Association of increasing burn severity in mice with delayed mobilization of circulating angiogenic cells

Development of a Novel Covalently Bonded Conjugate of Caprylic Acid Tripeptide (Isoleucine-Leucine-Aspartic Acid) for Wound-Compatible and Injectable Hydrogel to Accelerate Healing

Third-degree burn injuries pose a significant health threat. Safer, easier-to-use, and more effective techniques are urgently needed for their treatment. We hypothesized that covalently bonded conjugates of fatty acids and tripeptides can form wound-compatible hydrogels that can accelerate healing. We first designed conjugated structures as fatty acid-aminoacid1-amonoacid2-aspartate amphiphiles (Cn acid-AA1-AA2-D), which were potentially capable of self-assembling into hydrogels according to the structure and properties of each moiety. We then generated 14 novel conjugates based on this design by using two Fmoc/tBu solid-phase peptide synthesis techniques; we verified their structures and purities through liquid chromatography with tandem mass spectrometry and nuclear magnetic resonance spectroscopy. Of them, 13 conjugates formed hydrogels at low concentrations (≥0.25% w/v), but C8 acid-ILD-NH2 showed the best hydrogelation and was investigated further. Scanning electron microscopy revealed that C8 acid-ILD-NH2 formed fibrous network structures and rapidly formed hydrogels that were stable in phosphate-buffered saline (pH 2-8, 37 °C), a typical pathophysiological condition. Injection and rheological studies revealed that the hydrogels manifested important wound treatment properties, including injectability, shear thinning, rapid re-gelation, and wound-compatible mechanics (e.g., moduli G″ and G', ~0.5-15 kPa). The C8 acid-ILD-NH2(2) hydrogel markedly accelerated the healing of third-degree burn wounds on C57BL/6J mice. Taken together, our findings demonstrated the potential of the Cn fatty acid-AA1-AA2-D molecular template to form hydrogels capable of promoting the wound healing of third-degree burns.

Estudo pré-clínico de queimaduras experimentais tratadas com fotobiomodulação e membrana amniótica humana, isoladas e associadas

Resumo Objetivo: avaliar o efeito da fotobiomodulação com laser de baixa intensidade 660 nm isoladamente ou associada à membrana amniótica humana no reparo de queimaduras de espessura parcial em ratos. Método: estudo experimental com 48 ratos Wistar machos, randomizados em quatro grupos: Controle, Membrana Amniótica Humana, Terapia a Laser de Baixa Intensidade e Terapia a Laser de Baixa Intensidade associado à Membrana Amniótica Humana. As características histopatológicas das amostras de pele foram analisadas aos 7 e 14 dias após a queimadura. Os dados obtidos foram submetidos aos testes de Kolmogorov-Smirnov e Mann Whitney. Resultados: a análise histológica das lesões por queimadura mostrou a diminuição da inflamação (p <0,0001) e aumento da proliferação de fibroblastos (p <0,0001), principalmente nos 7 dias em todos os tratamentos relacionados ao grupo controle. Aos 14 dias, a maior efetividade na aceleração do processo cicatricial foi significativa (p<0,0001) no grupo Terapia a Laser de Baixa Intensidade associado à Membrana Amniótica Humana. Conclusão: a associação das terapias de fotobiomodulação à membrana amniótica humana permitiu comprovar redução no tempo do processo cicatricial das lesões experimentais, estimulando sua proposição como protocolo de tratamento em queimaduras de espessura parcial.

Estudio preclínico de quemaduras experimentales tratadas con fotobiomodulación y membrana amniótica humana, solas y combinadas

Resumen Objetivo: evaluar el efecto de la fotobiomodulación con láser de baja intensidad 660 nm de sola o combinada con la membrana amniótica humana en la reparación de quemaduras de espesor parcial en ratas. Método: estudio experimental con 48 ratas Wistar macho, aleatorizadas en cuatro grupos: Control, Membrana Amniótica Humana, Terapia con Láser de Baja Intensidad y Terapia con Láser de Baja Intensidad combinada con la Membrana Amniótica Humana. Las características histopatológicas de las muestras de piel fueron analizadas a los 7 y 14 días después de la quemadura. Los datos obtenidos fueron sometidos a las pruebas de Kolmogorov-Smirnov y Mann-Whitney. Resultados: el análisis histológico de las lesiones por quemadura mostró una disminución de la inflamación (p <0,0001) y un aumento de la proliferación de fibroblastos (p <0,0001) principalmente a los 7 días en todos los tratamientos en comparación con el grupo control; a los 14 días, en el grupo de Terapia con Láser de Baja Intensidad combinada con la Membrana Amniótica Humana la mayor efectividad en la aceleración del proceso de cicatrización fue significativa (p<0,0001). Conclusión: la asociación de terapias de fotobiomodulación con la membrana amniótica humana permitió comprobar que hubo una reducción en el tiempo del proceso de cicatrización de lesiones experimentales, lo cual favorece que se proponga como protocolo de tratamiento en quemaduras de espesor parcial.

Early cutaneous inflammatory response at different degree of burn and its significance for clinical diagnosis and management

A complete characterization of the burn wound based on cutaneous architectural changes and inflammatory response is extremely important to provide evidence for progressive changes in the burn wound. Burn wounds are highly susceptible to conversion into deeper wounds, which need special care and attention; thereby, the complete characterization of burn wound type and their subsequent inflammatory status in the cutaneous system at the earliest is of paramount importance. Inflammatory markers at different degrees will help clinicians devise better and more specific treatment strategies for each burn type. The present study is carried out to profile pro-inflammatory gene expression along with immune cell quantification, vascular perfusion, and histopathological assessment in the cutaneous system of murine models. The study revealed that burn injury caused an immediate increase in vascular perfusion in superficial and partial-thickness burns, whereas there was a decrease in vascular perfusion in full-thickness burns. An influx of lymphocytes at the edges of burn wounds in each type of burn injury was well-orchestrated with the event of vascular perfusion. Further, pro-inflammatory gene expression profiling revealed significant upregulation vis-à-vis upregulation of TNF-α and MCP-1 genes, with an increase in the number of neutrophils following 72 h of injury that evidently cemented the conversion of superficial burn into partial-thickness burn. The molecular findings were profoundly supported by the histopathological changes. Thus, our foundational studies show distinct characteristic cutaneous changes correlated with the expression of key pro-inflammatory genes in three different types of burn injuries. Characterization of these cutaneous inflammatory responses provides a promising future for medical interventions involved with different degrees of burn injury, and it will also help in the pre-clinical testing of therapies for burn injury.

