Nanotechnology Enables Stem Cell Growth around PEEK Hip Implants

Scientists at the University of Glasgow in Scotland, UK, are working to harness the regenerative power of stem cells to improve orthopaedic implant surgery. They are collaborating with surgeons at Glasgow’s Southern General Hospital to develop a new type of orthopaedic hip implant.

In hip replacement surgery, the head of the thigh bone is removed and replaced with an implant which is held in place by a rod fixed inside the marrow along the length of the bone.

Marrow is a rich source of mesenchymal stem cells, which have the potential to divide, or ‘differentiate’, into other types of cells such as skin, muscle or bone which can improve the process of healing. However, stem cells can also differentiate into cells which have no use in therapy. Artificially controlling the final outcome to ensure the desired type of cells are created is very difficult, even under laboratory conditions.

When conventional implants are fixed into bone marrow, stem cells usually differentiate into a buildup of soft tissue which, combined with the natural loss of bone density that occurs as people age, can weaken the bond between the implant and the body. Treatment requires expensive and painful surgery.

The team at the University of Glasgow have found a reliable method to encourage bone cell growth around a PEEK implant. The method uses electron beam lithography to impart the required structure onto a nickel film. This film is then inserted into the mould where the part is produced in one step. The technology is similar to that used for the manufacture of Blu Ray discs and DVDs.

Dr Matthew Dalby of the university’s Institute of Molecular, Cell and Systems Biology, explained: “Last year, we developed a plastic surface which allowed a level of control over stem cell differentiation which was previously impossible. The surface, created at the university’s James Watt Nanofabrication Centre, is covered in tiny pits 120 nanometres across.” He added: “By covering an implant in this surface, we can ensure that the mesenchymal stem cells differentiate into bone cells. This will help the implant site repair itself much more effectively than has ever been possible before and could well mean that implants will last for the rest of a patient’s life.”

Dr Nikolaj Gadegaard, senior lecturer in biomedical engineering, explained: “The inertness of PEEK has made it difficult to use in implants outside of spinal surgery before. However, our nanopatterned surface may allow the plastic to interact with stem cells in the hip and enable an effective integration between the implant and the body for the first time.” He added: “Although our nanopatterned surface is complex, the process of production is similar to that which makes Blu Ray discs, which means that future mass production of the implant is a very real possibility.”

Dominic Meek, consultant in orthopaedics and trauma surgery at Glasgow’s Southern General Hospital, has been participating in the development of the new implant. He said: “It’s an extremely exciting project to be working on, with implications for improving a wide range of joint replacements and other orthopaedic surgeries. We’re keen to see a prototype ready for use in orthopaedic surgery within 3 to 8 years.”

The research to date has been funded by the Biotechnology and Biological Sciences Research Council (BBSRC), the Medical Research Council (MRC), the Engineering and Physical Sciences Research Council (EPSRC (including the University’s Knowledge Transfer Account (KTA) in nanotechnology)), the Scottish Government’s Chief Scientist Office and the European FP7 project NaPANIL.