View of a bone screw inside a human finger

Surgical screws made of bone could be used in jaw and foot surgery

Image credit: surgebright

Biomechanical engineers have worked with a start-up to create surgical screws made from human bone in a project called “Bonescrews”. Having already rolled out basic bone screws in hospitals in Austria, they are now developing tougher bone screws capable of withstanding large forces.

For decades, orthopaedic surgeons have used metal screws and plates - normally steel or titanium - to hold badly broken bones together while the injuries heal. These fixtures are treated by the body as foreign bodies, can cause pain, limited movement and infection and sometimes must be subsequently removed with highly invasive surgery.

In an effort to provide an alternative to these implants, engineers from Graz University of Technology (TU Graz) are working with Surgebright, a start-up founded by a GP specialising in orthopaedics, in order to create more bio-compatible alternatives to metal surgical screws.

This has resulted in the development of surgical screws made from human bone material. They are formed from the dense, tough middle layer of bone found in the femur (thigh bone). The femur is often cited as the strongest bone in the body, as well as the longest.

The donated bone is collected from organ donors and must be carefully selected as suitable to be adapted into a surgical implant. A particularly important consideration is the size of the miniature tubes which contain blood vessels and nerves, the Harversian canals, which strongly affect the performance of the screws.

“There is a big difference between working with metal screws and screws made of biomaterial,” said Dr Gerhard Sommer of the Institute of Biomechanics at TU Graz, who is working on the project. “The mechanical principles are the same, but we also have to consider that donated bone material shrinks somewhat during sterilisation and two hours after the operation expands again in the body and becomes more elastic.”

Adopting these screws to fix together broken bones could mean that screws would never have to be removed in a second painful operation, as the material - recognised as belonging in the human body - would heal into the host’s bone following the surgery.

The technology is already being rolled out in 14 hospitals in Austria and, according to the researchers, the transplant has already proved so effective it is no longer visible in an X-ray performed a year after the surgery.

Now, the researchers are continuing to work with Surgebright to develop new prototypes of bone screws specifically for foot and jaw surgery, which presents new challenges.

Testing bone screws under laboratory conditions

surgebright

Image credit: surgebright

“We have to completely rethink the bone screw for application in foot and jaw surgery and want to develop prototypes for application in foot and jaw surgery, said Dr Sommer.

“In maxillary surgery, extremely small screws are necessary, approximately 20mm long, which have to withstand great stresses because relative to size, the jaw muscle is the most powerful muscle in the human body. In foot surgery, although the screws are bigger, between four and six centimetres long, they are also exposed to large forces.”

The team is currently investigating the forces within the bone structure of the foot and jaw, in order to determine the necessary strength of the new bone screws: tweaking the design of the thread could improve the strength considerably.

Bioengineers and materials scientists around the world are developing new bio-compatible materials and devices intended to sit within the body for long periods without causing disturbance or infection. For example, earlier this year Harvard University researchers unveiled a type of surgical glue inspired by slug slime which adheres to wet surfaces, while robots made from living tissue could be employed to travel through the human body, searching for signs of disease.

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