Reflective polymer makes light work for doctors

Researchers at the University of California have developed a biodegradable polymer implant capable of reflecting light that will allow doctors to monitor the healing of stitched wounds or the delivery of drugs.

Porous silicon is a nanostructured material which reflects certain wavelengths of light that are not absorbed by the human body. This allows doctors to view the material when it is internal by shining light on to the area.

But porous silicon is not readily accepted by human tissue, is too rigid and can corrode. So the San Diego-based team has created a material that is flexible, biocompatible and robust but with the same optical properties.

A porous chip with nanometre-scale holes is created by treating a silicon wafer with an electrochemical etch, that is by placing it in a chemical bath and applying an electrical current. This erodes the surface of the wafer, leaving behind the pattern of holes. The molten polymer is cast into the pores before the silicon is dissolved away, leaving behind a flexible, biocompatible replica of the chip, said UCSD professor of chemistry Michael J Sailor.

‘The polymer is similar to that in medical sutures, but it is also used in other applications such as coatings for coronary artery stents [used to keep the artery open], and as an implantable carrier for drugs,’ he said. ‘In these latter two applications the polymer film is impregnated with medication such as chronic pain, anti-cancer, anti-inflammatory or anti-rejection drugs. As the polymer dissolves the drug is released, usually over several weeks.’

The reflective polymer can be monitored using a simple flashlight-based spectrometer. The degradation of its reflection provides an indication of how much the implant has dissolved, showing the quantity of the drug delivered or how well the skin is healing over a stitched site.