Mechanical properties of the skin: a comparison between two suction cup methods

The Use of Fish Skin Grafts in Children as a New Treatment of Deep Dermal Burns-Case Series with Follow-Up after 2 Years and Measurement of Elasticity as an Objective Scar Evaluation

Background: Wound healing in deep dermal burn injuries continues to be a challenge in paediatrics. In the absence quick and spontaneous wound closure, split-thickness skin grafting is often necessary. Since the development of a new type of acellular fish matrix, which is very similar to the human skin matrix, skin closure and wound conditioning can be achieved without split-thickness skin grafting. Methods: The following study shows a case series of 20 children in whom a fish skin graft was used. The aim was to develop an algorithm for selecting and using fish skin and its long-term results after one and two years. Acellular fish skin worked as a granulation base for wound healing and also as a substitute for split-thickness skin grafts. Results: There was no evidence of infection. Skin transplants and, thus, additional operations could be avoided. The follow-up examinations showed an excellent result, both objectively by means of elasticity measurements (DermalabCombo®) and in the subjective assessment of the skin as part of the Patient and Observer Scar Assessment Scale (POSAS). Conclusion: Fish skin grafts are a good alternative to split-thickness skin grafts for deep dermal wounds. These results should be further analysed with a larger number of patients in future publications.

Viscoelastic Properties of Human Facial Skin and Comparisons with Facial Prosthetic Elastomers

Prosthesis discomfort and a lack of skin-like quality is a source of patient dissatisfaction with facial prostheses. To engineer skin-like replacements, knowledge of the differences between facial skin properties and those for prosthetic materials is essential. This project measured six viscoelastic properties (percent laxity, stiffness, elastic deformation, creep, absorbed energy, and percent elasticity) at six facial locations with a suction device in a human adult population equally stratified for age, sex, and race. The same properties were measured for eight facial prosthetic elastomers currently available for clinical usage. The results showed that the prosthetic materials were 1.8 to 6.4 times higher in stiffness, 2 to 4 times lower in absorbed energy, and 2.75 to 9 times lower in viscous creep than facial skin (p < 0.001). Clustering analyses determined that facial skin properties fell into three groups-those associated with body of ear, cheek, and remaining locations. This provides baseline information for designing future replacements for missing facial tissues.

Non-Invasive in Vivo Quantification of Directional Dependent Variation in Mechanical Properties for Human Skin

Skin is the body’s largest organ, and it shows non-linear and anisotropic behavior under the deformation. This behavior of the skin is due to the waviness and preferred orientation (in a particular direction) of collagen fibers. This preferred orientation of collagen fibers results in natural pre-tension and anisotropy of the skin. The knowledge of natural skin pre-tension and anisotropy is essential during incisions and surgery. The available suction-based devices quantify the anisotropy through the displacement field and cannot measure the stress-strain relation in particular directions. Therefore, in the current study, an in vivo full-field measurement suction apparatus was developed to measure the stress and strain of skin in all planar directions through a single experiment. First, this apparatus was tested on silicone substrates of known properties, and then it was used to test the skin of 12 human forearms. Further, to check the effect of hand stability on the measurements, the obtained results of the skin were compared with the results of a standard test performed in the same skin using a steady setup. The consistency between these two results confirms that the stability of the hand does not influence the measurements of skin properties. Furthermore, using the developed apparatus, the skin’s anisotropy and its relation with the Kraissl’s lines orientation was quantified by measuring the toe and linear moduli at an interval of one degree. The minimum and maximum values of the toe and linear moduli were 0.52 ± 0.09 and 0.59 ± 0.11 MPa, and 3.09 ± 0.47 and 5.52 ± 1.13 MPa, respectively. Also, the direction of maximum moduli was found almost similar to Kraissl’s lines’ orientation. These results confirm the contribution of skin pre-tension on the anisotropy of the skin. The present apparatus mimics the tissue expansion procedure, where observation of the test may be helpful in the selection of size and shape of the expander.

