Skin aging as a mechanical phenomenon: The main weak links

Abstract

From a mechanical point of view, human skin appears as a layered composite containing the stiff thin cover layer presented by the stratum corneum, below which are the more compliant layers of viable epidermis and dermis and further below the much more compliant adjacent layer of subcutaneous white adipose tissue (sWAT). Upon exposure to a strain, such a multi-layer system demonstrates structural instabilities in its stiffer layers, which in its simplest form is the wrinkling. These instabilities appear hierarchically when the mechanical strain in the skin exceeds some critical values. Their appearance is mainly dependent on the mismatch in mechanical properties between adjacent skin layers or between the skin and sWAT, on the adhesive strength and thickness ratios between the layers, on their bending and tensile stiffness as well as on the value of the stress existing in single layers. Gradual reduction of elastic fibers in aging significantly reduces the skin’s ability to bend, prompting an up to 4-fold reduction of its stability against wrinkling, thereby explaining the role of these fibers in skin aging. While chronological and extrinsic aging differently modify these parameters, they lead to the same end result, reducing the critical strain required for the onset of instabilities. Comparing of mechanical properties of the skin presented as a bi-, tri- or tetra-layer structure demonstrates the particular importance of the papillary dermis in skin aging and provides the arguments to consider the undulations on the dermal-epidermal and dermal-sWAT interfaces as the result of mechanical bifurcation, leading to structural instabilities inside of the skin. According to this model, anti-aging strategies should focus not as much on the reinforcement of the dermis, but rather aim to treat the elastic mismatch between different adjacent layers in the skin and sWAT as well as the adhesion between these layers.

Dermal adipose tissue has high plasticity and undergoes reversible dedifferentiation in mice

“…Thus, interventions blocking the dedifferentiation of dermal adipocytes may represent a novel antiscarring and antifibrosis strategy. Since dWAT is an important component of the skin, it also represents a potential source of lipids, cytokines, and extracellular matrix (4, 23), which would have an impact on skin aging and quality (48). In view of the highly dynamic nature and significance of dWAT, as well as its reversible dedifferentiation capacity, there is ample opportunity in the future to selectively intervene in this layer of adipocytes to maintain skin homeostasis under physiological and pathophysiological conditions.…”

Transcriptome Profile of Human Fibroblasts in an Ex Vivo Culture

“…Due to structural and functional changes, the skin shows obvious signs of the passing time [1]. The most important and prominent sign of aging is skin wrinkling [23]. Ongoing efforts for preserving a youthful appearance demonstrate that youthfulness is considered a prerequisite for beauty [4].…”

Construction of Sandwich-like cell sheets with natural electrospun gelatin/chitosan nanofibrous delivered plasmid VEGF for accelerated wound healing

“…The morphology of gelatin/chitosan nanofibrous clearly demonstrates that gelatin concentration was very important in obtaining fine and large gelatin/chitosan fibers, more gelatin in membrane exhibited much higher mechanical strength than the composite containing more chitosan. The mechanical property of skin is important to its structure, appearance and functionality [23], so the mechanical strength of electrospun nanofibrous is also important for the cell sheets construction and wound healing. However, electrospun nanofibrous of natural biomaterials usually possess inferior mechanical properties and fast degradation rates, crosslinking is a common approach for improving the mechanical and degradation properties of natural biomaterials for tissue engineering applications [24].…”