Nanomechanical characterization of biomaterial surfaces: Polymer coatings that elute drugs

"Drug-eluting" biomaterials control the release of a drug into the tissue surrounding an implant with the goal of inducing proper healing responses in a localized area around the device. This chapter explores the application of scanning probe microscopy (SPM) to the nanomechanical characterization of drug-eluting coatings containing high concentrations of drugs mixed with hydrophobic polymers or hydrophobically associating hydrogels. As SPM nanomechanical characterization indirectly measures changes in the chemical composition of regions on the surface of the drug-polymer mixtures, some challenges arise in determining the chemical composition in the regions of interest. For example, in mixtures of dexamethasone in poly(butyl methacrylate) (PBMA), after exposure to water, small protrusions of segregated dexamethasone elute drug and leave pits as elution proceeds. Similarly, in mixtures of simvastatin in poly(butylene terephthalate) (PBT)-poly(ethylene oxide) (PEO) polymer, after exposure to water, amorphous simvastatin is forced to the surface of the coatings.