Three-Dimensional Histological Structures of the Human Dermis

3D Bioprinting a Novel Skin Co-Culture Model Using Human Keratinocytes and Fibroblasts

3D bioprinting can generate the organized structures found in human skin for a variety of biological, medical, and pharmaceutical applications. Challenges in bioprinting skin include printing different types of cells in the same construct while maintaining their viability, which depends on the type of bioprinter and bioinks used. This study evaluated a novel 3D bioprinted skin model containing human keratinocytes (HEKa) and human dermal fibroblasts (HDF) in co-culture (CC) using a high-viscosity fibrin-based bioink produced using the BioX extrusion-based bioprinter. The constructs containing HEKa or HDF cells alone (control groups) and in CC were evaluated at 1, 10, and 20 days after bioprinting for viability, immunocytochemistry for specific markers (K5 and K10 for keratinocytes; vimentin and fibroblast specific protein [FSP] for fibroblasts). The storage, loss modulus, and viscosity properties of the constructs were also assessed to compare the effects of keratinocytes and fibroblasts individually and combined, providing important insights when bioprinting skin. Our findings revealed significantly higher cell viability in the CC group compared to individual keratinocyte and fibroblast groups, suggesting the combined cell presence enhanced survival rates. Additionally, proliferation rates of both cell types remained consistent over time, indicating non-competitive growth within the construct. Interestingly, keratinocytes exhibited a greater impact on the viscoelastic properties of the construct compared to fibroblasts, likely due to their larger size and arrangement. These insights contribute to optimizing bioprinting strategies for skin tissue engineering and emphasize the important role of different cell types in 3D skin models.

Multiphysics modelling of the impact of skin deformation and strain on microneedle-based transdermal therapeutic delivery

Microneedle patches (MNs) hold enormous potential to facilitate the minimally-invasive delivery of drugs and vaccines transdermally. However, the micro-mechanics of skin deformation significantly influence the permeation of therapeutics through the skin. Previous studies often fail to appreciate the complexities in microneedle-skin mechanical interactions. This may impede the accuracy of MNs pre-clinical assessments. Here, we develop a multiphysics finite element model which simulates the biomechanics of microneedle skin penetration and the subsequent permeation of therapeutics. Employing the aqueous pore path hypothesis, we consider how strain (induced through the insertion of a MN), affects pore geometry in the skin and therefore the diffusion of therapeutics. Our models show that considering the insertion-induced skin deformation alone reduces the transdermal permeation of insulin by 25%, while considering the effect of strain can reduce the overall permeation by a further 45% over 24 hours. Our model also indicates that once the mechanical strain is removed i.e. through removal or dissolution of the array, the permeation through the skin will recover. Furthermore, our results indicate that the delivery of high molecular weight compounds may be most susceptible to strain-induced changes in drug permeation. These findings could have significant implications for the preferred type of microneedle administration when targeting, for example, intradermal or transdermal delivery. STATEMENT OF SIGNIFICANCE: This manuscript presents an advanced computational model of microneedle insertion into human skin. Here, we adopt a multiphysics modelling strategy, where we predict the influence of microneedle insertion on skin deformation and strain and how that influences subsequent therapeutic permeation through the skin. Our model predicts that whether or not the microneedle remains in situ, the resultant change in tissue deformation and strain has a major impact on how quickly the therapeutic diffuses through the skin. This has important implications for transdermal device design, administration strategies and protocols and associated clinical studies, where either intradermal or transdermal therapeutic delivery is being targetted.

Extracellular Matrix Limits Nanoparticle Diffusion and Cellular Uptake in a Tissue-Specific Manner

Overexpression and remodeling of the extracellular matrix (ECM) in cancer and other diseases may significantly reduce the ability of nanoparticles to reach target sites, preventing the effective delivery of therapeutic cargo. Here, we evaluate how tissue-specific properties of the ECM affect nanoparticle diffusion using fluorescence video microscopy and cellular uptake via flow cytometry. In addition, we determined how poly(ethylene glycol) (PEG) chain length and branching influence the ability of PEGylated nanoparticles to overcome the ECM barrier from different tissues. We found that purified collagen, in the absence of other ECM proteins and polysaccharides, presented a greater barrier to nanoparticle diffusion compared to the decellularized ECM from the liver, lung, and small intestine submucosa. Nanoparticles with dense PEG coatings achieved up to ∼2000-fold enhancements in diffusion rate and cellular uptake up to ∼5-fold greater than non-PEGylated nanoparticles in the presence of the ECM. We also found nanoparticle mobility in the ECM varied significantly between tissue types, and the optimal nanoparticle PEGylation strategy to enhance ECM penetration was strongly dependent on ECM concentration. Overall, our data support the use of low molecular weight PEG coatings which provide an optimal balance of nanoparticle penetration through the ECM and uptake in target cells. However, tissue-specific enhancements in ECM penetration and cellular uptake were observed for nanoparticles bearing a branched PEG coating. These studies provide insights into tissue specific ECM barrier functions, which can facilitate the design of nanoparticles that effectively transport through target tissues, improving their therapeutic efficacy.

