Design of an artificial skin. II. Control of chemical composition

Outcomes of Dermal Regeneration Templates in Irradiated and Nonirradiated Scalp Defects

OBJECTIVES

Dermal regeneration templates (DRTs) are frequently used to treat scalp defects. The aim was to compare the time course of healing for DRTs in scalp defects with and without preoperative radiation.

METHODS

The authors conducted a retrospective cohort study of DRT-based scalp reconstruction at 2 academic medical centers between 2013 and 2022. Information was collected on demographic variables, comorbidities, medication use, history of radiation, and DRT outcomes. The primary outcome was DRT loss, defined as exposed calvarium or DRT detachment based on postoperative follow-up documentation. Kaplan-Meier survival analysis and multivariable Cox proportional-hazard regressions were used to compare DRT loss in irradiated and nonirradiated defects. Multivariable logistic regressions were used to compare 30-day postoperative complications (infection, hematoma, or seroma) in irradiated and nonirradiated defects.

RESULTS

In total, 158 cases were included. Twenty-eight (18%) patients had a preoperative history of radiation to the scalp. The mean follow-up time after DRT placement was 2.6 months (SD: 4.5 mo). The estimated probability of DRT survival at 2 months was 91% (95% CI: 83%-100%) in nonirradiated patients and 65% (95% CI: 48%-88%) in irradiated patients. In the 55 patients with a bony wound base, preoperative head radiation was associated with a higher likelihood of DRT loss (hazard ratio: 11). Half the irradiated defects experienced uncomplicated total wound closure using Integra Wound Matrix Dressing with or without second-stage reconstruction.

CONCLUSIONS

Dermal regeneration template can offer durable coverage in nonirradiated scalp defects. Although DRT loss is more likely in irradiated scalp defects, successful DRT-based reconstruction is possible in select cases.

Current Approaches to Wound Repair in Burns: How far Have we Come From Cover to Close? A Narrative Review

Burn injuries are a significant global health concern, with more than 11 million people requiring medical intervention each year and approximately 180,000 deaths annually. Despite progress in health and social care, burn injuries continue to result in socioeconomic burdens for victims and their families. The management of severe burn injuries involves preventing and treating burn shock and promoting skin repair through a two-step procedure of covering and closing the wound. Currently, split-thickness/full-thickness skin autografts are the gold standard for permanent skin substitution. However, deep burns treated with split-thickness skin autografts may contract, leading to functional and appearance issues. Conversely, defects treated with full-thickness skin autografts often result in more satisfactory function and appearance. The development of tissue-engineered dermal templates has further expanded the scope of wound repair, providing scar reductive and regenerative properties that have extended their use to reconstructive surgical interventions. Although their interactions with the wound microenvironment are not fully understood, these templates have shown potential in local infection control. This narrative review discusses the current state of wound repair in burn injuries, focusing on the progress made from wound cover to wound closure and local infection control. Advancements in technology and therapies hold promise for improving the outcomes for burn injury patients. Understanding the underlying mechanisms of wound repair and tissue regeneration may provide new insights for developing more effective treatments in the future.

Type I collagen concentration affects neurite outgrowth of adult rat DRG explants by altering mechanical properties of hydrogels

Type I collagen is a predominant fibrous protein that makes up the extracellular matrix. Collagen enhances cell attachment and is commonly used in three-dimensional culture systems, to mimic the native extracellular environment, for primary sensory neurons such as dorsal root ganglia (DRG). However, the effects of collagen concentration on adult rat DRG neurite growth have not been assessed in a physiologically relevant, three-dimensional culture. This study focuses on the effects of type I collagen used in a methacrylated hyaluronic acid (MAHA)-laminin-collagen gel (triple gel) on primary adult rat DRG explants in vitro. DRGs were cultured in triple gels, and the neurite lengths and number of support cells were quantified. Increased collagen concentration significantly reduced neurite length but did not affect support cell counts. Mechanical properties, fiber diameter, diffusivity, and mesh size of the triple gels with varying collagen concentration were characterized to further understand the effects of type I collagen on hydrogel property that may affect adult rat DRG explants. Gel stiffness significantly increased as collagen concentration increased and is correlated to DRG neurite length. Collagen concentration also significantly impacted fiber diameter but there was no correlation with DRG neurite length. Increasing collagen concentration had no significant effect on mesh size and diffusivity of the hydrogel. These data suggest that increasing type I collagen minimizes adult rat DRG explant growth in vitro while raising gel stiffness. This knowledge can help develop more robust 3D culture platforms to study sensory neuron growth and design biomaterials for nerve regeneration applications.

Human Placenta-Derived Mesenchymal Stem Cells Combined With Artificial Dermal Scaffold Enhance Wound Healing in a Tendon-Exposed Wound of a Rabbit Model

To overcome the difficulty of vascular regeneration in exposed tendon wounds, we combined human placenta-derived mesenchymal stem cells (hPMSCs) with an artificial dermal scaffold and assessed their role in promoting vascular regeneration and wound healing in vivo. hPMSCs were isolated from the human placenta and characterized based on their morphology, phenotypic profiles, and pluripotency. New Zealand rabbits were used to establish an exposed tendon wound model, and hPMSCs and artificial dermal scaffolds were transplanted into the wounds. The results of gross wound observations and pathological sections showed that hPMSCs combined with artificial dermal scaffold transplantation increased the vascularization area of the wound, promoted wound healing, and increased the survival rate of autologous skin transplantation. Following artificial dermal scaffold transplantation, hPMSCs accelerated the vascularization of the dermal scaffold, and the number of fibroblasts, collagen fibers, and neovascularization in the dermal scaffold after 1 week were much higher than those in the control group. Immunohistochemical staining further confirmed that the expression of the vascular endothelial cell marker, CD31, was significantly higher in the combined transplantation group than in the dermal scaffold transplantation group. Our findings demonstrated that hPMSCs seeded onto artificial dermal scaffold could facilitate vascularization of the dermal scaffold and improve tendon-exposed wound healing.

Integra® Dermal Regeneration Template: From Design to Clinical Use

Integra^® Dermal Regeneration Template (IDRT, Integra LifeSciences, Princeton, NJ, USA) is a bilayer membrane developed, by Yannas and Burke in the 1980s, to fulfill the unmet need of surgeons having a readily available off-the-shelf dermal regeneration method. IDRT is composed of a sheet of porous cross-linked type I collagen and glycosaminoglycans, with a semi-permeable silicone sheet cover. IDRT is bio-engineered, from adult bovine Achilles tendons and chondroitin-6-sulfate derived from shark cartilage, in a multi-step process involving cross-linking using glutaraldehyde. By design, the composition, porosity, and biodegradation rate of IDRT guides the mechanism of wound repair towards a regenerative pathway. Its mechanism of action involves four distinct phases: imbibition, fibroblast migration, neovascularization, and remodeling/maturation. Originally developed for the post-excisional treatment of deep-partial to full-thickness burns where autograft is limited, over the years its use has expanded to reconstructive surgery.