Toward clinical elastography of dermal tissues: A medical device to probe skin's elasticity through suction, with subsurface imaging via optical coherence tomography

The mechanical behavior of dermal tissues is unarguably recognized for its diagnostic ability and in the last decades received a steadily increasing interest in dermatology practices. Among the various methods to investigate the mechanics of skin in clinical environments, suction-based ones are especially noteworthy, thanks to their qualities of minimal invasiveness and relative simplicity of setups and data analysis. In such experiments, structural visualization of the sample is highly desirable, both in its own right and because it enables elastography. The latter is a technique that combines the knowledge of an applied mechanical stimulus and the visualization of the induced deformation to result in a spatially resolved map of the mechanical properties, which is particularly important for an inhomogeneous and layered material such as skin. We present a device, designed for clinical trials in dermatology practices, that uses a handheld probe to (1) deliver a suction-based, controlled mechanical stimulus and (2) visualize the subsurface structure via optical coherence tomography. We also present a device-agnostic data-analysis framework, consisting of a Python library, released in the public domain. We show the working principle of the setup on a polymeric model and on a volunteer's skin.

Loss of skin elasticity is associated with pulmonary emphysema, biomarkers of inflammation, and matrix metalloproteinase activity in smokers

BACKGROUND

Elastin breakdown and the resultant loss of lung elastic recoil is a hallmark of pulmonary emphysema in susceptible individuals as a consequence of tobacco smoke exposure. Systemic alterations to the synthesis and degradation of elastin may be important to our understanding of disease phenotypes in chronic obstructive pulmonary disease. We investigated the association of skin elasticity with pulmonary emphysema, obstructive lung disease, and blood biomarkers of inflammation and tissue protease activity in tobacco-exposed individuals.

METHODS

Two hundred and thirty-six Caucasian individuals were recruited into a sub-study of the University of Pittsburgh Specialized Center for Clinically Orientated Research in chronic obstructive pulmonary disease, a prospective cohort study of current and former smokers. The skin viscoelastic modulus (VE), a determinant of skin elasticity, was recorded from the volar forearm and facial wrinkling severity was determined using the Daniell scoring system.

RESULTS

In a multiple regression analysis, reduced VE was significantly associated with cross-sectional measurement of airflow obstruction (FEV1/FVC) and emphysema quantified from computed tomography (CT) images, β = 0.26, p = 0.001 and β = 0.24, p = 0.001 respectively. In emphysema-susceptible individuals, elasticity-determined skin age was increased (median 4.6 years) compared to the chronological age of subjects without emphysema. Plasma biomarkers of inflammation (TNFR1, TNFR2, CRP, PTX3, and SAA) and matrix metalloproteinase activity (MMP1, TIMP1, TIMP2, and TIMP4) were inversely associated with skin elasticity.

CONCLUSIONS

We report that an objective non-invasive determinant of skin elasticity is independently associated with measures of lung function, pulmonary emphysema, and biomarkers of inflammation and tissue proteolysis in tobacco-exposed individuals. Loss of skin elasticity is a novel observation that may link the common pathological processes that drive tissue elastolysis in the extracellular matrix of the skin and lung in emphysema-susceptible individuals.

Tensile behavior and structural characterization of pig dermis

Skin, the outermost layer of the body, fulfills a broad range of functions, protecting internal organs from damage and infection, while regulating the body's temperature and water content via the exchange of heat and fluids. It must be able to withstand and recover from extensive deformation and damage that can occur during growth, movement, and potential injuries. A detailed investigation of the evolution of the collagen architecture of the dermis as a function of deformation is conducted, which reveals new aspects that help us to understand the mechanical response of skin. Juvenile pig is used as a model material because of its similarity to human skin. The dermis is found to have a tridimensional woven structure of collagen fibers, which evolves with deformation. After failure, we observe that the fibers have straightened and aligned in the direction of tension. The effects of strain-rate change, cyclic loading, stress relaxation, and orientation are quantitatively established. Digital image correlation techniques are implemented to quantify skin's anisotropy; measurements of the Poisson ratio are reported. This is coupled with transmission electron microscopy which enables obtaining quantitative strain parameters evaluated through the orientation and curvature of the collagen fibers and their changes, for the first time in all three dimensions of the tissue. A model experiment using braided human hair in tension exhibits a similar J-curve response to skin, and we propose that this fiber configuration is at least partially responsible for the monotonic increase of the tangent modulus of skin with strain. The obtained results are intended to serve as a basis for structurally-based models of skin. STATEMENT OF SIGNIFICANCE: Our study reveals a new aspect of the dermis: it is comprised of a tridimensional woven structure of collagen fibers, which evolves with deformation. This is enabled by primarily two techniques, transmission electron microscopy on three perpendicular planes and confocal images with second harmonic generation fluorescence of collagen, captured at different intervals of depth. After failure, the fibers have straightened and aligned in the direction of tension. Digital image correlation techniques are implemented to quantify skin's anisotropy; measurements of the Poisson ratio are reported. A model experiment using braided human hair in tension exhibits a similar J-curve response to skin, and we propose that this fiber configuration is at least partially responsible for the monotonic increase of the tangent modulus of skin with strain.