Injectable Liposome-Loaded Hydrogel Formulations with Controlled Release of Curcumin and α-Tocopherol for Dental Tissue Engineering

An injectable hydrogel formulation is developed utilizing low- and high-molecular-weight chitosan (LCH and HCH) incorporated with curcumin and α-tocopherol-loaded liposomes (Lip/Cur+Toc). Cur and Toc releases are delayed within the hydrogels. The injectability of hydrogels is proved via rheological analyses. In vitro studies are conducted using human dental pulp stem cells (hDPSCs) and human gingival fibroblasts (hGFs) to examine the biological performance of the hydrogels toward endodontics and periodontics, respectively. The viability of hDPSCs treated with the hydrogels with Lip/Cur+Toc is the highest till day 14, compared to the neat hydrogels. During odontogenic differentiation tests, alkaline phosphatase (ALP) enzyme activity of hDPSCs is induced in the Cur-containing groups. Biomineralization is enhanced mostly with Lip/Cur+Toc incorporation. The viability of hGFs is the highest in HCH combined with Lip/Cur+Toc while wound healing occurs almost 100% in both (Lip/Cur+Toc@LCH and Lip/Cur+Toc@HCH) after 2 days. Antioxidant activity of Lip/Cur+Toc@LCH on hGFs is significantly the highest among the groups. Antimicrobial tests demonstrate that Lip/Cur+Toc@LCH is more effective against Escherichia coli whereas so is Lip/Cur+Toc@HCH against Staphylococcus aureus. The antimicrobial mechanism of the hydrogels is investigated for the first time through various computational models. LCH and HCH loaded with Lip/Cur+Toc are promising candidates with multi-functional features for endodontics and periodontics.

Effect of Skin Barrier on Atopic Dermatitis

The skin acts as the body's primary physical and immune barrier, maintaining the skin microbiome and providing a physical, chemical, and immune barrier. A disrupted skin barrier plays a critical role in the onset and advancement of inflammatory skin conditions such as atopic dermatitis (AD) and contact dermatitis. This narrative review outlines the relationship between AD and skin barrier function in preparation for the search for possible markers for the treatment of AD.

Porous Functionally Graded Scaffold prepared by a single-step freeze-drying process. A bioinspired approach for wound care

Nowadays, chronic wounds are the major cause of morbidity worldwide and the healthcare costs related to wound care are a billion-dollar issue; chronic wounds involve a non-healing process that makes necessary the application of advanced wound dressings to promote skin integrity recovery. Functionally Graded Scaffolds (FGSs) are currently driving interest as promising candidates in mimicking the skin tissue environment and, thus, in enhancing a faster and more effective wound healing process. Aim of the present work was to design and develop a porous FGS based on κ-carrageenan (κCG) for the management of chronic skin wounds; a freeze-drying process was optimized to obtain in a single-step a three-layered FGS characterized by a pore size gradient functional to mimic the structure of native skin tissue. In addition to κCG, arginine and whey protein isolate were used as multifunctional agents for FGS preparation; these substances can not only intervene in some stages of wound healing but are able to establish non-covalent interactions with κCG, which were responsible for the production of layers with different pore size, water content capability and mechanical properties. Cell migration, adhesion and proliferation within the FGS structure were evaluated in vitro on fibroblasts and FGS wound healing potential was also studied in vivo on a murine model.

