Tracheal autograft prefabrication using microfibrillar collagen and bone morphogenetic protein

To investigate the feasibility of prefabricating a tracheal autograft capable of microvascular free tissue transfer using microfibrillar collagen (Avitene) as a carrier for bone morphogenetic protein (BMP).

Using heterotopic bone induction and soft tissue molding, an attempt was made to prefabricate a homologous tracheal autograft in a rodent free flap model. In 12 male Sprague-Dawley rats, linear troughs were dissected along the length of the gracillis muscle, filled with BMP-saturated microfibrillar collagen, molded around a silicone tracheal stent, and left pedicled on the femoral vessels. Untreated microfibrillar collagen was buried in muscle at a distant control site in 3 animals. Autografts were susequently evaluated for lumen integrity, vascular patency, and bone induction at 3 weeks.

With the exception of 2 nonviable grafts, rings of heterotopic bone were created in all 10 animals. Rings spanning at least one third of the tracheal circumference maintained a noncollapsible lumen. Microfibrillar collagen was replaced by cancellous bone that reproduced the exact shape and volume of the collagen carrier. The lumen was lined by smooth fibroplasia, and there was no significant inflammatory response, bone exposure, or overgrowth. Soft tissue between rings allowed longitudinal flexibility, homologous to the native trachea. Bone induction did not occur in any of the control sites.

Microfibrillar collagen is an effective carrier for BMP and may serve as the ideal substrate for tracheal reconstruction without the need for stenting. The potential use of BMP to bioengineer microvascular free flaps with intrinsic skeletal support has an unlimited potential and will add a new dimension to head and neck reconstruction.