The Use of Biologic Scaffolds in the Treatment of Chronic Nonhealing Wounds

Uso de una matriz autóloga en el tratamiento de úlceras de pie diabético, con espectroscopia de infrarrojo cercano y medidor de pH dérmico

OBJECTIVE

Evaluate the efficiency of an autologous whole blood clot (WBC) matrix on diabetic foot ulcers (DFU), and analyse its immune response with near-infrared spectroscopy (NIRS) and pH measurement.

METHOD

Three patients were treated with a WBC. The matrix was produced at the point of care, using a WBC system. A WBC gel was formed and applied onto the wounds. The gel remained in place with primary and secondary dressings.

RESULTS

Wound-size reduction was 70% after two applications, 97.6% after three applications, and 90.9% after four applications. The NIRS skeletal muscle oxygen saturation (StO2) increased in all cases.

CONCLUSION

The autologous matrix was efficient in treating DFU. The wound area surface reduced after each application and wound healing was achieved in all cases. More studies are needed to understand the benefits of using a WBC matrix on DFU.

Skin wound healing assisted by angiogenic targeted tissue engineering: A comprehensive review of bioengineered approaches

Skin injuries and in particular, chronic wounds, are one of the major prevalent medical problems, worldwide. Due to the pivotal role of angiogenesis in tissue regeneration, impaired angiogenesis can cause several complications during the wound healing process and skin regeneration. Therefore, induction or promotion of angiogenesis can be considered as a promising approach to accelerate wound healing. This article presents a comprehensive overview of current and emerging angiogenesis induction methods applied in several studies for skin regeneration, which are classified into the cell, growth factor, scaffold, and biological/chemical compound-based strategies. In addition, the advantages and disadvantages of these angiogenic strategies along with related research examples are discussed in order to demonstrate their potential in the treatment of wounds.

Composite sponges from sheep decellularized small intestinal submucosa for treatment of diabetic wounds

Despite the fast development of technology in the world, diabetic foot wounds cause deaths and massive economical losses. Diabetes comes first among the reasons of non traumatic foot amputations. To reduce the healing time of these fast progressing wounds, effective wound dressings are in high demand. In our study, sheep small intestinal submucosa (SIS) based biocompatible sponges were prepared after SIS decellularization and their wound healing potential was investigated on full thickness skin defects in a diabetic rat model. The decellularized SIS membranes had no cytotoxic effects on human fibroblasts and supported capillary formation by HUVECs in a fibroblast-HUVEC co-culture. Glutaraldehyde crosslinked sponges of three different compositions were prepared to test in a diabetic rat model: gelatin (GS), gelatin: hyaluronic acid (GS:HA) and gelatin: hyaluronic acid: SIS (GS:HA:SIS). The GS:HA:SIS sponges underwent a 24.8 ± 5.4% weight loss in a 7-day in vitro erosion test. All sponges had a similar Young's modulus under compression but GS:HA:SIS had the highest (5.00 ± 0.04 kPa). Statistical analyses of histopathological results of a 12-day in vivo experiment revealed no significant difference among the control, GS, GS:HA, and GS:HA:SIS transplanted groups in terms of granulation tissue thickness, collagen deposition, capillary vessel formation, and foreign body reaction (P > 0.05). On the other hand, in the GS:HA:SIS transplanted group 80% of the animals had a complete epidermal regeneration and this was significantly different than the control group (30%, P < 0.05). Preclinical studies revealed that the ECM of sheep small intestinal submucosa can be used as an effective biomaterial in diabetic wound healing.

The sequential effects of a multifactorial detergent based decellularization process on bovine pericardium

Decellularization is a promising method for obtaining extracellular matrix scaffolds (ECM) to be used as replacement material in reconstructive procedures. The effectiveness of decellularization and the alterations to the ECM vary, depending on several factors, including the tissue source, composition and density. With an optimized decellularization process, decellularized scaffolds can preserve the spatial and temporal ECM microenvironment, which play an integral role in modulating cell migration, proliferation and differentiation. The exploration of a variety of decellularization protocols has led to mixed outcomes and comparisons between decellularization protocols could not attribute these differences to any single step in a multiple-step process. This study aimed to characterize the effects of each step of a multifactorial decellularization method on the scaffold structure and mechanical integrity of bovine pericardium. Each step of the decellularization process and the effect on the tissue was assessed using hematoxylin and eosin staining, electron microscopy, total protein, ECM protein and triglyceride quantification. The biomechanical properties were assessed using uniaxial tensile strength testing. Cell lysis occurred mainly during the detergent and alcohol steps. Collagen structural damage occurred during the detergent and alcohol steps, with no significant decreased in collagen concentration. No significant damage to elastin could be shown throughout the process, however glycosaminoglycans were significantly removed by detergent treatment. Triglycerides were removed mostly by the alcohol treatment. The strength of the pericardium decreased somewhat after each step of the protocol. It is important to characterize each decellularization protocol with regards to the decellularization efficiency and the effect on the ECM proteins structure and function to accurately evaluatein vivooutcomes.

Nanotechnology-Based Medical Devices for the Treatment of Chronic Skin Lesions: From Research to the Clinic

Chronic wounds, such as pressure ulcers, diabetic ulcers, venous ulcers and arterial insufficiency ulcers, are lesions that fail to proceed through the normal healing process within a period of 12 weeks. The treatment of skin chronic wounds still represents a great challenge. Wound medical devices (MDs) range from conventional and advanced dressings, up to skin grafts, but none of these are generally recognized as a gold standard. Based on recent developments, this paper reviews nanotechnology-based medical devices intended as skin substitutes. In particular, nanofibrous scaffolds are promising platforms for wound healing, especially due to their similarity to the extracellular matrix (ECM) and their capability to promote cell adhesion and proliferation, and to restore skin integrity, when grafted into the wound site. Nanotechnology-based scaffolds are emphasized here. The discussion will be focused on the definition of critical quality attributes (chemical and physical characterization, stability, particle size, surface properties, release of nanoparticles from MDs, sterility and apyrogenicity), the preclinical evaluation (biocompatibility testing, alternative in vitro tests for irritation and sensitization, wound healing test and animal wound models), the clinical evaluation and the CE (European Conformity) marking of nanotechnology-based MDs.