Three-dimensional model of normal human dermal tissue using serial tissue sections

Background: This study aims to construct a three-dimensional model of skin dermis utilizing continuous tissue sections, with the primary objective of obtaining anatomical structure data for normal human dermal tissues. Methods: Normal skin tissue specimens were acquired, paraffin-embedded, and subjected to HE staining. Panoramic images of skin sections were captured using a microscope. Tissue section images were aligned using the SIFT and StackReg image alignment methods, with analysis conducted using the OpenCV module. Mimics17 software facilitated the reconstruction of the skin dermal 3D model, enabling the calculation of dermal porosity and the void diameter. Results: Panoramic skin slices exhibited high-resolution differentiation of dermal fibers and cellular structures. Both SIFT and StackReg image alignment methods yielded similar results, although the SIFT method demonstrated greater robustness. Successful reconstruction of the three-dimensional dermal structure was achieved. Quantitative analysis revealed a dermal porosity of 18.96 ± 4.41% and an average pore diameter of 219.29 ± 34.27 μm. Interestingly, the porosity of the dermis exhibited a gradual increase from the papillary layer to the fourth layer, followed by a transient decrease and then a gradual increase. The distribution of the mean pore diameter mirrored the pattern observed in porosity distribution. Conclusion: Utilizing the continuous skin tissue slice reconstruction technique, this study successfully reconstructed a high-precision three-dimensional tissue structure of the skin. The quantitative analysis of dermal tissue porosity and average pore diameter provides a standardized dataset for the development of biomimetic tissue-engineered skin.

Use of collagen and auricular cartilage in bioengineering: scaffolds for tissue regeneration

The aim of this study was the development of collagen and collagen/auricular cartilage scaffolds for application in dermal regeneration. Collagen was obtained from bovine tendon by a 72 h-long treatment, while bovine auricular cartilage was treated for 24 h and divided into two parts, external (perichondrium, E) and internal (elastic cartilage, I). The scaffolds were prepared by mixing collagen (C) with the internal part (CI) or the external part (CE) in a 3:1 ratio. Differential scanning calorimetry, scanning electron microscopy (SEM) analysis, microcomputed tomography imaging (micro-CT) and swelling degree were used to characterize the scaffolds. Cytotoxicity, cell adhesion, and cell proliferation assays were performed using the cell line NIH/3T3. All samples presented a similar denaturation temperature (Td) around 48 °C, while CE presented a second Td at 51.2 °C. SEM micrographs showed superficial pores in all scaffolds and micro-CT exhibited interconnected pore spaces with porosity above 60% (sizes between 47 and 149 µm). The order of swelling was CE < CI < C and the scaffolds did not present cytotoxicity, showing attachment rates above 75%-all samples showed a similar pattern of proliferation until 168 h, whereas CI tended to decrease after this time. The scaffolds were easily obtained, biocompatible and had adequate morphology for cell growth. All samples showed high adhesion, whereas collagen-only and collagen/external part scaffolds presented a better cell proliferation rate and would be indicated for possible use in dermal regeneration.

Extracellular vesicles on the move: Traversing the complex matrix of tissues

Extracellular vesicles are small particles involved in intercellular signaling. They are produced by virtually all cell types, transport biological molecules, and are released into the extracellular space. Studies on extracellular vesicles have become more numerous in recent years, leading to promising research on their potential impact on health and disease. Despite significant progress in understanding the bioactivity of extracellular vesicles, most in vitro and in vivo studies overlook their transport through the extracellular matrix in tissues. The interaction or free diffusion of extracellular vesicles in their environment can provide valuable insights into their efficacy and function. Therefore, understanding the factors that influence the transport of extracellular vesicles in the extracellular matrix is essential for the development of new therapeutic approaches that involve the use of these extracellular vesicles. This review discusses the importance of the interaction between extracellular vesicles and the extracellular matrix and the different factors that influence their diffusion. In addition, we evaluate their role in tissue homeostasis, pathophysiology, and potential clinical applications. Understanding the complex interaction between extracellular vesicles and the extracellular matrix is critical in order to develop effective strategies to target specific cells and tissues in a wide range of clinical applications.

How long to wait after local infiltration anaesthesia: systematic review

BACKGROUND

Conflicting evidence exists regarding the optimal waiting time for stable analgesic and vasoconstrictive effects after local infiltration of lidocaine with epinephrine. An objective review is needed to dispel surgical dogma.

METHODS

This systematic review (PROSPERO ID: CRD42022362414) included RCTs and prospective cohort studies. Primary outcomes were (1) onset of analgesia and (2) onset of stable hypoperfusion, assessed directly, or measured indirectly using perfusion imaging. Other data extracted include waiting strategies, means of outcome assessment, anaesthetic concentrations, volume/endpoint of infiltration, and injection sites. Methodological quality was evaluated using the Cochrane risk-of-bias tool for randomized trials. Articles describing waiting strategies were critically appraised by the Joanna Briggs Institute tools.

