Microskin grafting of rabbits with pigskin xenograft overlay

The micrograft concept for wound healing: strategies and applications

The standard of care for wound coverage is to use an autologous skin graft. However, large or chronic wounds become an exceptionally challenging problem especially when donor sites are limited. It is important that the clinician be aware of various treatment modalities for wound care and incorporate those methods appropriately in the proper clinical context. This report reviews an alternative to traditional meshed skin grafting for wound coverage: micrografting. The physiological concept of micrografting, along with historical context, and the evolution of the technique are discussed, as well as studies needed for micrograft characterization and future applications of the technique.

An easy way to prepare microskin grafts

The conventional technique to produce microskin grafts is a relatively time-consuming procedure. We developed an easy method by using a trimmed circular dermacarrier with the non-grooved side up and driving forward in the meshgraft instrument through six different angles that were 30 degrees apart. The tiny skin particles obtained by this method not only saved operation time but also survived well in the grafted wounds.

A mixture of allogeneic and autologous microskin grafting of rabbit skin wounds with Biobrane overlay

A mixture of allogeneic and autologous microskin grafts (10:1 expansion ratio) were transplanted and overlain with Biobrane, on to full-thickness skin wounds (8.0 x 5.0 cm in size) in 16 rabbits. They were divided into two groups: in group I, the expansion ratio of both allo- and autograft was 20:1; in group II, the expansion ratio of allo- and autograft was 15:1 and 30:1 respectively. On day 9, all wounds of group I and II were almost completely resurfaced with neoepithelium. There was no serious rejection reaction within the neoepithelium and the wounds were maintained completely resurfaced after day 9. There were scales on the epithelialized wound which were more numerous in group II than in group I. Histological examination revealed that these wounds were resurfaced with well-differentiated epithelium which contained two different histological patterns. They were identified as the survived transplanted allogeneic and autologous microskin grafts, each having their own characteristic histological features and different sex chromosome. Thus both the largely expanded allogeneic and autologous microskin grafts could proliferate together and contribute to the resurfacing of the wound. With this method, the rabbit skin wound could be resurfaced completely after the ninth postoperative day with markedly minimized amounts of autologous and allogeneic grafts.

Allogeneic microskin grafting of rabbits' skin wounds

Allogeneic microskin grafts (expansion ratio of 10:1), overlain with Biobrane, were applied to 30 rabbits. There were two groups. In group I, the allogeneic donor microskin grafts were transplanted without specific management. In group II, the donor skin was treated with ultraviolet (312 nm) irradiation to depress Langerhans cells immediately before the transplantation. Histological examination of these grafted wounds in the early stage showed that these micrografts proliferated actively with increased mitotic figures and became regularly stratified under the conditions provided by the Biobrane. By day 9, these wounds in group I were almost resurfaced with neoepithelium. In group II, the rate of regeneration of the neoepithelium was slower than those of group I. Subsequently there was rejection with moderate mononuclear infiltration, hydropic degeneration and satellite necrosis of basal and suprabasal keratinocytes, and local destruction of epithelium. Grossly these reactions caused 'melting' of the neoepithelium and resulted in raw areas. These rejections were more severe about 2 weeks after transplantation and then subsided gradually. Mild cellular infiltration continued to prevent the formation of rete ridges and the dermoepidermal junction was smooth at all times. Langerhans cells could not be found in these grafted wounds using OKT-6 and S100 stain. In spite of the destruction caused by these rejections in both groups, 25 wounds were completely resurfaced with well-differentiated neoepithelium by day 21. This study revealed that the transplanted allogeneic microskin grafts could proliferate to form neoepithelium and resurface the skin wounds of rabbits.

Widely expanded postage stamp skin grafts using a modified Meek technique in combination with an allograft overlay

A method for obtaining widely expanded postage stamp autografts, first described in 1963 by C.P. Meek, has been evaluated in our burns unit. The technique, in which an expansion ratio of 1:9 is achieved with the aid of special prefolded gauzes, was combined with an overlay of glycerol-preserved allografts applied 1 week after grafting. This delay did not appear to affect graft take. In a series of 16 consecutive skin graft procedures performed on 10 patients with extensive burns, the mean epithelialization rate was 90 per cent (range 70-100 per cent) within 5 weeks. Cosmetic results were comparable to those achieved with widely expanded mesh grafts. The Meek technique utilizes small pieces of autograft, and has proved to be a practical alternative to mesh grafts when donor sites are limited.

Microskin grafting of rabbit skin wounds with Biobrane overlay

Biobrane was used to overlay micrografts and the wound using the microskin grafting technique with an expansion ratio of 10:1 in 16 rabbits. The rabbits were divided randomly into four groups, with four rabbits in each group, for evaluating the wound conditions on days 7, 10, 12 and 14. Histological examination of the removed Biobrane showed a variable degree of entrapment of inflammatory cells within the nylon fabric. Biobrane adhered well to the wounds although many wrinkles containing fluid accumulations were noted on day 7. By 10, 12 and 14 days all the wounds become dry and their Biobrane adhered completely. Histological examination of the grafted wound on day 7 showed active proliferation and spread of micrografts. In the later groups, the neoepidermis increased in thickness and differentiated into skin with a normal texture. On day 10, the wounds were almost completely resurfaced with neoepithelium. The growth of these grafts progressed smoothly as the adherent Biobrane was kept on the wound for 12 or 14 days. In these animal studies, the overlain Biobrane provided favourable conditions for the successful growth of micrografts.

Microskin autograft with pigskin xenograft overlay: a preliminary report of studies on patients

Split-thickness pigskin graft (STPSG) was used to replace allograft skin for microskin grafting in 16 patients, nine of whom were burn patients, five suffered from traumatic defects and two from diabetic ulcers. The expansion ratios used in these patients ranged from 8:1 to 12:1. The STPSG preparation described was found to be safe for clinical application. The autogenous donor skin was excised from the inguinal area, and the donor site was primarily closed. There were no instances of donor site morbidity. The majority of the STPSG overlays adhered to the wound firmly. Histological examination showed that the microskin grafts proliferated actively immediately beneath the STPSG overlay. The time for the wound to be fully resurfaced varied from 13 to 21 days depending on the expansion ratio employed. There were only two episodes of pseudomonas infection and no further grafting was required in any of the patients. In this study the pigskin xenograft was found to provide a suitable environment for the epithelialization of microskin autografts. When allograft is not available, this is an alternative way of ensuring successful microskin grafting.