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

The autologous biotube, developed by using in-body tissue architecture technology, is one of the most promising small-diameter vascular grafts in regenerative medicine. The walls of the biotubes obtained by a traditional silicone mold-based method were very thin, and this is still the primary obstacle while handling anastomosis, even though these biotubes have adequate pressure resistance ability. This pilot study showed the effect of optical stimulation of subcutaneous tissue formation in the body during the preparation of the biotubes. A blue light-emitting diode (LED) was embedded into a silicone rod as a mold. The biotube was prepared by placing the luminescent molds into the dorsal subcutaneous pouches of a pair of beagles (each weighing ~10 kg) for 2 weeks under photoirradiation. The wall thickness of the obtained biotubes was 506.9 ± 185.7 µm, which was remarkably more than that of the previous biotubes prepared by 2 months of embedding similarly in beagles' subcutaneous pouches (thickness, 77.2 ± 14.8 µm). Many capillaries with smooth muscle cells were infiltrated into the wall and concentrated in the internal layer. Interestingly, the formation of elastic fibers had already started along with collagen fibers, mostly with a regular circumferential orientation. The short-term in-body optical stimulation resulted in the rapid formation of a biotube. These phenomena will allow easy surgical handling and may induce vascular maturation in histology during the acute phase after implantation.