Human acellular dermal wound matrix: evidence and experience

A chronic wound fails to complete an orderly and timely reparative process and places patients at increased risk for wound complications that negatively impact quality of life and require greater health care expenditure. The role of extracellular matrix (ECM) is critical in normal and chronic wound repair. Not only is ECM the largest component of the dermal skin layer, but also ECM proteins provide structure and cell signalling that are necessary for successful tissue repair. Chronic wounds are characterised by their inflammatory and proteolytic environment, which degrades the ECM. Human acellular dermal matrices, which provide an ECM scaffold, therefore, are being used to treat chronic wounds. The ideal human acellular dermal wound matrix (HADWM) would support regenerative healing, providing a structure that could be repopulated by the body's cells. Experienced wound care investigators and clinicians discussed the function of ECM, the evidence related to a specific HADWM (Graftjacket^® regenerative tissue matrix, Wright Medical Technology, Inc., licensed by KCI USA, Inc., San Antonio, TX), and their clinical experience with this scaffold. This article distills these discussions into an evidence‐based and practical overview for treating chronic lower extremity wounds with this HADWM.     

The role of endogenous and exogenous enzymes in chronic wounds: A focus on the implications of aberrant levels of both host and bacterial proteases in wound healing

Cutaneous wound healing is orchestrated by a number of physiological pathways that ultimately lead to reformation of skin integrity and the production of functional scar tissue. The remodeling of a wound is significantly affected by matrix metalloproteinases (MMPs), which act to control the degradation of the extracellular matrix (ECM). Regulation of MMPs is imperative for wound healing as excessive levels of MMPs can lead to disproportionate destruction of the wound ECM compared to ECM deposition. In addition to human MMPs, bacterial proteases have been found to be influential in tissue breakdown and, as such, have a role to play in the healing of infected wounds. For example, the zinc‐metalloproteinase, elastase, produced by Pseudomonas aeruginosa, induces degradation of fibroblast proteins and proteoglycans in chronic wounds and has also been shown to degrade host immune cell mediators. Microbial extracellular enzymes have also been shown to degrade human wound fluid and inhibit fibroblast cell growth. It is now being acknowledged that host and bacterial MMPs may act synergistically to cause tissue breakdown within the wound bed. Several studies have suggested that bacterial‐derived secreted proteases may act to up‐regulate the levels of MMPs produced by the host cells. Together, these findings indicate that bacterial phenotype in terms of protease producing potential of bacteria should be taken into consideration during diagnostic and clinical intervention of infected wound management. Furthermore, both host MMPs and those derived from infecting bacteria need to be targeted in order to increase the healing capacity of the injured tissue. The aim of this review is to investigate the evidence suggestive of a relationship between unregulated levels of both host and bacterial proteases and delayed wound healing.     

Chronic wound fluid—thinking outside the box

Chronic wounds are associated with an altered wound milieu that results from an imbalance in extracellular matrix (ECM) homeostasis. This alteration is characterized by an increased destruction and degradation of components of the ECM with a concomitant lack of synthesis of these elements. Traditionally wound fluid has been considered a reflection of the internal wound milieu. It has been used to monitor and reflect on the chronic status of a wound or to measure the efficacy of wound treatment. However, on closer inspection of chronic wound fluid, certain components of the fluid, particularly matrix metalloproteinases (MMPs) and their subcomponents (MMP‐9) have been found to exist at higher levels in wound fluid than in the corresponding wound. There is mounting evidence that much of the destructive effects observed in chronic wounds may be compounded by components of the wound exudate which are corrosive in nature resulting in a continuum of ECM breakdown. Isolation of these components has identified MMPs, in particular MMP‐9 as dominant in this destructive process. Additionally an association has been made between high bacterial levels and elevated MMP9 in chronic wounds. Agents that have efficacy against MMP‐9 and significant antibacterial potency thus provide a dual defense against chronic wounds. It is likely that these agents cause a change in the chronic wound fluid components that more closely resemble the balance of proteases and growth factors seen acute wounds, thus triggering a positive wound healing process. Nanocrystalline silver appears to fulfill these criteria. A strategy is suggested whereby wound fluid is directly targeted to diminish the corrosive wound fluid elements in an attempt to break the ongoing destructive inflammatory cycle. This presents a relatively new treatment paradigm attempting to influence wound healing by working from without to initiate changes within.     

