An Improved Humanized Mouse Model for Excisional Wound Healing Using Double Transgenic Mice

Cross-Linked Electrospun pH-Sensitive Nanofibers Adsorbed with Temporin-Ra for Promoting Wound Healing

Bioresponsive nanodrug delivery systems have excellent potential in tissue engineering applications. Poly-anionic and poly-cationic biopolymers have provided a superior platform for designing pH-sensitive drug delivery systems. In this regard, hyaluronic acid-chitosan-polyvinyl alcohol complex nanofibers with high quality and reproducibility were produced by optimizing the solution preparation process. In addition, the synthesized composite nanofiber, with 66.82 kN/mm toughness, 200% swelling ratio, and 60% porosity, exhibited excellent properties to meet the requirements of the ideal wound dressing. Green cross-linking with citric acid prevented the destruction of the nanofiber even after prolonged immersion in biological solutions. ζ potential studies demonstrated that the synthesized nanofiber has a negative surface charge (∼-30) at physiological pH. The pK_a of the temporin-Ra peptide is about 10, and as a result the peptide molecules have a net positive charge in physiological conditions. Therefore, peptide molecules immobilized on the synthesized scaffold based on surface adsorption. In vivo evaluation has proven that the wound bed has an alkaline environment, facilitating peptide release from the nanofiber scaffold. Electrospun nanofibers can imitate the architecture of the extracellular matrix for accelerating wound healing. In vitro investigation showed better adhesion, proliferation, migration, and fibroblast cell growth on peptide-loaded nanofiber samples than other groups. In vivo studies on full-thickness wounds in the mouse model indicated that the designed nanofiber was gradually absorbed without causing dryness or infection. On day 6, the peptide-loaded nanofiber revealed 60% wound closure compared to the control group (17%). In addition, based on histological studies, the composite nanofiber demonstrated excellent tissue repair ability, hence these active nanofiber mats can be a good alternative to existing wound dressings. Gene expression studies show that the antimicrobial peptide promotes the inflammatory phase of wound healing in a shorter time frame by accelerating the tumor necrosis factor-α cytokine response.

Biomaterial mediated immunomodulation: An interplay of material environment interaction for ameliorating wound regeneration

Chronic wounds are the outcome of an imbalanced inflammatory response caused by sustenance of immune microenvironment. In this context, tissue engineered graft played great role in healing wounds but faced difficulty in scar remodelling, immune rejection and poor vascularization. All the limitations faced are somewhere linked with the immune cells involved in healing. In this consideration, immunomodulatory biomaterials bridge a large gap with the delivery of modulating factors for triggering key inflammatory cells responsible towards interplay in the wound micro-environment. Inherent physico-chemical properties of biomaterials substantially determine the nature of cell-materials interaction thereby facilitating differential cytokine gradient involved in activation or suppression of inflammatory signalling pathways, and followed by surface marker expression. This review aims to systematically describe the interplay of immune cells involved in different phases in the wound microenvironment and biomaterials. Additionally, it also focuses on modulating innate immune cell responses in the context of triggering the halted phase of the wound healing, i.e., inflammatory phase. The various strategies are highlighted for modulation of wound microenvironment towards wound regeneration including stem cells, cytokines, growth factors, vitamins, and anti-inflammatory agents to induce interactive ability of biomaterials with immune cells. The last section focuses on prospective approaches and current potential strategies for wound regeneration. This includes the development of different models to bridge the gap between mouse models and human patients. Emerging new tools to study inflammatory response owing to biomaterials and novel strategies for modulation of monocyte and macrophage behaviour in the wound environment are also discussed.

Protocol for the Splinted, Human-like Excisional Wound Model in Mice

While wound healing in humans occurs primarily through re-epithelization, in rodents it also occurs through contraction of the panniculus carnosus, an underlying muscle layer that humans do not possess. Murine experimental models are by far the most convenient and inexpensive research model to study wound healing, as they offer great variability in genetic alterations and disease models. To overcome the obstacle of contraction biasing wound healing kinetics, our group invented the splinted excisional wound model. While other rodent wound healing models have been used in the past, the splinted excisional wound model has persisted as the most used model in the field of wound healing. Here, we present a detailed protocol of updated and refined techniques necessary to utilize this model, generate results with high validity, and accurately analyze the collected data. This model is simple to conduct and provides an easy, standardizable, and replicable model of human-like wound healing.