A bio-inspired nano-material recapitulating the composition, ultra-structure, and function of the glycosaminoglycan-rich extracellular matrix of nucleus pulposus

The nucleus pulposus (NP) of intervertebral disc represents a soft gel consisting of glycosaminoglycans (GAGs)-rich extracellular matrix (ECM). Significant loss of GAGs and normal functions are the most prevalent changes in degenerated disc. Attempts targeted to incorporate GAGs into collagen fibrous matrices have been made but the efficiency is very low, and the resulting structures showed no similarity with native NP. Inspired by the characteristic composition and structures of the ECM of native NP, here, we hypothesize that by chemically modifying the collagen (Col) and hyaluronic acid (HA) and co-precipitating with GAGs, a bio-inspired nano-material recapitulating the composition, ultra-structure and function of the GAG-rich ECM will be fabricated. Compositionally, the bio-inspired nano-material namely Aminated Collagen-Aminated Hyaluronic Acid-GAG (aCol-aHA-GAG) shows a record high GAG/hydroxyproline ratio up to 39.1:1 in a controllable manner, out-performing that of the native NP. Ultra-structurally, the nano-material recapitulates the characteristic 'nano-beads' (25 nm) and 'bottle-brushes' (133 nm) features as those found in native NP. Functionally, the nano-material supports the viability and maintains the morphological and phenotypic markers of bovine NP cells, and shows comparable mechanical properties of native NP. This work contributes to the development of a compositionally, structurally, and functionally biomimetic nano-material for NP tissue engineering.

Composition and Performance of Autologous Engineered Skin Substitutes for Repair or Regeneration of Excised, Full-Thickness Burns

Prompt and permanent wound closure after burn injuries remains a requirement for patient recovery. Historically, split-thickness skin autograft (STAG) has served as the prevailing standard of care for closure of extensive, deep burns. Because STAG availability may be insufficient in life-threatening burns, alternatives have been evaluated for safety and efficacy of wound closure. Since the 1970s, alternatives consisting of cultured epidermal keratinocytes, and/or acellular dermal substitutes were studied and translated into services and devices that facilitated wound closure, survival, and recovery after major burns. Cultured epithelial autografts (CEA) promoted epidermal closure of wounds but were not stable during long-term recovery. An acellular dermal substitute consisting of collagen and glycosaminoglycans (C-GAG) provided more uniform dermal repair, and reduced needs for epidermal harvesting but was subject to loss from microbial contamination. More recently, an autologous engineered skin substitute (ESS) has been reported and includes a C-GAG polymer populated with fibroblasts and keratinocytes which form basement membrane. ESS can be applied clinically over a vascularized dermal substitute and generates stable wound closure that is smooth, soft, and strong. Despite these advances, no current alternatives for permanent wound closure restore the anatomy and physiology of uninjured skin. Current alternatives act by mechanisms of wound healing, not by developmental biology by which skin forms in utero with pigment, hair, sweat and sebaceous glands, microvasculature, and nerve. Until full-thickness burns are restored with all of the normal structures and functions of uninjured skin, regenerative medicine of skin will remain an ambitious aspiration for future researchers and engineers to achieve.

Personalized Scaffolds for Diabetic Foot Ulcer Healing Using Extracellular Matrix from Induced Pluripotent Stem-Reprogrammed Patient Cells

Diabetic foot ulcers (DFU) are chronic wounds sustained by pathological fibroblasts and aberrant extracellular matrix (ECM). Porous collagen-based scaffolds (CS) have shown clinical promise for treating DFUs but may benefit from functional enhancements. Our previous work showed fibroblasts differentiated from induced pluripotent stem cells are an effective source of new ECM mimicking fetal matrix, which notably promotes scar-free healing. Likewise, functionalizing CS with this rejuvenated ECM showed potential for DFU healing. Here, we demonstrate for the first time an approach to DFU healing using biopsied cells from DFU patients, reprogramming those cells, and functionalizing CS with patient-specific ECM as a personalized acellular tissue engineered scaffold. We took a two-pronged approach: 1) direct ECM blending into scaffold fabrication; and 2) seeding scaffolds with reprogrammed fibroblasts for ECM deposition followed by decellularization. The decellularization approach reduced cell number requirements and maintained naturally deposited ECM proteins. Both approaches showed enhanced ECM deposition from DFU fibroblasts. Decellularized scaffolds additionally enhanced glycosaminoglycan deposition and subsequent vascularization. Finally, reprogrammed ECM scaffolds from patient-matched DFU fibroblasts outperformed those from healthy fibroblasts in several metrics, suggesting ECM is in fact able to redirect resident pathological fibroblasts in DFUs towards healing, and a patient-specific ECM signature may be beneficial.

Skin regeneration, repair, and reconstruction: present and future

Background

Large skin defects caused by trauma (e.g., burns) or due to other reasons (e.g., tumor-related skin resections) require sufficient skin replacement. The constant improvement of innovative methods of skin replacement and skin expansion mean that even burn victims with more than 80% body surface burned have a realistic chance of survival. Due to these new developments, not only has survival rate increased, but also quality of life has increased tremendously over the past decades.

Methods

The aim of this review is to present an overview of current standards and future trends concerning the treatment of skin defects. The main focus is placed on the most important technologies and future trends.

Results

Autologous skin grafting was developed more than 3500 years ago. Several approaches and techniques have been discovered and established in burn care and plastic surgery since then. Great achievements were made during the 19th and 20th centuries. Many of these old and new techniques are still part of modern burn and plastic surgery. Today, autologous skin grafting is still considered to be the gold standard for many wounds, but new technologies have been developed, ranging from biological to synthetic skin replacement materials.

Conclusion

Today, old and new technologies are available which allow us new treatment concepts. All this has led to the reconstructive clockwork for reconstructive surgery of the 21st century.

Biocompatible Synthetic Polymers for Tissue Engineering Purposes

Synthetic polymers have been an integral part of modern society since the early 1960s. Besides their most well-known applications to the public, such as packaging, construction, textiles and electronics, synthetic polymers have also revolutionized the field of medicine. Starting with the first plastic syringe developed in 1955 to the complex polymeric materials used in the regeneration of tissues, their contributions have never been more prominent. Decades of research on polymeric materials, stem cells, and three-dimensional printing contributed to the rapid progress of tissue engineering and regenerative medicine that envisages the potential future of organ transplantations. This perspective discusses the role of synthetic polymers in tissue engineering, their design and properties in relation to each type of application. Additionally, selected recent achievements of tissue engineering using synthetic polymers are outlined to provide insight into how they will contribute to the advancement of the field in the near future. In this way, we aim to provide a guide that will help scientists with synthetic polymer design and selection for different tissue engineering applications.