The extracellular matrix in wound healing: a closer look at therapeutics for chronic wounds

Disappointing results with the use of exogenous recombinant growth factors in chronic wounds have redirected the focus to the extracellular matrix (ECM). Newer research has clearly changed our view on the role of the ECM in tissue repair and dismissed the dogma that the sole function of ECM is a passive physical support for cells. It is now clear that intact or fragmented ECM molecules are capable of transducing signals pivotal for cell processes in wound healing primarily via integrin interactions in concert with growth factor activation. In addition, our knowledge about ECM molecules in minute concentrations with biological activity, but devoid of significant structural influence, is increasing. This article reviews the multifaceted molecular roles of ECM in the normal wound-healing process and some molecular abnormalities in chronic wounds, and touches on potential therapies based on the developments of tissue biology.     

Ratios of activated matrix metalloproteinase-9 to tissue inhibitor of matrix metalloproteinase-1 in wound fluids are inversely correlated with healing of pressure ulcers

Previous analyses of fluids collected from chronic, nonhealing wounds found elevated levels of inflammatory cytokines, elevated levels of proteinases, and low levels of growth factor activity compared with fluids collected from acute, healing wounds. This led to the general hypothesis that chronic inflammation in acute wounds produces elevated levels of proteinases that destroy essential growth factors, receptors, and extracellular matrix proteins, which ultimately prevent wounds from healing. To test this hypothesis further, pro- and activated matrix metalloproteinases (MMP-2 and MMP-9), tissue inhibitors of metalloproteinases (TIMP-1 and TIMP-2), and the ratios of MMPs/TIMPs were assayed in fluids and biopsies collected from 56 patients with chronic pressure ulcers. Specimens included ulcers treated for 0, 10, and 36 days with conventional therapy or with exogenous cytokine therapies. Quantitative assay data were correlated with the amount of healing. The average MMP-9/TIMP-1 ratio in fluids from 56 ulcers decreased significantly as the chronic pressure ulcers healed. Furthermore, the average MMP-9/TIMP-1 ratio was significantly lower for fluids collected on day 0 from wounds that ultimately healed well (> or =85% reduction in initial wound volume) compared with wounds that healed poorly (< 50% wound volume reduction). These data show that the ratio of MMP-9/TIMP-1 levels is a predictor of healing in pressure ulcers and they provide additional support for the hypothesis that high levels of MMP activity and low levels of MMP inhibitor impair wound healing in chronic pressure ulcers.     

