Bacterial adherence and biofilm formation on medical implants : a review

Biofilms are a complex group of microbial cells that adhere to the exopolysaccharide matrix present on the surface of medical devices. Biofilm-associated infections in the medical devices pose a serious problem to the public health and adversely affect the function of the device. Medical implants used in oral and orthopedic surgery are fabricated using alloys such as stainless steel and titanium. The biological behavior, such as osseointegration and its antibacterial activity, essentially depends on both the chemical composition and the morphology of the surface of the device. Surface treatment of medical implants by various physical and chemical techniques are attempted in order to improve their surface properties so as to facilitate bio-integration and prevent bacterial adhesion. The potential source of infection of the surrounding tissue and antimicrobial strategies are from bacteria adherent to or in a biofilm on the implant which should prevent both biofilm formation and tissue colonization. This article provides an overview of bacterial biofilm formation and methods adopted for the inhibition of bacterial adhesion on medical implants

Novel polymer synthesis methodologies using combination of thermally and photochemically-induced nitroxide mediated polymerisation

The combination of thermally- and photochemically-induced polymerization using light sensitive alkoxyamines was investigated. The thermally driven polymerizations were performed via the cleavage of the alkoxyamine functionality, whereas the photochemically-induced polymerizations were carried out either by nitroxide mediated photo-polymerization (NMP2) or by a classical type II mechanism, depending on the structure of the light-sensitive alkoxyamine employed. Once the potential of the various structures as initiators of thermally- and photo-induced polymerizations was established, their use in combination for block copolymer syntheses was investigated. With each alkoxyamine investigated, block copolymers were successfully obtained and the system was applied to the post-modification of polymer coatings for application in patterning and photografting.

Weak acid extractable metals in Bramble Bay, Queensland, Australia : temporal behaviour, enrichment and source apportionment

Sediment samples were taken from six sampling sites in Bramble Bay, Queensland, Australia between February and November in 2012. They were analysed for a range of heavy metals including Al, Fe, Mn, Ti, Ce, Th, U, V, Cr, Co, Ni, Cu, Zn, As, Cd, Sb, Te, Hg, Tl and Pb. Fraction analysis, enrichment factors and Principal Component Analysis –Absolute Principal Component Scores (PCA-APCS) were carried out in order to assess metal pollution, potential bioavailability and source apportionment. Cr and Ni exceeded the Australian Interim Sediment Quality Guidelines at some sampling sites, while Hg was found to be the most enriched metal. Fraction analysis identified increased weak acid soluble Hg and Cd during the sampling period. Source apportionment via PCA-APCS found four sources of metals pollution, namely, marine sediments, shipping, antifouling coatings and a mixed source. These sources need to be considered in any metal pollution control measure within Bramble Bay.

Effectiveness of two forms of grouted reinforced confinement methods to hollow concrete masonry panels

This paper presents a study on the effectiveness of two forms of reinforced grout confining systems for hollow concrete block masonry. The systems considered are: (1) a layer of grout directly confining the unreinforced masonry, and (2) a layer of grout indirectly confining the unreinforced masonry through block shells. The study involves experimental testing and finite-element (FE) modeling of six diagonally loaded masonry panels containing the two confining systems. The failure mode, the ultimate load, and the load-deformation behaviors of the diagonally loaded panels were successfully simulated using the finite-element model. In-plane shear strength and stiffness of the masonry thus determined are used to evaluate some selected models of the confined masonry shear including the strut-and-tie model reported in the literature. The evaluated strut width is compared with the prediction of the FE model and then extended for rational prediction of the strength of confined masonry shear walls.

Toughness and toughening mechanisms of porous thin films

Toughness is the ability of a material to deform plastically and to absorb energy before fracture. The first of its kind, this book covers the most recent developments in the toughening of hard coatings and the methodologies for measuring the toughness of thin films and coatings. The book looks at the present status of toughness for coatings and discusses high-temperature nanocomposite coatings, porous thin films, laser treated surface layers, cracking resistance, indentation techniques, sliding contact fracture, IPN hybrid composites for protection, and adhesion strength.

