AMROBS: All-Metal Replicas of Biological Surfaces—A Novel Approach Combining Established Techniques

Biomimetic work often concerns to biological surfaces and their interaction with the environment. Liquid handling, barrier function and protection against heat, pathogens and predators, to name just a few, require biological surfaces to exhibit specific material properties—properties that often are not suited for specific measurements under lab conditions. In particular, the lack of the necessary sample toughness or conductivity can prove difficult to perform certain experiments. Hence, we present a novel approach to achieve all-metal replicas from biological surfaces (AMROBS). Resulting replicas exhibit microscale accurate replication of morphological topography while providing tough, conductive subjects for investigation and easy chemical surface modification. Combining established techniques like polymer casting (e.g., silicone), chemical silver precipitation and electroplating, all-metal replicas of several technical and biological surfaces (e.g., diffraction foils, lizard skin, flat bug surface) were produced and compared to their original counterparts with regard to morphology and functionality. By using scanning electron microscopy and video analysis, we show that a high degree of replication accuracy is achievable, and conclude the future possibilities of AMROBS in a comprehensive discussion, including the general “do’s” and “do nots” of metal replication following this approach.

Silver Precipitation Using Sodium Dithionite in Cyanide Media

The nature of the reaction and the main parameters affecting Ag precipitation rate in the system Ag⁺-CN^--S₂O₄^2- are studied. From the results obtained, a process of chemical precipitation for Ag recovery is proposed, using an environmentally-friendly reducing reagent (sodium dithionite, Na₂S₂O₄), leaving a residual content of Ag into the permitted environmental levels (-1 Ag). The levels of CN^- in liquids wastes are of the order of 0.816 mol L^-1, and they can be treated by ozonization processes for inerting cyanide. The results obtained indicate that Ag precipitation is achieved in less than 1 hour, with recoveries close to 99%, at room temperature. Silver precipitation is characterized by an induction period followed by a precipitation period, leaving a metal amount in solution less than 1 mg L^-1. The main kinetic parameters studied lead to obtain the following apparent reaction orders: with respect to the initial [S₂O₄^2-] was <em>n</em> = 1.675, with respect to [CN^-] was -1.24, with respect to [OH^-] was ≈0 (between 10^-4 and 10^-2 mol L^-1) and with respect to the initial [Ag⁺] was 0.524. An activation energy of 77 kJ mol^-1 was obtained. Under these conditions, Ag precipitation in the system Ag⁺-CN^--S₂O₄^2- is controlled by chemical reaction, characterized by high activation energy, and is independent of the hydrodynamic variables of the system.

Effect of Chlorhexidine Pretreatment on Bond Strength Durability of Caries–affected Dentin Over 2-Year Aging in Artificial Saliva and Under Simulated Intrapulpal Pressure

SUMMARY Objective To evaluate the influence of 2% and 5% chlorhexidine (CHX) pretreatment on bond durability of a self-etching adhesive to normal (ND) and caries-affected (AD) dentin after 2-years of aging in artificial saliva and under simulated intrapulpal pressure (IPP). Methods One hundred twenty freshly extracted carious teeth were ground to expose ND and AD. Specimens were distributed into three equal groups (n=40) according to whether the dentin substrates were pretreated with 2% or 5% CHX or with water (control). Clearfil SE Bond (Kuraray) was applied to both substrates and composite cylinders (0.9 mm diameter and 0.7 mm height) were formed. Pretreatment and bonding were done while the specimens were subjected to 15 mm Hg IPP. After curing, specimens were aged in artificial saliva at 37°C and under IPP at 20 mm Hg until being tested after 24 hours or 2 years (n=20/group). Microshear bond strength was evaluated. Failure modes were determined using a scanning electron microscope (SEM) at 400× magnification. Data were statistically analyzed using three-way analysis of variance (ANOVA); one-way ANOVA tests, and t-test (p&lt;0.05). Additional specimens (n=5/group) were prepared to evaluate interfacial silver precipitation. Results For the 24-hour groups, there were no significant differences among the ND groups and AD groups. For ND aged specimens, the 5% CHX group had the highest value followed by the 2% CHX and control groups, although the difference was statistically insignificant. For AD aged specimens, the 5% CHX group revealed statistically higher bond values compared to the 2% CHX and control groups. Fracture modes were predominately adhesive and mixed. Different interfacial silver depositions were recorded. Conclusions Two percent or 5% CHX pretreatment has no adverse effect on the 24-hour bonding to ND and AD. Five percent CHX was able to diminish the loss in bonding to AD after 2years of aging in artificial saliva and under simulated IPP.

Silver Precipitation in Energy-Scavenging Aluminum Nitride Resonators

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Nature of the silver precipitation obtained by cementation from thiosulphate solutions

The morphology and composition of the deposits formed on the surface of magnesium disk during cementation from thiosulphate solutions (0.0025–0.1M) [Ag(S2O3)2]3− + 0.5M S2O3 2− have been studied. A porous deposit with low adhesion is formed on the surface of the magnesium metal substrate. Within a wide range of [Ag(S2O3)2]3− ion concentrations, sulfur as well as silver are constituents of the deposit at the initial stages of cementation and at the end of the reaction. This is attributed to the electrochemical behaviour of magnesium in thiosulphate solutions resulting in the exceeding of current limit on cathode for pure silver reduction. Hence, parallel electrochemical reactions take place that are very close in their values to the standard redox potentials of reduction of [Ag(S2O3)2]3− ions to Ag0 and S2O32− ions to S2−. Sulfur content in the cement deposits increases with the decrease in [Ag(S2O3)2]3− ion concentration and increase in cementation time. This tendency is also observed with the decreasing solution temperature.