Novel bone cements for joint repair
Biological cements that mimic the properties of bone are being developed by researchers at Queen’s University Belfast and the University of Leeds, both in the UK. If successful, the material could be used to repair fractures in spinal injuries.
Traditional bone cements are composed of polymethyl methacrylate (PMMA) and are used to fill the gap between the bone and the joint replacement. But they are stiff, brittle and prone to cracking.
The material being investigated by the researchers is composed of alpha-tricalcium phosphate, calcium phosphate, calcium carbonate and hydroxyapatite. ‘We are looking to evolve this composition over the project,’ says Dr Fraser Buchanan of Queen’s. When combined with an aqueous solution of disodium hydrogen phosphate and allowed to set, the mixture forms a calcium deficient hydroxyapatite, which is close to the composition of bone.
One of the areas the team is researching is bone replacement in vertebrae, particularly for spinal fractures, where large pieces may have splintered off. The cement could be injected for a less invasive form of treatment.
The Leeds team is using computer modelling to predict the optimal materials needed to mimic the mechanical properties of the bone, while the Queen’s group is manufacturing and characterising those materials through in vitro and in vivo testing.
‘We are trying to optimise stiffness to reduce stress between the bone and the cement while retaining the strength, which is difficult. And it has to be injectable through a needle,’ says Dr Nicholas Dunne, also of Queen’s.
Cracking remains a major concern, adds Buchanan. ‘The occasional large pore can act as a stress concentrator. The key is to get the porosity evenly distributed, which requires quality control.’ The scientists want to optimise delivery of the material, as well as work on its ability to break down and be absorbed.
Dr David Farrar, Biomaterials Technology Manager at the Smith & Nephew Research Centre in Heslington, UK, says, ‘The challenge [of bioresorbable cements] is guaranteeing that you will get new bone, and that the rate at which it is absorbed matches the rate at which new bone is growing in to replace it.’
Farrar believes the new material could be ‘a step in the right direction. Polymethyl methacrylate cements could never be replaced by bone, but within a year or two of being implanted, ceramic cements could’.
The project, funded by a £500,000 grant from the EPSRC, is scheduled to run until September 2011. ‘Hopefully we can optimise the properties of the cement for a particular anatomical site,’ says Buchanan.
Polymer Research Cluster, Queen's University of Belfast