An optimization of the manufacturing process of corporeal screws made of synthetic bone

The manufacturing of corporeal screws made with hydroxyapatite and calcium is discussed. It is a biocompatible material and fragile. For this purpose, M8 screws with Phillips tightening slots were developed. They were manufactured in a three-dimensional printer. After this, the screws were tested under compression on a universal testing machine. The load speed was applied with a rate of 1 mm/min. The results showed that the screws tested before the sterilization process with a STERRAD® system, failed with a load of 172.89 ± 10.62 N. On the other hand, when the screws were tested after the sterilization, the peak load was 129.47 ± 9.32 N. The sterilization involved two steps. In the first, the specimens were dried with plasma at low temperature and, in the second, they were sterilized with a mixture of hydrogen peroxide vapor at 50 °C. The mechanical properties were changed in an acceptable range. In parallel, other screws were sterilized in an autoclave system. The specimens were exposed in a saturated steam atmosphere at 135 °C during 15 min. The geometry and structural integrity changed markedly. This sterilization process is not advisable for this purpose. The screws were easily fixed in porcine vertebrae. The manufacturing process is innovative and cheaper than the existing manufacturing process for screws made of titanium for the same purpose.