Vascularization of the dermal support enhances wound re-epithelialization by in situ delivery of epidermal keratinocytes

Diameter-dependent classification of dermal vasculature using optical coherence tomography angiography

Background

Dermal blood vessels beneath the epidermis play critical roles in epidermal homeostasis and are functionally divided into several types, such as capillaries. Optical coherence tomography angiography (OCTA) is a powerful tool for the non-invasive assessment of dermal vasculature. However, the classification of vessel types has been limited. To address this issue, we proposed an algorithm for diameter-dependent classification that preserves three-dimensional (3D) information using OCTA.

Methods

OCTA data were acquired by a prototype swept-source-type optical coherence tomography (OCT) system, which was processed through several imaging filters: an optical microangiography (OMAG) imaging filter, a vesselness imaging filter, and a diameter map filter. All vessels were visually classified into three types based on their diameters, as micro-vessels, intermediate vessels, and thick vessels. Aging-related alterations and their association with the epidermis were investigated for each vessel type. The measurements were conducted on the cheeks of 124 female subjects aged 20-79 years.

Results

The 3D vascular structure was visualized by applying our proposed post-processing filters. Based on visual assessment, the thresholds for the diameters of the micro, intermediate and thick vessels were set at 80 and 160 µm. It was found that micro-vessels were predominantly located in the upper layer of the dermis and thick vessels in the deeper layer. Analysis of vessel metrics revealed that the volume density of the micro-vessels decreased significantly with age (r=-0.36, P<0.001) and was positively correlated with epidermal thickness (r=0.50, P<0.001). In contrast, the volume density of thick vessels significantly increased with age (r=0.2, P<0.05) and was not significantly correlated with epidermal thickness (r=0.13, P≥0.05).

Conclusions

In this study, we proposed a 3D quantification method using OCTA for dermal blood vessels and various vessel metrics, such as vessel volume density. This proposed classification will be beneficial for determining the function of the dermal vasculature and its diagnostic applications.

Characteristics of dermal vascularity in melasma and solar lentigo

BACKGROUND /PURPOSE

Melasma and solar lentigo (SL) are major benign hyperpigmented lesions, and both have been shown to involve the dermal vasculature. This review discusses current knowledge regarding the clinical characteristics of dermal vascularity in melasma and SL, as well as the results of relevant molecular biological investigations.

METHODS

PubMed and Google Scholar were searched in December 2023 to identify articles related to melasma, SL, and the dermal vasculature in these lesions.

RESULTS

Vascular morphologies in melasma and SL have been detected by histological and non-invasive methods, including modalities such as optical coherence tomography. Biological studies have indicated that factors secreted from vascular endothelial cells, such as stem cell factor and endothelin-1, can promote melanogenesis. With respect to phototherapy, blood vessel-targeting laser treatments are expected to provide long-term suppression of pigmentation, but this regimen is only effective when dilated capillaries are visible.

CONCLUSION

In both melasma and SL, clinical and experimental investigations are revealing the contributions of dermal vascularity to hyperpigmentation. More effective treatment may require identification of hyperpigmentation subtypes. In the future, knowledge of treatment (including phototherapy) is expected to accumulate through reliable and validated non-invasive measurements.

Reconstruction of the human nipple-areolar complex: a tissue engineering approach

Introduction: Nipple-areolar complex (NAC) reconstruction after breast cancer surgery is challenging and does not always provide optimal long-term esthetic results. Therefore, generating a NAC using tissue engineering techniques, such as a decellularization-recellularization process, is an alternative option to recreate a specific 3D NAC morphological unit, which is then covered with an in vitro regenerated epidermis and, thereafter, skin-grafted on the reconstructed breast. Materials and methods: Human NACs were harvested from cadaveric donors and decellularized using sequential detergent baths. Cellular clearance and extracellular matrix (ECM) preservation were analyzed by histology, as well as by DNA, ECM proteins, growth factors, and residual sodium dodecyl sulfate (SDS) quantification. In vivo biocompatibility was evaluated 30 days after the subcutaneous implantation of native and decellularized human NACs in rats. In vitro scaffold cytocompatibility was assessed by static seeding of human fibroblasts on their hypodermal side for 7 days, while human keratinocytes were seeded on the scaffold epidermal side for 10 days by using the reconstructed human epidermis (RHE) technique to investigate the regeneration of a new epidermis. Results: The decellularized NAC showed a preserved 3D morphology and appeared white. After decellularization, a DNA reduction of 98.3% and the absence of nuclear and HLA staining in histological sections confirmed complete cellular clearance. The ECM architecture and main ECM proteins were preserved, associated with the detection and decrease in growth factors, while a very low amount of residual SDS was detected after decellularization. The decellularized scaffolds were in vivo biocompatible, fully revascularized, and did not induce the production of rat anti-human antibodies after 30 days of subcutaneous implantation. Scaffold in vitro cytocompatibility was confirmed by the increasing proliferation of seeded human fibroblasts during 7 days of culture, associated with a high number of living cells and a similar viability compared to the control cells after 7 days of static culture. Moreover, the RHE technique allowed us to recreate a keratinized pluristratified epithelium after 10 days of culture. Conclusion: Tissue engineering allowed us to create an acellular and biocompatible NAC with a preserved morphology, microarchitecture, and matrix proteins while maintaining their cell growth potential and ability to regenerate the skin epidermis. Thus, tissue engineering could provide a novel alternative to personalized and natural NAC reconstruction.

