Effect of Tricalcium Phosphate Foam and Paste Bone Grafting Materials Designed for Improved Surgical Handling on Osteogenesis in a Sheep Scapula Model

Abstract

Reconstruction of critical-size bone defects (CSDs) with complex defect morphologies remains clinically challenging. The desire to avoid autograft harvesting has prompted an increasing quest for adequate synthetic bone grafting materials. The clinical success rates, which have been achieved with bioactive β-tricalcium phosphate granules (TCP-G) demonstrate that these materials have become an excellent alternative graft choice. In order to improve surgical handling properties, TCP-G have been combined with natural polymers for creating paste- and foam-like materials, which can easily be molded into any desired shape when grafting a given bony defect or deploying them with a syringe. This study assessed the effect of a TCP paste (TCP-P) and a TCP-foam (TCP-F) bone grafting material as compared to TCP-G on bone formation and osteogenic marker expression after 1, 3, 6, 12, and 18 months of implantation in CSD in the sheep scapula and tested the hypothesis that the addition of natural polymers would not diminish the osteogenic properties of TCP-P and TCP-F. The bone and bone graft material area fractions were determined histomorphometrically in order to quantify bone formation and bone graft material resorption. Immunohistochemical analysis of collagen type I, osteocalcin, and bone sialoprotein expression in the various cell and matrix components of the bone tissue was performed on resin-embedded sections for characterizing the osteogenic and bioactive properties of the test materials. By 6 months, all three TCP materials facilitated excellent defect regeneration with further bone remodeling at 12 and 18 months. TCP-F and TCP-P induced greater osteocalcin expression and exhibited more advanced graft material resorption at 1 and 6 months, respectively. At 18 months, all three grafting materials were almost fully resorbed with the original bony architecture being restored. Taken together, the hyaluronic acid and methylcellulose components in TCP-P and porcine collagen components in TCP-F did not diminish the osteogenic capacity of TCP-P and TCP-F, which exhibited an even slightly higher resorbability and enhancement effect on OC expression by osteoblasts.