Cellular events and biomarkers of wound healing

Researchers have identified several of the cellular events associated with wound healing. Platelets, neutrophils, macrophages, and fibroblasts primarily contribute to the process. They release cytokines including interleukins (ILs) and TNF-α, and growth factors, of which platelet-derived growth factor (PDGF) is perhaps the most important. The cytokines and growth factors manipulate the inflammatory phase of healing. Cytokines are chemotactic for white cells and fibroblasts, while the growth factors initiate fibroblast and keratinocyte proliferation. Inflammation is followed by the proliferation of fibroblasts, which lay down the extracellular matrix. Simultaneously, various white cells and other connective tissue cells release both the matrix metalloproteinases (MMPs) and the tissue inhibitors of these metalloproteinases (TIMPs). MMPs remove damaged structural proteins such as collagen, while the fibroblasts lay down fresh extracellular matrix proteins. Fluid collected from acute, healing wounds contains growth factors, and stimulates fibroblast proliferation, but fluid collected from chronic, nonhealing wounds does not. Fibroblasts from chronic wounds do not respond to chronic wound fluid, probably because the fibroblasts of these wounds have lost the receptors that respond to cytokines and growth factors. Nonhealing wounds contain high levels of IL1, IL6, and MMPs, and an abnormally high MMP/TIMP ratio. Clinical examination of wounds inconsistently predicts which wounds will heal when procedures like secondary closure are planned. Surgeons therefore hope that these chemicals can be used as biomarkers of wounds which have impaired ability to heal. There is also evidence that the application of growth factors like PDGF will help the healing of chronic, nonhealing wounds.KEY WORDS: Cytokines, growth factors, matrix metalloproteinases, platelet-derived growth factor, wound healingIn the last 30 or so years, researchers have identified several of the cellular and biochemical events associated with wound healing. The process is becoming clearer, with the understanding of the cells and chemicals that help wounds to heal, and of those that inhibit healing. Investigators are trying to analyze the chemicals in chronic wounds in order to determine their condition and fitness for closure. A major advance is the clinical application of some of these chemicals to improve outcomes in wound healing.In this paper we look at the biology of normal and abnormal healing, see if wounds analysis can predict poor healing, and review some literature on the clinical applications of this knowledge.     

Extracellular matrix/stromal vascular fraction gel conditioned medium accelerates wound healing in a murine model

Conditioned medium (CM) is a new treatment modality in regenerative medicine and has shown a successful outcome in wound healing. We recently introduced extracellular matrix/stromal vascular fraction gel (ECM/SVF‐gel), an adipose‐derived stem cell and adipose native extracellular matrix‐enriched product for cytotherapy. This study aimed to evaluate the effect of CM from ECM/SVF‐gel (Gel‐CM) on wound healing compared with the conventional CM from adipose tissue (Adi‐CM) and stem cell (SVF‐CM). In vitro wound healing effect of three CMs on keratinocytes and fibroblasts was evaluated in terms of proliferation property, migratory property, and extracellular matrix production. In vivo, two full‐thickness wounds were created on the back of each mice. The wounds were randomly divided to receive Gel‐CM, Adi‐CM, SVF‐CM, and PBS injection. Histologic observations and collagen content of wound skin were made. Growth factors concentration in three CMs was further quantified. In vitro, Gel‐CM promoted the proliferation and migration of keratinocytes and fibroblasts and enhanced collagen I synthesis in fibroblasts compared to Adi‐CM and SVF‐CM. In vivo, wound closure was faster, and dermal and epidermal regeneration was improved in the Gel‐CM‐treated mice compared to that in Adi‐CM and SVF‐CM‐treated mice. Moreover, The growth factors concentration (i.e., vascular endothelial growth factor, basic fibroblast growth factor, hepatocyte growth factor, and transforming growth factor‐β) in Gel‐CM were significantly higher than those in Adi‐CM and SVF‐CM. Gel‐CM generated under serum free conditions significantly enhanced wound healing effect compared to Adi‐CM and SVF‐CM by accelerating cell proliferation, migration, and production of ECM. This improved trophic effect may be attributed to the higher growth factors concentration in Gel‐CM. Gel‐CM shows potential as a novel and promising alternative to skin wound healing treatment. But limitations include the safety and immunogenicity studies of Gel‐CM still remain to be clearly clarified and more data on mechanism study are needed.     