RESULTS

Twenty-four articles were analysed, comprising 1013 participants. Ten investigated analgesia onset. Their pooled mean was 2.1 min (range 0.4-9.0 min). This varied with anatomic site and targeted nerve diameter. Fourteen articles investigated onset of stable hypoperfusion. Four observed bleeding intraoperatively, finding the minimum time to hypoperfusion at 7.0 min in the eyelid skin and 25.0 min in the upper limb. The ten remaining studies used perfusion imaging, reporting a wide range of results (0.0-30.0 min) due to differences in anatomic sites and depth, resolution and artefacts. Studies using near-infrared reflectance spectroscopy and hyperspectral imaging correlated with clinical observations. Thirteen articles discussed waiting strategies, seven relating to large-volume tumescent local infiltration anaesthesia. Different waiting strategies exist for emergency, arthroscopic and cosmetic surgeries, according to the degree of hypoperfusion required. In tumescent liposuction, waiting 10.0-60.0 min is the norm.

CONCLUSION

Current literature suggests that around 2 min are required for most patients to achieve complete analgesia in all sites and with all anaesthesia concentrations. Waiting around 7 min in eyelids and at least 25 min in other regions results in optimal hypoperfusion. The strategies discussed inform decisions of when and how long to wait.

Preparation of laser microporous porcine acellular dermal matrix and observation of wound transplantation

To prepare a new type of porcine acellular dermis matrix (PADM) with the new laser microporous technique and verify its safety and feasibility. A novel porcine acellular dermis matrix (ADM) was prepared by using sequential combined decellularization of trypsin, neutral protease and SDS solution method and fully rinsed with ultrasonic wave. Specific laser microporous technology was used to prepare the laser micropore porcine acellular dermal matrix (LPADM). SD rats were chose as the animal models and autologous skin was transplanted by one-step method to observe and detect the graft activity, immunogenicity and vascularization degree of the novel PADM. A porcelain white, shiny, soft and elastic dermal matrix was prepared in this study, the results showed low DNA residue and low cytotoxicity. HE staining and SEM observation revealed that the PADM had neither residual cells nor cell fragments, while the collagen bundles were intact and orderly arranged. All the SD rats survived. No infection or skin allergy was found after surgery. None of the animals lost weight. Histological examination showed that the LPADM was fully vascularized with little tissue destruction in the experiment group. Immunohistochemical staining for CD31 showed ideal vascularization in the experiment group, and immunohistochemical staining for TNF-α showed there were no statistical significance of inflammatory reaction in both groups. This study demonstrated that the novel PADM prepared by sequential combined decellularization of trypsin, neutral protease and SDS solution method and new laser microporous technique was effective and safe in animal transplantation.

Fascia Layer-A Novel Target for the Application of Biomaterials in Skin Wound Healing

As the first barrier of the human body, the skin has been of great concern for its wound healing and regeneration. The healing of large, refractory wounds is difficult to be repaired by cell proliferation at the wound edges and usually requires manual intervention for treatment. Therefore, therapeutic tools such as stem cells, biomaterials, and cytokines have been applied to the treatment of skin wounds. Skin microenvironment modulation is a key technology to promote wound repair and skin regeneration. In recent years, a series of novel bioactive materials that modulate the microenvironment and cell behavior have been developed, showing the ability to efficiently facilitate wound repair and skin attachment regeneration. Meanwhile, our lab found that the fascial layer has an indispensable role in wound healing and repair, and this review summarizes the research progress of related bioactive materials and their role in wound healing.

Understanding Formulation and Temperature Effects on Dermal Transport Kinetics by IVPT and Multiphysics Simulation

PURPOSE

It is often unclear how complex topical product formulation factors influence the transport kinetics through skin tissue layers, because of multiple confounding attributes. Environmental factors such as temperature effect are also poorly understood. In vitro permeation testing (IVPT) is frequently used to evaluate drug absorption across skin, but the flux results from these studies are from a combination of mechanistic processes.

METHOD

Two different commercially available formulations of oxybenzone-containing sunscreen cream and continuous spray were evaluated by IVPT in human skin. Temperature influence between typical skin surface temperature (32°C) and an elevated 37°C was also assessed. Furthermore, a multiphysics-based simulation model was developed and utilized to compute the flux of modeled formulations.

