This presentation is an overview of atomic force microscopy (AFM) methodologies applied to crosslinked polyacrylamide and polyvinyl pyrrolidone based lubricious coatings as well as drug-eluting polymeric coatings (block copolymers, blends), under variable humidity and aqueous immersion. (Research was performed in open collaborations with members of an industrial consortium, IPRIME.) Beyond rich surface morphologies and their dependence on hydration, the imaging contrast derived from nanomechanics and/or tip-sample adhesion aids in the identification of components in coatings and thereby assesses phase segregation, local crystallization or other sources of heterogeneity. In the case of drug-eluting coatings, AFM is complemented by confocal Raman imaging to add chemical and crystallinity contrast as well as depth perception.<br/>Defect structures such as craters, pinholes, fissures and wrinkles (for the case of UV-crosslinked, sponge-deposited polyvinyl pyrrolidone coatings) largely disappear at high humidity as well as under aqueous immersion, with the concomitant appearance of crystallites due to the diffusion and aggregation of crosslinking additives. Nanomechanical probing during complete hydration cycles identifies reversible glass-to-rubber transitions that are further distinguished by degree of crosslinking. Tip-sample adhesion is also strongly sensitive to humidity-controlled glass-rubber transitions (dependent on crosslinking), and reveals significant differences between thin and thick coatings in the case of polyacrylamide. Nanotribological methods further reveal crosslinking-derived differences in coating behavior, especially pertinent to wear. Colloid-probe AFM methodologies are developed and utilized to explore normal and shear response in the gel state under aqueous immersion. In all cases mapped, distance-dependent force measurements ("force spectroscopy") – both slow (force volume) and high-frequency modes (e.g., peak/pulse force) – provide deeper insights into material properties.<br/>The overarching emphasis of this presentation is on (i) commonly available AFM modes to obtain information well beyond simple surface topography; (ii) the enabling "humidity knob", and full aqueous immersion, to study changes in polymeric materials due to hydration as well as small-molecule diffusion within and from polymeric coatings; (iii) the importance of multichannel data acquisition and high data throughput to creative applications of AFM.

Probing the morphology, hydration, mechanics and tribology of biomedical coatings with environmental AFM

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.