Accelerated epithelialization and improved wound healing metrics in porcine full‐thickness wounds transplanted with full‐thickness skin micrografts

Autologous Meshed Graft Healing Within the Interstice versus Surrounding Adhered Split Thickness Skin Sites: Where Should Tissue Biopsies be Taken to Assess Tissue-Level Histoarchitecture?

INTRODUCTION

Meshed split thickness skin grafts are a common treatment for full thickness wounds because they allow for expansion of skin taken from a relatively small donor site. Meshed wound healing is not homogenous as sites that are in direct contact with the grafts display distinct healing characteristics compared to areas that are not in contact with the grafts, and this may affect study outcomes reliant on tissue biopsies. This study aims to characterize the differences between adhered split thickness skin (aSTS) sites and aSTS-free sites from tissue punch biopsies.

METHODS

Wounds were created in Duroc pigs and were excised down to subcutaneous tissue, split thickness skin graft was harvested, meshed, and was either applied to the prepared wound beds or wounds were left nongrafted. Full thickness punch biopsies (3 mm diameter) from either the aSTS area, aSTS-free, or nongrafted area were taken at each time point, processed, Hematoxylin and Eosin- or Herovici-stained, and imaged. Images were used to quantify histoarchitectural characteristics.

RESULTS

In the grafted wounds, epidermis formation and undulated rete ridge appendages were noticeable early in healing in aSTS sites. Dermal thickness was elevated in the aSTS-free and nongrafted wounds. Cellularity was greater in the aSTS-free compared to the aSTS sites. The aSTS site most closely resembled uninjured skin with respect to collagen types. Collagen fiber orientation was higher in the aSTS-free compared to the nongrafted sites (P < 0.05).

CONCLUSIONS

These data show that within a single grafted burn wound, healing is a heterogenous process. An improved understanding of the heterogeneity of healing wounds and timing of return to normal skin function in different areas will help researchers to conduct more nuanced histoarchitecture outcome-based translational research in preclinical and clinical trials.

Novel Techniques in Fractional Skin Replacement

The gold standards for coverage of wounds that cannot be primarily closed are full thickness skin grafts (FTSGs) and split thickness skins graft (STSGs). FTSGs harvest sites generally require primary closure, which limits availability, especially when treating larger wounds. STSGs have many shortcomings, including donor site morbidity. Fractional autologous skin replacement can be utilized in conjunction with or in lieu of STSGs to both improve graft outcomes of large wounds and to decrease donor site morbidity. Skin can be mechanically or chemically fractionated. Fractionated skin can be advantageous, as adnexal structures provide additional functionality without donor site morbidity. In this review, we will discuss current and emerging techniques in fractional skin replacement.

The Wound Reporting in Animal and Human Preclinical Studies (WRAHPS) Guidelines

Preclinical studies for wound healing disorders are an essential step in translating discoveries into therapies. Also, they are an integral component of initial safety screening and gaining mechanistic insights using an in vivo approach. Given the complexity of the wound healing process, existing guidelines for animal testing do not capture key information due to the inevitable variability in experimental design. Variations in study interpretation are increased by complexities associated with wound aetiology, wounding procedure, multiple treatment conditions, wound assessment, and analysis, as well as lack of acknowledgement of limitation of the model used. Yet, no standards exist to guide reporting crucial experimental information required to interpret results in translational studies of wound healing. Consistency in reporting allows transparency, comparative, and meta-analysis studies and avoids repetition and redundancy. Therefore, there is a critical and unmet need to standardise reporting for preclinical wound studies. To aid in reporting experimental conditions, The Wound Reporting in Animal and Human Preclinical Studies (WRAHPS) Guidelines have now been created by the authors working with the Wound Care Collaborative Community (WCCC) GAPS group to provide a checklist and reporting template for the most frequently used preclinical models in support of development for human clinical trials for wound healing disorders. It is anticipated that the WRAHPS Guidelines will standardise comprehensive methods for reporting in scientific manuscripts and the wound healing field overall. This article is not intended to address regulatory requirements but is intended to provide general guidelines on important scientific considerations for such studies.