Combining bioengineered human skin with bioprinted cartilage for ear reconstruction

Microtia is a congenital disorder that manifests as a malformation of the external ear leading to psychosocial problems in affected children. Here, we present a tissue-engineered treatment approach based on a bioprinted autologous auricular cartilage construct (EarCartilage) combined with a bioengineered human pigmented and prevascularized dermo-epidermal skin substitute (EarSkin) tested in immunocompromised rats. We confirmed that human-engineered blood capillaries of EarSkin connected to the recipient's vasculature within 1 week, enabling rapid blood perfusion and epidermal maturation. Bioengineered EarSkin displayed a stratified epidermis containing mature keratinocytes and melanocytes. The latter resided within the basal layer of the epidermis and efficiently restored the skin color. Further, in vivo tests demonstrated favorable mechanical stability of EarCartilage along with enhanced extracellular matrix deposition. In conclusion, EarCartilage combined with EarSkin represents a novel approach for the treatment of microtia with the potential to circumvent existing limitations and improve the aesthetic outcome of microtia reconstruction.

Perspective on the application of medicinal plants and natural products in wound healing: A mechanistic review

Wound is defined as any injury to the body such as damage to the epidermis of the skin and disturbance to its normal anatomy and function. Since ancient times, the importance of wound healing has been recognized, and many efforts have been made to develop novel wound dressings made of the best material for rapid and effective wound healing. Medicinal plants play a great role in the wound healing process. In recent decades, many studies have focused on the development of novel wound dressings that incorporate medicinal plant extracts or their purified active compounds, which are potential alternatives to conventional wound dressings. Several studies have also investigated the mechanism of action of various herbal medicines in wound healing process. This paper attempts to highlight and review the mechanistic perspective of wound healing mediated by plant-based natural products. The findings showed that herbal medicines act through multiple mechanisms and are involved in various stages of wound healing. Some herbal medicines increase the expression of vascular endothelial growth factor (VEGF) and transforming growth factor-β (TGF-β) which play important role in stimulation of re-epithelialization, angiogenesis, formation of granulation tissue, and collagen fiber deposition. Some other wound dressing containing herbal medicines act as inhibitor of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and inducible nitric oxide synthase (iNOS) protein expression thereby inducing antioxidant and anti-inflammatory properties in various phases of the wound healing process. Besides the growing public interest in traditional and alternative medicine, the use of herbal medicine and natural products for wound healing has many advantages over conventional medicines, including greater effectiveness due to diverse mechanisms of action, antibacterial activity, and safety in long-term wound dressing usage.

Biofabrication of thick vascularized neo-pedicle flaps for reconstructive surgery

Wound chronicity due to intrinsic and extrinsic factors perturbs adequate lesion closure and reestablishment of the protective skin barrier. Immediate and proper care of chronic wounds is necessary for a swift recovery and a reduction of patient vulnerability to infection. Advanced therapies supplemented with standard wound care procedures have been clinically implemented to restore aberrant tissue; however, these treatments are ineffective if local vasculature is too compromised to support minimally-invasive strategies. Autologous "flaps", which are tissues equipped with their own hierarchical vascular supply, can be harvested from one region of the patient and transplanted to the wound where it is reperfused upon microsurgical anastomosis to appropriate recipient vessels. Despite the success of autologous flap transfer, these procedures are extremely invasive, incur obligatory donor-site morbidity, and require sufficient donor-tissue availability, microsurgical expertise, and specialized equipment. 3D-bioprinting modalities, such as extrusion-based bioprinting, can be used to address the clinical constraints of autologous flap transfer, primarily addressing donor-site morbidity and tissue availability. This advancement in regenerative medicine allows the biofabrication of heterogeneous tissue structures with high shape fidelity and spatial resolution to generate biomimetic constructs with the anatomically-precise geometries of native tissue to ensure tissue-specific function. Yet, meaningful progress toward this clinical application has been limited by the lack of vascularization required to meet the nutrient and oxygen demands of clinically relevant tissue volumes. Thus, various criteria for the fabrication of functional tissues with hierarchical, patent vasculature must be considered when implementing 3D-bioprinting technologies for deep, chronic wounds.

