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Using the soft lithographic technique, microcontact printing, we demonstrate an example of how a biocompatible polymer can be easily patterned upon another polymer substrate, creating a surface with two spatially different properties. A poly(dimethylsiloxane) mold allowed the patterning of a negative replica of an E-PROM microchip, forming a spatially defined pattern with a period of approximately 1 μm. The amphiphilic biocompatible polymer, poly(lactic acid)−poly(ethylene glycol) (PLA−PEG), was used as the “ink” in order to block off areas of a hydrophobic, polystyrene (PS) substrate. This created a surface with two properties:  2−3 μm strips of PLA−PEG polymer, which resists protein adsorption, divided by micrometer strips of PS. The ability of the patterning technique to provide a true heterogeneous surface was analyzed using atomic force microscopy, while fluorescence microscopy provided a high-contrast method by which to trace the position of specific molecules. We believe this technique to be an elegant demonstration of how the properties of polymers can be exploited in order to arrange molecules at a surface, avoiding the more difficult use of gold, self-assembly, or self-assembled monolayers.

We have used albumin-modified atomic force microscope (AFM) tips to probe interactions with a range of hydrophilic polymer brush surfaces and protein. Copolymers of poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) (PEO−PPO−PEO) (Pluronics) adsorbed onto polymer interfaces have been shown in previous studies to modify adsorption properties of blood components [using surface plasmon resonance (SPR) and AFM]. Here we have employed protein-coated AFM probes to study a series of PEO−PPO−PEO-coated interfaces prepared with a range of PEO and PPO molecular weights. Subsequent force−distance experiments have shown a good correlation between the forces of adhesion of an albumin-functionalized AFM probe with the various PEO−PPO−PEO surfaces and the adsorption trends of albumin onto these polymeric surfaces observed with SPR. The data suggest that the size of the hydrophobic PPO segment of the Pluronic is a major determinant of the polymer protein resistance properties. In addition, as the PEO layer density increased, a reduction of interaction force was measured because of the formation of a steric barrier from the PEO polymer brush. Such studies suggest that AFM may be employed as a novel method to assess “biocompatibility” and to rapidly screen surface-engineered surfaces with micrometer spatial resolution.

This paper describes the formation of highly defined two-dimensional protein arrays onto a polymeric substrate expressing biotin functionalities at its surface. Micron-scale arrays of avidin were created by exploiting its interaction with biotin, thereby creating a versatile patterned surface onto which any biotinylated species can be subsequently immobilized. The patterning process utilized the technique of microfluidic networks (μFN) to spatially confine the flow of protein solution on a substrate. We describe methods developed to control protein deposition with nanometer-scale precision. Utilizing atomic force microscopy (AFM), these patterned surfaces were analyzed to the molecular level. In addition, the applicability of this technique to a wider range of substrates has been investigated. In particular, developments within the μFN technique have enabled the successful formation of protein micropatterns onto a highly hydrophilic surface, a substrate which is generally not suited to the technique of μFN.

A scanning probe microscope employing a shear force feedback mechanism as used in most near-field scanning optical microscopes has been utilized to provide phase images of a patterned protein boundary. The microscope employed a dithering fiber optic tip and tuning fork method of tip−sample distance control. The effect of tip vibration amplitude upon the phase contrast is investigated, and possible contrast mechanisms are discussed.

A novel liquid flow cell allows atomic force microscopy (AFM) images to be obtained under defined hydrodynamic flow conditions, enabling reaction fluxes calculated from proposed heterogeneous reaction mechanisms to be compared with those determined experimentally. The cell employs an inclined jet to direct a fluid flow at the sample surface to cover the area under investigation including the AFM scanning cantilever tip. The flow pattern and velocity were calculated by using the finite element fluid dynamics program FIDAP and confirmed by placing an electrode at the sample position and measuring the limiting current for the one-electron oxidation of potassium hexacyanoferrate(II) in water as a function of flow rate. The operation of the cell has been further confirmed by the direct measurement of the dissolution rate of calcite exposed to a flow of 0.98 mM aqueous HCl by deducing the rate of removal of the surface from the change of the z-piezo voltage. The rate constant k1 = 0.035 cm s^-1 obtained for the dissolution step was in excellent agreement with the value (0.043 ± 0.015) cm s^-1 found from independent channel flow cell experiments. The dissolution of the (&onemacr;10) and (110) faces of salicylic acid (SA) single crystals in water and in solutions of salicylic acid was studied as a function of flow rate and was found to be consistent with a model combining a constant rate of dissolution with a simultaneous reprecipitation having a first-order dependence on [SA]0, with the flux J = kd − kp[SA]0 where the parameters are %@mt;sys@%%@ital@%k%@rsf@%%@sx@%d%@be@%&onemacr;10%@sxx@%%@mx@% = 3 × 10^-9 mol cm^-2 s^-1 and %@mt;sys@%%@ital@%k%@rsf@%%@sx@%p%@be@%&onemacr;10%@sxx@%%@mx@% = 1.74 × 10^-4 cm s^-1 for the (&onemacr;10) face and %@mt;sys@%%@ital@%k%@rsf@%%@sx@%d%@be@%110%@sxx@%%@mx@% = 1.5 × 10^-8 mol cm^-2 s^-1 and %@mt;sys@%%@ital@%k%@rsf@%%@sx@%p%@be@%110%@sxx@%%@mx@% = 1.06 × 10^-3 cm s^-1 for the (110) face.

The hydroxide-driven dissolution of the polymer hydroxypropyl methylcellulose phthalate (HPMCP) in aqueous solution is studied using atomic force microscopy. The novel technique of employing the surface-averaged z-piezo voltage as a direct measure of the mean absolute surface height is described, so as, after appropriate calibration, to permit the ready inference of dissolution fluxes. In the case of interest the following dissolution rate law was established:  j/g·cm^-2·s^-1 = 105.0[OH^-] over the pH range 8.0−9.2, where j is the flux of the dissolving polymer and [OH^-] is measured in mol cm^-3.