Testing bone substitutes in a small animal model of revision arthroplasty

This study evaluated a modification of the rat-pin model to enable testing of bone substitute materials. The model was characterized using the ceramic, beta-tricalcium phosphate (betaTCP) as a filler.

The effect of osteogenic growth factors on bone growth into a ceramic filled defect around an implant

Currently available synthetic bone substitutes perform poorly compared to autograft. It is hoped that by adding osteogenic growth factors to the materials, new bone formation could be increased and the clinical outcome improved. In this study, IGF-1, bFGF and TGFbeta1, alone and in combination, were absorbed onto a carrier of P-tricalcium phosphate (PTCP) and implanted into a defect around a hydroxyapatite-coated, stainless steel implant in the proximal tibia of rat in a model of revision arthroplasty. Animals were sacrificed at 6 and 26 weeks for routine histology and histomorphometry and mechanical push out tests. The results show that only bFGF had a significant effect on ceramic resorption. The groups that received bFGF and bFGF in combination with TGFbeta1 had smaller and fewer betaTCP particles remaining in the defect at 6 and 26 weeks. No growth factor combination significantly enhanced new bone formation or the mechanical strength of the implant. These results indicate that, of the growth factors tested, only bFGF had any beneficial effect on the host response to the implant, perhaps by delaying osteoblast differentiation and thereby prolonging osteoclast access to the ceramic. (C) 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.

Bone growth into a ceramic-filled defect around an implant - The response to transforming growth factor beta 1

Synthetic bone substitutes provide an alternative to autograft but do not give equivalent clinical results. Their performance may be enhanced by adding osteogenic growth factors. In this study, TGFbeta1 was absorbed on to a carrier of 0 tricalcium phosphate and Gelfoam(R) and used to fill a defect around a tibial implant in a rat model of revision arthoplasty.

Comparative Characterisation of 3-D Hydroxyapatite Scaffolds Developed via Replication of Synthetic Polymer Foams and Natural Marine Sponges

The production of complex inorganic forms, based on naturally occurring scaffolds offers an exciting avenue for the construction of a new generation of ceramic-based bone substitute scaffolds. The following study reports an investigation into the architecture (porosity, pore size distribution, pore interconnectivity and permeability), mechanical properties and cytotoxic response of hydroxyapatite bone substitutes produced using synthetic polymer foam and natural marine sponge performs. Infiltration of polyurethane foam (60 pores/in2) using a high solid content (80wt %), low viscosity (0.126Pas) hydroxyapatite slurry yielded 84-91% porous replica scaffolds with pore sizes ranging from 50µm - 1000µm (average pore size 577µm), 99.99% pore interconnectivity and a permeability value of 46.4 x10-10m2. Infiltration of the natural marine sponge, Spongia agaricina, yielded scaffolds with 56- 61% porosity, with 40% of pores between 0-50µm, 60% of pores between 50-500µm (average pore size 349 µm), 99.9% pore interconnectivity and a permeability value of 16.8 x10-10m2. The average compressive strengths and compressive moduli of the natural polymer foam and marine sponge replicas were 2.46±1.43MPa/0.099±0.014GPa and 8.4±0.83MPa /0.16±0.016GPa respectively. Cytotoxic response proved encouraging for the HA Spongia agaricina scaffolds; after 7 days in culture medium the scaffolds exhibited endothelial cells (HUVEC and HDMEC) and osteoblast (MG63) attachment, proliferation on the scaffold surface and penetration into the pores. It is proposed that the use of Spongia agaricina as a precursor material allows for the reliable and repeatable production of ceramic-based 3-D tissue engineered scaffolds exhibiting the desired architectural and mechanical characteristics for use as a bone 3 scaffold material. Moreover, the Spongia agaricina scaffolds produced exhibit no adverse cytotoxic response.