Skin Changes During Ageing

The skin provides the primary protection for the body against external injuries and is essential in the maintenance of general homeostasis. During ageing, resident cells become senescent and the extracellular matrix, mainly in the dermis, is progressively damaged affecting the normal organization of the skin and its capacity for repair. In parallel, extrinsic factors such as ultraviolet irradiation, pollution, and intrinsic factors such as diabetes or vascular disease can further accelerate this phenomenon. Indeed, numerous mechanisms are involved in age-induced degradation of the skin and these also relate to non-healing or chronic wounds in the elderly. In particular, the generation of reactive oxygen species seems to play a major role in age-related skin modifications. Certainly, targeting both the hormonal status of the skin or its surface nutrition can slow down age-induced degradation of the skin and improve healing of skin damage in the elderly. Skin care regimens that prevent radiation and pollution damage, and reinforce the skin surface and its microbiota are among the different approaches able to minimize the effects of ageing on the skin.

Optimizing the nanostructure of graphene oxide/silver/arginine for effective wound healing

In this study, we introduce a novel graphene oxide/silver/arginine (GO/Ag/Arg) nanohybrid structure, which can act as an angiogenesis promoter and provide antibacterial nanostructure for improving the wound healing process. GO/Ag nanostructure has been optimized in terms of the GO/Ag mass ratio and pH values using central composite design and the response surface method to increase the Ag loading efficiency. Then, Arg was chemically introduced to the surface of GO/Ag nanostructure. Electrospun polycaprolactone (PCL)-GO/Ag/Arg nanocomposite was successfully fabricated and characterized. The synthesized nanocomposite demonstrated not only a great antibacterial effect on both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacterial species, but appropriate biocompatibility against L929 fibroblastic cell lines. The results demonstrated that the preparation of the PCL-GO/Ag/Arg nanocomposite at a concentration of 1.0 wt% GO/Ag/Arg possessed the best biological and mechanical features. In vivo experiments also revealed that the use of optimized PCL-GO/Ag/Arg nanocomposite, after 12 d of treatment, led to significant increase in the healing process and also regeneration of the wound via reconstruction of a thickened epidermis layer on the wound surface, which was confirmed by histological analysis. In conclusion, the proposed approach can introduce a novel notion for preparing antibacterial material that significantly promotes angiogenesis.

Induced Granulation Tissue but not Artificial Dermis Enhances Early Host-Graft Interactions in Full-Thickness Burn Wounds

BACKGROUND

Cellular grafts used for skin repair require rapid integration with the host tissue to remain viable and especially to nourish the epidermal cells. Here, we evaluated the responses in the split-thickness skin grafts (STSGs) grafted on three differently treated wound beds: directly on excised wound bed (EX), on an artificial dermal template (DT) and on granulation tissue (GT) induced by cellulose sponge.

METHODS

In ten burn patients, after excision, a test area was divided into three sections: One transplanted with STSG instantaneously and two sections had a pre-treatment for 2 weeks with either DT or a cellulose sponge inducing granulation tissue formation and thereafter grafted with STSGs.

RESULTS

One week after grafting, the STSGs on GT demonstrated most endothelial CD31⁺ staining, largest average vessel diameters as well as most CD163⁺ staining of M2-like macrophages and most MIB1⁺ proliferating epidermal cells, suggesting an active regenerative environment. STSGs on DT had smallest vessel diameters and the least CD163⁺ macrophages. STSGs on EX had the least CD31⁺ cells and the least MIB1⁺ proliferating cells. After 3 months, this reactivity in STSGs had subsided, except increased dermal cell proliferation was observed in STSGs on EX.

CONCLUSIONS

Results show that pre-treatment of wound bed and induction of granulation tissue formation can accelerate host-graft interaction by stimulating graft vasculature and inducing cell proliferation.

Biomaterials for Skin Substitutes

Patients with extensive burns rely on the use of tissue engineered skin due to a lack of sufficient donor tissue, but it is a challenge to identify reliable and economical scaffold materials and donor cell sources for the generation of a functional skin substitute. The current review attempts to evaluate the performance of the wide range of biomaterials available for generating skin substitutes, including both natural biopolymers and synthetic polymers, in terms of tissue response and potential for use in the operating room. Natural biopolymers display an improved cell response, while synthetic polymers provide better control over chemical composition and mechanical properties. It is suggested that not one material meets all the requirements for a skin substitute. Rather, a composite scaffold fabricated from both natural and synthetic biomaterials may allow for the generation of skin substitutes that meet all clinical requirements including a tailored wound size and type, the degree of burn, the patient age, and the available preparation technique. This review aims to be a valuable directory for researchers in the field to find the optimal material or combination of materials based on their specific application.

