Development of a bioartificial new intestinal segment using an acellular matrix scaffold

Intestinal rehabilitation for short‐bowel syndrome is an integral part of modern intestinal transplant programmes. The mortality of patients with short‐bowel syndrome is most significant in individuals with a residual small bowel of <50 cm, as shown by a 5‐year survival rate of 57%.¹ Total parenteral nutrition and intestinal transplantation are options to extend life but are still plagued by serious complications and, in the case of transplantation, immunosuppression. As an alternative, several bowel elongation procedures have been described,²,³,⁴ but have had limited clinical success and new techniques are warranted. The minimum length of bowel required to allow sufficient absorption of nutrients has not been confirmed.¹,⁵ Elongation of even a few centimetres may allow these patients to receive nutritional rehabilitation and become independent from total parenteral nutrition, and possibly avoid transplantation. We hypothesised that an acellular dermal matrix (ADM, AlloDerm, LifeCell Corporation, Branchburg, New Jersey, USA) scaffold placed in continuity with defunctionalised jejunal limb allows mucosal growth and intestinal elongation. We evaluated the morphology of neoformed intestine in ACI (August × Copenhagen‐Irish) rats at different time points using two different types of anastomosis. Tubular scaffolds with an intraluminal diameter of approximately 0.3 cm were constructed using rehydrated ADM segments of 1 cm² and 0.78–1.77 mm thickness, and oriented with a luminal basement membrane and a serosal dermal surface. In group A (n = 5), the ADM graft was interposed in continuity with the jejunum using an interrupted end‐to‐end single‐layer anastomosis. In group B (n = 11), the grafts were placed as blind‐ended pouches to the defunctionalised jejunal limb. Postoperatively, animals were maintained on a liquid diet for 48 h followed by solid‐rat chow and killed at different time‐points postoperatively. Tissue samples for histological examination were obtained across the anastomosis. Survival and body weight were evaluated in both groups. All animals in group A were killed in the first week as a result of peritonitis. All animals in group B survived and increased body weight appropriately. Tissue samples showed a progressive increase in the amount of cell infiltrate in the matrix (table 1, fig 1). After 2 weeks, acute inflammation was replaced by full‐thickness ingrowths of capillaries and myofibroblasts. Epithelial regeneration into the anastomosis was first seen at 2 weeks, and well‐formed branching crypts were seen at 4 weeks of transplantation. Goblet cells and absorptive cells with brush border were present at 4 months of transplantation. Morphologically intact regenerated mucosa extending across the anastomosis to the grafts was observed at 6 months of transplantation. To date, there is limited literature on the bioengineered intestine. Vacanti et al,⁶,⁷,⁸ developed a cystic structure in which neomucosa forms in a biodegradable polymer in rodents. Once formed, the neointestinal cyst is anastomosed in continuity with the native bowel without causing feeding problems, but some animals had small bare areas of the cysts that lacked neomucosa.⁷ We did not report such bare areas in our model; furthermore, there was progressive growth of the neomucosa in the ADM over time. It is possible that immediate contact of the ADM scaffold with the intestinal structures and with luminal content provided trophic stimuli for the new intestinal segment.⁹ Another possible factor for the observed growth in our model may be the effects of small‐bowel resection on the development of neointestine. It is well known that post resection gut mucosa growth factors have a stimulatory effect on intestinal regeneration.¹⁰ In conclusion, we have demonstrated that ADM can be successfully used as a scaffold to generate a bioartificial new intestinal segment in vivo, and we propose this method as a basis for developing new intestinal elongation techniques.

Table 1 Histology results of group B at different time points .

Time after anastomosis	Status of anastomosis	Status of alloderm	Epithelial regeneration
2 days	Intact	Minimal acute inflammation	No
2 weeks	Intact but inflamed	Minimal acute inflammation. Proliferation of fibroblasts and endothelial cells	Early budding of crypts at bowel edge of anastomosis
4–5 weeks	Intact but inflamed	Less acute inflammation	Same as 2 weeks
		Full‐thickness ingrowths of capillaries and myofibroblasts
4–6 months	Intact with granulation tissue around sutures	Full‐thickness capillaries and fibroblasts and haemosiderin‐laden macrophages	Regenerating crypts with goblet cells, and rudimentary villi with absorptive cells with brush border

Figure 1 Photomicrographs of the anastomosis between the acellular dermal matrix (ADM) and small bowel at 4 months of transplantation. (A) Leading edge of regenerating epithelium with villus formation (V). Note a bit of remaining bare graft surface to the left of the villus, H&E ×20. (B) Regenerating crypts with goblet cells. Some residual collagen from the ADM can be seen nearby (arrow), H&E ×20. (C) Epithelium along the edge of the villus in (A) showing goblet cells (arrows) and absorptive cells with brush border, H&E ×60. (D) Vascularisation of the ADM just beneath the regenerating crypts, H&E ×40.