Organic photovoltaics using thin gold film as an alternative anode to indium tin oxide

Indium Tin Oxide (ITO) is the most commonly used anode as a transparent electrode and more recently as an anode for organic photovoltaics (OPVs). However, there are significant drawbacks in using ITO which include high material costs, mechanical instability including brittleness and poor electrical properties which limit its use in low-cost flexible devices. We present initial results of poly(3-hexylthiophene): phenyl-C61-butyric acid methyl ester OPVs showing that an efficiency of 1.9% (short-circuit current 7.01 mA/cm2, open-circuit voltage 0.55 V, fill factor 0.49) can be attained using an ultra thin film of gold coated glass as the device anode. The initial I-V characteristics demonstrate that using high work function metals when the thin film is kept ultra thin can be used as a replacement to ITO due to their greater stability and better morphological control.

Investigating the population structure of Queensland invasive Streptococcus pneumoniae isolates in children: Using a modified multi-locus variable number of tandem repeat analysis and a novel minimum SNPs capsular typing method

This research investigated the use of DNA fingerprinting to characterise the bacteria Streptococcus pneumoniae or pneumococcus, and hence gain insight into the development of new vaccines or antibiotics. Different bacterial DNA fingerprinting methods were studied, and a novel method was developed and validated, which characterises different cell coatings that pneumococci produce. This method was used to study the epidemiology of pneumococci in Queensland before and after the introduction of the current pneumococcal vaccine. This study demonstrated that pneumococcal disease is highly prevalent in children under four years, that the bacteria can `switch' its cell coating to evade the vaccine, and that some DNA fingerprinting methods are more discriminatory than others. This has an impact on understanding which strains are more prone to cause invasive disease. Evidence of the excellent research findings have been published in high impact internationally refereed journals.

Development of a new design expression for the in-plane shear capacity of the partially grouted concrete masonry walls

Partially grouted masonry walls subjected to in-plane shear exhibit a complex behaviour because of the influence of the aspect ratio, the pre-compression, the grouting pattern, the ratios of the horizontal and the vertical reinforcements, the boundary conditions and the characteristics of the constituent materials. The existing in-plane shear expressions for the partially grouted masonry are formulated as sum of strength of three parameters, namely, the masonry, the reinforcement and the axial force. The parameter ‘masonry’ includes the wall aspect ratio and the masonry compressive strength; the aspect ratio of the unreinforced panel inscribed into the grouted cores and bond beams are not considered, although failure is often dominated by these unreinforced masonry panels. This paper describes the dominance of these panels, particularly those that are squat, to the shear capacity of whole of shear walls. Further, the current design formulae are shown highly un-conservative by many researchers; this paper provides a potential reason for this un-conservativeness. It is shown that by including an additional term of the unreinforced panel aspect ratio a rational design formula could be established. This new expression is validated with independent test results reported in the literature – both Australian and overseas; the predictions are shown to be conservative.

Plasma polymerization of 1,1,1-trichloroethane yields a coating with robust antibacterial surface properties

Novel, highly chlorinated surface coatings were produced via a one-step plasma polymerization (pp) of 1,1,1-trichloroethane (TCE), exhibiting excellent antimicrobial properties against the vigorously biofilm-forming bacterium Staphylococcus epidermidis.

