Wound tissue can utilize a polymeric template to synthesize a functional extension of skin

Towards the development of sensation-enabled skin substitutes

Recent advances in cell and biofabrication technologies have contributed to the development of complex human organs. In particular, several skin substitutes are being generated using tissue engineering and regenerative medicine (TERM) technologies. However, recent studies mainly focus on the restoration of the dermis and epidermis layers rather than the regeneration of a fully functional innervated skin organ. Innervation is a critical step in functional tissue repair which has been overlooked in the current TERM studies. In the current study, we highlight the importance of sensation in the skin as the largest sensory organ in the human body. In large non-healing skin wounds, the skin sensation is severely diminished or completely lost and ultimately lead to chronic pain and wound healing process interruption. Current therapeutics for restoring skin sensation after trauma are limited. Recent regenerative medicine-based studies could successfully induce neural networks in skin substitutes, but the effectiveness of these technologies in enhancing sensory capability needs further investigation.

The Human Neonatal Skin Fibroblast, an Available Cell Source for Tissue Production and Transplantation, Exhibits Low Risk of Immunogenicity In Vitro

The immunogenicity of allogeneic skin fibroblasts in transplantation has been controversial. Whether this controversy comes from a natural heterogeneity among fibroblast subsets or species-specific differences between human and mouse remains to be addressed. In this study, we sought to investigate whether fibroblasts derived from either adult or neonatal human skin tissues could induce different immune responses toward phagocytosis and T cell activation using in vitro co-culture models. Our results indicate that both phagocytosis and T cell proliferation are reduced in the presence of neonatal skin fibroblasts compared to adult skin fibroblasts. We also show that neonatal skin fibroblasts secrete paracrine factors that are responsible for reduced T cell proliferation. In addition, we show that neonatal skin fibroblasts express less class II human leukocyte antigen (HLA) molecules than adult skin fibroblasts after interferon gamma priming, which might also contribute to reduced T cell proliferation. In conclusion, this study supports the use of allogeneic neonatal skin fibroblasts as a readily available cell source for tissue production and transplantation to treat patients with severe injuries.

Biomimetic tri-layered artificial skin comprising silica gel-collagen membrane-collagen porous scaffold for enhanced full-thickness wound healing

Full-thickness wounds are severe cutaneous damages with destroyed self-healing function, which need efficient clinical interventions. Inspired by the hierarchical structure of natural skin, we have for the first time developed a biomimetic tri-layered artificial skin (TLAS) comprising silica gel-collagen membrane-collagen porous scaffold for enhanced full-thickness wound healing. The TLAS with the thickness of 3-7 mm displays a hierarchical nanostructure consisting of the top homogeneous silica gel film, the middle compact collagen membrane, and the bottom porous collagen scaffold, exquisitely mimicking the epidermis, basement membrane and dermis of natural skin, respectively. The 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide/N-Hydroxysuccinimide-dehydrothermal (EDC/NHS-DHT) dual-crosslinked collagen composite bilayer, with a crosslinking degree of 79.5 %, displays remarkable biocompatibility, bioactivity, and biosafety with no risk of hemolysis and pyrogen reactions. Notably, the extra collagen membrane layer provides a robust barrier to block the penetration of silica gel into the collagen porous scaffold, leading to the TLAS with enhanced biocompatibility and bioactivity. The full-thickness wound rat model studies have indicated the TLAS significantly facilitates the regeneration of full-thickness defects by accelerating re-epithelization, collagen deposition and migration of skin appendages. The highly biocompatible and bioactive tri-layered artificial skin provides an improved treatment for full-thickness wounds, which has great potential in tissue engineering.

Combinatorial strategies for cell transplantation in traumatic spinal cord injury

Spinal cord injury (SCI) substantially reduces the quality of life of affected individuals. Recovery of function is therefore a primary concern of the patient population and a primary goal for therapeutic interventions. Currently, even with growing numbers of clinical trials, there are still no effective treatments that can improve neurological outcomes after SCI. A large body of work has demonstrated that transplantation of neural stem/progenitor cells (NSPCs) can promote regeneration of the injured spinal cord by providing new neurons that can integrate into injured host neural circuitry. Despite these promising findings, the degree of functional recovery observed after NSPC transplantation remains modest. It is evident that treatment of such a complex injury cannot be addressed with a single therapeutic approach. In this mini-review, we discuss combinatorial strategies that can be used along with NSPC transplantation to promote spinal cord regeneration. We begin by introducing bioengineering and neuromodulatory approaches, and highlight promising work using these strategies in integration with NSPCs transplantation. The future of NSPC transplantation will likely include a multi-factorial approach, combining stem cells with biomaterials and/or neuromodulation as a promising treatment for SCI.

Dermal Regeneration Template in the Management and Reconstruction of Burn Injuries and Complex Wounds: A Review

Background

Dermal scaffolds have created a paradigm shift for burn and wound management by providing improved healing and less scarring, while improving cosmesis and functionality. Dermal regeneration template (DRT) is a bilayer membrane for dermal regeneration developed by Yannas and Burke in the 1980s. The aim of this review is to summarize clinical evidence for dermal scaffolds focusing on DRT for the management and reconstruction of burn injuries and complex wounds.

Methods

A comprehensive search of PubMed was performed from the start of indexing through November 2022. Articles reporting on DRT use in patients with burns, limb salvage, and wound reconstruction were included with focus on high-level clinical evidence.

Results

DRT has become an established alternative option for the treatment of full-thickness and deep partial-thickness burns, with improved outcomes in areas where cosmesis and functionality are important. In the management of diabetic foot ulcers, use of DRT is associated with high rates of complete wound healing with a low risk of adverse outcomes. DRT has been successfully used in traumatic and surgical wounds, showing particular benefit in deep wounds and in the reconstruction of numerous anatomical sites.

Conclusions

Considerable clinical experience has accrued with the use of DRT beyond its original application for thermal injury. A growing body of evidence from clinical studies reports the successful use of DRT to improve clinical outcomes and quality of life across clinical indications at a number of anatomical sites.

