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Evaluation of artificial skin (Integra) in a rodent model
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Burns Vol. 23, Supplement No. 1, pp. $30-$32, 1997 Copyright © 1997 Elsevier Science Ltd for ISBI. All rights reserved Printed in Great Britain 0305-4179/97 $17.00 + 0.00
PII: S0305-4179(96)00098-8
Evaluation of artificial skin (lntegra) in a rodent model W. W. K. King 1, P. K. Lam', C. T. Liew 2, W. S. Ho' and A. K. C. Li' 1Division of Head & Neck/Plastic & Reconstructive Surgery, Department of Surgery and 2Department of Anatomical and Cellular Pathology, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, Hong Kong
The biocompatibility of artificial skin (Integra) has been investigated in clean surgical wounds of 20 guinea-pigs. A rectangular 3 x 3 cm full-thickness skin defect with excision carried down to the panniculus carnosus was prepared on the dorsal area of the guinea-pig. A thin layer of silver sulfadiazine cream was applied and artificial skin was placed to cover the wound. At day 14, the uppermost silicone layer was removed. Good take of the artificial skin was observed in 18 of 20 animals. Microscopy showed good vascular ingrowth in 14 of the 18 animals. The remaining four animals showed necrotic tissue, absence of vascularization and haemorrhage in the wound bed. Two of the 20 wounds showed purulent discharge. In this animal model, clinical 'take" of the neodermis was achieved in 18/20 animals (90 per cent), while vascular ingrowth was observed in only 14/20 animals (70 per cent). These results suggested that artificial skin in clean surgical wound is readily biologically incorporated into surrounding viable tissue. © 1997 Elsevier Science Ltd for ISBI. All rights reserved.
Burns, Vol. 23, Supplement No. 1, $30-$32, 1997
Introduction Autologous split-thickness skin graft is the gold standard for burn wound closure. However, in severe burns involving more than 50 per cent of the body surface area, autografting is limited by the paucity of donor sites. Various skin substitutes such as allograft, porcine xenograft and human amniotic membrane have been used as temporary dressings 1. The bilayer artificial skin (Integra) developed by Yannas and Burke provides early wound coverageL It is composed of an upper silicone membrane and a lower sponge sheet of collagen cross-linked with glycosaminoglycan (Collagen-GAG). The optimal pore size, 50+20 #m (mean+SD), of the artificial skin allows the infiltration of cellular tufts of fibroblasts and capillaries when it is placed on the wound bedL This cell-infiltrated Collagen-GAG membrane
gradually becomes a biosynthetic neodermis. Artificial skin can minimize the need for autologous dermis in skin grafting. In the USA, multicentre trials involving 106 patients showed that the clinical take rate of artificial skin was 80 per cent, which was comparable to the take rate of non-autograft materials4,L In this study, evaluation of the clinical take rate of the neodermis of artificial skin in a rodent model was carried out and correlation of the clinical take rate with the histological evidence of vascularization, which is an indicator of the biological incorporation of the neodermis into adjacent viable tissue.
Materials and method Dunkin Hartley strain (body wt 700-800 g) guineapigs supplied by the University Animal Unit were used in this study. The guinea-pigs were anaesthetized with pentobarbital (45 mg/kg) by intraperitoneal injection. Artificial skin soaked in 70 per cent isopropyl alcohol was thoroughly rinsed twice in sterile normal saline for 15 min prior to application. A 3 x 3 cm full-thickness excision down to the panniculus carnosus was created on the dorsal surface of the animal. A thin layer of silver sulfadaizine cream was applied and artificial skin with silicone membrane upwards was placed to cover the wound. The artificial skin was then secured by saline gauze. Artificial skin was tested on 20 animals. At day 14, the uppermost silicone layer was removed. Clinically, the 'take' rate of the artificial skin was recorded. Punch biopsy was also taken for histology.
