One of the most common causes of implant failure is peri-implantitis, which is caused by bacterial biofilm formation on the surfaces of dental implants. Modification of the surface nanotopography has been suggested to affect bacterial adherence to implants. Silver nanoparticles are also known for their antibacterial properties. In this study, titanium alloy implants were surface modified following silver plating, anodisation and sintering techniques to create a combination of silver, titanium dioxide and hydroxyapatite (HA) nanocoatings. Their antibacterial performance was quantitatively assessed by measuring the growth of Streptococcus sanguinis, proportion of live/dead cells and lactate production by the microbes over 24 h. Application of a dual layered silver-HA nanocoating to the surface of implants successfully inhibited bacterial growth in the surrounding media (100% mortality), whereas the formation of bacterial biofilm on the implant surfaces was reduced by 97.5%. Uncoated controls and titanium dioxide nanocoatings showed no antibacterial effect. Both silver and HA nanocoatings were found to be very stable in biological fluids with material loss, as a result of dissolution, to be less than 0.07% for the silver nanocoatings after 24 h in a modified Krebs-Ringer bicarbonate buffer. No dissolution was detected for the HA nanocoatings. Thus, application of a dual layered silver-HA nanocoating to titanium alloy implants creates a surface with antibiofilm properties without compromising the HA biocompatibility required for successful osseointegration and accelerated bone healing.

Diamond and diamond-like carbon (DLC) thin films possess a number of unique and attractive material properties that are unattainable from Si and other materials. These include high values of Young's modulus, hardness, tensile strength and high thermal conductivity, low thermal expansion coefficient combined with low coefficients of friction and good wear resistance. As a consequence, they are finding increasing applications in micro-electro-mechanical systems (MEMS). This paper reviews these distinctive material properties from an engineering design point of view and highlights the applications of diamond and DLC materials in various MEMS devices. Applications of diamond and DLC films in MEMS are in two categories: surface coatings and structural materials. Thin diamond and DLC layers have been used as coatings mainly to improve the wear and friction of micro-components and to reduce stiction between microstructures and their substrates. The high values of the elastic modulus of diamond and DLC have been exploited in the design of high frequency resonators and comb-drives for communication and sensing applications. Chemically modified surfaces and structures of diamond and DLC films have both been utilized as sensor materials for sensing traces of gases, to detect bio-molecules for biological research and disease diagnosis.

Micro-electro-mechanical system, MEMS, is a rapidly growing interdisciplinary technology dealing with the design and manufacture of miniaturized machines with the major dimensions at the scale of tens, to perhaps hundreds, of micrometres. Because they depend on the cube of a representative dimension, component masses and inertias rapidly become small as size decreases whereas surface and tribological effects, which often depend on area, become increasingly important. Although our explanations of macroscopic tribological phenomena often involve individual events occurring at the micro-scale, when the overall component size is itself miniaturized it may be necessary to re-evaluate some conventional tribological solutions. While the absolute loads are small in such micro-devices, the tribological requirements, especially in terms of longevity—which may be limited by wear rather than friction—are particularly demanding and will require imaginative and novel solutions.

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The biocompatibility of silver and nanohydroxyapatite coatings on titanium dental implants with human primary osteoblast cells Salaie, RN

Medical grade titanium alloy is widely used for bone/dental implants, but the material alone has no innate antimicrobial properties that would reduce infection risk following surgery. However, silver nanoparticles (Ag NPs) are known to be antibacterial. This study investigated the growth of Ag NPs on titanium dioxide nanotubes (TiO NTs) on Ti-6Al-4V discs. The TiO NTs were grown on the Ti alloy using an electrochemical method, and then decorated with Ag NPs. The Ag NPs were synthesised by chemical reduction using δ-gluconolactone. A silver ammonia solution (silver nitrate + liquid ammonia) was used as the source of silver. Two separate approaches were used: (1) The δ-gluconolactone was mixed with the silver ammonia and then exposed to the TiO NTs (the 'mixing method'), which produced micron-sized clusters of the Ag NPs. (2) The TiO NTs were exposed to the silver ammonia first and then to δ-gluconolactone (the 'sequential addition method'), which resulted in the formation of nano-sized clusters of the nanoparticles. The Ag-TiO composites were confirmed by scanning electron microscopy and the elements analysed using energy dispersive X-ray spectroscopy (EDS). The composite coatings were exposed to a simulated body fluid for 24 h in order to determine the total Ag released. The release from the micron-sized clusters from the mixing method (14.6 ± 0.67 ppm) was higher than that from the nano-sized clusters (4.05 ± 0.36 ppm) when 0.015 M of silver ammonia was used. Additionally, Staphylococcus aureus, was cultured on the composite coatings for 24 h. Both the micron- and nano-sized clusters of the Ag NPs were found to be antibacterial using the Live/Dead assay. Overall, δ-gluconolactone was successfully used to reduce silver to Ag NPs on the surface of TiO NTs. The sequential addition method was the preferred method of synthesis because of its slower silver release, better coverage of the Ag-NPs on the TiO NTs and strong antibacterial properties.

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