Comparing ectopic bone growth induced by rhBMP-2 on an absorbable collagen sponge in rat and rabbit models

Area of Science:

• Biomaterials Science
• Regenerative Medicine
• Orthopedic Surgery

Background:

• Recombinant human Bone Morphogenetic Protein-2 (rhBMP-2) is a bone morphogen used as an autograft substitute for spinal fusion.
• It is typically incorporated onto an absorbable collagen sponge (ACS) carrier in the operating room.
• While rhBMP-2/ACS effectiveness is established, further understanding of its performance is needed.

Purpose of the Study:

• To determine if fluid released from rhBMP-2/ACS implants can induce bone growth at ectopic sites.
• To quantify protein retention in ACS under simulated intraoperative conditions.
• To compare in vivo bone formation by rhBMP-2 solution versus rhBMP-2/ACS implants.

Main Methods:

• In vitro assessment of rhBMP-2 protein retention in ACS after varying soak times and compression.
• In vivo ectopic implantation of rhBMP-2/ACS constructs and rhBMP-2 solution in rat and rabbit models.
• Histological evaluation of ossicle formation at 4 and 12 weeks post-implantation.

Main Results:

• Over 95% of rhBMP-2 protein was retained by ACS in simulated intraoperative conditions (15-min soak, compression).
• rhBMP-2 solution alone did not induce bone formation in rats or rabbits.
• rhBMP-2/ACS implants induced significant ossicle formation in rats (22/24 sites), with no significant changes in size/shape over time. Rabbits showed a lower ossification rate.

Conclusions:

• The rhBMP-2/ACS carrier effectively retains the morphogen, preventing significant loss during handling.
• rhBMP-2 requires a carrier like ACS for effective in vivo bone induction at ectopic sites.
• rhBMP-2/ACS is a viable option for promoting bone formation, though species-dependent responses may occur.