Effectiveness of fire needle combining with moist healing dressing to promote the growth of granulation tissue in chronic wounds: A case report

In this case study, we analyzed the wound-healing process of a patient with a chronic wound who underwent fire needle treatment, and we tracked the coverage of granulation tissue and decrease of slough and exudate. An 85-year-old man had repeated right shoulder and back pain, itching, and skin festering for more than 1.5 years. A fire needle was administered combined with moist dressing once every 5 days to promote wound healing. After six rounds of fire needle treatment, granulation tissue formed over the surface of the wound base, the depth of the wound had become shallow, and the wound area was reduced. No complications occurred during the intervention. Fire needle therapy combined with a moist wound-healing dressing can be an effective alternative approach in managing chronic wounds.

The Antimicrobial Effectiveness and Cytotoxicity of the Antibiotic-Loaded Chitosan: ECM Scaffolds

Background: The development of multifunctional wound dressings with the ability to control hemostasis, limit infection and promote rapid wound healing and constructive tissue remodeling has been a challenge for many years. In view of these challenges, a hybrid scaffold platform was developed that combined two different extracellular matrices (ECM): ECM from decellularized mammalian tissue and ECM (chitosan) from crustaceans. Both types of ECM have well established clinical benefits that support and promote wound healing and control hemostasis. This scaffold platform could also be augmented with antibiotics to provide bactericidal activity directly to the wound site. Methods: Four different scaffold formulations were developed containing chitosan supplemented with either 20% or 50% urinary bladder matrix (UBM) hydrogel or 1% (w/v) or 10% (w/v) UBM–ECM particulates. 100% chitosan scaffolds were used as controls. The scaffolds were augmented with either minocycline or rifampicin. Escherichia Coli and Staphylococcus Aureus were used to assesses antimicrobial efficacy and duration of activity, while neutral red uptake assays were performed to establish direct and indirect cytotoxicity. Results: Results showed that scaffold handling properties, scaffold integrity over time and the efficacy and release rate of loaded antibiotics could be modified by altering scaffold composition. Moreover, antibiotics were easily released from the scaffold and could remain effective for up to 24 h by modifying the scaffold composition. Variable results with cytotoxicity testing show that further work is required to optimize the scaffold formulations but these proof of principle experiments suggest that these scaffolds have potential as bioactive wound dressings.

Modulating neutrophil extracellular traps for wound healing

A diabetic microenvironment primes neutrophils for NETosis, a process of formation of neutrophil extracellular traps (NETs) that further degrades the neutrophils and makes them unavailable for the early-stage inflammatory processes. Mechanistically, simple modification of arginine residues of histones to citrulline by peptidylarginine deiminase (PAD4) enzyme is considered to be a prerequisite for NETosis. In fact, under diabetic conditions, an increase in PAD4-mediated NET formation is considered as one of the reasons for impaired wound healing. Therefore, in the present work, an alginate-GelMa (generally recognized as safe category by FDA, USA) based hydrogel scaffold containing a tripeptide (Thr-Asp-F-amidine) that inhibits PAD4 is developed, based on the hypothesis that inhibiting PAD4 enzyme might offer a way to enhance wound healing under diabetic conditions. The scaffolds are thoroughly characterized for their physicochemical and biological properties. Furthermore, neutrophil-scaffold interactions in terms of NETosis ability and release of other related biomarkers are studied. The wound healing ability is evaluated by a cell migration assay. In vivo wound healing efficacy of the developed scaffolds is demonstrated using a diabetic rat model. The results suggest a reduction in NETosis in the presence of a PAD4 inhibitor. Thus, the study demonstrates a novel scaffold system to deliver the PAD4 inhibitor that can be used to modulate NETosis and improve wound healing.

Enhanced wound healing via collagen-turnover-driven transfer of PDGF-BB gene in a murine wound model

Wound healing is a complex biological process that requires coordinated cell proliferation, migration, and extracellular matrix production/remodeling, all of which are inhibited/delayed in chronic wounds. In this study, a formulation was developed that marries a fibrin-based, provisional-like matrix with collagen mimetic peptide (CMP)/PDGF gene-modified collagens, leading to the formation of robust gels that supported temporally controlled PDGF expression and facile application within the wound bed. Analysis employing in vitro co-gel scaffolds confirmed sustained and temporally controlled gene release based on matrix metalloproteinase (MMP) activity, with ~30% higher PDGF expression in MMP producing fibroblasts as-compared with non-MMP-expressing cells. The integration of fibrin with the gene-modified collagens resulted in co-gels that strongly supported both fibroblast cell recruitment/invasion as well as multiple aspects of the longer-term healing process. The excisional wound healing studies in mice established faster wound closure using CMP-modified PDGF polyplex-loaded co-gels, which exhibited up to 24% more wound closure (achieved with ~2 orders of magnitude lower growth factor dosing) after 9 days as compared to PDGF-loaded co-gels, and 19% more wound closure after 9 days as compared to CMP-free polyplex loaded co-gels. Moreover, minimal scar formation as well as improved collagen production, myofibroblast activity, and collagen orientation was observed following CMP-modified PDGF polyplex-loaded co-gel application on wounds. Taken together, the combined properties of the co-gels, including their stability and capacity to control both cell recruitment and cell phenotype within the murine wound bed, strongly supports the potential of the co-gel scaffolds for improved treatment of chronic non-healing wounds.

Regenerative Wound Surgery: Practical Application of Regenerative Medicine in the OR

Chronic nonhealing wounds cause significant morbidity and mortality and remain a challenging condition to treat. Regenerative wound surgery involves operative debridement of wounds to remove dead and healing-impaired tissue and bacterial contamination and, subsequently, the application of regenerative medicine treatments to accelerate healing. Regenerative treatments aim to restore native tissue structure and function by targeting biological mechanisms underlying impaired healing. A wide range of regenerative modalities are used for treating chronic and complex wounds, including decellularized scaffolds, living engineered donor tissues, autologous stem cells, and recombinant growth factors. Each of these modalities has specific and sometimes complex requirements for implementation. The advanced wound care team, including OR staff members, should be aware of how these products are used and regulated. This article highlights some of the common and emerging regenerative treatments that are applied in wound surgery and focuses on how the products are used practically in the OR.