Objective Non-Invasive Bio-Parametric Evaluation of Regenerated Skin: A Comparison of Two Acellular Dermal Substitutes

Several dermal substitutes are available on the market, but there is no precise indication that helps surgeons choose the proper one. Few studies have tried to compare different xenogeneic bioengineered products, but no objective bio-parametric comparison has been made yet. Fifteen patients who underwent skin reconstruction with Integra® or Pelnac® were retrospectively evaluated. After at least 12 months of follow-up, an objective and quantitative assessment of several skin biophysical properties, such as color, texture, elasticity, hydration, glossiness and trans-epidermal water loss, were measured with non-invasive skin measurement devices. The grafted skin showed a reduction of the superficial hydration level and a tendency to lower values of trans-epidermal water loss with both dermal substitutes. Melanic and hemoglobin pigmentation were higher in comparison to the donor site in both groups, while a melanic pigmentation increase versus the surrounding skin was seen just with Integra®. Finally, the skin was found to be more elastic when reconstructed with Integra®. The skin barrier appeared to be intact in both groups. Hence, these substitutes are valuable means of skin regeneration. Integra® seems to be more advantageous for reconstructing areas that need more skin flexibility.

Sequential treatment for diabetic foot ulcers in dialysis patients: A case report

BACKGROUND

Diabetic foot ulcers (DFUs) are common in patients with diabetes, especially those undergoing hemodialysis. In severe cases, these ulcers can cause damage to the lower extremities and lead to amputation. Traditional treatments such as flap transposition and transfemoral amputation are not always applicable in all cases. Therefore, there is a need for alternative treatment methods.

CASE SUMMARY

This report describes a 62-year-old female patient who was admitted to the hospital with plantar and heel ulcers on her left foot. The patient had a history of renal failure and was undergoing regular hemodialysis. Digital subtraction angiography showed extensive stenosis and occlusion in the left superficial femoral artery, left peroneal artery and left posterior tibial artery. Following evaluation by a multidisciplinary team, the patient was diagnosed with type 2 DFUs (TEXAS 4D). Traditional treatments were deemed unsuitable, and the patient was treated with endovascular surgery in the affected area, in addition to supportive medical treatment, local debridement, and sequential repair using split-thickness skin and tissue-engineered skin grafts combined with negative pressure treatment. After four months, the wound had completely healed, and the patient was able to walk with a walking aid.

CONCLUSION

This study demonstrates a new treatment method for DFUs was successful, using angioplasty, skin grafts, and negative pressure.

Bioinspired Hierarchical Carbon Structures as Potential Scaffolds for Wound Healing and Tissue Regeneration Applications

Engineered bio-scaffolds for wound healing provide an attractive treatment option for tissue engineering and traumatic skin injuries since they can reduce dependence on donors and promote faster repair through strategic surface engineering. Current scaffolds present limitations in handling, preparation, shelf life, and sterilization options. In this study, bio-inspired hierarchical all-carbon structures comprising carbon nanotube (CNT) carpets covalently bonded to flexible carbon fabric have been investigated as a platform for cell growth and future tissue regeneration applications. CNTs are known to provide guidance for cell growth, but loose CNTs are susceptible to intracellular uptake and are suspected to cause in vitro and in vivo cytotoxicity. This risk is suppressed in these materials due to the covalent attachment of CNTs on a larger fabric, and the synergistic benefits of nanoscale and micro-macro scale architectures, as seen in natural biological materials, can be obtained. The structural durability, biocompatibility, tunable surface architecture, and ultra-high specific surface area of these materials make them attractive candidates for wound healing. In this study, investigations of cytotoxicity, skin cell proliferation, and cell migration were performed, and results indicate promise in both biocompatibility and directed cell growth. Moreover, these scaffolds provided cytoprotection against environmental stressors such as Ultraviolet B (UVB) rays. It was seen that cell growth could also be tailored through the control of CNT carpet height and surface wettability. These results support future promise in the design of hierarchical carbon scaffolds for strategic wound healing and tissue regeneration applications.

Pharmacological Functions, Synthesis, and Delivery Progress for Collagen as Biodrug and Biomaterial

Collagen has been widely applied as a functional biomaterial in regulating tissue regeneration and drug delivery by participating in cell proliferation, differentiation, migration, intercellular signal transmission, tissue formation, and blood coagulation. However, traditional extraction of collagen from animals potentially induces immunogenicity and requires complicated material treatment and purification steps. Although semi-synthesis strategies such as utilizing recombinant E. coli or yeast expression systems have been explored as alternative methods, the influence of unwanted by-products, foreign substances, and immature synthetic processes have limited its industrial production and clinical applications. Meanwhile, macromolecule collagen products encounter a bottleneck in delivery and absorption by conventional oral and injection vehicles, which promotes the studies of transdermal and topical delivery strategies and implant methods. This review illustrates the physiological and therapeutic effects, synthesis strategies, and delivery technologies of collagen to provide a reference and outlook for the research and development of collagen as a biodrug and biomaterial.

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.

Hemostatic Collagen Sponge with High Porosity Promotes the Proliferation and Adhesion of Fibroblasts and Osteoblasts

The use of biomaterial for tissue repair involves the interaction between materials and cells, and the coagulum formation represents the first step of tissue healing. This process is particularly critical in the oral cavity, where the wounds are immediately subjected to the masticatory mechanical stress, saliva invasion, and bacterial attack. Therefore, the present study aimed to explore the structural features and the biological activities of a hemostatic collagen sponge on human gingival fibroblasts (HGFs) and human oral osteoblasts (HOBs). The microstructure of the collagen sponge was characterized by a scanning electron microscope (SEM) and histological analysis. The porosity was also calculated. To investigate biological activities, HGFs and HOBs were cultured on the collagen sponges, and their adhesion was observed at SEM on the third day, while cell viability was investigated at the third and seventh days by Tetrazolium (MTT) assay. For osteoblasts seeded on collagen sponge the mineralization ability was also evaluated by alkaline phosphatase (ALP) assay at the seventh day, and by Alizarin red staining on the 14th. Furthermore, the gene expression of ALP and osteocalcin (OCN) was investigated after 3, 7 and 14 days. SEM images of the sponge without cells showed a highly porous 3D structure, confirmed by the measurement of porosity that was more than 90%. The samples cultured were characterized by cells uniformly distributed and adhered to the sponge surface. Proliferation ended up being promoted, as well as the mineralization ability of the osteoblasts, mainly at the mature stage. In conclusion, this collagen sponge could have a potential use for tissue healing.