Design of an elastic porous injectable biomaterial for tissue regeneration and volume retention

Soft tissue reconstruction currently relies on two main approaches, one involving the implantation of external biomaterials and the second one exploiting surgical autologous tissue displacement. While both methods have different advantages and disadvantages, successful long-term solutions for soft tissue repair are still limited. Specifically, volume retention over time and local tissue regeneration are the main challenges in the field. In this study the performance of a recently developed elastic porous injectable (EPI) biomaterial based on crosslinked carboxymethylcellulose is analyzed. Nearly quantitative volumetric stability, with over 90% volume retention at 6 months, is observed, and the pore space of the material is effectively colonized with autologous fibrovascular tissue. A comparative analysis with hyaluronic acid and collagen-based clinical reference materials is also performed. Mechanical stability, evidenced by a low-strain elastic storage modulus (G') approaching 1kPa and a yield strain of several tens of percent, is required for volume retention in-vivo. Macroporosity, along with in-vivo persistence of at least several months, is instead needed for successful host tissue colonization. This study demonstrates the importance of understanding material design criteria and defines the biomaterial requirements for volume retention and tissue colonization in soft tissue regeneration. STATEMENT OF SIGNIFICANCE: We present the design of an elastic, porous, injectable (EPI) scaffold suspension capable of inducing a precisely defined, stable volume of autologous connective tissue in situ. It combines volume stability and vascularized tissue induction capacity known from bulk scaffolds with the ease of injection in shear yielding materials. By comparative study with a series of clinically established biomaterials including a wound healing matrix and dermal fillers, we establish design rules regarding rheological and compressive mechanical properties as well as degradation characteristics that rationally underpin the volume stability and tissue induction in a high-performance biomaterial. These design rules should allow to streamline the development of new colonizable injectables.

Conventional and Recent Trends of Scaffolds Fabrication: A Superior Mode for Tissue Engineering

Tissue regeneration is an auto-healing mechanism, initiating immediately following tissue damage to restore normal tissue structure and function. This falls in line with survival instinct being the most dominant instinct for any living organism. Nevertheless, the process is slow and not feasible in all tissues, which led to the emergence of tissue engineering (TE). TE aims at replacing damaged tissues with new ones. To do so, either new tissue is being cultured in vitro and then implanted, or stimulants are implanted into the target site to enhance endogenous tissue formation. Whichever approach is used, a matrix is used to support tissue growth, known as ‘scaffold’. In this review, an overall look at scaffolds fabrication is discussed, starting with design considerations and different biomaterials used. Following, highlights of conventional and advanced fabrication techniques are attentively presented. The future of scaffolds in TE is ever promising, with the likes of nanotechnology being investigated for scaffold integration. The constant evolvement of organoids and biofluidics with the eventual inclusion of organ-on-a-chip in TE has shown a promising prospect of what the technology might lead to. Perhaps the closest technology to market is 4D scaffolds following the successful implementation of 4D printing in other fields.

Conventional and Recent Trends of Scaffolds Fabrication: A Superior Mode for Tissue Engineering

Tissue regeneration is an auto-healing mechanism, initiating immediately following tissue damage to restore normal tissue structure and function. This falls in line with survival instinct being the most dominant instinct for any living organism. Nevertheless, the process is slow and not feasible in all tissues, which led to the emergence of tissue engineering (TE). TE aims at replacing damaged tissues with new ones. To do so, either new tissue is being cultured in vitro and then implanted, or stimulants are implanted into the target site to enhance endogenous tissue formation. Whichever approach is used, a matrix is used to support tissue growth, known as ‘scaffold’. In this review, an overall look at scaffolds fabrication is discussed, starting with design considerations and different biomaterials used. Following, highlights of conventional and advanced fabrication techniques are attentively presented. The future of scaffolds in TE is ever promising, with the likes of nanotechnology being investigated for scaffold integration. The constant evolvement of organoids and biofluidics with the eventual inclusion of organ-on-a-chip in TE has shown a promising prospect of what the technology might lead to. Perhaps the closest technology to market is 4D scaffolds following the successful implementation of 4D printing in other fields.

Bioabsorbable poly(4-hydroxybutyrate) (P4HB) fibrous membranes as a potential dermal substitute

Dermal substitutes are indispensable for repairing large full-thickness skin defects. Only a few biomaterials for dermal substitution have been put into clinical practice. Therefore, novel artificial dermal substitutes that can meet clinical requirements are in urgent need. Biodegradable poly(4-hydroxybutyrate) (P4HB), which has been approved by the U.S. FDA, can be considered as a possible alternative biomaterial to construct dermal substitutes. In this work, three-dimensional P4HB fibrous membranes were constructed by an electrospinning technique. These P4HB fibrous membranes showed excellent air-permeability, and better water uptake capacity compared to P4HB strip and polycaprolactone (PCL) fibrous membrane controls. The in vitro hemocompatibility and cytotoxicity of P4HB fibrous membranes were investigated. In vivo Sprague-Dawley (SD) rat model studies revealed that P4HB fibrous membranes can be used as artificial dermis to improve wound healing for full-thickness skin defects.

Engineering Bioactive Scaffolds for Skin Regeneration

Large skin wounds pose a major clinical challenge. Scarcity of donor site and postsurgical scarring contribute to the incomplete or partial loss of function and aesthetic concerns in skin wound patients. Currently, a wide variety of skin grafts are being applied in clinical settings. Scaffolds are used to overcome the issues related to the misaligned architecture of the repaired skin tissues. The current review summarizes the contribution of biomaterials to wound healing and skin regeneration and addresses the existing limitations in skin grafting. Then, the clinically approved biologic and synthetic skin substitutes are extensively reviewed. Next, the techniques for modification of skin grafts aiming for enhanced tissue regeneration are outlined, and a summary of different growth factor delivery systems using biomaterials is presented. Considering the significant progress in biomaterial science and manufacturing technologies, the idea of biomaterial-based skin grafts with the ability for scarless wound healing and reconstructing full skin organ is more achievable than ever.

