Dispase/detergent treated dermal matrix as a dermal substitute

New hope for esophageal stricture prevention: A prospective single-center trial on acellular dermal matrix

BACKGROUND

Given the high incidence of esophageal cancer in China, an increasing number of patients there are undergoing endoscopic mucosal dissection (ESD). Although the 5-year survival rate after ESD can exceed 95%, esophageal stricture, the most common and serious postoperative complication, affects the long-term prognosis of patients and the quality of life. Autologous mucosal grafts have proven to be successful in preventing stricture after ESD for early esophageal cancer.

AIM

To examine the viability of acellular dermal matrix (ADM) as an alternative to autologous mucosa for the prevention of stricture after ESD.

METHODS

This is a prospective, single-center, controlled study. Consecutive patients who underwent ESD surgery and were willing to undergo autologous mucosal transplantation were recruited between January 1 and December 31, 2017. Consecutive patients who underwent ESD surgery and were willing to undergo ADM transplantation were recruited between January 1 to December 31, 2019. A final three-year follow-up of patients who received transplants was conducted.

RESULTS

Based on the current incidence of esophageal stricture, the sample size required for both the autologous mucosal graft group and the ADM group was calculated to be 160 cases. Due to various factors, a total of 20 patients with autologous mucosal grafts and 25 with ADM grafts were recruited. Based on the inclusion exclusion and withdrawal criteria, 9 patients ultimately received autologous mucosal grafts and completed the follow-up, while 11 patients received ADM grafts and completed the follow-up. Finally, there were 2 cases of stenosis in the autologous mucosal transplantation group with a stenosis rate of 22.22% and 2 cases of stenosis in the ADM transplantation group with a stenosis rate of 18.18%, with no significant difference noted between the groups (P = 0.94).

CONCLUSION

In this prospective, single-center, controlled trial, we compared the effectiveness of autologous mucosa transplantation and ADM for the prevention of esophageal stricture. Due to certain condition limitations, we were unable to recruit sufficient subjects meeting our target requirements. However, we implemented strict inclusion, exclusion, and withdrawal criteria and successfully completed three years of follow-up, resulting in valuable clinical insights. Based on our findings, we hypothesize that ADM may be similarly effective to autologous mucosal transplantation in the prevention of esophageal stricture, offering a comparable and alternative approach. This study provides a new therapeutic idea and direction for the prevention of esophageal stricture.

Decellularization of Skin Tissue

Biomaterials science encompasses elements of medicine, biology, chemistry, materials, and tissue engineering. They are engineered to interact with biological systems to treat, augment, repair, or replace lost tissue function. The choice of biomaterial depends on the procedure being performed, the severity of the patient's condition, and the surgeon's preference. Prostheses made from natural-derived biomaterials are often derived from decellularized extracellular matrix (ECM) of animal (xenograft) or human (allograft) origin. Advantages of using ECM include their resemblance in morphology and three-dimensional structures with that of tissue to be replaced. Due to this, scientists all over are now focusing on naturally derived biomaterials which have been shown to possess several advantages compared to synthetic ones, owing to their biocompatibility, biodegradability, and remodeling properties. Advantages of a naturally derived biomaterial enhance their application for replacement or restoration of damaged organs/tissues. They adequately support cell adhesion, migration, proliferation, and differentiation. Naturally derived biomaterials can induce extracellular matrix formation and tissue repair when implanted into a defect by enhancing attachment and migration of cells from surrounding environment. In the current chapter, we will focus on the natural and synthetic dermal matrix development and all of the progress in this field.

Application of an acellular dermal matrix to a rabbit model of oral mucosal defects

Acellular dermal matrices (ADMs) are increasingly used for the restoration of soft-tissue defects of the oral cavity due to their ability to facilitate faster healing and reduce scar formation without rejection. However, few studies have focused on the histopathology and biological mechanisms involved in their use. The aim of the present study was to observe tissue growth, histopathologic changes and altered biomolecular signatures that occur during the repair of oral defects in rabbit models over time, either with or without the employment of ADM. Animals were sacrificed 1, 2 and 4 weeks following surgery and histological changes were evaluated using hematoxylin and eosin staining. Reverse transcription-polymerase chain reaction and western blot analysis were used to determine changes in the expression of vascular endothelial growth factor (VEGF) and glucose transporter 1 (GLUT1). It was demonstrated that wounds treated with ADM exhibited a weak inflammatory reaction and faster epithelialization and revascularization compared with untreated wounds. This may have been caused by the elevated levels of VEGF and GLUT1 protein detected in the ADM-treated defects. Thus, treating wounds of the oral mucosa with an ADM improves pathological responses compared with those with an untreated wound. The current study demonstrates the underlying mechanisms by which ADM promotes wound healing in defects of the oral mucosa and the results provide further evidence for the use of ADM in clinical settings for the repair of mucosal defects.

Dermis, acellular dermal matrix, and fibroblasts from different layers of pig skin exhibit different profibrotic characteristics: evidence from in vivo study

To explore the profibrotic characteristics of the autografted dermis, acellular dermal matrix, and dermal fibroblasts from superficial/deep layers of pig skin, 93 wounds were established on the dorsa of 7 pigs. 72 wounds autografted with the superficial/deep dermis and acellular dermal matrix served as the superficial/deep dermis and acellular dermal matrix group, respectively, and were sampled at 2, 4, and 8 weeks post-wounding. 21 wounds autografted with/without superficial/deep dermal fibroblasts served as the superficial/deep dermal fibroblast group and the control group, respectively, and were sampled at 2 weeks post-wounding. The hematoxylin and eosin staining showed that the wounded skin thicknesses in the deep dermis group (superficial acellular dermal matrix group) were significantly greater than those in the superficial dermis group (deep acellular dermal matrix group) at each time point, the thickness of the cutting plane in the deep dermal fibroblast group was significantly greater than that in the superficial dermal fibroblast group and the control group. The western blots showed that the α-smooth muscle actin expression in the deep dermis group (superficial acellular dermal matrix group) was significantly greater than that in the superficial dermis group (deep acellular dermal matrix group) at each time point. In summary, the deep dermis and dermal fibroblasts exhibited more profibrotic characteristics than the superficial ones, on the contrary, the deep acellular dermal matrix exhibited less profibrotic characteristics than the superficial one.

