[Experimental study on the recycling of denatured acellular dermal matrix after burn]

To explore the feasibility of burn denatured acellular dermal matrix (DADM) as dermal substitute in repairing wounds.

(1) Nine Wistar rats received a deep partial-thickness scald on the back. Full-thickness wounded skin was collected on post scald day (PBD) 1, 2, and 3 (with 3 rats at each time point), and it was treated with 2.5 g/L trypsin/0.5% Triton X-100 to remove cells to prepare DADM, respectively called DADM-1 d, DADM-2 d, and DADM-3 d. Another 3 rats without scald injury were treated with the same method as above to prepare acellular dermal matrix (ADM) to serve as control. Gross and histological observations and microbiological and biomechanical tests, including ultimate tensile strength, maximum tension, stretched length at breaking, stress-strain relationship, were conducted for the resulting ADM and DADM. (2) Another 64 rats were divided into ADM group and DADM-1 d, DADM-2 d, and DADM-3 d groups according to the random number table, with 16 rats in each group. A skin flap in size of 2.0 cm×1.8 cm was raised on the back of each rat. The above-mentioned ADM, DADM-1 d, DADM-2 d, and DADM-3 d were cut into pieces in the size of 1.8 cm×1.5 cm, and they were respectively implanted under the skin flaps of rats in corresponding group. At post surgery week (PSW) 1, 3, 5, or 9, 4 rats in each group were used to observe wound healing condition and change in implants with naked eye, and histological observation of the implants was conducted. Data were processed with one-way analysis of variance and t test.

(1) The freshly prepared DADM was milky white, soft in texture with flexibility, but poor in elasticity as compared with ADM. No epithelial structure or cellular component was observed in ADM or DADM under light microscope. Collagen fibers of DADM were seen to be thickened unevenly and arranged in disorder and eosinophilic. All microbiological results of DADM were negative. There was no statistically significant difference among DADM-1 d, DADM-2 d, and DADM-3 d in levels of ultimate tensile strength, maximum tension, stretched length at breaking, and stress-strain relationship (with F values from 0.088 to 3.591, P values all above 0.05). Values of the above-mentioned four indexes were the highest in DADM-3 d, they were respectively (13.0 ± 2.4) MPa, (61 ± 4) N, (173 ± 7)%, (45.7 ± 2.0)%. Values of the four indexes of ADM were respectively (19.0 ± 2.6) MPa, (95 ± 4) N, (201 ± 5)%, (62.5 ± 2.2)%, which were higher than those of DADM-1 d, DADM-2 d, and DADM-3 d (with t values from 6.424 to 17.125, P values all below 0.01). (2) No exudate or swelling in the wounds of rats, and no contraction or curling of implants were observed in every group at PSW 1, but inflammatory cells infiltration and Fbs inward migration were observed in the wound. At PSW 3, the growth of hair was normal in the wound in DADM-1 d, DADM-2 d, and ADM groups, but few and scattered hair grew in DADM-3 d group. The inflammatory cells decreased, while Fbs increased, and new capillaries were found to grow inwardly in each group. The decrease in inflammatory cells was slightly delayed in DADM-3 d group. At PSW 5, hair growth became normal, and implants shrank and thinned with fiber membrane wrapped densely and bundles of ingrowing large caliber blood vessels in all groups. The dermal matrix in each group merged with the surrounding normal tissue. At PSW 9, ADM and DADM became white, thin, and soft tissue sheet which was closely connected with the inner side of the flap. There was no infiltration of inflammatory cells in implants in either group. The collagen fibers arranged regularly and densely, and they were integrated with normal collagen tissue.

The burned DADM does not have obvious immunogenicity, but with good biocompatibility. It is prospective to become as a dermal substitute in repairing wounds.