Results The artificial skin was examined at day 14 postgrafting. The silicone membranes were easily peeled off. On inspection, 18 (90%) out of 20 animals showed good adherence to the w o u n d bed without
King et al.: Evaluation of artificial skin in a rodent model
$31
observable purulent discharge. Punch biopsies were taken for histological examination from these 18 animals. In 14 of the 18 animals, there was good neovascularization (Figure la).. Some red blood cells were present within the pores of the neodermis. Scanty activated fibroblasts and macrophages were seen lining some of the pores. The interface between the artificial skin dermis and grafted wound bed showed diffused and firm adhesion with granulationlike tissue formation. A high magnification of a Masson trichrome stain of the punch biopsy demonstrated some red cells in the pores (Figure lb). The pores were lined by green-colour stained collagenous strands. Two of the 14 animals had mild inflammation. However, four of the 18 animals showed acute inflammation without evidence of neovascularization (Figure lc). The pores of the neodermis were packed with polymorphonuclear leucocytes. There was disintegration of the collagen of the small pores which coalesced into bigger irregular size pores. The interface between the artificial skin and the recipient wound had become partially detached. In two out of the 20 animals, purulent discharge and clot formation were observed after peeling off the silicone membrane. No histology was performed on these two animals because most of the artificial dermis had dissolved. Discussion
These results showed that while 18 of 20 animals (90 per cent) had clinical 'take' of the artificial skin at day 14, microscopic examination revealed adequate vascular ingrowth in the neodermis in only 14 of the 20 animals (70 per cent). Therefore, if all 18 animals were to receive autografting, upon removal of the silicone membrane, successful autografting would not be expected to be greater than 77.7 per cent (14/18). The maximal possible take rate of 77.7 per cent for autografting as shown in this animal study is comparable to the 85 per cent take rate for autografts applied in patients with burns wounds successfully covered with artificial skin 6. In this animal study, the Collagen-GAG of artificial skin showed good macroscopic and microscopic adherence to the recipient bed without evidence of severe infection. The dermis component of the artificial skin consists of highly purified type I collagen harvested from bovine tendon and is of low antigenicity. This is confirmed by the fact that 12 of the 14 adherent and vascularized neodermis showed no evidence of acute inflammation. Mild inflammation was observed in only two of the 14 wounds. This study confirms that the collagen based neodermis is inert, biocompatible and readily biologically integrated into adjacent tissue when there is no infectious complication. These results suggest that clinical 'take' of the neodermis is best confirmed by a punch biopsy for histology study. In the absence of histological evidence of vascularization, a subsequent skingrafting procedure using the neodermis as the recipient bed is not expected to be successful.
Figure 1. a, Low-power photomicrograph of artificial skin
14 days after grafting. There was no inflammation and the artificial dermis was firmly attached to the wound bed. (Haematoxylin and eosin stain, 120 x ) b, High-powered photomicrograph of same wound as in a. The pores were mostly intact and showed no significant inflammation or disintegration. The collagenous material was stained in a green colour. (Mason trichrome stain, 360 x .) c, Low-power photomicrograph showed a failed artificial skin with pores filled by acute inflammatory cells which disintegrated the collagen leading to the formation of larger pores. The artificial skin was detached from the recipient wound bed. (Masson trichrome stain, 150 x .)
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References 1 Alsbjorn B. Biologic wound coverings in burn treatment. World ] Surg 1992; 16: 43-46. 2 Yannas IV, Burke JF. Design of an artificial skin. 1. Basic design principles. J Biomed Mat Res 1980; 14: 65-81. 3 Ronald GT, Burke JF. Progress in b u m treatment and use of artificial skin. World J Surg 1990; 14: 819-824. 4 Heimbach D, Luterman A, Burke JF et al. Artificial dermis for major burns: a multi-center randomized clinical trial. Ann Surg 1988; 208: 313-320.
Burns: Vol. 23, Suppl. No. 1, 1997 5 Burke JF, Yannas IV, Quinby WC et al. Successful use of a physiological acceptable artificial skin in the treatment of extensive burn injury. Ann Surg 1981; 194: 413-428. 6 Jaksic T, Burke JF. The use of artificial skin for burns. Ann Rev Med 1987; 38: 107-117.
Correspondence should be addressed to: Professor Walter W. K. King, Department of Surgery, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, H o n g Kong.
