Hard graft - bioactive skeletal repair

Materials World magazine
30 Apr 2013

In the past 20 years, materials scientists have joined the search for remedies to problems associated with bone disease. Rachel Lawler attended Professor Serena Best’s Bioactive Materials for Skeletal Repair lecture for the London Materials Society on 18 April 2013 to find out more.

A person with osteoporosis need only stumble and they could break their femur,’ Co-Director of the Cambridge Centre for Medical Materials and Professor of Materials Science at University of Cambridge, Serena Best explained the struggle facing those who suffer with degenerative bone disease. Two of the most common diseases affect bones in very different ways. Osteoporosis causes bone to gradually deteriorate, reducing the skeleton’s mechanical properties. ‘We see increased fragility in these patients simply because there is less bone there,’ says Best. Osteoarthritis brings another problem for medical professionals as it damages the protective cartilage, allowing bones to become worn as they grind against joints. These diseases require very different materials solutions, but materials science is not at the forefront of treatment for these illnesses.

Today, the solution for 95% of patients needing bone grafts is found in transplants either from a donor or from a different site within the patient’s own body. With donated bones there is always a risk of rejection, but taking a graft from the patient’s own body is not without limits. This procedure requires two operations and is obviously restricted by the availability of lesser-used bones.

Just 5% of bone grafts make use of artificial material. Best described the work that has been undertaken by teams both in London and Cambridge over the past 20 years to improve the functionality of one of the synthetic solutions – hydroxyapatite (HA). Her team tried to produce bone grafts closer in composition to bone material than pure HA to improve functionality.

The team tried the approach of adding ionic substitutions in the apatite crystal lattice to encourage quicker bone repair, using a silicate substituted calcium phosphate and compared its performance to a pure HA graft. The two substances were used for grafts in a fault in a femur bone and while both performed well, the length of the boundaries in the silicate were significantly different and the silicate substituted material was found to enhance bone repair. Electron microscopy offers some insights into a possible mechanism that might explain the behaviour, but further work is required to understand why the silicate material performed better.

But while this looks promising for the development of bone grafts, patients in need of cartilage repair require an alternative solution. Also at Cambridge, Dr Andrew Lynn began developing a biodegradable scaffold for weakened joints. ‘His idea was to have a material that was cartilage-like at the surface but mineral-like at the bone contact point,’ says Best. The scaffold is made from a mixture of collagen and glycosaminoglycans, the same materials found in human cartilage, and is freeze-dried to create microscopic pores in its surface. These pores allow the top of the implant to be infiltrated by cartilage cells, while the lower area of the implant will be attractive to bone cells.

‘As people live longer, we’re going to have more and more aging bones,’ says Best. ‘Anything we can do to help bone damage will aid the quality of life of these patients.’ These developments may offer some promise.