Accelerated Expansion of Epidermal Keratinocyte and Improved Dermal Reconstruction Achieved by Engineered Amniotic Membrane

Human Acellular Amniotic Membrane as Skin Substitute and Biological Scaffold: A Review of Its Preparation, Preclinical Research, and Clinical Application

Human acellular amniotic membrane (HAAM) has emerged as a promising tool in the field of regenerative medicine, particularly for wound healing and tissue regeneration. HAAM provides a natural biological scaffold with low immunogenicity and good anti-infective and anti-scarring results. Despite its potential, the clinic application of HAAM faces challenges, particularly with respect to the preparation methods and its low mechanical strength. This review provides a comprehensive overview of HAAM, covering its preparation, sterilization, preclinical research, and clinical applications. This review also discusses promising decellularization and sterilization methods, such as Supercritical Carbon Dioxide (SC-CO2), and the need for further research into the regenerative mechanisms of HAAM. In addition, we discuss the potential of HAAM as a skin dressing and cell delivery system in preclinical research and clinical applications. Both the safety and effectiveness of HAAM have been validated by extensive research, which provides a robust foundation for its clinical application.

Recent Approaches to the Modification of Collagen Biomatrix as a Corneal Biomatrix and Its Cellular Interaction

Over the last several decades, numerous modifications and advancements have been made to design the optimal corneal biomatrix for corneal epithelial cell (CECs) or limbal epithelial stem cell (LESC) carriers. However, researchers have yet to discover the ideal optimization strategies for corneal biomatrix design and its effects on cultured CECs or LESCs. This review discusses and summarizes recent optimization strategies for developing an ideal collagen biomatrix and its interactions with CECs and LESCs. Using PRISMA guidelines, articles published from June 2012 to June 2022 were systematically searched using Web of Science (WoS), Scopus, PubMed, Wiley, and EBSCOhost databases. The literature search identified 444 potential relevant published articles, with 29 relevant articles selected based on inclusion and exclusion criteria following screening and appraising processes. Physicochemical and biocompatibility (in vitro and in vivo) characterization methods are highlighted, which are inconsistent throughout various studies. Despite the variability in the methodology approach, it is postulated that the modification of the collagen biomatrix improves its mechanical and biocompatibility properties toward CECs and LESCs. All findings are discussed in this review, which provides a general view of recent trends in this field.

Comparing the Effects of Two Cryoprotectant Protocols, Dimethyl-Sulfoxide (DMSO) and Glycerol, on the Recovery Rate of Cultured Keratinocytes on Amniotic Membrane

Background: Off-the-shelf supply of viable engineered tissue is critical for effective and fast treatment of life-threatening injuries such as deep burns. An expanded keratinocyte sheet on the human amniotic membrane (KC sheet-HAM) is a beneficial tissue-engineering product for wound healing. To access an on-hand supply for the widespread application and overcome the time-consuming process, it is necessary to develop a cryopreservation protocol that guarantees the higher recovery of viable keratinocyte sheets after freeze-thawing. This research aimed to compare the recovery rate of KC sheet-HAM after cryopreservation by dimethyl-sulfoxide (DMSO) and glycerol. Methods: Amniotic membrane was decellularized with trypsin, and keratinocytes were cultured on it to form a multilayer, flexible, easy-to-handle KC sheet-HAM. The effects of 2 different cryoprotectants were investigated by histological analysis, live-dead staining, and proliferative capacity assessments before and after cryopreservation. Results: KCs well adhered and proliferated on the decellularized amniotic membrane and successfully represented 3 to 4 stratified layers of epithelialization after 2 to 3 weeks culture period; making it easy to cut, transfer, and cryopreserve. However, viability and proliferation assay indicated that both DMSO and glycerol cryosolutions have detrimental effects on KCs, and KCs-sheet HAM could not recover to the control level after 8 days of culture post-cryo. The KC sheet lost its stratified multilayer nature on AM, and sheet layers were reduced in both cryo-groups compared to the control. Conclusion: Expanding keratinocytes on the decellularized amniotic membrane as a multilayer sheet made a viable easy-to-handle sheet, nonetheless cryopreservation reduced viability and affected histological structure after thawing. Although some viable cells were detectable, our research highlighted the need for a better cryoprotectant protocol other than DMSO and glycerol, specific for the successful banking of viable tissue constructs.