A Biomimetic, Bilayered Antimicrobial Collagen-Based Scaffold for Enhanced Healing of Complex Wound Conditions

Chronic, nonhealing wounds in the form of diabetic foot ulcers (DFUs) are a major complication for diabetic patients. The inability of a DFU to heal appropriately leads to an open wound with a high risk of infection. Current standards of care fail to fully address either the underlying defective wound repair mechanism or the risk of microbial infection. Thus, it is clear that novel approaches are needed. One such approach is the use of multifunctional biomaterials as platforms to direct and promote wound healing. In this study, a biomimetic, bilayered antimicrobial collagen-based scaffold was developed to deal with the etiology of DFUs. An epidermal, antimicrobial collagen/chitosan film for the prevention of wound infection was combined with a dermal collagen-glycosaminoglycan scaffold, which serves to support angiogenesis in the wound environment and ultimately accelerate wound healing. Biophysical and biological characterization identified an 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide cross-linked bilayered scaffold to have the highest structural stability with similar mechanical properties to products on the market, exhibiting a similar structure to native skin, successfully inhibiting the growth and infiltration of Staphylococcus aureus and supporting the proliferation of epidermal cells on its surface. This bilayered scaffold also demonstrated the ability to support the proliferation of key cell types involved in vascularization, namely, induced pluripotent stem cell derived endothelial cells and supporting stromal cells, with early signs of organization of these cells into vascular structures, showing great promise for the promotion of angiogenesis. Taken together, the results indicate that the bilayered scaffold is an excellent candidate for enhancement of diabetic wound healing by preventing wound infection and supporting angiogenesis.

Nanomaterials-Functionalized Hydrogels for the Treatment of Cutaneous Wounds

Hydrogels have been utilized extensively in the field of cutaneous wound treatment. The introduction of nanomaterials (NMs), which are a big category of materials with diverse functionalities, can endow the hydrogels with additional and multiple functions to meet the demand for a comprehensive performance in wound dressings. Therefore, NMs-functionalized hydrogels (NMFHs) as wound dressings have drawn intensive attention recently. Herein, an overview of reports about NMFHs for the treatment of cutaneous wounds in the past five years is provided. Firstly, fabrication strategies, which are mainly divided into physical embedding and chemical synthesis of the NMFHs, are summarized and illustrated. Then, functions of the NMFHs brought by the NMs are reviewed, including hemostasis, antimicrobial activity, conductivity, regulation of reactive oxygen species (ROS) level, and stimulus responsiveness (pH responsiveness, photo-responsiveness, and magnetic responsiveness). Finally, current challenges and future perspectives in this field are discussed with the hope of inspiring additional ideas.

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 grafting treatment of adolescent lower limb avulsion injury

Background

Under the influence of various factors, the number of lower extremity avulsion injuries in adolescents is increasing year by year. The main modality of treatment is skin grafting. There are many types of skin grafting. Although many studies on skin grafting after avulsion injuries have been published in the past few decades, there are differences in the treatment options for adolescents with post avulsion injuries.

Main body

Thorough debridement and appropriate skin grafts are essential for the surgical management of avulsion injuries for optimal prognosis. In the acquisition of grafts, progress has been made in equipment for how to obtain different depths of skin. The severity of the avulsion injury varies among patients on admission, and therefore the manner and type of skin grafting will vary. Especially in adolescents, graft survival and functional recovery are of great concern to both patients and physicians. Therefore, many efforts have been made to improve survival rate and activity.

Conclusion

This review summarizes the principles of treatment of avulsion injuries, the historical development of skin grafts, and the selection of skin grafts, hoping to be helpful for future research.

Negative pressure wound therapy on complex extremity wounds requiring coverage with a meshed bilayer wound matrix: a retrospective analysis

OBJECTIVE

The treatment of complex extremity wounds is technically challenging. In this 5-year retrospective review, we compared the use of Integra Meshed Bilayer Wound Matrix (IMBWM; Integra LifeSciences, US) followed by a split-thickness skin graft (STSG) combined with negative pressure wound therapy (NPWT) versus IMBWM followed by STSG alone for the management of these wounds.

METHOD

Data from patients undergoing management using IMBWM for a complex extremity wound coverage were collected.

RESULTS

Among the 109 patients studied, the wounds of 62 patients were managed using IMBWM and NPWT, and 47 were managed using IMBWM alone. The most common aetiology of these injuries was trauma. Wound size and location were similar for each group, ranging in size from 2-30cm² and being primarily on the forearm, followed by the leg and arm. There was a significantly greater take of the IMBWM+STSG with NPWT (96.8%) compared to without NPWT (85.1%, p=0.03). There were significantly fewer reapplications of the dermal matrix required in the NPWT group (3.2%) versus the non-NPWT group (14.9%, p=0.03). There were significantly fewer postoperative complications, prior to STSG, in the NPWT group (3.2%) versus the non-NPWT group (14.9%, p=0.03).

CONCLUSION

The combination of IMBWM with NPWT leads to a higher success rate, and can reduce the number of dermal matrix reapplications and postoperative complications, in the setting of complex extremity wounds. The use of IMBWM in combination with NPWT has the potential to improve both surgical procedures and patient outcomes in this setting.

Can a Scaffold Enriched with Mesenchymal Stem Cells Be a Good Treatment for Spinal Cord Injury?

Spinal cord injury (SCI) is a worldwide highly crippling disease that can lead to the loss of motor and sensory neurons. Among the most promising therapies, there are new techniques of tissue engineering based on stem cells that promote neuronal regeneration. Among the different types of stem cells, mesenchymal stem cells (MSCs) seem the most promising. Indeed, MSCs are able to release trophic factors and to differentiate into the cell types that can be found in the spinal cord. Currently, the most common procedure to insert cells in the lesion site is infusion. However, this causes a low rate of survival and engraftment in the lesion site. For these reasons, tissue engineering is focusing on bioresorbable scaffolds to help the cells to stay in situ. Scaffolds do not only have a passive role but become fundamental for the trophic support of cells and the promotion of neuroregeneration. More and more types of materials are being studied as scaffolds to decrease inflammation and increase the engraftment as well as the survival of the cells. Our review aims to highlight how the use of scaffolds made from biomaterials enriched with MSCs gives positive results in in vivo SCI models as well as the first evidence obtained in clinical trials.

