Repair of segmental bone defects with fiber-reinforced composite: a study of material development and an animal model on rabbits

摘要

The Repair of segmental defects in load-bearing long bones is a challenging task because of the diversity ofthe load affecting the area; axial, bending, shearing and torsional forces all come together to test the stability/integrity of the bone. The natural biomechanical requirements for bone restorative materials include strength to withstand heavy loads, and adaptivity to conform into a biological environment without disturbing ordamaging it. Fiber-reinforced composite (FRC) materials have shown promise, as metals and ceramics havebeen too rigid, and polymers alone are lacking in strength which is needed for restoration. The versatility ofthe fiber-reinforced composites also allows tailoring of the composite to meet the multitude of bone propertiesin the skeleton.The attachment and incorporation of a bone substitute to bone has been advanced by different surfacemodification methods. Most often this is achieved by the creation of surface texture, which allows bonegrowth, onto the substitute, creating a mechanical interlocking. Another method is to alter the chemicalproperties of the surface to create bonding with the bone – for example with a hydroxyapatite (HA) or abioactive glass (BG) coating.A novel fiber-reinforced composite implant material with a porous surface was developed for bonesubstitution purposes in load-bearing applications. The material’s biomechanical properties were tailored withunidirectional fiber reinforcement to match the strength of cortical bone. To advance bone growth onto thematerial, an optimal surface porosity was created by a dissolution process, and an addition of bioactive glassto the material was explored. The effects of dissolution and orientation of the fiber reinforcement were alsoevaluated for bone-bonding purposes. The Biological response to the implant material was evaluated in a cellculture study to assure the safety of the materials combined. To test the material’s properties in a clinicalsetting, an animal model was used. A critical-size bone defect in a rabbit’s tibia was used to test the materialin a load-bearing application, with short- and long-term follow-up, and a histological evaluation of theincorporation to the host bone.The biomechanical results of the study showed that the material is durable and the tailoring of the propertiescan be reproduced reliably. The Biological response - ex vivo - to the created surface structure favours theattachment and growth of bone cells, with the additional benefit of bioactive glass appearing on the surface.No toxic reactions to possible agents leaching from the material could be detected in the cell culture studywhen compared to a nontoxic control material. The mechanical interlocking was enhanced - as expected -with the porosity, whereas the reinforcing fibers protruding from the surface of the implant gave additionalstrength when tested in a bone-bonding model. Animal experiments verified that the material is capable ofwithstanding load-bearing conditions in prolonged use without breaking of the material or creating stressshielding effects to the host bone. A Histological examination verified the enhanced incorporation to hostbone with an abundance of bone growth onto and over the material. This was achieved with minimal tissuereactions to a foreign body.An FRC implant with surface porosity displays potential in the field of reconstructive surgery, especiallyregarding large bone defects with high demands on strength and shape retention in load-bearing areas or flatbones such as facial / cranial bones. The benefits of modifying the strength of the material and adjusting thesurface properties with fiber reinforcement and bone-bonding additives to meet the requirements of differentbone qualities are still to be fully discovered.