The Effects of Aloe vera Cream on the Expression of CD4+ and CD8+ Lymphocytes in Skin Wound Healing

The aim of this study is to explore the effect of topical application of Aloe vera on skin wound healing. Thirty-six male Sprague-Dawley rats weighing 150–200 grams were divided into four groups. All groups were anesthetized, shaved, and exposed to round full-thickness punch biopsy on the back: group I (control); group II (treated with 1% Aloe vera cream); group III (treated with 2% Aloe vera cream); and group IV (treated with madecassol®). The treatments were given once a day. Macroscopic and microscopic examination were observed at 5, 10, and 15 days after skin biopsy. Skin specimens were prepared for histopathological study using H&E stain and IHC stain against CD4⁺ and CD8⁺ lymphocytes. All the data were analyzed using SPSS16. The result showed that topical application of 1% and 2% Aloe vera cream significantly reduced the percentage of the wound, leucocytes infiltration, angiogenesis, and expression of CD8⁺ lymphocytes and increased the epidermal thickness and the expression of CD4⁺ lymphocytes (p ≤ 0,05). There was no significant difference in the number of fibroblasts in all groups. Topical application of 1% and 2% Aloe vera cream has wound healing potential via their ability to increase the ratio of CD4⁺/CD8⁺ lymphocytes in the wound area.

What happens to an acellular dermal matrix after implantation in the human body? A histological and electron microscopic study

Acellular matrices are used for various purposes and they have been studied extensively for their potential roles in regenerating tissues or organs. The acellular matrix generates physiological cues that mimic the native tissue microenvironment. Acellular dermal matrix (ADM) is a soft connective tissue graft generated by a decellularization process that preserves the intact extracellular skin matrix. Upon implantation, this structure serves as a scaffold for donor-side cells to facilitate subsequent incorporation and revascularization. In breast reconstruction, ADM is used mainly for lower pole coverage and the shaping of a new breast. It helps control the positioning of the implant in the inframammary fold, and prevents the formation of contractile pseudocapsule around the breast implant. In this study, we provide a comprehensive histological description of ADM used for human breast reconstruction over the course of several months following implementation. Using immunohistochemical methods (a panel of 12 antibodies) coupled with optical and transmission electron microscopy, we confirmed that the original acellular dermal matrix became recolonized by fibroblasts and myofibroblasts, and also by various other free cells of the connective tissue (lymphocytes, macrophages and multinucleated giant cells, granulocytes, mast cells) after implantation into the patient’s body. Within the implanted ADM, there was a relatively rapid ingrowth of blood vessels. Lymphatic vessels were only detected in one case 9 months after the implantation of the ADM. These results suggest that lymphangiogenesis is a longer process than angiogenesis.

Effect of Compound 21, a Selective Angiotensin II Type 2 Receptor Agonist, in a Murine Xenograft Model of Dupuytren Disease

BACKGROUND

Although surgical excision and intralesional collagenase injection are mainstays in Dupuytren disease treatment, no effective medical therapy exists for recurrent disease. Compound 21, a selective agonist of the angiotensin II type 2 receptor, has been shown to protect against fibrosis in models of myocardial infarction and stroke. The authors investigated the potential use of compound 21 in the treatment of Dupuytren disease.

METHODS

Human dermal fibroblasts were treated in vitro with compound 21 and assessed for viability using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, migration by means of scratch assay, and profibrotic gene transcription by means of quantitative reverse transcription polymerase chain reaction. Compound 21 effects in vivo were assessed using a xenograft model. Dupuytren disease cord specimens from patients undergoing open partial fasciectomy were divided into two segments. Segments were implanted under the dorsal skin of nude mouse pairs. Beginning on day 5, one mouse from each pair received daily intraperitoneal injections of compound 21 (10 μg/kg/day), and the other received vehicle. On day 10, segments were explanted and submitted for immunohistochemistry.

RESULTS

Human dermal fibroblasts treated with compound 21 displayed decreased migration and decreased gene expression of connective tissue growth factor, fibroblast specific protein-1, transforming growth factor-β1, Smad3, and Smad4. Dupuytren disease segments from compound 21-treated mice demonstrated significantly reduced alpha-smooth muscle actin and Ki67 staining, with increased density of CD31 staining vessels.

