Cell fragments and collagen structure of cell-free dermal substitutes

The antigenicity of inartificial dermis can be minimized by removing cell components while keeping the intrinsic structures. To minimize the antigenicity, the cell fragments must be wiped off as clearly as possible. Thus, the test of cell fragments is very important for the evaluation of dermal matrix production. And in the process of the production, the structure must be kept integrated to avoid scar formation resulting from breakage. By new methods, we have produced swine acellular dermal matrix （SADM） and goat acellular dermal matrix （GADM） without using glutaraldehyde. In this study, we tested the cell fragments and collagen structure of these two dermal substitutes.

Nanomaterials for the delivery of bioactive factors to enhance angiogenesis of dermal substitutes during wound healing

Dermal substitutes provide a template for dermal regeneration and reconstruction.They constitutes an ideal clinical treatment for deep skin defects.However,rapid vascularization remains as a major hurdle to the development and application of dermal substitutes.Several bioactive factors play an important regulatory role in the process of angiogenesis and an understanding of the mechanism of achieving their effective delivery and sustained function is vital.Nanomaterials have great potential for tissue engineering.Effective delivery of bioactive factors(including growth factors,peptides and nucleic acids)by nanomaterials is of increasing research interest.This paper discusses the process of dermal substitute angiogenesis and the roles of related bioactive factors in this process.The application of nanomaterials for the delivery of bioactive factors to enhance angiogenesis and accelerate wound healing is also reviewed.We focus on new systems and approaches for delivering bioactive factors for enhancing angiogenesis in dermal substitutes.

Pre-clinical evaluation of soybean-based wound dressings and dermal substitute formulations in pig healing and non-healing in vivo models

In the last decade,a new class of natural biomaterials derived from de-fatted soybean fl our processed by either thermoset or extraction procedures has been developed.These biomaterials uniquely combine adaptability to various clinical applications to proven tissue regeneration properties.In the present work,the biomaterials were formulated either as hydrogel or as paste formulation and their potential as wound dressing material or as dermal substitute was assessed by two in vivo models in pig skin:The healing full-thickness punch biopsy model and the non-healing full-thickness polytetrafl uoroethylene(PTFE)chamber model.The results clearly show that collagen deposition is induced by the presence of these biomaterials.A unique pattern of early infl ammatory response,eliciting neutrophils and controlling macrophage infi ltration,is followed by tissue cell colonization of the wound bed with a signifi cant deposition of collagen fi bers.The study also highlighted the importance in the use of optimal formulations and appropriate handling upon implantation.In large size,non-healing wounds,wound dermis was best obtained with the paste formulation as hydrogels appeared to be too loose to ensure lasting scaff olding properties.On the contrary,packing of the granules during the application of paste reduced biomaterial degradation rate and prevent the penetration of newly vascularized tissue,thus impeding grafting of split-thickness autologous skin grafts on the dermal substitute base.

Evaluation of the cytotoxicity of cell free dermal substitutes using the 3-（4,5-dimethylthiazol-2-yl）-2,5-diphenyl tetrazolium bromide method

Background The cytotoxicity of dermal substitutes may be increased by the very processes used to deplete the cells. The present research aimed to investigate the method for monitoring the cytotoxicity of cell-free dermal substitutes using 3-（4,5-dimethylthiazol-2-yl）-2,5-diphenyl tetrazolium bromide （MI-I-） method. Methods The cytotoxicity of four dermal substitutes was evaluated using the MIF method according to the standards set by the Chinese State Food and Drug Administration （SFDA）. Swine acellular dermal matrix （SADM） and goat acellular dermal matrix （GADM） were produced using a repeated freeze-thaw method. Human dermal matrix glutaraldehyde composite （HADM-G） and SADM cross-linked with glutaraldehyde （SADM-G） were produced using conventional methods. Results The cytotoxicity of all dermal substitutes ranged from Grade 0 to Grade 1, meeting the standards of the Chinese FDA. The OD490 of both SADM and GADM was higher than that of either HADM-G or SADM-G （P 〈0.05）. Conclusion Dermal substitutes produced by the freeze-thaw method are less cytotoxic than those produced using conventional methods.

A single-stage bilayered skin reconstruction using Glyaderm■as an acellular dermal regeneration template results in improved scar quality:an intra-individual randomized controlled trial

Background:Absence of almost the entire reticular dermal layer is inherent to the use of autologous split-thickness skin grafting(STSG)to close full-thickness wounds,often resulting in hypertrophic scars and contractures.Many dermal substitutes have been developed,but unfortunately most have varying results in terms of cosmetic and/or functional improvement as well as patient satisfac-tion,in addition to high costs.Bilayered skin reconstruction using the human-derived glycerolized acellular dermis(Glyaderm■)has been reported to result in significantly improved scar quality using a two-step procedure.Unlike the necessary two-step procedure for most commercially available dermal substitutes,in this study we aimed to investigate the use of Glyaderm■in a more cost-effective single-stage engrafting.This is a method which,if autografts are available,is preferred by the majority of surgeons given the reduction in costs,hospitalization time and infection rate.Methods:A prospective,randomized,controlled,intra-individual,single-blinded study was per-formed,investigating the simultaneous application of Glyaderm■and STSG vs.STSG alone in full-thickness burns or comparable deep skin defects.During the acute phase,bacterial load,graft take and time to wound closure were assessed and were the primary outcomes.Aesthetic and functional results(secondary outcomes)were evaluated at 3,6,9 and 12 months follow-up using subjective and objective scar measurement tools.Biopsies for histological analysis were taken at 3 and 12 months.Results:A total of 66 patients representing 82 wound comparisons were included.Graft take(>95%),pain management and healing time were comparable in both groups.At 1 year follow-up,the overall Patient and Observer Scar Assessment Scale assessed by the patient was significantly in favour of sites where Glyaderm■was used.Not infrequently,patients attributed this difference to improved skin sensation.Histological analysis showed the presence of a well-formed neodermis,with donor elastin present for up to 12 months.Conclusions:A single-stage bilayered reconstruction with Glyaderm■and STSG results in optimal graft take without loss of Glyaderm■nor the overlaying autografts due to infection.The presence of elastin in the neodermis was demonstrated during long-term follow-up in all but one patient,which is a crucial factor contributing to the significantly improved overall scar quality as evaluated by the blinded patients.

Skin tissue engineering advances in severe burns:review and therapeutic applications

Current advances in basic stem cell research and tissue engineering augur well for the development of improved cultured skin tissue substitutes:a class of products that is still fraught with limitations for clinical use.Although the ability to grow autologous keratinocytes in-vitro from a small skin biopsy into sheets of stratified epithelium(within 3 to 4 weeks)helped alleviate the problem of insufficient donor site for extensive burn,many burn units still have to grapple with insufficient skin allografts which are used as intermediate wound coverage after burn excision.Alternatives offered by tissue-engineered skin dermal replacements to meet emergency demand have been used fairly successfully.Despite the availability of these commercial products,they all suffer from the same problems of extremely high cost,sub-normal skin microstructure and inconsistent engraftment,especially in full thickness burns.Clinical practice for severe burn treatment has since evolved to incorporate these tissue-engineered skin substitutes,usually as an adjunct to speed up epithelization for wound closure and/or to improve quality of life by improving the functional and cosmetic results long-term.This review seeks to bring the reader through the beginnings of skin tissue engineering,the utilization of some of the key products developed for the treatment of severe burns and the hope of harnessing stem cells to improve on current practice.