Our ARC Discovery Project (“Order from Chaos“) is aimed toward discovering how to improve polymer surface coatings — such as those that will be useful in advanced manufacturing of new materials. In the previous post, I discussed the discovery of how to make functional coatings from one chemical compound EBiB. Our latest published research describes a systematic investigation of three similar chemical compounds and is working towards establishing more general rules that could be applied more widely.

Using structurally-related esters, lead author Solmaz Saboohi found the plasma deposition could proceed either through the α regime (lower pressure, collisional) or through the γ regime (higher pressure, collisionless). Analysis of the plasma phase and the deposited films showed noticeable differences under either conditions and markedly different coatings produced.

This discovery is helping us to understand the deposition characteristics of small molecular weight esters, which will hopefully be extended and generalised towards other compounds in the future.

Results have been recently published in the Royal Society of Chemistry journal Physical Chemistry Chemical Physics.

Link to article on publisher’s site.

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.

Citation:

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

http://journals.plos.org/plospathogens/article?id=info:doi/10.1371/journal.ppat.1005598

Important factors in the design of anti-infective materials and their surface coatings.

Plasma polymerized coatings that release nitric oxide are compatible with human cells and have a bacteriostatic property. Image (C) Royal Society of Chemistry.

Nitric oxide (NO) plays an incredibly important role in biology which is just beginning to be understood.  From pulmonary dilation to wound healing, nitric-oxide based medical therapies are a huge and growing sector of human health.

A further aspect is NO’s ability to interfere with bacterial biofilm formation on surfaces. This opens up the way for new surface coatings that can release NO to stop infections from taking hold on medical devices.  A particularly challenging problem, however, is how to easily make surface coatings that store this reactive gas molecule. Furthermore, how can one make such a device containing a volatile, reactive molecule that has a long shelf-life?

Our new publication in Chemical Communications by Thomas Michl and Hans Griesser from the Mawson Institute, University of South Australia shows a method by which coatings that release NO can be deposited on virtually any substrate material.  Instead of volatile NO being trapped in the material, the surface coating contains a stable precursor of NO (an polymer containing a nitrosooxy group) that releases NO when exposed to solutions. Materials that were stored on the shelf for up to 2 months retained a bacteriostatic ability showing promise for their anti-biofilm ability. Importantly, when exposed to human stem cells, good compatibility was demonstrated showing that the material coatings were selectively bacteriostatic while being well tolerated by human cells.

The ability to deposit onto a range of different materials used in the medical industry as well as very good shelf life shows great promise for fabricating advanced medical devices with bacteriostatic properties.

Link to article:

Nitric oxide releasing plasma polymer coating with bacteriostatic properties and no cytotoxic side effects

We have just published another study on polymer brush gradients in Langmuir.

Polymer Brush Gradients Grafted from Plasma-Polymerized Surfaces

Published in: Bryan R. Coad; Tugba Bilgic; Harm-Anton Klok; Langmuir  Article ASAP DOI: 10.1021/la501380m Copyright © 2014 American Chemical Society

This work describes a 3 step method for grafting polymer brushes from any substrate. Subsequent work (which happened to be accepted and published first) shows a 2 step method (see post here).

These two works show good understanding of different systems.  First, two different plasma polymer gradients were fabricated based on octadiene/allylamine and ethanol/ethylisobromobutyrate, and polymer grafting was shown for hydroxyethyl methacrylate (HEMA), dimethyl acrylamide (DMA), and poly(ethyleneglycol) methacrylate (PEGMA).  Last, we have show in this work gradient brushes grown from silicon wafers, and previously, from plastic coverslips.

I was especially pleased with this work as it gave me an opportunity to work with Prof. Harm-Anton Klok from EPFL in Switzerland.  Prof. Klok’s work was an inspiration for me during my PhD and I am very glad to have the chance to work with him in a nice collaboration.

Many thanks goes to him and his student, Tugba Bilgic, for helping me with this work.

Just published communication in RSC Advances.

A new study published from the Mawson Institute and the Wark at UniSA and QUT reveals how a straightforward plasma deposition of an inexpensive compound leads to effective antibacterial surfaces.

Chlorinated surfaces rapidly kill Staphylococcus epidermidis on contact.  The action occurs rapidly and there is little difference if the prepared surface is dry, wet or washed.

Read more about this research here.

Just published in RSC Advances, a new paper from work I did with Johan Linden, Mikael Larsson, Bill Skinner, and Magnus Nyden:

Polyethyleneimine for copper absorption: kinetics, selectivity and efficiency in artificial seawater

image copyright Royal Society of Chemistry

Link to paper in RSC Advances

The surprising result was that a simple, industrial polymer was so effective at first binding metal ions but then, over time, having a greater affinity only for copper leaving the film to be enriched only in this metal.

Thus, copper can be scavenged selectively from low concentration seawater solutions.  This has implications for removal of toxic copper from marinas — an environmental problem caused by leaching of copper from antifouling marine coatings.

One Step ATRP Initiator Immobilization on Surfaces Leading to Gradient-Grafted Polymer Brushes

by Bryan Coad, Katie Styan and Laurence Meagher

Just came out in ASAP (as soon as publishable)

Image copyright the American Chemical Society

Link is here (requires a subscription for full text): http://pubs.acs.org/doi/abs/10.1021/am501052d

If you don’t have a subscription, follow this link as a limited number of full text copies are available:

http://pubs.acs.org/articlesonrequest/AOR-CB5HTBqSBR89C48fJEtH