Preclinical study of experimental burns treated with photobiomodulation and Human Amniotic Membrane, both isolated and associated

OBJECTIVE

to evaluate the effect of photobiomodulation with low-level 660 nm laser alone or associated with Human Amniotic Membrane in the repair of partial-thickness burns in rats.

METHOD

an experimental study conducted with 48 male Wistar rats, randomized into four groups: Control, Human Amniotic Membrane, Low-Level Laser Therapy, and Low-Level Laser Therapy associated with Human Amniotic Membrane. The histopathological characteristics of the skin samples were analyzed 7 and 14 days after the burn. The data obtained were submitted to the Kolmogorov-Smirnov and Mann-Whitney tests.

RESULTS

the histological analysis of the burn injuries showed a decrease in inflammation (p<0.0001) and an increase in proliferation of fibroblasts (p<0.0001) mainly at 7 days in all treatments related to the control group. At 14 days, the greater effectiveness in accelerating the healing process was significant (p<0.0001) in the Low-Level Laser Therapy group associated with the Human Amniotic Membrane.

CONCLUSION

the association of photobiomodulation therapies with the Human Amniotic Membrane allowed verifying a reduction in the healing process time of the experimental lesions, stimulating its proposal as a treatment protocol in partial-thickness burns.

Comparison of Thermal Burn-Induced and Excisional-Induced Scarring in Animal Models: A Review of the Literature

Significance: Scar formation is a natural result of mammalian wound healing. In humans and other mammals, however, deep dermal wounds and thermal injuries often result in formation of hypertrophic scars, leading to substantial morbidity and lending great importance to development of therapeutic modalities for burn scars. Clinical Issues: Thus, preclinical burn wound models that adequately simulate processes underlying human burn-induced wound healing, particularly those processes leading to chronic inflammation and development of hypertrophic scars, are critical to developing further treatment paradigms for clinical use. Approach: In this study, we review literature describing various burn models, focusing on their characteristics and the functional readouts that lead to generation of useful data. We also briefly discuss recent work using human ex vivo skin culture as an alternative to animal models, as well as our own development of rabbit ear wound models for burn scars, and assess the pros and cons of these models compared to other models. Future Direction: Understanding of the strengths and weaknesses of preclinical burn wound models will enable choice of the most appropriate wound model to answer particular clinically relevant questions, furthering research aimed at treating burn scars.

Curcumin preconditioning enhances the efficacy of adipose-derived mesenchymal stem cells to accelerate healing of burn wounds

Background

Following recent findings from our group that curcumin preconditioning augments the therapeutic efficacy of adipose-derived stem cells in the healing of diabetic wounds in rats, we aimed to investigate the regenerative effects of curcumin preconditioned adipose-derived mesenchymal stem cells (ASCs) for better recovery of acid inflicted burns in this study.

Methods

ASCs were preconditioned with 5 μM curcumin for 24 hours and assessed for proliferation, migration, paracrine release potential and gene expression comparative to naïve ASCs. Subsequently, the healing capacity of curcumin preconditioned ASCs (Cur-ASCs) versus naïve ASCs was examined using acidic wounds in rats. For this, acid inflicted burns of 20 mm in diameter were made on the back of male Wistar rats. Then, 2 × 10⁶ cells of Cur-ASCs and naïve ASCs were intradermally injected in the wound periphery (n = 6) for comparison with an untreated saline control. Post-transplantation, wounds were macroscopically analysed and photographed to evaluate the percentage of wound closure and period of re-epithelization. Healed wound biopsies were excised and used for histological evaluation and expression analysis of wound healing markers at molecular level by quantitative PCR and western blotting.

Results

We found that Cur-ASCs exhibited greater proliferation, migration and paracrine potential in vitro. Further, Cur-ASCs showed more effective recovery than naïve ASCs as exhibited by gross morphology, faster wound closure and earlier re-epithelialization. Masson’s trichrome and hematoxylin and eosin staining demonstrated the improved architecture of the healing burns, as evidenced by reduced infiltration of inflammatory cells, compact collagen and marked granulation in Cur-ASC treated rats. Corroborating these findings, molecular assessment showed significantly reduced expressions of pro-inflammatory factors (interleukin-1 beta, interleukin-6, tumor necrosis factor alpha) a with striking upsurge of an oxidative marker (superoxide dismutase 1), pro-angiogenic factors (vascular endothelial growth factor, hepatocyte growth factor, hypoxia-inducible factor-1 alpha) and collagen markers (transforming growth factor beta 1, fibroblast growth factor-2, collagen type 1 alpha 1), verifying that Cur-ASCs modulate the regulation of pro-inflammatory and healing markers at burn sites.

Conclusions

Treatment with Cur-ASCs resulted in faster re-epithelization of acid inflicted burns compared to the treatment with naïve ASCs. Based on observed findings, we suggest the transplantation of Cur-ASCs is a valuable therapy for the potent clinical management of acidic burns.

