ArF excimer laser debrides burns without destruction of viable tissue: A pilot study.

INTRODUCTION: Recent evidence indicates that early removal of eschar by tangential debridement can promote healing. Laser debridement can be used for debridement of areas that prove challenging for debridement using tangential excision. In particular, irradiation with an ArF excimer laser ablates desiccated eschar and is self-terminating, preserving hydrated or viable tissue. METHODS: Thermal burns were created on the flanks of two outbred, female Yorkshire pigs using aluminum bars heated to 70°C and applied for different lengths of time. Three days after injury, burns were debrided using an ArF excimer laser (193nm). Tissue was harvested immediately after debridement and 7days after debridement (10days after burn). RESULTS: Data from a pilot study demonstrates that ArF excimer laser irradiation removes burn eschar and promotes healing at 10days after burn. ArF excimer laser debridement is self-terminating and preserves underlying and adjacent perfused tissue. Potentially, this modality would be ideal for the complex curvilinear structures of the body.

Topical Delivery of Immunosuppression to Prolong Xenogeneic and Allogeneic Split-Thickness Skin Graft Survival.

Cadaveric skin allograft is the current standard of treatment for temporary coverage of large burn wounds. Porcine xenografts are viable alternatives but undergo α-1,3-galactose (Gal)-mediated hyperacute rejection and are lost by post-operative day (POD) 3 because of naturally occurring antibodies to Gal in primate recipients. Using baboons, we previously demonstrated that xenografts from GalT-KO swine (lacking Gal) provided wound coverage comparable with allografts with systemic immunosuppression. In this study, we investigate topical immunosuppression as an alternative to prolong xenograft survival. Full-thickness wounds in baboons were created and covered with xenogeneic and allogeneic split-thickness skin grafts (STSGs). Animals were treated with slow-release (TyroSphere-encapsulated) topical formulations (cyclosporine-A [CSA] or Tacrolimus) applied 1) directly to the STSGs only, or 2) additionally to the wound bed before STSG and 1). Topical CSA did not improve either xenograft or allograft survival (median: treated grafts = 12.5 days, control = 14 days; P = 0.27) with similar results when topical Tacrolimus was used. Pretreatment of wound beds resulted in a significant reduction of xenograft survival compared with controls (10 vs 14 days; P = 0.0002), with comparable results observed in allografts. This observation was associated with marked reduction of inflammation on histology with Tacrolimus and not CSA. Prolongation of allograft and xenograft survival after application to full-thickness wound beds was not achieved with the current formulation of topical immunosuppressants. Modulation of inflammation within the wound bed was effective with Tacrolimus pretreatment before STSG application and may serve as a treatment strategy in related fields.

Nanoparticles and nanofibers for topical drug delivery.

This review provides the first comprehensive overview of the use of both nanoparticles and nanofibers for topical drug delivery. Researchers have explored the use of nanotechnology, specifically nanoparticles and nanofibers, as drug delivery systems for topical and transdermal applications. This approach employs increased drug concentration in the carrier, in order to increase drug flux into and through the skin. Both nanoparticles and nanofibers can be used to deliver hydrophobic and hydrophilic drugs and are capable of controlled release for a prolonged period of time. The examples presented provide significant evidence that this area of research has - and will continue to have - a profound impact on both clinical outcomes and the development of new products.

Fibronectin Interaction and Enhancement of Growth Factors: Importance for Wound Healing.

Significance: This critical review focuses on interactions between cells, fibronectin (FN), and growth factors (GF). Recent Advances: Initially, the extracellular matrix (ECM) was thought to serve simply as a reservoir for GFs that would be released as soluble ligands during proteolytic degradation of ECM. This view was rather quickly extended by the observation that ECM could concentrate GFs to the pericellular matrix for more efficient presentation to cell surface receptors. However, recent reports support much more complex interactions among GFs and ECM molecules, particularly FN, and the way these interactions can fine-tune cell responses to the microenvironment. Critical Issues: Wounds that are unable to synthesize and sustain a functional ECM cannot optimally benefit from endogenous or exogenous GFs. Therefore, GF treatments have recently focused on utilizing ECM molecules as delivery vehicles. Thus, ECM can influence GF stability and activity, and GFs can modulate the ECM activity. Hence, both individually and together, ECM and GFs modulate cells that in turn control the type and level of GFs and ECM in the pericellular environment that ultimately results in new tissue generation. Although many ECM components are important for optimal tissue regeneration and wound healing, FN stands out as absolutely critical not only for wound healing and tissue regeneration but also for embryogenesis and morphogenesis. Future Directions: Understanding ECM/GF interactions will greatly facilitate our understanding of normal wound repair and regeneration, the failure of wounds to heal, and how the latter can be salvaged with proper ECM/GF combinations.