* Extracellular Matrices for Bone Regeneration: A Literature Review

The gold standard material for bone regeneration is still autologous bone, a mesenchymal tissue that consists mainly of extracellular matrix (ECM) (90% v/v) and little cellular content (10% v/v). However, the fact that decellularized allogenic bone grafts often present a clinical performance comparable to autologous bone grafts demonstrates the crucial role of ECM in bone regeneration. For long, the mechanism by which bone allografts function was not clear, but recent research has unveiled many unique characteristics of ECM that seem to play a key role in tissue regeneration. This is further confirmed by the fact that synthetic biomaterials with composition and properties resembling bone ECM present excellent bone regeneration properties. In this context, ECM molecules such as glycosaminoglycans (GAGs) and self-assembly peptides (SAPs) can improve the performance of bone regeneration biomaterials. Moreover, decellularized ECM derived either from native tissues such as bone, cartilage, skin, and tooth germs or from cells such as osteoblasts, chondrocytes, and stem cells has shown promising results in bone regeneration applications. Understanding the role of ECM in bone regeneration is crucial for the development of the next generation of biomaterials for bone tissue engineering. In this sense, this review addresses the state-of-the-art on this subject matter.

Development of a new method for the preparation of an acellular allodermis, quality control and cytotoxicity testing

Demand for use of acellular allodermis is high but commercially appropriate products are not used routinely because of very high price and limited availability. These facts did motivate us to prepare acellular allodermis using a new, simple and less expensive method. We have developed a original method for preparation of acellular allogeneic dermis based on action of a proteolytic enzyme in combination with distilled water. Hypotonic environment in comparison with SDS or Triton ansure no toxicity of the final product. Trials for determination of optimal trypsin concentrations, temperature and time of action were performed. According to our results, the use of 2.5% trypsin/EDTA solution overnight at +4 °C was proving to be optimal. The histology confirmed absence of cells in the prepared dermis. No toxicity of final acellular dermis was confirmed by three independent tests (agar diffusion test contact cytotoxicity test and grow curve). The prepared acellular dermis seems to be suitable not only for direct clinical use, but it can be used as a scaffold for cell cultivation as well.

A Meta-analysis of Postoperative Complications of Tissue Expander/Implant Breast Reconstruction Using Acellular Dermal Matrix

BACKGROUND

Acellular dermal matrix (ADM) is commonly used for tissue expander/implant breast (TE/I-based) reconstruction. But the relation between ADM and postoperative complications remains controversial. A few meta-analyses were conducted in 2011-2012 and the result revealed that ADM can increase the risk of complications. The purpose of our study is to offer updated evidence for ADM clinical application by analyzing the effect of ADM on complications of TE/I-based breast reconstruction.

METHODS

The literature published from January 2010 to February 2015 was searched in EMbase, Medline, Science Direct, the Cochrane Central Register of Controlled Trials (CENTRAL), CBMdisc, CNKI, VIP, and the references of those included studies were also searched by hand. According to inclusive criteria, 11 studies were selected and the values were extracted from the included literature. Complications with four different categories assigned for overall complications, infection, hematoma/seroma, and explantation were collected. RevMan 5.1 was used for meta-analysis. The evidence level was assessed by using the GRADE system.

RESULTS

Eleven published studies were included. The results showed that compared to the control group, the ADM group increased the rate of overall complications (OR = 1.33, 95% CI 1.03-1.70, p = 0.03), infection (OR = 1.47, 95% CI 1.04-2.06, p = 0.03), hematoma/seroma (OR = 1.66, 95% CI 1.13-2.44, p = 0.01), but there was no significant difference in explantation (OR = 1.37, 95% CI 0.89-2.11, p = 0.15). Based on the GRADE system, all the evidence was at level C and weak recommendation.

CONCLUSIONS

In TE/I-based breast reconstruction, ADM increased the incidence of overall complications, infection, and hematoma/seroma; the incidence of explantation remains unknown. For the poor quality of the original studies, a prudent choice is suggested; and more high-quality, large-sample studies are needed.

NO LEVEL ASSIGNED

This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors http://www.springer.com/00266.

Clinical application and histological properties of autologous tissue-engineered skin equivalents using an acellular dermal matrix

We developed a transplantable tissue-engineered skin equivalent composed of autologous cultured keratinocytes, fibroblasts, and a decellularized allogeneic dermis (acellular allogeneic dermal matrix; ADM) obtained from cadavers. In a process taking 3 weeks, cultured autologous keratinocytes from burn patients were expanded and then grown on ADMs. The tissue-engineered autologous skin equivalents (TESEs) were then transplanted in a one-stage procedure to the debrided third-degree burn wounds of 4 patients. The mean graft survival rate was 96%. Delayed graft loss and graft fragility were not observed. Histological and immunohistological findings indicated that the transplanted TESE had similar characteristics to normal human split-thickness skin grafts. These results suggest that the TESE using ADM can be used for permanent repair of full-thickness skin defects.

Three-Dimensional Histological Structures of the Human Dermis

Spatial information has been shown to be critical for cell differentiation and function. Therefore, a better understanding of skin microstructures is very important for biomimetic and bioengineered scaffolds of engineering skin. The purpose of the study was to generate collagen/elastin-based three-dimensional (3D) images of human dermis to further understand the microstructures of the skin, which is believed to be helpful in the fabrication of bionic engineered skin. Skin samples were fixed, embedded, serially sectioned, stained with aldehyde-fuchsin, and photographed as serial panoramas. Dermal subregions were divided according to dermal depth and distance to hair follicle. The porosity, pore diameters, and wall thickness of human acellular dermal matrix (ADM) were measured by microcomputed tomography (micro-CT). Three-dimensional reconstructed images of collagen and elastic fibers were generated. Our results showed that there were fewer elastic fibers in the subregions close to hair follicles than in the subregions far away from hair follicles (p<0.001), but the collagen fibers were evenly distributed. Both collagen and elastic fibers were found in fewer numbers in the layers either close to the epidermis or close to the hypodermis. The mean proportions of collagen fibers and elastic fibers in the whole dermis were 28.96%±14.63% and 8.06%±3.75%, respectively. The porosity of ADM calculated by micro-CT was 68.3%±5.8%. The mean pore diameter of ADM was 131.2±96.8 μm, and the wall thickness of pores was 207.2±251.7 μm. This study represents for the first time that 3D histological cutaneous structures have been presented, which may be helpful for the next generation of skin engineering.