Delivery of a peptide/microRNA blend via electrospun antimicrobial nanofibres for wound repair

Downregulation of microRNA-31 (miR-31) and microRNA-132 (miR-132) has been associated with delayed wound healing. Therefore, it was hypothesised that intracellular delivery of miR-31 and miR-132, both as individual and blend formulations, could promote tissue repair. The use of a blend could minimise potential toxicity and achieve synergistic effects, thus maximising the therapeutic effect. miR-31 and miR-132 were condensed with a 30-mer positively charged amphipathic peptide, RALA, to form nanocomplexes with an average size <200 nm and zeta-potential ≥10 designed to facilitate cellular internalisation. This enabled a fold increase in miR-31 and miR-132 expression of ≥100,000 in a murine fibroblast cell line (NCTC-929) and a skin human keratinocyte cell line (HaCaT), with intracellular delivery >70% for individual and blend formulations. Moreover, incubation with the nanocomplexes increased the migration of HaCaT cells ≥25% at 4 and 8 h post-incubation, as well as downregulation of EMP-1 and RASA1 and HB-EGF and RASA1, target genes for miR-31 and miR-132, respectively. Electrospinning was then employed to produce an alginate/polyvinyl alcohol/ciprofloxacin nanofibrous wound patch to facilitate the controlled delivery of the nanocomplexes. Nanofibres were crosslinked with glutaraldehyde to improve stability in aqueous solvents, and they were proven to be biocompatible with antimicrobial activity without cellular attachment to avoid injury upon removal. RALA/miR nanoparticles were incorporated to the nanofibrous wound dressing and in vivo wound healing studies using C57BL/6J mice demonstrated a >60% acceleration in the wound closure rate at Day 7 post-wounding, a ≥1.5 increase in epidermal thickness, and a ≥2 increase in blood vessel count with respect to commercial and untreated controls. Taken together, this data proves that delivery of RALA/miR-31 and RALA/miR-132 from an alginate/polyvinyl alcohol/ciprofloxacin nanofibrous wound dressing constitutes an advanced therapy for wound healing, by accelerating wound closure and improving healed tissue quality. STATEMENT OF SIGNIFICANCE: In this study, we report for the first time the use of the RALA peptide to deliver two miRNA 31 & 132 simultaneously from an electrospun patch. Both miRs have been shown to be downregulated in wounds and this study endeavoured to deliver a blend of the miRs from a nanofibre patch. Electrospinning was used to produce an alginate/polyvinyl alcohol/ciprofloxacin wound patch to enable controlled delivery of the miRs without cellular attachment to the wound with the added benefit of anti-microbial activity. Application of the nanofibre patch loaded with the blended RALA/miR nanoparticles demonstrated a synergistic effect with acceleration of wound closure rate, a significant increase in epidermal thickness and blood vessel count with respect to commercial and untreated controls.

Use of wound edge inversion (epibole) to generate recalcitrant and inflamed diabetic wounds

Robust and predictive pre-clinical models of recalcitrant diabetic wounds are critical for advancing research efforts toward improving healing. Murine models have logistic and genetic benefits versus larger animals; however, native murine healing inadequately represents clinically recalcitrant wounds in humans. Furthermore, current humanization techniques employing devices, deleterious mutations or chemical agents each carry model-specific limitations. To better replicate human wounds in a mouse, we developed a novel wound-edge inversion (WEI) technique that mimics the architecture of epibole and mitigates contracture, epithelialization, and consequently wound closure. In this study, we evaluated the reliability and durability of the WEI model in wild-type and obese diabetic mice and compared to healing after (i) punch biopsy, (ii) mechanical/silicone stenting or (iii) exogenous oxidative stressors. In wild-type mice, WEI demonstrated favourable closure characteristics compared to both control and stented wounds, however, wounds progressed to closure by 4 weeks. In contrast, diabetic WEI wounds persisted for 6-10 weeks with reduced contracture and epithelialization. In both diabetic and wild-type mice, WEI sites demonstrated persistence of inflammatory populations, absence of epithelialization, and histologic presence of alpha-SMA positive granulation tissue when compared to controls. We conclude that the WEI technique is particularly valuable for modelling recalcitrant diabetic wounds with sustained inflammation and dysfunctional healing.

