The aim of the project is to develop a new form of processing for resorbable osteosynthesis devices, using continuous fibre-reinforced polymeric materials.
Poly-L-lactide and poly-L/DL-lactides have been synthesized for reinforcement fibers and matrix material respectively. Melt-spun P-L-LA fibers of a strength of 800 MPa have been embedded in an amorphous P-L/Dl-LA 70:30 matrix by compression moulding. Ethyleneoxide sterilized samples have been tested in vitro and in vivo. Satisfying bending modulus has been reached (6 GPa). Yet with 50% strength retention after 10 weeks a fast degradation occured which could be related to residual monomers. By this fast degradation 70% resorption after 1 year could be observed in the non-functional animal studies in rabbits. Only mild inflammatory reaction confirmed a good biocompatibility of the materials even during the resorption period.
Further effort has to concentrate on the reduction of initial monomer content. The high advantage of the processing method to orient the fibers in the device will be utilized in prototype samples like osteosynthesis plate with fixation holes.
Taking the main degradable polymers known as a basis, a material has to be chosen which meets the requirements regarding processability, mechanical behaviour and degradation kinetics.
After fibre processing, the embedding of the fibres in the matrix has to be performed with good fibre-matrix adhesion and a high alignment. The intention is to prevent the diffusion of tissue fluids at the fibre-matrix interface, and to obtain maximum strength of the device over an accountable period of time.
The product properties will be tested in vitro. To this end samples are to be prepared both with a rectangular and a circular cross-section, which are subjected to bending and torsional stresses respectively. Degradation will be achieved by immersing the devices in buffered saline at elevated temperatures. Animal tests are unavoidable to test the tissue reaction during the resorption process as well as to substantiate the data of degradation collected in the in vitro tests.
The progress beyond the state of the art is to modify a pultrusion for processing resorbable biomaterials and to develop long-term resorbable fibre materials, which are not so far available, but which are needed for osteosynthesis.