Glycosaminoglycan-Based Cryogels as Scaffolds for Cell Cultivation and Tissue Regeneration

Cryogels are a class of macroporous, interconnective hydrogels polymerized at sub-zero temperatures forming mechanically robust, elastic networks. In this review, latest advances of cryogels containing mainly glycosaminoglycans (GAGs) or composites of GAGs and other natural or synthetic polymers are presented. Cryogels produced in this way correspond to the native extracellular matrix (ECM) in terms of both composition and molecular structure. Due to their specific structural feature and in addition to an excellent biocompatibility, GAG-based cryogels have several advantages over traditional GAG-hydrogels. This includes macroporous, interconnective pore structure, robust, elastic, and shape-memory-like mechanical behavior, as well as injectability for many GAG-based cryogels. After addressing the cryogelation process, the fabrication of GAG-based cryogels and known principles of GAG monomer crosslinking are discussed. Finally, an overview of specific GAG-based cryogels in biomedicine, mainly as polymeric scaffold material in tissue regeneration and tissue engineering-related controlled release of bioactive molecules and cells, is provided.

The Effect of Size of Materials Formed or Implanted In Vivo on the Macrophage Response and the Resultant Influence on Clinical Outcome

Both the chemistry and size of a material formed in vivo, or an implanted biomaterial, can alter the in vivo host response. Within the size range covered within this review, over 1 μm, chemistry is only important if the solid material is unstable and leeching small molecules. The macrophage activity and the resultant inflammatory response, however, are related to the size of the solid material. The premise of this review is that differences in size of the solid material, in different cases, can be the reason why there is some individual-to-individual variation in response. Specifically, the inflammatory response is enhanced when the size is between 1-50 μm. This will be looked at for three configurations: spherical particulate (silicone oil or gel from breast implants), elongated particulate (monosodium urate [MSU] crystals in gout or in kidney stones), and fibers (e.g., polyester used in fabric implants). These specific examples were selected because many still believe that the clinical outcome for each is controlled by the surface chemistry, when in fact it is the size. In each case, specific studies will be highlighted to either show a mechanism for creating different sizes and therefore a differential biological response (first three) or how changing the size and shape (diameter and spacing of fibers, in this example) can affect the response and can help explain the different responses to fabric implants found in vivo within the 1-50 μm size range. It was found that polyester fibers under 70 μm had a significant increase in macrophage response. Further, it was found that compounds found in synovial fluid could limit MSU crystal size. In addition, it was shown that plasma with low triglyceride levels emulsifies silicone oils to a greater extent than plasma with higher triglyceride levels. Therefore, in three cases it appears that differences in the inflammatory response between individuals and between different implants could be explained just by the size of the material formed or implanted.

Ice Templating Soft Matter: Fundamental Principles and Fabrication Approaches to Tailor Pore Structure and Morphology and Their Biomedical Applications

Porous scaffolds are widely used in biomedical applications where pore size and morphology influence a range of biological processes, including mass transfer of solutes, cellular interactions and organization, immune responses, and tissue vascularization, as well as drug delivery from biomaterials. Ice templating, one of the most widely utilized techniques for the fabrication of porous materials, allows control over pore morphology by controlling ice formation in a suspension of solutes. By fine-tuning freezing and solute parameters, ice templating can be used to incorporate pores with tunable morphological features into a wide range of materials using a simple, accessible, and scalable process. While soft matter is widely ice templated for biomedical applications and includes commercial and clinical products, the principles underpinning its ice templating are not reviewed as well as their inorganic counterparts. This review describes and critically evaluates fundamental principles, fabrication and characterization approaches, and biomedical applications of ice templating in polymer-based biomaterials. It describes the utility of porous scaffolds in biomedical applications, highlighting biological mechanisms impacted by pore features, outlines the physical and thermodynamic mechanisms underpinning ice templating, describes common fabrication setups, critically evaluates complexities of ice templating specific to polymers, and discusses future directions in this field.

Historical Evolution of Skin Grafting-A Journey through Time

Autologous skin grafting was developed more than 3500 years ago. Several approaches and techniques have been discovered and established in burn care since then. Great achievements were made during the 19th and 20th century. Many of these techniques are still part of the surgical burn care. Today, autologous skin grafting is still considered to be the gold standard for burn wound coverage. The present paper gives an overview about the evolution of skin grafting and its usage in burn care nowadays.

The Development of Tissue Engineering Scaffolds Using Matrix from iPS-Reprogrammed Fibroblasts

Tissue engineering solutions have been widely explored for enhanced healing of skin wounds. Diabetic foot ulcers (DFU) are particularly challenging wounds to heal for a variety of reasons, including aberrant ECM, dysregulation of vascularization, and persistent inflammation. Tissue engineering approaches, such as porous collagen-based scaffolds, have shown promise in replacing the current treatments of surgical debridement and topical treatments. Collagen-glycosaminoglycan scaffolds, which are FDA approved for diabetic foot ulcers, can benefit from further functionalization by incorporation of additional signaling factors or extracellular matrix molecules. One option for this is to incorporate matrix from a rejuvenated cell source, as wounds in younger patients heal more quickly. Induced pluripotent stem cells (iPS) are generated from somatic cells and share many functional similarities with embryonic stem cells (ES), while avoiding the ethical concerns. Fibroblasts differentiated from iPS cells have been shown to enrich their ECM with glycosaminoglycan (GAGs), collagen Type III and fibronectin, to have an increased ECM production, and to be pro-angiogenic. Here we describe a technique to grow matrix from post-iPS fibroblasts, and to develop a scaffold from this matrix, in combination with collagen, with the goal of enhancing wound healing. By activating scaffolds with extracellular matrix (ECM) from fibroblasts derived from an iPS source (post-iPSF), the scaffolds are enriched with beneficial elements like GAGs, collagen type III, fibronectin, and VEGF. We believe these scaffolds can enhance skin regeneration and that the techniques can be modified for other tissue engineering applications.

Nanofibrous Gelatin-Based Biomaterial with Improved Biomimicry Using D-Periodic Self-Assembled Atelocollagen

Design of bioinspired materials that mimic the extracellular matrix (ECM) at the nanoscale is a challenge in tissue engineering. While nanofibrillar gelatin materials mimic chemical composition and nano-architecture of natural ECM collagen components, it lacks the characteristic D-staggered array (D-periodicity) of 67 nm, which is an important cue in terms of cell recognition and adhesion properties. In this study, a nanofibrous gelatin matrix with improved biomimicry is achieved using a formulation including a minimal content of D-periodic self-assembled atelocollagen. We suggest a processing route approach consisting of the thermally induced phase separation of the gelatin based biopolymeric mixture precursor followed by chemical-free material cross-linking. The matrix nanostructure is characterized using field emission gun scanning electron microscopy (FEG-SEM), transmission electron microscopy (TEM), wide angle X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR). The cell culture assays indicate that incorporation of 2.6 wt.% content of D-periodic atelocollagen to the gelatin material, produces a significant increase of MC3T3-E1 mouse preosteoblast cells attachment and human mesenchymal stem cells (hMSCs) proliferation, in comparison with related bare gelatin matrices. The presented results demonstrate the achievement of an efficient route to produce a cost-effective, compositionally defined and low immunogenic “collagen-like” instructive biomaterial, based on gelatin.

