Fabrication of Pre-Determined Shape of Bone Segment With Collagen-Hydroxyapatite Scaffold and Autogenous Platelet-Rich Plasma

Background:  Reconstruction of large segment of bony defects is frequently needed in hand surgery. Autogenous bone grafting is considered the standard in management of these bony defects but has limited source of graft material. Collagen and hydroxyapatite have been used as bone-filling materials and are known to serve as the osteoconductive scaffold for bone regeneration. On the other hand, platelet-rich plasma is a kind of natural source of growth factors, and has been used successfully in bone regeneration and improving wound healing. This study was designed to evaluate the effectiveness of using biohybrids of platelet-rich plasma and collagen-hydroxyapatite beads for fabricating of protrusive bone in a rabbit animal model.

Methods: Biomaterial beads comprised of particulate hydroxyapatite dispersed in fibrous collagen (type I) matrices were prepared and filled in the ringed polytetrafluoroethylene (PTFE) artificial vascular graft (3 cm long, 1 cm in diameter). New Zealand White rabbits were each implanted with two cylindrical PTFE artificial vascular graft over both iliac crests (n = 16). A 2 x 0.5 cm opening was created at the side of each PTFE chamber to allow the content of chamber in contact with the bone marrow of the ileum. The chambers were empty (groups A and D), filled with type I collagen/hydroxyapatite beads (groups B and C). In groups C and D, autologous platelet rich plasma (PRP) was given by transcutaneous injection method into the chambers every week. After 12 weeks, the animals were sacrificed and the chambers were harvested for radiological and histological analysis.

Results: In plain radiographs, the group C chambers had significantly higher bone tissue engineered (average calcified density 0.95, average calcified area 61.83%) compared with other groups (P < 0.001). In histological examination, there was a creeping substitution of the implant by the in-growth of fibrovascular tissue in group C. Abundant fibrovascular networks positioned interstitially between these biomaterial beads in all parts of chamber. Degradation of these beads and newly formed capillaries and osteoids around the degraded matrixes are shown. The continually calcification in the matrixes or degraded matrixes is evidenced by the strong green fluorescence observed under the confocal microscope. In group B, looser architecture without evidence of tissue in-growth was shown. In the scaffold absent groups (A and D), there was only fibrous tissue shown within the chamber.

Conclusions: In this study, we have demonstrated a feasible approach to fabricate an osseous tissue that meets clinical need. Using the type I collagen/ hydroxyapatite gel beads matrixes and intermittent injection of autologous platelet-rich-plasma, specific 3D osseous tissues with fibrovascular network structure from pre-exist bony margin were successfully created in an in vivo animal model.