| A bilayer construct is proposed to make use of a bone-binding ceramic layer that will be integrated into the subchondral locale of a cartilage defect, combined with an upper layer of hydrogel that mimics the extracellular matrix of cartilage. A suitable scaffold for engineered cartilage should possess the mechanical integrity of host tissue and be long-term degradable, as the replacement by natural hyaline tissue will be a slow process. Glycol chitosan, a water soluble derivative of the cationic polysaccharide chitosan, was selected as the material for the tissue engineering matrix. It has chemical characteristics similar to the abundant proteoglycans found in cartilage, and fits the mechanical needs for a hydrophilic slowly-degrading network. As the base for the implant, hydroxyapatite was chosen for its known oseointegrative capability and biocompatibility.;To join the two phases of the device together, covalent linkages between photoreactive methacrylate groups were used. The targeted coupling agent for surface modification of the hydroxyapatite was 3-methacryloxypropyltrimethoxysilane. The reactivity of alkoxy silanes with surface hydroxyl groups as in hydroxyapatite is well understood. The initial glycol chitosan was fractionated to reduce its molecular weight and increase solubility and ultimate biodegradation rate. Subsequently, glycidyl methacrylate was used to add reactive moieties to the chitosan backbone. Ultraviolet photocrosslinking with a water-soluble free radical initiator was the method selected to simultaneously gel the glycol chitosan and bind it to the hydroxyapatite surface. The resulting construct proved to have no toxic effects on chondrocyte cells, and presents a novel method for cartilage tissue engineering. |
