By: 8 December 2016
Screws that fit the body’s notches

Researchers in Germany have developed a new bioceramic screw nail that could be used to replace the titanium and steel components currently used to set complex bone fractures.

Metal components must be surgically removed post-surgery, at considerable expense and discomfort to the patient, to avoid triggering inflammation or allergies in sensitive patients.

These complaints could soon become history, however, as researchers from the Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM have partnered with the university hospitals of Giessen-Marburg and Bonn and the University of Bremen to develop a bioceramic implant screw nail. The new biomedical component, dubbed a ‘scrail’, is made of calcium phosphate, which greatly resembles the composition of bone material.


Reduced risk of injury to tendons and bones

According to Sebastian Hein from Fraunhofer IFAM, important project tasks included designing the screw nail according to ceramic requirements and hardening it. In contrast with previous medical screws made from titanium or polymer, the new screw nail will not be screwed into the bone, but rather carefully hammered in. For this reason, the researchers have developed a specially shaped thread for the screw nail that allows it to be introduced with a minimum of rotations and reduces the risk of damage to tendons and bones.

In contrast to metal components, the ceramic screw nail integrates into the bone and does not have to be removed, since the two most-used bioceramic materials – calcium phosphate and hydroxyapatite – are very similar to bone material. This is a distinct advantage over polymer screws, which disintegrate in the body and give rise to degradation products that can cause inflammation. Additionally, after the disintegration of the screws, cavities can form in bones, rendering them unstable and more prone to breaking. Ceramic-based screw nails do not disintegrate, but instead bond with the bone. Ideally, they can even accelerate bone growth, says Hein.


Patient-specific implants

The greatest challenge for the development team at Fraunhofer IFAM and Bremen University was attaining the maximum strength of the material, since ceramics are fairly breakable. With the help of injection-moulding technology, researchers pour hydroxyapatite powder into screw nail moulds and heat them. Using the right process parameters delivers components with optimised stability. The procedure is particularly suited to mass production, as it is inexpensive and allows for flexible mould design. Hydroxyapatite powder can also be used in conjunction with 3D printers, thus enabling the production of patient-specific implants.

Hein anticipates that the screw nail will soon be ready to use in operations, as calcium phosphate has already been tested for biocompatibility and has been in use as a material in medical applications for several years. Furthermore, medical tests in sheep have shown that the screw nail could be inserted much more quickly and precisely than standard screws, which was “an effect totally unexpected from our side,” said Hein. As a result, the operation time is shortened and the patient is under anaesthetic for less time.


Source: World Federation of Societies of Anaesthesiologists