Buccal mucosa repair with electrospun silk fibroin matrix in a rat model

INTRODUCTION

Biomimic electrospun matrix derived from silk fibroin nanofiber solution was recently prepared in our group. The feasibility of the matrix as mucosa repair scaffold was evaluated in a rat model in the present study.

METHODS

Full thickness wound was established on the buccal mucosa of male Wister rats via microscopic oral surgery. 80 rats were randomly assigned into 4 groups: (1) silk fibroin matrix, (2) commercial cowhide acellular dermal matrix (Heal-All), (3) commercial acellular dermal matrix of human skin (RENOV), and (4) vaseline gauze, respectively.

RESULTS

The silk fibroin matrix showed similar repair performance compared to the commercial acellular dermal matrices, implying promising applications in mucosa regeneration. More importantly, the silk fibroin matrix showed better wound healing ability, improved wound shrinkage inhibition, and reduced local immunological incompatibility.

CONCLUSIONS

The silk fibroin scaffold performed satisfied in scar tissue inhibition and epidermis regeneration. Taking into account its improved mechanical properties, the biomimic electrospun silk matrix could become a promising substitute of acellular dermal matrix in clinical applications.

Acellular dermal matrices and radiotherapy in breast reconstruction: a systematic review and meta-analysis of the literature

The increasing use of commercially available acellular dermis matrices for postmastectomy breast reconstruction seems to have simplified the surgical procedure and enhanced the outcome. These materials, generally considered to be highly safe or with only minor contraindications due to the necessary manipulation in preparatory phases, allow an easier one-phase surgical procedure, in comparison with autologous flaps, offering a high patient satisfaction. Unfortunately, the claim for a higher rate of complications associated with irradiation at the implant site, especially when the radiation therapy was given before the reconstructive surgery, suggested a careful behaviour when this technique is preferred. However, this hypothesis was never submitted to a crucial test, and data supporting it are often discordant or incomplete. To provide a comprehensive analysis of the field, we searched and systematically reviewed papers published after year 2005 and registered clinical trials. On the basis of a meta-analysis of data, we conclude that the negative effect of the radiotherapy on the breast reconstruction seems to be evident even in the case of acellular dermis matrices aided surgery. However, more trials are needed to make solid conclusions and clarify the poor comprehension of all the factors negatively influencing outcome.

The in vivo evaluation of tissue-based biomaterials in a rat full-thickness abdominal wall defect model

Hernias are defects in which an anatomical fascia is breached resulting in ectopic positioning of an organ into an orifice which routinely does not contain it. Intervention often involves repositioning translocated organs and repair of damaged fascia using exogenous grafts. Despite hernia prevalence, repairs can still fail due to postoperative complications, such as chronic pain and decreased mobility. This study compared repair capacities and characterized the foreign body response elicited by a number of hernia repair grafts to deduce their bulk inflammatory properties while also concluding the point in their fabrication when these are inferred. Materials derived from human dermis (Alloderm(®) ), porcine dermis (Permacol™, patch A, patch D and Strattice(®) ), porcine small-intestinal submucosa (Surgisis™) and a synthetic (multifilament Surgipro™) were implanted into a rat full-thickness abdominal wall excision model, incubated for up to 2 years and characterized histopathologically. Surgisis™ resorbed the fastest of the materials tested (1-3 months) resulting in a mechanically stable parietal peritoneum. Decellularization using sodium dodecyl sulfate (patch A) stimulated a large early inflammatory response which ultimately may have contributed to increased resorption of porcine dermal matrix however the remaining materials typically persisted throughout the 2-year incubation. Cross-linking porcine dermis using 1,6-hexamethylene disocyanate (vs. an identical noncross-linked counterpart) showed no difference in cell recruitment or material integration over 2 years. Typically Strattice(®) and Alloderm(®) recruited larger early populations of cells than Permacol™; however, over extended periods of time in vivo this response normalized.

Autologous skin reconstruction by combining epidermis and acellular dermal matrix tissue derived from the skin of giant congenital melanocytic nevi

Giant congenital melanocytic nevi (GCMN) are defined as nevi greater than 20 cm in diameter. It is difficult to completely remove GCMN because of the lack of available skin grafts for covering the resultant defects. This study examined whether it is possible to produce reconstructed skin by combining epidermal and acellular dermal matrix (ADM) tissue derived from excised GCMN. GCMN skin samples were obtained with the informed consent of volunteer patients. The abilities of hypertonic saline (1 N NaCl), 0.05% trypsin, 0.1% SDS (sodium dodecyl sulfate), and phosphate buffered saline (PBS) to decellularize GCMN tissue were compared. The specimens were incubated in one of the test solutions at 37 °C for 48 h, before being washed with PBS at 4 °C for 14 days. Residual nuclei, residual DNA, nevus tissue viability, and the structural integrity of the basement membrane and capillaries were evaluated before treatment, and after 48 h' treatment with or without 7 or 14 days' washing. We tried to produce reconstructed skin by combining the resultant ADM with enzymatically separated GCMN epidermal tissue. The histological structure of the reconstructed skin was examined after it had been cultured for 5 days. In the SDS group, most cells had been removed after 48 h, and the DNA content of the ADM was significantly lower than in the other groups. As for viability, no significant difference was detected among the groups. The basement membrane and capillaries remained intact in all groups. After 5 days' culturing, the epidermis had become attached to the ADM in all groups, except the SDS group. SDS displayed a superior decellularization ability compared with the other methods; however, it cannot be used to produce reconstructed skin because of its toxicity. In conclusion, we produced reconstructed skin that was devoid of nevus cells by combining GCMN epidermal tissue with GCMN-derived ADM produced with NaCl or trypsin. This is a promising treatment strategy for giant nevus.