Burns Vol. 23, Supplement No. 1, pp. $30-$32, 1997 Copyright © 1997 Elsevier Science Ltd for ISBI. All rights reserved Printed in Great Britain 0305-4179/97 $17.00 + 0.00
PII: S0305-4179(96)00098-8
Evaluation of artificial skin (lntegra) in a rodent model W. W. K. King 1, P. K. Lam', C. T. Liew 2, W. S. Ho' and A. K. C. Li' 1Division of Head & Neck/Plastic & Reconstructive Surgery, Department of Surgery and 2Department of Anatomical and Cellular Pathology, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, Hong Kong
The biocompatibility of artificial skin (Integra) has been investigated in clean surgical wounds of 20 guinea-pigs. A rectangular 3 x 3 cm full-thickness skin defect with excision carried down to the panniculus carnosus was prepared on the dorsal area of the guinea-pig. A thin layer of silver sulfadiazine cream was applied and artificial skin was placed to cover the wound. At day 14, the uppermost silicone layer was removed. Good take of the artificial skin was observed in 18 of 20 animals. Microscopy showed good vascular ingrowth in 14 of the 18 animals. The remaining four animals showed necrotic tissue, absence of vascularization and haemorrhage in the wound bed. Two of the 20 wounds showed purulent discharge. In this animal model, clinical 'take" of the neodermis was achieved in 18/20 animals (90 per cent), while vascular ingrowth was observed in only 14/20 animals (70 per cent). These results suggested that artificial skin in clean surgical wound is readily biologically incorporated into surrounding viable tissue. © 1997 Elsevier Science Ltd for ISBI. All rights reserved.
Burns, Vol. 23, Supplement No. 1, $30-$32, 1997
Introduction Autologous split-thickness skin graft is the gold standard for burn wound closure. However, in severe burns involving more than 50 per cent of the body surface area, autografting is limited by the paucity of donor sites. Various skin substitutes such as allograft, porcine xenograft and human amniotic membrane have been used as temporary dressings 1. The bilayer artificial skin (Integra) developed by Yannas and Burke provides early wound coverageL It is composed of an upper silicone membrane and a lower sponge sheet of collagen cross-linked with glycosaminoglycan (Collagen-GAG). The optimal pore size, 50+20 #m (mean+SD), of the artificial skin allows the infiltration of cellular tufts of fibroblasts and capillaries when it is placed on the wound bedL This cell-infiltrated Collagen-GAG membrane
gradually becomes a biosynthetic neodermis. Artificial skin can minimize the need for autologous dermis in skin grafting. In the USA, multicentre trials involving 106 patients showed that the clinical take rate of artificial skin was 80 per cent, which was comparable to the take rate of non-autograft materials4,L In this study, evaluation of the clinical take rate of the neodermis of artificial skin in a rodent model was carried out and correlation of the clinical take rate with the histological evidence of vascularization, which is an indicator of the biological incorporation of the neodermis into adjacent viable tissue.
Materials and method Dunkin Hartley strain (body wt 700-800 g) guineapigs supplied by the University Animal Unit were used in this study. The guinea-pigs were anaesthetized with pentobarbital (45 mg/kg) by intraperitoneal injection. Artificial skin soaked in 70 per cent isopropyl alcohol was thoroughly rinsed twice in sterile normal saline for 15 min prior to application. A 3 x 3 cm full-thickness excision down to the panniculus carnosus was created on the dorsal surface of the animal. A thin layer of silver sulfadaizine cream was applied and artificial skin with silicone membrane upwards was placed to cover the wound. The artificial skin was then secured by saline gauze. Artificial skin was tested on 20 animals. At day 14, the uppermost silicone layer was removed. Clinically, the 'take' rate of the artificial skin was recorded. Punch biopsy was also taken for histology.