Anti-Ageing Protein β-Klotho Rejuvenates Diabetic Stem Cells for Improved Gene-Activated Scaffold Based Wound Healing

Skin wounds can lead to serious morbidity complications in diabetic patients due to the reduced healing potential of autologous stem cells. One reason for the low functional potency of stem cells from diabetic patients (diabetic stem cells) is attributed to their senescent-like nature. Here, we investigated if an anti-ageing protein, β-klotho, could be used to rejuvenate diabetic stem cells and to promote pro-angiogenic gene-activated scaffold (GAS)-induced functional response for wound healing applications. Human stem cells derived from the adipose tissue (adipose-derived stem cells (ADSCs)) of normal and diabetic (type 2) donors were used for the study. We report that the β-klotho priming facilitated inflammatory signal pruning by reducing interleukin-8 release by more than half while concurrently doubling the release of monocyte chemoattractant protein-1. Additionally, β-klotho priming enhanced the pro-angiogenic response of diabetic ADSCs on GAS by dampening the release of anti-angiogenic factors (i.e., pigment epithelium-derived factor, tissue inhibitor of metalloproteinase-1 and thrombospondin-1) while simultaneously supporting the expression of pro-angiogenic factors (i.e., Vascular Endothelial Growth Factor (VEGF), angiopoietin-2 and angiogenin). Finally, we show that β-klotho pre-treatment expedites the cellular expression of matrix proteins such as collagen IV and collagen VI, which are implicated in tissue maturation. Taken together, our study provides evidence that the synergistic effect of the pro-angiogenic GAS and β-klotho activation effectively accelerates the functional development of diabetic ADSCs for wound healing applications.

Chondroitin sulfate modified 3D porous electrospun nanofiber scaffolds promote cartilage regeneration

3D electrospun nanofibrous scaffolds have been developed for cartilage regeneration, however, there is no consensus on the preferable method for biocompatible scaffolds that enhance regeneration and attenuate inflammation. We designed a 3D porous electrospun polylactic acid (PLA) @gelatin-based scaffold by a novel method. Chondroitin sulfate (CS), commonly used in clinical cartilage treatment, is capable of regulating cartilage formation and inhibiting inflammation. Thus we further functionalized the 3D scaffold by crosslinking of CS, assuming that CS-functionalized scaffold (CSS) would promote cartilage regeneration and modulate inflammation. We confirmed that CSS exhibits not only appropriate reversible compressibility and mechanical property, but also appropriate biocompatibility, allowing cell proliferation. In vitro, the potential of CSS for chondrogenic differentiation was improved compared to control and PLA@gelatin scaffold as chondrogenic markers Collagen2 and Aggrecan was significantly increased. Meanwhile, significant reduction in two crucial inflammatory factors (NO and PGE2) in CSS group demonstrated inflammation inhibition. In vivo, rabbit cartilage defects were created and CSS effectively promoted cartilage repair. Additionally, superior anti-inflammation effect of CSS was demonstrated by reduction in iNOS and PGES, enzymes producing NO and PGE2, respectively by immunohistology. Our results indicated the preferable property of CSS for cartilage regeneration and its potential in immunoregulation.

Novel application of autologous micrografts in a collagen-glycosaminoglycan scaffold for diabetic wound healing

BACKGROUND

Therapeutic strategies that successfully combine two techniques-autologous micrografting and biodegradable scaffolds-offer great potential for improved wound repair and decreased scarring. In this study we evaluate the efficacy of a novel modification of a collagen-glycosaminoglycan scaffold with autologous micrografts using a murine dorsal wound model.

METHODS

db/db mice underwent dorsal wound excision and were treated with a collagen-glycosaminoglycan scaffold (CGS), a modified collagen-glycosaminoglycan scaffold (CGS+MG) or simple occlusive dressing (Blank). The modified scaffold was created by harvesting full thickness micrografts and transplanting these into the collagen-glycosaminoglycan membrane. Parameters of wound healing, including cellular proliferation, collagen deposition, keratinocyte migration, and angiogenesis were assessed.

RESULTS

The group treated with the micrograft-modified scaffold healed at a faster rate, showed greater cellular proliferation, collagen deposition, and keratinocyte migration with higher density and greater maturity of microvessels. The grafts remained viable within the scaffold with no evidence of rejection. Keratinocytes were shown to migrate from the wound border and from the micrograft edges towards the center of the wound, while cellular proliferation was present both at the wound border and wound bed.

CONCLUSION

We report successful treatment of diabetic wounds with a novel collagen-glycosaminoglycan scaffold modified with full-thickness automicrografts. Differences in cellular migration and proliferation offer maiden evidence on the mechanisms of wound healing. Clinically, the successful scaffold engraftment, micrograft viability and improved wound healing offer promising results for the development of a new therapeutic modality for wound repair.

The Role of Dermal Regenerative Templates in Complex Lower Extremity Wounds

Dermal regenerative templates (DRTs) provide an option for management of complex lower extremity wounds. DRTs may be used to achieve definitive wound closure by serving as a scaffold for local tissue infiltration. Healing with a DRT interface leads to histologic and structural properties similar to native skin. DRTs can be applied over deep wounds with exposed critical structures that may have required a local or free flap. DRTs are a valuable option for lower extremity limb reconstruction.

Complex approach to skin repair in an extensively burned child: a case study

The limited amount of donor sites and loss of dermis are major challenges in the therapy of extensively burned patients. Here, we present a complex treatment approach of an eight-year-old boy with full-thickness burns on 90% of the total body surface area, using simple and efficient techniques of tissue engineering. To obtain sufficient skin for grafting we repeatedly harvested the same anatomical areas. Acceleration of donor site healing was achieved by treatment with a suspension of noncultured autologous skin cells (NASC) and acellular porcine dermis (Xe-Derma (XD), Czech Republic). Moreover, such wound management allowed up to six reharvestings, compared with one-to-three procedures following routine treatment. Bilayer Integra template (Integra LifeSciences Corp., US) was used as the dermal substitute in over 60% of full-thickness burns. Following successful vascularisation of the neodermis in 3-4 weeks, the templates were covered with meshed split-thickness skin grafts (STSG), or Meek autografts, and facilitated by NASC/XD. We may conclude that such a 'sandwich' technique approach, combining four biological covers (Integra, STSG, NASC and XD), significantly contributed to the successful skin repair of the patient.