Tailor-made natural and synthetic grafts for precise urethral reconstruction

Injuries to the urethra can be caused by malformations, trauma, inflammation, or carcinoma, and reconstruction of the injured urethra is still a significant challenge in clinical urology. Implanting grafts for urethroplasty and end-to-end anastomosis are typical clinical interventions for urethral injury. However, complications and high recurrence rates remain unsatisfactory. To address this, urethral tissue engineering provides a promising modality for urethral repair. Additionally, developing tailor-made biomimetic natural and synthetic grafts is of great significance for urethral reconstruction. In this work, tailor-made biomimetic natural and synthetic grafts are divided into scaffold-free and scaffolded grafts according to their structures, and the influence of different graft structures on urethral reconstruction is discussed. In addition, future development and potential clinical application strategies of future urethral reconstruction grafts are predicted.

Characterization of decellularized chicken skin as a tissue engineering scaffold

Decellularization has been applied on many tissues and organs to obtain biomaterials for the applications in tissue engineering. In this study, decellularization and characterization of chicken skin was performed to provide comprehensive information and in-depth details on this material as a potential tissue scaffold. Application of Triton X-100 and sodium dodecyl sulfate (SDS) on tissues in different time intervals as two decellularization protocols were compared according to various aspects such as removal of cellular components, DNA quantification, protection of extracellular matrix (ECM), mechanical properties and cytocompatibility to find the optimum technique during preparation of decellularized scaffold. The results showed that treatment with SDS revealed better results when compared with Triton X-100 regarding to preserve tissue structure and morphology although there was no difference on efficiency of decellularization. In general, the tissues decellularized with SDS demonstrated higher level of cytocompatibility and better mechanical properties in comparison with samples treated with Triton X-100. In conclusion, this study revealed that decellularized chicken skin is a cheap, abundant, and biocompatible material that supports cell attachment, growth, and proliferation. Therefore, it could be used as a proper candidate to prepare scaffolds for the further studies on tissue engineering especially for skin tissue engineering. Decellularized chicken skin was prepared and characterized as an abundant, cheap, and biocompatible material for using it as a tissue scaffold. Tissues were treated with Triton X-100 and sodium dodecyl sulfate (SDS) in various time points and samples were compared regarding to cell removal, cell viability, mechanical properties, and preservation of extracellular matrix. 24 hours of decellularization with SDS could be the optimum method to prepare decellularized chicken skin as a scaffold for skin tissue engineering. This article is protected by copyright. All rights reserved.

A comprehensive review on methods for promotion of mechanical features and biodegradation rate in amniotic membrane scaffolds

Amniotic membrane (AM) is a biological tissue that surrounds the fetus in the mother's womb. It has pluripotent cells, immune modulators, collagen, cytokines with anti-fibrotic and anti-inflammatory effect, matrix proteins, and growth factors. In spite of the biological characteristics, some results have been released in preventing the adhesion on traumatized surfaces. Application of the AM as a scaffold is limited due to its low biomechanical resistance and rapid biodegradation. Therefore, for using the AM during surgery, its modification by different methods such as cross-linking of the membrane collagen is necessary, because the cross-linking is an effective way to reduce the rate of biodegradation of the biological materials. In addition, their cross-linking is likely an efficient way to increase the tensile properties of the material, so that they can be easily handled or sutured. In this regard, various methods related to cross-linking of the AM subsuming the composite materials, physical cross-linking, and chemical cross-linking with the glutraldehyde, carbodiimide, genipin, aluminum sulfate, etc. are reviewed along with its advantages and disadvantages in the current work.