Adipose-Derived Stromal Cells Seeded in Pullulan-Collagen Hydrogels Improve Healing in Murine Burns

Burn scars and scar contractures cause significant morbidity for patients. Recently, cell-based therapies have been proposed as an option for improving healing and reducing scarring after burn injury, through their known proangiogenic and immunomodulatory paracrine effects. Our laboratory has developed a pullulan-collagen hydrogel that, when seeded with mesenchymal stem cells (MSCs), improves cell viability and augments their proangiogenic capacity in vivo. Concurrently, recent research suggests that prospective isolation of cell subpopulations with desirable transcriptional profiles can be used to further improve cell-based therapies. In this study, we examined whether adipose-derived stem cell (ASC)-seeded hydrogels could improve wound healing following thermal injury using a murine contact burn model. Partial thickness contact burns were created on the dorsum of mice. On days 5 and 10 following injury, burns were debrided and received either ASC hydrogel, ASC injection alone, hydrogel alone, or no treatment. On days 10 and 25, burns were harvested for histologic and molecular analysis. This experiment was repeated using CD26⁺/CD55⁺ FACS-enriched ASCs to further evaluate the regenerative potential of ASCs in wound healing. ASC hydrogel-treated burns demonstrated accelerated time to reepithelialization, greater vascularity, and increased expression of the proangiogenic genes MCP-1, VEGF, and SDF-1 at both the mRNA and protein level. Expression of the profibrotic gene Timp1 and proinflammatory gene Tnfa was downregulated in ASC hydrogel-treated burns. ASC hydrogel-treated burns exhibited reduced scar area compared to hydrogel-treated and control wounds, with equivalent scar density. CD26⁺/CD55⁺ ASC hydrogel treatment resulted in accelerated healing, increased dermal appendage count, and improved scar quality with a more reticular collagen pattern. Here we find that ASC hydrogel therapy is effective for treating burns, with demonstrated proangiogenic, fibromodulatory, and immunomodulatory effects. Enrichment for CD26⁺/CD55⁺ ASCs has additive benefits for tissue architecture and collagen remodeling postburn injury. Research is ongoing to further facilitate clinical translation of this promising therapeutic approach. Impact statement Burns remain a significant public health burden. Stem cell therapy has gained attention as a promising approach for treating burns. We have developed a pullulan-collagen biomimetic hydrogel scaffold that can be seeded with adipose-derived stem cells (ASCs). We assessed the delivery and activity of our scaffold in a murine contact burn model. Our results suggest that localized delivery of ASC hydrogel treatment is a promising approach for the treatment of burn wounds, with the potential for rapid clinical translation. We believe our work will have broad implications for both hydrogel therapeutics and regenerative medicine and will be of interest to the general scientific community.

Maintaining Inducibility of Dermal Follicle Cells on Silk Fibroin/Sodium Alginate Scaffold for Enhanced Hair Follicle Regeneration

The extracellular matrix (ECM) is important for maintaining cell phenotype and promoting cell proliferation and differentiation. In order to better solve the problem of skin appendage regeneration, a combination of mechanical/enzymatic digestion methods was used to self-extract dermal papilla cells (DPCs), which were seeded on silk fibroin/sodium alginate scaffolds as seed cells to evaluate the possibility of skin regeneration/regeneration of accessory organs. Scanning electron microscopy (SEM) graphs showed that the interconnected pores inside the scaffold had a pore diameter in the range of 153-311 μm and a porosity of 41-82%. Immunofluorescence (IF) staining and cell morphological staining proved that the extracted cells were DPCs. The results of a Cell Counting Kit-8 (CCK-8) and Calcein-AM/PI live-dead cell staining showed that the DPCs grew well in the composite scaffold extract. Normal cell morphology and characteristics of aggregation growth were maintained during the 3-day culture, which showed that the silk fibroin/sodium alginate (SF/SA) composite scaffold had good cell-compatibility. Hematoxylin-eosin (H&E) staining of tissue sections further proved that the cells adhered closely and aggregated to the pore wall of the scaffold, and retained the ability to induce differentiation of hair follicles. All these results indicate that, compared with a pure scaffold, the composite scaffold promotes the adhesion and growth of DPCs. We transplanted the SF/SA scaffolds into the back wounds of SD rats, and evaluated the damage model constructed in vivo. The results showed that the scaffold inoculated with DPCs could accelerate the repair of the skin and promote the regeneration of the hair follicle structure.

Injury Characteristics and von Willebrand Factor for the Prediction of Acute Respiratory Distress Syndrome in Patients With Burn Injury: Development and Internal Validation

OBJECTIVE

To derive and validate a prediction model for the development of ARDS in burn-injured patients.

SUMMARY BACKGROUND DATA

Burn injury carries the highest incidence of acute respiratory distress syndrome (ARDS) among all predisposing conditions, but few studies exist on risk factors in these patients. Studies employing biomarkers and clinical risk factors for predicting ARDS mortality have recently been examined but none exist for onset of ARDS nor in patients with burn injury.

METHODS

This was a prospective multicenter study of 113 patients with isolated burn injury or inhalation injury. Clinical variables and plasma biomarkers representative of endothelial injury, epithelial injury, or inflammation were collected within 24 hours of admission. The most parsimonious model was chosen by considering discrimination, calibration, and model fit.

RESULTS

Among the biomarkers measured in patients with burn injuries, a one-standard deviation increase in log-transformed levels of the A2 domain of von Willebrand factor in the first 24 hours was most strongly associated with the development of ARDS (OR 7.72; 95% CI: 1.64-36.28, P = 0.03). Of candidate models, a 3-variable model with %TBSA, inhalation injury, and von Willebrand factor-A2 had comparable discrimination to more complex models (area under the curve: 0.90; 95% CI 0.85-0.96). The 3-variable model had good model fit by Hosmer-Lemeshow test (P = 0.74) and maintained similar discrimination after accounting for performance optimism (Bootstrapped area under the curve: 0.90; 95% CI: 0.84-0.95).