Wound‐healing effect of adipose stem cell‐derived extracellular matrix sheet on full‐thickness skin defect rat model: Histological and immunohistochemical study

The potential use of extracellular matrix (ECM) as a source of wound dressing material has recently received much attention. The ECM is an intricate network of various combinations of elastin, collagens, laminin, fibronectin, and proteoglycans that play a key role in stimulating cell proliferation and differentiation. We evaluated the efficacy of an ECM sheet derived from human adipose tissue as a wound dressing material to enhance healing. We prepared a novel porous ECM sheet dressing scaffold from human adipose tissue. in vitro analysis of the ECM sheets showed efficient decellularisation; absence of immunostimulatory components; and the presence of a wide number of angiogenic and bioactive factors, including collagen, elastin, and proteoglycans. To evaluate in vivo efficacy, full‐thickness excisional wounds were created on the dorsal skin of a rat, and the ECM sheets; secondary healing foam wound dressing, Healoderm; or a conventional dressing were applied to each wound site. Photographs were taken every other day, and the degree of reepithelialisation of the wounds was determined. Application of an ECM sheet dressing enhanced the macroscopic wound‐healing rate on days 4, 7, and 10 compared with that in the control group. Microscopic analysis indicated that the reepithelialisation rate of the wound was higher in the ECM group compared with that in the control group; the reepithelialisation rate was better than that of the secondary healing foam wound dressing. Moreover, a denser and more organised granulation tissue was formed in the ECM sheet group compared with that in the secondary healing foam wound dressing and control groups. The ECM sheet also showed the highest microvessel density compared with the secondary healing foam wound dressing and control groups. Based on these data, we suggest that a bioactive ECM sheet dressing derived from human adipose can provide therapeutic proteins for wound healing.     

Interactions of cytokines, growth factors, and proteases in acute and chronic wounds

A healing wound represents a complex series of interactions between cells, soluble mediators, and extracellular matrix. Within this multifaceted environment, there are multiple regulatory points which control the ordered series of events that lead to normal tissue repair. An alteration in this physiologic network can lead to the development of a chronic wound. This article presents an update on the numerous mediators that exist within the wound environment in both acute normal healing and chronic nonhealing wounds. We also present a hypothesis which may provide a conceptual pathophysiologic mechanism with which to understand all chronic wounds.     

Matrix metalloproteinases in vascular physiology and disease

Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases that primarily degrade components of the extracellular matrix (ECM). Remodeling of the ECM by MMPs is important in both physiological and pathological processes, including organ generation/regeneration, angiogenesis, wound healing, inflammation and tumor growth. In the vasculature, MMPs play a role in beneficial processes such as angiogenesis, collateral artery formation and thrombus resolution. However, MMP expression is also implicated in the pathogenesis of vascular diseases such as atherosclerosis, aortic aneurysms, plaque rupture and neointimal hyperplasia after balloon angioplasty. Here, we review the structure, functions and roles of MMPs in both neovascularization and vascular pathology and discuss the potential of, and challenges that face, adapting MMPs as therapeutic targets in vascular disease.     

Protease levels are significantly altered in pediatric burn wounds

Burn wounds contain high levels of protease activity due to the need to remodel the damaged extracellular matrix proteins. While necessary, excessive protease activity can lead to improper wound healing and is associated with increased contraction and fibrosis. No studies to date have investigated the expression changes of all the collagenases and elastases in burn wounds. The present study compares gene expression changes and changes in collagenase and elastase activity between burn wound eschar and normal skin in a pediatric population. Deidentified pediatric tissues were used for these experiments. Burn wound tissue was excised as part of normal standard care within a week from injury; normal skin was removed during elective plastic surgery procedures. RNA-sequencing was performed and significant results were confirmed with qRT-PCR. Activity assays showed a significant increase in both collagenase and elastase activity in the burn wound tissue compared to the normal skin. Western blotting and substrate zymography of tissue homogenates evaluated the results at the protein levels. Four elastases and three collagenases were determined to be significantly upregulated in the wound tissues by both RNA-sequencing and qRT-PCR. Cathepsin V was the only protease that was significantly downregulated. All but one metalloproteinase studied was significantly upregulated. None of the serine proteases were significantly altered in the wound tissues. In conclusion, matrix metalloproteinases appear to be the most highly elevated proteases after a pediatric burn wound injury, at least within the first 3–7 days. The data warrant further investigation into the effects of MMPs on burn wound healing.     

