The objective of this study was to evaluate the osteoinductivity of composite
chitosan-nano-hydroxyapatite scaffolds in a rat muscle pouch model. Previous in vitro
characterization demonstrated the ability of the scaffolds to promote bone regeneration and
as a carrier for local delivery of BMP-2. Composite microspheres were prepared using a
co-precipitation method, and scaffolds were fabricated using an acid wash to adhere beads
together. To determine the in vivo osteoinductivity of the scaffolds, the following groups
(n = 6) were implanted into muscle pouches created in the latissimus dorsi of Sprague
Dawley rats: (A) lyophilized scaffolds without rhBMP-2, (B) lyophilized scaffolds with
rhBMP-2, (C) non-lyophilized scaffolds with rhBMP-2, and (D) absorbable collagen sponge
with rhBMP-2 (control). Groups B, C, and D were loaded with 4 mL of a 9.0 μg/mL solution
of rhBMP-2 for 48 h. The rats were sacrificed after one month and samples were analyzed
for amount of residual implant material, new bone, and osteoid. Although the experimental
groups displayed minimal degradation after one month, all of the scaffolds contained small
amounts of woven bone and considerable amounts of osteoid. Approximately thirty percent
of the open space available for tissue ingrowth in the scaffolds contained new bone or
osteoid in the process of mineralization. The ability of the composite scaffolds (with and
without BMP-2) to promote ectopic bone growth in vivo was demonstrated.