Erik Boelen and colleagues at Maastricht University, the Netherlands, have developed a hydrogel biomaterial that, unlike existing implants, completely fills the cavity left by a removed disc nucleus. These spinal implants can also mimic natural discs more closely than existing implants.

The key to the new hydrogel is its swelling property. The material is implanted through a small opening as a dry xerogel. Once in situ, the gel takes up water, expanding to fill the cavity. Additionally, the gel has been designed to be clearly visible by magnetic resonance imaging (MRI) and computer tomography (CT), which not only allows doctors to accurately place the implant during surgery, but can later be used to confirm that the gel has swollen sufficiently.

Traditionally, surgeons treating degenerative disc disease have had to resort to spinal fusion, removing the diseased disc and locking together the two adjacent vertebrae. However, the resulting loss of local mobility places more strain on neighbouring discs, potentially triggering more back problems in the future.

If the disease is caught at an early stage the diseased disc can be replaced by Boelen's artificial, hydrogel-based disc, which can be inserted into the spine. Not only is this procedure is far less invasive than spinal fusion, but full spinal mobility is retained.

Initial testing in animal models has shown that the gel does not cause significant side effects. The next step for Boelen is to study the long term fatigue behaviour of his biomaterial, which will have to cope with significant loads during bending and lifting, and to ensure that the implant will not leak out of the cavity.

James R Mitchell Crow