Design expressions for the in-plane shear capacity of confined masonry shear walls containing squat panels

In-plane shear capacity formulation of reinforced masonry is commonly conceived as the sum of the capacities of three parameters, viz, the masonry, the reinforcement, and the precompression. The term “masonry” incorporates the aspect ratio of the wall without any regard to the aspect ratio of the panels inscribed (and hence confined) by the vertical and the horizontal reinforced grout cores. This paper proposes design expressions in which the aspect ratio of such panels is explicitly included. For this purpose, the grouted confining cores are regarded as a grid of confining elements within which the panels are positioned. These confined masonry panels are then considered as building blocks for multi-bay, multi-storied confined masonry shear walls and analyzed using an experimentally validated macroscopic finite-element model. Results of the analyzes of 161 confined masonry walls containing panels of height to length ratio less than 1.0 have been regressed to formulate design expressions. These expressions have been first validated using independent test data sets and then compared with the existing equations in some selected international design standards. The concept of including the unreinforced masonry panel aspect ratio as an additional term in the design expression for partially grouted/confined masonry shear walls is recommended based on the conclusions from this paper.

Reduced graphene oxide growth on 316L stainless steel for medical applications

We report a new method for the growth of reduced graphene oxide (rGO) on the 316L alloy of stainless steel (SS) and its relevance for biomedical applications. We demonstrate that electrochemical etching increases the concentration of metallic species on the surface and enables the growth of rGO. This result is supported through a combination of Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM), density functional theory (DFT) calculations and static water contact angle measurements. Raman spectroscopy identifies the G and D bands for oxidized species of graphene at 1595 cm(-1) and 1350 cm(-1), respectively, and gives an ID/IG ratio of 1.2, indicating a moderate degree of oxidation. XPS shows -OH and -COOH groups in the rGO stoichiometry and static contact angle measurements confirm the wettability of rGO. SEM and AFM measurements were performed on different substrates before and after coronene treatment to confirm rGO growth. Cell viability studies reveal that these rGO coatings do not have toxic effects on mammalian cells, making this material suitable for biomedical and biotechnological applications.

Perylene-based profluorescent nitroxides for the rapid monitoring of polyester degradation upon weathering: An assessment

A profluorescent nitroxide possessing an isoindoline nitroxide moiety linked to a perylene fluorophore was developed to monitor radical mediated degradation of melamine-formaldehyde crosslinked polyester coil coatings in an industry standard accelerated weathering tester. Trapping of polyester-derived radicals (most likely C-radicals) that are generated during polymer degradation leads to fluorescent closed-shell alkoxy amines, which was used to obtain time-dependent degradation profiles to assess the relative stability of different polyesters towards weathering. The nitroxide probe couples excellent thermal stability and satisfactory photostability with high sensitivity and enables detection of free radical damage in polyesters under conditions that mimic exposure to the environment on a time scale of hours rather than months or years required by other testing methods. There are indications that the profluorescent nitroxide undergoes partial photo-degradation in the absence of polymer-derived radicals. Unexpectedly, it was also found that UV-induced fragmentation of the NO–C bond in closed-shell alkoxy amines leads to regeneration of the profluorescent nitroxide and the respective C-radical. The maximum fluorescence intensity that could be achieved with a given probe concentration is therefore not only determined by the amount of polyester radicals formed during accelerated weathering, but also by the light-driven side reactions of the profluorescent nitroxide and the corresponding alkoxy amine radical trapping products. Studies to determine the optimum probe concentration in the polymer matrix revealed that aggregation and re-absorption effects lowered the fluorescence intensity at higher concentrations of the profluorescent nitroxide, but too low probe concentrations, where these effects would be avoided, were not sufficient to trap the amount of polyester radicals formed upon weathering. The optimized experimental conditions were used to assess the impact of temperature and UV irradiance on polymer degradation during accelerated weathering.

Catalyst-free plasma enhanced growth of graphene from sustainable sources

Details of a fast and sustainable bottom-up process to grow large area high quality graphene films without the aid of any catalyst are reported in this paper. We used Melaleuca alternifolia, a volatile natural extract from tea tree plant as the precursor. The as-fabricated graphene films yielded a stable contact angle of 135°, indicating their potential application in very high hydrophobic coatings. The electronic devices formed by sandwiching pentacene between graphene and aluminum films demonstrated memristive behavior, and hence, these graphene films could find use in nonvolatile memory devices also.