Polymer coating kills bacteria

Ton Loontjens worked in industry for about 35 years before he was appointed Professor of Biomedical Materials at the University of Groningen. One of his focal points is the development of immobilized polymer coatings that kill bacteria on contact. They could be used on implants, or even to paint hospital walls. ‘I am an academic researcher with an industrial background, which is in my opinion a valuable combination.’

Patients who receive a medical implant have a considerable chance of contracting a serious infection. Bacteria enter the body during the operation and colonize the surface of the implant. Coatings exist which slowly release antimicrobials, but they have two drawbacks: patients receive a continuous infusion of the drug into their body fluids and the drug will eventually be depleted.

‘My vision is to develop an immobilized coating which kills bacteria when they touch the surface’, says Loontjens. And he is getting close, with several patents pending and all sorts of tests underway. His secret ingredient? He has discovered a compound that allows him to build branched polymers, which form a versatile coating.

Career

This compound, what is known as a chain extender, was developed by Loontjens and his colleagues at chemical company DSM. ‘It is called carbonyl bis caprolactam or CBC. It was developed to couple two polymer chains in a controlled fashion. These polymers have better mechanical properties.’ Interestingly, when used below 100^oC (instead of above 250^oC, as is the case during chain extension) CBC appeared to have a unique property: polymers could be prepared that were stable below 100^oC, but grew when heated. More importantly, the end groups of each branch of this branched polymer were available for connecting biomedical compounds.

In one option Loontjens connected quaternary ammonium ions to the polymer, which kill bacteria on contact. This resulted in an antimicrobial coating. The quaternary ammonium ions are fixed to the coating, so they don’t leach into the body fluids. Loontjens developed this coating at the University of Groningen where he started work in 2005. ‘My career has been a bit unusual. Right after secondary school, I got a job. It was only later, at the age of 24, that I started to study chemistry at Radboud University Nijmegen.’ When he graduated at the age of nearly 30, he initially looked for a PhD project. ‘But then my supervisor told me that by the time I had finished my PhD I might be too old for companies to hire me.’

PhD

So he started working at DSM, first in research, then in management and then back in research again, as Principal Scientist. ‘At that stage, I started wondering if I could get a part-time professorship.’ He had always been interested in scientific work, in particular in developments that result in practical applications. Although he was co-author of more than 70 scientific papers and had filed 70 patent applications, he would need a PhD to become a professor.

He accomplished this at the age of 60, and three months later was offered a professorship at the University of Groningen. Loontjens works at the Zernike Institute for Advanced Materials in the Department of Polymer Chemistry, and works closely with the Biomedical Engineering group of the University Medical Center Groningen.

Company

National budgets for training PhD students are not open to people over 65. ‘So in the last few years I have worked with postdocs who are funded by industry. But that suits me well, as I am also very much interested in applied work.’ Looking back at his career, he describes himself as an ‘academic researcher with an industrial background’, which in his opinion is a valuable combination.

The work on the coating is entering an interesting phase. ‘We initially tested the coating on glass, and now it also works on PDMS rubber, a material which is widely used in biomedical applications.’ And apart from using it to coat implants, Loontjens is thinking about turning it into a paint which would create self-disinfecting walls in hospitals.

‘I’ve also got my own company that is working on a process to produce blocked isocyanates for biomedical polymers, building partly on the work that University of Groningen Professor of Polymer Chemistry Pennings did many years ago.’ Working towards commercial applications means he can’t reveal all just yet. He smiles: ‘The patents haven’t all been published. And we don’t want to give away which products are in the pipeline!’ But he is confident that we’ll hear more from that very pipeline.

In 1967 the Department of Polymer Science (Laboratorium voor Polymeerchemie) and its educational program were officially established. With this, the University of Groningen was the first university in the Netherlands to host a department solely dedicated to polymer science. This will be celebrated on 30 June with a symposium.

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