Utility of Acellular Allograft Dermis in the Care of Elderly Burn Patients

Autologous Skin Grafts, versus Tissue-engineered Skin Constructs: A Systematic Review and Meta-analysis

For over 100 years, autologous skin grafts have remained the gold standard for the reconstruction of wounds but are limited in availability. Acellular tissue-engineered skin constructs (acellular TCs) and cellular tissue-engineered skin constructs (cellular TCs) may address these limitations. This systematic review and meta-analysis compare outcomes between them.

Methods

A systematic review was conducted using PRISMA guidelines, querying MEDLINE, Embase, Web of Science, and Cochrane to assess graft incorporation, failure, and wound healing. Case reports/series, reviews, in vitro/in vivo work, non-English articles or articles without full text were excluded.

Results

Sixty-six articles encompassing 4076 patients were included. No significant differences were found between graft failure rates (P = 0.07) and mean difference of percent reepithelialization (p = 0.92) when split-thickness skin grafts were applied alone versus co-grafted with acellular TCs. Similar mean Vancouver Scar Scale was found for these two groups (p = 0.09). Twenty-one studies used at least one cellular TC. Weighted averages from pooled results did not reveal statistically significant differences in mean reepithelialization or failure rates for epidermal cellular TCs compared with split-thickness skin grafts (p = 0.55).

Conclusions

This systematic review is the first to illustrate comparable functional and wound healing outcomes between split-thickness skin grafts alone and those co-grafted with acellular TCs. The use of cellular TCs seems promising from preliminary findings. However, these results are limited in clinical applicability due to the heterogeneity of study data, and further level 1 evidence is required to determine the safety and efficacy of these constructs.

Results of Experimental Hernioplasty with Acellular Dermal Matrix

We performed a comprehensive assessment of the acellular dermal matrix obtained during the detergent-enzymatic treatment of the porcine dermis. Acellular dermal matrix was used for the experimental treatment of a hernial defect in a pig using the sublay method. Sixty days after the surgery, biopsy specimens were obtained from the area of hernia repair. The acellular dermal matrix can be easily modeled depending on the size and shape of the defect during surgical procedures, can eliminate the defect of the anterior abdominal wall, and is resistant to cutting by the suture material. Histological examination demonstrated replacement of the acellular dermal matrix with newly formed connective tissue.

The Role of Skin Substitutes in Acute Burn and Reconstructive Burn Surgery: An Updated Comprehensive Review

Burns disrupt the protective skin barrier with consequent loss of cutaneous temperature regulation, infection prevention, evaporative losses, and other vital functions. Chronically, burns lead to scarring, contractures, pain, and impaired psychosocial well-being. Several skin substitutes are available and replace the skin and partially restore functional outcomes and improve cosmesis. We performed a literature review to update readers on biologic and synthetic skin substitutes to date applied in acute and reconstructive burn surgery. Improvement has been rapid in the development of skin substitutes in the last decade; however, no available skin substitute fulfills criteria as a perfect replacement for damaged skin.

Advances in Skin Tissue Bioengineering and the Challenges of Clinical Translation

Skin tissue bioengineering is an emerging field that brings together interdisciplinary teams to promote successful translation to clinical care. Extensive deep tissue injuries, such as large burns and other major skin loss conditions, are medical indications where bioengineered skin substitutes (that restore both dermal and epidermal tissues) are being studied as alternatives. These may not only reduce mortality but also lessen morbidity to improve quality of life and functional outcome compared with the current standards of care. A common objective of dermal-epidermal therapies is to reduce the time required to accomplish stable closure of wounds with minimal scar in patients with insufficient donor sites for autologous split-thickness skin grafts. However, no commercially-available product has yet fully satisfied this objective. Tissue engineered skin may include cells, biopolymer scaffolds and drugs, and requires regulatory review to demonstrate safety and efficacy. They must be scalable for manufacturing and distribution. The advancement of technology and the introduction of bioreactors and bio-printing for skin tissue engineering may facilitate clinical products' availability. This mini-review elucidates the reasons for the few available commercial skin substitutes. In addition, it provides insights into the challenges faced by surgeons and scientists to develop new therapies and deliver the results of translational research to improve patient care.

Use of Meshed Acellular Dermal Allograft as a Lining Material After Orbital Exenteration

PURPOSE

To evaluate the surgical outcome and safety of acellular human dermal allograft as a new lining material to the exposed orbit after exenteration.

METHODS

Retrospective case series of patients who underwent orbital exenteration followed by reconstruction with meshed-type acellular dermal allograft from 2009 to 2018 in a single tertiary institution.

