ICMCTF2015 Session D1: Anti-bacterial Coatings, Surface Functionalization, Surgical Instruments

Oxynitrides of transition metals show tunable optical, mechanical, electrical, and bio-related properties when the ratio of oxygen to nitrogen is varied. TaOxNy and TaOxNy-Ag nanocomposite films were deposited by reactive co-sputtering with the variation of O/N ratios. After deposition, the films' mechanical properties were first examined. Next, the samples were tested for their biocompatibility using 3-T-3 cells, as well as for their antibacterial behaviors against Escherichia coli.

The results show that these films' hardness as well as the toughness could reach the maximum when the ratio of O/N was near 0.4. However, from the biocompatibility testing, it was found that the O/N ratio should be near the transition of semiconductor to conductor. It was also found that the antibacterial efficiency of TaOxNy-Ag film against Escherichia coli could be much improved, comparing with that of TaOxNy film. The effect of Ag on the biocompatibility of TaOxNy-Ag was found insigificant. The viability of the cells was examined using MTT assay.

Electroactive polymers are the most interesting class of polymers used as smart materials in various applications, such as the development of sensors and actuators for biomedical applications in areas as smart prosthesis, implantable biosensors and biomechanical signal monitoring, among others. For acquiring or applying the electrical signal from/to the piezoelectric material, suitable electrodes can be produced from Ti based coatings with tailored multifunctional properties, as conductivity and antibacterial characteristics, obtained by the inclusion of Ag. This work reports on Ti_1-xAg_x electrodes and Ag-TiN_y electrodes deposited by d. c. and pulsed magnetron sputtering at room temperature on poly(vinylidene fluoride)(PVDF). In the first system (Ti_1-xAg_x electrodes), silver content was varied from 0-100 at. %. For the second system (Ag-TiN_y electrodes), the nitrogen content changed between 0 to 40.3 at. % by increasing the nitrogen gas flow between 0 sccm and 15 sccm and the ratio Ti/Ag changed from 13.4 to 2.2 being clearly the visible decrease on the Ti content in the reactive mode.

The X-Ray Diffraction (XRD) results revealed that the deposition conditions preserve the polymer structure and suggested the presence of crystalline Tiβ phase in pure titanium coating and fcc-Ag phase in pure silver coating for the Ti_1-xAg_x system. For the Ag-TiN_y system it is possible to detect a fcc TiN structure and a fcc Ag phase. Sheet resistivity values show a typical behavior of a binary alloy system, varying between 0.12 and 28.5 Ω/sq for the Ti_1-xAg_x electrodes. For the second system the sheet resistivity decrease with the nitrogen content from 12.0 Ω/sq with 0 at. % to 2.8 Ω/sq for 40.3 at. % of N. The piezoelectricity of the different samples show similar values, showing values from 19.6 to 27.6 pCN^-1 for the Ti_x-1Ag_x system and 13.6 pCN^-1 as minimum for the Ag-TiN_y system, achieved for the highest N content. In order to assess the mechanical behavior of the as-sputtered films, the film/substrate system was loaded unidirectionally using a tensile machine. The stress-strain curves were analyzed and correlated with the structural data. Moreover, the antibacterial activity of the samples was assessed and it was verified that samples from the second series (Ag-TiN_y) present antibacterial activity, in contrast of the first series (Ti_1-xAg_x).

Biomaterial implants are susceptible to the attachment of contaminating bacteria, leading to bacterial biofilm formation. Biofilm microorganisms are highly resistant to antibiotic therapy, requiring up to 1000 times the concentration of antimicrobials to eradicate. The presence of multiple types of microorganisms in polymicrobial biofilm further increases the resistance of biofilm to antimicrobial therapy. Treatment of biofilm-based infection is often unsuccessful and may require removal of the implant and multi-stage revision processes to correct. Several strategies have been developed for the prevention and treatment of biofilm-based infection. Local delivery strategies to increase the concentration of antimicrobial at the site of the often poorly vascularized infected tissue include coatings on devices to slowly release antimicrobials and/or biofilm dispersal agents at a therapeutically effective concentration. These coatings may be prefabricated to specific implant materials or applied at the point of care with clinician-selected antibiotics. In preliminary in vitro and in vivo studies, combining antibiotics with specific biofilm inhibitors, such as cis-2 decenoic acid or D-amino acids, has been found to have additive or synergistic effects in reducing biofilm. Incorporation of these anti-biofilm agents into and controlling release from traditional local delivery systems can be challenging due to the hydrophobic nature of many biofilm inhibitors. Controlling release of biofilm inhibitors as well as antibiotics from these delivery systems is essential not only to ensure therapeutic efficacy but also to prevent concentrations from reaching those that may induce toxicity or inhibit healing in affected tissue. Implant coatings under investigation for local delivery of biofilm inhibitors include chitosan, electrospun nanofiber membranes, and phosphatidylcholine coatings, among others. Modifications to common local delivery systems such as calcium sulfate or polymethylmethacrylate, controlling release of antibiotic through the application of coatings or enhancing porosity, have demonstrated efficacy in treating established infections in animal models of osteomyelitis. Degradable local delivery systems can be useful as an adjunct to systemic antibiotic therapy to prevent and treat implant-associated biofilm infection.