Integra Dermal Regeneration Template in reconstructive surgery for cutaneous tumours: a two-year retrospective review

OBJECTIVE

Integra Dermal Regeneration Template (IDRT) (Integra LifeSciences, US) is a bioengineered dermal matrix that has been widely used in burn reconstruction since its first description. However, little is reported on its use in oncologic dermatological defects. Our objective was to evaluate reconstruction using IDRT on cutaneous tumour defects.

METHOD

We conducted a two-year retrospective review of patients with skin tumours who had an excision surgery, followed by reconstruction with IDRT, as a mid-step towards a final autograft procedure: a split-thickness skin graft. The records of all patients at a single academic institution were queried from the electronic medical record using data obtained from the operating surgeon.

RESULTS

We identified 13 patients with different tumour types and locations. The mean defect size was 105.92cm². The matrix take rate was 92.3% and average postoperative day for definite autograft was 20 days. Patients were followed for a period of up to 12 months. Of the patients, one had exposed bone without periosteum; another patient showed recurrence six months after matrix placement, requiring a new second two-stage IDRT-autograft procedure before radiation therapy. Patients reported complete satisfaction with the cosmetic, functional and oncological results. No cases of infection were encountered.

CONCLUSION

IDRT is a valid option for the reconstruction of oncologic surgical defects of the skin and can be used in different anatomical locations. Specifically, it is an alternative to the reconstructive ladder when grafts and local flaps are not possible in those patients, and an option for patients who will eventually need adjuvant radiotherapy.

Reactive oxygen species-degradable polythioketal urethane foam dressings to promote porcine skin wound repair

Porous, resorbable biomaterials can serve as temporary scaffolds that support cell infiltration, tissue formation, and remodeling of nonhealing skin wounds. Synthetic biomaterials are less expensive to manufacture than biologic dressings and can achieve a broader range of physiochemical properties, but opportunities remain to tailor these materials for ideal host immune and regenerative responses. Polyesters are a well-established class of synthetic biomaterials; however, acidic degradation products released by their hydrolysis can cause poorly controlled autocatalytic degradation. Here, we systemically explored reactive oxygen species (ROS)-degradable polythioketal (PTK) urethane (UR) foams with varied hydrophilicity for skin wound healing. The most hydrophilic PTK-UR variant, with seven ethylene glycol (EG7) repeats flanking each side of a thioketal bond, exhibited the highest ROS reactivity and promoted optimal tissue infiltration, extracellular matrix (ECM) deposition, and reepithelialization in porcine skin wounds. EG7 induced lower foreign body response, greater recruitment of regenerative immune cell populations, and resolution of type 1 inflammation compared to more hydrophobic PTK-UR scaffolds. Porcine wounds treated with EG7 PTK-UR foams had greater ECM production, vascularization, and resolution of proinflammatory immune cells compared to polyester UR foam-based NovoSorb Biodegradable Temporizing Matrix (BTM)-treated wounds and greater early vascular perfusion and similar wound resurfacing relative to clinical gold standard Integra Bilayer Wound Matrix (BWM). In a porcine ischemic flap excisional wound model, EG7 PTK-UR treatment led to higher wound healing scores driven by lower inflammation and higher reepithelialization compared to NovoSorb BTM. PTK-UR foams warrant further investigation as synthetic biomaterials for wound healing applications.

Evaluation of contraction of the split-thickness skin graft using three dermal matrices in the treatment of burn contractures: a randomized clinical trial

Burn injuries commonly result in serious sequelae (such as skin contractures) in surviving patients, for which no single optimal solution is known. The goal of this study was to compare the late contraction of autologous skin grafts with or without dermal matrices used in the treatment of patients with burn contractures. This parallel design prospective, randomized, and controlled clinical trial included patients with burn contracture treated using autologous skin grafts and dermal matrix. Patients were randomly assigned to one of the four groups: Integra® matrix (n=10), Pelnac® matrix (n=10), Matriderm® matrix (n=9), or a Control Group (n=10, without dermal matrix, only skin graft). The boundaries of skin defect were marked and transferred to a flat sterile surface for area measurement. The current area of the skin grafts was measured during surgery and compared with those obtained at 1, 3, 6, and 12 months postoperatively. Twelve months after surgery, the Control Group presented lower rates of skin graft contraction than Integra® (p<0.01), Matriderm® (p=0.01), and Pelnac® (p<0.01) groups. Pelnac® resulted in larger skin graft contraction than Matriderm® (p<0.01) and Integra® (p=0.02), while differences between Integra® and Matriderm® were not significant (p=0.16). The comparison between intraoperative and 12 months after surgery showed that the worst mean rates of skin graft contraction were from the Pelnac® (51.79%) and Matriderm® (59.17%). In patients with burn contractures, the use of these three dermal matrices did not reduce or avoid the occurrence of late contraction of the skin graft, so their use for this purpose should be carefully evaluated.

Strategies for extremity reconstruction with exposed bones and tendons using acellular dermal matrices: concept of sequential vascularization

We report 3 cases of patients treated with Bilayer Wound Matrix over exposed structures. In all patients, dermal matrices revascularization occurred sequentially over the course of 6–12 weeks, leading to successful wound closure. Acellular dermal matrices allow more difficult areas with poor vascularity to be covered from the ‘inside-out’.