Skin mechanical properties and modeling: A review

The mechanical properties of the skin are important for various applications. Numerous tests have been conducted to characterize the mechanical behavior of this tissue, and this article presents a review on different experimental methods used. A discussion on the general mechanical behavior of the skin, including nonlinearity, viscoelasticity, anisotropy, loading history dependency, failure properties, and aging effects, is presented. Finally, commonly used constitutive models for simulating the mechanical response of skin are discussed in the context of representing the empirically observed behavior.

Quantifying fibrosis in head and neck cancer treatment: An overview

BACKGROUND

Fibrosis is a common late complication of radiotherapy and/or surgical treatment for head and neck cancers. Fibrosis is difficult to quantify and formal methods of measure are not well recognized. The purpose of this review was to summarize the methods available to quantify neck fibrosis.

METHODS

A PubMed search of articles was carried out using key words "neck" and "fibrosis."

RESULTS

Many methods have been used to assess fibrosis, however, there is no preferred methodology. Specific to neck fibrosis, most studies have relied upon hand palpation rating scales. Indentation and suction techniques have been used to mechanically quantify neck fibrosis. There is scope to develop applications of ultrasound, dielectric, bioimpedance, and MRI techniques for use in the neck region.

CONCLUSION

Quantitative assessment of neck fibrosis is sought after in order to compare treatment regimens and improve quality of life outcomes in patients with head and neck cancer.

Single treatment of grades II and III cellulite using a minimally invasive 1,440-nm pulsed Nd:YAG laser and side-firing fiber: an institutional review board-approved study with a 24-month follow-up period

BACKGROUND

Cellulite represents one of the common topographic alterations to the skin surface and one of the structural changes to the subdermal fat and septal band of the posterolateral thighs. Currently, no treatment exists to address this entity with a multifactorial genesis that produces long-term beneficial outcomes. This clinical study evaluated the safety and efficacy of the 1,440-nm laser and the duration of the clinical benefits during 2 years.

METHODS

Initially, 25 healthy women with thigh cellulite were enrolled in this prospective institutional review board (IRB)-approved study. For grade II cellulite, the laser fiber delivered up to 1,000 J of energy to the undersurface of the entire involved skin. For grade III cellulite, the laser fiber distributed 1,300 to 1,500 J of energy to melt the subdermal fat, subcise the taut septal bands, and heat the reticular dermis. Baseline and posttreatment analyses included standardized high-resolution photography, skin elasticity measurements, ultrasound scanning for dermal thickness, histology, investigator global assessment scores, and recording of adverse events.

RESULTS

Of the 24 subjects who underwent treatment, only 20 were available for the 6-month follow-up assessment. Objective measurements at 2 years demonstrated an increase over the baseline mean skin elasticity (34 %) and mean dermal thickness (11 %), as well as an increase in the average percentage of dermal thickening determined by ultrasound imaging. Independent investigator global assessments were rated higher for grade II subjects than for grade III subjects throughout the 2-year follow-up period. Mild adverse events disappeared by the third month.

CONCLUSIONS

This IRB-conducted clinical trial, as part of a multicenter study for Food and Drug Administration approval, demonstrated the safety and efficacy of a single minimally invasive treatment for grades II and III thigh cellulite during a 2-year follow-up period.

