Development of in vivo tissue-engineered microvascular grafts with an ultra small diameter of 0.6 mm (MicroBiotubes): acute phase evaluation by optical coherence tomography and magnetic resonance angiography.

Biotubes, i.e., in vivo tissue-engineered connective tubular tissues, are known to be effective as vascular replacement grafts with a diameter greater than several millimeters. However, the performance of biotubes with smaller diameters is less clear. In this study, MicroBiotubes with diameters <1 mm were prepared, and their patency was evaluated noninvasively by optical coherence tomography (OCT) and magnetic resonance angiography (MRA). MicroBiotube molds, containing seven stainless wires (diameter 0.5 mm) covered with silicone tubes (outer diameter 0.6 mm) per mold, were embedded into the dorsal subcutaneous pouches of rats. After 2 months, the molds were harvested with the surrounding capsular tissues to obtain seven MicroBiotubes (internal diameter 0.59 ± 0.015 mm, burst pressure 4190 ± 1117 mmHg). Ten-mm-long MicroBiotubes were allogenically implanted into the femoral arteries of rats by end-to-end anastomosis. Cross-sectional OCT imaging demonstrated the patency of the MicroBiotubes immediately after implantation. In a 1-month follow-up MRA, high patency (83.3 %, n = 6) was observed without stenosis, aneurysmal dilation, or elongation. Native-like vascular structure was reconstructed with completely endothelialized luminal surfaces, mesh-like elastin fiber networks, regular circumferential orientation of collagen fibers, and α-SMA-positive cells. Although the long-term patency of MicroBiotubes still needs to be confirmed, they may be useful as an alternative ultra-small-caliber vascular substitute.