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The present study investigates the multiphasic nature of the mechanical behavior of human dermis. Motivated by experimental observations and by consideration of its composition, a quadriphasic model of the dermis is proposed, distinguishing solid matrix components, interstitial fluid and charged constituents moving within the fluid, i.e., anions and cations. Compression and tensile experiments with and without change of osmolarity of the bath are performed to characterize the chemo-mechanical coupling in the dermis. Model parameters are determined through inverse analysis. The computations predict a dominant role of the permeability in the determination of the temporal evolution of the mechanical response of the tissue. In line with the previous studies on other tissues, the analysis shows that an ideal model based on Donnan's equilibrium overestimates the osmotic pressure in skin for the case of very dilute solutions. The quadriphasic model is applied to predict changes in dermal cell environment and therefore alterations in what is called the "mechanome," associated with skin stretch. The simulations indicate that skin deformation causes a variation in several local variables, including in particular the electric field associated with a deformation-induced non-homogeneous distribution of fixed charges., (© 2024. The Author(s).)

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., (© 2024. The Author(s).)

We studied the effect of platelet lysate and platelet-poor plasma from patients with trophic ulcers with and without type 2 diabetes mellitus on proliferation, migration, and apoptosis of human dermal fibroblast, mesenchymal stem cells, and endothelial cells. It is shown that plasma obtained from patients with type 2 diabetes mellitus produced inhibitory effects.

Finite element models in conjunction with adequate constitutive relations are pivotal in several physiological and medical applications related to both native and engineered tissues, allowing to predict the tissue response under various loading states. In order to get reliable results, however, the validation of the constitutive models is crucial. Therefore, the main purpose of this work is to provide an experimental-computational approach to the biomechanical investigation of soft tissues such as the dermis. This is accomplished by implementing and validating three widely adopted hyperelastic constitutive models (the Ogden, the Holzapfel, and the Gasser-Ogden-Holzapfel laws) supposed to be adequate to reproduce human reticular dermis mechanical behavior. Biaxial experimental data have represented the basis for the determination of the respective material parameters identified thanks to the definition of a cost function accounting for the discrepancy between experimental and predicted data. Afterwards, the experimental tests have been reproduced through finite element simulations. Hence, the constitutive laws have been validated comparing experimental and numerical outcomes in terms of displacements of four reference points and stress-strain relations. Hence, an experimental-numerical framework is proposed for the investigation of collagenous tissues, which could become more accurate with larger and independent experimental datasets. Graphical abstract ᅟ.

Lymphatic vessels transport fluid, antigens, and immune cells to the lymph nodes to orchestrate adaptive immunity and maintain peripheral tolerance. Lymphangiogenesis has been associated with inflammation, cancer metastasis, autoimmunity, tolerance and transplant rejection, and thus, targeted lymphatic ablation is a potential therapeutic strategy for treating or preventing such events. Here we define conditions that lead to specific and local closure of the lymphatic vasculature using photodynamic therapy (PDT). Lymphatic-specific PDT was performed by irradiation of the photosensitizer verteporfin that effectively accumulates within collecting lymphatic vessels after local intradermal injection. We found that anti-lymphatic PDT induced necrosis of endothelial cells and pericytes, which preceded the functional occlusion of lymphatic collectors. This was specific to lymphatic vessels at low verteporfin dose, while higher doses also affected local blood vessels. In contrast, light dose (fluence) did not affect blood vessel perfusion, but did affect regeneration time of occluded lymphatic vessels. Lymphatic vessels eventually regenerated by recanalization of blocked collectors, with a characteristic hyperplasia of peri-lymphatic smooth muscle cells. The restoration of lymphatic function occurred with minimal remodeling of non-lymphatic tissue. Thus, anti-lymphatic PDT allows control of lymphatic ablation and regeneration by alteration of light fluence and photosensitizer dose.