LEVEL OF EVIDENCE II

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Full-field bulge test for planar anisotropic tissues: part I--experimental methods applied to human skin tissue

The nonlinear anisotropic properties of human skin tissue were investigated using bulge testing. Full-field displacement data were obtained during testing of human skin tissues procured from the lower back of post-mortem human subjects using 3-D digital image correlation. To measure anisotropy, the dominant fiber direction of the tissue was determined from the deformed geometry of the specimen. Local strains and stress resultants were calculated along both the dominant fiber direction and the perpendicular direction. Variation in anisotropy and stiffness was observed between specimens. The use of stress resultants rather than the membrane stress approximation accounted for bending effects, which are significant for a thick nonlinear tissue. Of the six specimens tested, it was observed that specimens from older donors exhibited a stiffer and more isotropic response than those from younger donors. It was seen that the mechanical response of the tissue was negligibly impacted by preconditioning or the ambient humidity. The methods presented in this work for skin tissue are sufficiently general to be applied to other planar tissues, such as pericardium, gastrointestinal tissue, and fetal membranes. The stress resultant-stretch relations will be used in a companion paper to obtain material parameters for a nonlinear anisotropic hyperelastic model.

Alternative splicing and tissue-specific elastin misassembly act as biological modifiers of human elastin gene frameshift mutations associated with dominant cutis laxa

Elastin is the extracellular matrix protein in vertebrates that provides elastic recoil to blood vessels, the lung, and skin. Because the elastin gene has undergone significant changes in the primate lineage, modeling elastin diseases in non-human animals can be problematic. To investigate the pathophysiology underlying a class of elastin gene mutations leading to autosomal dominant cutis laxa, we engineered a cutis laxa mutation (single base deletion) into the human elastin gene contained in a bacterial artificial chromosome. When expressed as a transgene in mice, mutant elastin was incorporated into elastic fibers in the skin and lung with adverse effects on tissue function. In contrast, only low levels of mutant protein incorporated into aortic elastin, which explains why the vasculature is relatively unaffected in this disease. RNA stability studies found that alternative exon splicing acts as a modifier of disease severity by influencing the spectrum of mutant transcripts that survive nonsense-mediated decay. Our results confirm the critical role of the C-terminal region of tropoelastin in elastic fiber assembly and suggest tissue-specific differences in the elastin assembly pathway.

Objective scar assessment tools: a clinimetric appraisal

BACKGROUND

Scars may lead to an array of cosmetic, psychological, and functional problems. Different scar features can be distinguished (i.e., color, thickness, relief, pliability, and surface area) that are clinically relevant and contribute to the quality and judgment of a scar. Today, objective evaluation of these scar features is indispensable for practicing evidence-based medicine (e.g., to evaluate the outcome of clinical trials). In this review, an overview and update are given on the most relevant noninvasive objective measurement tools for scar evaluation.

METHODS

A PubMed literature search was performed. Articles evaluating the clinimetric properties of noninvasive scar assessment tools were included. The selected objective measurement tools were then critically reviewed with respect to the clinimetric properties of reliability, validity, and feasibility.

RESULTS

In total, 75 articles were selected and 23 different noninvasive measurement methods were evaluated.

CONCLUSION

Based on the scar features color, thickness, relief, pliability, and surface area, the best measurement tools that are currently available were recommended.

Development of compression-controlled low-level laser probe system: towards clinical application

Various physico-chemical tissue optical clearing (TOC) methods have been suggested to maximize photon density in tissue. In order to enhance photon density, a compression-controlled low-level laser probe (CCLLP) system was developed by utilizing the principle of mechanical tissue compression. Negative compression (NC) was applied to the laser probes built in various diameters and simultaneously the laser was irradiated into ex-vivo porcine skin samples. Laser photon density (LPD) was evaluated as a function of NC and probe diameter by analyzing 2D diffusion images of the laser exposures. The CCLLP system resulted in a concentrated laser beam profile, which means enhancement of the LPD. As indicators of LPD, the laser peak intensity increased and the full width at half maximum (FWHM) decreased as a function of NC. The peak intensity at –30 kPa increased 2.74, 3.22, and 3.64 fold at laser probe diameters of 20, 30, and 40 mm, respectively. In addition, sample temperature was measured with a thermal camera and increased 0.4 K at –30 kPa after 60 s of laser irradiation as a result of enhanced LPD. The CCLLP system effectively demonstrated enhancement of the LPD in tissue and potentially its clinical feasibility.

Randomized, blinded split abdomen study evaluating skin shrinkage and skin tightening in laser-assisted liposuction versus liposuction control

BACKGROUND

Laser-assisted liposuction has shown great potential in facilitating fat removal, improving patient recovery time, and decreasing postoperative side effects. Clinical experience has indicated superior skin tightening after laser-assisted liposuction than with liposuction alone.