Preparation and characterization of genipin-crosslinked rat acellular spinal cord scaffolds

The feasibility of rat acellular spinal cord scaffolds for tissue engineering applications was investigated. Fresh rat spinal cords were decellularized and crosslinked with genipin (GP) to improve their structural stability and mechanical properties. The GP-crosslinked spinal cord scaffolds possessed a porous structure with an average pore diameter of 31.1 μm and a porosity of 81.5%. The resultant scaffolds exhibited a water uptake ratio of 229%, and moderate in vitro degradation rates of less than 5% in phosphate-buffered saline (PBS) and slightly more than 20% in trypsin-containing buffer, within 14 days. The ultimate tensile strength and elastic modulus of GP-crosslinked spinal cord scaffolds were determined to be 0.193±0.064 MPa and 1.541±0.082 MPa, respectively. Compared with glutaraldehyde (GA)-crosslinked acellular spinal cord scaffolds, GP-crosslinked scaffolds demonstrated similar microstructure and mechanical properties but superior biocompatibility as indicated by cytotoxicity evaluation and rat mesenchymal stem cell (MSC) adhesion behavior. Cells were able to penetrate throughout the crosslinked scaffold due to the presence of an interconnected porous structure. The low cytotoxicity of GP facilitated cell proliferation and extracellular matrix (ECM) secretion in vitro on the crosslinked scaffolds over 7 days. Thus, these GP-crosslinked spinal cord scaffolds show great promise for tissue engineering applications.

Regeneration of mature dermis by transplanted particulate acellular dermal matrix in a rat model of skin defect wound

Native mammalian extracellular matrix (ECM) has been made in various forms including particles, sheet and mesh which are appropriate for site-specific applications. The ECM particles are usually created by homogenization method and have a wider size distribution. This needs to be improved to produce more uniform ECM particles. In present study, we had successfully developed a method for preparing particulate acellular dermal matrix (PADM) in different gauges. The resultant PADM was approaching a rectangular parallelepiped or cubic shape, with a better or narrower size distribution than other ECM particles in previous reports. It also retained ultrastructure and functional molecules of native ECM. In vivo performances were evaluated after implantation of PADM in an acute full-thickness skin defect wound in rats. Histological analysis showed that allogeneic PADM used as dermal regeneration template could facilitate maturation and improving collagen bundle structure of regenerated dermis at the endpoint of 20 weeks post-surgery. The PADM could be used for further investigation in analyzing the impacts of cellularly and/or molecularly modified PADM on soft tissue regeneration.

Evaluation of dermal substitute in a novel co-transplantation model with autologous epidermal sheet

The development of more and more new dermal substitutes requires a reliable and effective animal model to evaluate their safety and efficacy. In this study we constructed a novel animal model using co-transplantation of autologous epidermal sheets with dermal substitutes to repair full-thickness skin defects. Autologous epidermal sheets were obtained by digesting the basement membrane (BM) and dermal components from rat split-thickness skins in Dispase II solution (1.2 u/ml) at 4 °C for 8, 10 and 12 h. H&E, immunohistochemical and live/dead staining showed that the epidermal sheet preserved an intact epidermis without any BM or dermal components, and a high percentage of viable cells (92.10 ± 4.19%) and P63 positive cells (67.43 ± 4.21%) under an optimized condition. Porcine acellular dermal matrixes were co-transplanted with the autologous epidermal sheets to repair full-thickness skin defects in Sprague-Dawley rats. The epidermal sheets survived and completely re-covered the wounds within 3 weeks. Histological staining showed that the newly formed stratified epidermis attached directly onto the dermal matrix. Inflammatory cell infiltration and vascularization of the dermal matrix were not significantly different from those in the subcutaneous implantation model. Collagen IV and laminin distributed continuously at the epidermis and dermal matrix junction 4 weeks after transplantation. Transmission electron microscopy further confirmed the presence of continuous lamina densa and hemidesmosome structures. This novel animal model can be used not only to observe the biocompatibility of dermal substitutes, but also to evaluate their effects on new epidermis and BM formation. Therefore, it is a simple and reliable model for evaluating the safety and efficacy of dermal substitutes.

Acellular dermal matrix seeded with adipose-derived stem cells as a subcutaneous implant

BACKGROUND

Soft tissue augmentation using autologous materials usually is associated with high resorption rates. To obtain more durable soft tissue filler, acellular dermal matrix (ADM) was seeded with adipose-derived stem cells (ASCs) in this study.

METHODS

For ADM preparation, split-thickness skin was obtained from the dorsum of two Fischer rats. Harvested skin was acellularized to obtain ADM and subsequently seeded in vitro with ASCs isolated from the same rats. Subcutaneous soft tissue augmentation was carried out in the dorsal area of 20 Fischer rats. The implant materials were ADM (group 1), ADM with ASCs (group 2), collagen type 1 gel (group 3), and collagen type 1 gel with ASCs (group 4). Each specimen was harvested after 8 weeks for quantitative evaluation of thickness, vascular density, and collagen content.

RESULTS

Histologic analysis showed that ASCs were successfully seeded onto ADM. The thickness of the implanted material and the vascular density were highest 8 weeks postoperatively in group 2. The subpanniculus layer became significantly thicker in group 3 than in group 4. The collagen content was significantly higher in group 2 than in the other groups.

CONCLUSION

These findings suggest that ADM seeded with ASCs forms the best implant material in terms of volume maintenance, vascular density, and collagen content.

Flexor tendon tissue engineering: acellularization of human flexor tendons with preservation of biomechanical properties and biocompatibility

OBJECTIVE

Acellular human tendons are a candidate scaffold for tissue engineering flexor tendons of the hand. This study compared acellularization methods and their compatibility with allogeneic human cells.

METHOD

Human flexor tendons were pretreated with 0.1% ethylenediaminetetracetic acid (EDTA) for 4  h followed by 24  h treatments of 1% Triton X-100, 1% tri(n-butyl)phosphate, or 0.1% or 1% sodium dodecyl sulfate (SDS) in 0.1% EDTA. Outcomes were assessed histologically by hematoxylin and eosin and SYTO green fluorescent nucleic acid stains and biochemically by a QIAGEN DNeasy kit, Sircol collagen assay, and 1,9 dimethylmethylene blue glycosaminoglycan assay. Mechanical data were collected using a Materials Testing System to pull to failure tendons acellularized with 0.1% SDS. Acellularized tendons were re-seeded in a suspension of human dermal fibroblasts. Attachment of viable cells to acellularized tendon was assessed biochemically by a cell viability assay and histologically by a live/dead stain. Data are reported as mean±standard deviation.

