In-body optical stimulation formed connective tissue vascular grafts, "biotubes," with many capillaries and elastic fibers

An in vivo study on endothelialized vascular grafts produced by autologous biotubes and adipose stem cells (ADSCs)

Currently, commercial synthetic vascular grafts made from Dacron and ePTFE for small-diameter, vascular applications (<6 mm) show limited reendothelization and are less compliant, often resulting in thrombosis and intimal hyperplasia. Although good blood compatibility can be achieved in autologous arteries and veins, the number of high quality harvest sites is limited, and the grafts are size-mismatched for use in the fistula or cardiovascular bypass surgery; thus, alternative small graft substitutes must be developed. A biotube is an in vivo, tissue-engineered approach for the growth of autologous grafts through the subcutaneous implantation of an inert rod through the inflammation process. In the present study, we embedded silicone rods with a diameter of 2 mm into the dorsal subcutaneous tissue of rabbits for 4 weeks to grow biotubes. The formation of functional endothelium cells aligned on the inner wall surface was achieved by seeding with adipose stem cells (ADSCs). The ADSCs-seeded biotubes were implanted into the carotid artery of rabbits for more than 1 month, and the patency rates and remodeling of endothelial cells were observed by angiography and fluorescence staining, respectively. Finally, the mechanical properties of the biotube were also evaluated. The fluorescence staining results showed that the ADSCs differentiated not only into endothelia cells but also into smooth muscle cells. Moreover, the patency of the ADSCs-seeded biotube remained high for at least 5 months. These small-sized ADSCs-seeded vascular biotubes may decrease the rate of intimal hyperplasia during longer implantation times and have potential clinical applications in the future.

Utilizing the Foreign Body Response to Grow Tissue Engineered Blood Vessels in Vivo

It is well known that the number of patients requiring a vascular grafts for use as vessel replacement in cardiovascular diseases, or as vascular access site for hemodialysis is ever increasing. The development of tissue engineered blood vessels (TEBV's) is a promising method to meet this increasing demand vascular grafts, without having to rely on poorly performing synthetic options such as polytetrafluoroethylene (PTFE) or Dacron. The generation of in vivo TEBV's involves utilizing the host reaction to an implanted biomaterial for the generation of completely autologous tissues. Essentially this approach to the development of TEBV's makes use of the foreign body response to biomaterials for the construction of the entire vascular replacement tissue within the patient's own body. In this review we will discuss the method of developing in vivo TEBV's, and debate the approaches of several research groups that have implemented this method.

Development of an in vivo tissue-engineered vascular graft with designed wall thickness (biotube type C) based on a novel caged mold

Small-diameter biotube vascular grafts developed by in-body tissue architecture had high patency at implantation into rabbit carotid arteries or rat abdominal aortas. However, the thin walls (34 ± 14 μm) of the original biotubes made their implantation difficult into areas with low blood flow volumes or low blood pressure due to insufficient mechanical strength to maintain luminal shape. In this study, caged molds with several windows were designed to prepare more robust biotubes. The molds were assembled with silicone tubes (external diameter 2 mm) and cylindrical covers (outer diameter 7 mm) with 12 linear windows (1 × 9 mm). After the molds were embedded into beagle dorsal subcutaneous pouches for 4 weeks, type C (cage) biotubes were obtained by completely extracting the surrounding connective tissues from the molds and removing the molds. The biotube walls (778 ± 31 μm) were formed at the aperture (width 1 mm) between the silicone rods and the covers by connective cell migration through the windows of the covers. Excellent mechanical properties (external pressure resistance, approximately 4 times higher than beagle native femoral arteries; burst strength, approximately 2 times higher than original biotubes) were obtained. In the acute phase of implantation of the biotubes into beagle femoral arteries, perfect patency was obtained with little stenosis and no aneurysmal dilation. The type C biotubes may be useful for implantation into peripheral arteries or veins in addition to aortas.