Highly Efficient Self-Healing Multifunctional Dressing with Antibacterial Activity for Sutureless Wound Closure and Infected Wound Monitoring

Wound healing represents a major clinical and public healthcare problem that is frequently challenged by infection risks, detrimental consequences on the surrounding tissues, and difficulties to monitor the healing process. Here we report on a novel self-healing, antibacterial, and multifunctional wound dressing for sutureless wound closure and real-time monitoring of the healing parameters. The self-healing elastomer contains cetyltrimethylammonium bromide (CTAB) and has high mechanical toughness (35 MJ m^-3 ), biocompatibility, and outstanding antibacterial activity (bactericidal rate is ≈90% in 12 h), enabling the wound dressing to effectively inhibit bacterial growth and accelerate infected wound healing. In vivo tests based on full-thickness skin incision model shows that the multifunctional wound dressing can help in contracting wound edges and facilitate wound closure and healing, as could be evidenced by notably dense and well-organized collagen deposition. The test provides an evidence that the integrated sensor array within the multifunctional wound dressing can monitor temperature, pH, and glucose level of the wound area in real-time, providing reliable and timely information of the condition of the wound. Ultimately, the reported multifunctional dressing would be of high value in managing the burden associated with wound healing via personalised monitoring and treatment approaches, digital and other people-centred solutions for health care.

Mesenchymal stromal cells in wound healing applications: role of the secretome, targeted delivery and impact on recessive dystrophic epidermolysis bullosa treatment

Mesenchymal stromal cells (MSCs) are multi-potent stromal-derived cells capable of self-renewal that possess several advantageous properties for wound healing, making them of interest to the field of dermatology. Research has focused on characterizing the unique properties of MSCs, which broadly revolve around their regenerative and more recently discovered immunomodulatory capacities. Because of ease of harvesting and expansion, differentiation potential and low immunogenicity, MSCs have been leading candidates for tissue engineering and regenerative medicine applications for wound healing, yet results from clinical studies have been variable, and promising pre-clinical work has been difficult to reproduce. Therefore, the specific mechanisms of how MSCs influence the local microenvironment in distinct wound etiologies warrant further research. Of specific interest in MSC-mediated healing is harnessing the secretome, which is composed of components known to positively influence wound healing. Molecules released by the MSC secretome can promote re-epithelialization and angiogenesis while inhibiting fibrosis and microbial invasion. This review focuses on the therapeutic interest in MSCs with regard to wound healing applications, including burns and diabetic ulcers, with specific attention to the genetic skin disease recessive dystrophic epidermolysis bullosa. This review also compares various delivery methods to support skin regeneration in the hopes of combating the poor engraftment of MSCs after delivery, which is one of the major pitfalls in clinical studies utilizing MSCs.

Extracellular Matrix-Based Biomaterials for Cardiovascular Tissue Engineering

Regenerative medicine and tissue engineering strategies have made remarkable progress in remodeling, replacing, and regenerating damaged cardiovascular tissues. The design of three-dimensional (3D) scaffolds with appropriate biochemical and mechanical characteristics is critical for engineering tissue-engineered replacements. The extracellular matrix (ECM) is a dynamic scaffolding structure characterized by tissue-specific biochemical, biophysical, and mechanical properties that modulates cellular behavior and activates highly regulated signaling pathways. In light of technological advancements, biomaterial-based scaffolds have been developed that better mimic physiological ECM properties, provide signaling cues that modulate cellular behavior, and form functional tissues and organs. In this review, we summarize the in vitro, pre-clinical, and clinical research models that have been employed in the design of ECM-based biomaterials for cardiovascular regenerative medicine. We highlight the research advancements in the incorporation of ECM components into biomaterial-based scaffolds, the engineering of increasingly complex structures using biofabrication and spatial patterning techniques, the regulation of ECMs on vascular differentiation and function, and the translation of ECM-based scaffolds for vascular graft applications. Finally, we discuss the challenges, future perspectives, and directions in the design of next-generation ECM-based biomaterials for cardiovascular tissue engineering and clinical translation.

Evaluation of canine bone marrow-derived mesenchymal stem cells for experimental full-thickness cutaneous wounds in a diabetic rat model

BACKGROUND

The wound healing potential of canine bone marrow-derived mesenchymal stem cells (BMSCs) was evaluated in the excisional wound of streptozotocin-induced diabetic rats.

RESEARCH DESIGN AND METHODS

Xenogenic BMSCs were collected aseptically from the iliac crest of healthy canine donors under general anesthesia. Full-thickness experimental wounds (20 × 20 mm²) on the dorsum of forty-eight adult healthy Wistar white rats. The wounds were assigned randomly to three treatment groups: PBS (Group A) or BMSCs (Group B) injected into the wound margins on days 0, 7, and 14 or BMSCs (Group C) injected into the wound margins on days 7, 14, and 21 post-wounding. The degree of wound healing was evaluated based on macroscopical, hemato-biochemical, histopathological, and histochemical parameters.

RESULTS

The results indicated granulation tissue formation with reduced exudation and peripheral swelling in the treatment groups compared to the control group A. Similarly, the degree of wound contraction was significantly higher in groups B and C animals than group A on days 14 and 21 post-wounding. The transplantation of BMSCs resulted in early drying of wounds, granulation tissue appearance, and enhanced cosmetic appearance.

CONCLUSION

The histopathological, histochemical, and gross findings suggested the therapeutic potential of xenogeneic mesenchymal stem cell therapy in managing diabetic wounds.

ABBREVIATIONS

BMSCs-bone marrow-derived mesenchymal stem cells, PBS-phosphate-buffered saline, MSCs-mesenchymal stem cells, FBS-fetal bovine serum, ECM-extracellular matrix.

Healing hard-to-heal diabetic foot ulcers: the role of dehydrated amniotic allograft with cross-linked bovine-tendon collagen and glycosaminoglycan matrix

The treatment of diabetic foot ulcers is complex and costly with an increased risk for infection, which may even lead to amputation. This prospective case series aims to assess the effectiveness of a dehydrated amniotic membrane allograft combined with a bilayer dermal matrix for healing complicated foot ulcers in patients with comorbidities. A total of six patients with complicated full-thickness ulcers and comorbidities, such as diabetes and peripheral vascular disease were treated with this technique. Each wound was measured intraoperatively just before graft application, at 14 days after application, and then at weeks 4, 8, and 12. Changes in wound volume and area were compared over time. One patient had complete wound closure by week eight, a second patient by week 12. The other four patients had wounds that decreased in size during the course of 12 weeks. The mean decrease in wound volume was 73.5% post-removal of the bilayer dermal matrix after two weeks of application. At week 12, the mean decrease in wound area and volume were 93.2% and 97.1%, respectively. This case series provides initial evidence that the combination of dehydrated amniotic membrane allograft with bilayer dermal matrix promotes complete wound closure in patients with comorbidities that may impede wound healing. Further clinical trials are needed to confirm these results.

