Year of Publication

2005

Degree Type

Thesis

College

Graduate School

Department

Biomedical Engineering

First Advisor

Ahmed El-Ghannam

Abstract

Repair of bone defects is a major challenge in orthopaedic surgery. Current bone graft treatments, including autografts, allografts and xenografts, have many limitations making it necessary to develop a biomaterial to be a bone graft substitute. One such biomaterial is bioactive resorbable silica-calcium phosphate nanocomposite (SCPC). SCPC was processed using a 3D rapid prototyping technique and sintered at different temperatures to create porous scaffolds. SEM analyses and mercury intrusion porosimetry showed SCPC to be highly porous with micro- and nanopores. BET analysis indicated that SCPC had high surface area. Mechanical testing demonstrated that SCPC had a compressive strength similar to trabecular bone. Analysis of different thermal treatment temperatures indicated as the temperature was increased, the porosity decreased and the mechanical strength increased. When loaded with rhBMP-2 (SCPC-rhBMP-2), SCPC provided a sustained release profile of rhBMP-2 for 14 days. This was shown to be a greater release than hydroxyapatite (HA)-rhBMP-2. After immersion in SBF, ICP analyses showed the calcium concentration of SBF dropped drastically after one day of immersion. In conjunction, FTIR showed the formation of a hydroxyapatite layer on the SCPC surface and was confirmed by SEM. SCPC thermally treated at 850 ??C demonstrated the greatest dissolution/precipitation reactions when immersed in SBF. Processing the SCPC-rhBMP-2 hybrid using a rapid prototyping technique allowed for an exact replica of the rabbit ulna to be fabricated. This was implanted into a 10 mm segmental defect in the rabbit ulna. CT scans during the healing of the defect showed intimate union between SCPC-rhBMP-2 and the bone and about 65% healing of the defect after 4 weeks. Rabbits were euthanized after 12 and 16 weeks. Digital images show almost complete healing of the defect after 16 weeks. Torsional testing of the ulna after 12 weeks demonstrated restoration of maximum torque and angle at failure. Histological evaluation after 12 weeks showed the regenerated bone has all the morphological characteristics of mature bone. Through in-vitro and in-vivo testing, it can be recommended that the porous bioactive SCPC can serve as a successful delivery system for biological growth factors and serve as an alternative to autologous bone grafting.

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