Electrospun PCL/PLA Scaffolds Are More Suitable Carriers of Placental Mesenchymal Stromal Cells Than Collagen/Elastin Scaffolds and Prevent Wound Contraction in a Mouse Model of Wound Healing

Mesenchymal stem/stromal cells (MSCs) exert beneficial effects during wound healing, and cell-seeded scaffolds are a promising method of application. Here, we compared the suitability of a clinically used collagen/elastin scaffold (Matriderm) with an electrospun Poly(ε-caprolactone)/poly(l-lactide) (PCL/PLA) scaffold as carriers for human amnion-derived MSCs (hAMSCs). We created an epidermal-like PCL/PLA scaffold and evaluated its microstructural, mechanical, and functional properties. Sequential spinning of different PCL/PLA concentrations resulted in a wide-meshed layer designed for cell-seeding and a dense-meshed layer for apical protection. The Matriderm and PCL/PLA scaffolds then were seeded with hAMSCs, with or without Matrigel coating. The quantity and quality of the adherent cells were evaluated in vitro. The results showed that hAMSCs adhered to and infiltrated both scaffold types but on day 3, more cells were observed on PCL/PLA than on Matriderm. Apoptosis and proliferation rates were similar for all carriers except the coated Matriderm, where apoptotic cells were significantly enhanced. On day 8, the number of cells decreased on all carrier types except the coated Matriderm, which had consistently low cell numbers. Uncoated Matriderm had the highest percentage of proliferative cells and lowest apoptosis rate of all carrier types. Each carrier also was topically applied to skin wound sites in a mouse model and analyzed in vivo over 14 days via optical imaging and histological methods, which showed detectable hAMSCs on all carrier types on day 8. On day 14, all wounds exhibited newly formed epidermis, and all carriers were well-integrated into the underlying dermis and showing signs of degradation. However, only wounds treated with uncoated PCL/PLA maintained a round appearance with minimal contraction. Overall, the results support a 3-day in vitro culture of scaffolds with hAMSCs before wound application. The PCL/PLA scaffold showed higher cell adherence than Matriderm, and the effect of the Matrigel coating was negligible, as all carrier types maintained sufficient numbers of transplanted cells in the wound area. The anti-contractive effects of the PCL/PLA scaffold offer potential new therapeutic approaches to wound care.

Electrospun Biomaterials in the Treatment and Prevention of Scars in Skin Wound Healing

Electrospinning is a promising method for the rapid and cost-effective production of nanofibers from a wide variety of polymers given the high surface area morphology of these nanofibers, they make excellent wound dressings, and so have significant potential in the prevention and treatment of scars. Wound healing and the resulting scar formation are exceptionally well-characterized on a molecular and cellular level. Despite this, novel effective anti-scarring treatments which exploit this knowledge are still clinically absent. As the process of electrospinning can produce fibers from a variety of polymers, the treatment avenues for scars are vast, with therapeutic potential in choice of polymers, drug incorporation, and cell-seeded scaffolds. It is essential to show the new advances in this field; thus, this review will investigate the molecular processes of wound healing and scar tissue formation, the process of electrospinning, and examine how electrospun biomaterials can be utilized and adapted to wound repair in the hope of reducing scar tissue formation and conferring an enhanced tensile strength of the skin. Future directions of the research will explore potential novel electrospun treatments, such as gene therapies, as targets for enhanced tissue repair applications. With this class of biomaterial gaining such momentum and having such promise, it is necessary to refine our understanding of its process to be able to combine this technology with cutting-edge therapies to relieve the burden scars place on world healthcare systems.

Delivery of RALA/siFKBPL nanoparticles via electrospun bilayer nanofibres: An innovative angiogenic therapy for wound repair

