Form-function relationships often have tradeoffs: if a material is tough, it is often inflexible, and vice versa. This is particularly relevant for the elephant trunk, where the skin should be protective yet elastic. To investigate how this is achieved, we used classical histochemical staining and second harmonic generation microscopy to describe the morphology and composition of elephant trunk skin. We report structure at the macro and micro scales, from the thickness of the dermis to the interaction of 10 μm thick collagen fibers. We analyzed several sites along the length of the trunk to compare and contrast the dorsal-ventral and proximal-distal skin morphologies and compositions. We find the dorsal skin of the elephant trunk can have keratin armor layers over 2 mm thick, which is nearly 100 times the thickness of the equivalent layer in human skin. We also found that the structural support layer (the dermis) of the elephant trunk contains a distribution of collagen-I (COL1) fibers in both perpendicular and parallel arrangement. The bimodal distribution of collagen is seen across all portions of the trunk, and is dissimilar from that of human skin where one orientation dominates within a body site. We hypothesize that this distribution of COL1 in the elephant trunk allows both flexibility and load-bearing capabilities. Additionally, when viewing individual fiber interactions of 10 μm thick collagen, we find the fiber crossings per unit volume are five times more common than in human skin, suggesting that the fibers are entangled. We surmise that these intriguing structures permit both flexibility and strength in the elephant trunk. The complex nature of the elephant skin may inspire the design of materials that can combine strength and flexibility. Advanced microscopy shows that the skin along the elephant’s trunk is anisotropic; elephant skin has an armor thicker than an Armadillo shell, with entangled protein fibers that provide additional stiffness.

Despite the substantial impact of skin scarring on patients and the healthcare system, there is a lack of strategies to prevent scar formation, let alone methods to remodel mature scars. Here, we took a unique approach inspired by how healthy hairbearing skin undergoes physiological remodelling during the regular cycling of hair follicles. In this pilot clinical study, we tested if hair follicles transplanted into human scars can facilitate tissue regeneration and actively remodel fibrotic tissue, similar to how they remodel the healthy skin. We collected full-thickness skin biopsies and compared the morphology and transcriptional signature of fibrotic tissue before and after transplantation. We found that hair follicle tranplantation induced an increase in the epidermal thickness, interdigitation of the epidermal-dermal junction, dermal cell density, and blood vessel density. Remodelling of collagen type I fibres reduced the total collagen fraction, the proportion of thick fibres, and their alignment. Consistent with these morphological changes, we found a shift in the cytokine milieu of scars with a long-lasting inhibition of pro-fibrotic factors TGFβ1, IL13, and IL-6. Our results show that anagen hair follicles can attenuate the fibrotic phenotype, providing new insights for developing regenerative approaches to remodel mature scars.

Background Healthcare workers around the world are experiencing skin injury due to the extended use of personal protective equipment (PPE) during the COVID-19 pandemic. These injuries are the result of high shear stresses acting on the skin, caused by friction with the PPE. This study aims to provide a practical lubricating solution for frontline medical staff working a 4+ hours shift wearing PPE. Methods A literature review into skin friction and skin lubrication was conducted to identify products and substances that can reduce friction. We evaluated the lubricating performance of commercially available products in vivo using a custom-built tribometer. Findings Most lubricants provide a strong initial friction reduction, but only few products provide lubrication that lasts for four hours. The response of skin to friction is a complex interplay between the lubricating properties and durability of the film deposited on the surface and the response of skin to the lubricating substance, which include epidermal absorption, occlusion, and water retention. Interpretation Talcum powder, a petrolatum-lanolin mixture, and a coconut oil-cocoa butter-beeswax mixture showed excellent long-lasting low friction. Moisturising the skin results in excessive friction, and the use of products that are aimed at 'moisturising without leaving a non-greasy feel' should be prevented. Most investigated dressings also demonstrate excellent performance.

BACKGROUND Studies highlighting the role of hair follicles (HFs) in wound healing have raised the challenge of bringing this knowledge to clinical applications. A successful translation is the transplantation of scalp HFs into chronic wounds to promote healing. OBJECTIVE To characterize scar formation and hair growth in nonhealing ulcers after transplantation. PATIENTS AND METHODS Nonhealing ulcers were treated with hair transplantation to promote wound healing. Hair follicles were harvested from the patient's scalp and inserted into the wound bed. Wound repair and hair growth were assessed clinically. Further analyses were performed in situ, using biopsies from the central and peripheral scar. RESULTS Rapid wound closure and differences of scar quality and hair growth between the central and peripheral wound areas were observed: the periphery healed with no hair shaft survival and an almost scarless appearance, the center healed with a fibrotic scar, with some hair shaft growth. In situ analyses revealed differences in dermal remodeling and collagen formation between central and peripheral scar areas. CONCLUSION Besides confirming the effectiveness of this therapy to promote wound healing in human skin, location-dependent disparities in scar quality and hair growth raise the intriguing question whether they are due to clinically important differences in mechanical forces and/or wound microenvironments between ulcer center and periphery.

Plantar skin on the soles of the feet has a distinct morphology and composition that is thought to enhance its tolerance to mechanical loads, although the individual contributions of morphology and composition have never been quantified. Here, we combine multiscale mechanical testing and computational models of load bearing to quantify the mechanical environment of both plantar and nonplantar skin under load. We find that morphology and composition play distinct and complementary roles in plantar skin’s load tolerance. More specifically, the thick stratum corneum provides protection from stress-based injuries such as skin tears and blisters, while epidermal and dermal compositions provide protection from deformation-based injuries such as pressure ulcers. This work provides insights into the roles of skin morphology and composition more generally and will inform the design of engineered skin substitutes as well as the etiology of skin injury.

The skin protects us from physical damage, bacterial invasion, and chemical hazards; guards against dehydration; and regulates our body temperature. In the case of injury, it is essential that the human body trigger a dynamic and complex wound healing response, which when successful leads to a full skin repair. Yet, human skin does not regenerate, meaning it cannot fully regain properties of uninjured skin. The development of advanced biomaterials presents new approaches to support skin repair and steer healing toward regeneration. In this chapter, we will cover the structure and function of various skin components, the mechanism of wound healing and its variable outcomes dependent on body site differences and developmental stages, as well as insight into how biomaterials can be used to target the skin and rewire the repair process.