Hierarchical double-layer microneedles accomplish multicenter skin regeneration in diabetic full-thickness wounds

INTRODUCTION

Managing large chronic wounds presents significant challenges because of inadequate donor sites, infection, and lack of structural support from dermal substitutes. Hydrogels are extensively used in various forms to promote chronic wound healing and provide a three-dimensional spatial structure, through growth factors or cell transport.

OBJECTIVES

We present a novel multicenter regenerative model that is capable of regenerating and merging simultaneously to form a complete layer of skin. This method significantly reduces wound healing time compared to the traditional centripetal healing model. We believe that our model can improve clinical outcomes and pave the way for further research into regenerative medicine.

METHODS

We prepared a novel multi-island double-layer microneedle (MDMN) using gelatin-methacryloylchitosan (GelMA-CS). The MDMN was loaded with keratinocytes (KCs) and dermal fibroblasts (FBs). Our aim in this study was to explore the therapeutic potential of MDMN in a total skin excision model.

RESULTS

The MDMN model replicated the layered structure of full-thickness skin and facilitated tissue regeneration and healing via dual omni-bearing. Multi-island regeneration centres accomplished horizontal multicentric regeneration, while epidermal and dermal cells migrated synchronously from each location. This produced a healing area approximately 4.7 times greater than that of the conventional scratch tests. The MDMN model exhibited excellent antibacterial properties, attributed to the chitosan layer. During wound healing in diabetic mice, the MDMN achieved earlier epidermal coverage and faster wound healing through multi-island regeneration centres and the omnidirectional regeneration mode. The MDMN group displayed an accelerated wound healing rate upon arrival at the destination (0.96 % ± 0.58 % vs. 4.61 % ± 0.32 %). Additionally, the MDMN group exhibited superior vascularization and orderly collagen deposition.

CONCLUSION

The present study presents a novel skin regeneration model using microneedles as carriers of autologous keratinocytes and dermal fibroblasts, which allows for omni-directional, multi-center, and full-thickness skin regeneration.

Application of a minimally invasive full-thickness autologous microcolumn skin harvesting device for donor site tissue collection and augmenting wound healing in a porcine wound model

Using a 6-week porcine full-thickness excisional wound grafting model, we evaluated the Autologous Regeneration of Tissue (ART®) System, a novel skin harvesting device designed to collect autologous full-thickness autologous microcolumns (FTAM) at 0.5 mm in diameter. The donor skin sites were harvested using the ART® System and compared to split-thickness skin grafts (STSGs). Recipient sites were divided into three treatment groups: FTAM, STSG and Untreated control. Comparing the FTAM donor sites to the STSG donor sites, we observed significantly faster re-epithelization by Day 4 (p < 0.05), earlier adnexal structures and rete ridge formation by Week 3, and increased collagen and elastin content by Week 6. We also observed an increased rate of healing at the FTAM donor site whilst limiting donor site morbidity compared to traditional STSG donor sites. Time to recipient site closure was 2.4 weeks for STSG treated, 3.3 weeks for FTAM treated and 4.1 weeks for the Untreated control (p < 0.05). The STSG and FTAM recipient sites reached complete re-epithelialization by Weeks 4 and 5, respectively which was significantly faster compared to the Untreated control. However, the FTAM recipient site received only 10% of the donor site tissue relative to the recipient site area and the amount of donor site tissue grafted on the STSG recipient sites was 5× more than the FTAM recipient sites. Additionally, the FTAMs harvested by the ART® System augmented recipient wound site healing as a result of 'epithelial island' expansion in contrast to Untreated control sites that closed primarily by contracture.