Preparation and characterization of decellularized rooster comb as a scaffold for tissue engineering applications

Decellularization is a method that has been widely used in tissue engineering especially in the last 20 years. In this study decellularized rooster comb was prepared and characterized for using it as a tissue scaffold. Treatment of tissues with sodium dodecyl sulfate (SDS) and Triton X-100 as two decellularization procedures in different time points were compared according to different parameters such as cytocompatibility, cell removal, preservation of extracellular matrix (ECM), and mechanical properties to find the optimum technique. Even though there was no difference regarding to efficiency on cell removal, SDS demonstrated better results on protection of tissue morphology in comparison with Triton X-100. Therefore, in general the samples treated with SDS showed higher levels of mechanical properties and cytocompatibility in comparison with Triton X-100 applied tissues. In the cuisines of many countries, rooster comb is discarded as a waste material however, in this study it was demonstrated that decellularized rooster comb could be utilized as a cheap, easily obtainable, and biocompatible scaffold. In conclusion, it was revealed that decellularized rooster comb is a promising biomaterial for using as scaffold and it is expected to be utilized for the further studies in particular on skin tissue engineering.

Evaluation of Radiosterilized Glyercerolated Amniotic Membranes as a Substrate for Cultured Human Epithelial Cells

Human amniotic membrane (HAM) is a biomaterial with biological properties beneficial to tissue repair, serving as a substrate for cell cultivation. Irradiation is used for tissue sterilization, but can damage the HAM structure. The objective of this paper was to construct a skin substitute, composed of human keratinocytes cultured on glycerolated HAMs, and to evaluate the influence radiation on subsequent cell culture growth. Four batches of HAMs were glycerolated, and half of them were radio-sterilzed with 25 kGy. Non-irradiated glycerolated HAM (ni-HAM) and irradiated glycerolated HAM (i-HAM) samples were then de-epithelized and analyzed using optical microscopy (Picrossirius staining), immunofluorescence and electron microscopy. Subsequently, keratinocytes were cultured on ni- and i-HAMs, and either immersed or positioned at the air-liquid interface. The basement membranes of the ni-HAM group remained intact following de-epithelialization, whereas the i-HAM group displayed no evidence or remnant presence of these membranes. Concerning the keratinocyte cultures, the ni-HAM substrate promoted the growth of multi-layered and differentiated epithelia. Keratinocytes cultured on i-HAM formed epithelium composed of three layers of stratification and discrete cell differentiation. The glycerolated HAM was compatible with cultured epithelia, demonstrating its potential as a skin substitute. Irradiation at 25 kGy caused structural damage to the amnion.

Human acellular amniotic membrane implantation for lower third nasal reconstruction: a promising therapy to promote wound healing

Background

The lower third of the nose is one of the most important cosmetic units of the face, and its reconstructive techniques remain a big challenge. As an alternative approach to repair or regenerate the nasal tissue, the biomaterial-based strategy has been extensively investigated. The aim of this study is to determine the safety and efficacy of human acellular amniotic membrane (HAAM) to repair the full-thickness defects in the lower third of the nose in humans.

Methods

In this study, 180 patients who underwent excision of skin lesions of the lower third of the nose from 2012 to 2016 were included; of the patients, 92 received HAAM and Vaseline gauze treatments, and the other 88 patients received Vaseline gauze treatment only. The haemostasis time and the duration of operation were recorded during surgery; after surgery, the time to pain disappearance, scab formation and wound healing, and the wound healing rate were measured.

Results

Immediately after the HAAM implantation, a reduction of the haemostasis time and an accelerated disappearance of pain were observed. Compared with the control group, the formation and detachment of scab in patients who received the HAAM implantation were notably accelerated, postoperatively. When the diameter of the lesion exceeded 5 mm, the HAAM implantation was found to enhance the wound healing, although this enhancement was not seen when the diameter was less than 5 mm. Additionally, the HAAM implantation significantly reduced bleeding, wound infection and scar formation, postoperatively.

Conclusions

HAAM-assisted healing is a promising therapy for lower third nasal reconstruction leading to rapid wound healing and fewer complications and thus has considerable potential for extensive clinical application in repairing skin wounds.

Trial registration

ChiCTR1800017618, retrospectively registered on July 08, 2018.