Knee and hip joint prosthesis are being widely used worldwide, as a result of the increase of life expectancy, with concerns about the quality of life of patients and costs involved in the treatment of patients requiring placement of orthopedic prostheses. However, even with the advanced materials used today, the failure of medical devices is still a concern in the medical field. One of the major causes of failure is the microbial colonization, being Staphylococcus epidermidis one of the major nosocomial pathogens associated with orthopedic prostheses infections.

Therefore, the introduction of multifunctional coatings in the biomaterial could be a step to improve their physical, mechanical, tribological and biological properties and consequently to avoid the revision surgeries by microbial infection.

The main goal of this work was to produce multifunctional Ag-ZrCN for antibacterial coatings for hip prostheses. Although silver is described as having a potent antibacterial effect in the history of medicine, studies concerning Ag-ZrCN biomaterial’s coatings, showed no antibacterial effect, since silver is present on its metallic form. Indeed antibacterial activity depends of the released Ag+ from metallic silver. Therefore, the proposed challenge of this work is to enhance the ionization of silver, in order to achieve their release to the biological environment and promote its action on microorganisms, preventing its development. Silver antibacterial activity of these coatings was achieved by an activation procedure, by immersion of the samples in an oxidizing solution for 5 minutes.

Metallic silver (content up to 20 at. %) in ZrCN matrix, was deposited onto stainless steel 316L, by DC reactive magnetron.

ICP-OES technique was used to quantify silver ion release on the samples and the antibacterial activity was assessed by the halo test, using Staphylococcus epidermidis IE 186 strain.

Previously to activation the results showed no antibacterial activity and no significant release of silver ions, in opposition to activated samples, that show significant changes in morphology, which may be related with the formation of oxidized nano silver based masses, that allow improving biocidal Ag⁺ formation and mobility, providing a constant concentration of Ag+ ions in aqueous environments, killing or inhibiting bacteria growth .

Silver activation ensures the silver oxidation and consequently silver ion release, translating in antibacterial effect.

Development of biodegradable implants is indeed fascinating and among them magnesium and its alloys assume significance. Nevertheless, rapid corrosion, generation of a large volume of hydrogen gas, accumulation of hydrogen bubbles in gas pockets adjacent to the implant and an increase in local pH of the body fluid, limit their utilization. Surface medication by plasma electrolytic oxidation (PEO) is a viable approach since it delays the rate of corrosion attack during the initial periods of implantation and decreases the extent of hydrogen evolution. However, the higher pore density facilitates quicker infiltration of the corrosive medium into the inner regions of the PEO coating and subsequently down to the substrate, thus deteriorating its corrosion resistance by changing its local pH. During PEO, the choice of suitable current modes could produce significant changes in the discharge events, both in terms of discharge intensity and density. Any change in the discharge events would alter the coating microstructure, thickness, roughness, porosity, all of which is likely to influence the corrosion resistance. This leads to the questions that will it be possible to choose hybrid current modes (combination of unipolar and bipolar) to optimize the characteristics of the PEO coatings? If so, which type of hybrid current mode (unipolar followed by bipolar or bipolar followed by unipolar) is better? Will the characteristics of the coatings prepared by the hybrid current modes are better than those prepared only under unipolar or bipolar current modes? The present work aims to get a better understanding of these aspects. The PEO coatings were prepared using an alkaline silicate-fluoride electrolyte under unipolar, bipolar and hybrid current modes. The morphological features of the coatings were characterized by scanning electron microscopy while their structural characteristics were evaluated by X-ray diffraction measurements. Corrosion resistance of the coatings in Hank’s balanced salt solution (HBSS) was evaluated by potentiodynamic polarization studies. The findings of the study reveal that by a careful choice of hybrid current modes, it is possible to alter the characteristics of the PEO coatings and their corrosion resistance in HBSS, thus making them suitable for biomedical applications. (This work was supported by the National Research Foundation of Korea (NRF), South Korea Grant funded by the Korean government (MEST) (2011-0028709, 2013R1A1A2012322 & 2014R1A4A1005309. This paper was supported by the research funds of Chonbuk National University, South Korea in 2014).