Whey protein-loaded 3D-printed poly (lactic) acid scaffolds for wound dressing applications

Chronic skin wounds pose a global clinical challenge, necessitating effective treatment strategies. This study explores the potential of 3D printed Poly Lactic Acid (PLA) scaffolds, enhanced with Whey Protein Concentrate (WPC) at varying concentrations (25, 35, and 50% wt), for wound healing applications. PLA's biocompatibility, biodegradability, and thermal stability make it an ideal material for medical applications. The addition of WPC aims to mimic the skin's extracellular matrix and enhance the bioactivity of the PLA scaffolds. Fourier Transform Infrared Spectroscopy results confirmed the successful loading of WPC into the 3D printed PLA-based scaffolds. Scanning Electron Microscopy (SEM) images revealed no significant differences in pore size between PLA/WPC scaffolds and pure PLA scaffolds. Mechanical strength tests showed similar tensile strength between pure PLA and PLA with 50% WPC scaffolds. However, scaffolds with lower WPC concentrations displayed reduced tensile strength. Notably, all PLA/WPC scaffolds exhibited increased strain at break compared to pure PLA. Swelling capacity was highest in PLA with 25% WPC, approximately 130% higher than pure PLA. Scaffolds with higher WPC concentrations also showed increased swelling and degradation rates. Drug release was found to be prolonged with increasing WPC concentration. After seven days of incubation, cell viability significantly increased in PLA with 50% WPC scaffolds compared to pure PLA scaffolds. This innovative approach could pave the way for personalized wound care strategies, offering tailored treatments and targeted drug delivery. However, further studies are needed to optimize the properties of these scaffolds and validate their effectiveness in clinical settings.

Prevention and Treatment of Burn Scar Contracture: A Practical Review

Burn contracture affects close to one-third of all burn patients, leading to significant functional impairment and costs. Effective prevention and treatment strategies are necessary to decrease morbidity and unnecessary costs. This scoping review aimed to summarize prevention and treatment strategies used for management of burn scar contractures published in the literature since 2000. A comprehensive PubMed review was performed in October 2022 to identify methods of burn contracture prevention and treatments. Non-English, duplicate, and unavailable articles were excluded. Data were extracted including publication year, techniques, and outcomes. A total of 327 publications met criteria for inclusion. Most articles were published in 2011 (n = 22). Treatment strategies were discussed in 82.9% of studies, prevention in 16.5%, and both in 0.6%. The most common areas discussed included the upper extremity (n = 127) and neck (n = 102). Flaps were the most frequently used method (n = 208), followed by autografts (n = 89). Most preventative therapies were still in early stages of development. Burn contracture management requires a highly individualized approach with many available reconstructive techniques available. Further research is needed to improve prevention techniques and decrease morbidity and cost to patients.

Full-thickness skin columns: A method to reduce healing time and donor site morbidity in deep partial-thickness burns

The current standard of care for the coverage of large wounds often involves split thickness skin grafts (STSGs) which have numerous limitations. One promising technique that has gained traction is fractional autologous skin grafting using full-thickness skin columns (FTSC). Harvesting occurs orthogonally by taking numerous individual skin columns containing the epidermis down through the dermis and transferring them to the wound bed. The purpose of this porcine study was to investigate the efficacy of implanting FTSCs directly into deep partial-thickness burn wounds, as well as examining donor site healing at the maximal harvest density. It was hypothesised that by utilising FTSCs, the rate of healing in deep partial thickness burns can be improved without incurring the donor morbidity seen in other methods of skin grafting. Deep partial-thickness burns were created on the dorsum of female red duroc swine, debrided 3 days later and FTSCs were implanted at varying expansion ratios directly into the burn wounds. At day 14, 1:50 expansion ratio showed significantly faster re-epithelialisation compared to the debrided burn control and 1:200. Donor sites (at 7%-10% harvest density) were 100% re-epithelialised by day 7. Additionally, the maximal harvest density was determined to be 28% in an ex vivo model, which then five donor sites were harvested at 28% density on a red duroc swine and compared to five STSG donor sites. At maximal harvest density, FTSC donor sites were significantly less hypopigmented compared to STSGs, but no significant differences were observed in re-epithelialisation, contraction, blood flow or dermal thickness. In conclusion, implantation directly into deep partial-thickness burns is a viable option for the application of FTSCs, favouring lower expansion ratios like 1:50 or lower. Little difference in donor site morbidity was observed between FTSC at a maximal harvest density of 28% and STSGs, exceeding the optimal harvest density.