RESULTS

There were 14 eyes (2 right, 12 left) of 14 patients (6 men, 8 women). Mean age at operation was 69.1 ± 16.5 years. Indication for surgery was malignancy in all patients. One patient underwent subtotal exenteration, while the rest underwent total exenteration. SureDerm Meshed was used in 12 patients, AlloDerm Meshed in 1, and CGDerm Meshed in 1. Mean follow-up period was 12.1 months. Full or nearly full epithelialization occurred in 10 of 14 patients (71.4%) at 1 month and 9 of 12 patients (75.0%) at 3 months. There was delayed epithelialization in 3 patients due to poor wound care (n = 1), adjuvant radiotherapy (n = 1), and adjuvant radiotherapy followed by cerebrospinal fluid leak (n = 1).

CONCLUSIONS

Meshed acellular human dermal allograft showed good success in reconstruction after orbital exenteration and may be considered as an alternative lining material to split-thickness skin graft after orbital exenteration.

Short-term changes of human acellular dermal matrix (Megaderm) in a mouse model

BACKGROUND

Physicians tend to overcorrect when applying the acellular dermal matrix for reconstructive option because of volume decrement problem after absorption comparing with initial volume. However, there are no studies on the exact volume decrement and absorption rate with commercial products in South Korea. To figure out absorption rate of acellular dermal matrix product in South Korea (Megaderm), authors designed this experiment.

METHODS

Nine mice were used and randomly divided into three groups by the time with sacrificing. The implant (Megaderm) was tailored to fit a cuboid form (1.0 cm× 1.0 cm in length and width and 2.0 mm in thickness). A skin incision was made at anterior chest with blade #15 scalpel with exposing the pectoralis major muscle. As hydrated Megaderm was located upon the pectoralis major muscle, the skin was sutured with Ethilon #5-0. After the surgical procedure, each animal group was sacrificed at 4, 8, and 12 weeks, respectively, for biopsies and histological analysis of the implants. All samples were stained with routine hematoxylin and eosin staining and Masson's trichrome staining and the thickness were measured. A measurements were analyzed using Friedman test. Statistically, the correlation between thicknesses of Megaderm before and after implantation was analyzed.

RESULTS

After sacrificing the animal groups at postoperative 4, 8, 12 weeks, the mean tissue thickness values were 2.10± 1.03 mm, 2.17± 0.21 mm, and 2.40± 0.20 mm (p= 0.368), respectively. The remaining ratios after absorption comparing with after initial hydrated Megaderm were 82.7%, 85.4%, and 94.5%, respectively. In histopathological findings, neovascularization and density of collagenous fiber was increased with time.

CONCLUSION

Author's hypothesis was absorption rate of implant would be increased over time. But in this experiment, there is no statistical significance between mean absorption thickness of implant and the time (p= 0.368). Also it can be affected by graft site, blood supply, and animals that were used in the experiment.

Culture of Keratinocytes for Transplantation without the Need of Feeder Layer Cells

Patients with large burn wounds have a limited amount of healthy donor skin. An alternative for the autologous skin graft is transplantation with autologous keratinocytes. Conventionally, the keratinocytes are cultured with mouse feeder layer cells in medium containing fetal calf serum (FCS) to obtain sufficient numbers of cells. These xenobiotic materials can be a potential risk for the patient. The aim of the present study was to investigate if keratinocytes could be expanded in culture without the need of a feeder layer and FCS. Keratinocytes were cultured on tissue culture plastic with or without collagen type IV coating in medium containing Ultroser G (serum substitute) and keratinocyte growth factor (KGF). An in vitro skin equivalent model was used to examine the capacity of these cells to form an epidermis. Keratinocytes in different passages (P2, P4, and P6) and freshly isolated cells were studied. Keratinocytes grown on collagen type IV were able to form an epidermis at higher passage numbers than cells grown in the absence of collagen type IV (P4 and P2, respectively). In both cases the reconstructed epidermis showed an increased expression of Ki-67, SKALP, involucrin, and keratin 17 compared to normal skin. Only 50,000 keratinocytes grown on collagen type IV in P4 were needed to form 1 cm2 epidermis, whereas 150,000 of freshly isolated keratinocytes were necessary. Using this culture technique sufficient numbers of keratinocytes, isolated from 1 cm2 skin, were obtained to cover 400 cm2 of wound surface in 2 weeks. The results show that keratinocytes can be cultured without the need of a fibroblast feeder layer and FCS and that these cells are still able to create a fully differentiated epidermis. This culture technique can be a valuable tool for the treatment of burn wounds and further development of tissue engineered skin.