Scaffolds Functionalized with Matrix from Induced Pluripotent Stem Cell Fibroblasts for Diabetic Wound Healing

Diabetic foot ulcers (DFUs) are chronic wounds, with 20% of cases resulting in amputation, despite intervention. A recently approved tissue engineering product-a cell-free collagen-glycosaminoglycan (GAG) scaffold-demonstrates 50% success, motivating its functionalization with extracellular matrix (ECM). Induced pluripotent stem cell (iPSC) technology reprograms somatic cells into an embryonic-like state. Recent findings describe how iPSCs-derived fibroblasts ("post-iPSF") are proangiogenic, produce more ECM than their somatic precursors ("pre-iPSF"), and their ECM has characteristics of foetal ECM (a wound regeneration advantage, as fetuses heal scar-free). ECM production is 45% higher from post-iPSF and has favorable components (e.g., Collagen I and III, and fibronectin). Herein, a freeze-dried scaffold using ECM grown by post-iPSF cells (Post-iPSF Coll) is developed and tested vs precursors ECM-activated scaffolds (Pre-iPSF Coll). When seeded with healthy or DFU fibroblasts, both ECM-derived scaffolds have more diverse ECM and more robust immune responses to cues. Post-iPSF-Coll had higher GAG, higher cell content, higher Vascular Endothelial Growth Factor (VEGF) in DFUs, and higher Interleukin-1-receptor antagonist (IL-1ra) vs. pre-iPSF Coll. This work constitutes the first step in exploiting ECM from iPSF for tissue engineering scaffolds.

The effects of cross-linking a collagen-elastin dermal template on scaffold bio-stability and degradation

MatriDerm is a collagen-elastin dermal template that promotes regeneration in full-thickness wound repair. Due to its noncross-linked status, MatriDerm biodegrades quickly in a wound. Facilitating vascularization and dermal repair, it is desirable for MatriDerm to remain present until the wound healing process is complete, optimizing tissue regeneration and reducing wound contraction. The aim of this study was to investigate the effect of cross-linking MatriDerm on its mechanical and biological properties and to enhance its regenerative functionality. MatriDerm was chemically cross-linked and characterized in comparison with noncross-linked MatriDerm. Scaffold properties including surface morphology, protein release and mechanical strength were assessed. Cell-scaffold interaction, cell proliferation and migration were examined using human dermal fibroblasts. Scaffold biodegradation and its impact on wound healing and contraction were studied in a mouse model. Results showed that cross-linked MatriDerm displayed a small reduction in pore size, significantly less protein loss and a threefold increase in tensile strength. A significant increase in fibroblast proliferation and migration was observed in cross-linked MatriDerm with reduced scaffold contraction in vitro. In the mouse model, noncross-linked MatriDerm was almost completely biodegraded after 14 days whereas cross-linked MatriDerm remained intact. No significant difference in wound contraction was found between scaffolds. In conclusion, cross-linked MatriDerm showed a significant increase in stability and strength, enhancing its durability and cell-scaffold interaction. in vivo analysis showed cross-linked MatriDerm had a reduced biodegradation rate with a similar host response. The extended structural integrity of cross-linked MatriDerm could potentially facilitate improved skin tissue regeneration, promoting the formation of a more pliable scar.

Production and characterization of poly lactic-co-glycolic acid particles containing anti-inflammatory substances for skin lesion recovery

Poly lactic-co-glycolic acid particles are biodegradable and biocompatible drug delivery systems that provide a controlled release of drugs in specific sites. These characteristics minimize the occurrence of side effects related to overdosing. To overcome the issues associated with the conservative treatment for wound healing, the objective of this work was to develop a poly lactic-co-glycolic acid particles system to deliver anti-inflammatory compounds (epigallocatechin gallate and asiaticoside) to fibroblasts. Nanoscale (~200 nm) and microscale (~10 µm) poly lactic-co-glycolic acid particles were produced using two different protocols. Nanoscale particles reduced cell proliferation by 46% compared with untreated human skin fibroblasts, whereas microscale particles did not affect fibroblast viability significantly. The toxicity of nanoparticles and the nontoxic nature of microparticles were confirmed in live and dead cell staining experiments. In vitro drug release assays showed that particles containing epigallocatechin gallate and asiaticoside were able to release most of their payload during the first 8 h of incubation. The treatment of lipopolysaccharide-stimulated fibroblasts with epigallocatechin gallate- and asiaticoside-loaded microparticles effectively suppressed the expression of inflammatory factors: tumor necrosis factor-α, interleukin-1β, and interleukin-6. In this study, we found that the optimal size of biodegradable poly lactic-co-glycolic acid particles for the delivery of physiologically active substances to fibroblasts is about 10 μm. Moreover, our findings indicate that poly lactic-co-glycolic acid particles of this size can be effectively applied to ameliorate tissue regeneration by delivering physiologically active substances to improve skin lesion recovery.

Design and biofabrication of dermal regeneration scaffolds: role of oligomeric collagen fibril density and architecture

Aim: To evaluate dermal regeneration scaffolds custom-fabricated from fibril-forming oligomeric collagen where the total content and spatial gradient of collagen fibrils was specified. Materials & methods: Microstructural and mechanical features were verified by electron microscopy and tensile testing. The ability of dermal scaffolds to induce regeneration of rat full-thickness skin wounds was determined and compared with no fill control, autograft skin and a commercial collagen dressing. Results: Increasing fibril content of oligomer scaffolds inhibited wound contraction and decreased myofibroblast marker expression. Cellular and vascular infiltration of scaffolds over the 14-day period varied with the graded density and orientation of fibrils. Conclusion: Fibril content, spatial gradient and orientation are important collagen scaffold design considerations for promoting vascularization and dermal regeneration while reducing wound contraction.

The life-cycles of skin replacement technologies

INTRODUCTION

Skin Replacement Technologies (SRTs) emerged as skin alternatives for burns, large excisions or trauma. The original publications represent the available knowledge on a subject and can be modeled as a logistic S-curve which depicts the technology's evolution life-cycle. The Technology Innovation Maturation Evaluation (TIME) model was previously introduced to study the life-cycles of biotechnologies.

METHODS

PubMed database was searched 1900-2015 to review relevant publications. All skin replacement or regeneration products on the US market were included. The TIME model was applied to assess evolutionary patterns for each technology.

RESULTS AND DISCUSSION

Three SRT clusters were identified: processed biologics technologies (PBT), extracellular matrix technologies (EMT), and cell-based technologies (CBT). Publications on EMTs and CBTs start decades after PBTs, however, are greater in number and follow an ascending trend. PBTs reached a plateau, suggesting near-senescence. The CBT curve was non-logarithmic and the TIME model could not be applied. The technology initiation point (Ti) for PBTs was 1939 and the establishment point (Te) 1992. For EMT, Ti was 1966 and Te 2010. Sixty-one products were identified (49 EMTs, 7 CBTs, 5 PBTs). PBTs appeared 11 years after Te and EMTs four years prior Te. Thirty-seven products in the EMT category, and one in the PBT category, were developed before Te. The most common FDA regulatory mechanism for SRT was found to be 510(k) followed by HCT/P 361.

