How to improve chemical functionality in deposited films

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.

MIB EIB ETMA

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.

Phys chem chem phys

 

Peering into the Plasma Black Box

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:

plasma

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?

plasma

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.

Hyperthermal Intact Molecular Ions Play Key Role in Retention of ATRP Surface Initiation Capability of Plasma Polymer Films from Ethyl α-Bromoisobutyrate

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.

 

Where are we heading with anti-infective medical devices?

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.

Group Photo 2016

Group picture March 2016-3

Group photo of Coad and Griesser research groups taken 1/3/2016 by Thomas Michl.

Back row (L to R): Altaf Hossain, Solmaz Saboohi, Carla Giles, Steph Lamont-Friedrich, Alasdair Cross, Bryan Coad, Hans Griesser, Htwe Mon, Javad Naderi, Thomas Michl

Front row (L to R): Hongfang Wang, Israt Biva

Order from Chaos: Our new ARC Discovery Grant

In the 20th century, polymers (plastics) were highly valued for their bulk properties – being lightweight and mouldable into any form. Their ubiquity has truly revolutionised the way in which we live our lives. In the 21st century, we will transform the way in which we use polymers from passive, bulk materials into thin film coatings that can be applied to virtually any underlying material. Thus, metals, ceramics, glass, even textiles and paper can be covered with a polymeric coating that will enhance their functional surface properties.

Plasma treatment of a cell-culture plate

Understanding the plasma polymeristion process will help to innovate coatings on biointerfacing surfaces

One technology for making these polymeric coatings uses a state of matter known as plasma. It was previously thought that little control could be exerted over plasma polymerisations because the chaotic nature of this high-energy technique produced polymers with a scrambled structure. Led by Professor Hans Griesser, our new Australian Research Council Discovery Project titled “Order from Chaos” will help us understand how to bring order to the plasma polymerisation process and harness it to make more sophisticated polymer coatings with enhanced functionality.

Outcomes from this project will allow us to functionalise materials that will have wide use in every-day life: as coatings for textiles, medical sensors, automotive and aerospace industries. Particularly for life-sciences, plasma polymerisation is already used to improve the properties of diagnostic tools for biology (passive coatings), but our new understanding will allow more complicated surface coatings to be applied: e.g. biointerfacing surfaces as low-fouling surface coatings, or scaffolds on which to engineer tissues. It is because we will demonstrate how to add value and do more with the plasma polymerisation process that we see very good potential to help to develop Australia’s advanced manufacturing sector.


An Australian Research Council Discovery Project was awarded to Prof Hans Griesser, Prof Robert Short, Dr Bryan Coad, and Dr Andrew Michelmore for the years 2016 – 2018.

New ways of thinking about the use of antibiotic drugs

Picture1

Surface coatings with covalently attached caspofungin are effective in eliminating fungal pathogens J. Mater. Chem. B, 2015, DOI: 10.1039/C5TB00961H. Click here.

We often think of pharmaceuticals as “little magic bullets” that circulate around the body once swallowed or injected. But targeting can be hit or miss for antimicrobial agents because sometimes the infection can be highly localized and associated with a particular material like when present on the surface of a catheter. Traditional drug administration has the “ammunition” circulating around the body to non-target areas and therefore, diluted greatly.  Additionally, bacterial or fungal infections on surfaces are tough to eradicate from the outside-in because they “armoured” by a protective matrix of slime. The result is that the valuable ammunition goes largely wasted and the attack against the problem biofilm is often too weak to eliminate it. A very serious complication can arise from the development of resistance because bugs live by the adage that what does not kill them, makes them stronger.

For devices that are commonly colonised by harmful fungal invaders (such as catheters, breathing tubes, and hip and knee implants), it would be better to incorporate the drug onto the material with a surface coating, present at high concentrations, which could kill the very first bugs that try to attach and settle on the surface.

In this work, (published now in Journal of Materials Chemistry B) we asked the question whether a potent antifungal drug called caspofungin could still act as an effective antifungal agent by eliminating potential fungal colonisers after being irreversibly bound or tethered onto a surface. What is interesting for our research group, and the pharmaceutical industry, is to see whether or not drugs could be now formulated as part of a surface coating (a 2-dimensional surface administration) as compared to the traditional mechanism of action which is understood to be the freely circulating drug in 3-dimensions.

