Hybrid RF/IR transcutaneous telemetry for power and high-bandwidth data.

As neuroprosthetic control systems continue to advance and increase in channel density, there will be a constant need to deliver data at higher bandwidths in and out of the body. Currently, RF telemetry and inductive coupling are the most commonly used methods for transmitting power and electronic data between implants and external systems, and state of the art systems can deliver data rates up to hundreds of kilobits per second. However, it is difficult to operate implanted medical RF links at higher data rates due to electromagnetic compatibility (EMC) constraints. In this study, we investigate the potential for hybrid telemetry systems that use constant-frequency RF inductive links for power and transcutaneous infrared (IR) signals for data. We show that with commercially available infrared communication components, data rates of up to 40 Mbits per second can be transmitted out across 5 mm of skin with an internal device power dissipation under 100 mW.

Adhesion mapping of chemically modified and poly(ethylene oxide)-grafted glass surfaces.

Two-dimensional mapping of the adhesion pull-off forces was used to study the origin of surface heterogeneity in the grafted poly(ethylene oxide) (PEO) layer. The variance of the pull-off forces measured over the µm-sized regions after each chemical step of modifying glass surfaces was taken to be a measure of the surface chemical heterogeneity. The attachment of γ-glycidoxypropyltrimethoxy silane (GPS) to glass decreased the pull-off forces relative to the clean glass and made the surface more uniform. The subsequent hydrolysis of the terminal epoxide groups resulted in a larger surface heterogeneity which was modeled by two populations of the terminal hydroxyl groups, each with its own distribution of adhesion forces and force variance. The activation of the hydroxyls with carbonyldiimmidazole (CDI) healed the surface and lowered its adhesion, however, the force variance remained rather large. Finally, the grafting of the α,ω-diamino poly(ethyleneoxide) chains to the CDI-activated glass largely eliminated adhesion except at a few discrete regions. The adhesion on the PEO grafted layer followed the Poisson distribution of the pull-off forces. With the exception of the glass surface, a correlation between the water contact angles and the mean pull-off forces measured with the Si(3)N(4) tip surfaces was found for all modified glass surfaces.

A constant compliance force modulation technique for scanning force microscopy (SFM) imaging of polymer surface elasticity.

A new method of force modulation scanning force microscopy (SFM) imaging based on a constant compliance feedback loop is presented. The feedback adjusts the loading force applied by the SFM tip to the surface in order to maintain a constant compliance beneath the tip. The new method, constant compliance force modulation (CCFM), has the advantage of being able to quantify the loading force exerted by the tip onto the sample surface and thus to estimate the elastic modulus of the material probed by the SFM tip. Once the elastic modulus of one region is known, the elastic moduli of other surface regions can be estimated from the spatial map of loading forces using the Hertz model of deformation. Force vs. displacement measurements made on one surface locality could also be used to estimate the local modulus. Several model surfaces, including a rubber-toughened epoxy polymer blend which showed clearly resolved compliant rubber phases within the harder epoxy matrix, were analyzed with the CCFM technique to illustrate the method's application.

Novel Method of Measuring Cantilever Deflection during an AFM Force Measurement.

A combination of a reflection interference contrast microscope (RICM) and the atomic force microscope (AFM) was used to monitor the cantilever-surface separation distance during force measurements using the streptavidin-biotin recognition pairs. The RICM showed that the cantilever loses contact with the surface before the final rupture of the adhesive bonds is measured by the AFM detection system. This finding suggests that the immobilization of biotin by physisorbed albumin and subsequent binding of streptavidin might have created a cross-linked protein network whose cohesion is tested by the AFM cantilever with the immobilized biotin ligands.

Adhesion Force Measurements Using an Atomic Force Microscope Upgraded with a Linear Position Sensitive Detector.

The atomic force microscope (AFM), in addition to providing images on an atomic scale, can be used to measure the forces between surfaces and the AFM probe. The potential uses of mapping the adhesive forces on the surface include a spatial determination of surface energy and a direct identification of surface proteins through specific protein-ligand binding interactions. The capabilities of the AFM to measure adhesive forces can be extended by replacing the four-quadrant photodiode detection sensor with an external linear position sensitive detector and by utilizing a dedicated user-programmable signal generator and acquisiton system. Such an upgrade enables the microscope to measure in the larger dynamic range of adhesion forces, improves the sensitivity and linearity of the measurement, and eliminates the problems inherent to the multiple repetitious contacts between the AFM probe and the specimen surface.

Manipulation of Proteins on Mica by Atomic Force Microscopy.

The atomic force microscope was used to image adsorption of a monoclonal IgM on mica in real time. Under the smallest possible force we could achieve (<4 nN), the cantilever tip behaved as a molecular broom and was observed to orient protein aggregates in strands oriented perpendicularly to the facet of the cantilever tip. Rotating the scan direction preserved the orientational relationship, as seen by the formation of rotated strands. When the applied force was increased, the distance between the strands increased, indicating the amount of protein that can be swept depends on the applied force. The effect of scanning increased the apparent surface coverage of IgM. Manipulation of a deposited fibrinogen layer with a 4-nN repulsive force was observed only after tens of minutes, but not to the extent that strands formed, indicating a greater adhesion between the fibrinogen and mica than between IgM and mica. With an applied repulsive force of 30 nN, fibrinogen strands formed and the protein was manipulated to produce the block letter U. At a much higher repulsive force, the entire scanning area was swept clean.