A liposome/gelatin methacrylate nanocomposite hydrogel system for delivery of stromal cell-derived factor-1α and stimulation of cell migration

Chronic, non-healing skin and soft tissue wounds are susceptible to infection, difficult to treat clinically, and can severely reduce a patient's quality of life. A key aspect of this issue is the impaired recruitment of mesenchymal stem cells (MSCs), which secrete regenerative cytokines and modulate the phenotypes of other effector cells that promote healing. We have engineered a therapeutic delivery system that can controllably release the pro-healing chemokine stromal cell derived factor-1α (SDF-1α) to induce the migration of MSCs. In order to protect the protein cargo from hydrolytic degradation and control its release, we have loaded SDF-1α in anionic liposomes (lipoSDF) and embedded them in gelatin methacrylate (GelMA) to form a nanocomposite hydrogel. In this study, we quantify the release of SDF-1α from our hydrogel system and measure the induced migration of MSCs in vitro via a transwell assay. Lastly, we evaluate the ability of this system to activate intracellular signaling in MSCs by using Western blots to probe for the phosphorylation of key proteins in the mTOR pathway. To our knowledge, this is the first study to report the delivery of liposomal SDF-1α using a nanocomposite approach. The results of this study expand on our current understanding of factors that can be modified to affect MSC behavior and phenotype. Furthermore, our findings contribute to the development of new hydrogel-based therapeutic delivery strategies for clinical wound healing applications. STATEMENT OF SIGNIFICANCE: Chronic, non-healing wounds promote an inflammatory environment that inhibits the migration of mesenchymal stem cells (MSCs), which secrete pro-healing and regenerative cytokines. The goal of this project is to apply principles of tissue engineering to achieve controllable release of the pro-healing chemokine SDF-1α to modulate the intracellular signaling and migratory behavior of MSCs. In this work, we introduce a nanocomposite strategy to tailor the release of SDF-1α using a liposome/gelatin methacrylate hydrogel approach. We are the first group to report the delivery of liposomal SDF-1α using this strategy. Our findings aim to further elucidate the role of MSCs in directing wound healing and guide the development of immunomodulatory and therapeutic delivery strategies for clinical wound healing applications.

A case report on the effect of micrografting in the healing of chronic and complex burn wounds

Different approaches can be used to repair extensive burn injury and chronic wounds, including full and split thickness skin grafts, temporising matrices and scaffolds, and composite cultured skin products. The use of non-cultured or autologous skin cells suspension in chronic burn is well established, but despite this no significant literature has been realized. The Rigenera micrografting technology is an innovative technique allowing to obtain a suspension of autologous micrografts that can be applied over the wounds in a combined methodology specifically developed and based on the both injections of the wound edges and spraying over the wound bed of this suspension. A black male patient with open wounds on the back already treated with a traditional split skin graft, present a 10% of wounds not healing. Then, the patient was treated with micrografts suspension obtained by mechanical disaggregation of small split skin biopsies using the Rigeneracons medical device. Micrografts were directly injected and sprayed in the wounds. The combination of injection and sprayed micrografts solution over the wounds achieved full closure over 10% over a period of 6 months. The follow up more than 2 years showed stable wounds with no breakdown in the epidermis. The final cosmetic and functional results obtained with micrografting on chronic burn wounds is a valid alternative when all the other options cannot provide wound closure.

Natural composite dressings based on collagen, gelatin and plant bioactive compounds for wound healing: A review

Skin wound dressings are commonly used to stimulate and enhance skin tissue repair. Even if wounds seem easy to repair for clinicians and to replicate in an in vitro set-up for scientists, chronic wounds remain currently an open challenge in skin tissue engineering for patients with complementary diseases. The seemingly simple process of skin healing hides a heterogenous sequence of events, specific timing, and high level of organization and coordination among the involved cell types. Taken together, all these aspects make wound healing a unique process, but we are not yet able to completely repair the chronic wounds or to reproduce them in vitro with high fidelity. This review highlights the main characteristics and properties of a natural polymer, which is widely used as biomaterial, namely collagen and of its denatured form, gelatin. Available wound dressings based on collagen/gelatin and proposed variants loaded with bioactive compounds derived from plants are presented. Applications of these composite biomaterials are discussed with emphasis on skin wound healing. A perspective on current issues is given in the light of future research. The emerging technologies support the development of innovative dressings based exclusively on natural constituents, either polymeric or bioactive compounds.

Distinct Patterns of Hair Graft Survival After Transplantation Into 2 Nonhealing Ulcers: Is Location Everything?

BACKGROUND

Studies highlighting the role of hair follicles (HFs) in wound healing have raised the challenge of bringing this knowledge to clinical applications. A successful translation is the transplantation of scalp HFs into chronic wounds to promote healing.

OBJECTIVE

To characterize scar formation and hair growth in nonhealing ulcers after transplantation.

PATIENTS AND METHODS

Nonhealing ulcers were treated with hair transplantation to promote wound healing. Hair follicles were harvested from the patient's scalp and inserted into the wound bed. Wound repair and hair growth were assessed clinically. Further analyses were performed in situ, using biopsies from the central and peripheral scar.

RESULTS

Rapid wound closure and differences of scar quality and hair growth between the central and peripheral wound areas were observed: the periphery healed with no hair shaft survival and an almost scarless appearance, the center healed with a fibrotic scar, with some hair shaft growth. In situ analyses revealed differences in dermal remodeling and collagen formation between central and peripheral scar areas.

CONCLUSION

Besides confirming the effectiveness of this therapy to promote wound healing in human skin, location-dependent disparities in scar quality and hair growth raise the intriguing question whether they are due to clinically important differences in mechanical forces and/or wound microenvironments between ulcer center and periphery.

Fabrication Strategies of Scaffolds for Delivering Active Ingredients for Tissue Engineering

Designing scaffolds with optimum properties is an essential factor for tissue engineering success. They can be seeded with isolated cells or loaded with drugs to stimulate the body ability to repair or regenerate the injured tissues by acting as centers for new tissue formation. Recently, scaffolds gained a significant interest as principal candidates for tissue engineering due to overcoming the autograft or allograft's associated problems. The advancement of the tissue engineering field relies mainly on the introduction of new biomaterials for scaffolds' fabrication. This review presents and criticizes different scaffolds' fabrication techniques with particular emphasis on the fibrous, injectable in situ forming, foam, 3D freeze-dried, 3D printed, and 4D scaffolds. This article highlights on scaffolds' composition which would be beneficial for developing scaffolds that could potentially help to meet the demand for both drug delivery and tissue regeneration.

