Green chemistry gives 'benign by design' coatings

Green chemistry is being employed to develop revolutionary drug delivery methods that are more effective and less toxic and could benefit millions of patients.

Conventional drug coating techniques can damage the drugs themselves

Chemists at The University of Nottingham are developing new methods for coating drugs in plastics, using methods that do not damage the latest generation of delicate biopharmaceutical drugs.

Professor Steve Howdle, who studies green chemistry processes at the University, said: “Many very potent new drugs based on proteins are being discovered all the time. But a major problem the pharmaceutical industry faces is that they have to be wrapped up in plastic to be delivered to the patient, so that there is controlled release of the drug over time. Many of these new proteins are fragile and are damaged by high temperatures and harsh solvents used in conventional processes.”

Professor Howdle’s research focuses on exploiting the unique properties of supercritical CO2 - a solvent, with physical properties between those of a gas and a liquid. At near-room temperature and under modest pressure, supercritical carbon dioxide blurs the boundaries between liquid and gaseous states.

The process can be used to make polymer drug coatings, using biodegradable plastics, just like those used in dissolvable surgical stitches. The polymer is used to encapsulate the drug before it is injected into the body.

Professor Howdle said: “Our process works in CO2 at close to room temperatures so the molecule is not damaged by the mixing process, and we don’t use normal solvents we don’t have toxic residues left behind in the product and potentially ending up in the patient.

“The plastics are solids but when they are put under high pressure from CO2, they turn into liquids - they melt, and under these conditions, the bioactive drugs can be mixed in. So we take particles of the drug and wrap every single one up in biodegradable polymer, for injection under the skin.”

Conventional chemical processes often use high temperatures or volatile, and potentially toxic, solvents - requiring special handling and recycling measures to prevent them from escaping into the atmosphere. The principles of green chemistry herald a new approach that is “benign by design” - both in terms of the process itself, its impact on patients and on the environment.