Results The artificial skin was examined at day 14 postgrafting. The silicone membranes were easily peeled off. On inspection, 18 (90%) out of 20 animals showed good adherence to the w o u n d bed without
King et al.: Evaluation of artificial skin in a rodent model
$31
observable purulent discharge. Punch biopsies were taken for histological examination from these 18 animals. In 14 of the 18 animals, there was good neovascularization (Figure la).. Some red blood cells were present within the pores of the neodermis. Scanty activated fibroblasts and macrophages were seen lining some of the pores. The interface between the artificial skin dermis and grafted wound bed showed diffused and firm adhesion with granulationlike tissue formation. A high magnification of a Masson trichrome stain of the punch biopsy demonstrated some red cells in the pores (Figure lb). The pores were lined by green-colour stained collagenous strands. Two of the 14 animals had mild inflammation. However, four of the 18 animals showed acute inflammation without evidence of neovascularization (Figure lc). The pores of the neodermis were packed with polymorphonuclear leucocytes. There was disintegration of the collagen of the small pores which coalesced into bigger irregular size pores. The interface between the artificial skin and the recipient wound had become partially detached. In two out of the 20 animals, purulent discharge and clot formation were observed after peeling off the silicone membrane. No histology was performed on these two animals because most of the artificial dermis had dissolved. Discussion
These results showed that while 18 of 20 animals (90 per cent) had clinical 'take' of the artificial skin at day 14, microscopic examination revealed adequate vascular ingrowth in the neodermis in only 14 of the 20 animals (70 per cent). Therefore, if all 18 animals were to receive autografting, upon removal of the silicone membrane, successful autografting would not be expected to be greater than 77.7 per cent (14/18). The maximal possible take rate of 77.7 per cent for autografting as shown in this animal study is comparable to the 85 per cent take rate for autografts applied in patients with burns wounds successfully covered with artificial skin 6. In this animal study, the Collagen-GAG of artificial skin showed good macroscopic and microscopic adherence to the recipient bed without evidence of severe infection. The dermis component of the artificial skin consists of highly purified type I collagen harvested from bovine tendon and is of low antigenicity. This is confirmed by the fact that 12 of the 14 adherent and vascularized neodermis showed no evidence of acute inflammation. Mild inflammation was observed in only two of the 14 wounds. This study confirms that the collagen based neodermis is inert, biocompatible and readily biologically integrated into adjacent tissue when there is no infectious complication. These results suggest that clinical 'take' of the neodermis is best confirmed by a punch biopsy for histology study. In the absence of histological evidence of vascularization, a subsequent skingrafting procedure using the neodermis as the recipient bed is not expected to be successful.
Figure 1. a, Low-power photomicrograph of artificial skin
14 days after grafting. There was no inflammation and the artificial dermis was firmly attached to the wound bed. (Haematoxylin and eosin stain, 120 x ) b, High-powered photomicrograph of same wound as in a. The pores were mostly intact and showed no significant inflammation or disintegration. The collagenous material was stained in a green colour. (Mason trichrome stain, 360 x .) c, Low-power photomicrograph showed a failed artificial skin with pores filled by acute inflammatory cells which disintegrated the collagen leading to the formation of larger pores. The artificial skin was detached from the recipient wound bed. (Masson trichrome stain, 150 x .)
$32
References 1 Alsbjorn B. Biologic wound coverings in burn treatment. World ] Surg 1992; 16: 43-46. 2 Yannas IV, Burke JF. Design of an artificial skin. 1. Basic design principles. J Biomed Mat Res 1980; 14: 65-81. 3 Ronald GT, Burke JF. Progress in b u m treatment and use of artificial skin. World J Surg 1990; 14: 819-824. 4 Heimbach D, Luterman A, Burke JF et al. Artificial dermis for major burns: a multi-center randomized clinical trial. Ann Surg 1988; 208: 313-320.
Burns: Vol. 23, Suppl. No. 1, 1997 5 Burke JF, Yannas IV, Quinby WC et al. Successful use of a physiological acceptable artificial skin in the treatment of extensive burn injury. Ann Surg 1981; 194: 413-428. 6 Jaksic T, Burke JF. The use of artificial skin for burns. Ann Rev Med 1987; 38: 107-117.
Correspondence should be addressed to: Professor Walter W. K. King, Department of Surgery, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, H o n g Kong.