Grp1-associated scaffold protein (Grasp), the product of a retinoic acid-induced gene in P19 embryonal carcinoma cells, is expressed primarily in brain, heart, and lung of the mouse. We report herein that Grasp transcripts are also found in mouse skin in which the Grasp gene is robustly induced following acute ultraviolet-B (UVB) exposure. Grasp(-/-) mice were found to exhibit delayed epidermal proliferation and a blunted apoptotic response after acute UVB exposure. Immunohistochemical analyses revealed that the nuclear residence time of the tumor suppressor protein p53 was reduced in Grasp(-/-) mice after UVB exposure. Taken together, our results suggest that a physiological role of Grasp may be to regulate skin homeostasis after UVB exposure, potentially by influencing p53-mediated apoptotic responses in skin.

Skin is a barrier which protects injured tissues, and thus, skin regeneration is one of many important medical issues. Tissue engineering is an attractive approach to make artificial tissue or regenerate lost tissues. While constituting artificial tissues, cells must infiltrate through scaffolds, maintaining viability and proliferation. However, a three-dimensional tissue culture involves stressful environments due to several reasons such as mass or gas transport and high cell density. Once stressed, cells produce reactive oxygen species, resulting in alleviating cellular viability and activity. Spirulina is well known to have antioxidant molecules, which have been known to modulate oxidative stress to cells. Electrospun nanofiber has widely been used as a scaffold to mimic natural extracellular matrix. In this research, we assessed Spirulina extract-imbedded nanofiber as a scaffold for an artificial skin tissue. Spirulina extract was proven to positively affect viability and proliferation of mouse fibroblasts. In addition, fibroblasts infiltrated through Spirulina extract-imbedded electrospun nanofiber without cytotoxicity.

Neonatal human dermal fibroblasts cultured in vitro synthesize an organized and physically substantial three-dimensional extracellular matrix, without the addition of exogenous matrix components or synthetic scaffolds. De novo matrix synthesis proceeds in an orderly manner over a 21-d culture period and beyond. Analysis of the fibroblast phenotype, i.e., matrix synthesis by the fibroblasts, suggests that both serum and serum-free conditions are conducive to the production of a human tissue-engineered "dermal equivalent". We report that given the appropriate permissive environment, the fibroblasts establish and grow a tissue in vitro, which bears striking biochemical and physical resemblance to normal human dermis.

A delicate balance between synthesis and degradation of extracellular matrix (ECM) by matrix metalloproteinases (MMPs) is an essential feature of tissue remodeling. We have recently demonstrated that keratinocyte releasable stratifin, also known as 14-3-3 sigma protein, plays a critical role in modulating collagenase (MMP-1) mRNA expression in human dermal fibroblasts. In this study, we further characterized the collagenase stimulatory effect of stratifin in dermal fibroblasts and evaluated its effect in the presence and absence of insulin. Our data indicate that stratifin increases the expression of collagenase mRNA more than 20-fold in dermal fibroblasts, grown in either Dulbecco's modified Eagle's medium (DMEM) plus 2% or 10% fetal bovine serum (FBS). Collagenase stimulatory effect of stratifin was completely blocked, when fibroblasts were cultured in test medium consisting of 50% keratinocyte serum-free medium (KSFM) and 50% DMEM. The collagenase suppressive effect of test medium was directly proportional to the volume of KSFM used. As this medium contained insulin, we then evaluated the collagenase stimulatory effect of stratifin in dermal fibroblasts in the presence and absence of insulin. The results revealed that stratifin significantly increased the expression of collagenase mRNA/18S (*p < 0.05, n = 3) ratio, while insulin significantly decreased the expression of collagenase mRNA/18S (*p < 0.05, n = 3) ratio. The insulin inhibitory effect on collagenase mRNA expression was time and dose dependent. The maximal inhibitory effect of insulin was seen at 36 h post treatment. In conclusion, stratifin stimulates the expression of collagenase mRNA expression in dermal fibroblasts and this effect is suppressed by insulin treatment.