RESULT

Compared with the DNA content of fresh tendons (551±212  ng DNA/mg tendon), only SDS treatments significantly decreased DNA content (1% SDS [202.8±37.4  ng DNA/mg dry weight tendon]; 0.1% SDS [189±104  ng DNA/mg tendon]). These findings were confirmed by histology. There was no decrease in glycosaminoglycans or collagen following acellularization with SDS. There was no difference in the ultimate tensile stress (55.3±19.2 [fresh] vs. 51.5±6.9 [0.1% SDS] MPa). Re-seeded tendons demonstrated attachment of viable cells to the tendon surface using a viability assay and histology.

CONCLUSION

Human flexor tendons were acellularized with 0.1% SDS in 0.1% EDTA for 24  h with preservation of mechanical properties. Preservation of collagen and glycoaminoglycans and re-seeding with human cells suggest that this scaffold is biocompatible. This will provide a promising scaffold for future human flexor tendon tissue engineering studies to further assess biocompatibility through cell proliferation and in vivo studies.

Development and characterization of acellular porcine corneal matrix using sodium dodecylsulfate

PURPOSE

The objective of this study was to produce a porcine corneal acellular matrix (ACM) and assess its possibility for biomedical applications.

METHODS

Porcine corneas were treated with various concentrations of sodium dodecylsulfate for different lengths of time. Optimal conditions for processing the ACM were noted regarding removal of all cellular components and retention of the spatial arrangement of the corneal stroma. The physical characteristics (including water absorption and light transmittance), biomechanics, and cytotoxicity of the ACM were also found to be conserved. Subsequently, ACM was transplanted into the interlaminar stroma of rabbit corneas. The transparency and structures of the collagen fibers were determined.

RESULTS

By immersing corneal tissues in isotonic buffer containing 0.1% sodium dodecylsulfate for 7 hours, we were able to produce an ACM whose cells were completely removed, without disrupting collagen layer structure. Although water absorption and light transmittance of the ACM decreased when compared with natural corneal stroma, ACM showed similar biomechanical properties and biocompatibility as natural ones. After xenotransplantation into rabbit corneal stromal layers for 4 weeks, both ACM and rabbit corneas showed complete transparency. Almost 1 year postoperatively, the corneas remained transparent with regular stromal structures and ACM appeared stable in situ without deliquescence or immunological rejection.

CONCLUSIONS

A simple and valid method to produce decellularized corneal matrix has been successfully developed. These acellular matrices similar to natural corneas in structure, strength, and transparency have tremendous potential for corneal transplantation as ideal implants for donors and for tissue engineering applications as suitable scaffolds.

Application of acellular dermal matrix for intestinal elongation in animal models

AIM: To investigate the efficacy of acellular dermal matrix (ADM) for intestinal elongation in animal models.

METHODS: Japanese white big-ear rabbits (n = 9) and Wuzhishan miniature pigs (n = 5) were used in the study. Home-made and commercial ADM materials were used as grafts, respectively. A 3-cm long graft was interposed in continuity with the small bowel and a side-to-side anastomosis, distal to the graft about 3-4 cm, was performed. The animals were sacrificed at 2 wk, 4 wk, 8 wk and 3 mo after surgery and the histological changes were evaluated under light microscope and electron microscope.

RESULTS: The animals survived after the operation with no evidence of peritonitis and sepsis. Severe adhesions were found between the graft and surrounding intestine. The grafts were completely absorbed within postoperative two or three months except one. Histological observation showed inflammation in the grafts with fibrinoid necroses, infiltration of a large amount of neutrophils and leukomonocytes, and the degree varied in different stages. The neointestine with well-formed structures was not observed in the study.

CONCLUSION: It is not suitable to use acellular dermal matrix alone as a scaffold for the intestinal elongation in animal models.

Preparation of the acellular scaffold of the spinal cord and the study of biocompatibility

STUDY DESIGN

Acellular spinal cord was prepared through chemical extraction, and its biocompatibility was studied.

OBJECTIVE

Acellular scaffolds have been developed from various materials for tissue reconstruction, except for spinal cord. The objective of this study was to prepare acellular spinal cord and examine the biocompatibility of the scaffold.

SETTING

This study was conducted at the Department of Orthopedics, Xinqiao Hospital, The Third Military Medical University, Chongqing, China.

METHODS

The morphology of the acellular segments was revealed by scanning electron microscopy, immunohistochemistry, and hematoxylin and eosin stain. Biocompatibility was studied by immunohistochemistry.

RESULTS

Results show that in spinal cord scaffolds, cells, myelin sheath and axon of nerve fibers were eliminated, and three-dimensional supports of extracellular matrix were reserved. The component analytical results of the acellular spinal cord indicate that they contain laminin, fibronectin and collagen, which can facilitate and induce the regeneration of injured nerves, and enhance the adhesion and proliferation of cells. The acellular spinal cord has a three-dimensional structure and excellent biocompatibility.

CONCLUSION

Our data indicate that acellular spinal cord has certain biological properties and it may be a potential alternative scaffold for spinal cord tissue engineering.

Use of Homologous Acellular Dermal Matrix for Abdominal Wall Reconstruction in Rats

Homologous acellular dermal matrix graft (HADMG) has been used for the reconstructions of bowel, bladder, or urethra, but its suitability in the reconstruction of abdominal wall has not been tested. Therefore an experimental study was performed to evaluate the use of HADMG for the reconstruction of abdominal wall defects in weanling rats. Thirty weanling Wistar rats were used. A patch of abdominal wall 20 x 20 mm in dimension was removed. The defects were reconstructed with HADMGs that were derived from rat skin and prepared through a detergent enzymatic method. The reconstructed abdominal walls were evaluated as hernia rate and graft take ratio, excised and prepared for histological examination at 21 (n = 10), 40 (n = 10), and 90 (n = 10) days postoperation. The healing of repaired abdominal walls was uneventful. Histological evaluation demonstrated the migration of fibroblasts and neovascularization within the HADMG. Hernia in four rats were developed at 90 days. Neither significant wound contraction nor inflammation was seen at 21, 40, and 90 days after surgery in wounds receiving HADMGs. Thus, the use of a HADMG for reconstructing the abdominal wall in weanling rats has not given rise to any complications. HADMG has progressively remodeled into fibrous tissue. It appears to represent an important alternative substitute for the reconstruction of abdominal wall.