CONCLUSIONS

The 3-variable model with %TBSA, inhalation injury, and von Willebrand factor could be used to better identify at-risk patients for both the study and prevention of ARDS in patients with burn injury.

Combination of the stromal vascular fraction and platelet-rich plasma accelerates the wound healing process: pre-clinical study in a Sprague-Dawley rat model

Background

Adipose-derived stem cells (ADSCs) improve wound healing owing to their angiogenic potency. However, the production of large quantities of ADSCs for clinical applications is laborious. In this study, the efficacy of the stromal vascular fraction (SVF; non-expanded ADSCs) combined with platelet-rich plasma (PRP) which contains abundant growth factors, for wound healing was evaluated using an animal model.

Methods

PRP from venous blood and SVF from lipoaspirates were harvested from six donors. PRP, SVF, SVF + PRP, and saline solution as a negative control were injected to second degree burn wounds in the backs of 24 male Sprague-Dawley rats. On the seventh day after injection, rats were euthanized and wounds were analyzed microscopically and macroscopically.

Results

Wounds closed faster in the SVF + PRP group than in the control group or PRP or SVF alone groups, with less inflammation, prominent signs of re-epithelization, more skin appendages and blood vessels, and a higher rate of hair growth. No infection or rat death occurred during the trial.

Conclusions

The combination of SVF and PRP may provide an additive stimulatory effect to support angiogenesis and accelerate the wound healing process; accordingly, this combination is a potential alternative to ADSC treatment.

Non-Propellant Foams of Green Nano-Silver and Sulfadiazine: Development and In Vivo Evaluation for Burn Wounds

PURPOSE

A non-propellant based foam (NPF) system was developed incorporating the antibiotics, pectin capped green nano-silver and sulfadiazine (SD) for the topical treatment of burn wounds as a convenient alternative to the existing therapies.

METHODS

NPF were prepared using various surfactants and oils forming a nanoemulsion. Anti-microbial studies by resazurin microtitre assay, ex vivo diffusion, in vivo skin permeation and deposition studies, and acute irritation studies were carried out. NPF was applied onto secondary thermal wounds manifested on mice models followed by macroscopic and histological examinations.

RESULTS

NPF had an average globule size of <75 nm. The viscosity was ~10 cP indicating the feasibility of expulsion from the container upon actuation. With no skin irritation, the foams showed a higher skin deposition of SD. A high contraction and an evident regeneration of the skin tissue upon treatment with NPF indicated a good recovery from the thermal injury was apparent from the histology studies.

CONCLUSION

NPF represents an alternative topical formulation that can be employed as a safe and effective treatment modality for superficial second degree (partial thickness) burn wounds. With a minimal requirement of mechanical force, the no-touch application of NPF makes it suitable for sensitive and irritant skin surfaces.

Self-Assembly of Metallo-Nucleoside Hydrogels for Injectable Materials That Promote Wound Closure

Injectable hydrogels are increasingly being used as scaffolds for in situ tissue engineering and wound healing. Most of these injectable hydrogels are made from polymers, and there are fewer examples of such soft materials made via self-assembly of low-molecular weight gelators. We report the room-temperature synthesis of a functional hydrogel formed by mixing cytidine (C) with 0.5 equiv each of B(OH)₃ and AgNO₃. The structural basis for this supramolecular hydrogel (C-B-C·Ag⁺) involves orthogonal formation of cytidine borate diesters (C-B-C) and Ag⁺-stabilized C-C base pairs, namely, the C·Ag⁺·C dimer. The C-B-C·Ag⁺ hydrogels, which can have high water content (at least 99.6%), are stable (no degradation after 1 year in the light), stimuli-responsive, and self-supporting, with elastic moduli of up to 10⁴ Pa. Incorporation of Ag⁺ ions into the gel matrix endows the C-B-C·Ag⁺ hydrogel with significant antibacterial capability. Importantly, the rapid switching between the sol and gel states for this supramolecular hydrogel, as a response to shear stress, enables 3D printing of a flexible medical patch made from the C-B-C·Ag⁺ hydrogel. The C-B-C·Ag⁺ hydrogel was used to promote the closure of burn wounds in a mouse model.

The Cutaneous Inflammatory Response to Thermal Burn Injury in a Murine Model

Many burn interventions aim to target the inflammatory response as a means of enhancing healing or limiting hypertrophic scarring. Murine models of human burns have been developed, but the inflammatory response to injury in these models has not been well defined. The aim of this study was to profile inflammatory cell populations and gene expression relative to healing and scarring in a murine model of thermal burns. Cutaneous injuries were created on the dorsal region of C57Bl/6 mice using a heated metal rod. Animals were euthanized at selected time points over ten weeks, with the lesions evaluated using macroscopic measurements, histology, immunofluorescent histochemistry and quantitative PCR. The burn method generated a reproducible, partial-thickness injury that healed within two weeks through both contraction and re-epithelialization, in a manner similar to human burns. The injury caused an immediate increase in pro-inflammatory cytokine and chemokine expression, coinciding with an influx of neutrophils, and the disappearance of Langerhans cells and mast cells. This preceded an influx of dendritic cells and macrophages, a quarter of which displayed an inflammatory (M1) phenotype, with both populations peaking at closure. As with human burns, the residual scar increased in size, epidermal and dermal thickness, and mast cell numbers over 10 weeks, but abnormal collagen I-collagen III ratios, fibre organization and macrophage populations resolved 3–4 weeks after closure. Characterisation of the inflammatory response in this promising murine burn model will assist future studies of burn complications and aid in the preclinical testing of new anti-inflammatory and anti-scarring therapies.

