Formation of New Tissue from an Arteriovenous Loop in the Absence of Added Extracellular Matrix

Abstract

A major requirement for the microsurgical repair of contour defects of the skin, for example, following removal of a skin cancer on the face, is a mass of vascularised subcutaneous tissue. Such tissue can be generated in vivo using basic tissue engineering principles. In previous studies in our laboratory, we have used a model comprising an arteriovenous (AV) shunt loop sandwiched in artificial dermis, placed in a cylindrical plastic growth chamber, and inserted subcutaneously to grow new connective tissue progressively up to 4 weeks. To learn more about the basic growth characteristics with this model, the same AV shunt loop within a chamber without added extracellular matrix was inserted subcutaneously into the groins of rats for 2, 4, or 12 weeks (n = 5 per group). There was a progressive increase in the mass and volume of tissue such that the chamber was two-thirds full after 12 weeks. Histological examination showed that at 2 weeks there was evidence of fibroblast and vascular outgrowth from the AV shunt, with the formation of granulation tissue, surrounded by a mass of coagulated exudate. At 4 weeks the connective tissue deposition was more extensive, with a mass of more mature granulation tissue containing considerable collagen. By 12 weeks there was an extensive, well vascularized mass of mature fibrous tissue. The blood vessels and residual adventitia of the AV shunt were the likely source of growth factors and of the cells which populated the chamber with new maturing connective tissue. A patent AV shunt in an isolated chamber appears to be the minimal requirement for the generation of new vascularized tissue that is potentially suitable for microsurgical transplantation.

Cardiac Tissue Engineering in an In Vivo Vascularized Chamber

“…23 Here the cells grow in parallel with the newly developing capillary bed to form a vascularized interconnected network of cardiac tissue. We have previously shown in both rat 21 and mouse 38 chambers that other implanted tissues and cells, such as muscle, 17 myoblasts, 17 fat, 39 pancreatic islets, 40 fetal tissue, and fibroblasts, 16 can survive with this methodology. By seeding cardiomyocytes into a chamber in the rat, we have grown a living piece of cardiac tissue with a volume of Ϸ0.2 mL and thickness up to 1983 m, which easily exceeds the dimensions expected to be supported by diffusion alone (Figure 6).…”

“…Angiogenesis becomes essential to successfully engineer tissues with a thickness Ͼ200 m. 15 Our group has successfully generated vascularized tissue that incorporates its own supportive extracellular matrix by placement of an atriovenous blood vessel loop (AV loop) inside a semi-sealed polycarbonate chamber that is implanted into the groin of a rat. 16 This encapsulated tissue is supplied by its own vascular pedicle and is transplantable by microsurgical techniques to other parts of the body, 16 or possibly to an extracorporeal circulation in vitro. This model supports the survival and growth of adipose tissue, 17 implanted skeletal muscle myoblasts, 17 and fibroblasts.…”

A new approach to tissue engineering of vascularized skeletal muscle

“…It is based on the AV loop model first described more than two decades ago by Erol and Spira for the successful vascularization of a full thickness skin graft [16]. The model was enhanced by Morrison and coworkers who inserted the loop into isolation chambers resulting in a successful vascularisation of polymer-and gel matrices [11,17]. This group also demonstrated the superiority of the AV loop as vascular carrier in comparison to the vascular bundle in terms of vascular density and capacity for generation of new tissue [18].…”

Current opportunities and challenges in skeletal muscle tissue engineering

“…First, implantation in vivo of muscle constructs gives the foreign body reaction that results in ingrowth of a supportive capillary network that subsequently promotes and maintains viability (Tanaka et al, 2000;Mian et al, 2000;Saxena et al, 2001;Beier et al, 2006). Nevertheless, to engineer thicker, functional tissue, an integrated vascular system is required.…”