Development of wound healing scaffolds with precisely-triggered sequential release of therapeutic nanoparticles

Natural bioactive cue profiles are generally transient with cues switching on/off to coordinate successful outcomes. Dysregulation of these sequences typically leads to disease. Successful wound healing, for example, should progress sequentially through hemostasis, inflammation, granulation tissue formation, and maturation. Chronic wounds, such as diabetic foot ulcers, suffer from uncoordinated signaling, and arrest and cycle between the inflammation and granulation stages. Traditionally, therapeutic delivery in tissue engineering has focused on sustaining delivery of key signaling factors; however, temporal and sequential delivery have increasingly come into focus. To fully take advantage of these signaling systems, a scaffold or matrix material that can house the delivery system is desirable. In this work, we functionalized a collagen-based scaffold - which has proven regenerative potential in wounds - with on-demand delivery of nanoparticles. Building on our previous work with ultrasound-responsive alginate that shows near-zero baseline release and a rapid release in response to an ultrasound trigger, we developed two novel scaffolds. In the first version, homogeneously-distributed microparticles of alginate were incorporated within the collagen-glycosaminoglycan (GAG) scaffold; ultrasound-triggered release of platelet derived growth factor (PDGF) loaded gold nanoparticles was demonstrated; and their maintained bioactivity confirmed. In the second version, pockets of alginate that can be individually loaded and triggered with ultrasound, were incorporated. The ability to sequentially release multiple therapeutics within these scaffolds using ultrasound was successfully confirmed. These platforms offer a precise and versatile way to deliver therapeutic nanoparticles within a proven regenerative template, and can be used to deliver and probe timed therapeutic delivery in wound healing and other tissue engineering applications.

Mimicking the Hierarchical Organization of Natural Collagen: Toward the Development of Ideal Scaffolding Material for Tissue Regeneration

Biological materials found in living organisms, many of which are proteins, feature a complex hierarchical organization. Type I collagen, a fibrous structural protein ubiquitous in the mammalian body, provides a striking example of such a hierarchical material, with peculiar architectural features ranging from the amino acid sequence at the nanoscale (primary structure) up to the assembly of fibrils (quaternary structure) and fibers, with lengths of the order of microns. Collagen plays a dominant role in maintaining the biological and structural integrity of various tissues and organs, such as bone, skin, tendons, blood vessels, and cartilage. Thus, "artificial" collagen-based fibrous assemblies, endowed with appropriate structural properties, represent ideal substrates for the development of devices for tissue engineering applications. In recent years, with the ultimate goal of developing three-dimensional scaffolds with optimal bioactivity able to promote both regeneration and functional recovery of a damaged tissue, numerous studies focused on the capability to finely modulate the scaffold architecture at the microscale and the nanoscale in order to closely mimic the hierarchical features of the extracellular matrix and, in particular, the natural patterning of collagen. All of these studies clearly show that the accurate characterization of the collagen structure at the submolecular and supramolecular levels is pivotal to the understanding of the relationships between the nanostructural/microstructural properties of the fabricated scaffold and its macroscopic performance. Several studies also demonstrate that the selected processing, including any crosslinking and/or sterilization treatments, can strongly affect the architecture of collagen at various length scales. The aim of this review is to highlight the most recent findings on the development of collagen-based scaffolds with optimized properties for tissue engineering. The optimization of the scaffolds is particularly related to the modulation of the collagen architecture, which, in turn, impacts on the achieved bioactivity.

Engineered Skin Substitute Regenerates the Skin with Hair Follicle Formation

Currently, engineered skin substitutes (ESS) are unable to regenerate cutaneous appendages. Recent studies have shown that skin-derived precursors (SKPs), which are extensively available, have the potential to induce hair follicle neogenesis. Here, we demonstrate that ESS consisting of culture-expanded SKPs and epidermal stem cells (Epi-SCs) reconstitute the skin with hair follicle regeneration after grafting into nude mice. SKPs seeded in a C-GAG matrix proliferated and expressed higher levels of hair induction signature genes—such as Akp2, Sox2, CD133 and Bmp6—compared to dermal fibroblasts. Moreover, when ESS prepared by seeding a mixture of culture-expanded murine SKPs and human adult Epi-SCs into a C-GAG matrix was grafted into full-thickness skin wounds in nude mice, black hairs were generated within 3 weeks. Immunofluorescence analysis showed that the SKPs were localized to the dermal papillae of the newly-formed hair follicle. Our results indicate that SKPs can serve as the hair-inductive cells in ESS to furnish it with hair genesis potential

Matriderm dermal substitute in the treatment of post traumatic hand's fingertip tissue loss

INTRODUCTION

Treatment of fingers tissue loss is particularly challenging as it often necessitates advanced reconstructive techniques such as flaps or grafts, with esthetic and functional results that are not always as good as hoped for, with long healing times. Recently, along with tissue engineering development, numerous types of dermal substitute have been commercialized, with promising possibilities of treatment in finger tissue loss. In the author's unit, Matriderm^® is the most commonly used dermal substitute. As described by the manufacturer, this scaffold is designed to be covered with a split-thickness skin graft. In using a two-step procedure, the authors realized that in most cases of fingertips injuries, at three weeks follow-up, the wound appeared in an advanced state of healing, which permitted to avoid grafting.

MATERIAL AND METHODS

Between October 2017 and October 2018, 27 fingers have been included in this study. Patients have been divided in two groups: those treated with Matriderm^® alone (15 fingers) and those who had a skin graft three weeks after the first surgery (12 fingers). At the 6-month follow-up, authors evaluated the esthetic results with the Vancouver Scar Scale (VSS), the functional results with Quick Disability of the Arm, Shoulder and Hand (qDASH) score, and sensibility by the mean of two-point discrimination test (2-PD).