A dual deformable liposomal ointment functionalized with retinoic acid and epidermal growth factor for enhanced burn wound healing therapy

A dual deformable liposomal ointment functionalized with TRA and EGF remarkably promoting wound healing.

Accelerate Healing of Severe Burn Wounds by Mouse Bone Marrow Mesenchymal Stem Cell-Seeded Biodegradable Hydrogel Scaffold Synthesized from Arginine-Based Poly(ester amide) and Chitosan

Severe burns are some of the most challenging problems in clinics and still lack ideal modalities. Mesenchymal stem cells (MSCs) incorporated with biomaterial coverage of burn wounds may offer a viable solution. In this report, we seeded MSCs to a biodegradable hybrid hydrogel, namely ACgel, that was synthesized from unsaturated arginine-based poly(ester amide) (UArg-PEA) and chitosan derivative. MSC adhered to ACgels. ACgels maintained a high viability of MSCs in culture for 6 days. MSC seeded to ACgels presented well in third-degree burn wounds of mice at 8 days postburn (dpb) after the necrotic full-thickness skin of burn wounds was debrided and filled and covered by MSC-carrying ACgels. MSC-seeded ACgels promoted the closure, reepithelialization, granulation tissue formation, and vascularization of the burn wounds. ACgels alone can also promote vascularization but less effectively compared with MSC-seeded ACgels. The actions of MSC-seeded ACgels or ACgels alone involve the induction of reparative, anti-inflammatory interleukin-10, and M2-like macrophages, as well as the reduction of inflammatory cytokine TNFα and M1-like macrophages at the late inflammatory phase of burn wound healing, which provided the mechanistic insights associated with inflammation and macrophages in burn wounds. For the studied regimens of these treatments, no toxicity was identified to MSCs or mice. Our results indicate that MSC-seeded ACgels have potential use as a novel adjuvant therapy for severe burns to complement commonly used skin grafting and, thus, minimize the downsides of grafting.

Delivery systems of current biologicals for the treatment of chronic cutaneous wounds and severe burns

While wound therapy remains a clinical challenge in current medical practice, much effort has focused on developing biological therapeutic approaches. This paper presents a comprehensive review of delivery systems for current biologicals for the treatment of chronic wounds and severe burns. The biologicals discussed here include proteins such as growth factors and gene modifying molecules, which may be delivered to wounds free, encapsulated, or released from living systems (cells, skin grafts or skin equivalents) or biomaterials. Advances in biomaterial science and technologies have enabled the synthesis of delivery systems such as scaffolds, hydrogels and nanoparticles, designed to not only allow spatially and temporally controlled release of biologicals, but to also emulate the natural extracellular matrix microenvironment. These technologies represent an attractive field for regenerative wound therapy, by offering more personalised and effective treatments.

Topical Reformulation of Valsartan for Treatment of Chronic Diabetic Wounds

Chronic wounds are among the most devastating and difficult to treat consequences of diabetes. Dysregulation of the skin renin-angiotensin system is implicated in abnormal wound healing in diabetic and older adults. Given this, we sought to determine the effects of topical reformulations of the angiotensin type 1 receptor blockers losartan and valsartan and the angiotensin-converting enzyme inhibitor captopril on wound healing in diabetic and aged mice with further validation in older diabetic pigs. The application of 1% valsartan gel compared with other tested formulations and placebo facilitated and significantly accelerated closure time and increased tensile strength in mice, and was validated in the porcine model. One percent of valsartan gel-treated wounds also exhibited higher mitochondrial content, collagen deposition, phosphorylated mothers against decapentaplegic homologs 2 and 3 and common mothers against decapentaplegic homolog 4, alpha-smooth muscle actin, CD31, phospho-vascular endothelial growth factor receptor 2, and p42/44 mitogen-activated protein kinase. Knockout of the angiotensin subtype 2 receptors abolished the beneficial effects of angiotensin type 1 receptor blockers, suggesting a role for angiotensin subtype 2 receptors in chronic wound healing.

Knockout of Angiotensin AT2 receptors accelerates healing but impairs quality

Wounds are among the most common, painful, debilitating and costly conditions in older adults. Disruption of the angiotensin type 1 receptors (AT₁R), has been associated with impaired wound healing, suggesting a critical role for AT₁R in this repair process. Biological functions of angiotensin type 2 receptors (AT₂R) are less studied. We investigated effects of genetically disrupting AT₂R on rate and quality of wound healing. Our results suggest that AT₂R effects on rate of wound closure depends on the phase of wound healing. We observed delayed healing during early phase of wound healing (inflammation). An accelerated healing rate was seen during later stages (proliferation and remodeling). By day 12, fifty percent of AT₂R^−/− mice had complete wound closure as compared to none in either C57/BL6 or AT₁R^−/− mice. There was a significant increase in AT₁R, TGFβ₁ and TGFβ₂ expression during the proliferative and remodeling phases in AT₂R^−/− mice. Despite the accelerated closure rate, AT₂R^−/− mice had more fragile healed skin. Our results suggest that in the absence of AT₂R, wound healing rate is accelerated, but yielded worse skin quality. Elucidating the contribution of both of the angiotensin receptors may help fine tune future intervention aimed at wound repair in older individuals.

Zwitterionic hydrogels promote skin wound healing

Skin traumas are among the most common health problems in the world, and are routinely treated with wound dressings such as bandages and gauze. Traditional dressings are typically made of dry cotton, which tends to adhere to the wound, causing scab formation and bacterial infections. Ideally, a dressing should accelerate wound healing while avoiding any side effects or complications. Recent studies have found that wet dressings, especially hydrogels, can provide a moist environment for wounds that mimics the in vivo environment, thus facilitating debridement of necrotic tissue, enhancing tissue regeneration, and avoiding scab formation. Zwitterionic hydrogels exhibit strong hydration, are biomimetic in nature, and show excellent anti-fouling properties; their resulting high water content, excellent biocompatibility, and negligible interactions with proteins and cells make them ideal wet wound dressings. In this work, we demonstrated that zwitterionic hydrogels, especially poly-carboxybetaine (PCB) hydrogels, can efficiently promote skin wound healing. Skin wounds treated with zwitterionic hydrogels healed significantly better than those treated with PHEMA hydrogels and the commercial product DuoDerm. Moreover, these zwitterionic hydrogels can be easily coated on cotton gauze or bandage pads for easy handling and application. The findings in this work hold great promise for the development of next-generation wound dressings to improve healthcare.