Decellularization and preservation of human skin: A platform for tissue engineering and reconstructive surgery

A matrix derived from natural tissue functions as a highly biocompatible and versatile scaffold for tissue engineering applications. It can act as a supportive construct that provides a niche for colonization by host cells. In this work, we describe a cost-effective, reliable and reproducible protocol for decellularization and preservation of human skin as a potential soft tissue replacement. The decellularized human skin is achieved using purely chemical agents without any enzymatic steps. The suitability of the proposed method for the preservation of the extracellular matrix (ECM) structure and its main components and integrity were evaluated using histological and immunohistochemical analysis. Cryopreservation and final sterility were conducted using programmable freeze-drying and gamma irradiation. The architecture, basement membrane and 3D structure of ECM can be successfully preserved after decellularization. Our protocol was found to be appropriate to maintain key proteins such as collagen type I, III, IV and laminin in the structure of final scaffold. This protocol offers a novel platform for the preparation of a dermal substitute for potential clinical applications. STATEMENT OF SIGNIFICANCE: Clinical application of naturally-based scaffolds for verity of health problems obliges development of a reproducible and effective technology that does not change structural and compositional material properties during scaffold preparation and preservation. Lack of an effective protocol for the production of biological products using decellularization method is still remaining. This effort is directing to solve this challenge in order to accomplish the off-the -shelf availability of decellularized dermal scaffold in market for clinical application.

Acellular and cellular approaches to improve diabetic wound healing

Chronic diabetic wounds represent a huge socioeconomic burden for both affected individuals and the entire healthcare system. Although the number of available treatment options as well as our understanding of wound healing mechanisms associated with diabetes has vastly improved over the past decades, there still remains a great need for additional therapeutic options. Tissue engineering and regenerative medicine approaches provide great advantages over conventional treatment options, which are mainly aimed at wound closure rather than addressing the underlying pathophysiology of diabetic wounds. Recent advances in biomaterials and stem cell research presented in this review provide novel ways to tackle different molecular and cellular culprits responsible for chronic and nonhealing wounds by delivering therapeutic agents in direct or indirect ways. Careful integration of different approaches presented in the current article could lead to the development of new therapeutic platforms that can address multiple pathophysiologic abnormalities and facilitate wound healing in patients with diabetes.

Biomaterials to Mimic and Heal Connective Tissues

Connective tissue is one of the four major types of animal tissue and plays essential roles throughout the human body. Genetic factors, aging, and trauma all contribute to connective tissue dysfunction and motivate the need for strategies to promote healing and regeneration. The goal here is to link a fundamental understanding of connective tissues and their multiscale properties to better inform the design and translation of novel biomaterials to promote their regeneration. Major clinical problems in adipose tissue, cartilage, dermis, and tendon are discussed that inspire the need to replace native connective tissue with biomaterials. Then, multiscale structure-function relationships in native soft connective tissues that may be used to guide material design are detailed. Several biomaterials strategies to improve healing of these tissues that incorporate biologics and are biologic-free are reviewed. Finally, important guidance documents and standards (ASTM, FDA, and EMA) that are important to consider for translating new biomaterials into clinical practice are highligted.

Skin tissue engineering: wound healing based on stem-cell-based therapeutic strategies

Normal wound healing is a dynamic and complex multiple phase process involving coordinated interactions between growth factors, cytokines, chemokines, and various cells. Any failure in these phases may lead wounds to become chronic and have abnormal scar formation. Chronic wounds affect patients' quality of life, since they require repetitive treatments and incur considerable medical costs. Thus, much effort has been focused on developing novel therapeutic approaches for wound treatment. Stem-cell-based therapeutic strategies have been proposed to treat these wounds. They have shown considerable potential for improving the rate and quality of wound healing and regenerating the skin. However, there are many challenges for using stem cells in skin regeneration. In this review, we present some sets of the data published on using embryonic stem cells, induced pluripotent stem cells, and adult stem cells in healing wounds. Additionally, we will discuss the different angles whereby these cells can contribute to their unique features and show the current drawbacks.

A value analysis of microsurgical lower extremity reconstruction vs. acellular urinary bladder matrix (UBM) for radiation wounds of the lower extremity

In the USA, external beam radiation is offered to patients as an alternative to surgery for non-melanoma skin cancers. While this technique may be useful in highly specific patient populations, recalcitrant chronic radiation wounds can result. These complex wounds ultimately may require major reconstructive surgery to achieve closure. Porcine urinary bladder matrix (UBM) may be effective in the treatment of radiation wounds and eliminating the need for vascularized tissue transfers. A case report of an elderly male with bilateral radiation wounds of the lower extremity, one extremity treated with free flap reconstruction and the other with porcine urinary bladder matrix, is presented.

Current and Future Perspectives on Skin Tissue Engineering: Key Features of Biomedical Research, Translational Assessment, and Clinical Application

The skin is responsible for several important physiological functions and has enormous clinical significance in wound healing. Tissue engineered substitutes may be used in patients suffering from skin injuries to support regeneration of the epidermis, dermis, or both. Skin substitutes are also gaining traction in the cosmetics and pharmaceutical industries as alternatives to animal models for product testing. Recent biomedical advances, ranging from cellular-level therapies such as mesenchymal stem cell or growth factor delivery, to large-scale biofabrication techniques including 3D printing, have enabled the implementation of unique strategies and novel biomaterials to recapitulate the biological, architectural, and functional complexity of native skin. This progress report highlights some of the latest approaches to skin regeneration and biofabrication using tissue engineering techniques. Current challenges in fabricating multilayered skin are addressed, and perspectives on efforts and strategies to meet those limitations are provided. Commercially available skin substitute technologies are also examined, and strategies to recapitulate native physiology, the role of regulatory agencies in supporting translation, as well as current clinical needs, are reviewed. By considering each of these perspectives while moving from bench to bedside, tissue engineering may be leveraged to create improved skin substitutes for both in vitro testing and clinical applications.

Biomaterials: Foreign Bodies or Tuners for the Immune Response?