Chronic wounds – is cellular ‘reception’ at fault? Examining integrins and intracellular signalling

As with all physiologic processes, chronic wounds are associated with unique intracellular and cellular/extracellular matrix (ECM) receptor types and signalling messages. These cellular receptors mediate responses of the epidermis to provisional wound matrix and change in form and number in cases of impaired wound healing. Integrins are the major cell‐surface receptors for cell adhesion and migration and epidermal keratinocytes express several integrins that bind ECM ligands in provisional wound ECM. Integrin receptors and more particularly integrin clusters and focal adhesion points appear to influence epidermal and dermal cell matrix interactions, cell motility, cell phenotype and ultimate healing trajectory. In chronic wounds, a variety of changes in receptors have been identified: decreased integrin α5β1 receptors affect the integration of fibronectin and subsequent keratinocyte migration; integrin αvβ6 stimulate transforming growth factor (TGF)‐β and may increase the susceptibility to ulceration and fibrosis; however, TGF‐β signal receptors have been found to be dysfunctional in many chronic wounds; additionally receptor interactions result in increased senescent cells including fibroblasts, myofibroblasts and even keratinocytes – this produces a degradative ECM and wound bed and corrosive chronic wound fluid. The activation or inhibition of integrin receptors by various agents may provide an excellent means of influencing wound healing. This process offers an earlier intervention into the wound healing cascade promoting intrinsic healing and elaboration of growth factors and ECM proteins, which may be more cost effective than the traditional attempts at extrinsic addition of these agents.     

In vitro binding of matrix metalloproteinase-2 (MMP-2), MMP-9, and bacterial collagenase on collagenous wound dressings

Chronic wounds are characterized by failure in wound-healing response and a delay in healing or nonclosure of the wounds. This results in a high effort in clinical treatment and/or home care. A major difference between acute wounds and chronic wounds is the imbalance of proteinase inhibitors and proteinase activity that regulates the degradation and regeneration of the extracellular matrix proteins. Collagen and collagen/oxidized regenerated cellulose dressings act as a competitive substrate for matrix metalloproteinase-2, matrix metalloproteinase-9, and bacterial collagenase and influence this imbalance positively. Both wound dressings, approved for chronic wound treatment, the bovine collagen type I sponge and the oxidized regenerated cellulose collagen sponge, did not differ significantly in their sorption profiles for all enzymes. In general, binding was enhanced with a longer incubation time. The density of the device and the accessible surface, which can be controlled by the manufacturing process, are the crucial factors for the efficiency of the wound dressing.     

Endogenous hepatocyte growth factor ameliorates chronic renal injury by activating matrix degradation pathways

BACKGROUND: Hepatocyte growth factor (HGF) has been shown to promote tubule repair and renal regeneration following acute injury; however, whether HGF also modulates the development and progression of chronic renal diseases that are characterized by progressive tissue fibrosis is uncertain. To examine this question, this study investigated the functional consequence of blocking endogenous HGF signaling in vivo in a model of chronic renal disease. The effects of HGF on the processes of matrix synthesis and degradation in cultured renal epithelial cells were also examined. METHODS: The level of activity of the HGF/c-met axis was examined in rats following 5/6 nephrectomy at multiple time points. To determine the effects of HGF in modulating chronic renal injury, HGF action was blocked in remnant kidney rats using an anti-HGF antibody. The effects of HGF on extracellular matrix (ECM) synthesis and degradation were examined in renal epithelial cells by (35)S-methionine labeling, Western blotting, and zymographic analysis. RESULTS: An increase in renal and systemic production of HGF coupled with an increase in renal c-met was observed in rats with remnant kidneys. When HGF action was blocked by the administration of an anti-HGF antibody, rats experienced a rapid decrease in glomerular filtration rate and increased renal fibrosis. Kidney sections from the antibody-treated rats displayed a marked increase in ECM accumulation and in alpha-smooth muscle actin-positive cells in both the interstitium and tubular epithelium. In vitro studies revealed that HGF reduced net ECM accumulation by human proximal tubule cells (HKC), and this effect was abolished by incubating cells with an anti-HGF antibody. HGF did not alter the ECM synthetic rate in HKC cells. Rather, it markedly increased collagenase such as matrix metalloproteinase-9 (MMP-9) protein expression, as evidenced by Western blotting and zymographic analysis. HGF also decreased the expression of tissue inhibitors of matrix metalloproteinase-1 (TIMP-1) and TIMP-2, the endogenous inhibitors of MMPs. CONCLUSION: These results suggest that HGF is a potent antifibrogenic factor both in vitro and in vivo. Endogenous activation of HGF tends to preserve kidney structure and function in rats with chronic renal disease by activating matrix degradation pathways.     