Immediate burn excision fails to reduce injury progression.

The contact thermal injury model in the pig was used to determine whether immediate burn excision could alter the extent of injury progression. It was hypothesized that immediate excision of burns would prevent or reduce tissue necrosis in the uninjured interspaces. Four comb burns were created on the back of each animal, using a brass comb preheated in hot water (100 °C) for 5 minutes. This brass comb produced four distinctive burns sites separated by three "interspaces" of unburned skin, which were to undergo progressive injury. Immediately after burn creation, half of the full-thickness burns were excised leaving the unburned interspaces intact. Two full-thickness excisional wounds per pig with the dimensions identical to the comb burns were included as controls. Burn injury progression was microscopically assessed and reported as the percentage of unburned interspaces that progressed to full-thickness necrosis 7 days after injury. Scar formation was grossly evaluated on day 28 after injury and reported as the total surface area (in square centimeters) of the scar. A total of 24 combs with 72 interspaces were evenly distributed among the three groups. The unburned interspaces of both comb burns and excised comb burns had undergone progressive injury and were 100% dead (24/24; i.e., necrotic and/or apoptotic) 7 days postinjury (95% confidence interval, 86-100%) for both. However, interspaces of the control excisional wounds maintained complete viability, that is, no necrosis or apoptosis (0/24 [0%]; 95% confidence interval, 0-14%; P < .001). There was no significant difference in both surface area and depth of scar resulting from excised and nonexcised comb burns. Immediate burn excision neither prevented nor limited burn injury progression.

Deformation gradients imprint the direction and speed of en masse fibroblast migration for fast healing.

En masse cell migration is more relevant compared with single-cell migration in physiological processes of tissue formation, such as embryogenesis, morphogenesis, and wound healing. In these situations, cells are influenced by the proximity of other cells including interactions facilitated by substrate mechanics. Here, we found that when fibroblasts migrated en masse over a hydrogel, they established a well-defined deformation field by traction forces and migrated along a trajectory defined by field gradients. The mechanics of the hydrogel determined the magnitude of the gradient. For materials stiff enough to withstand deformation related to cellular traction forces, such patterns did not form. Furthermore, migration patterns functioned poorly on very soft matrices where only a minimal traction gradient could be established. The largest degree of alignment and migration velocity occurred on the gels with the largest gradients. Granulation tissue formation in punch wounds of juvenile pigs was correlated strongly with the modulus of the implanted gel, in agreement with in vitro en masse cell migration studies. These findings provide basic insight into the biomechanical influences on fibroblast movement in early wounds and relevant design criteria for the development of tissue-engineered constructs that aim to stimulate en masse cell recruitment for rapid wound healing.

Ultrafast and fast bioerodible electrospun fiber mats for topical delivery of a hydrophilic peptide.

Biodegradable polymers that provide localized controlled delivery of therapeutics within hours to days may have an impact on the topical treatment of skin burns. Here we report for the first time the utility of tyrosine-derived polycarbonate terpolymer electrospun fiber mats as tunable drug delivery matrices. "Ultrafast" (<24 h) and "fast"-eroding (<7 days) terpolymers were identified. The degradation kinetics of both terpolymers was similar (<20% of initial molecular weight after 7 days), while erosion was significantly different (<1 and 4 days for ultrafast and fast fibers, respectively). To assess the delivery kinetics, a hydrophilic peptide (P12) was incorporated into the fibers as a model drug. The tunability of polymer composition and its control over release kinetics resulted in significantly different P12 delivery timeframes: total of 9 h ("ultrafast" via polymer erosion) and 4 days ("fast" via diffusion). The biocompatibility of these fibers was confirmed in a porcine excisional wound model by the (i) lack of inflammatory response to the terpolymers and their degradation products, and (ii) normal progression of healing evaluated for 28 days. These results suggest that electrospun tyrosine-derived fibers offer the potential for topical therapies that require ultrafast or fast dose-controlled delivery of the therapeutic.