The perspectives of regenerative medicine are still severely hampered by the host response to biomaterial implantation, despite the robustness of technologies that hold the promise to recover the functionality of damaged organs and tissues. In this scenario, the cellular and molecular events that decide on implant success and tissue regeneration are played at the interface between the foreign body and the host inflammation, determined by innate and adaptive immune responses. To avoid adverse events, rather than the use of inert scaffolds, current state of the art points to the use of immunomodulatory biomaterials and their knowledge-based use to reduce neutrophil activation, and optimize M1 to M2 macrophage polarization, Th1 to Th2 lymphocyte switch, and Treg induction. Despite the fact that the field is still evolving and much remains to be accomplished, recent research breakthroughs have provided a broader insight on the correct choice of biomaterial physicochemical modifications to tune the reaction of the host immune system to implanted biomaterial and to favor integration and healing.

Cell encapsulation: Overcoming barriers in cell transplantation in diabetes and beyond

Cell-based therapy is emerging as a promising strategy for treating a wide range of human diseases, such as diabetes, blood disorders, acute liver failure, spinal cord injury, and several types of cancer. Pancreatic islets, blood cells, hepatocytes, and stem cells are among the many cell types currently used for this strategy. The encapsulation of these "therapeutic" cells is under intense investigation to not only prevent immune rejection but also provide a controlled and supportive environment so they can function effectively. Some of the advanced encapsulation systems provide active agents to the cells and enable a complete retrieval of the graft in the case of an adverse body reaction. Here, we review various encapsulation strategies developed in academic and industrial settings, including the state-of-the-art technologies in advanced preclinical phases as well as those undergoing clinical trials, and assess their advantages and challenges. We also emphasize the importance of stimulus-responsive encapsulated cell systems that provide a "smart and live" therapeutic delivery to overcome barriers in cell transplantation as well as their use in patients.

Tunable Hydrogels Derived from Genetically Engineered Extracellular Matrix Accelerate Diabetic Wound Healing

Hydrogels composed of solubilized decellularized extracellular matrix (ECM) are attractive materials because they combine the complexity of native ECM with injectability and ease of use. Nevertheless, these materials are typically only tunable by altering the concentration, which alters the ligand landscape, or by incorporating synthetic components, which can result in an unfavorable host response. Herein, we demonstrate the fabrication of genetically tunable ECM-derived materials, by utilizing wild type (WT) and (thrombospondin-2 knockout) TSP-2 KO decellularized skins to prepare hydrogels. The resulting materials exhibited distinct mechanical properties characterized by rheology and different concentrations of collagens when characterized by quantitative proteomics. Mixtures of the gels achieved intermediate effects between the WT and the KO, permitting tunability of the gel properties. In vivo, the hydrogels exhibited tunable cell invasion with a correlation between the content of TSP-2 KO hydrogel and the extent of cell invasion. Additionally, TSP-2 KO hydrogels significantly improved diabetic wound healing at 10 and 21 days. Furthermore, hydrogels derived from genetically engineered in vitro cell-derived matrix mimicked the trends observed for tissue-derived matrix, providing a platform for faster screening of novel manipulations and easier clinical translation. Overall, we demonstrate that genetic engineering approaches impart tunability to ECM-based hydrogels and can result in materials capable of enhanced regeneration.

Efficacy and safety of extracorporeal shock wave therapy for acute and chronic soft tissue wounds: A systematic review and meta-analysis

This study aimed to evaluate and compare the effects of extracorporeal shock wave therapy (ESWT) and conventional wound therapy (CWT) for acute and chronic soft tissue wounds. All English-language articles on ESWT for acute and chronic soft tissue wounds indexed in PubMed, Medline, Embase, Cochrane Central Register of Controlled Trials, Cochrane Library, Physiotherapy Evidence Database, and HealthSTAR published prior to June 2017 were included, as well as corresponding articles cited in reference lists of related review articles. The methodological quality of the selected studies was assessed with the Cochrane Collaboration's "risk of bias" tool. Study design, subject demographics, wound aetiology, treatment protocols, assessment indexes, and follow-up duration were extracted. The fixed or random-effects model was used to calculate the pooled effect sizes according to studies' heterogeneity. Ten randomised controlled trials (RCTs) involving 473 patients were included in this systematic review and meta-analysis. The meta-analysis showed that ESWT statistically significantly increased the healing rate of acute and chronic soft tissue wounds 2.73-fold (odds ratio, OR = 3.73, 95% confidence interval, CI: 2.30-6.04, P < .001) and improved wound-healing area percentage by 30.45% (Standardized Mean Difference (SMD) = 30.45; 95% CI: 23.79-37.12; P < .001). ESWT reduced wound-healing time by 3 days (SMD = -2.86, 95% CI:-3.78 to -1.95, P < .001) for acute soft tissue wounds and 19 days (SMD = -19.11, 95% CI: -23.74 to -14.47, P < .001) for chronic soft tissue wounds and the risk of wound infection by 53% (OR = 0.47, 95% CI: 0.24-0.92, P = .03) when compared with CWT alone. Serious adverse effects were not reported. ESWT showed better therapeutic effects on acute and chronic soft tissue wounds compared with CWT alone. However, higher-quality and well-controlled RCTs are needed to further assess the role of ESWT for acute and chronic soft tissue wounds.

Stem Cells for Skeletal Muscle Tissue Engineering

Volumetric muscle loss (VML) is a debilitating condition wherein muscle loss overwhelms the body's normal physiological repair mechanism. VML is particularly common among military service members who have sustained war injuries. Because of the high social and medical cost associated with VML and suboptimal current surgical treatments, there is great interest in developing better VML therapies. Skeletal muscle tissue engineering (SMTE) is a promising alternative to traditional VML surgical treatments that use autogenic tissue grafts, and rather uses isolated stem cells with myogenic potential to generate de novo skeletal muscle tissues to treat VML. Satellite cells are the native precursors to skeletal muscle tissue, and are thus the most commonly studied starting source for SMTE. However, satellite cells are difficult to isolate and purify, and it is presently unknown whether they would be a practical source in clinical SMTE applications. Alternative myogenic stem cells, including adipose-derived stem cells, bone marrow-derived mesenchymal stem cells, perivascular stem cells, umbilical cord mesenchymal stem cells, induced pluripotent stem cells, and embryonic stem cells, each have myogenic potential and have been identified as possible starting sources for SMTE, although they have yet to be studied in detail for this purpose. These alternative stem cell varieties offer unique advantages and disadvantages that are worth exploring further to advance the SMTE field toward highly functional, safe, and practical VML treatments. The following review summarizes the current state of satellite cell-based SMTE, details the properties and practical advantages of alternative myogenic stem cells, and offers guidance to tissue engineers on how alternative myogenic stem cells can be incorporated into SMTE research.