CONCLUSION

Innovation is an indicator of the evolution of technology. The number of publications can be used as a metric of this evolution and the fact that the SRT field falls under such pattern demonstrates that SRT is an innovation-based industry. EMT is the most efficient cluster. Few products from SRT registered a commercial success, and from those that did, those technologies were generally found to be part of the most productive cluster, 1st in concept, conceptually simple, easily regulated and produced, cost and clinically efficient, reimbursable, able to solve a specific problem efficiently, had a platform technology design that allowed for further innovation and adaptation for other uses and, as found by application of the TIME model, appear prior to technology establishment.

Handheld instrument for wound-conformal delivery of skin precursor sheets improves healing in full-thickness burns

The current standard of care for patients with severe large-area burns consists of autologous skin grafting or acellular dermal substitutes. While emerging options to accelerate wound healing involve treatment with allogeneic or autologous cells, delivering cells to clinically relevant wound topologies, orientations, and sizes remains a challenge. Here, we report the one-step in situ formation of cell-containing biomaterial sheets using a handheld instrument that accommodates the topography of the wound. In an approach that maintained cell viability and proliferation, we demonstrated conformal delivery to surfaces that were inclined up to 45° with respect to the horizontal. In porcine pre-clinical models of full-thickness burn, we delivered mesenchymal stem/stromal cell-containing fibrin sheets directly to the wound bed, improving re-epithelialization, dermal cell repopulation, and neovascularization, indicating that this device could be introduced in a clinical setting improving dermal and epidermal regeneration.

Experimental models for cutaneous hypertrophic scar research

Human skin wound repair may result in various outcomes with most of them leading to scar formation. Commonly seen in many cutaneous wound healing cases, hypertrophic scars are considered as phenotypes of abnormal wound repair. To prevent the formation of hypertrophic scars, efforts have been made to understand the mechanism of scarring following wound closure. Numerous in vivo and in vitro models have been created to facilitate investigations into cutaneous scarring and the development of antiscarring treatments. To select the best model for a specific study, background knowledge of the current models of hypertrophic scars is necessary. In this review, we describe in vivo and in vitro models for studying hypertrophic scars, as well as the distinct characteristics of these models. The choice of models for a specific study should be based on the characteristics of the model and the goal of the study. In general, in vivo animal models are often used in phenotypical scar formation analysis, development of antiscarring treatment, and functional analyses of individual genes. In contrast, in vitro models are chosen to pathway identification during scar formation as well as in high-throughput analysis in drug development. Besides helping investigators choose the best scarring model for their research, the goal of this review is to provide knowledge for improving the existing models and development of new models. These will contribute to the progress of scarring studies.

Comparative long-term study between two dermal regeneration templates for the reconstruction of burn scar contractures in humans: Clinical and histological results

The advent of dermal regeneration templates has fostered major advances in the treatment of acute burns and their sequelae, in the last three decades. Both data on morphological aspects of the newly-formed tissue, and clinical trials comparing different templates, are few. The goal of this study was to prospectively analyze the outcome of randomized patients treated with two of the existing templates, followed by thin skin autograft. They are both 2 mm-thick bovine collagen templates (Matriderm® and Integra®), the latter includes a superficial silicone layer. Surgery was performed on patients with impaired mobility resulting from burn sequelae (n = 12 per template) in a two-step procedure. Negative pressure therapy was applied after surgery; patients were monitored for 12 months. No intra or postoperative complications were observed. Data on scar skin quality (Vancouver scar scale), rate of mobility recovery, and graft contraction were recorded; as well as morphological analyses at light microscopical level. Improvement in mobility and skin quality were demonstrated along with graft contraction, in all patients. The double layer template showed the best performance in retraction rate, skin quality and mobility recovery. The subepidermal newly-formed connective tissue showed no histoarchitectural differences between the templates. The double layer template was not absorbed up to 12 months after placement.

Benefits of cryopreserved human amniotic membranes in association with conventional treatments in the management of full-thickness burns

The use of split-thickness skin autografts (STSA) with dermal substitutes is the gold standard treatment for third-degree burn patients. In this article, we tested whether cryopreserved amniotic membranes could be beneficial to the current treatments for full-thickness burns. Swines were subjected to standardised full-thickness burn injuries, and then were randomly assigned to treatments: (a) STSA alone; (b) STSA associated with the dermal substitute, Matriderm; (c) STSA plus human amniotic membrane (HAM); and (d) STSA associated with Matriderm plus HAM. Clinical and histological assessments were performed over time. We also reported the clinical use of HAM in one patient. The addition of HAM to classic treatments reduced scar contraction. In the presence of HAM, skin wound healing displayed high elasticity and histological examination showed a dense network of long elastic fibres. The presence of HAM increased dermal neovascularization, but no effect was observed on the recruitment of inflammatory cells to the wound. Moreover, the use of HAM with classical treatments in one human patient revealed a clear benefit in terms of elasticity. These results give initial evidence to consider the clinical application of HAM to avoid post-burn contractures and therefore facilitate functional recovery after deep burn injury.

The Basics of Integra Dermal Regeneration Template and its Expanding Clinical Applications

First developed for coverage of burn wounds, Integra (Integra LifeSciences) is a synthetic acellular dermal regeneration template that provides a base for revascularization and neodermal formation. The use of Integra has slowly grown and has now become an important consideration along the reconstructive ladder. This article reviews the basic science of Integra and provides an overview of the many expanding applications based on anatomic location.