Evaluation of Permacol as a cultured skin equivalent

Skin loss following severe burn requires prompt wound closure to avoid such complications as fluid and electrolyte imbalance, infection, immune suppression, and pain. In clinical situations in which insufficient donor skin is available, the development of cultured skin equivalents (dermal matrices seeded with keratinocytes and fibroblasts) may provide a useful alternative. The aim of this study was to assess the suitability of a porcine-derived dermal collagen matrix (Permacol) to function as a cultured skin equivalent in supporting the growth of keratinocytes in vitro and providing cover to full thickness wounds in the BALB C/nude mouse model. A histological comparison was against Glycerol treated-Ethylene Oxide Sterilised Porcine Dermis (Gly-EO Dermis) which has successfully been used as a cultured skin equivalent in previous studies. Both Gly-EO Dermis and to a lesser extent Permacol were able to support the growth of cultured keratinocytes following a 16-day period of cell culture, however, this study was only able to demonstrate the presence of an epidermal layer on Gly-EO dermis 2 weeks after grafting onto full-thickness wounds in the BALB C/nude mouse model.

Development of acellular dermis from porcine skin using periodic pressurized technique

In this work, a new method for producing acellular dermis (ADM), a natural scaffold used for dermal replacement, from porcine skin was developed. Fresh porcine skin from local slaughterhouse was dehaired by sodium sulphide following by epidermis removal using glycerol. After fat removal by chloroform/methanol (2/1 v/v) solvent, cellular components were removed using enzymatic treatment incorporated with a periodic pressurized technique. The effects of enzyme type (trypsin and dispase II) and periodic pressurized conditions on the efficiency of cell removal were investigated. When periodic pressure was applied, enzymatic treatment time could be shorten since the enzyme solution was able to penetrate into tight dermis. As a result, cells could be easily removed from porcine skin as noticed quantitatively by DNA assay and qualitatively by H&E staining. When enzyme refreshment was introduced into the decellularized process, the percentage of cell removal was further enhanced. This ensured that no inhibitions effect from the removed cells on enzyme-substrate interaction. Moreover, short-time enzymatic treatment with periodic pressurized technique could prevent the disruption of dermal structure, as observed by SEM. Dispase II can be used to remove cell better than trypsin in the periodic pressurized technique. However, in vivo study indicated that numerous fibroblast from the host tissue infiltrated into ADM prepared using both enzymes. Neo-collagen and neo-capillaries were produced in both implanted ADMs. The result elucidated that the use of periodic pressurized technique with enzymatic treatment has a high potential to be a new method to produce ADM for skin tissue engineering.

In vitro and in vivo proposal of an artificial esophagus

Artificial materials and autologous tissues used for esophageal reconstruction often induce complications like stenosis and leakage at long-term follow-up. This study evaluates the possibility to obtain in vitro an implantable tissue-engineered esophagus composed of homologous esophageal acellular matrix and autologous smooth muscle cells (SMCs). Acellular matrices obtained by detergent-enzymatic method did not present any major histocompatibility complex marker and expressed bFGF as protein, showing angiogenic activity in vivo on the chick embryo chorioallantoic membrane (CAM). Moreover, they supported cell adhesion, and inasmuch as just after 24 h from seeding, the scaffold appeared completely covered by SMCs. To verify the biocompatibility of our constructs, defects created in the porcine esophageal wall were covered using homologous acellular matrices with and without cultures of autologous SMCs. At 3 week from surgery, the patches composed of only acellular matrices showed a more severe inflammatory response and were negative for alpha-smooth muscle actin immunostaining. In contrast, the cell-matrix implants presented ingrowth of SMCs, showing an early organization into small fascicules. Collectively, these results suggest that patches composed of homologous esophageal acellular matrix and autologous SMCs may represent a promising tissue-engineering approach for the repair of esophageal injuries.

The application of new biosynthetic artificial skin for long-term temporary wound coverage

Temporary dressings protect wounds from desiccation and infection. In our previous study, we used meshed acellular porcine dermis (APD) to enhance wound healing and decrease wound contraction; however, the wounds showed meshed scar. In this study, we produced an artificial skin composed of a cross-linked silicon sheet on the surface of APD which we have called silicone acellular porcine dermis (SAPD). This new artificial skin can protect the wound long enough to promote wound healing either by second intention or covered long enough until cultured epithelium autograft (CEA) or autologous skin graft can be harvested for permanent coverage. We delivered 4 cm x 5 cm full-thickness wound on the back of 350 g Sprague-Dawley rats. Thirty-six rats were divided into two groups. Eighteen rats had SAPD and the other 18 were covered with Biobrane. The wounds were first examined 2 weeks after grafting and followed weekly for an additional 4 weeks to evaluate the wound and study pathological changes by using H.E. and Masson's stains. Wound size was calculated by ruler and analyzed by Student's t-test. At the 2-week inspection, both SAPD and Biobrane showed tight adherence to the wound with no change of wound size. Both the SAPD and Biobrane dermal templates were pink. In the Biobrane-covered group, the wounds contracted soon after the tie-over dressing was removed. Its dermal layer is a layer of thin porcine dermal substance, which was promptly digested by tissue hyaluronidase and provides no real dermal template. In the SAPD-covered group however, the wound size was maintained significantly from third to sixth week after grafting (p<0.001). SAPD was designed with thick epidermal silicone and a well-organized porcine dermis so that it incorporates into the recipient wound. Clinically the silicone layer of SAPD dislodged from APD about 6-7 weeks after grafting and was followed by dermal matrix exposure and infection. In pathological examination, much like a human skin graft, new vessels were found in APD about 1 week after grafting with minimal inflammatory cells infiltrated in the graft and wound. Six weeks after grafting, the collagen of APD incorporated into the wound, showing palisade arrangement and no sign of rejection. In the Biobrane group however, the wounds showed severe inflammation, the porcine dermal matrix was digested and disappeared 3 weeks after coverage. In conclusion, SAPD is a thick biosynthetic artificial skin, which protects the rat wound significantly longer than Biobrane and prevents contraction. We expect that using of SAPD for temporary wound coverage will provide enough time to grow autologous-cultured epithelium or to reharvest skin grafts.