Instructive microenvironments in skin wound healing: Biomaterials as signal releasing platforms

Skin wound healing aims to repair and restore tissue through a multistage process that involves different cells and signalling molecules that regulate the cellular response and the dynamic remodelling of the extracellular matrix. Nowadays, several therapies that combine biomolecule signals (growth factors and cytokines) and cells are being proposed. However, a lack of reliable evidence of their efficacy, together with associated issues such as high costs, a lack of standardization, no scalable processes, and storage and regulatory issues, are hampering their application. In situ tissue regeneration appears to be a feasible strategy that uses the body's own capacity for regeneration by mobilizing host endogenous stem cells or tissue-specific progenitor cells to the wound site to promote repair and regeneration. The aim is to engineer instructive systems to regulate the spatio-temporal delivery of proper signalling based on the biological mechanisms of the different events that occur in the host microenvironment. This review describes the current state of the different signal cues used in wound healing and skin regeneration, and their combination with biomaterial supports to create instructive microenvironments for wound healing.

Pro-angiogenic impact of SDF-1α gene-activated collagen-based scaffolds in stem cell driven angiogenesis

Ensuring an adequate angiogenic response during wound healing is a prevailing clinical challenge in biomaterials science. To address this, we aimed to develop a pro-angiogenic gene-activated scaffold (GAS) that could activate MSCs to produce paracrine factors and influence angiogenesis and wound repair. A non-viral polyethyleneimine (PEI) nanoparticles carrying a gene encoding for stromal derived factor-1 alpha (SDF-1α) was combined with a collagen-chondroitin sulfate scaffold to produce the GAS. The ability of this platform to enhance the angiogenic potential of mesenchymal stem cells (MSCs) was then assessed. We found that the MSCs on GAS exhibited early over-expression of SDF-1α mRNA with the activation of angiogenic markers VEGF and CXCR4. Exposing endothelial cells to conditioned media collected from GAS supported MSCs promoted a 20% increase in viability and 33% increase in tubule formation (p < 0.05). Furthermore, the conditioned media promoted a 50% increase in endothelial cell migration and wound closure (p < 0.005). Gene expression analysis of the endothelial cells revealed that the functional response was associated with up-regulation of angiogenic genes; VEGF, CXCR4, eNOS and SDF-1α. Overall, this study shows collagen-based scaffolds combined with SDF-1α gene therapy can provide enhanced pro-angiogenic response, suggesting a promising approach to overcome poor vasculature during wound healing.

Stem Cells and Engineered Scaffolds for Regenerative Wound Healing

The normal wound healing process involves a well-organized cascade of biological pathways and any failure in this process leads to wounds becoming chronic. Non-healing wounds are a burden on healthcare systems and set to increase with aging population and growing incidences of obesity and diabetes. Stem cell-based therapies have the potential to heal chronic wounds but have so far seen little success in the clinic. Current research has been focused on using polymeric biomaterial systems that can act as a niche for these stem cells to improve their survival and paracrine activity that would eventually promote wound healing. Furthermore, different modification strategies have been developed to improve stem cell survival and differentiation, ultimately promoting regenerative wound healing. This review focuses on advanced polymeric scaffolds that have been used to deliver stem cells and have been tested for their efficiency in preclinical animal models of wounds.

Tissue specific microenvironments: a key tool for tissue engineering and regenerative medicine

The accumulated evidence points to the microenvironment as the primary mediator of cellular fate determination. Comprised of parenchymal cells, stromal cells, structural extracellular matrix proteins, and signaling molecules, the microenvironment is a complex and synergistic edifice that varies tissue to tissue. Furthermore, it has become increasingly clear that the microenvironment plays crucial roles in the establishment and progression of diseases such as cardiovascular disease, neurodegeneration, cancer, and ageing. Here we review the historical perspectives on the microenvironment, and how it has directed current explorations in tissue engineering. By thoroughly understanding the role of the microenvironment, we can begin to correctly manipulate it to prevent and cure diseases through regenerative medicine techniques.

Optimization and integration of nanosilver on polycaprolactone nanofibrous mesh for bacterial inhibition and wound healing in vitro and in vivo

Bacterial infection is a major hurdle to wound healing, and the overuse of antibiotics have led to global issue, such as emergence of multidrug-resistant bacteria, even "super bacteria". On the contrary, nanosilver (NS) can kill bacteria without causing resistant bacterial strains. In this study, NS was simply generated in situ on the polycaprolactone (PCL) nanofibrous mesh using an environmentally benign and mussel-inspired dopamine (DA). Scanning electron microscopy showed that NS uniformly formed on the nanofibers of PCL mesh. Fourier transform infrared spectroscopy revealed the step-by-step preparation of pristine PCL mesh, including DA coating and NS formation, which were further verified by water contact angle changing from hydrophobic to hydrophilic. To optimize the NS dose, the antibacterial activity of PCL/NS against Staphylococcus aureus, Escherichia coli and Acinetobacter baumannii was detected by bacterial suspension assay, and the cytotoxicity of NS was evaluated using cellular morphology observation and Cell Counting Kit-8 (CCK8) assay. Then, inductively coupled plasma atomic emission spectrometry exhibited that the optimized PCL/NS had a safe and sustained silver release. Moreover, PCL/NS could effectively inhibit bacterial infection in an infectious murine full-thickness skin wound model. As demonstrated by the enhanced level of proliferating cell nuclear antigen (PCNA) in keratinocytes and longer length of neo-formed epidermis, PCL/NS accelerated wound healing by promoting re-epithelialization via enhancing keratinocyte proliferation in infectious wounds.

