PhD, starting year 4, National University of Singapore
Antibacterial coatings for biomedical applications
Investigations have established that bacteria can survive on dry inanimate surfaces up to months. Such bacteria-inhabited surfaces within clinical environments leads to an increased risk of hospital-associated infections by serving as a reservoir of pathogens, which are easily transmitted by contact either directly to patients or via the hands of healthcare workers. A potential solution to solve this issue can be the use of antibacterial coatings on "high touch" areas that can either inhibit bacterial adhesion or kill bacteria. These coatings can be fabricated as plastic sheets that can be placed over the surfaces or it can be in the form of a spray. However, several challenges exist in the fabrication of an ideal antibacterial coating like (i) safety of the materials used (ii) high bactericidal efficacy that needs to be sufficiently long-lasting and resistant to wear and tear under the different conditions within a hospital (iii) scalability of the fabrication procedure and last but not the least (iv) cost of the materials used. My research targets at using naturally derived polymers and metal ions to fabricate "immobilized" coatings that are stable and durable. Different surface modification techniques are employed to evaluate coating characteristics. Another aspect that I am interested in is in the use of copper in antibacterial coatings, as opposed to the more frequently used silver because copper is cheaper and less toxic than silver. However the use of copper alloys and metals in hospitals are sometimes limited because they cannot be used over surfaces that need to be optically transparent (such as monitors, instrument panels) and it may not be feasible to replace every furniture with that made out of copper. As such, I am trying to develop copper-containing transparent coatings with long-term efficacy. I hope my research can be translated to real,commercial application some day and benefit the healthcare sector.
Abstract: Phosphate-based glass fibres (PGF) of the general formula Na(2)O-CaO-P(2)O(5) are degradable in an aqueous environment, and therefore can function as antibacterial delivery systems through the inclusion of ions such as copper. In this study, PGF with varying amounts of copper oxide (CuO) were developed for potential uses in wound healing applications. PGF with 0, 1, 5 and 10 mol% CuO were produced with different diameters and characterised in terms of structural and antibacterial properties. The effect of CuO and fibre pulling speed on the glass properties were investigated using rapid differential scanning calorimetry, differential thermal analysis and X-ray diffraction. The effect of two fibre diameters on short-term (3 h) attachment and killing against Staphylococcus epidermidis were investigated and were related to their rate of degradation in deionised water, as well as copper ion release measured using ion chromatography. Thermal analysis showed that there was a significant increase in the PGF glass transition temperature as the CuO content increased. There was a significant decrease in the rate of degradation with increasing CuO content and an increase in fibre diameter. Over 6 h, both the amount and rate of copper ions released increased with CuO content, as well as a reduction in fibre diameter thus increasing the surface area to volume ratio. There was a decrease in the number of viable staphylococci both attached to the CuO-containing fibres and in the surrounding environment.
Pub.: 09 Dec '04, Pinned: 28 Jul '17
Abstract: A simple, easily up-scalable swell-encapsulation-shrink technique was used to incorporate small 2.5 nm copper nanoparticles (CuNPs) into two widely used medical grade polymers, polyurethane, and silicone, with no significant impact on polymer coloration. Both medical grade polymers with incorporated CuNPs demonstrated potent antimicrobial activity against the clinically relevant bacteria, methicillin-resistant Staphylococcus aureus and Escherichia coli. CuNP-incorporated silicone samples displayed potent antibacterial activity against both bacteria within 6 h. CuNP-incorporated polyurethane exhibited more efficacious antimicrobial activity, resulting in a 99.9% reduction in the numbers of both bacteria within just 2 h. With the high prevalence of hospital-acquired infections, the use of antimicrobial materials such as these CuNP-incorporated polymers could contribute to reducing microbial contamination associated with frequently touched surfaces in and around hospital wards (e.g., bed rails, overbed tables, push plates, etc.).
Pub.: 30 Sep '15, Pinned: 28 Jul '17
Abstract: Plasma immersion ion implantation (PIII) was used to modify medical-grade PVC coated by triclosan and bronopol to enhance the antibacterial properties. The surface was first activated by O2 plasma to produce more hydrophilic groups so that triclosan and bronopol could be coated more effectively on the surface. Subsequently, an argon plasma treatment was conducted under optimal conditions to improve the antibacterial properties of the triclosan and bronopol-coated PVC samples. The modified surfaces were characterized by XPS, ATR-FTIR, SEM, and contact angle measurements. The antibacterial properties were evaluated utilizing the method of plate-counting of Staphylococcus aureus (gram positive) and Escherichia coli (gram negative). Our experimental results show that the plasma-modified PVC with bronopol exhibits good antibacterial properties while the favorable bulk properties of PVC are retained. The plasma-modified PVC with triclosan has better antibacterial performance against E. coli than bronopol. The change in the antibacterial effect on the modified PVC with time was also investigated and the antibacterial effect was observed to decrease with time.
Pub.: 12 Jul '05, Pinned: 28 Jul '17
Abstract: Fabrication of antibacterial surfaces is an approach to reduce environmental bacterial burden and risk of infection transmission. Antibacterial coatings based on cationic polymers have been commonly used for this purpose, but coating methods to immobilize these polymers over large area substrates are limited. Herein, we report a facile aqueous-based method of immobilizing quaternized chitosan (QCS) on polymer and metal substrates via electrostatic interaction with substrate-anchored multivalent polyphosphate ions to form transparent antibacterial coatings of micron thickness. The QCS coatings are noncytotoxic and yet demonstrate a high killing efficacy against two clinically relevant bacteria, Staphylococcus aureus and Pseudomonas aeruginosa, when challenged with bacteria-loaded droplets or contacted with a bacteria-loaded dry surface. The coatings were stable when subjected to wiping, and the QCS-coated substrates retained their efficacy and could be reused for multiple cycles after wiping the contaminated surface with 70% ethanol. A distinct advantage of this coating method is the ease of scale-up using spray coating for preparation of uniform large area coatings.
Pub.: 25 Aug '16, Pinned: 28 Jul '17
Abstract: Bacterial contamination of surfaces and the associated infection risk is a significant threat to human health. Some natural antibacterial polymers with low toxicity are promising coating materials for alleviating pathogenic colonization on surfaces. However, widespread application of these polymers as antibacterial coatings is constrained by coating techniques which are not easily scalable due to stringent reaction conditions. Herein, thiol-ol reaction involving oxidative conjugation between thiol and hydroxyl groups is demonstrated as a facile technique to graft two natural polymer derivatives, agarose (AG) and quaternized chitosan (QCS), as antibacterial coatings on polymer and metal substrates. The substrate surfaces are first treated with oxygen plasma followed by UV-induced grafting of the polymers under atmospheric conditions. Dimercaprol, a FDA-approved drug, is used as both surface anchor and cross-linker of the polymer chains during grafting. The AG coating achieves >2 log reduction in Pseudomonas aeruginosa and Staphylococcus aureus biofilm formation, while the QCS coating reduces bacterial count from contaminated droplets on its surface by >95%. The coatings are noncytotoxic and exhibits a high degree of stability under conditions expected in their potential applications as antibacterial coating for biomedical devices (for AG), and for preventing pathogen transmission in the environment (for QCS).
Pub.: 19 Dec '16, Pinned: 28 Jul '17