Design Specifications • Defined as a device which can apply controlled tensile and shear loads to a guinea pig surrogate in preparation for a living subject wound model • Design criteria include • Have a reliable/repeatable function • Perform for a period of 30 days • No excessive supervision or maintenance is required • No unnecessary harm is inflicted on the guinea pig • Upon satisfying the design objective, this technology will enable researchers to gather information that may help prevent excessive scaring and develop new therapies for skin wound healing

  5. Concept Design Process EXTERNAL FRAMES DESIGN CONFIGURATION • Configure load applicators to apply tension and shear to wound • Secure mechanical stimulus to model LOAD APPLICATORS CONTROL SYSTEM • Apply load via stepper motor and linear actuator • Control load applicators through LabView interface

  6. Analysis Methods and Results:Synthetic Skin Testing • An experiment was developed to quantify the effect of shear loading on a wound model • Opposing forces were applied to a polymeric composite • Displacement was recorded through digital image correlation • The results yielded initial load-displacement parameters which have been implemented into the design process

  7. Analysis Methods and Results:Finite Element Analysis • FEA model performed using ANSYS software • Analysis parameters • Linear elastic, isotropic, homogeneous material • μ = 0.45 and E = 1.6 MPa • Shear loading of 1 N on wound edges • Force yielded less than 1 mm of displacement • Initial analysis shows the significance of the skin-tissue composition in the model results

  8. Device Configuration 150 g Tethered to control system 75 g 75 g FORCE TRANSMISSION A-A = Tension, B-B & C-C = Shear For a 2 mm stroke, the actuator delivers a maximum load of 150 g SPINE A Guinea Pig Surrogate B C WOUND B C FRONT VIEW OF DEVICE A TOP VIEW OF WOUND

  9. Unique Design Innovations 4 mm • Stationary leg retainer • Small and compact • Multiple orientations • Allows translation of vertical motion to horizontal motion • Control 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

  10. Summary • Ongoing design, research and evaluation effort • Future applications include • IACUC approval for future studies • Hypothesis testing of scar formation mechanisms • Test association with natural 'tension lines' which currently guide surgical technique

  11. Special Thanks to • Bernie (Machinist) • Clyde (Mobile Frame) • Meagan (Synthetic Skin Experiment) • Dr. Gong (Animal Specialist) • Dr. Meekisho (FEA) • Dr. Wern (Control System) • Funding provided by • Division of Plastic and Reconstructive Surgery (OHSU) • Questions?

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