Superabsorbent crosslinked carboxymethyl cellulose-PEG hydrogels for potential wound dressing applications

This study focused on the synthesis and comprehensive characterization of environmentally friendly hydrogel membranes based on carboxymethyl cellulose (CMC) for wound dressing and skin repair substitutes. These new CMC hydrogels were prepared with two degrees of functionalization (DS=0.77 and 1.22) and chemically crosslinked with citric acid (CA) for tuning their properties. Additionally, CMC-based hybrids were prepared by blending with polyethylene glycol (PEG, 10wt.%). The results demonstrated that superabsorbent hydrogels (SAP) were produced with swelling degree typically ranging from 100% to 5000%, which was significantly dependent on the concentration of CA crosslinker and the addition of PEG as network modifier. The spectroscopical characterizations indicated that the mechanism of CA crosslinking was mostly associated with the chemical reaction with CMC hydroxyl groups and that PEG played an important role on the formation of a hybrid polymeric network. These hydrogels presented very distinct morphological features depended on the degree of crosslinking and the surface nanomechanical properties (e.g., elastic moduli) were drastically affected (from approximately 0.08GPa to 2.0GPa) due to the formation of CMC-PEG hybrid nanostructures. These CMC-based hydrogels were cytocompatible considering the in vitro cell viability responses of over 95% towards human embryonic kidney cells (HEK293T) used as model cell line.

Development and characterisation of a low-concentration sodium dodecyl sulphate decellularised porcine dermis

The aim of this study was to adapt a proprietary decellularisation process for human dermis for use with porcine skin. Porcine skin was subject to: sodium chloride (1 M) to detach the epidermis, trypsin paste to remove hair follicles, peracetic acid (0.1% v/v) disinfection, washed in hypotonic buffer and 0.1% (w/v) sodium dodecyl sulphate in the presence of proteinase inhibitors followed by nuclease treatment. Cellular porcine skin, decellularised porcine and human dermis were compared using histology, immunohistochemistry, GSL-1 lectin (alpha-gal epitope) staining, biochemical assays, uniaxial tensile and in vitro cytotoxicity tests. There was no microscopic evidence of cells in decellularised porcine dermis. DNA content was reduced by 98.2% compared to cellular porcine skin. There were no significant differences in the biomechanical parameters studied or evidence of cytotoxicity. The decellularised porcine dermis retained residual alpha-gal epitope. Basement membrane collagen IV immunostaining was lost following decellularisation; however, laminin staining was retained.

Porcine Urinary Bladder Matrix for Management of Infected Radiation Mastectomy Wound

We present a case report on the successful healing of a Pseudomonas infection wound in a 52-year-old female with morbid obesity, noninsulin dependent diabetes mellitus and a history of tobacco use, who presented with Stage IIIA (T3, N2, Mo) infiltrating ductal carcinoma. The patient received neoadjuvant chemotherapy prior to her bilateral skin-sparing total mastectomies with right axillary sentinel lymphadenectomy. She also had staged reconstruction with temporary breast implants and plans for deep inferior epigastric perforator flaps. Two months after chest wall and regional nodal radiation therapy, she developed a marked soft tissue reaction to radiation. She underwent over 10 right chest wall open wound radical debridements resulting in a tissue defect of 25 cm in length, by 20 cm in width, by 10 cm in depth. Despite surgical debridement, intravenous antibiotics, hyperbaric oxygen therapy, colistin spray therapy, and heat lamp therapy, the infection failed to resolve and the wound failed to heal. She was left with an open wound that was extremely painful and required chronic pain management with opioids. The patient later was found to have developed a multidrug-resistant Pseudomonas infection in her wound. However, the experimental placement of a porcine bladder matrix (ACell©, Inc., Columbia, MD) on the wound resulted in the complete relief of pain just three days after the application of the product. After two weekly applications of ACell©, her infection completely resolved and she was beginning to grow islands of new epidermis over her non-healing mastectomy wound.

Dedifferentiated Chondrocytes in Composite Microfibers As Tool for Cartilage Repair

Tissue engineering (TE) approaches using biomaterials have gain important roles in the regeneration of cartilage. This paper describes the production by microfluidics of alginate-based microfibers containing both extracellular matrix (ECM)-derived biomaterials and chondrocytes. As ECM components gelatin or decellularized urinary bladder matrix (UBM) were investigated. The effectiveness of the composite microfibers has been tested to modulate the behavior and redifferentiation of dedifferentiated chondrocytes. The complete redifferentiation, at the single-cell level, of the chondrocytes, without cell aggregate formation, was observed after 14 days of cell culture. Specific chondrogenic markers and high cellular secretory activity was observed in embedded cells. Notably, no sign of collagen type 10 deposition was determined. The obtained data suggest that dedifferentiated chondrocytes regain a functional chondrocyte phenotype when embedded in appropriate 3D scaffold based on alginate plus gelatin or UBM. The proposed scaffolds are indeed valuable to form a cellular microenvironment mimicking the in vivo ECM, opening the way to their use in cartilage TE.

Anti-Microbial Biopolymer Hydrogel Scaffolds for Stem Cell Encapsulation

Biopolymer hydrogels are an attractive class of materials for wound dressings and other biomedical applications because of their ease of use and availability from biomass. Here, we present a hydrogel formation approach based on alginate and chitosan. Alginate is conventionally cross-linked using multivalent ions such as Ca²⁺ but in principle any polycationic species can be used such as polyelectrolytes. Exchanging the cross-linking Ca²⁺ ions partially with chitosan, which at pH 7 has available positive charges as well as good interactions with Ca²⁺, leads to an improved Young’s modulus. This gel is non-toxic to mammalian cells and hence allows conveniently for stem cell encapsulation since it is based on two-component mixing and gel formation. Additionally, the chitosan is known to have a bactericidal effect which is retained when using it in the alginate–chitosan gel formation and the formed hydrogels displayed bactericidal effects against P. aeruginosa and S. aureus. The combination of anti-bacterial properties, inclusion of stem cells, and the hydrogel nature would provide an ideal environment for complex wound healing.

