Medical implants are often coated in polymer films that help the body adhere to the implant. These polymer films are usually created via a process called chemical vapor deposition (CVD) polymerization, whereby the initial compounds are evaporated, activated at high temperature, and deposited onto surfaces, where they polymerize. However, until recently no one has been able to develop a suitable CVD coating for degradable implants, such as surgical sutres, tissue-culturing scaffolds, and stents.
But now an international team, that includes researchers from Karlsruhe Institute of Technology, Germany, the University of Michigan, USA, and Northwestern Polytechnical University, China, is reporting that they have made a breakthrough, as they claim to have synthesized a CVD polymer with a degradable backbone. Publishing their results in the journal Angewandte Chemie, they explain the challenge and opportunity as follows;
“Polymers prepared by chemical vapor deposition (CVD) polymerization have found broad acceptance in research and industrial applications. However, their intrinsic lack of degradability has limited wider applicability in many areas, such as biomedical devices or regenerative medicine,” adding that, “These coatings address an unmet need in the biomedical polymer field, as they provide access to a wide range of reactive polymer coatings that combine interfacial multifunctionality with degradability.” By using a different type of bond between the polymers, the researchers have been able to solve this problem.
As the online scientific journal Phys.org explains, “The team applied co-polymerization of two special monomer types: The para-cyclophanes usually used for this method were combined with cyclic ketene acetals. While classical polymers on the basis of para-cyclophanes are linked by carbon-carbon bonds exclusively, ketene acetal is repositioned during polymerization, such that ester bonds (e.g. bonds between carbon and oxygen atoms) are formed in the polymer backbone. Ester bonds can be cleaved in aqueous medium.”
Better still, the rate of degradation is also adjustable, because, as Lahann explains, “The degradation rate depends on the ratio of both monomer types and on the side groups of the monomers. Polar side groups make the polymer film less water-repellent and accelerate degradation, as water can enter more easily. In this way, the degradation rate can be adapted to application.”
The picture at the top of the page shows a microscopic fluorescence image of the biodegradable coating with structures printed onto it for test purposes.
Importantly, the team have already proved that the degraded products are non-toxic, and the medical world is beginning to take note. But now, plastic coating specialists and polymer film traders are also considering the importance of the development, as the process may well have applications beyond biodegradable medical equipment.
As Professor Joerg Lahann, Co-Director of the Institute of Functional Interfaces of Karlsruhe Institute of Technology (KIT), explains, “Our new degradable polymer films might be applied for functionalization and coating of surfaces in biosciences, medicine, or food packaging.” Furthermore, because the process allows for the production of polymer films with “functional groups” as ‘anchor sites’ for fluorescent dyes, biomolecules, or any manner of active substances, then many other applications may be possible.
If the process can be scaled up to an industrial scale at an economic rate, then where would you apply a non-toxic, biodegradable, reactive polymer coating?
Photo credit: KIT