Decellularized corneal lenticule embedded compressed collagen: toward a suturable collagenous construct for limbal reconstruction

Recently, compressed collagen has attracted much attention as a potential alternative for a limbal epithelial stem cell (LESC) carrier to treat limbal stem cell deficiency (LSCD), in that it can provide mechanically improved collagen fibrillar structures compared to conventional collagen hydrogel. However, its clinical efficacy as an LESC carrier has not yet been studied through in vivo transplantation due to limited mechanical strength that cannot withstand a force induced by surgical suturing and low resistance to enzymatic degradation. This study firstly presents a suturable LESC carrier based on compressed collagen in the form of a biocomposite. The biocomposite was achieved by integrating a decellularized corneal lenticule, which is a decellularized stromal tissue obtained from corneal refractive surgery, inside a compressed collagen to form a sandwich structure. A suture retention test verified that the biocomposite has a much higher suture retention strength (0.56 ± 0.12 N) compared to the compressed collagen (0.02 ± 0.01 N). The biocomposite also exhibited more than 3 times higher resistance to enzymatic degradation, indicating long-term stability after transplantation. In vitro cell culture results revealed that the biocomposite effectively supported the expansion and stratification of the LESCs with expressions of putative stem cell and differentiated corneal epithelial cell markers. Finally, the biocomposite verified its clinical efficacy by stably delivering the LESCs onto an eye of a rabbit model of LSCD and effectively reconstructing the ocular surface.

Healing Effects of Dried and Acellular Human Amniotic Membrane and Mepitelas for Coverage of Skin Graft Donor Areas; A Randomized Clinical Trial

Objective

To compare the healing effects of dried and acellular human amniotic membrane and Mepitel for coverage of split-thickness graft donor site (STGDS).

Methods

Twenty patients who underwent STGDS regeneration surgery in identical anatomic regions were enrolled in this randomized controlled clinical trial conducted in Hazrate Fatemeh hospital (Iran). Patients were randomly assigned in 3 groups of wound dressing; group A by Mepitel, group B AmiCare (Dried amniotic membrane) and group C OcuReg-A (Acellular amniotic membrane). Re-epithelization rate (healing time), pain sensation, scar formation and infection rate were assessed till complete healing was achieved.

Results

Our results showed no significant difference between Amicare, OcuReg-A and Mepitel in the features analyzed by us including: Re-epithelization rate (healing time) P value; 0.573, Pain sensation P value: day 4 th: 0.131, day8 th: 0.93 and day 12 th: 0.365, Scar formation P value>0.05and Infection rate.

Conclusion

Our findings confirmed the safety and efficacy of AmiCare (dried amniotic membrane) and OcuReg-A (Acellular amniotic membrane) in treatment of split-thickness donor site in comparison with Mepitel as a standard wound dressing. Trial registration number: IRCT201511118177N12.

Human Amniotic Membrane: A Versatile Scaffold for Tissue Engineering

The human amniotic membrane (hAM) is a collagen-based extracellular matrix derived from the human placenta. It is a readily available, inexpensive, and naturally biocompatible material. Over the past decade, the development of tissue engineering and regenerative medicine, along with new decellularization protocols, has recast this simple biomaterial as a tunable matrix for cellularized tissue engineered constructs. Thanks to its biocompatibility, decellularized hAM is now commonly used in a broad range of medical fields. New preparation techniques and composite scaffold strategies have also emerged as ways to tune the properties of this scaffold. The current state of understanding about the hAM as a biomaterial is summarized in this review. We examine the processing techniques available for the hAM, addressing their effect on the mechanical properties, biodegradation, and cellular response of processed scaffolds. The latest in vitro applications, in vivo studies, clinical trials, and commercially available products based on the hAM are reported, organized by medical field. We also look at the possible alterations to the hAM to tune its properties, either through composite materials incorporating decellularized hAM, chemical cross-linking, or innovative layering and tissue preparation strategies. Overall, this review compiles the current literature about the myriad capabilities of the human amniotic membrane, providing a much-needed update on this biomaterial.