Promoting tissue regeneration by modulating the immune system

The immune system plays a central role in tissue repair and regeneration. Indeed, the immune response to tissue injury is crucial in determining the speed and the outcome of the healing process, including the extent of scarring and the restoration of organ function. Therefore, controlling immune components via biomaterials and drug delivery systems is becoming an attractive approach in regenerative medicine, since therapies based on stem cells and growth factors have not yet proven to be broadly effective in the clinic. To integrate the immune system into regenerative strategies, one of the first challenges is to understand the precise functions of the different immune components during the tissue healing process. While remarkable progress has been made, the immune mechanisms involved are still elusive, and there is indication for both negative and positive roles depending on the tissue type or organ and life stage. It is well recognized that the innate immune response comprising danger signals, neutrophils and macrophages modulates tissue healing. In addition, it is becoming evident that the adaptive immune response, in particular T cell subset activities, plays a critical role. In this review, we first present an overview of the basic immune mechanisms involved in tissue repair and regeneration. Then, we highlight various approaches based on biomaterials and drug delivery systems that aim at modulating these mechanisms to limit fibrosis and promote regeneration. We propose that the next generation of regenerative therapies may evolve from typical biomaterial-, stem cell-, or growth factor-centric approaches to an immune-centric approach.

STATEMENT OF SIGNIFICANCE

Most regenerative strategies have not yet proven to be safe or reasonably efficient in the clinic. In addition to stem cells and growth factors, the immune system plays a crucial role in the tissue healing process. Here, we propose that controlling the immune-mediated mechanisms of tissue repair and regeneration may support existing regenerative strategies or could be an alternative to using stem cells and growth factors. The first part of this review we highlight key immune mechanisms involved in the tissue healing process and marks them as potential target for designing regenerative strategies. In the second part, we discuss various approaches using biomaterials and drug delivery systems that aim at modulating the components of the immune system to promote tissue regeneration.

Do Processing Methods Make a Difference in Acellular Dermal Matrix Properties?

BACKGROUND

The use of acellular dermal matrices (ADMs) has become the standard of practice in many reconstructive and aesthetic surgical applications. Different methods used to prepare the allograft tissue for surgical use can alter the ADMs natural properties. Aseptic processing has been shown to retain the natural properties of ADMs more favorably than terminally sterilized ADMs. Terminal sterilization has been historically linked to alteration of biological materials. In vitro work was conducted to compare ADM processing methods.

OBJECTIVES

Characterize aseptically processed ADMs and compare cell-matrix interaction characteristics to terminally sterilized ADMs.

METHODS

Two aseptically processed ADMs, FlexHD Pliable and BellaDerm, were characterized via histological evaluation, biomechanical integrity, enzymatic degradation, and in vitro cell studies. FlexHD Pliable was compared to Alloderm Ready-to-Use (RTU).

RESULTS

Histological evaluation revealed that FlexHD Pliable had a uniform, open structure compared to BellaDerm. Mechanical characterization demonstrated that BellaDerm had higher strength and stiffness compared to FlexHD Pliable, which maintained higher elasticity. Immunohistochemical analysis verified that key matrix proteins remained intact after aseptic processing. Cell studies found that fibroblasts attached more readily, and proliferated faster on FlexHD Pliable compared to BellaDerm. Additionally, fibroblasts infiltrated into FlexHD Pliable from both sides and on the dermal side in BellaDerm and produced an abundance of multi-layered matrix proteins (collagen, fibronectin) when compared to AlloDerm RTU which was sparse.

CONCLUSIONS

Aseptically processed FlexHD Pliable and BellaDerm provide a suitable, biocompatible option for tissue repair and regeneration in aesthetic and reconstructive surgical applications.

A Novel Reticular Dermal Graft Leverages Architectural and Biological Properties to Support Wound Repair

Supplemental Digital Content is available in the text.

Background:

Acellular dermal matrices (ADMs) are frequently used in reconstructive surgery and as scaffolds to treat chronic wounds. The 3-dimensional architecture and extracellular matrix provide structural and signaling cues for repair and remodeling. However, most ADMs are not uniformly porous, which can lead to heterogeneous host engraftment. In this study, we hypothesized that a novel human reticular ADM (HR-ADM; AlloPatch Pliable, Musculoskeletal Transplant Foundation, Edison, N.J.) when aseptically processed would have a more open uniform structure with retention of biological components known to facilitate wound healing.

Methods:

The reticular and papillary layers were compared through histology and scanning electron microscopy. Biomechanical properties were assessed through tensile testing. The impact of aseptic processing was evaluated by comparing unprocessed with processed reticular grafts. In vitro cell culture on fibroblasts and endothelial cells were performed to showcase functional cell activities on HR-ADMs.

Results:

Aseptically processed HR-ADMs have an open, interconnected uniform scaffold with preserved collagens, elastin, glycosaminoglycans, and hyaluronic acid. HR-ADMs had significantly lower ultimate tensile strength and Young’s modulus versus the papillary layer, with a higher percentage elongation at break, providing graft flexibility. These preserved biological components facilitated fibroblast and endothelial cell attachment, cell infiltration, and new matrix synthesis (collagen IV, fibronectin, von Willebrand factor), which support granulation and angiogenic activities.

Conclusions:

The novel HR-ADMs provide an open, interconnected scaffold with native dermal mechanical and biological properties. Furthermore, aseptic processing retains key extracellular matrix elements in an organized framework and supports functional activities of fibroblasts and endothelial cells.

Engineered Biopolymeric Scaffolds for Chronic Wound Healing

Skin regeneration requires the coordinated integration of concomitant biological and molecular events in the extracellular wound environment during overlapping phases of inflammation, proliferation, and matrix remodeling. This process is highly efficient during normal wound healing. However, chronic wounds fail to progress through the ordered and reparative wound healing process and are unable to heal, requiring long-term treatment at high costs. There are many advanced skin substitutes, which mostly comprise bioactive dressings containing mammalian derived matrix components, and/or human cells, in clinical use. However, it is presently hypothesized that no treatment significantly outperforms the others. To address this unmet challenge, recent research has focused on developing innovative acellular biopolymeric scaffolds as more efficacious wound healing therapies. These biomaterial-based skin substitutes are precisely engineered and fine-tuned to recapitulate aspects of the wound healing milieu and target specific events in the wound healing cascade to facilitate complete skin repair with restored function and tissue integrity. This mini-review will provide a brief overview of chronic wound healing and current skin substitute treatment strategies while focusing on recent engineering approaches that regenerate skin using synthetic, biopolymeric scaffolds. We discuss key polymeric scaffold design criteria, including degradation, biocompatibility, and microstructure, and how they translate to inductive microenvironments that stimulate cell infiltration and vascularization to enhance chronic wound healing. As healthcare moves toward precision medicine-based strategies, the potential and therapeutic implications of synthetic, biopolymeric scaffolds as tunable treatment modalities for chronic wounds will be considered.