Retrospective real‐world comparative effectiveness of ovine forestomach matrix and collagen/ORC in the treatment of diabetic foot ulcers

The retrospective pragmatic real‐world data (RWD) study compared the healing outcomes of diabetic foot ulcers (DFUs) treated with either ovine forestomach matrix (OFM) (n = 1150) or collagen/oxidised regenerated cellulose (ORC) (n = 1072) in out‐patient wound care centres. Median time to wound closure was significantly (P = .0015) faster in the OFM group (14.6 ± 0.5 weeks) relative to the collagen/ORC group (16.4 ± 0.7). A sub‐group analysis was performed to understand the relative efficacy in DFUs requiring longer periods of treatment and showed that DFUs treated with OFM healed up to 5.3 weeks faster in these challenging wounds. The percentage of wounds closed at 36 weeks was significantly improved in OFM treated DFUs relative to the collagen/ORC. A Cox proportional hazards analysis showed OFM‐treated wounds had a 18% greater probability of healing versus wounds managed with collagen/ORC, and the probability increased to 21% when the analysis was adjusted for multiple variables. This study represents the first large retrospective RWD analysis comparing OFM and collagen/ORC and supports the clinical efficacy of OFM in the treatment of DFUs.     

In vitro and in vivo studies on matrix metalloproteinases interacting with small intestine submucosa wound matrix

Small intestine submucosa (SIS), a bioactive extracellular matrix (ECM) containing critical components of the ECM including collagens, proteoglycans, and glycosaminoglycans, has been widely used for wound healing. The purpose of this study was to investigate the interaction between SIS and matrix metalloproteinases (MMPs). MMP-1, MMP-2, and MMP-9 displayed different binding affinities, indicated by a loss in activity in solution upon incubation with SIS at 53·8%, 85·9%, and 36·9% over 24 hours, respectively. A cell migration study was conducted to evaluate the effects of MMPs and SIS on keratinocytes. The results indicated that MMPs inhibit keratinocyte migration in vitro, and that the inhibition can be significantly reduced by pre-incubating the MMP solution with SIS. To evaluate activity in vivo a diabetic mouse wound healing study was conducted. Biopsy samples were collected on different days for analysis of MMP levels by gelatin zymography. MMP activity was found to be attenuated by SIS treatment on day 3 after wounding. On day 7, the attenuation became less significant indicating that the MMP binding ability of SIS had become saturated. SIS was able to reduce MMP activity immediately, and may reduce the inhibitory effects of MMPs on keratinocyte migration.     