CONCLUSIONS

Compound 21 significantly decreases expression of profibrotic genes and decreases myofibroblast proliferation as indicated by reduced Ki67 and alpha-smooth muscle actin expression. These findings support compound 21 as a potential novel treatment modality for Dupuytren disease.

Delayed post mastectomy breast reconstructions with allogeneic acellular dermal matrix prepared by a new decellularizationmethod

Acellular dermal matrix (ADM) is a tissue graft of allogeneic origin from post-mortem tissue donors prepared by an innovative decellularization process. The newly developed non-toxic and low cost decellularization process of cadaver origin dermis included ADM in breast reconstruction procedures proved to help coverage of the lower-pole of breast expanders or implants. As the results have shown, it did help to eliminate autologous dermis donor site morbidity along with shortening the operation time by avoiding elevation of additional muscle or fascia during the operation. Main aims of this article include histology evaluation of allogeneic acellular dermal matrix prepared by a new decellularization method and presentation of clinical results of its use. A total of 22 patients underwent 26 ADM based breast reconstructions. The mean patient's follow up was 12.6 months. Average total size of ADM used for one breast was 273 cm². Post-operative complications occurred in 3 patients including one expander infection, one expander extrusion and one expander pocket disfiguration. Microscopic analysis of tissue samples has confirmed incorporation of the acellular dermal matrices into the surrounding connective tissue without any noticeable immune reaction. In a majority of the ADM samples we found pseudocapsullar formation on implant side of samples without acute or chronic inflammatory cells. The use of ADM prepared by new preparation method in expansive post mastectomy breast reconstruction was associated by a relatively low complication rate resulting in good outcomes.

Vascular Network Formation by Human Microvascular Endothelial Cells in Modular Fibrin Microtissues

Microvascular endothelial cells (MVEC) are a preferred cell source for autologous revascularization strategies, since they can be harvested and propagated from small tissue biopsies. Biomaterials-based strategies for therapeutic delivery of cells are aimed at tailoring the cellular microenvironment to enhance the delivery, engraftment, and tissue-specific function of transplanted cells. In the present study, we investigated a modular tissue engineering approach to therapeutic revascularization using fibrin-based microtissues containing embedded human MVEC and human fibroblasts (FB). Microtissues were formed using a water-in-oil emulsion process that produced populations of spheroidal tissue modules with a diameter of 100-200 µm. The formation of MVEC sprouts within a fibrin matrix over 7 days in culture was dependent on the presence of FB, with the most robust sprouting occurring at a 1:3 MVEC:FB ratio. Cell viability in microtissues was high (>90%) and significant FB cell proliferation was observed over time in culture. Robust sprouting from microtissues was evident, with larger vessels developing over time and FB acting as pericyte-like cells by enveloping endothelial tubes. These neovessels were shown to form an interconnected vascular plexus over 14 days of culture when microtissues were embedded in a surrounding fibrin hydrogel. Vessel networks exhibited branching and inosculation of sprouts from adjacent microtissues, resulting in MVEC-lined capillaries with hollow lumens. Microtissues maintained in suspension culture aggregated to form larger tissue masses (1-2 mm in diameter) over 7 days. Vessels formed within microtissue aggregates at a 1:1 MVEC:FB ratio were small and diffuse, whereas the 1:3 MVEC:FB ratio produced large and highly interconnected vessels by day 14. This study highlights the utility of human MVEC as a cell source for revascularization strategies, and suggests that the ratio of endothelial to support cells can be used to tailor vessel characteristics. The modular microtissue format may allow minimally invasive delivery of populations of prevascularized microtissues for therapeutic applications.

Controlled water vapor transmission rate promotes wound-healing via wound re-epithelialization and contraction enhancement

A desirable microenvironment is essential for wound healing, in which an ideal moisture content is one of the most important factors. The fundamental function and requirement for wound dressings is to keep the wound at an optimal moisture. Here, we prepared serial polyurethane (PU) membrane dressings with graded water vapor transmission rates (WVTRs), and the optimal WVTR of the dressing for wound healing was identified by both in vitro and in vivo studies. It was found that the dressing with a WVTR of 2028.3 ± 237.8 g/m²·24 h was able to maintain an optimal moisture content for the proliferation and regular function of epidermal cells and fibroblasts in a three-dimensional culture model. Moreover, the dressing with this optimal WTVR was found to be able to promote wound healing in a mouse skin wound model. Our finds may be helpful in the design of wound dressing for wound regeneration in the future.

