A method to analyze the influence of mechanical strain on dermal collagen morphologies

Uniaxial mechanical stretch properties correlated with three-dimensional microstructure of human dermal skin

The intact and healthy skin forms a barrier to the outside world and protects the body from mechanical impact. The skin is a complex structure with unique mechano-elastic properties. To better direct the design of biomimetic materials and induce skin regeneration in wounds with optimal outcome, more insight is required in how the mechano-elastic properties emerge from the skin's main constituents, collagen and elastin fibers. Here, we employed two-photon excited autofluorescence and second harmonic generation microscopy to characterize collagen and elastin fibers in 3D in 24 human dermis skin samples. Through uniaxial stretching experiments, we derive uni-directional mechanical properties from resultant stress-strain curves, including the initial Young's modulus, elastic Young's modulus, maximal stress, and maximal and mid-strain values. The stress-strain curves show a large variation, with an average Young's modules in the toe and linear regions of 0.1 MPa and 21 MPa. We performed a comprehensive analysis of the correlation between the key mechanical properties with age and with microstructural parameters, e.g., fiber density, thickness, and orientation. Age was found to correlate negatively with Young's modulus and collagen density. Moreover, real-time monitoring during uniaxial stretching allowed us to observe changes in collagen and elastin alignment. Elastin fibers aligned significantly in both the heel and linear regions, and the collagen bundles engaged and oriented mainly in the linear region. This research advances our understanding of skin biomechanics and yields input for future first principles full modeling of skin tissue.

Biomaterial-based mechanical regulation facilitates scarless wound healing with functional skin appendage regeneration

Scar formation resulting from burns or severe trauma can significantly compromise the structural integrity of skin and lead to permanent loss of skin appendages, ultimately impairing its normal physiological function. Accumulating evidence underscores the potential of targeted modulation of mechanical cues to enhance skin regeneration, promoting scarless repair by influencing the extracellular microenvironment and driving the phenotypic transitions. The field of skin repair and skin appendage regeneration has witnessed remarkable advancements in the utilization of biomaterials with distinct physical properties. However, a comprehensive understanding of the underlying mechanisms remains somewhat elusive, limiting the broader application of these innovations. In this review, we present two promising biomaterial-based mechanical approaches aimed at bolstering the regenerative capacity of compromised skin. The first approach involves leveraging biomaterials with specific biophysical properties to create an optimal scarless environment that supports cellular activities essential for regeneration. The second approach centers on harnessing mechanical forces exerted by biomaterials to enhance cellular plasticity, facilitating efficient cellular reprogramming and, consequently, promoting the regeneration of skin appendages. In summary, the manipulation of mechanical cues using biomaterial-based strategies holds significant promise as a supplementary approach for achieving scarless wound healing, coupled with the restoration of multiple skin appendage functions.

A Free Fatty Acid Synthetic Agonist Accelerates Wound Healing and Improves Scar Quality in Mice

BACKGROUND

Impaired wound healing is a health problem around the world, and the search for a novel product to repair wounded skin is a major topic in the field. GW9508 is a synthetic molecule described as a selective agonist of free fatty acid receptors (FFARs) 1 and 4, and there is evidence of its anti-inflammatory effects on several organs of the body.

PURPOSE

Here, we aimed to evaluate the effects of topical GW9508 on wound healing in mice.

RESEARCH DESIGN

First, we used bioinformatic methods to determine the expression of FFAR1 and FFAR4 mRNA in the skin from a human cell atlas assembled with single-cell transcriptomes. Next, we employed 6-week-old C57BL6J mice with 2 wounds inflicted in the back. The mice were randomly divided into 2 groups, a control group, which received topical vehicle, and a treatment group, which received GW9508, for 12 days. The wound was monitored by photographic documentation every 2 days, and samples were collected at day 6 and 12 post injury for RT-PCR, western blot and histology analyses.

RESULTS

FFAR1 and FFAR4 mRNA are expressed in skin cells in similar amounts to those in other tissues. Topical GW9508 accelerated wound healing and decreased gene expression of IL-10 and metalloproteinase 9 on days 6 and 12 post injury. It increased the quantity of Collagen I and improved the organization of collagen fibres. Conclusions: Our results show that GW9508 could be an attractive drug treatment for wounded skin. Future studies need to be performed to assess the impact of GW9508 in chronic wound models.

Three-dimensional analysis of load-dependent changes in the orientation of dermal collagen fibers in human skin: A pilot study

The availability of quantitative structural data on the orientation of collagen fibers is of crucial importance for understanding the behavior of connective tissues. These fibers can be visualized using a variety of imaging techniques, including second harmonic generation (SHG) microscopy. However, characterization of the collagen network requires the accurate extraction of parameters from imaging data. To this end, several automated processes have been developed to identify the preferred orientation of collagen fibers. Common methods include fast Fourier transforms and curvelet transforms, but these tools are mostly used to infer a single preferred orientation. The purpose of this pilot study was to develop an easy procedure for comprehensively comparing multiple human skin samples with the goal of analyzing load-dependent changes via SHG microscopy. We created a 3D model based upon 2D image stacks that provide fiber orientation data perpendicular and parallel to the plane of the epidermis. The SHG images were analyzed by CurveAlign to obtain angle histogram plots containing information about the multiple fiber orientations in each single image. Subsequently, contour plots of the angle histogram intensities were created to provide a useful visual plotting method to clearly show the anomalies in the angle histograms in all samples. Our results provided additional details on how the collagen network carries a load. In fact, analysis of SHG images indicated that increased stretch was accompanied by an increase in the alignment of fibers in the loading direction. Moreover, these images demonstrated that more than one type of preferred orientation is present. In particular, the 3D network of fibers appears to have two preferred orientations in the planes both perpendicular and parallel to the plane of the epidermis.

Degradable collagen/sodium alginate/polyvinyl butyral high barrier coating with water/oil-resistant in a facile and effective approach

Degradable bio-based materials have been widely considered as functional coatings, however, it is a great challenge to fabricate biodegradable coatings with high barrier, water- and oil- resistance. In this work, such coatings were fabricated by using collagen fibers (CF), sodium alginate (SA), and polyvinyl butyral (PVB). CF and SA were mixed evenly and coated on Ca²⁺ pretreated filter paper. It was mainly due to the electrostatic adsorption between collagen fibers and sodium alginate, and the crosslinking between the adsorption products and Ca²⁺. By coating PVB solution, the barrier performance was further improved. Notably, the composite exhibited excellent water vapor resistance (48 g/m²·24 h), water resistance (31 g/m²), oil resistance (kit rating: 12/12) and good mechanical properties. This degradable, environmentally friendly, and simple composite paper method has excellent barrier properties, mechanical properties and fluorine-free properties, and will have many applications in the food and packaging fields.