Infection control is a major issue for healthcare facilities world-wide and as such reports of outbreaks of various infections, such as MRSA, C-diff or the winter vomiting bug are seldom out of the media. Interestingly these outbreaks appear to be worsening due to the build-up of resistance towards pretty much all currently known antibiotics but perhaps also to the increasing number of patients that are being treated. In short, the more persons in the system, it seems the more likely it is that infection will spread. This latter finding points strongly towards the spread of surface-borne bacteria and viruses as the main cause of the problems that are currently being faced.
In order to try to help stem the spread of infections a number of approaches are being taken by researchers worldwide. These include the development of materials that switch on a ‘destructive capacity’ when exposed to light and materials which contain known biocidal materials such as silver and copper ions.
At Tyndall the Advanced Materials and Surfaces Group led by Prof Martyn Pemble are active in the development of both of these accepted approaches as well as in the development of other, perhaps more novel approaches. This Group uses a variety of methods to grow perhaps the best known example of a photo-activated material capable of destroying organic material- titanium dioxide TiO2. Used also in self-cleaning window glass such as the Activ™ Glass made in the UK by Pilkington, TiO2 can absorb light in the uv part of the spectrum and as a result slowly oxidise organic materials, producing small product species such as carbon dioxide and water. The organic materials in question can also include bacteria and viruses- the coatings don’t distinguish between these species and other types of organic films or dirt. From the perspective of using these materials as surface coatings in hospitals or other healthcare environments, the issue becomes one of trying to make the coating absorb light in the (harmless) visible part of the spectrum whilst maintaining the level of destructive power that it exhibits when irradiated with (harmful) uv light. This turns out to be far from trivial. Despite a large number of reports which claim to have achieved this goal, the results are actually quite unconvincing and these materials are not routinely deployed as infection control surfaces in real world environments.
At Tyndall we are utilizing our extensive knowledge of oxide thin film chemistry to try to tackle this issue in a way which will make a real difference. Doping is one route that we are examining, although the effective doping of TiO2 is a highly controversial area. The preparation of hybrid materials, such as the chitosan-based materials highlighted above, is another approach that we are utilizing. At Tyndall we also benefit in this area from expertise in materials modeling. The Group led by Dr Michael Nolan performs extensive studies of the nature of TiO2 surfaces in the presence of various dopant species. We are currently working with healthcare professionals so as to ensure that our studies are directed along those avenues which have the most chance of being successful in terms of making a real difference to the issue in question.
Going left to right, the first 8 samples represent chitosan-based thin films prepared by simple drop-casting. Chitosan is a material which is derived from chitin- a naturally occurring tough polysaccharide material that is found in the shells of crustaceans and molluscs. Note that LMW – low molecular weight, MMW = medium molecular weight and TEOS = tetraethoxy silane, a silica precursor. Some chitosan samples have been deliberately ‘doped’ with silver nanoparticles (Ag) or particles of titanium dioxide (TiO2).
The results simply labeled TiO2 and TiO2Cu on the right hand side of the graph are samples of TiO2 and Cu-doped TiO2 grown by atomic layer deposition (ALD).
Despite the fact that chitosan is known to have significant anti-microbial and anti-fungal activity, it may be seen that in these particular experiments the most effective samples in terms of the inhibition of E-coli growth are the chitosan-free samples, of which the TiO2-Cu sample is arguably the best. Copper is well-known for its high level of anti-microbial activity and so this result is not so surprising but what is perhaps surprising is the fact that some of the doped chitosan samples have ‘comparable’ levels of activity to that of the TiO2-Cu sample, see the data for the LMWChiTiO2 and LMWChiAg samples. At Tyndall we are developing various approaches for the fabrication of chitosan-based materials, including those samples that are constructed so as to form photonic band gap materials and those samples which may be grown in flexible substrates using roll-to-roll technologies.