Supportive properties of basement membrane layer of human amniotic membrane enable development of tissue engineering applications

Human amniotic membrane (HAM) has been widely used as a natural scaffold in tissue engineering due to many of its unique biological properties such as providing growth factors, cytokines and tissue inhibitors of metalloproteinases. This study aimed at finding the most suitable and supportive layer of HAM as a delivery system for autologous or allogeneic cell transplantation. Three different layers of HAM were examined including basement membrane, epithelial and stromal layers. In order to prepare the basement membrane, de-epithelialization was performed using 0.5 M NaOH and its efficiency was investigated by histological stainings, DNA quantification, biomechanical testing and electron microscopy. Adipose-derived stromal cells (ASCs) and a human immortalized keratinocyte cell line (HaCaT) were seeded on the three different layers of HAM and cultured for 3 weeks. The potential of the three different layers of HAM to support the attachment and viability of cells were then monitored by histology, electron microscopy and (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Moreover, mechanical strengths of the basement membrane were assessed before and after cell culture. The results indicated that the integrity of extra cellular matrix (ECM) components was preserved after de-epithelialization and resulted in producing an intact basement amniotic membrane (BAM). Moreover, all three layers of HAM could support the attachment and proliferation of cells with no visible cytotoxic effects. However, the growth and viability of both cell types on the BAM were significantly higher than the other two layers. We conclude that growth stimulating effectors of BAM and its increased mechanical strength after culturing of ASCs, besides lack of immunogenicity make it an ideal model for delivering allogeneic cells and tissue engineering applications.

Immunomodulatory Effects of Human Cryopreserved Viable Amniotic Membrane in a Pro-Inflammatory Environment In Vitro

INTRODUCTION

Chronic wounds remain a major clinical challenge. Human cryopreserved viable amniotic membrane (hCVAM) is among the most successful therapies, but the mechanisms of action remain loosely defined. Because proper regulation of macrophage behavior is critical for wound healing with biomaterial therapies, we hypothesized that hCVAM would positively regulate macrophage behavior in vitro, and that soluble factors released from the hCVAM would be important for this effect.

MATERIALS AND METHODS

Primary human pro-inflammatory (M1) macrophages were seeded directly onto intact hCVAM or cultured in separation via transwell inserts (Soluble Factors) in the presence of pro-inflammatory stimuli (interferon-γ and lipopolysaccharide) to simulate the chronic wound environment. Macrophages were characterized after 1 and 6 days using multiplex gene expression analysis of 37 macrophage phenotype- and angiogenesis-related genes via NanoString™, and protein content from conditioned media collected at days 1, 3 and 6 was analyzed via enzyme linked immunosorbent assays.

RESULTS AND DISCUSSION

Gene expression analysis showed that Soluble Factors promoted significant upregulation of pro-inflammatory marker IL1B on day 1 yet downregulation of TNF on day 6 compared to the M1 macrophage control. In contrast, intact hCVAM, which includes both extracellular matrix, viable cells, and soluble factors, promoted downregulation of pro-inflammatory markers TNF, CCL5 and CCR7 on day 1 and endothelial receptor TIE1 on day 6, and upregulation of the anti-inflammatory marker IL10 on day 6 compared to the M1 Control. Other genes related to inflammation and angiogenesis (MMP9, VEGF, SPP1, TGFB1, etc.) were differentially regulated between the Soluble Factors and intact hCVAM groups at both time points, though they were not expressed at significantly different levels compared to the M1 Control. Interestingly, Soluble Factors promoted increased secretion of the proinflammatory cytokine tumor necrosis factor-α (TNF-α), while direct contact with hCVAM inhibited secretion of TNF, relative to the M1 Control. Both Soluble Factors and intact hCVAM inhibited secretion of MMP9 and VEGF, pro-inflammatory proteins that are critical for angiogenesis and remodeling, compared to the M1 Control, with intact hCVAM having a stronger effect.

CONCLUSIONS

In a simulated pro-inflammatory environment, intact hCVAM has distinct anti-inflammatory effects on primary human macrophages, and direct macrophage contact with intact hCVAM is required for these effects. These findings are important for the design of next generation immunomodulatory biomaterials for wound repair and regenerative medicine that may include living cells, soluble factors, or a controlled drug delivery system.

