Plasma polymerization has sometimes been a called a black art. How else to describe a process that takes a well-defined chemical structure, puts it in an electric field and shakes it about at 1 million times per second until it brightly glows and then chuck it at a surface and see what forms?
A poorly-controlled plasma polymerization might be imagined like this:
But how to control this process? During high-energy reactions, how do we prevent the formation of random polymer spaghetti? And can we figure out the rules for forming better defined plasma polymers with increased functional group retention?
While this example is greatly oversimplified, it emphasizes the point that when we use a well-controlled bolt of lightning to make surface coatings (albeit a cold one), we would rather have a less chaotic “scrambling” of the chemical in favour of more ordered and controlled deposits. The whole purpose of this is so that we can then use the intact bromine motif to perform other chemical reactions off of the surface.
I wrote about our ARC Discovery Grant “Order from Chaos” previously. With this project, we hope to discover some more fundamental rules that allow us to understand how to prepare functional polymeric coatings from fragile chemical precursors.
Our latest publication describes progress towards this aim as we try and write the lost instructions for the plasma black box. Here, lead author Solmaz Saboohi and the team from the Future Industries Institute describe new understanding arising from the use of analytical instrumentation to probe and compare the plasma phase and the resulting surface deposit that allows for “soft landing” of the excited chemical fragments. Contrary to conventional wisdom, using higher pressures — instead of lower ones — allows for better structural retention. In this regime, hyperthermal ions dominate in the plasma phase and are deposited to form plasma polymers with increased functionality.
You can find the publication here. Also, the article is open access.
Saboohi, S.; Coad, B. R.; Michelmore, A.; Short, R. D.; Griesser, H. J. Hyperthermal Intact Molecular Ions Play Key Role in Retention of ATRP Surface Initiation Capability of Plasma Polymer Films from Ethyl α-Bromoisobutyrate. ACS applied materials & interfaces 2016, 10.1021/acsami.6b04477.
The research area of antimicrobial surface coatings really started to take off around 2000, So the idea of incorporating antimicrobials onto the surface of medical devices is not a new one.
With more than 16 years’ research now, only a handful of products have made it into the clinic with the goal of saving lives by combating infectious agents that colonize surfaces. Their usage is not very wide-spread. But why is this so?
It is helpful to take as an example the most well-known antimicrobial products which are based on silver. One criticism is that the antimicrobial mechanism of silver is very broad — based on electrostatic interactions — and there is potential for interference with the biochemical machinery not only for pathogens but also for host cells. This idea of selectivity (harming only pathogens and not host cells) is exactly why when you go to a doctor to fight a nasty bacterial infection, you get an effective and approved antibiotic drug, and not a glass of silver nanoparticles.
So surfaces that incorporate antibiotic drugs may be promising for their ability to kill or inhibit microbial colonisation and have a well-known window of safety approved for their use.
Our latest publication on this topic is a mini-review called “Anti-infective Surface Coatings: Design and Therapeutic Promise against Device-Associated Infections”. Published in the open access journal PLOS Pathogens, the review is called a Pearl (i.e. “pearls of wisdom”) following the editorial guidance that it should be a “lesson that lasts”.
Our “Pearl” gets to the promises and pitfalls, as seen in a few literature examples, of how to best interface antibiotic surface coatings with pathogens. While there have been some innovative solutions, we are still a long way off from developing implantable devices that are both effective and compatible with the host. Will this take another 16 years until we see such devices enter the market? Probably not. An acceleration is taking place with nearly one paper published every day on the broad topic. We point out that the nexus between promise and pitfall is likely to narrow with a greater emphasis on collaboration between materials scientists, microbiologists, and clinicians. Indeed, in our own work, as can be seen by the co-authors on the paper, assembling a team with interdisciplinary skill sets is likely to create advances in this area.
Coad BR, Griesser HJ, Peleg AY, Traven A (2016) Anti-infective Surface Coatings: Design and Therapeutic Promise against Device-Associated Infections. PLoS Pathog 12(6): e1005598. doi:10.1371/journal.ppat.1005598
Important factors in the design of anti-infective materials and their surface coatings.