But how can one be sure that the drug is irreversibly attached to the surface? After all, drugs could be initially weakly bound to surfaces but then, desorb back into solution. Then we would then not be able to claim that this mechanism of action is any different to drugs administered systemically. So we turned this question on its head: we attempted to not only bind our target drug (caspofungin) to the surface, but we also tried two similar drugs that we knew wouldn’t be able to bind strongly.  Surprisingly, what we found was that all three drugs initially had the ability to attach to the surface, albeit through weak forces that could be disrupted through soaking. Next we were able to investigate with rigorous washing procedures how we could remove all traces of weakly-adsorbed drugs from the surface, convincing us that only caspofungin, which exclusively possessed the ability to bind to the surface through permanent bonds, was covalently attached.

Armed with this knowledge, we challenged these caspofungin-bound surface coatings with four different Candida species which are common in infected medical devices. The caspofungin surface coatings were found to kill all of these species to some degree, with nearly complete elimination (98%) of one of the most prevalent fungal pathogens, Candida albicans.

Caspofungin has never before shown active killing against fungal pathogens when formulated as a surface coating and now represents a new way of thinking about this drug. This could influence the way medical devices are made or the thinking around traditional drug administration and dosing. The next step in our research will be to show precisely how this drug is able to disrupt and kill the cell when it settles on the surface by investigating its mechanism of action.  We see this research as importantly contributing to a clinical need for new anti-infective materials and surface coatings — especially the need for therapies specifically targeting fungal pathogens and the use of antifungal drugs.

Published in Royal Society of Chemistry: Journal of Materials Chemistry B

B.R. Coad, S.J. Lamont-Friedrich,  L. Gwynne,   M. Jasieniak,   S.S. Griesser,   A. Traven,  A.Y. Peleg and H.J. Griesser  Surface coatings with covalently attached caspofungin are effective in eliminating fungal pathogens J. Mater. Chem. B, 2015, DOI: 10.1039/C5TB00961H


Dr. Bryan Coad is a Senior Research Fellow and Group Leader of the Mycology / Surface Interfaces Group at the Future Industries Institute at the University of South Australia. He possesses over 15 years’ experience in the development of biomaterials and bioactive surface coatings. His research is aligned with clinical need for novel strategies for using antibiotic compounds reducing the development of antimicrobial resistance. He is developing these strategies with support from the Australian Government through competitive granting schemes and is bringing innovative medical devices to market by actively engaging with industry.

 

Future Industries Institute (FII)

Starting 31st August, the Mawson Institute, The Ian Wark Research Institute, and the Centre for Envrionmental Risk Assessment and Remediation (CERAR) will no longer exist as separate entities.

The university has merged these three institutes into the Future Industries Institute (FII).

For my research group, not much will initially change as my position as Senior Research Fellow will continue on in the new institute.

We’re looking forward to the new opportunities that will come in the Future.

Best Poster awards at ASBTE conference

Giresser Coad Group

L to R: Hans Griesser, Stephanie Lamont-Friedrich, Lauren Gwynne, Israt Biva, Altaf Hossain, Bryan Coad

Mycology / Surface Interfaces Group (MSIG) members Stephanie-Lamont Friedrich, Lauren Gwynne, and Altaf Hossain won the best poster awards at the recent ISSIB / ASBTE conference in Sydney (April 2015).

This was a fantastic achievement in winning both of the conference poster awards for MSIG researchers. Stephanie and Lauren (co-presenters) won for their poster entitled “Micro-patterned arrays for investigating the contact-killing mechanism of antifungal surfaces” and Altaf won for his poster “Investigation of natural antifungal compounds and surface coatings“.

Congratulations to Steph, Lauren, and Altaf!

 

New bacteriostatic surfaces that release nitric oxide

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

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

New Publication in Microbiology Australia

What is the role of surface chemistry and materials science in combating fungal disease?

In my article in Microbiology Australia, I give my perspective on how scientists are transforming surface interfaces into active surfaces through nano-scale surface modifications: On the surface of it: the role of materials science in developing antifungal therapies and diagnostics.