FK506-binding protein-like (FKBPL) has previously been shown to inhibit angiogenesis viain vitro and in vivo experimentation. Thus, it was proposed that the delivery of a siRNA targeting FKBPL could hold great potential in promoting angiogenesis for advanced wound healing applications. An effective delivery system has been utilised to encapsulate the siFKBPL to form nanoparticles, thereby improving cellular entry and eliciting a potent angiogenic response. In this study, nanoparticles were formed via condensation of siFKBPL with RALA; a novel, cationic 30 mer amphipathic peptide. Nanoparticles prepared at a N:P ratio of 6 demonstrated an average particle size of 76.6nm with a zeta potential of +16.5mV. Treatment of HMEC-1 cells at N:P 6 resulted in a transfection efficiency of 33.7%, negligible cytotoxicity, and significant knockdown of endogenous FKBPL expression. Functionally, treatment with RALA/siFKBPL resulted in significant improvements in cell migration and endothelial tubule formation in vitro. The process of electrospinning was employed to fabricate a nanofibrous wound patch to facilitate the controlled delivery of the RALA/siFKBPL nanoparticles. Alginate/poly-(vinyl alcohol) was electrospun following electrospinning of Chitosan/poly-(vinyl alcohol) to form a bilayered wound patch. Subsequently, the nanofibres were crosslinked to improve stability, before nanoparticle incorporation via soak loading. In vivo wound healing studies using C57BL/6J mice demonstrated a significant increase in angiogenesis when the RALA/siFKBPL nanoparticles were delivered from the bilayered wound patch; a 326% increase in blood vessel density was observed compared to untreated wounds. Taken together, this data demonstrates that delivery of RALA/siFKBPL nanoparticles from the bilayered wound patch represents an innovative wound healing therapy.

Animal Models for Studies of Keloid Scarring

Significance: Keloid scarring is a disfiguring fibroproliferative disorder that can significantly impair the quality of life in affected individuals. The mechanisms that initiate keloid scarring are incompletely understood, and keloids remain one of the most challenging skin conditions to treat. Keloids are unique to humans; thus, the lack of adequate animal models has hindered research efforts aimed at prevention and effective therapeutic intervention. Recent Advances: In the absence of a suitable animal model, keloid researchers often rely on studying excised keloid scar tissue and keloid-derived cultured cells. Recently, in vivo models have been described that involve transplantation to mice of reconstructed skin containing keloid-derived fibroblasts and/or keratinocytes. These mouse-human hybrid animal models display some similarities with keloids and may enable investigation of novel therapies, although no model yet recapitulates all the features of human keloid scarring. Critical Issues: Differences in skin physiology and modes of healing contribute to challenges in modeling keloids in laboratory animals. Furthermore, recent studies suggest that cells of the immune system contribute to keloid pathology. The need to use immunodeficient hosts for transplanted human keloid cells in recently described animal models precludes studying the role of the immune system in keloid scarring. Future Directions: Future animal models may take advantage of humanized mice with immune systems reconstituted using human immune cells. Such models, when combined with grafted tissues prepared using keloid-derived cells, might enable investigation of complex interactions between systemic and local factors that combine to promote keloid scar formation and may aid in the development of novel therapies.

Single-Cell Gene Expression Analysis and Evaluation of the Therapeutic Function of Murine Adipose-Derived Stromal Cells (ASCs) from the Subcutaneous and Visceral Compartment

Introduction

Adipose-derived stromal cells (ASCs) are a promising resource for wound healing and tissue regeneration because of their multipotent properties and cytokine secretion. ASCs are typically isolated from the subcutaneous fat compartment, but can also be obtained from visceral adipose tissue. The data on their equivalence diverges. The present study analyzes the cell-specific gene expression profiles and functional differences of ASCs derived from the subcutaneous (S-ASCs) and the visceral (V-ASCs) compartment.

Material and Methods

Subcutaneous and visceral ASCs were obtained from mouse inguinal fat and omentum. The transcriptional profiles of the ASCs were compared on single-cell level. S-ASCs and V-ASCs were then compared in a murine wound healing model to evaluate their regenerative functionality.

Results

On a single-cell level, S-ASCs and V-ASCs displayed distinct transcriptional profiles. Specifically, significant differences were detected in genes associated with neoangiogenesis and tissue remodeling (for example, Ccl2, Hif1α, Fgf7, and Igf). In addition, a different subpopulation ecology could be identified employing a cluster model. Nevertheless, both S-ASCs and V-ASCs induced accelerated healing rates and neoangiogenesis in a mouse wound healing model.

Conclusion

With similar therapeutic potential in vivo, the significantly different gene expression patterns of ASCs from the subcutaneous and visceral compartments suggest different signaling pathways underlying their efficacy. This study clearly demonstrates that review of transcriptional results in vivo is advisable to confirm the tentative effect of cell therapies.