Deferoxamine preconditioning to restore impaired HIF-1α-mediated angiogenic mechanisms in adipose-derived stem cells from STZ-induced type 1 diabetic rats

OBJECTIVES

Both excessive and insufficient angiogenesis are associated with progression of diabetic complications, of which poor angiogenesis is an important feature. Currently, adipose-derived stem cells (ADSCs) are considered to be a promising source to aid therapeutic neovascularization. However, functionality of these cells is impaired by diabetes which can result from a defect in hypoxia-inducible factor-1 (HIF-1), a key mediator involved in neovascularization. In the current study, we sought to explore effectiveness of pharmacological priming with deferoxamine (DFO) as a hypoxia mimetic agent, to restore the compromised angiogenic pathway, with the aid of ADSCs derived from streptozotocin (STZ)-induced type 1 diabetic rats ('diabetic ADSCs').

MATERIALS AND METHODS

Diabetic ADSCs were treated with DFO and compared to normal and non-treated diabetic ADSCs for expression of HIF-1α, VEGF, FGF-2 and SDF-1, at mRNA and protein levels, using qRT-PCR, western blotting and ELISA assay. Activity of matrix metalloproteinases -2 and -9 were measured using a gelatin zymography assay. Angiogenic potential of conditioned media derived from normal, DFO-treated and non-treated diabetic ADSCs were determined by in vitro (in HUVECs) and in vivo experiments including scratch assay, three-dimensional tube formation testing and surgical wound healing models.

RESULTS

DFO remarkably enhanced expression of noted genes by mRNA and protein levels and restored activity of matrix metalloproteinases -2 and -9. Compromised angiogenic potential of conditioned medium derived from diabetic ADSCs was restored by DFO both in vitro and in vivo experiments.

CONCLUSION

DFO preconditioning restored neovascularization potential of ADSCs derived from diabetic rats by affecting the HIF-1α pathway.

LPS-Stimulated Human Skin-Derived Stem Cells Enhance Neo-Vascularization during Dermal Regeneration

High numbers of adult stem cells are still required to improve the formation of new vessels in scaffolds to accelerate dermal regeneration. Recent data indicate a benefit for vascularization capacity by stimulating stem cells with lipopolysaccharide (LPS). In this study, stem cells derived from human skin (SDSC) were activated with LPS and seeded in a commercially available dermal substitute to examine vascularization in vivo. Besides, in vitro assays were performed to evaluate angiogenic factor release and tube formation ability. Results showed that LPS-activated SDSC significantly enhanced vascularization of the scaffolds, compared to unstimulated stem cells in vivo. Further, in vitro assays confirmed higher secretion rates of proangiogenic as well as proinflammatoric factors in the presence of LPS-activated SDSC. Our results suggest that combining activated stem cells and a dermal substitute is a promising option to enhance vascularization in scaffold-mediated dermal regeneration.

Naturally Occurring Extracellular Matrix Scaffolds for Dermal Regeneration: Do They Really Need Cells?

The pronounced effect of extracellular matrix (ECM) scaffolds in supporting tissue regeneration is related mainly to their maintained 3D structure and their bioactive components. These decellularized matrix scaffolds could be revitalized before grafting via adding stem cells, fibroblasts, or keratinocytes to promote wound healing. We reviewed the online published literature in the last five years for the studies that performed ECM revitalization and discussed the results of these studies and the related literature. Eighteen articles met the search criteria. Twelve studies included adding cells to acellular dermal matrix (ADM), 3 studies were on small intestinal mucosa (SIS), one study was on urinary bladder matrix (UBM), one study was on amniotic membrane, and one study included both SIS and ADM loaded constructs. We believe that, in chronic and difficult-to-heal wounds, revitalizing the ECM scaffolds would be beneficial to overcome the defective host tissue interaction. This belief still has to be verified by high quality randomised clinical trials, which are still lacking in literature.

Dermal papilla cells improve the wound healing process and generate hair bud-like structures in grafted skin substitutes using hair follicle stem cells

Tissue-engineered skin represents a useful strategy for the treatment of deep skin injuries and might contribute to the understanding of skin regeneration. The use of dermal papilla cells (DPCs) as a dermal component in a permanent composite skin with human hair follicle stem cells (HFSCs) was evaluated by studying the tissue-engineered skin architecture, stem cell persistence, hair regeneration, and graft-take in nude mice. A porcine acellular dermal matrix was seeded with HFSCs alone and with HFSCs plus human DPCs or dermal fibroblasts (DFs). In vitro, the presence of DPCs induced a more regular and multilayered stratified epidermis with more basal p63-positive cells and invaginations. The DPC-containing constructs more accurately mimicked the skin architecture by properly stratifying the differentiating HFSCs and developing a well-ordered epithelia that contributed to more closely recapitulate an artificial human skin. This acellular dermal matrix previously repopulated in vitro with HFSCs and DFs or DPCs as the dermal component was grafted in nude mice. The presence of DPCs in the composite substitute not only favored early neovascularization, good assimilation and remodeling after grafting but also contributed to the neovascular network maturation, which might reduce the inflammation process, resulting in a better healing process, with less scarring and wound contraction. Interestingly, only DPC-containing constructs showed embryonic hair bud-like structures with cells of human origin, presence of precursor epithelial cells, and expression of a hair differentiation marker. Although preliminary, these findings have demonstrated the importance of the presence of DPCs for proper skin repair.