Retrospective study of the application of acellular dermis in reconstructing full-thickness skin defects

The purpose of the article is to evaluate the acellular dermis' utility in reconstructing full-thickness defects after scar contracture releasing and giant nevus resection. From the year 2012 to 2014, 18 consecutive patients underwent composite graft (thin autograft and alloderma) transplantation. Among these patients, 16 patients suffered from burned scar contracture in the upper extremities, and two young cases were met with giant nevus on the upper extremity. Ten of 13 adult cases with upper extremity scar affection were chosen for a comparative study. Twenty hands were randomly allocated into group A and group B. The thick autograft was used to repair one upper extremity in group B, and the composite grafts were used to cover the other upper extremity in group A. Besides appraisal of the recipient sites' function and aesthetics, donor sites were also estimated after a mean of 12 months' follow-up through the Vancouver Scar Score Scale. After evaluation in the above comparative study through the Vancouver Score Scale, in the recipient evaluation, no statistical difference was found in the pigmentation score between two groups, while statistical difference was achieved in other aspects (vascularity, pliability, height). In the donor site's evaluation, statistical difference was established between the two groups in all facets. One adult patient was dissatisfied with the hypertrophic scar on the donor site, and about almost a half of the area became a hypertrophic scar in the recipient site. No atrophic change occurred; one little girl, suffering from large nevus, was operated on by removing nearly the whole giant nevus on the upper limb. Unfortunately, she presented with finger tip necrosis occurring. The finger tip was not ultimately preserved and was repaired with an abdomen flap. Acellular dermal matrix is an excellent option and a useful tool for reconstructing large full-thickness skin defects after releasing burned scar contracture and removing giant nevus. With thin-skin graft meshed, a donor site's presentation brings courage to patients, while recipient sites can reach nearly the same elasticity and function compared to thick-grafted skin.

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 flour 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 polytetrafluoroethylene (PTFE) chamber model. The results clearly show that collagen deposition is induced by the presence of these biomaterials. A unique pattern of early inflammatory response, eliciting neutrophils and controlling macrophage infiltration, is followed by tissue cell colonization of the wound bed with a significant deposition of collagen fibers. 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 scaffolding 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.

Acellular dermal matrix in the management of the burn patient

Although the principles of burn management are still primarily focused on survival, as advances are realized in resuscitation, nutrition, and wound management, the functional and aesthetic outcomes following burn injury have become increasingly important. Acellular dermal matrix materials, which allow surgeons to minimize skin graft donor site morbidity in the process of repairing injured areas, play a role in addressing these important issues. Many favorable reports have been published, but they are generally characterized by small sample sizes, limited objective testing, and retrospective analysis. There does appear to be some evidence for ADM application in patient populations in whom donor site availability (those with massive burns) or morbidity (children, the elderly) is a concern, but more studies are needed. In this article, the authors discuss the current applications for ADM in burn management, review the existing literature, and present opportunities for future research.

Coverage of gingival recession defects using acellular dermal matrix allograft with or without beta-tricalcium phosphate

The aim of this study was to investigate the effect of beta-tricalcium phosphate (β-TCP) particles in combination with acellular dermal matrix (ADM) allograft in gingival recession. Experimental gingival recession defects were created in beagle dogs and randomly assigned to one of the following groups: ADM, ADM + β-TCP, or coronally positioned flap (CPF; control). Tissues were histologically examined at 4, 8, or 16 weeks following treatment. A greater thickness of gingiva was observed at the sites treated in both the ADM + β-TCP and ADM groups than in the CPF group. The ADM + β-TCP group showed a statistically significant increase in both new bone and cementum formations compared to the ADM group. The results suggest that the combination of β-TCP and ADM is more effective in promoting new bone and cementum formations than ADM graft alone.

Epiflex(®) a new decellularised human skin tissue transplant: manufacture and properties

The manufacture and initial testing of a new human tissue transplant is described. Epiflex(®) is a human acellular dermis transplant that is manufactured from skin recovered from screened consenting donors according to validated and approved methods. The transplant is approved as a drug in Germany. The safety, stability and usability of the transplant are discussed with respect to the results of sterility, residual moisture content and rehydration tests. Histological and confocal laser scanning microscopy experiments and analysis of oxygen and water vapour permeability demonstrate that the native extracellular matrix structure and transport properties of human connective tissue are retained in the transplant. Results from initial clinical investigations suggest that Epiflex(®) can be used successfully in the treatment of burns, hypertrophic scars and as a transplant seeded with autologous dermal fibroblasts for soft-tissue regeneration in settings with wound healing problems following multi-modal treatments for sarcomas of the extremities.

Nonlinear and anisotropic tensile properties of graft materials used in soft tissue applications

BACKGROUND

The mechanical properties of extracellular matrix grafts that are intended to augment or replace soft tissues should be comparable to the native tissue. Such grafts are often used in fiber-reinforced tissue applications that undergo multi-axial loading and therefore knowledge of the anisotropic and nonlinear properties are needed, including the moduli and Poisson's ratio in two orthogonal directions within the plane of the graft. The objective of this study was to measure the tensile mechanical properties of several marketed grafts: Alloderm, Restore, CuffPatch, and OrthADAPT.

