Knee and hip replacements are big operations. In the UK, patients can wait years for an operation which takes months to recover from, yet research indicates that nearly 20% of hip replacement surgeries simply replace a failed implant. Indeed, most hip implants have to be replaced after only 15 years.
This is because the tough alloys used rub against the bone into which they’ve been implanted; causing wear, and shortening the life of the implant.
The solution, according to Antoni Tomsia, a scientist at California’s Lawrence Berkeley lab, is `a coating which adheres to the metal surface of the implant and promotes the formation of hydroxyapatite (the inorganic component of natural bone)’
Working with physicist Eduardo Saiz, Tomsia has developed a family of `bioactive’ silicate glasses and a simple technique for applying them to metallic implants in layers that are between 20 – 200 micro m thick.
Precursor powders are painted on the metal surface, which is heated to temperatures of 800 – 900 degrees C and then cooled suddenly. At these temperatures the titanium implant remains solid but the glass becomes liquid and uniformly coats the full surface of the implant. The risk of thermal stress during this process is minimised by the ability to adjust the coating so that the thermal coefficient of the glass and the metal alloy are equal.
Results from in-vitro tests show that exposure to simulated body fluid causes the coating to develop a layer of hydroxyapatite on its outer surface, a development that could significantly extend the life of medical implants.