Effect of synthetic peptides on osteoblast adhesion

The quality of the early cell/material interactions is responsible for the long-term functional properties of any implanted device. Accordingly, "next generation" dental/orthopedic biomaterials should be able to promote osteoblast adhesion thus improving the integration process between surgically placed implants and biological tissues. Recent studies have identified a wide range of biochemical signals that can be exploited to promote adhesion, migration, proliferation and differentiation of cells. The clinical use of natural factors to promote osteoblast adhesion is complicated because those are often insoluble and unstable macromolecules and, in addition, it is difficult to obtain them in high quantities, with good purity grade and at low cost. A valid alternative could be the use of short peptides carrying the minimum active sequence of the natural macromolecular factor. This paper describes the properties of two classes of peptides, promoting different adhesion mechanisms, to enhance rat bone marrow osteoblast adhesion both to polystyrene and to acellular bone matrix.

Collagenous matrices as release carriers of exogenous growth factors

We have investigated the use of natural and synthetic collagenous matrices as carriers of exogenous growth factors. A bladder acellular matrix (BAM) was processed from rat bladder and compared with sponge matrix of porcine type 1 collagen. The lyophilized matrices were rehydrated by the aqueous solutions of basic fibroblast growth factor (bFGF), hepatocyte growth factor (HGF), platelet derived growth factor-BB (PDGF-BB), vascular endothelial growth factor (VEGF), insulin like growth factor-1 (IGF-1) and heparin binding epidermal growth factor-like growth factor (HB-EGF), to obtain the matrix incorporating each growth factor. The rehydration method enabled the growth factor protein to distribute into the matrix homogeneously. In vivo release test in the mouse subcutis revealed that, the property of BAM for growth factor release was similar to that of collagen sponge. Among the growth factors examined, bFGF release was the most sustained, followed by HGF and PDGF-BB. bFGF released from the two matrices showed similar in vivo angiogenic activity at the mouse subcutis in a dose-dependent manner. These findings demonstrate that the collagenous matrices function as release carriers of growth factors. This feature is promising to create a scaffold, which has a nature to control the tissue regeneration actively.

Process development of an acellular dermal matrix (ADM) for biomedical applications

The object of this study was to compare the extent of decellularization at each critical step of processing porcine skin to produce an acellular dermal matrix (ADM) for biomedical applications. The results demonstrated that the removal of epidermis using treatment with 0.25% trypsin for 18 h and 0.1% sodium dodecyl sulfate (SDS) for 12 h at room temperature was beneficial for the subsequent treatment to remove cells in the dermal structure. Lengthy incubation in 0.25% trypsin (12 h) and then 560 units/l Dispase (12 h) at 25 degrees C of small pieces of porcine skin from which the epidermis had been removed efficiently removed cells and cellular components from the skin. Histological examinations revealed that the epidermis, dermal fibroblasts, and epidermal appendages were completely removed by these treatments, and the basic dermal architecture of collagen bundles was that of a loose meshwork. Examinations by TEM showed that the characteristics of collagen fibers in the ADM were retained after complete removal of cells present under optimal conditions defined in this study. SDS-PAGE and size-exclusion HPLC revealed that collagen fibers in the ADM were mostly type I and showed two typical component peaks identified as oligomers and monomers, respectively.

Closure of Abdominal Wall Defects Using Acellular Dermal Matrix

BACKGROUND

After some abdominal surgical procedures, the abdominal wall defect may be too large for closure by tension-free approximation of the wound margins because of tissue loss or swelling of the abdominal viscera. A variety of absorbable and nonabsorbable prosthetic materials have been used for emergency abdominal wall reconstruction. Of these materials, polytetrafluoroethylene (PTFE) sheets have proved to be the most efficacious.

METHODS

This study compared the efficacy of allogenic acellular dermal matrix (ADM) and PTFE as prosthetic materials for wound closure in rats with surgical, full-thickness, 2 x 3-cm abdominal wounds. Healing was studied among animals with and those without experimentally induced peritonitis for 21 days after surgery.

RESULTS

Acellular dermal matrix became vascularized and incorporated into the wound bed and was partially or fully epithelialized without the need for skin grafting. As a result, little superficial bleeding was seen, and ADM effectively closed the wounds even in the presence of peritonitis. Wounds treated with ADM also showed a significant reduction in wound area (sterile:p < 0.001; contaminated:p < 0.05). In contrast, PTFE temporarily closed the wounds, but was not incorporated into them. It consequently evoked the formation of extensive underlying granulation tissue that showed significant superficial bleeding when the PTFE was removed. Very limited wound contraction occurred in PTFE-treated wounds, and some instances of evisceration and fistula formation were observed. Wounds treated with both types of material showed significant amounts of adhesion to visceral organs underlying the wound site.

CONCLUSIONS

Acellular dermal matrix exhibits a number of favorable features relative to PTFE for closing sterile or contaminated full-thickness abdominal wall defects.

Angiogenic response induced by acellular aortic matrix in vivo

In this study, we investigated the angiogenic response induced by acellular aortic matrices implanted in vivo onto the chick embryo chorioallantoic membrane (CAM), a useful model for such investigation. Results showed that acellular matrices were able to induce a strong angiogenic response comparable to that of fibroblast growth factor 2 (FGF-2), a well-known angiogenic cytokine. The angiogenic response was further increased when exogenous FGF-2 or transforming growth factor beta 1 (TGF-beta1) were added to the matrices and inhibited by the addition of an anti-FGF-2 or anti-TGF-beta1 antibodies. The response may be considered dependent on a direct angiogenic effect exerted by the matrices and in part also by the presence of FGF-2 and TGF-beta1 in the acellular matrices.