RESULTS

Drug transport kinetics differed significantly between the two drug products. Flux was greatly influenced by the environmental temperature. The multiphysical simulation results could reproduce the experimental observations. The computation further indicated that the drug diffusion coefficient plays a dominant role in drug transport kinetics, influenced by the water content which is also affected by temperature.

CONCLUSION

The in vitro testing and bottom-up simulation shed insight into the mechanism of dermal absorption kinetics from dissimilar topical products.

Biocompatible Synthetic Polymers for Tissue Engineering Purposes

Synthetic polymers have been an integral part of modern society since the early 1960s. Besides their most well-known applications to the public, such as packaging, construction, textiles and electronics, synthetic polymers have also revolutionized the field of medicine. Starting with the first plastic syringe developed in 1955 to the complex polymeric materials used in the regeneration of tissues, their contributions have never been more prominent. Decades of research on polymeric materials, stem cells, and three-dimensional printing contributed to the rapid progress of tissue engineering and regenerative medicine that envisages the potential future of organ transplantations. This perspective discusses the role of synthetic polymers in tissue engineering, their design and properties in relation to each type of application. Additionally, selected recent achievements of tissue engineering using synthetic polymers are outlined to provide insight into how they will contribute to the advancement of the field in the near future. In this way, we aim to provide a guide that will help scientists with synthetic polymer design and selection for different tissue engineering applications.

3D-printed dermis-specific extracellular matrix mitigates scar contraction via inducing early angiogenesis and macrophage M2 polarization

Scar contraction frequently happens in patients with deep burn injuries. Hitherto, porcine dermal extracellular matrix (dECM) has supplied microenvironments that assist in wound healing but fail to inhibit scar contraction. To overcome this drawback, we integrate dECM into three-dimensional (3D)-printed dermal analogues (PDA) to prevent scar contraction. We have developed thermally gelled, non-rheologically modified dECM powder (dECMp) inks and successfully transformed them into PDA that was endowed with a micron-scale spatial structure. The optimal crosslinked PDA exhibited desired structure, good mechanical properties as well as excellent biocompatibility. Moreover, in vivo experiments demonstrated that PDA could significantly reduced scar contraction and improved cosmetic upshots of split thickness skin grafts (STSG) than the commercially available dermal templates and STSG along. The PDA has also induced an early, intense neovascularization, and evoked a type-2-like immune response. PDA's superior beneficial effects may attribute to their desired porous structure, the well-balanced physicochemical properties, and the preserved dermis-specific ECM cues, which collectively modulated the expression of genes such as Wnt11, ATF3, and IL1β, and influenced the crucial endogenous signalling pathways. The findings of this study suggest that PDA is a clinical translatable material that possess high potential in reducing scar contraction.

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Current dermal analogues have supplied microenvironments that assist in wound healing but cannot inhibit scar contraction.

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dECMp ink was formulated and transformed into PDA endowed with a micron-scale designed spatial structure.

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The PDAs were neatly superior to split thickness skin grafts and commercial dermal templates in hindering scar contraction.

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The transcriptome data may reveal how at the molecular level the IS and skin wounds respond to biomaterial stimuli.

Effect of collagen degradation on the mechanical behavior and wrinkling of skin

Chronological skin aging is a complex process that is controlled by numerous intrinsic and extrinsic factors. One major factor is the gradual degradation of the dermal collagen fiber network. As a step toward understanding the mechanistic importance of dermal tissue in the process of aging, this study employs analytical and multiscale computational models to elucidate the effect of collagen fiber bundle disintegration on the mechanical properties and topography of skin. Here, human skin is modeled as a soft composite with an anisotropic dermal layer. The anisotropy of the tissue is governed by collagen fiber bundles with varying densities, average fiber alignments, and normalized alignment distributions. In all finite element models examined, collagen fiber bundle degradation results in progressive decreases in dermal and full-thickness composite stiffness. This reduction is more profound when collagen bundles align with the compression axis. Aged skin models with low collagen fiber bundle densities under compression exhibit notably smaller critical wrinkling strains and larger critical wavelengths than younger skin models, in agreement with in vivo wrinkling behavior with age. The propensity for skin wrinkling can be directly attributable to the degradation of collagen fiber bundles, a relationship that has previously been assumed but unsubstantiated. While linear-elastic analytical models fail to capture the postbuckling behavior in skin, nonlinear finite element models can predict the complex bifurcations of the compressed skin with different densities of collagen bundles.

