In Situ Electrochemical-AFM and Cluster-Ion-Profiled XPS Characterization of an Insulating Polymeric Membrane as a Substrate for Immobilizing Biomolecules.

The electrochemical oxidation of ortho-aminophenol (oAP) by cyclic voltammetry (CV), on platinum substrates in neutral solution, produces a polymeric film (PoAP) that grows to a limiting thickness of about 10 nm. The insulating film has potential use as a bioimmobilizing substrate, with its specificity depending on the orientation of its molecular chains. Prior investigations suggest that the film consists of alternating quinoneimine and oAP units, progressively filling all the platinum sites during the electrosynthesis. This work concerns the evaluation of the growth orientation of PoAP chains, which until now was deduced only from indirect evidence. Atomic force microscopy (AFM) has been used in situ with an electrochemical cell so that PoAP deposition on a specific area can be observed, thus avoiding any surface reorganization during ex situ transport. In parallel with microscopy, XPS experiments have been performed using cluster ion beams to profile this film, which is exceptionally thin, without damage while retaining molecular information.

Gelatine and gelatine/elastin nanocomposites for vascular grafts: processing and characterization.

This study involves the preparation, microstructural, physical, mechanical, and biological characterization of novel gelatine and gelatine/elastin gels for their use in the tissue engineering of vascular grafts. Gelatine and gelatine/elastin nanocomposite gels were prepared via a sol-gel process, using soluble gelatine. Gelatine was subsequently cross-linked by leaving the gels in 1% glutaraldehyde. The cross-linking time was optimized by assessing the mass loss of the cross-linked gels in water and examining their mechanical properties in dynamic mechanical tests. Atomic force microscopy (AFM) studies revealed elastin nanodomains, homogeneously distributed and embedded in a bed of gelatine nanofibrils in the 30/70 elastin/gelatine gel. It was concluded that the manufactured nanocomposite gels resembled natural arteries in terms of microstructure and stiffness. The biological characterization involved the culture of rat smooth muscle cells (SMCs) on tubular gelatine and gelatine/ elastin nanocomposite gels, and measurements of the scaffold diameter and the cell density as a function of time.

Calibration of AFM cantilever stiffness: a microfabricated array of reflective springs.

Calibration of the spring constant of atomic force microscope (AFM) cantilevers is necessary for the measurement of nanonewton and piconewton forces, which are critical to analytical applications of AFM in the analysis of polymer surfaces, biological structures and organic molecules. We have developed a compact and easy-to-use reference standard for this calibration. The new artifact consists of an array of 12 dual spiral-cantilever springs, each supporting a mirrored polycrystalline silicon disc of 160 microm in diameter. These devices were fabricated by a three-layer polysilicon surface micromachining method, including a reflective layer of gold on chromium. We call such an array a Microfabricated Array of Reference Springs (MARS). These devices have a number of advantages. Cantilever calibration using this device is straightforward and rapid. The devices have very small inertia, and are therefore resistant to shock and vibration. This means they need no careful treatment except reasonably clean laboratory conditions. The array spans the range of spring constant from around 0.16 to 11 N/m important in AFM, allowing almost all contact-mode AFM cantilevers to be calibrated easily and rapidly. Each device incorporates its own discrete gold mirror to improve reflectivity. The incorporation of a gold mirror both simplifies calibration of the devices themselves (via Doppler velocimetry) and allows interferometric calibration of the AFM z-axis using the apparent periodicity in the force-distance curve before contact. Therefore, from a single force-distance curve, taking about one second to acquire, one can calibrate the cantilever spring constant and, optionally, the z-axis scale. These are all the data one needs to make accurate and reliable force measurements.