Microstructure and in vitro degradation performance of Mg-Zn-Mn alloys for biomedical application.

Manganese and zinc were selected as alloying elements to develop a Mg-based ternary alloy for biomedical applications, taking into account the good biocompatibility of these metals. The microstructures of Mg-Zn-Mn alloys containing 0.5 or 1.0 mass% of manganese and 1.0 or 1.5 mass% of zinc were investigated by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. Their corrosion properties were assessed by means of potentiodynamic polarization and electrochemical impedance spectroscopy measurements performed in Ringer's physiological solution that simulates bodily fluids. All tested samples are two-phase alloys formed by a Mg-based matrix, consisting of a Mg-Zn-Mn solid solution, and a Mg-Zn binary phase. The electrochemical results show an improvement of the corrosion behavior of the investigated alloys with increasing Zn and Mn content. This is attributed to the formation of a partially protective Mg(OH)(2) surface film whose protective capabilities are increased by the alloying elements. The reduced influence of the Mg-Zn intermetallic compound on the corrosion rate of Mg-Zn-Mn alloys in the presence of a partially protective surface layer can be ascribed to an increasing resistance between the Mg-Zn-Mn solid solution and the second phase, thereby decreasing the effective driving force for microgalvanic corrosion. Owing to its highest corrosion protective ability, the Mg-1.5Zn-1Mn alloy is a promising candidate for the development of degradable implants, such as screws, plates, and rods.

Influence of noble metals alloying additions on the corrosion behaviour of titanium in a fluoride-containing environment.

Titanium alloys exhibit excellent corrosion resistance in most aqueous media due to the formation of a stable oxide film, and some of these alloys (particularly Ti-6Al-7Nb) have been chosen for surgical and odontological implants for their resistance and biocompatibility. Treatment with fluorides (F(-)) is known to be the main method for preventing plaque formation and dental caries. Toothpastes, mouthwashes, and prophylactic gels can contain from 200 to 20,000 ppm F(-) and can affect the corrosion behaviour of titanium alloy devices present in the oral cavity. In this work, the electrochemical corrosion behaviour of Ti-1M alloys (M = Ag, Au, Pd, Pt) was assessed in artificial saliva of pH = 3.0 containing 910 ppm F(-) (0.05 M NaF) through open circuit potential, E(OC), and electrochemical impedance spectroscopy (EIS) measurements. The corrosion behaviour of the Ti-6Al-7Nb commercial alloy was also evaluated for comparison. E (OC) measurements show an active behaviour for all the titanium alloys in fluoridated acidified saliva due to the presence of significant concentrations of HF and HF(2) (-) species that dissolve the spontaneous air-formed oxide film giving rise to surface activation. However, an increase in stability of the passive oxide layer and consequently a decrease in surface activation is observed for the Ti-1M alloys. This behaviour is confirmed by EIS measurements. In fact, the Ti-6Al-7Nb alloy exhibits lower impedance values as compared with Ti-1M alloys, the highest values being measured for the Ti-1Au alloy. The experimental results show that the corrosion resistance of the studied Ti-1M alloys is similar to or better than that of Ti-6Al-7Nb alloy currently used as biomaterial, suggesting their potential for dental applications.

In vitro corrosion behaviour of Ti-Nb-Sn shape memory alloys in Ringer's physiological solution.

The nearly equiatomic Ni-Ti alloy (Nitinol) has been widely employed in the medical and dental fields owing to its shape memory or superelastic properties. The main concern about the use of this alloy derives form the fact that it contains a large amount of nickel (55% by mass), which is suspected responsible for allergic, toxic and carcinogenic reactions. In this work, the in vitro corrosion behavior of two Ti-Nb-Sn shape memory alloys, Ti-16Nb-5Sn and Ti-18Nb-4Sn (mass%) has been investigated and compared with that of Nitinol. The in vitro corrosion resistance was assessed in naturally aerated Ringer's physiological solution at 37°C by corrosion potential and electrochemical impedance spectroscopy (EIS) measurements as a function of exposure time, and potentiodynamic polarization curves. Corrosion potential values indicated that both Ni-Ti and Ti-Nb-Sn alloys undergo spontaneous passivation due to spontaneously formed oxide film passivating the metallic surface, in the aggressive environment. It also indicated that the tendency for the formation of a spontaneous oxide is greater for the Ti-18Nb-5Sn alloy. Significantly low anodic current density values were obtained from the polarization curves, indicating a typical passive behaviour for all investigated alloys, but Nitinol exhibited breakdown of passivity at potentials above approximately 450 mV(SCE), suggesting lower corrosion protection characteristics of its oxide film compared to the Ti-Nb-Sn alloys. EIS studies showed high impedance values for all samples, increasing with exposure time, indicating an improvement in corrosion resistance of the spontaneous oxide film. The obtained EIS spectra were analyzed using an equivalent electrical circuit representing a duplex structure oxide film, composed by an outer and porous layer (low resistance), and an inner barrier layer (high resistance) mainly responsible for the alloys corrosion resistance. The resistance of passive film present on the metals' surface increases with exposure time displaying the highest values to Ti-18Nb-4Sn alloy. All these electrochemical results suggest that Ti-Nb-Sn alloys are promising materials for biomedical applications.

Electromagnetic interference to infusion pumps from GSM mobile phones.

Electromagnetic interference (EMI) to critical care medical devices has been reported by various groups. Previuos studies have demonstrated that infusion and syringe pumps are susceptible of false alarm buzzing and block, when exposed to various EMI sources. Whether these events may have clinical relevance is still debated. The risk of EMI depends on several factors such as phone emitted power, distance and carrier frequency. We investigated the EMI on infusion and siringe pumps from GSM phones at various distances and emitted powers. Malfunctions were observed in 4/7 infusion pumps and 1/4 syringe pumps exposed to mobiles at their maximum output, for distances as long as 30 cm. The maximum power not inducing any malfunction even at 0 cm distance was also determined. The selection of a proper maximum power class reduces significantly the risk of EMI. Such a function is already built in the GSM standard and thus represents one of the feasible solutions to the EMI problem in hospitals.

Identification of the preferential gaze position through elevation of visual fatigue in a selected group of VDU operators. A preliminary study.

A selected group of VDU workers were tested in an attempt to achieve objective evidence of visual fatigue and to identify a preferential monitor/gaze position during a particular work setting. Each subject was scored in a two-phase test. The highest mean scores were achieved when the monitor was lowered with respect to the primary/gaze position; the scores obtained with the monitor in primary or upward gaze position were significantly lower (p < 0.001). The downward gaze position should be considered more comfortable for both innervational and anatomical factors, as stated in previous studies of ocular mobility. A reduction of vertical saccades could also play a role in lessening visual fatigue in this gaze position.