The pig as a model system for investigating the recruitment and contribution of myofibroblasts in skin healing

In the skin-healing field, porcine models are regarded as a useful analogue for human skin due to their numerous anatomical and physiological similarities. Despite the widespread use of porcine models in skin healing studies, the initial origin, recruitment and transition of fibroblasts to matrix-secreting contractile myofibroblasts are not well defined for this model. In this review, we discuss the merit of the pig as an animal for studying myofibroblast origin, as well as the challenges associated with assessing their contributions to skin healing. Although a variety of wound types (incisional, partial thickness, full thickness, burns) have been investigated in pigs in attempts to mimic diverse injuries in humans, direct comparison of human healing profiles with regards to myofibroblasts shows evident differences. Following injury in porcine models, which often employ juvenile animals, myofibroblasts are described in the developing granulation tissue at 4 days, peaking at Days 7-14, and persisting at 60 days post-wounding, although variations are evident depending on the specific pig breed. In human wounds, the presence of myofibroblasts is variable and does not correlate with the age of the wound or clinical contraction. Our comparison of porcine myofibroblast-mediated healing processes with those in humans suggests that further validation of the pig model is essential. Moreover, we identify several limitations evident in experimental design that need to be better controlled, and standardisation of methodologies would be beneficial for the comparison and interpretation of results. In particular, we discuss anatomical location of the wounds, their size and depth, as well as the healing microenvironment (wet vs. moist vs. dry) in pigs and how this could influence myofibroblast recruitment. In summary, although a widespread model used in the skin healing field, further research is required to validate pigs as a useful analogue for human healing with regards to myofibroblasts.

Addressing Full-Thickness Skin Defects: A Review of Clinically Available Autologous Skin Replacements

Autologous keratinocyte culture, and combinations of scaffolds, different cell types, solutions of macromolecules, or growth factors have contributed to the resurfacing of full-thickness skin defects. Ideally, a treatment for full-thickness skin defects should not merely reestablish continuity of the surface of the skin but should restore its structure to allow skin to function as a dynamic biological factory that can participate in protein synthesis, metabolism, and cell signaling, and form an essential part of the body's immune, nervous, and endocrine systems. This paper provides a review of clinically available autologous skin replacements, highlighting the importance of regenerating an organ that will function physiologically.

An aligned porous electrospun fibrous scaffold with embedded asiatic acid for accelerating diabetic wound healing

The diabetic non-healing wound is one of the most common complications of diabetics. The long-term stimulus of oxidative stress, inflammation and infection caused by the hyperglycemic microenvironment in the wound site always leads to a delayed healing process of the diabetic wound. To address this issue, in this study, we prepared an asiatic acid (AA)-embedded aligned porous poly(l-lactic acid) (PLLA) electrospun fibrous scaffold (AA-PL) for accelerating diabetic wound healing. The results showed that the electrospun fibers with nanopores on the surfaces were aligned in a single direction, while the AA was well embedded in the fibers and can be continuously released from them. The in vitro results revealed that the AA-PL scaffolds can effectively alleviate the H2O2-induced oxidative stress damage to HaCat cells and downregulate the LPS-induced pro-inflammatory cytokine (IL-1β, TNF-α, IL6) gene expression in RAW 264.7 macrophage cells. Moreover, the growth of E. coli and S. aureus could be inhibited by the AA-PL scaffolds. The in vivo study further demonstrated that the AA-PL scaffolds can accelerate the re-epithelization, angiogenesis and extracellular matrix formation of a wound by relieving the high oxidative stress, inflammation and infection in the diabetic wound site. This study suggests that the combination of hierarchical structures (nanopores on the aligned fibers) with the controllable release of AA from the scaffolds is an efficient and innovative strategy for the treatment of diabetic non-healing wounds.

