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Technical Brief

A Protocol for Measuring Pull-off Stress of Wound-Treatment Polymers

[+] Author and Article Information
Vitaly O. Kheyfets, Rita C. Thornton, Mikala Kowal

Department of Biomedical Engineering,
The University of Texas at San Antonio,
San Antonio, TX 78249

Ender A. Finol

Department of Biomedical Engineering,
The University of Texas at San Antonio,
San Antonio, TX 78249
e-mail: ender.finol@utsa.edu

1Corresponding author.

Manuscript received September 10, 2013; final manuscript received April 3, 2014; accepted manuscript posted April 11, 2014; published online May 12, 2014. Assoc. Editor: Sean S. Kohles.

J Biomech Eng 136(7), 074501 (May 12, 2014) (5 pages) Paper No: BIO-13-1420; doi: 10.1115/1.4027412 History: Received September 10, 2013; Revised April 03, 2014; Accepted April 11, 2014

Skin wounds and burns compromise the body's natural barrier to bacteria and other pathogens. While many forms of wound dressings are available, polymeric films are advantageous for various reasons, ranging from the ease of application to durability. One common drawback of using polymeric films for a wound bandage is that the films tend to adhere to common inanimate objects. Patients spend hours in contact with soft and hard materials pressed against their skin, which, if the skin was dressed with a polymeric film, would inflict further wound damage upon body movement. In this work, we present a novel technique that allowed for measuring polymeric tackiness, after a long incubation period, with materials regularly encountered in a hospital or home setting, and soft fabrics. The polymers were exposed to an environment intended to simulate daily conditions and the technique is designed to perform multiple experiments simultaneously with ease. Four commercially available polymers (new-skin, no-sting skin-prep, skin shield, and Silesse) were tested as proof-of-concept to gather preliminary data for an overall assessment of wound treatment efficacy, resulting in the estimation of pull-off stress of the polymers from a specimen of porcine skin. Silesse did not reveal a measurable tackiness, no-sting skin-prep had the highest mean tackiness (13.8 kPa), while the mean tackiness between new-skin and skin shield was approximately equal (9.8 kPa vs. 10.1 kPa, respectively), p = 0.05. Future work on polymeric fluids for wound dressing applications should include tensile stress and dynamic viscosity estimations.

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Figures

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Fig. 1

Pull-off testing apparatus and nomenclature: (a) pull-off stress testing assembly configured for the Bose Electroforce T3200 testing apparatus; (b) radial insert ball bearing system; and (c) close-up of the Block-Skin-Polymer-Dolly assembly clamped to the load cell top plate and metal stoppers.

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Fig. 2

(a) Schematic showing primary testing components by layer. The load cell top and bottom plates are made of Plexiglas ® and machined to accommodate the load cell threading. (b) A picture of weight distributed over 12 samples curing inside an incubator.

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Fig. 3

Protocol for conducting pull-off testing between polymeric films intended as wound dressings and soft fabrics: (a) a clamp is laid atop a flat piece of pig hide with polymer applied; (b) a dolly and cloth are compressed onto the skin through the clamp. This assembly can be made simultenously and placed in incubation as shown in Fig. 2; (c) a custom made part containing a threaded shaft; and (d) as the assembly is placed on the bottom base for testing, the custom part (shown in c) is pressed through the clamp and the fabric is secured to the shaft.

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Fig. 6

Mean and standard error of the work of separation with skin for three commercial products: New-skin (24.9 ± 2.4 J/m2), no-sting skin-prep (37.8 ± 5.4 J/m2), and skin shield (28.6 ± 4.6 J/m2).

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Fig. 5

Mean and standard error of pull-off stress with skin for three commercial products: New-skin (9.8 ± 0.8 kPa), no-sting skin-prep (13.8 ± 1.4 kPa), and skin shield (10.1 ± 1.4 kPa). The insert shows exemplary Force vs. displacement data for skin shield. Silesse is not shown as it revealed no measurable tackiness.

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Fig. 4

Appearance of dolly and skin after pull-off experiment for the 4 polymeric films. All 3 modes of detachment are present among the films: (1) failure in the adhesive strength at the polymer-skin interface; (2) failure in the adhesive strength at the polymer-dolly interface; and (3) failure in the structural integrity of the cured polymer.

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