A biphasic multilayer computational model of human skin

The present study investigates the layer-specific mechanical behavior of human skin. Motivated by skin’s histology, a biphasic model is proposed which differentiates between epidermis, papillary and reticular dermis, and hypodermis. Inverse analysis of ex vivo tensile and in vivo suction experiments yields mechanical parameters for each layer and predicts a stiff reticular dermis and successively softer papillary dermis, epidermis and hypodermis. Layer-specific analysis of simulations underlines the dominating role of the reticular dermis in tensile loading. Furthermore, it shows that the observed out-of-plane deflection in ex vivo tensile tests is a direct consequence of the layered structure of skin. In in vivo suction experiments, the softer upper layers strongly influence the mechanical response, whose dissipative part is determined by interstitial fluid redistribution within the tissue. Magnetic resonance imaging-based visualization of skin deformation in suction experiments confirms the deformation pattern predicted by the multilayer model, showing a consistent decrease in dermal thickness for large probe opening diameters.

Targeting Tunable Physical Properties of Materials for Chronic Wound Care

Chronic wounds caused by infections, diabetes, and radiation exposures are becoming a worldwide growing medical burden. Recent progress highlighted the physical signals determining stem cell fates and bacterial resistance, which holds potential to achieve a better wound regeneration in situ. Nanoparticles (NPs) would benefit chronic wound healing. However, the cytotoxicity of the silver NPs (AgNPs) has aroused many concerns. This review targets the tunable physical properties (i.e., mechanical-, structural-, and size-related properties) of either dermal matrixes or wound dressings for chronic wound care. Firstly, we discuss the recent discoveries about the mechanical- and structural-related regulation of stem cells. Specially, we point out the currently undocumented influence of tunable mechanical and structural properties on either the fate of each cell type or the whole wound healing process. Secondly, we highlight novel dermal matrixes based on either natural tropoelastin or synthetic elastin-like recombinamers (ELRs) for providing elastic recoil and resilience to the wounded dermis. Thirdly, we discuss the application of wound dressings in terms of size-related properties (i.e., metal NPs, lipid NPs, polymeric NPs). Moreover, we highlight the cytotoxicity of AgNPs and propose the size-, dose-, and time-dependent solutions for reducing their cytotoxicity in wound care. This review will hopefully inspire the advanced design strategies of either dermal matrixes or wound dressings and their potential therapeutic benefits for chronic wounds.

Constitutive description of skin dermis: Through analytical continuum and coarse-grained approaches for multi-scale understanding

Although there are many successful descriptions of the mechanical response of dermis at different levels of complexity and incorporating varying degrees of the physical phenomena involved in deformation, observations indicate that the unraveling of fibers involves a complex three-dimensional process in which they interact in ways that resemble a braided pattern. Here we develop two complementary treatments to gain a better understanding of the mechanical response of dermis: a) an analytical treatment incorporating fibril stiffness, interfibrillar frictional sliding, and the effect of lateral fibers on the extension of a primary fiber; b) a coarse-grained molecular dynamics model comprised of an array of parallel curved fibrils simulating a fiber. Interfibrillar frictional sliding and stiffness are also captured. Both analytical and molecular dynamics models operate at a scale compatible with the wavelength of collagen fibers (~10 µm). The constitutive description presented here incorporates important physical processes taking place during deformation of dermis and thus represents an advance in our understanding of these phenomena. STATEMENT OF SIGNIFICANCE: Microstructural observations of the dermis of skin during tensile deformation indicate that the unraveling of fibers involves a complex three-dimensional process which replicates the effects of braiding. Two complementary constitutive modeling treatments were developed to gain a better understanding of the mechanical response of dermis: an analytical treatment incorporating fibril stiffness, interfibrillar sliding, and the effect of transverse fibers; and a coarse-grained molecular dynamics model describing the fibril bundling effect. An important novel aspect of the current contribution is the recognition that tridimensional collagen fiber arrangements play an important role in the mechanical response. The constitutive description presented here incorporates physical processes taking place during deformation of the dermis and thus represents an advance in our understanding of these phenomena.