OBJECTIVES

The aim of the present study was to obtain quantitative, objective data for comparing tissue shrinkage and skin tightening achieved by laser-assisted liposuction versus liposuction alone.

METHODS

Ten female subjects from the author's private practice with unwanted abdominal adiposity and mild to moderate skin laxity were enrolled. On the abdominal skin of each patient, the corners of four rectangular regions (approximately 5 × 5 cm each) were tattooed with India ink and randomly assigned to treatment with laser-assisted liposuction (Smartly MPX laser, Cynosure, Inc., Westford, Massachusetts) or with liposuction alone. The laser system permits individual as well as sequential emission of 1064-nm and 1320-nm wavelengths. Skin shrinkage was quantified by calculating the changes in surface area of the regions. Skin tightening was quantified by changes in the skin stiffness index measured in the treated regions.

RESULTS

One month and three months after treatment, the mean skin shrinkage ratios were significantly higher on the laser-treated side than on the suction side. One month after treatment with or without laser, the mean skin stiffness and skin tightening showed no statistically significant difference from baseline. Three months after treatment, the mean skin stiffness and skin tightening were significantly higher on the laser-treated side.

CONCLUSIONS

Laser-assisted liposuction has a statistically significant effect on skin shrinkage and tightening of the skin in the abdominal area when compared to liposuction alone.

In vivo skin elastography with high-definition optical videos

BACKGROUND/AIMS

Continuous measurements of biomechanical properties of skin provide potentially valuable information to dermatologists for both clinical diagnosis and quantitative assessment of therapy. This paper presents an experimental study on in vivo imaging of skin elastic properties using high-definition optical videos. The objective is to (i) investigate whether skin property abnormalities can be detected in the computed strain elastograms, (ii) quantify property abnormalities with a Relative Strain Index (RSI), so that an objective rating system can be established, (iii) determine whether certain skin diseases are more amenable to optical elastography and (iv) identify factors that may have an adverse impact on the quality of strain elastograms.

METHODS

There are three steps in optical skin elastography: (i) skin deformations are recorded in a video sequence using a high-definition camcorder, (ii) a dense motion field between two adjacent video frames is obtained using a robust optical flow algorithm, with which a cumulative motion field between two frames of a larger interval is derived and (iii) a strain elastogram is computed by applying two weighted gradient filters to the cumulative motion data.

RESULTS

Experiments were carried out using videos of 25 patients. In the three cases presented in this article (hypertrophic lichen planus, seborrheic keratosis and psoriasis vulgaris), abnormal tissues associated with the skin diseases were successfully identified in the elastograms. There exists a good correspondence between the shape of property abnormalities and the area of diseased skin. The computed RSI gives a quantitative measure of the magnitude of property abnormalities that is consistent with the skin stiffness observed on clinical examinations.

CONCLUSIONS

Optical elastography is a promising imaging modality that is capable of capturing disease-induced property changes. Its main advantage is that an elastogram presents a continuous description of the spatial variation of skin properties on the pixel level that would otherwise be impossible with other sensors. Its value will be further enhanced when used with a point-wise measuring device such as a cutometer that yields absolute elasticity values.

Approaches for optimizing the calibration standard of Tewameter TM 300

Calibration of devices measuring transepidermal water loss (TEWL) is in intensive discussion. Comparative studies revealed that comparable measuring systems, e.g. open and closed chamber systems, do not always deliver the same results, even when expressing the measured values in SI units, namely in g/m(2)/h. Therefore, adequate and reliable calibration procedures need to be established. We were able to test the reliability of a multi-step calibration algorithm for an open chamber system such as Tewameter TM 300. In order to achieve reliable measurements, the maintenance of stable microclimate conditions without air turbulences is mandatory. The TEWL values should be compared with those determined gravimetrically on heated skin simulators. The reproducibility of the results is warranted by consecutive measurements on different adjacent spots of a defined area. Preheating of the probe sensors is an effective approach for shortening the measuring time and gaining a rapid steady-state. The accurate calibration of the probe can be checked under laboratory conditions any time. The critical point of the calibration and ultimately the accuracy of in vivo measurements maintain the steady functional capacity of the probes during the entire duration of continuous studies. The studied calibration procedure ensures these requirements.