Endothelial progenitor cells and burn injury - exploring the relationship

Burn wounds result in varying degrees of soft tissue damage that are typically graded clinically. Recently a key participant in neovascularization, the endothelial progenitor cell, has been the subject of intense cardiovascular research to explore whether it can serve as a biomarker for vascular injury. In this review, we examine the identity of the endothelial progenitor cell as well as the evidence that support its role as a key responder after burn insult. While there is conflicting evidence with regards to the delta of endothelial progenitor cell mobilization and burn severity, it is clear that they play an important role in wound healing. Systematic and controlled studies are needed to clarify this relationship, and whether this population can serve as a biomarker for burn severity.

Acellular Hydrogels for Regenerative Burn Wound Healing: Translation from a Porcine Model

Currently available skin grafts and skin substitute for healing following third-degree burn injuries is fraught with complications, often resulting in long-term physical and psychological sequelae. Synthetic treatment that can promote wound healing in a regenerative fashion would provide an off-the-shelf, non-immunogenic strategy to improve clinical care of severe burn wounds. Here, we demonstrate vulnerary efficacy and accelerated healing mechanism of dextran-based hydrogel in third-degree porcine burn model. The model was optimized to allow examination of the hydrogel treatment for clinical translation and its regenerative response mechanisms. Hydrogel treatment accelerated third-degree burn wound healing by rapid wound closure, improved reepithelialization, enhanced extracellular matrix remodeling, and greater nerve reinnervation, compared to the dressing treated group. These effects appear to be mediated through the ability of the hydrogel to facilitate a rapid but brief initial inflammatory response that coherently stimulates neovascularization within the granulation tissue during the first week of treatment, followed by an efficient vascular regression to promote a regenerative healing process. Our results suggest that the dextran-based hydrogels may substantially improve healing quality and reduce skin grafting incidents and thus pave the way for clinical studies to improve the care of severe burn injury patients.

Comparison studies of the in vivo treatment of full-thickness excisional wounds and burns by an artificial bilayer dermal equivalent and J-1 acellular dermal matrix

The effects upon skin repair were compared between a homemade bilayer dermal equivalent (BDE), composed of a collagen/chitosan porous scaffold and a silicone membrane, and J-1 acellular dermal matrix (ADM), a commercial ADM that is used widely in China to treat various skin defects. Full-thickness excisional and burn wounds were prepared on the backs of pigs and then treated with the BDE and J-1 ADM. Biopsy specimens were harvested on days 7, 14, and 21 after surgery for gross, biochemical, and molecular examinations. In comparison with the burn wounds, the excisional wounds showed accelerated granular tissue formation and superior integration with the equivalents, regardless of their type. Immunohistochemical, immunofluorescence, real time quantitative polymerase chain reaction and Western blotting analyses showed that the vascularization rates in the excisional wounds group were also significantly faster than those of the burn group for both dermal equivalents. There was no significant difference between J-1 ADM and BDE treatment on the formation of newly formed blood vessels for the excisional wounds at days 7, 14, and 21. However, there was a significant difference in the number of nascent blood vessels formed in the burn wounds after treatment with J-1 ADM compared with BDE. The highest numbers of newly formed and mature blood vessels were present in the J-1 ADM-treated excisional wounds after 21 days. Ultrathin skin grafts were further transplanted on to the regenerated dermis for 28 days, resulting in the repair of the full-thickness wounds and production of a structure similar to normal skin.

Full-Thickness Thermal Injury Delays Wound Closure in a Murine Model

Objective: The contemporary treatment of a full-thickness burn consists of early eschar excision followed by immediate closure of the open wound using autologous skin. However, most animal models study burn wound healing with the persistence of the burn eschar. Our goal is to characterize a murine model of burn eschar excision to study wound closure kinetics. Approach: C57BL/6 male mice were divided into three groups: contact burn, scald burn, or unburned control. Mice were burned at 80°C for 5, 10, or 20 s. After 2 days, the eschar was excised and wound closure was documented until postexcision day 13. Biopsies were examined for structural morphology and α-smooth muscle actin. In a subsequent interval-excision experiment (80°C scald for 10 s), the burn eschar was excised after 5 or 10 days postburn to determine the effect of a prolonged inflammatory focus. Results: Histology of both contact and scald burns revealed characteristics of a full-thickness injury marked by collagen coagulation and tissue necrosis. Excision at 2 days after a 20-s burn from either scald or contact showed significant delay in wound closure. Interval excision of the eschar, 5 or 10 days postburn, also showed significant delay in wound closure. Both interval-excision groups showed prolonged inflammation and increased myofibroblasts. Innovation and Conclusions: We have described the kinetics of wound closure in a murine model of a full-thickness burn excision. Both contact and scald full-thickness burn resulted in significantly delayed wound closure. In addition, prolonged interval-excision of the eschar appeared to increase and prolong inflammation.

An injectable aldehyded 1-amino-3,3-diethoxy-propane hyaluronic acid–chitosan hydrogel as a carrier of adipose derived stem cells to enhance angiogenesis and promote skin regeneration

We report an injectable aldehyded 1-amino-3,3-diethoxy-propane (ADEP)–hyaluronic acid (AHA)–chitosan (CS) hydrogel.

