Injectable polymer implants stimulate rebuilding of bones

The need for artificial joint replacements in people with osteoarthritis could soon be bypassed with injectable polymer implants that stimulate rebuilding of bone structures.

The research is being headed by Bristol University’s team of stem cell and tissue engineering experts in collaboration with researchers from Qatar and Canada. Speaking to The Engineer, lead investigator Dr Wael Kafienah of Bristol explained the rationale behind the project.

‘In our articular joints — the elbow, knee and hip — the end of the bone is covered with a very smooth surface of cartilage and it’s this that provides the articulation. In the case of traumatic injuries to the joints, or osteoarthritis, what you get is a defect to the cartilage surface, which with time gets eroded and starts to cause a lot of pain,’ he said.

Normally at this stage, patients would be considered for metallic joint replacement, which requires extensive surgery and a protracted rehabilitation period.

There has been some research into regenerative solutions, but at present, cartilage implants created using stem cells can only be constructed as a solid shape, acting as an interim measure before the almost inevitable need for total joint replacement.

‘Our idea is to fill these defects, which are often very irregular, with a scaffold that can assume the full shape of the defect. The biomaterial is loaded with stem cells and therapeutic factors, which can recreate the cartilage and fill that defect so it regains its smoothness,’ said Kafienah.

Provided they can catch defects early, Kafienah believes injections of their material could delay the need for surgery and eventually circumvent metallic prosthetics altogether.

One key advantage of their material is its ease of use and preparation. The biomaterial starts as a liquid made up of carboxylic acid and water soluble diol monomers, as well as the stem cells and therapeutic additives. Because it is a liquid it can be injected to fill even the smallest micrcofractures in the cartilage surface.

Once in place the liquid is exposed to visible wavelength light that stimulates photocrosslinking of the monomers to form a biodegradable polymer.

Crucially, the polymer has elastomeric mechanical properties, so can substitute for the lost cartilage until the stem cells are able to create a natural scaffold — by which time the polymer degrades away.