Ablative versus non-ablative treatment of perioral rhytides. A randomized controlled trial with long-term blinded clinical evaluations and non-invasive measurements

BACKGROUND AND OBJECTIVE

To compare efficacy and side effects of CO(2) laser resurfacing and intense pulsed light (IPL) rejuvenation for treatment of perioral rhytides.

METHODS

Twenty-seven female subjects with perioral rhytides (class I-III) were randomly treated with either CO(2) laser or IPL (three monthly treatments). Efficacy was evaluated by patient self-assessments and blinded photographs up to 12 months postoperatively. Side effects were assessed clinically. Non-invasive measurements included: trans epidermal water loss (TEWL), skin reflectance, skin elasticity, and ultrasound.

RESULTS

CO(2) laser resurfacing resulted in higher degrees of patient satisfaction and clinical rhytide reduction compared to IPL rejuvenation up to 12 months postoperatively (patient evaluations, P < 0.05) (observer evaluations, P < 0.008). Laser-induced side effects included erythema, dyspigmentation, and milia whereas no side effects were observed after IPL rejuvenation. Non-invasive measurements showed a significant higher reduction of the subepidermal low-echogenic band in CO(2) laser treated areas versus IPL treated areas (12 months postoperatively, P < 0.001). Skin elasticity (expressed as Young's modulus) increased in both groups (P = ns). One month postoperatively a significant increase in TEWL values (P < 0.009) and skin redness% (P < 0.02) was found in CO(2) laser treated patients versus IPL treated patients. No significant differences were seen in skin pigmentation% during the observation period.

CONCLUSION

CO(2) laser resurfacing induces a significantly higher degree of clinical rhytide reduction followed by considerably more side effects compared to IPL rejuvenation in a homogeneous group of patients.

Development and evaluation of a high-frequency ultrasound-based system for in vivo strain imaging of the skin

The elastic properties of skin are of great interest in dermatology because they are affected by many pathological conditions. In this paper, a technique for in vivo mechanical strain imaging of the skin based on high-frequency ultrasound (HFUS) is presented. Elastic skin properties are assessed applying suction to the skin surface with a stepwise increased vacuum and estimating the resulting displacements in a spatially resolved manner. Acquired radio frequency (RF) echo signals and their envelope are analyzed for this purpose. A computer-controlled vacuum system with a digital pressure control loop was developed for precise and reproducible deformation. In a first processing step, the skin surface is segmented. Local axial strains inside the skin are estimated from axial displacements, which are estimated from consecutive echo signal frames analyzing the phase of the complex cross correlation function of analytical echo signals. Furthermore, speckle tracking is applied to estimate axial and lateral displacements and to quantify axial and lateral strains. The correlation coefficient of windowed echo signals compensated for displacements are used as a measure to validate the estimated strains, which is essential to accomplish reliable in vivo measurements. Phantom experiments were performed to validate the proposed technique. Results of in vivo measurements are presented, showing the potential for mechanical strain imaging in the skin in vivo.

Experiments on peeling adhesive tapes from human forearms

BACKGROUND/PURPOSE

Peeling of adhesive tape from hu-man skin can cause pain and trauma. The effects of the peel angle, peel rate, dwell time, subject, and order of testing were examined.

METHODS

Adhesive tape was peeled from the volar forearms of four human subjects. The tape was 25.4-mm-wide Durapore by 3M. The rates ranged from 100 to 10,000 mm/min, the peel angle from 90 degrees to 180 degrees, and the dwell time from one to 15 min. The tensile testing machines'recorded the peel force and the displacement of the end of the tape.

RESULTS

A range of maximum and average peel force values was observed. The peel force tended to be minimum for a peel angle around 150 degrees in most cases. As the peel rate was increased, the peel force generally tended to increases lightly, but the relationship was erratic. As the dwell time increased, the peel force increased and then settled down. Of the subjects tested, the skin of the oldest subject experienced the most displacement and highest peel forces(the maximum force over all tests was 3.6 N). The peel force tended to increase with repeated peeling from the same skin site. Compared with peeling from a rigid substrate such as steel, the peel force from skin was lower.

CONCLUSION

The results improve understanding of the factors affecting the peel force, which has been correlated previously with trauma caused by peeling adhesive tape from skin.