Cartilage mimicking materials for orthopaedic applications

Abstract

A treatment gap exists in the orthopaedic market. Partial joint repair, where an artificial material replaces localised chondral damage, has been proposed as a solution to fill this gap. Current options are, however, lacking. This work aimed to synthesise partial joint replacement materials that mimic the lubrication mechanisms of cartilage: biphasic and boundary lubrication.

In this work, materials that mimic the lubrication mechanisms of cartilage have been synthesised. Boundary lubrication: poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) modified ultra-high molecular weight polyethylene (PMPC-UHMWPE), PMPC modified polyoxymethylene (PMPC-POM) and PMPC modified polyethylene terephthalate (PMPC-PET). Biphasic lubrication: Polyvinyl alcohol cryogel (PVA-C) and double network (DN) hydrogel. Biphasic and boundary lubrication: PMPC modified triple network (PMPC TN) hydrogel.

PMPC-UHMWPE was shown to have favourable tribological properties. However, depletion of the boundary lubricant occurred at contact pressures below those found in the human knee. As it is unknown how this material would react when the boundary layer had depleted, it was concluded that this material would not be suitable as a bearing surface for partial joint repair.

PVA-C offered compressive moduli in the chondral range; however, its capacity for biphasic lubrication was unclear. More critically, this material exhibited failure below the peak loads found in the knee, and was therefore not considered suitable for use as a partial joint replacement material. Although, more physiologically relevant tests would be required to truly assess the suitability of this material.

A PMPC-TN hydrogel exhibited failure above the peak loads that occur in the human knee and exhibited good evidence that it was able to boundary and biphasically lubricate. This is the first report of a material that can mimic both lubrication modes of cartilage. These hydrogels were, however, hindered by their poor resistance to repeated loading cycles, which may in future be solved through the use of self-healing components or reinforcement by another load bearing element.

The biomimetic concepts and testing methodologies developed in this work may enable the synthesis of new materials that are a viable replacement for damaged or absent cartilage in human joints.