Skin Microcolumns as a Source of Paracrine Signaling Factors

Objective: We recently developed the approach of using “microcolumns” of autologous full-thickness skin tissue for wound repair. The small size of these micro skin tissue columns (MSTCs, ∼0.5 mm in diameter) allows donor sites to heal quickly without scarring. Treatment with MSTCs significantly accelerate wound healing, and suppled various skin cell types and skin structures to replenish the wound volume. This technology is now starting clinical use. In this study, we investigate whether MSTCs may also influence wound healing by releasing soluble signaling factors.

Approach: Freshly harvested MSTCs were incubated in culture medium for 24 h. The conditioned medium was collected and tested for its effects on migration and proliferation of human dermal fibroblasts, and its ability to induce tube formation by human umbilical vein endothelial cells (HUVECs). Proteins released into the conditioned medium were characterized by multiplex enzyme-linked immunosorbent assay (ELISA), and compared with medium conditioned by an equivalent mass of intact full-thickness skin.

Results: MSTC-conditioned medium increased fibroblast migration and proliferation, as well as HUVEC tube formation. MSTCs released many soluble factors known to play prominent roles in wound healing. A subset of proteins showed significantly different release profiles compared with intact full-thickness skin.

Innovation: The technology for harvesting and using MSTCs to augment wound healing was recently developed as an alternative to conventional autologous skin grafting. This study shows that MSTCs could also function as “cytokine factories.”

Conclusion: In addition to supplying autologous cells to repopulate the wound volume, MSTCs can also function as a source of growth factors and cytokines to further enhance wound healing.

Apparatus for Harvesting Tissue Microcolumns

This manuscript describes the production process for a laboratory apparatus, made from off-the-shelf components, that can be used to collect microcolumns of full-thickness skin tissue. The small size of the microcolumns allows donor sites to heal quickly without causing donor site scarring, while harvesting full-thickness tissue enables the incorporation of all cellular and extracellular components of skin tissue, including those associated with deeper dermal regions and the adnexal skin structures, which have yet to be successfully reproduced using conventional tissue engineering techniques. The microcolumns can be applied directly into skin wounds to augment healing, or they can be used as the autologous cell/tissue source for other tissue engineering approaches. The harvesting needles are made by modifying standard hypodermic needles, and they can be used alone for harvesting small amounts of tissue or coupled with a simple suction-based collection system (also made from commonly available laboratory supplies) for high-volume harvesting to facilitate studies in large animal models.

Evaluation of Donor Site Pain After Fractional Autologous Full-Thickness Skin Grafting

Background: Despite the development of numerous wound treatment alternatives, 25% to 50% of leg ulcers and >30% of foot ulcers are not fully healed after 6 months of treatment. Autologous skin grafting is a time-tested therapy for these wounds; however, the creation of a new wound in the donor area yields a considerable limitation to this procedure.

Innovation: Fractional autologous full-thickness skin grafting (FFTSG) is a technique wherein multiple small full-thickness skin grafts (FTSGs) are harvested with possibly minor donor-site comorbidities. The first device used to harvest FFTSG (ART™ system, Medline, Northfield, IL) is a device capable of harvesting >300 small FTSGs and transferring them to a target wound.

Objective: To better evaluate patients' clinical experience, we sought to evaluate pain at the donor site associated with this procedure.

Approach: Pain was assessed with numeric visual analog pain scales at days 1, 2, 4, and 7. Nine subjects underwent this procedure with only six of them reporting any level of pain on day 1, and none disclosing pain after day 2.

Conclusion: In this study, we evidenced that this device manages to harvest FTSGs with minimal associated pain. Future research will need to evaluate other aspects of the procedure as well as long-term outcomes at the donor and recipient areas.