Angiogenic response induced by acellular brain scaffolds grafted onto the chick embryo chorioallantoic membrane

The repair and regeneration of injured tissues and organs depend on the re-establishment of the blood flow needed for cellular infiltration and metabolic support. Among the various materials used in tissue reconstruction, acellular scaffolds have recently been utilized. In this study, we investigated the angiogenic response induced by acellular brain scaffolds implanted in vivo onto the chick embryo chorioallantoic membrane (CAM), a useful model for such investigations. The results show that acellular brain scaffolds are able to induce a strong angiogenic response, comparable to that of fibroblast growth factor-2 (FGF-2), a well known angiogenic cytokine. The response may be considered dependent on a direct angiogenic effect exerted by the scaffold, because no inflammatory infiltrate was detectable in CAM's mesenchyme beneath the implant. Acellular brain scaffolds might induce the release of endogenous angiogenic factors, such as FGF-2 and vascular endothelial growth factor (VEGF) released from the extracellular matrix of the developing CAM. In addition, the angiogenic response may depend, in part, also on the presence in the acellular matrix of transforming growth factor beta 1 (TGFbeta1).

Novel osteoblast-adhesive peptides for dental/orthopedic biomaterials

Next generation dental/orthopedic biomaterials must be designed to enhance and support osteoblast adhesion. The osteoblasts use different ways to adhere, that is, integrin- and proteoglycan-mediated mechanisms. The present study reports on the synthesis and osteoblast-adhesive properties of peptides carrying RGD motifs and of sequences mapped on human vitronectin. Our data suggest that osteoblast adhesion on polystyrene plates modified with a linear peptide, in which the GRGDSP sequence is repeated four times, was significantly higher when compared to the adhesion obtained using branched peptides, interestingly containing the same motif. Osteoblast adhesion assays on acellular bone matrix using this active peptide gave very promising results. We also demonstrated that a novel peptide, carrying the X-B-B-B-X-B-B-X motif (where B is a basic amino acid and X is a nonbasic residue), promotes proteoglycan-mediated osteoblast adhesion more efficiently with respect to the KRSR sequence that was recently proposed as heparan-sulfate binding peptide.

Use of porcine acellular dermal matrix as a dermal substitute in rats

OBJECTIVE

To examine porcine acellular dermal matrix (ADM) as a xenogenic dermal substitute in a rat model.

SUMMARY BACKGROUND DATA

Acellular dermal matrix has been used in the treatment of full-thickness skin injuries as an allogenic dermal substitute providing a stable wound base in human and animal studies.

METHODS

Xenogenic and allogenic ADMs were produced by treating porcine or rat skin with Dispase and Triton X-100. Full-thickness skin defects (225 mm2) were created on the dorsum of rats (n = 29), porcine or rat ADMs were implanted in them, and these were overlain with ultrathin split-thickness skin grafts (STSGs). In two adjacent wounds, 0.005- or 0.017-inch-thick autografts were implanted. In other experiments, the antimicrobial agent used during ADM processing (azide or a mixture of antibiotics) and the orientation of the implanted ADM (papillary or reticular side of ADM facing the STSG) were studied. Grafts were evaluated grossly and histologically for 30 days after surgery.

RESULTS

Significant wound contraction was seen at 14, 20, and 30 days after surgery in wounds receiving xenogenic ADM, allogenic ADM, and thin STSGs. Contraction of wounds containing xenogenic ADM was significantly greater than that of wounds containing allogenic ADM at 30 days after surgery. Graft take was poor in wounds containing xenogenic ADM and moderately good in those containing allogenic ADM. Wound healing was not significantly affected by the antimicrobial agent used during ADM preparation or by the ADM orientation.

CONCLUSION

Dispase-Triton-treated allogenic ADM was useful as a dermal substitute in full-thickness skin defects, but healing with xenogenic ADM was poor.

Long-term outcome of xenogenic dermal matrix implantation in immunocompetent rats

BACKGROUND

Acellular dermal matrix (ADM) has been used successfully in the treatment of full-thickness skin injuries as an allogenic dermal substitute. To assess the efficacy of xenogenic ADM in such wounds, we examined the long-term wound healing and immunological responses to porcine ADM in a rat model.

MATERIALS AND METHODS

Xenogenic and allogenic ADMs were produced by treating porcine (fresh or cryopreserved) or rat skin with dispase and Triton X-100. Full-thickness skin defects on the rat dorsum were implanted with porcine or rat ADMs and overlaid with split-thickness skin grafts (STSGs). Wounds were evaluated grossly and immunologically at 1, 6, and 12 months after surgery.

RESULTS

Extensive wound contraction was seen in wounds implanted with porcine ADM, but healing was significantly (P < 0.01) better in the rat ADM or STSG groups at 6 and 12 months postsurgery. Sera obtained from porcine ADM-implanted rats reacted strongly with porcine ADM and specifically with the papillary dermis and basal lamina. One month postsurgery, extensive inflammation but few intact mast cells were seen in wounds implanted with porcine ADM and significant (P < 0.02) levels of residual porcine ADM were detectable immunologically. Little inflammation was evident in the STSG or rat ADM groups at any time. Significant lymphocyte proliferation (P < 0.05) occurred in the 6- and 12-month groups in response to porcine, but not rat, ADM.

CONCLUSIONS

In wounds implanted with xenogenic ADM, a short-lived acute inflammatory response, long-lasting humoral and cell-mediated immune responses, and generally poor wound healing were observed.

Short bowel syndrome: experimental approach to increase intestinal surface in rats by gastric homologous acellular matrix

BACKGROUND/PURPOSE

In this preliminary work the authors used homologous acellular matrix obtained by the gastric wall to increase the small bowel surface in Sprague-Downey rats; through this experimental model the authors verified that homologous acellular matrix can support cell migration and the reconstruction of the intestinal wall.

METHODS

A tract of about 2 cm of tubular gastric acellular matrix was inserted with bilateral anastomosis in an isolated ileal loop, which was located in endoabdominal position through a short subcutaneous tunnel. Twelve animals were analyzed at each of the time-points ranging from 1 to 6 weeks after surgery.

RESULTS

Histologic evaluation showed that the implanted matrix can be reintegrated in the normal small bowel in a period ranging between 3 and 6 weeks from surgery. The implanted matrix was organized with 4 different tonacae from the third week after the surgery, without interruption at the site of the anastomosis.

CONCLUSIONS

To date, the authors do not have a demonstration of the function of the ileal loop reconstructed with this technique; based on these results the authors are engaged in an experimental trial of restoration of intestinal viability with the ileal prosthesis after 3 weeks to study its function.