Diamond is a promising material for different biomedical and biotechnological applications due to its outstanding properties, including high chemical stability and biocompatibility combined with excellent mechanical properties, electrical properties adjustable by doping, wide electrochemical potential window, etc. The properties of the diamond surface (wettability, conductivity, etc.) can be tailored by modification techniques in order to promote or suppress interactions with cells, proteins, RNA or DNA. In the current work we have investigated the interaction of neurons with ultrananocrystalline diamond (UNCD) films with different surface properties. The UNCD layers were prepared by microwave plasma chemical vapor deposition (MWCVD) from methane/nitrogen mixtures on silicon and glass substrates. The resulting coatings were composed of diamond nanocrystallites with a diameter up to 10 nm embedded in an a-C matrix with a grain boundary width of 1-1.5 nm. They were closed, uniform and relatively smooth with rms roughness of 12-14 nm, as revealed by atomic force microscopy (AFM). The intrinsic H-termination of the as-grown UNCD films was replaced by O-termination upon O₂ plasma or UV/O₃ treatment or by NH₂-termination after NH₃ plasma modification. Contact angle measurements and X-ray photoelectron spectroscopy (XPS) were used to study the differently prepared surfaces. Finally, the UNCD films with different terminations were applied as platforms for the attachment of circadian pacemaker and olfactory receptor neurons. The results for the proliferation and the viability of the cells in a period up to 14 days, expressed by the cell density, the KCl response and their spontaneous activity, were compared to those obtained for neurons on glass substrates with concanavalin A as an adhesion agent. An improved adhesion of the neurons on the modified UNCD without the application of adhesion proteins was demonstrated and applied for improvement of the cell culture preparation technique.

Dental arch wires are frequently used in orthodontics nowadays. The accumulated food debris adhered to such orthodontic appliance in oral cavity may lead to overgrowth of bacteria and subsequently results in dental caries. A super-hydrophobic surface of such dental appliances is believed to reduce these risks. Unfortunately, those super-hydrophobic surfaces based on the nano/micro morphology recently prepared by various routes are unsatisfactory in mechanical strength or bio- incompatible.

In this study, an electrochemical technology was used to develop nano/micro morphology on AISI 304 stainless steel, which is mostly used for dental arch wires. Through careful control of the anodic electrochemical dissolution process, nano/micro morphology was developed showing hydrophobic characteristic. Following a fluorocarbon coating, super-hydrophobic property was measured, which can be attributed to the synergistic effect of the nano/micro morphology and low surface energy of the fluorocarbon coating. It retains super-hydrophobic characteristic after being worn down 50 times using steel wool.

Keywords: super-hydrophobic; AISI 304 stainless steel; electrochemical; fluorocarbon; orthodontic.

Plasma nitriding can significantly improve both wear and corrosion resistance of austenitic stainless steels, if appropriate treatment conditions are chosen. Nickel, as an austenitic stabilizer for steel, can be replaced by manganese at lower cost. The absence of chromium in such alloys can also present the potential to beneficially suppress nitride precipitate formation during plasma nitriding, enabling a more efficient nitriding treatment, where a deep and highly supersaturated (expanded austenite) layer can form, without nitride precipitation, after a relatively short treatment time.

In this study, Hadfield austenitic manganese steels (traditional Mn-12 and a low-carbon weldable grade, with higher Mn content) were nitrided under low-pressure triode plasma conditions. Nitrided cross-sections were etched and examined by optical microscopy to characterize material core and treated surface microstructures. Glancing-angle XRD analysis was applied before and after nitriding to characterise surface phase evolution. Knoop microindentation hardness tests were also applied on nitrided cross-sections to obtain hardness-depth profiles. Tribological behaviour was evaluated by sliding wear and microabrasion testing. Open circuit potential and potentiodynamic polarization corrosion tests in 3.5wt% NaCl solution were applied before and after nitriding, to identify any changes in material corrosion properties.

Using nanoforms of inorganic metal oxides (and their complexes with polymeric and biomolecular systems) with fine conjugation strategies, one can explore extremely interesting and promising applications in the area of Healthcare: especially for development of smart biosensors, MRI agents, magnetic hyperthermia agents, wound-healing patches, drug delivery agents, antimicrobial agents and in wide-range of pharmaceutical formulations. This can be achieved via careful materials study to engineer them for establishment of their efficacy in such multiple applications. In this presentation, two such applications would be elaborated, namely: a) Iron oxide nanoparticles as efficient cancer-hyperthermia-cum-drug-delivery agent and b) mesoporous, self-assembled nanostrcutures for controlled-drug-release.

Magnetic nanoparticles have been investigated for their applications in cancer hyperthermia. If an appropriate drug is further conjugated to it, then the system can serve dual strategy to approcah the cancer cells, and lead them to destruction. Out of many systems explored by us, namely, manganites, iron oxides and nickel-cobaltites, the work related to iron oxide will be focused.

Fe₃O₄ (Fe) nanoparticles have been conjugated to curcumin (CU) molecules via a citrate (CA) linker (Fe-CA-CU) and have been explored for superoxide scavenging, tumor suppression, and cancer hyperthermia. These studies promise Fe-CA-CU as a good cancer hyperthermia-cum-tumor suppressant and antioxidant agent. These results would be discussed.

Second part of presentation would be on the use of various inorganic (silica) and organic (natural gel, aloevera) self-assembled nanostructures which work as drug reservoirs and release them in controlled fashion. The results related to silica microparticles with drug Cephalexin would be elaborated, which show promising controlled release of the drug for a duration of 48 hours. In another attempt a nano-porous self-assembled therapeutic bandage is synthesised using doctor-blade method. Drug curcumin is incorporated into it and is studied for drug release, antimicrobial property and radical-scavenging properties. These results drive us to a niche prototype of such medicinal topical patches for antimicrobial-anti-inflammatory and cell-rejuvenating bandage product. These results would be elaborated.