Transplantation of Amniotic Scaffold-Seeded Mesenchymal Stem Cells and/or Endothelial Progenitor Cells From Bone Marrow to Efficiently Repair 3-cm Circumferential Urethral Defect in Model Dogs

The treatment options for patients with a urethral defect are limited by the availability of autologous tissues. We hypothesized that transplantation of decellularized human amniotic scaffolds (dHAS) seeded with allogeneic bone marrow mesenchymal cells (BMSCs) and/or endothelial progenitor cells (EPCs) may serve as a promising repair strategy for long segment of circumferential urethral defect. To verify the hypothesis, with urinary catheterization, a 3-cm segment of whole urethra in 25 male mongrel dogs was excised and replaced by dHAS seeded with allogeneic BMSCs and/or EPCs. Postoperative observation and ascending urethrogram found that dHAS+BMSCs+EPCs and dHAS+EPCs groups demonstrated unhindered urination and capacious urethral caliber, which were similar to the normal group, while urethrostenosis was revealed in dHAS+BMSCs, dHAS, and sham-operated groups, with the shortest narrow section in dHAS+BMSCs group and the longest in sham-operated group. Urethral anatomy check and histological analyses showed that new urethral mucosa composed of stratified columnar epithelium completely covered on the inner surface of the graft site in dHAS+BMSCs+EPCs and dHAS+EPCs groups, but the middle epithelium was thin in dHAS+EPCs group, while incompletely covered in dHAS+BMSCs, dHAS, and sham-operated groups, and there were monolayer epithelial cells at the urethrostenosis in dHAS+BMSCs and dHAS groups. In addition, abundant new vessel and blood sinus showed at submucosa in dHAS+BMSCs+EPCs and dHAS+EPCs groups, instead of the scar tissue of collagen deposition and structural distortion at the urethrostenosis in dHAS+BMSCs, dHAS, and sham-operated groups. This study demonstrates that dHAS seeded with BMSCs+EPCs or EPCs can successfully repair a 3-cm circumferential urethral defect in model dogs, but the former works best. This technology may provide some references for human clinical trials on long segment of circumferential urethral defect repair.

Amniotic membrane in ophthalmology: properties, preparation, storage and indications for grafting-a review

The use of amniotic membrane in ophthalmic surgery and other surgical procedures in the fields of dermatology, plastic surgery, genitourinary medicine and otolaryngology is on the increase. Furthermore, amniotic membrane and its epithelial and mesenchymal cells have broad use in regenerative medicine and hold great promise in anticancer treatment. Amniotic membrane is a rich source of biologically active factors and as such, promotes healing and acts as an effective material for wound dressing. Amniotic membrane supports epithelialization and exhibits anti-fibrotic, anti-inflammatory, anti-angiogenic and anti-microbial features. Placentas utilised in the preparation of amniotic membrane are retrieved from donors undergoing elective caesarean section. Maternal blood must undergo serological screening at the time of donation and, in the absence of advanced diagnostic testing techniques, 6 months postpartum in order to cover the time window for the potential transmission of communicable diseases. Amniotic membrane is prepared by blunt dissection under strict aseptic conditions, then is typically transferred onto a nitrocellulose paper carrier, usually with the epithelial side up, and cut into multiple pieces of different dimensions. Amniotic membrane can be stored under various conditions, most often cryopreserved in glycerol or dimethyl sulfoxide or their mixture with culture medium or buffers. Other preservation methods include lyophilisation and air-drying. In ophthalmology, amniotic membrane is increasingly used for ocular surface reconstruction, including the treatment of persistent epithelial defects and non-healing corneal ulcers, corneal perforations and descemetoceles, bullous keratopathy, as well as corneal disorders with associated limbal stem cell deficiency, pterygium, conjunctival reconstruction, corneoscleral melts and perforations, and glaucoma surgeries.

Topical administration of cryopreserved living micronized amnion accelerates wound healing in diabetic mice by modulating local microenvironment

Approximately 25% of diabetic patients suffer from diabetic lower-extremity ulcer throughout their lives and 7%-20% of patients will eventually need an amputation despite standard care treatment. The development of new therapies to treat diabetic wounds is urgent. In this study, we used cryopreserved living micronized amnion (300-600 μm) to treat wounds in diabetic mice. Post-thaw micronized amnion retained high cell viability, as well as intact cell morphology and membrane structure. When transplanted onto the wounds of db/db mice, the cryopreserved living micronized amnion greatly promoted wound healing in diabetic mice mainly by secreting growth, inflammation, and chemotaxis-related factors that regulated macrophage migration and phenotype switch, recruited CD34⁺ progenitor cells, and increased neovascularization. In addition, the micronized amnion matrix can exist in the dermis and serve as a long-term dermal scaffold. These results demonstrated the potential of the cryopreserved living micronized amnion as a ready-to-use living dermal substitute that addresses multiple defective physiological processes of impaired wounds to treat diabetic ulcers and other chronic wounds in clinics.