Integration and regression of implanted engineered human vascular networks during deep wound healing

The ability of vascularized constructs to integrate with tissues may depend on the kinetics and stability of vascular structure development. This study assessed the functionality and durability of engineered human vasculatures from endothelial progenitors when implanted in a mouse deep burn-wound model. Human vascular networks, derived from endothelial colony-forming cells in hyaluronic acid hydrogels, were transplanted into third-degree burns. On day 3 following transplantation, macrophages rapidly degraded the hydrogel during a period of inflammation; through the transitions from inflammation to proliferation (days 5-7), the host's vasculatures infiltrated the construct, connecting with the human vessels within the wound area. The growth of mouse vessels near the wound area supported further integration with the implanted human vasculatures. During this period, the majority of the vessels (∼60%) in the treated wound area were human. Although no increase in the density of human vessels was detected during the proliferative phase, they temporarily increased in size. This growth peaked at day 7, the middle of the proliferation stage, and then decreased by the end of the proliferation stage. As the wound reached the remodeling period during the second week after transplantation, the vasculatures including the transplanted human vessels generally regressed, and few microvessels, wrapped by mouse smooth muscle cells and with a vessel area less than 200 μm² (including the human ones), remained in the healed wound. Overall, this study offers useful insights for the development of vascularization strategies for wound healing and ischemic conditions, for tissue-engineered constructs, and for tissue regeneration.

Dextran hydrogel scaffolds enhance angiogenic responses and promote complete skin regeneration during burn wound healing

Neovascularization is a critical determinant of wound-healing outcomes for deep burn injuries. We hypothesize that dextran-based hydrogels can serve as instructive scaffolds to promote neovascularization and skin regeneration in third-degree burn wounds. Dextran hydrogels are soft and pliable, offering opportunities to improve the management of burn wound treatment. We first developed a procedure to treat burn wounds on mice with dextran hydrogels. In this procedure, we followed clinical practice of wound excision to remove full-thickness burned skin, and then covered the wound with the dextran hydrogel and a dressing layer. Our procedure allows the hydrogel to remain intact and securely in place during the entire healing period, thus offering opportunities to simplify the management of burn wound treatment. A 3-week comparative study indicated that dextran hydrogel promoted dermal regeneration with complete skin appendages. The hydrogel scaffold facilitated early inflammatory cell infiltration that led to its rapid degradation, promoting the infiltration of angiogenic cells into the healing wounds. Endothelial cells homed into the hydrogel scaffolds to enable neovascularization by day 7, resulting in an increased blood flow significantly greater than treated and untreated controls. By day 21, burn wounds treated with hydrogel developed a mature epithelial structure with hair follicles and sebaceous glands. After 5 weeks of treatment, the hydrogel scaffolds promoted new hair growth and epidermal morphology and thickness similar to normal mouse skin. Collectively, our evidence shows that customized dextran-based hydrogel alone, with no additional growth factors, cytokines, or cells, promoted remarkable neovascularization and skin regeneration and may lead to novel treatments for dermal wounds.

Tie2-dependent knockout of HIF-1 impairs burn wound vascularization and homing of bone marrow-derived angiogenic cells

AIMS

Hypoxia-inducible factor 1 (HIF-1) is a heterodimer composed of HIF-1α and HIF-1β subunits. HIF-1 is known to promote tissue vascularization by activating the transcription of genes encoding angiogenic factors, which bind to receptors on endothelial cells (ECs) and bone marrow-derived angiogenic cells (BMDACs). In this study, we analysed whether HIF-1 activity in the responding ECs and BMDACs is also required for cutaneous vascularization during burn wound healing.

METHODS AND RESULTS

We generated mice with floxed alleles at the Hif1a or Arnt locus encoding HIF-1α and HIF-1β, respectively. Expression of Cre recombinase was driven by the Tie2 gene promoter, which is expressed in ECs and bone marrow cells. Tie2Cre(+) and Tie2Cre(-) mice were subjected to burn wounds of reproducible diameter and depth. Deficiency of HIF-1α or HIF-1β in Tie2-lineage cells resulted in delayed wound closure, reduced vascularization, decreased cutaneous blood flow, impaired BMDAC mobilization, and decreased BMDAC homing to burn wounds.

CONCLUSION

HIF-1 activity in Tie2-lineage cells is required for the mobilization and homing of BMDACs to cutaneous burn wounds and for the vascularization of burn wound tissue.

Fat grafting accelerates revascularisation and decreases fibrosis following thermal injury

BACKGROUND

Fat grafting has been shown clinically to improve the quality of burn scars. To date, no study has explored the mechanism of this effect. We aimed to do so by combining our murine model of fat grafting with a previously described murine model of thermal injury.

METHODS

Wild-type FVB mice (n=20) were anaesthetised, shaved and depilitated. Brass rods were heated to 100°C in a hot water bath before being applied to the dorsum of the mice for 10s, yielding a full-thickness injury. Following a 2-week recovery period, the mice underwent Doppler scanning before being fat/sham grafted with 1.5cc of human fat/saline. Half were sacrificed 4 weeks following grafting, and half were sacrificed 8 weeks following grafting. Both groups underwent repeat Doppler scanning immediately prior to sacrifice. Burn scar samples were taken following sacrifice at both time points for protein quantification, CD31 staining and Picrosirius red staining.