Human skin cell fractions fail to self-organize within a gellan gum/hyaluronic acid matrix but positively influence early wound healing

Split-thickness autografts still are the current gold standard to treat skin, upon severe injuries. Nonetheless, autografts are dependent on donor site availability and often associated to poor quality neoskin. The generation of dermal-epidermal substitutes by tissue engineering is seen as a promising strategy to overcome this problematic. However, solutions that can be safely and conveniently transplanted in one single surgical intervention are still very challenging as their production normally requires long culture time, and graft survival is many times compromised by delayed vascularization upon transplantation. This work intended to propose a strategy that circumvents the prolonged and laborious preparation period of skin substitutes and allows skin cells self-organization toward improved healing. Human dermal/epidermal cell fractions were entrapped directly from isolation within a gellan gum/hyaluronic acid (GG-HA) spongy-like hydrogel formed from an off-the-shelf dried polymeric network. Upon transplantation into full-thickness mice wounds, the proposed constructs accelerated the wound closure rate and re-epithelialization, as well as tissue neovascularization. A synergistic effect of the GG-HA matrix and the transplanted cells over those processes was demonstrated at early time points. Despite the human-derived and chimeric blood vessels found, the proposed matrix did not succeed in prolonging cells residence time and in sustaining the self-organization of transplanted human cells possibly due to primitive degradation. Despite this, the herein proposed approach open the opportunity to tackle wound healing at early stages contributing to re-epithelialization and neovascularization.

Microenvironment-induced myofibroblast-like conversion of engrafted keratinocytes

Myofibroblasts, recognized classically by α-smooth muscle actin (α-SMA) expression, play a key role in the wound-healing process, promoting wound closure and matrix deposition. Although a body of evidence shows that keratinocytes explanted onto a wound bed promote closure of a skin injury, the underlying mechanisms are not well understood. The basal layer of epidermis is rich in undifferentiated keratinocytes (UKs). We showed that UKs injected into granulation tissue could switch into α-SMA positive cells, and accelerate the rate of skin wound healing. In addition, when the epidermis sheets isolated from foreskin cover up the wound bed or are induced in vitro, keratinocytes located at the basal layers or adjacent sites were observed to convert into myofibroblast-like cells. Thus, UKs have a potential for myofibroblastic transition, which provides a novel mechanism by which keratinocyte explants accelerate skin wound healing.

Three types of dermal grafts in rats: the importance of mechanical property and structural design

Background

To determine how the mechanical property and micro structure affect tissue regeneration and angiogenesis, three types of scaffolds were studied. Acellular dermal matrices (ADM), produced from human skin by removing the epidermis and cells, has been widely used in wound healing because of its high mechanical strength. Collagen scaffolds (CS) incorporated with poly(glycolide-co-L-lactide) (PLGA) mesh forms a well-supported hybrid dermal equivalent poly(glycolide-co-L-lactide) mesh/collagen scaffolds (PMCS). We designed this scaffold to enhance the CS mechanical property. These three different dermal substitutes—ADM, CS and PMCSs are different in the tensile properties and microstructure.

Methods

Several basic physical characteristics of dermal substitutes were investigated in vitro. To characterize the angiogenesis and tissue regeneration, the materials were embedded subcutaneously in Sprague–Dawley (SD) rats. At weeks 1, 2, 4 and 8 post-surgery, the tissue specimens were harvested for histology, immunohistochemistry and real-time quantitative PCR (RT-qPCR).

Results

In vitro studies demonstrated ADM had a higher Young’s modulus (6.94 MPa) rather than CS (0.19 MPa) and PMCS (3.33 MPa) groups in the wet state. Compared with ADMs and CSs, PMCSs with three-dimensional porous structures resembling skin and moderate mechanical properties can promote tissue ingrowth more quickly after implantation. In addition, the vascularization of the PMCS group is more obvious than that of the other two groups. The incorporation of a PLGA knitted mesh in CSs can improve the mechanical properties with little influence on the three-dimensional porous microstructure. After implantation, PMCSs can resist the contraction and promote cell infiltration, neotissue formation and blood vessel ingrowth, especially from the mesh side. Although ADM has high mechanical strength, its vascularization is poor because the pore size is too small. In conclusion, the mechanical properties of scaffolds are important for maintaining the three-dimensional microarchitecture of constructs used to induce tissue regeneration and vascularization.