Generation of Two Biological Wound Dressings as a Potential Delivery System of Human Adipose-Derived Mesenchymal Stem Cells

Human adipose-derived mesenchymal stem cells (hADMSCs) are believed to be potential key factors for starting the regenerative process after tissue injury. However, an efficient method of delivering these regenerative cells to an external wound site is still lacking. Human amnion and pig skin have long been used as skin wound dressings for the treatment of burns and other skin lesions. Herein, we present the generation of two constructs using these two biomaterials as effective scaffolds for the culture of hADMSCs. It was found that hADMSCs seeded onto radiosterilized human amnion and pig skin are viable and proliferate. These cells are able to migrate over these scaffolds as demonstrated by using time-lapse microscopy. In addition, the scaffolds induce hADMSCs to secrete interleukin-10, an important negative regulator of inflammation, and interleukin-1β, a proinflammatory protein. The interplay between these two proteins has been proven to be vital for a balanced restoration of all necessary tissues. Thus, radiosterilized human amnion and pig skin are likely suitable scaffolds for delivery of hADMSCs transplants that could promote tissue regeneration in skin injuries like patients with burn injuries.

Naturally Occurring Extracellular Matrix Scaffolds for Dermal Regeneration: Do They Really Need Cells?

The pronounced effect of extracellular matrix (ECM) scaffolds in supporting tissue regeneration is related mainly to their maintained 3D structure and their bioactive components. These decellularized matrix scaffolds could be revitalized before grafting via adding stem cells, fibroblasts, or keratinocytes to promote wound healing. We reviewed the online published literature in the last five years for the studies that performed ECM revitalization and discussed the results of these studies and the related literature. Eighteen articles met the search criteria. Twelve studies included adding cells to acellular dermal matrix (ADM), 3 studies were on small intestinal mucosa (SIS), one study was on urinary bladder matrix (UBM), one study was on amniotic membrane, and one study included both SIS and ADM loaded constructs. We believe that, in chronic and difficult-to-heal wounds, revitalizing the ECM scaffolds would be beneficial to overcome the defective host tissue interaction. This belief still has to be verified by high quality randomised clinical trials, which are still lacking in literature.

Prospective randomized comparison of scar appearances between cograft of acellular dermal matrix with autologous split-thickness skin and autologous split-thickness skin graft alone for full-thickness skin defects of the extremities

BACKGROUND

The purpose of this study was to evaluate the clinical outcomes of cografting of acellular dermal matrix with autologous split-thickness skin and autologous split-thickness skin graft alone for full-thickness skin defects on the extremities.

METHODS

In this prospective randomized study, 19 consecutive patients with full-thickness skin defects on the extremities following trauma underwent grafting using either cograft of acellular dermal matrix with autologous split-thickness skin graft (nine patients, group A) or autologous split-thickness skin graft alone (10 patients, group B) from June of 2011 to December of 2012. The postoperative evaluations included observation of complications (including graft necrosis, graft detachment, or seroma formation) and Vancouver Scar Scale score.

RESULTS

No statistically significant difference was found regarding complications, including graft necrosis, graft detachment, or seroma formation. At week 8, significantly lower Vancouver Scar Scale scores for vascularity, pliability, height, and total score were found in group A compared with group B. At week 12, lower scores for pliability and height and total scores were identified in group A compared with group B.

CONCLUSIONS

For cases with traumatic full-thickness skin defects on the extremities, a statistically significant better result was achieved with cograft of acellular dermal matrix with autologous split-thickness skin graft than with autologous split-thickness skin graft alone in terms of Vancouver Scar Scale score.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, II.