RESULTS

All outcomes were overlapping in patients treated with or without skin graft: mean VSS was 2.3, mean qDASH was 13.3, and mean 2-PD was 7.7 mm.

CONCLUSIONS

The results obtained allow to consider Matriderm^® , used also without skin graft coverage, as a valid solution for treatment of fingertip tissue loss.

Optimization of extracellular matrix production from human induced pluripotent stem cell-derived fibroblasts for scaffold fabrication for application in wound healing

Extracellular matrix is a key component of all tissues, including skin and it plays a crucial role in the complex events of wound healing. These events are impaired in chronic wounds, with chronic inflammation and infection often present in these non-healing wounds. Many tissue engineering approaches for wound healing provide a scaffold to mimic the native matrix. Fibroblasts derived from iPS cells (iPSF) represent a novel source of matrix rich in pro-regenerative components, which can be used for scaffold fabrication to improve wound healing. However, in vitro production of matrix by cells for scaffold fabrication requires long cell culturing times which increases cost. The aim of this work is to optimize the iPSF matrix production by boosting matrix deposition, without affecting its composition. A good candidate technique to achieve this goal is macromolecular crowding, which is known to promote conversion of procollagen into mature collagen and its accumulation. We tested two molecular crowders, Ficoll and Carrageenan-in combination with ascorbic acid-over a prolonged period of time. Ficoll in combination with ascorbic acid notably increased collagen deposition and matrix dry weight compared to ascorbic acid alone, and did not affect matrix composition as measured by RT-PCR. Interestingly, Carrageenan did not affect collagen quantity, but it significantly increased glycosaminoglycan deposition. Finally, we successfully fabricated scaffolds from harvested matrix and confirmed their ability for cell growth and viability. This work lays the foundation for development of a time and cost effective protocol for novel iPSF ECM production for tissue engineering scaffolds.

In Vivo Cartilage Regeneration with Cell-Seeded Natural Biomaterial Scaffold Implants: 15-Year Study

Articular cartilage can be easily damaged from human's daily activities, leading to inflammation and to osteoarthritis, a situation that can diminish the patients' quality of life. For larger cartilage defects, scaffolds are employed to provide cells the appropriate three-dimensional environment to proliferate and differentiate into healthy cartilage tissue. Natural biomaterials used as scaffolds, attract researchers' interest because of their relative nontoxic nature, their abundance as natural products, their easy combination with other materials, and the relative easiness to establish Marketing Authorization. The last 15 years were chosen to review, document, and elucidate the developments on cell-seeded natural biomaterials for articular cartilage treatment in vivo. The parameters of the experimental designs and their results were all documented and presented. Considerations about the newly formed cartilage and the treatment of cartilage defects were discussed, along with difficulties arising when applying natural materials, research limitations, and tissue engineering approaches for hyaline cartilage regeneration.

Stem cell therapy in the heart: Biomaterials as a key route

Cardiovascular diseases are one of the main concerns, nowadays causing a high rate of mortality in the world. The majority of conventional treatment protects the heart from failure progression. As a novel therapeutic way, Regenerative medicine in the heart includes cellular and noncellular approaches. Despite the irrefutable privileges of noncellular aspects such as administration of exosomes, utilizing of miRNAs, and growth factors, they cannot reverse necrotic or ischemic myocardium, hence recruiting of stem cells to help regenerative therapy in the heart seems indispensable. Stem cell lineages are varied and divided into two main groups namely pluripotent and adult stem cells. Not only has each of which own regenerative capacity, benefits, and drawbacks, but their turnover also close correlates with the target organ and/or tissue as well as the stage and level of failure. In addition to inefficient tissue integration due to the defects in delivering methods and poor retention of transplanted cells, the complexity of the heart and its movement also make more rigorous the repair process. Hence, utilizing biomaterials can make a key route to tackle such obstacles. In this review, we evaluate some natural products which can help stem cells in regenerative medicine of the cardiovascular system.

Convergence of 3D printed biomimetic wound dressings and adult stem cell therapy

Biomimetically designed medical-grade polycaprolactone (mPCL) dressings are 3D-printed with pore architecture and anisotropic mechanical characteristics that favor skin wound healing with reduced scarring. Melt electrowritten mPCL dressings are seeded with human gingival tissue multipotent mesenchymal stem/stromal cells and cryopreserved using a clinically approved method. The regenerative potential of fresh or frozen cell-seeded mPCL dressing is compared in a splinted full-thickness excisional wound in a rat model over six weeks. The application of 3D-printed mPCL dressings decreased wound contracture and significantly improved skin regeneration through granulation and re-epithelialization compared to control groups. Combining 3D-printed biomimetic wound dressings and precursor cell delivery enhances physiological wound closure with reduced scar tissue formation.

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.

Recent innovations in artificial skin

The skin is a "smart", multifunctional organ that is protective, self-healing and capable of sensing and many forms of artificial skins have been developed with properties and functionalities approximating those of natural skin. Starting from specific commercial products for the treatment of burns, progress in two fields of research has since allowed these remarkable materials to be viable skin replacements for a wide range of dermatological conditions. This review maps out the development of bioengineered skin replacements and synthetic skin substitutes, including electronic skins. The specific behaviors of these skins are highlighted, and the performances of both types of artificial skins are evaluated against this. Moving beyond mere replication, highly advanced artificial skin materials are also identified as potential augmented skins that can be used as flexible electronics for health-care monitoring and other applications.

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 Pathobiology of Skin Aging: New Insights into an Old Dilemma

Long considered both physiologic and inevitable, skin aging is a degenerative phenomenon whereby both intrinsic and environmental factors conspire to produce an authentic disease. The consequences of this disorder are many and varied, ranging from atrophy and fragility to defective repair to deficient immunity and vulnerability to certain infections. The pathobiologic basis for skin aging remains poorly understood. At a cellular level, stem cell dysfunction and attrition appear to be key events, and both genetic and epigenetic factors are involved in a complex interplay that over time results in deterioration of our main protective interface with the external environment. Past and current understanding of the cellular and molecular intricacies of skin aging provide a foundation for future approaches designed to thwart the aging phenotype. Herein, the authors provide a review of current insights into skin aging, including the mechanisms of skin aging, the role of stem cells in skin aging and the implications of skin aging for the microbiome and for the development of cancer. Conquest of the oft overlooked disease of skin aging should have broad implications that transcend the integument and inform novel approaches to retarding aging and age-related dysfunction in those internal organs that youthful skin was designed to envelop and safeguard.