Conclusion

The results illustrated that tissue regeneration requires the proper pore size and an appropriate mechanical property like PMCS which could satisfy these conditions to sustain growth.

Is tissue augmentation a reality in biosurgery? An experimental study of endothelial cell invasion into tissue filler

New therapeutic approaches for wound treatment are evolving. Non healing wounds in oncology and after trauma may be cured by a novel technique of tissue augmentation with soft tissue fillers. The principle resides in filling the wound with collagen filler in order to seal the defect and promote healing. Successful angiogenesis forms the basis of tissue filler survival and determines the outcome of the healing process. During this study, basic data about endothelial cell invasion into collagen-made substratum was collected that could be used for neoangiogenesis studies in tissue augmentation techniques for large wound defect treatment. In the in vitro assay, the human umbilical vein endothelial cells (HUVEC) grow into a three-dimensional framework of collagenous tissue fillers, forming the basic step for angiogenesis. After heparins were used as chemotactic agents, a typical bell-shaped relationship between chemotaxis and agent concentrations was found. Significant cell infiltration was present in the assays with chemotactic agents. These observations support the potential for tissue augmentation with soft tissue fillers that could be used in acute and chronic non healing traumatic and oncology wounds after extensive surgical resections and radiotherapy.

Molecular Mechanisms of UV-Induced Apoptosis and Its Effects on Skin Residential Cells: The Implication in UV-Based Phototherapy

The human skin is an integral system that acts as a physical and immunological barrier to outside pathogens, toxicants, and harmful irradiations. Environmental ultraviolet rays (UV) from the sun might potentially play a more active role in regulating several important biological responses in the context of global warming. UV rays first encounter the uppermost epidermal keratinocytes causing apoptosis. The molecular mechanisms of UV-induced apoptosis of keratinocytes include direct DNA damage (intrinsic), clustering of death receptors on the cell surface (extrinsic), and generation of ROS. When apoptotic keratinocytes are processed by adjacent immature Langerhans cells (LCs), the inappropriately activated Langerhans cells could result in immunosuppression. Furthermore, UV can deplete LCs in the epidermis and impair their migratory capacity, leading to their accumulation in the dermis. Intriguingly, receptor activator of NF-κB (RANK) activation of LCs by UV can induce the pro-survival and anti-apoptotic signals due to the upregulation of Bcl-xL, leading to the generation of regulatory T cells. Meanwhile, a physiological dosage of UV can also enhance melanocyte survival and melanogenesis. Analogous to its effect in keratinocytes, a therapeutic dosage of UV can induce cell cycle arrest, activate antioxidant and DNA repair enzymes, and induce apoptosis through translocation of the Bcl-2 family proteins in melanocytes to ensure genomic integrity and survival of melanocytes. Furthermore, UV can elicit the synthesis of vitamin D, an important molecule in calcium homeostasis of various types of skin cells contributing to DNA repair and immunomodulation. Taken together, the above-mentioned effects of UV on apoptosis and its related biological effects such as proliferation inhibition, melanin synthesis, and immunomodulations on skin residential cells have provided an integrated biochemical and molecular biological basis for phototherapy that has been widely used in the treatment of many dermatological diseases.

Bioengineered skin substitutes

Bioengineered skin has great potential for use in regenerative medicine for treatment of severe wounds such as burns or chronic ulcers. Genetically modified skin substitutes have also been used as cell-based devices or "live bioreactors" to deliver therapeutics locally or systemically. Finally, these tissue constructs are used as realistic models of human skin for toxicological testing, to speed drug development and replace traditional animal-based tests in a variety of industries. Here we describe a method of generating bioengineered skin based on a natural scaffold, namely, decellularized human dermis and epidermal stem cells.

Biomaterials to prevascularize engineered tissues

Tissue engineering promises to restore tissue and organ function following injury or failure by creating functional and transplantable artificial tissues. The development of artificial tissues with dimensions that exceed the diffusion limit (1-2 mm) will require nutrients and oxygen to be delivered via perfusion (or convection) rather than diffusion alone. One strategy of perfusion is to prevascularize tissues; that is, a network of blood vessels is created within the tissue construct prior to implantation, which has the potential to significantly shorten the time of functional vascular perfusion from the host. The prevascularized network of vessels requires an extracellular matrix or scaffold for 3D support, which can be either natural or synthetic. This review surveys the commonly used biomaterials for prevascularizing 3D tissue engineering constructs.