COMPOSITE HYDROGELS FOR IMPLANTS

Hydrophilic composite structures are designed to mimic the transport a nd mechanical properties of natural soft tissue such as tendons, ligam ents and intervertebral discs. Mechanical and viscoelastic behaviour o f a soft composite material based on a hydrogel matrix reinforced with bundles of polyethylene therephthalate (PET) fibres is analysed. The typical J-shaped stress-strain behaviour, displayed by natural tendons and ligaments, is reproduced. The mechanical characteristics, such as the extent of the 'toe-in region' and the elastic modulus in the line ar region, can be controlled by varying the winding angle of the fibre s and the matrix composition. Dynamic mechanical analysis showed the d ual behaviour of the composite systems due to the progressive contribu tion of the PET fibres. Different poly(2-hydroxyethylmethacrylate)/pol ycaprolactone (PHEMA/PCL) semi-interpenetrating polymer networks (IPNs ) hydrogel composite systems reinforced with PET fibres have been inve stigated for potential use as intervertebral disc prostheses. Compress ion properties have been evaluated by static and dynamic tests. Uniaxi al compression tests on the swollen samples showed an increase of the modulus and maximum stress with increasing content of PCL and PET fibr es. Creep behaviour is also dependent on the hydrogel composition. The composite PHEMA/PCL hydrogels showed compression properties similar t o those expressed by canine intervertebral discs in different spinal l ocations.