M. Wei

Currently, the bone-repair biomaterials market is dominated by high modulus metals and their alloys. The problem of stress-shielding, which results from elastic modulus mismatch between these metallic materials and natural bone, has stimulated increasing research into the development of polymer-ceramic composite materials that can more closely match the modulus of bone. In this study, we prepared poly(l-lactic acid)/hydroxyapatite/poly(ε-caprolactone) (PLLA/HA/PCL) composites via a four-step process, which includes surface etching of the fiber, the deposition of the HA coating onto the PLLA fibers through immersion in simulated body fluid (SBF), PCL coating through a dip-coating process, and hot compression molding. The initial HA-coated PLLA fiber had a homogeneous and continuous coating with a gradient structure. The effects of HA: PCL ratio and molding temperature on flexural mechanical properties were studied and both were shown to be important to mechanical properties. Mechanical results showed that at low molding temperatures and up to an HA: PCL volume ratio of 1, the flexural strain decreased while the flexural modulus and strength increased. At higher mold temperatures with a lower viscosity of the PCL a HA: PCL ratio of 1.6 gave similar properties. The process successfully produced composites with flexural moduli near the lower range of bone. Such composites may have clinical use for load bearing bone fixation.

A fibrous precursor for bone repair composites was made by coating poly(L-lactide) (PLLA) fibers with hydroxyapatite (HA) using a biomimetic method. To enhance the bonding between the HA coating and the PLLA fiber, PLLA fibers were etched with either sodium hydroxide or sodium hypochlorite to generate carboxyl groups on fiber surfaces. The experiments were designed to determine the influence of etching on the fiber surface morphology and chemistry as well as the subsequent HA coating on the etched fiber surfaces. It was found that the etching pretreatment increased the roughness as well as the hydrophilicity of fibers, indicating that hydrolysis of PLLA chains had taken place on fiber surfaces. The etching pretreatment also promoted HA coating formation by introducing thicker coating on the surface of fibers with a longer etching time, a higher etching concentration, or with NaOCl as the etching agent. A mechanism of surface hydrolysis and oxidation of PLLA was proposed. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009