CUHK Passions and Pursuits

37 Fixing a Loose Screw Qin Ling experiments with bioactive implants T itanium plates or screws are normally used to fix difficult fractures and they remain permanent in the body. But Prof. Qin Ling ’s experimental implants simply dissolve within the body, reducing the risk of infection or the need for removal. That’s because they are made of magnesium rather than the hard metal that’s currently used. Magnesium is a micronutrient that the body needs to consume regularly, and is present in our diet. So as well as dissolving naturally, the new orthopedic implants have a secondary benefit in that they serve as a supplement of sorts to the body’s natural function. Magnesium is a ‘bioactive’ implant, whereas titanium or steel are ‘bioinert.’ Magnesium does not have the strength of permanent metallic implants such as titanium. That actually proves an advantage since the bones involved gradually strengthen around the join site. With a titanium implant, the body learns to rely on the metal for stabilization, and the bone does not regrow as well. Magnesium is also a co-factor in around 300 enzyme reactions in the body. Found in green and leafy vegetables, nuts such as almonds and cashews, soy milk and whole grains, the metal leads to better bone strength in those that consume it, as well as helping with muscle growth and to protect the nervous system. Working with hip injuries in particular, Professor Qin’s team has developed a magnesium screw that dissolves entirely within two years, aiding in the bone formation around the join site in the process. They had reported those findings in the journal Nature Medicine . His paper demonstrating good results in the fixation of magnesium screws to prevent joint collapse has appeared in Biomaterials , another top journal. Besides hip injuries, which are particularly dangerous for older patients since the patients often develop complications from other infections while in hospital, Professor Qin has also experimented with the use of magnesium implants to help heal tears of the anterior cruciate ligament. ACL tears are particularly common with younger patients, between the ages of 15 and 25. It’s difficult to suture the ligament back into place, often requiring doctors to drill a hole into the knee to fix a graft in place. With a normal metal screw, there is the risk that the constant wear and tear of the knee eventually results in the widening of its insertion tunnel. A magnesium screw, by contrast, stimulates bone growth around its insertion site, eventually dissolving in place. Professor Qin has already established the efficacy of magnesium implants in rats, rabbits and goats. Together with a collaborator at a hospital in Dalian in northern China, they have now successfully introduced magnesium screws in some 200 human patients, in a single-centre trial. The bipedal stance of humans creates different load-bearing issues in humans compared with quadrupeds. Other doctors are also using the same implants in experimental treatments in Europe. Such technology will contribute to the research and development of orthopaedic devices in Hong Kong. ‘Magnesium is not a new material, but we have found a new application on the medical side,’ Professor Qin explained. ‘It’s a material that is good for the body, and it’s part of the body.’ c c Professor Qin’s team develops a magnesium screw that dissolves entirely, aiding in the bone formation around the join site in the process (Source: Zhao DW, et al. Biomaterials 2016)