Skin tension or skin compression? Small circular wounds are likely to shrink, not gape.
ABSTRACT The final appearance of a scar may be influenced by tension or mechanical factors [Borges AF. Scar prognosis of wounds. Br J Plast Surg 1960;13:47-54; Arem AJ, Madden JW. Effects of stress on healing wounds. J Surg Res 1976;20:93-102; Burgess LP, Morin GV, Rand M, et al. Wound healing. Relationship of wound closing tension to scar width in rats. Arch Otolaryngol Head Neck Surg 1990;116:798-802; Meyer M, McGrouther DA. A study relating wound tension to scar morphology in the pre-sternal scar using Langer's technique. Br J Plast Surg 1991;44:291-4] Karl Langer suggested that information could be gained about the tension inherent in skin, in all directions, by observing the wound edge retraction that occurred after making circular skin incisions [Langer K. On the anatomy and physiology of the skin II. Skin tension. Br J Plast Surg 1978;31:93-106]. Circular wounds may be used to demonstrate the orientation of the dominant axis of 'tension' in the skin but is this always a tensile stress as opposed to a compressive stress? This is the second article in a series documenting the mechanical properties of circular punch biopsy wounds. The aim of this study was to make detailed observations of the dimensional distortions of circular wounds on the face and neck, from which deductions could be made with regard to mechanical stress. One hundred and seventy-five benign head and neck lesions were excised from 72 volunteers using circular dermal punch biopsies. The distortions of the resulting wounds were observed to be elliptical in most cases. Measurements were taken of the maximum and minimum diameters of the wound and expressed as ratios of the size of the punch biopsy used for excision. The change in area from the area of the punch biopsy to that of the wound was also calculated. The maximum diameter of the wound was smaller than the diameter of the punch biopsy in 40.6% of cases, the minimum diameter of the wound was smaller in 97.7% of cases and the area of the wound was smaller than that of the punch biopsy in 90.3%. These dimensional changes varied between sites (P=0.0005, P=0.0001 and P<0.0001, respectively). We conclude that the reported rhomboidal or lattice structure [Ridge MD, Wright V. The directional effects of skin. A bioengineering study of skin with particular reference to Langer's Lines. J Invest Dermatol 1966;46:341-6] of skin has individual components which are under tensional force due to elastic retraction. Wounds smaller than the rhomboidal unit will reduce in area, due to the intact tensional forces in the individual dermal components, giving an appearance of the skin overall being under compression. Larger wounds, disrupting more of the lattice structure, will gape.
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ABSTRACT: Over the years, an assortment of methods for determining residual stresses has been developed in the field of experimental mechanics. Adaptations of those methods to study residual strains and stresses in various biological structures found in humans, other mammals, viruses and an insect are reviewed. Methods considered include deflections from release of residual stresses, hole drilling and ring coring, strains upon dissection, the contour method, slitting (crack compliance), X-ray diffraction, photoelasticity, and membrane and shell displacements. Sources of residual stresses and strains are summarized and examples of their physiological role noted.Experimental Mechanics 01/2014; 54(4). · 1.57 Impact Factor
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ABSTRACT: Significance: Delayed wound healing is one of the most challenging complications of several diseases, including diabetes. There is a vast interest in finding efficient treatments that promote scarless wound healing. The ability of the fetus to regenerate skin wounds after injury has generated much interest in the fetus as a model of regeneration. In this review, we evaluate the role and differential regulation of inflammation, extracellular matrix (ECM) composition, and mechanical stress in determining wound phenotype after injury. Recent Advances: Comparisons between postnatal and fetal wounds have revealed many differences in the healing process. Fetal skin wound healing is characterized by a reduced inflammatory response, an ECM rich in type III collagen and high-molecular-weight hyaluronic acid (HMW-HA), and minimal mechanical stress. In contrast, adult wounds have a sustained inflammatory response, an ECM with increased type I collagen, and low-molecular-weight (LMW-HA) and are subject to significant mechanical load. Critical Issues: The differential regulation of these processes in the fetus compared with the adult plays a critical role in promoting regeneration in the fetus while resulting in scar formation in the adult. Future Directions: Understanding the significance of inflammation and biomechanical forces in wound healing may help in designing therapeutic strategies for the management of chronic nonhealing wounds.Advances in wound care. 04/2014; 3(4):344-355.
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ABSTRACT: Scars in humans of African continental ancestry heal with an exaggerated inflammatory response and a generally wider scar. Interleukin-10 is an anti-inflammatory and antifibrotic cytokine. A randomized controlled trial in Caucasians found that exogenous interleukin-10 resulted in improved macroscopic scar appearance and reduced scar redness. We investigated the effects of interleukin-10 on cutaneous scarring in volunteers of African ancestral origin in an exploratory, single-center, within-subject, double-blind randomized controlled trial. Fifty-six subjects received two of four potential prerandomized concentrations of interleukin-10 (5, 25, 100, and 250 ng/100 µL) in two full-thickness incisions on the upper inner arms. Anatomically matching incisions on the contralateral arm were treated with placebo. Scars were excised at 1 month for histological analysis and were redosed with the same regimen. Resultant excision scars were followed up for 12 months for scar width measurement and scoring. Scoring was performed by trial doctors, subjects, and a panel. Incisions treated with 100 ng/100 µL interleukin-10 had significantly reduced microscopic scar widths. Incisions treated with 5 and 25 ng/100 µL interleukin-10 were also narrower, but not significantly. There were no differences observed in pro-inflammatory or pro-fibrotic markers between interleukin-10 and placebo treatment. There was no long-term evidence that 100 ng/100 µL interleukin-10 had a therapeutic effect on macroscopic scar width or appearance, as excisions treated with this concentration were significantly wider than placebo between 8 and 12 months of maturation. Doctors showed a trend toward favoring the macroscopic appearance of placebo-treated excisions compared with those treated with 250 ng/100 µL interleukin-10. Panelists scored placebo-treated excisions as significantly better-appearing than those treated with 250 ng/100 µL interleukin-10. Doctors' scores showed a trend toward favoring treatment with 5 ng/100 µL interleukin-10 at 10 and 11 months post-excision. Subjects showed a trend toward favoring treatment with 5 ng/100 µL interleukin-10 between 5 and 9 months postexcision. Analysis of images of markedly improved scars revealed a potential subset of responders among those treated with 5 ng/100 µL interleukin-10. No concentration of interleukin-10 produced a statistically significant improvement in scarring compared with placebo.Wound Repair and Regeneration 05/2014; 22(3). · 2.77 Impact Factor