A Prospective Study of 20 Foot and Ankle Wounds Treated with Cryopreserved Amniotic Membrane and Fluid Allograft

We reviewed the background information and previous clinical studies that considered the use of allogeneic amniotic tissue and fluid (granulized amniotic membrane and amniotic fluid) in the treatment of chronic diabetic foot wounds. This innovation represents a relatively new approach to wound management by delivering a unique allograft of live human cells in a nonimmunogenic structural tissue matrix. Developed to fill soft tissue defects and bone voids and to convey antimicrobial and anti-inflammatory capabilities, granulized amniotic membrane and amniotic fluid does not require fetal death, because its procurement is performed with maternal consent during birth. In the present investigation, 20 chronic wounds (20 patients) that had been treated with standard wound therapy for a mean of 36.6 ± 31.58 weeks and with a mean baseline area of 10.15 ± 19.54 cm² were followed up during a 12-week observation period or until they healed. A total of 18 of the wounds (90%) healed during the 12-week observation period, and none of the wounds progressed to amputation. From our experience with the patients in the present case series, we believe that granulized amniotic membrane and amniotic fluid represents a useful option for the treatment of chronic diabetic foot wounds.     

Balance between matrix synthesis and degradation: a determinant of glomerulosclerosis

In glomerular health and disease, the balance between extracellular matrix (ECM) protein synthesis and degradation determines the amount of matrix that accumulates locally. While cell and whole animal regulation of ECM synthesis has been the subject of ongoing study, attention has become focused on proteases that degrade matrix components only recently. Two major ECM protease systems have been defined. The plasminogen activators (PAs) are serine proteases that have matrix-degrading capability and also activate plasminogen to plasmin. Plasmin not only degrades ECM proteins, but also may activate members of the matrix metalloproteinase (MMP) family which comprise the second major matrix-degrading system. Specific biological antagonists of both the PAs and the MMPs tightly regulate proteolysis by these enzymes. All of these enzymes and inhibitors have been detected in the kidney, and their expression may be altered to facilitate ECM accumulation in conditions associated with matrix expansion, such as glomerulosclerosis. Work is in progress to determine how these systems are regulated in the kidney and to further define their contribution to the sclerotic process.     

Mechanism of action of PROMOGRAN, a protease modulating matrix, for the treatment of diabetic foot ulcers

Proteases play a critical role in many of the physiologic processes of wound repair. However, if their activity becomes uncontrolled proteases can mediate devastating tissue damage and consequently they have been implicated in chronic wound pathophysiology. Previous studies have shown that chronic wound fluid contains elevated protease levels that have deleterious effects, degrading de novo granulation tissue and endogenous biologically active proteins such as growth factors and cytokines. Therefore, we have proposed that an effective therapeutic approach for chronic wounds would be to modify this hostile environment and redress this proteolytic imbalance. Using an ex vivo wound fluid model, we show the ability of a proprietary new wound treatment to bind and inactivate proteases. We have shown that the addition of this test material to human chronic wound fluid obtained from diabetic foot ulcer patients resulted in a significant reduction in the activities of neutrophil-derived elastase, plasmin, and matrix metalloproteinase when compared to wet gauze. This study provides mechanistic evidence to support the hypothesis that this novel treatment modality for chronic wounds physically modifies the wound microenvironment, and thereby promotes granulation tissue formation and stimulates wound repair.     

Changes in the extracellular matrix surrounding human chronic wounds revealed by 2‐photon imaging

Chronic wounds are a growing problem worldwide with no effective therapeutic treatments available. Our objective was to understand the composition of the dermal tissue surrounding venous leg ulcers and diabetic foot ulcers (DFU). We used novel 2‐photon imaging techniques alongside classical histology to examine biopsies from the edges of two common types of chronic wound, venous leg ulcers and DFU. Compared to normal intact skin, we found that collagen levels are significantly reduced throughout the dermis of venous leg ulcer biopsies and DFU, with a reduction in both fibril thickness and abundance. Both wound types showed a significant reduction in elastin in the upper dermis, but in DFU, the loss was throughout the dermis. Loss of extracellular matrix correlated with high levels of CD68‐ and CD18‐positive leukocytes. 2‐photon imaging of the extracellular matrix in the intact tissue surrounding a chronic wound with a hand‐held device may provide a useful clinical indicator on the healing progression or deterioration of these wounds.