METHODS

The degree of anisotropy and non-linearity within each graft was evaluated from uniaxial tensile tests and compared to their native tissue.

FINDINGS

The Alloderm graft was anisotropic in both the toe- and linear-region of the stress-strain response, was highly nonlinear, and generally had low properties. The Restore and CuffPatch grafts had similar stress-strain responses, were largely isotropic, had a linear-region modulus of 18MPa, and were nonlinear. OrthADAPT was anisotropic in the linear-region (131 MPA vs 47MPa in the toe-region) and was highly nonlinear. The Poisson ratio for all grafts was between 0.4 and 0.7, except for the parallel orientation of Restore which was greater than 1.0.

INTERPRETATION

Having an informed understanding of how the available grafts perform mechanically will allow for better assessment by the physician for which graft to apply depending upon its application.

The use of human deceased donor skin allograft in burn care

Burns are tissue wounds caused by thermal, electrical, chemical cold or radiation injuries. Deep injuries lead to dermal damage that impairs the ability of the skin to heal and regenerate on its own. Skin autografting following burn excision is considered the current gold standard of care, but lack of patient's own donor skin or unsuitability of the wound for autografting may require the temporary use of dressings or skin substitutes to promote wound healing, reduce pain, and prevent infection and abnormal scarring. These alternatives include deceased donor skin allograft, xenograft, cultured epithelial cells and biosynthetic skin substitutes. Allotransplantation is the transplantation of cells, tissues, or organs, sourced from a genetically non-identical member of the same species as the recipient. Human deceased donor skin allografts represent a suitable and much used temporizing option for skin cover following burn injury. The main advantages for its use include dermoprotection and promotion of reepithelialisation of the wound and their ability to act as skin cover until autografting is possible or re-harvesting of donor sites becomes available. Disadvantages of its use include the limited abundance and availability of donors, possible transmission of disease, the eventual rejection by the host and its handling storing, transporting and associated costs of provision. This paper will explore the role of allograft skin in burn care, defining the indications for its use in burn management and the future potential for allograft tissue banking.

Topical advances in wound care

There are fundamental differences between acute wounds that proceed to uncomplicated healing and those that become chronic wounds. Non-healing or chronic wounds can result from a combination of overlapping factors that prevent healing, including local tissue ischemia, repetitive trauma and ischemia/reperfusion injury, presence of tissue necrosis, impaired cellular and systemic host response to stress, and critical bacterial contamination. The bacterial burden in the wound contributes to a sustained inflammatory state, which inhibits normal progression to the proliferative phase of healing, thereby preventing restoration of tissue integrity. Appropriate wound bed preparation removes local barriers to healing and optimizes the tissue environment to achieve wound healing. It is an essential element of wound management that advances endogenous healing as well as the efficacy of topical and other wound therapy. This article will summarize a systematic approach to wound bed preparation using the "TIME" principle, and will highlight important advances in topical wound care.

Thermal and electrical injuries

Through progress in wound management, resuscitation, intensive care treatment, and a coordinated rehabilitation process, modern burn care has been able to deliver substantial increases in survival and improvement in functional outcomes for burn victims. The development of regionalized burn centers has contributed greatly to this progress. As the field of burns matures, burn centers are preparing to meet future challenges through collaborative efforts in disaster management and outcomes research.

Effect of In Vitro Gingival Fibroblast Seeding on the In Vivo Incorporation of Acellular Dermal Matrix Allografts in Dogs

BACKGROUND

Acellular dermal matrix allograft (ADMA) has been used in various periodontal procedures with successful results. Because ADMA has no blood vessels or cells, slower healing and incorporation are observed compared to a subepithelial connective tissue graft. Fibroblasts accelerate the healing process by regulation of matrix deposition and synthesis of a variety of growth factors. Thus, the objective of this study was to evaluate histologically if gingival fibroblasts affect healing and incorporation of ADMA in dogs when used as a subepithelial allograft.

METHODS

Gingival fibroblasts were established from explant culture from the connective tissue of keratinized gingiva collected from the maxilla of seven mongrel dogs. ADMA was seeded with gingival fibroblasts and transferred to dogs. Surgery was performed bilaterally, and the regions were divided into two groups: ADMA+F (ADMA containing fibroblasts) and ADMA (ADMA only). Biopsies were performed after 2, 4, and 8 weeks of healing.

RESULTS

The quantity of blood vessels was significantly higher in the ADMA+F group at 2 weeks of healing (Kruskal-Wallis; P <0.05). There was no statistical difference (P >0.05) in the number of cell layers, epithelial area, or inflammatory infiltrate between the two groups at any stage of healing.

CONCLUSION

The enhanced vascularization in vivo in early stages supports the important role of fibroblasts in improving graft performance and wound healing of cultured graft substitutes.