Polymer-based composite hip prostheses

A composite hip prosthesis (CHP) made from poly(ether-imide) reinforced with carbon and glass fibres was manufactured and characterized. The main objective of the study was to evaluate the effect of fibre organization on the mechanical properties of the composite femoral implant and compare with the bone. A stacking sequence of drop-off plies of carbon/glass fibres reinforcing poly(ether-imide) (PEI) constitutes a symmetrical and balanced CHP. The hip was manufactured according to the finite element modelling (FEM) design and using the compression moulding and water-jet technologies. The measured stress-strain data according to tensile, flexural and torsional tests showed agreement with the numerical calculation. Young's modulus and the strength in tension are uniform along the stem axis (40 GPa and 600 MPa, respectively) while the elastic modulus in bending varies from 10 to 60 GPa in the tip-head direction. The composite stem showed a linear load-displacement relation up to 4500 N without breaking. Mechanical behaviour of the CHP is compared to that of a canine femur. Comparison with metal prostheses has also been undertaken. CHPs control stress-strain distributions, and hence the mechanical signals to bone, through a material-structure design.