Regeneration of skeletal tissues has been recognized as a new means for reconstruction of
skeletal defects. We investigated the feasibility of an injectable and expandable porous implant
system for in situ regeneration of bone. Therefore, a composite biodegradable foaming
cement based on poly(propylene fumarate) was injected into a critical size defect made
in the rat tibia. Animals were divided into two groups comparing the foam in the experimental
group against sham-operated animals having a drill hole but no implant in the control
group. Eight animals were included in each group. Animals were sacrificed at 1, 3, and
7 weeks postoperatively. Implantation sites were then evaluated with histologic and histomorphometric
methods. Results of this study showed that defects did not heal in sham-operated
animals. In the experimental group, metaphyseal and cortical defects healed within
the first postoperative week by formation of immature woven bone. At the site of the cortical
drill hole defect, healing was noted to progress to complete closure by formation of mature
bone. Histomorphometry corroborated these findings and showed that metaphyseal
bone remodeling peaked at 1 week postoperatively and then decreased as healing of the cortical
defect progressed. This suggests that near-complete restoration of the original state of
the tibial bone occurred in this animal model supporting the concept of in situ bone regeneration
by application of engineered biodegradable porous scaffolds.