Urethral reconstruction with tissue-engineered human amniotic scaffold in rabbit urethral injury models

BACKGROUND

Mitigating urethral injury remains a great challenge for urologists due to lack of ideal biomaterials for urethroplasty. The application of amniotic membranes (AM) over other synthetic materials make it a better potential source for urethral reconstruction. We separated the basement layer of AM to obtain denuded human amniotic scaffold (dHAS) and then inoculated primary rabbit urethral epithelial cells on the surface of dHAS to define whether this strategy minimize potential rejection and maximize the biocompatibility of human AM.

MATERIAL/METHODS

After the successful acquisition of dHAS from AM, cell-seeded dHAS were prepared and characterized. Both cell-seeded dHAS and acellular dHAS were subcutaneously implanted. Immune responses were compared by histological evaluation and CD4 cell and CD8 cell infiltrations. Then they were applied as urethroplastic materials in the rabbit models of urethral injury to fully explore the feasibility and efficacy of tissue-engineered dHAS xenografts in urethral substitution application.

RESULTS

Mild inflammatory infiltration was observed in cell-seeded dHAS grafts, as revealed by fewer accumulations of CD4 cells and CD8 cells (or neutrophils or other immune cells). Urethral defects of rabbits in the urethroplastic group with dHAS implantation (n=6) were completely resolved in one month, while there were one infection and one fistula in the control group with acellular dHAS patches (n=6). Histopathological analysis revealed mild immune response in cell-seeded dHAS group (P<0.05).

CONCLUSIONS

Tissue-engineered dHAS minimize potential rejection and maximize the biocompatibility of AM, which makes it a potential ideal xenograft for urethral reconstruction.

Wound healing: an update

Wounds, both chronic and acute, continue to be a tremendous socioeconomic burden. As such, technologies drawn from many disciplines within science and engineering are constantly being incorporated into innovative wound healing therapies. While many of these therapies are experimental, they have resulted in new insights into the pathophysiology of wound healing, and in turn the development of more specialized treatments for both normal and abnormal wound healing states. Herein, we review some of the emerging technologies that are currently being developed to aid and improve wound healing after cutaneous injury.

Cell sheet engineering for regenerative medicine: current challenges and strategies

Substantial progress made in the areas of stem cell research and regenerative medicine has provided a number of innovative methods to repair or regenerate defective tissues and organs. Although previous studies regarding regenerative medicine, especially those involving induced pluripotent stem cells, have been actively promoted in the past decade, there remain some challenges that need to be addressed in order to enable clinical applications. Designed for use in clinical applications, cell sheet engineering has been developed as a unique, scaffold-free method of cell processing utilizing temperature-responsive cell culture vessels. Clinical studies using cell sheets have shown positive outcomes and will be translated into clinical practice in the near future. However, several challenges stand in the way of the industrialization of cell sheet products and the widespread acceptance of regenerative medicine based on cell sheet engineering. This review describes current strategies geared towards the realization of the regenerative medicine approach.

Strategies Demonstrating Efficacy in Reducing Wound Contraction In Vivo

SIGNIFICANCE

Scarring continues to present a significant clinical problem. Wound contraction leads to scarring and is mediated by myofibroblasts and contractile forces across the wound bed. Contracture formation can have a significant impact on the quality of life of the patient, particularly where function and appearance are affected.

RECENT ADVANCES

Novel tissue-engineered matrices, cell-based therapies, and medicinal therapeutics have shown significant reduction in wound contraction in in-vivo models, particularly at early time points. These have been accompanied in many cases by reduced numbers of myofibroblasts, and in some by increased angiogenesis and improved neodermal architecture.

CRITICAL ISSUES

There are no animal models that replicate all aspects of wound healing as seen in patients. Therefore, information obtained from in vivo studies should be assessed critically. Additional studies, in particular those that seek to elucidate the mechanisms by which novel therapies reduce contraction, are needed to gain sufficient confidence to move into clinical testing.

FUTURE DIRECTIONS

The use of knockout mouse models in particular has generated significant advances in knowledge of the mechanisms behind myofibroblast conversion and other factors involved in generating tension across the wound. Medicinal therapeutics and tissue-engineering approaches that seek to disrupt/alter these pathways hold much promise for future development and translation to clinical practice.