Replacement parts: Medical implants

Devices with nanoscale pores may be able to protect living tissue from the immune system's battery of weapons. Such devices could form the basis of implants for people with diabetes or other diseases.

In type I diabetes, the body launches an immune assault on itself, specifically on the insulin-producing beta-cells of the pancreas. Unable to make enough of their own insulin, children have to give themselves regular insulin injections.

The problem could be overcome by the transplantation of pancreatic cells from other people or even from animals (xenotransplantation). However, these tissues are recognised as 'foreign' and are rejected by the immune system.

One possibility is to use nanotechnology to create devices that provide a physical support and protective environment for donated living tissues.

Tejal Desai at Boston University, for example, has developed a silicon box a tenth of a millimetre across housing a sponge of fibrous collagen tissue containing pancreatic cells.

The box is porous, with holes 20 nm wide that can let glucose molecules in. The tissue in the implant detects levels of glucose and releases insulin as required. Immune cells and bulky molecules such as antibodies, however, cannot get through the nano-pores, so are unable to attack the transplanted cells.

So far this approach has been tested in rats with diabetes. The animals survived for several weeks without being given insulin. The product is now being developed by iMEDD, Inc. in Ohio, USA.