Combined multiphoton imaging and biaxial tissue extension for quantitative analysis of geometric fiber organization in human reticular dermis

The geometric organization of collagen fibers in human reticular dermis and its relationship to that of elastic fibers remain unclear. The tight packing and complex intertwining of dermal collagen fibers hinder accurate analysis of fiber orientation. We hypothesized that combined multiphoton microscopy and biaxial extension could overcome this issue. Continuous observation of fresh dermal sheets under biaxial extension revealed that the geometry of the elastic fiber network is maintained during expansion. Full-thickness human thigh skin samples were biaxially extended and cleared to visualize the entire reticular dermis. Throughout the dermis, collagen fibers straightened with increased inter-fiber spaces, making them more clearly identifiable after extension. The distribution of collagen fibers was evaluated with compilation of local orientation data. Two or three modes were confirmed in all superficial reticular layer samples. A high degree of local similarities in the direction of collagen and elastic fibers was observed. More than 80% of fibers had directional differences of ≤15°, regardless of layer. Understanding the geometric organization of fibers in the reticular dermis improves the understanding of mechanisms underlying the pliability of human skin. Combined multiphoton imaging and biaxial extension provides a research tool for studying the fibrous microarchitecture of the skin.

An enhanced staining method K-B-2R staining for three-dimensional nerve reconstruction

Background

Three-dimensional (3D) reconstruction of human peripheral nerves, as a useful tool to understand the nerve internal information and functional basis, has become an important area of research in the peripheral nerve field.

Methods

In this study, we proposed a two-dimensional (2D) Karnovsky–Roots toluidine blue ponceau 2R (K-B-2R) staining method based upon conventional Karnovsky–Roots staining. It significantly improved the ability to display nerve fascicles, motor and sensory nerve fiber textures. In this method, Karnovsky–Roots staining was carried out, followed by toluidine blue counterstain and ponceau 2R counterstain.

Results

Comparisons were conducted between the three methods in staining of median nerve sections, which showed similar distribution characters in acetylcholinesterase-positive sites. The additional counterstaining did not change the basis of Karnovsky–Roots staining. However, the resulting images from this new method significantly facilitated the subsequent 3D nerve reconstruction and 3D printing.

Conclusions

These results show that the new staining method significantly enhanced the display qualities of nerve fascicle edges and fiber textures of motor and sensory nerves and facilitated 3D nerve reconstruction.

Ex vivo nonlinear microscopy imaging of Ehlers-Danlos syndrome-affected skin

Ehlers-Danlos syndrome (EDS) is the name for a heterogenous group of rare genetic connective tissue disorders with an overall incidence of 1 in 5000. The histological characteristics of EDS have been previously described in detail in the late 1970s and early 1980s. Since that time, the classification of EDS has undergone significant changes, yet the description of the histological features of collagen morphology in different EDS subtypes has endured the test of time. Nonlinear microscopy techniques can be utilized for non-invasive in vivo label-free imaging of the skin. Among these techniques, two-photon absorption fluorescence (TPF) microscopy can visualize endogenous fluorophores, such as elastin, while the morphology of collagen fibers can be assessed by second-harmonic generation (SHG) microscopy. In our present work, we performed TPF and SHG microscopy imaging on ex vivo skin samples of one patient with classical EDS and two patients with vascular EDS and two healthy controls. We detected irregular, loosely dispersed collagen fibers in a non-parallel arrangement in the dermis of the EDS patients, while as expected, there was no noticeable impairment in the elastin content. Based on further studies on a larger number of patients, in vivo nonlinear microscopic imaging could be utilized for the assessment of the skin status of EDS patients in the future.

Polydimethylsiloxane incorporated with reduced graphene oxide (rGO) sheets for wound dressing application: Preparation and characterization

Toward fabricating a novel multifunctional wound dressing material, we incorporated a series of contents of reduced graphene oxide (rGO) sheets into polydimethylsiloxane (PDMS) matrix to prepare the rGO-PDMS composite membrane and be used for wound dressing. The pore structure, dispersion of rGO, physical properties, water vapor transmission rate (WVTR), cytotoxicity and antibacterial activity were studied. Finally, the effect of the rGO-PDMS composite membrane on wound healing was investigated on a murine full-thickness skin wound model. The rGO-PDMS composite membrane exhibited bionic performance (ordered pore structure and suitable WVTR), improved mechanical properties, good compatibility and effective antibacterial activity. In vivo experiment indicated that the rGO-PDMS composite membrane could accelerate wound healing via enhancement of the re-epithelialization and granulation tissue formation. These findings suggest that rGO doping PDMS uniquely resulted in a multifunctional material for potential use in wound dressing.