Neural stem cell delivery via porous collagen scaffolds promotes neuronal differentiation and locomotion recovery in spinal cord injury

Neural stem cell (NSC) grafts have demonstrated significant effects in animal models of spinal cord injury (SCI), yet their clinical translation remains challenging. Significant evidence suggests that the supporting matrix of NSC grafts has a crucial role in regulating NSC effects. Here we demonstrate that grafts based on porous collagen-based scaffolds (PCSs), similar to biomaterials utilized clinically in induced regeneration, can deliver and protect embryonic NSCs at SCI sites, leading to significant improvement in locomotion recovery in an experimental mouse SCI model, so that 12 weeks post-injury locomotion performance of implanted animals does not statistically differ from that of uninjured control animals. NSC-seeded PCS grafts can modulate key processes required to induce regeneration in SCI lesions including enhancing NSC neuronal differentiation and functional integration in vivo, enabling robust axonal elongation, and reducing astrogliosis. Our findings suggest that the efficacy and translational potential of emerging NSC-based SCI therapies could be enhanced by delivering NSC via scaffolds derived from well-characterized clinically proven PCS.

Decompressive craniectomy with scalp expansion graft using a temporary synthetic skin substitute in the pediatric population: case series and review of the literature

INTRODUCTION

The use of decompressive craniectomy in children is controversial and often reserved for patients with refractory intracranial hypertension. Following decompression, skin closure in select cases can be challenging due to brain herniation and swelling through the craniectomy defect. In these cases, partial cortical debridement is sometimes performed.

METHODS

We describe two cases in which a synthetic skin substitute was used to facilitate a tension-free closure, rather than performing a partial lobectomy.

RESULTS

At 6-month follow-up, both patients are at preoperative cognitive baseline, with some residual hemiparesis.

DISCUSSION

We believe that use of a synthetic skin substitute for skin closure after decompression is a suitable option for closure of traumatic scalp wounds and may contribute to improved functional outcome in patients with severe intraoperative brain swelling.

Scale and structure dependent solute diffusivity within microporous tissue engineering scaffolds

Diffusion of nutrients to cells cultured within three-dimensional scaffolds is fundamental for cell survival during development of the tissue construct, when no vasculature is present to aid transport. Significant efforts have been made to characterize the effect of structure on solute diffusivity in nanoporous hydrogels, yet a similar thorough characterization has not been attempted for microporous scaffolds. Here, we make use of freeze-dried collagen scaffolds, possessing pore sizes in the range 150-250 μm and isotropic or aligned morphology, to study the diffusivity of fluorescent dextran molecules. Fluorescence recovery after photobleaching is used to measure the self diffusivity of the solutes within single pores, while Fickian diffusion over scales larger than the pore size is studied by assessing the solute concentration profile within the materials over time. We show that, not only do the morphological parameters of the scaffolds significantly affect the diffusivity of the solutes, but also that the assessment of such diffusivity depends on the length scale of diffusion of the molecules under investigation, with the resulting diffusion coefficients being differently affected by the scaffold structure. The results provided can guide the design of scaffolds with tailored diffusivity and nutrient concentration profiles.

Collagen/GAG scaffolds activated by RALA-siMMP-9 complexes with potential for improved diabetic foot ulcer healing

Impaired wound healing of diabetic foot ulcers has been linked to high MMP-9 levels at the wound site. Strategies aimed at the simultaneous downregulation of the MMP-9 level in situ and the regeneration of impaired tissue are critical for improved diabetic foot ulcer (DFU) healing. To fulfil this aim, collagen/GAG (Col/GAG) scaffolds activated by MMP-9-targeting siRNA (siMMP-9) were developed in this study. The siMMP-9 complexes were successfully formed by mixing the RALA cell penetrating peptide with siMMP-9. The complexes formulated at N:P ratios of 6 to 15 had a diameter around 100 nm and a positive zeta potential about 40 mV, making them ideal for cellular uptake. In 2 dimensional (2D) culture of human fibroblasts, the cellular uptake of the complexes surpassed 60% and corresponded to a 60% reduction in MMP-9 gene expression in low glucose culture. In high glucose culture, which induces over-expression of MMP-9 and therefore serves as an in vitro model mimicking conditions in DFU, the MMP-9 gene could be downregulated by around 90%. In the 3D culture of fibroblasts, the siMMP-9 activated Col/GAG scaffolds displayed excellent cytocompatibility and ~60% and 40% MMP-9 gene downregulation in low and high glucose culture, respectively. When the siMMP-9 complexes were applied to THP-1 macrophages, the primary cell type producing MMP-9 in DFU, MMP-9 gene expression was significantly reduced by 70% and 50% for M0 and M1 subsets, in 2D culture. In the scaffolds, the MMP-9 gene and protein level of M1 macrophages decreased by around 50% and 30% respectively. Taken together, this study demonstrates that the RALA-siMMP-9 activated Col/GAG scaffolds possess high potential as a promising regenerative platform for improved DFU healing.

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.

Natural polypeptides-based electrically conductive biomaterials for tissue engineering

Fabrication of an appropriate scaffold is the key fundamental step required for a successful tissue engineering (TE). The artificial scaffold as extracellular matrix in TE has noticeable role in the fate of cells in terms of their attachment, proliferation, differentiation, orientation and movement. In addition, chemical and electrical stimulations affect various behaviors of cells such as polarity and functionality. Therefore, the fabrication approach and materials used for the preparation of scaffold should be more considered. Various synthetic and natural polymers have been used extensively for the preparation of scaffolds. The electrically conductive polymers (ECPs), moreover, have been used in combination with other polymers to apply electric fields (EF) during TE. In this context, composites of natural polypeptides and ECPs can be taken into account as context for the preparation of suitable scaffolds with superior biological and physicochemical features. In this review, we overviewed the simultaneous usage of natural polypeptides and ECPs for the fabrication of scaffolds in TE.