RESULTS

Doppler scanning demonstrated significantly greater flux in fat-grafted animals than saline-grafted animals at 4 weeks (fat=305±15.77mV, saline=242±15.83mV; p=0.026). Enzyme-linked immunosorbent assay (ELISA) analysis in fat-grafted animals demonstrated significant increase in vasculogenic proteins at 4 weeks (vascular endothelial growth factor (VEGF): fat=74.3±4.39ngml(-1), saline=34.3±5.23ngml(-1); p=0.004) (stromal cell-derived factor-1 (SDF-1): fat=51.8±1.23ngml(-1), saline grafted=10.2±3.22ngml(-1); p<0.001) and significant decreases in fibrotic markers at 8 weeks (transforming growth factor-ß1(TGF-ß): saline=9.30±0.93, fat=4.63±0.38ngml(-1); p=0.002) (matrix metallopeptidase 9 (MMP9): saline=13.05±1.21ngml(-1), fat=6.83±1.39ngml(-1); p=0.010). CD31 staining demonstrated significantly up-regulated vascularity at 4 weeks in fat-grafted animals (fat=30.8±3.39 vessels per high power field (hpf), saline=20.0±0.91 vessels per high power field (hpf); p=0.029). Sirius red staining demonstrated significantly reduced scar index in fat-grafted animals at 8 weeks (fat=0.69±0.10, saline=2.03±0.53; p=0.046).

CONCLUSIONS

Fat grafting resulted in more rapid revascularisation at the burn site as measured by laser Doppler flow, CD31 staining and chemical markers of angiogenesis. In turn, this resulted in decreased fibrosis as measured by Sirius red staining and chemical markers.

Hypoxia and hypoxia-inducible factor in the burn wound

The importance of hypoxia-inducible factor (HIF) in promoting angiogenesis and vasculogenesis during wound healing has been demonstrated. It is widely accepted that HIF activity can be promoted by many factors, including hypoxia in the wound or cytokines from inflammatory cells infiltrating the wound. However, there has not been a systematic exploration of the relationship between HIF activity and hypoxia in the burn wound. The location of the hypoxic tissue has not been clearly delineated. The time course of the appearance of hypoxia and the increased activity of HIF and appearance of HIF's downstream transcription products has not been described. The aim of this study was to utilize pimonidazole, a specific tissue hypoxia marker, to characterize the spatial and temporal course of hypoxia in a murine burn model and correlate this with the appearance of HIF-1α and its important angiogenic and vasculogenic transcription products vascular endothelial growth factor and SDF-1. Hypoxia was found in the healing margin of burn wounds beginning at 48 hours after burn and peaking at day 3 after burn. On sequential sections of the same tissue block, positive staining of HIF-1α, SDF-1, and vascular endothelial growth factor all occurred at the leading margin of the healing area and peaked at day 3, as did hypoxia. Immunohistochemical analysis was used to explore the characteristics of the hypoxic region of the wound. The localization of hypoxia was found to be related to cell growth and migration, but not to proliferation or inflammatory infiltration.

Aging impairs the mobilization and homing of bone marrow-derived angiogenic cells to burn wounds

Impaired wound healing in the elderly represents a major clinical problem. Delineating the cellular and molecular mechanisms by which aging impairs wound healing may lead to the development of improved treatment strategies for elderly patients with non-healing wounds. Neovascularization is an essential step in wound healing, and bone marrow-derived angiogenic cells (BMDACs) play an important role in vascularization. Using a mouse full-thickness burn wound model, we demonstrate that perfusion and vascularization of burn wounds were impaired by aging and were associated with dramatically reduced mobilization of BMDACs bearing the cell surface molecules CXCR4 and Sca1. Expression of stromal-derived factor 1 (SDF-1), the cytokine ligand for CXCR4, was significantly decreased in peripheral blood and burn wounds of old mice. Expression of hypoxia-inducible factor (HIF)-1α was detected in burn wounds from young (2-month-old), but not old (2-year-old), mice. When BMDACs from young donor mice were injected intravenously, homing to burn wound tissue was impaired in old recipient mice, whereas the age of the BMDAC donor mice had no effect on homing. Our results indicate that aging impairs burn wound vascularization by impairing the mobilization of BMDACs and their homing to burn wound tissue as a result of impaired HIF-1 induction and SDF-1 signaling.

Surgical approaches to create murine models of human wound healing

Wound repair is a complex biologic process which becomes abnormal in numerous disease states. Although in vitro models have been important in identifying critical repair pathways in specific cell populations, in vivo models are necessary to obtain a more comprehensive and pertinent understanding of human wound healing. The laboratory mouse has long been the most common animal research tool and numerous transgenic strains and models have been developed to help researchers study the molecular pathways involved in wound repair and regeneration. This paper aims to highlight common surgical mouse models of cutaneous disease and to provide investigators with a better understanding of the benefits and limitations of these models for translational applications.

Impaired angiogenesis and mobilization of circulating angiogenic cells in HIF-1alpha heterozygous-null mice after burn wounding

Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that controls vascular responses to hypoxia and ischemia. In this study, mice that were heterozygous (HET) for a null allele at the locus encoding the HIF-1alpha subunit (HET mice) and their wild-type (WT) littermates were subjected to a thermal injury involving 10% of the body surface area. HIF-1alpha protein levels were increased in burn wounds of WT but not of HET mice on day 2. The serum levels of stromal-derived factor 1alpha, which binds to CXCR4, were increased on day 2 in WT but not in HET mice. Circulating angiogenic cells were also increased on day 2 in WT but not in HET mice and included CXCR4(+)Sca1(+) cells. Laser Doppler perfusion imaging demonstrated increased blood flow in burn wounds of WT but not HET mice on day 7. Immunohistochemistry on day 7 revealed a reduced number of CD31(+) vessels at the healing margin of burn wounds in HET as compared with WT mice. Vessel maturation was also impaired in wounds of HET mice as determined by the number of alpha-smooth muscle actin-positive vessels on day 21. The remaining wound area on day 14 was significantly increased in HET mice compared with WT littermates. The percentage of healed wounds on day 14 was significantly decreased in HET mice. These data delineate a signaling pathway by which HIF-1 promotes angiogenesis during burn wound healing.