Three-dimensional digital reconstruction of skin epidermis and dermis

This study describes how three-dimensional (3D) human skin tissue is reconstructed, and provides digital anatomical data for the physiological structure of human skin tissue based on large-scale thin serial sections. Human skin samples embedded in paraffin were cut serially into thin sections and then stained with hematoxylin-eosin. Images of serial sections obtained from lighting microscopy were scanned and aligned by the scale-invariant feature transform algorithm. 3D reconstruction of the skin tissue was generated using Mimics software. Fibre content, porosity, average pore diameter and specific surface area of dermis were analysed using the ImageJ analysis system. The root mean square error and mutual information based on the scale-invariant feature transform algorithm registration were significantly greater than those based on the manual registration. Fibre distribution gradually decreased from top to bottom; while porosity showed an opposite trend with irregular average pore diameter distribution. A specific surface area of the dermis showed a 'V' shape trend. Our data suggested that 3D reconstruction of human skin tissue based on large-scale serial sections could be a valuable tool for providing a highly accurate histological structure for analysis of skin tissue. Moreover, this technology could be utilized to produce tissue-engineered skin via a 3D bioprinter in the future.

A Prospective Study Assessing Complication Rates and Patient-Reported Outcomes in Breast Reconstructions Using a Novel, Deep Dermal Human Acellular Dermal Matrix

The value proposition of an acellular dermal matrix (ADM) taken from the deep dermis is that the allograft may be more porous, allowing for enhanced integration and revascularization. In turn, this characteristic may attenuate complications related to foreign body reactions, seromas, and infection. However, this is juxtaposed against the potential loss of allograft structural integrity, with subsequent risk of malposition and extrusion. Despite the active use of novel, deep dermal ADMs, the clinical outcomes of this new technology has not been well studied.

METHODS

This is a prospective study to evaluate surgical and patient-reported outcomes using a deep dermal ADM, FlexHD Pliable. Surgical outcomes and BREAST-Q patient-reported outcomes were evaluated postoperatively at 2- and 6-month time points.

RESULTS

Seventy-two breasts (41 patients) underwent reconstruction. Complication rate was 12.5%, including 2 hematomas and 7 flap necroses. One case of flap necrosis led to reconstructive failure. Notably, there were no cases of infection, seroma, or implant extrusion or malposition. Average BREAST-Q scores were satisfaction with outcome (70.13 ± 23.87), satisfaction with breasts (58.53 ± 20.00), psychosocial well being (67.97 ± 20.93), sexual well being (54.11 ± 27.72), and physical well being (70.45 ± 15.44). Two-month postoperative BREAST-Q scores decreased compared with baseline and returned to baseline by 6 months. Postoperative radiation therapy had a negative effect on satisfaction with breasts (P = 0.004) and sexual well being (P = 0.006).

CONCLUSIONS

Deep dermal ADM is a novel modification of traditional allograft technology. Use of the deep dermal ADM yielded acceptably low complication rates and satisfactory patient-reported outcomes.

Biomimetic thermoplastic polyurethane porous membrane with hierarchical structure accelerates wound healing by enhancing granulation tissue formation and angiogenesis

Wound dressing with hierarchical structure enhances wound healing.

Biomimetic fibroblast-loaded artificial dermis with "sandwich" structure and designed gradient pore sizes promotes wound healing by favoring granulation tissue formation and wound re-epithelialization

The structure of dermal scaffolds greatly affects the engineered tissue's functions and the activities of seeded cells. Current strategies of dermal scaffold design tend to yield a homogeneous architecture with a uniform pore size. However, the structures of the human dermis are not homogeneous in terms of either interstitial spaces or architecture at different dermal depths. In the present study, a biomimetic fibroblasts-loaded artificial dermis composed of three-layer scaffolds with different pore sizes was prepared. The three-layer scaffolds, which look similar to a sandwich, mimic the natural structures of the human dermis, which has comparatively larger pores in the outer layers and smaller pores in the middle layer. The fibroblasts-loaded artificial dermis were shown to favor wound healing by promoting granulation tissue formation and wound re-epithelialization, as determined by a histological study and Western blotting. Our data indicated that the biomimetic fibroblasts-loaded artificial dermis with "Sandwich" structure and designed gradient pore sizes may hold promise as tissue-engineered dermis.

STATEMENT OF SIGNIFICANCE

Pore size effect on wound healing had been extensively studied. However, it is still not well understood whether dermal scaffolds with a uniform pore size are better than that with varied pore sizes, which are similar to human dermis as determined by our previous work. In our study, we demonstrated that the "sandwich" collagen scaffolds mimicking the natural structures of the human dermis significantly promoted wound healing compared with the "Homogeneous" scaffolds with a uniform pore size. These results may be helpful in the design of dermal scaffolds.