Endogenous Platelet-Rich Plasma Supplements/Augments Growth Factors Delivered via Porous Collagen-Nanohydroxyapatite Bone Substitute for Enhanced Bone Formation

Abstract

Polymer (acrylate) and ceramic bone cements are extensively used as bone void fillers and for implant fixation in orthopedics. These materials have micro- to nonporous architectures. Postimplantation, they may cause hypoxic and exothermic injuries to already compromised damage site. These materials also have limited interaction with surrounding tissue. In this work we have developed composite collagen-nanohydroxyapatite (CS) bone filler, mimicking porous architecture of trabecular bone. It was functionalized with clinically available bone active agents like bone morphogenetic protein-2 (rhBMP-2) and zoledronic acid (ZA). We investigated synergistic effects of the bone active molecules and endogenous platelet rich plasma (PRP), a source of growth factors on mineralization. Porous CS and collagen/gelatin/chiotosan polymer scaffold (SC) (without nanohydroxyapatite) were synthesized using cryogelation. PRP (10 μL) (∼5 × 106 cells), rhBMP-2 (5 μg) and ZA (10 μg) were used to functionalize scaffolds. Bone formation was evaluated at ectopic sites in abdominal pouch and 4.0 mm critical defect in tibia metaphysis of rats. Tissue mineralization was evaluated by micro-CT and histological analysis 12 weeks postimplantation. In vitro cell based studies revealed, PRP functionalization enhances osteoblast proliferation and activity on scaffolds. In vivo BMP+ZA+PRP functionalized scaffolds had higher amount (28 mm3) of mineralized tissue formation as compared to empty defect (20 mm3), suggesting that PRP can augment the osteoinductive properties of functionalized scaffolds both in vitro and in vivo. Enhanced cell infiltration and mineralization can be achieved via CS in comparison to SC, implying their use as porous bone void fillers and substitutes for autografts.