Fibrinogen and albumin adsorption on titanium nanoroughness gradients.

The influence of nanoscale roughness on protein adsorption has been efficiently studied through the application of Ti roughness gradients. Gradients were prepared by sputter deposition with a length of 76 mm and a range in RMS roughness varying linearly from 1 to 16 nm. They were then exposed to solutions containing either 1 mg/mL of fibrinogen or albumin. The amount of protein that adsorbed as a function of roughness was measured ex situ by electron microprobe analysis and compared to values obtained for smooth Ti films. The adsorption profiles of fibrinogen and albumin along the gradients were found to be highly similar when normalized by their respective amounts from smooth films, each showing a 50% increase in adsorption with roughness. A statistic called the average surface curvature was created to provide a plausible explanation for the similar adsorption behavior and connect findings from random topographies with earlier research on curved substrates like nanoparticles.

Maximum conductivity of packed nanoparticles and their polymer composites.

Adding conductive fillers to nonconductive polymers is a common way to make soft conductive materials such as conductive adhesives. An important issue is how to achieve high volume conductivity with acceptable mechanical performance. Two questions pertaining to this issue were studied in this paper. One question was whether the maximum conductivity benefits from larger or smaller particle sizes. The second was what is the maximum achievable conductivity. One incentive for this work is the recent availability of nanomaterials that provide opportunities to make conductive composites using much smaller particles than in the past. We found that the conductivity of platinum, carbon black, and silver particles in their polyurethane composites did not vary greatly with particle size (from micrometer to nanometer range). What was unexpected was that in all the composite examples, the highest conductivity achieved was only on the order of 1% of that of the pure bulk conductive materials. Further experiments to emulate these conductive composites with platinum, carbon black, copper, and nickel particles without polymer matrix showed similar results, indicating the issue is not simply dispersion homogeneity, nano versus macro particles, particle connectivity/percolation, or the presence of the matrix materials. We interpret this to mean that the composite systems are intrinsically limited by the contact between filler particles.