Mechanisms of pore formation in hydrogel scaffolds textured by freeze-drying

Whereas freeze-drying is a widely used method to produce porous hydrogel scaffolds, the mechanisms of pore formation involved in this process remained poorly characterized. To explore this, we focused on a cross-linked polysaccharide-based hydrogel developed for bone tissue engineering. Scaffolds were first swollen in 0.025% NaCl then freeze-dried at low cooling rate, i.e. -0.1 °C min^-1, and finally swollen in aqueous solvents of increasing ionic strength. We found that scaffold's porous structure is strongly conditioned by the nucleation of ice. Electron cryo-microscopy of frozen scaffolds demonstrates that each pore results from the growth of one to a few ice grains. Most crystals were formed by secondary nucleation since very few nucleating sites were initially present in each scaffold (0.1 nuclei cm^-3 °C^-1). The polymer chains are rejected in the intergranular space and form a macro-network. Its characteristic length scale coincides with the ice grain size (160 μm) and is several orders of magnitude greater than the mesh size (90 nm) of the cross-linked network. After sublimation, the ice grains are replaced by macro-pores of 280 μm mean size and the resulting dry structure is highly porous, i.e. 93%, as measured by high-resolution X-ray tomography. In the swollen state, the scaffold mean pore size decreases in aqueous solvent of increasing ionic strength (120 µm in 0.025% NaCl and 54 µm in DBPS) but the porosity remains the same, i.e. 29% regardless of the solvent. Finally, cell seeding of dried scaffolds demonstrates that the pores are adequately interconnected to allow homogenous cell distribution. STATEMENT OF SIGNIFICANCE: The fabrication of hydrogel scaffolds is an important research area in tissue engineering. Hydrogels are textured to provide a 3D-framework that is favorable for cell proliferation and/or differentiation. Optimum hydrogel pore size depends on its biological application. Producing porous hydrogels is commonly achieved through freeze-drying. However, the mechanisms of pore formation remain to be fully understood. We carefully analyzed scaffolds of a cross-linked polysaccharide-based hydrogel developed for bone tissue engineering, using state-of-the-art microscopic techniques. Our experimental results evidenced the shaping of hydrogel during the freezing step, through a specific ice-templating mechanism. These findings will guide the strategies for controlling the porous structure of hydrogel scaffolds.

Biomaterial Enhanced Regeneration Design Research for Skin and Load Bearing Applications

Biomaterial enhanced regeneration (BER) falls mostly under the broad heading of Tissue Engineering: the use of materials (synthetic and natural) usually in conjunction with cells (both native and genetically modified as well as stem cells) and/or biological response modifiers (growth factors and cytokines as well as other stimuli, which alter cellular activity). Although the emphasis is on the biomaterial as a scaffold it is also the use of additive bioactivity to enhance the healing and regenerative properties of the scaffold. Enhancing regeneration is both moving more toward regeneration but also speeding up the process. The review covers principles of design for BER as well as strategies to select the best designs. This is first general design principles, followed by types of design options, and then specific strategies for applications in skin and load bearing applications. The last section, surveys current clinical practice (for skin and load bearing applications) including limitations of these approaches. This is followed by future directions with an attempt to prioritize strategies. Although the review is geared toward design optimization, prioritization also includes the commercializability of the devices. This means a device must meet both the clinical performance design constraints as well as the commercializability design constraints.

Managing Wounds with Exposed Bone and Tendon with an Esterified Hyaluronic Acid Matrix (eHAM): A Literature Review and Personal Experience

The loss of extracellular matrix in combination with the exposure of structures such as bone and tendon pose a major challenge; the development of granulation tissue and subsequent reepithelialization over these structures is extremely slow and often may not happen at all. Replacement of the matrix has been shown to significantly increase the chances of healing since, with revascularization of the matrix, a wound bed is created that may either heal by secondary intention or via the application of a skin graft. A literature search on an esterified hyaluronic acid-based matrix (eHAM) returned five articles on the treatment of wounds with tendon and bone loss in which the eHAM was used. The etiologies of the wounds described varied among the articles, as did treatment modalities. However, all of them received proper debridement of necrosis with subsequent (although not always immediately) application of the eHAM. A very high percentage of all wounds reached the different primary endpoints in the studies, which were complete reepithelialization, complete coverage with granulation tissue and/or 10% coverage of the original wound size with epithelium, the latter being a strong indicator of the wound continuing to heal. The individual authors concluded that the esterified hyaluronic acid matrix (eHAM) is a valuable tool to assist in the complete healing of difficult to heal wounds.

Fibrin as a Tissue Adhesive and Scaffold with an Angiogenic Agent (FGF-1) to Enhance Burn Graft Healing In Vivo and Clinically

There is a need for a strategy to reduce scarring in meshed skin graft healing leading to a better cosmetic result without a significant increase in cost. The strategy in this paper is to increase the closure rate of a meshed skin graft to reduce scarring, which should also decrease the infection rate. Specifically, we used fibrin glue to attach all parts of the graft to the wound bed and added in an angiogenic growth factor and made the fibrin porous to further help the growth of blood vessels from the wound bed into the graft. There was a 10-day animal study and a one-month clinical study. Neither making the fibrin porous or adding an angiogenic agent (i.e., fibroblast growth factor-1 (FGF-1)) seemed to make a significant improvement in vivo or clinically. The use of fibrin on a meshed skin graft appears to speed up the regenerative healing rate leading to less scarring in the holes in the mesh. It appears to shorten the healing time by five days and keep the tissue stiffness close to normal levels vs. the doubling of the stiffness by the controls. A larger clinical study, however, is needed to definitively prove this benefit as well as the mechanism for this improvement.

The Feasibility of Using Pulsatile Electromagnetic Fields (PEMFs) to Enhance the Regenerative Ability of Dermal Biomaterial Scaffolds

Degradable regenerative scaffolds usually require adjunctive treatment to meet the clinical healing performance requirements. This study was designed to look at pulsatile electromagnetic fields (PEMF) as an adjunctive therapy for these scaffolds in skin wounds; however, no scaffold was used in this study in order to isolate the effects of PEMF alone. In this study, New Zealand rabbits received four full-thickness defects with a size of 3 cm × 3 cm on the dorsolateral aspect. The rabbits in the treatment group were placed in a chamber and subjected to a PEMF at six different predetermined frequency and intensity combinations for 2 h a day for a 2-week period. At the end of the 2-week period, the animals were sacrificed and tissue samples were taken. Half of each tissue sample was used for histomorphometric analysis and the other half was for tensile testing. The study showed an increased healing response by all the PEMF treatments compared to that in the control, although different combinations led to increases in different aspects of the healing response. This suggests that although some treatments are better for the critical clinical parameter—healing rate, it might be beneficial to use treatments in the early stages to increase angiogenesis before the treatment is switched to the one best for the healing rate to get an even better haling rate.

The development of a treatment pathway for dermal regenerative matrix (DRM)

The process of standardising burn care and creating protocols within burn centres has, at its core, evidence-based practice principles combined with the clinical experiences of burn care specialists. Although protocols and pathways have been created for certain topics of burn care, they tend to be tailored to the local individual needs of each burn centre, which is a limiting factor for consideration of larger/nationwide approaches. In order to continue to improve the short and long term outcomes after burn injuries, such as increasing the survival rate, reduction in the incidence of sepsis and organ failure, and improving wound healing and scarring, more generalised care pathways combining the recommendations of a nationwide working group of burn care specialists should be created around the topics of interest to ultimately improve patients' outcomes. We describe the steps put in place in Canada to design and adopt a nationwide protocol from a single burn centre on the topic of wound healing and dermal substitutes as the initial exemplary process. This report summarizes the Canadian experience for this type of initiative, which can be used as framework for developing additional guidelines/protocols in other relevant burn care related topics in Canada or other countries.