Giles H. W. Sanders

Spatially controlled cell engineering on biodegradable polymer surfaces

Controlling receptor‐mediated interactions between cells and template surfaces is a central principle in many tissue engineering procedures (1–3). Biomaterial surfaces engineered to present cell adhesion ligands undergo integrin‐mediated molecular interactions with cells (1, 4, 5), stimulating cell spreading, and differentiation (6–8). This provides a mechanism for mimicking natural cell‐to‐matrix interactions. Further sophistication in the control of cell interactions can be achieved by fabricating surfaces on which the spatial distribution of ligands is restricted to micron‐scale pattern features (9–14). Patterning technology promises to facilitate spatially controlled tissue engineering with applications in the regeneration of highly organized tissues. These new applications require the formation of ligand patterns on biocompatible and biodegradable templates, which control tissue regeneration processes, before removal by metabolism. We have developed a method of generating micron‐scale patterns of any biotinylated ligand on the surface of a biodegradable block copolymer, polylactide‐poly(ethylene glycol). The technique achieves control of biomolecule deposition with nanometer precision. Spatial control over cell development has been observed when using these templates to culture bovine aortic endothelial cells and PC12 nerve cells. Furthermore, neurite extension on the biodegradable polymer surface is directed by pattern features composed of peptides containing the IKVAV sequence (15, 16), suggesting that directional control over nerve regeneration on biodegradable biomaterials can be achieved.—Patel, N., Padera, R., Sanders, G. H. W., Cannizzaro, S. M., Davies, M. C., Langer, R., Roberts, C. J., Tendler, S. J. B., Williams, P. M., and Shakesheff, K. M. Spatially controlled cell engineering on biodegradable polymer surfaces. FASEB J. 12, 1447–1454 (1998)

The Discrimination of Drug Polymorphic Forms from Single Crystals Using Atomic Force Microscopy

established crystallization conditions (4). The only polymorphic Ardeshir Danesh,1 Xinyong Chen,1 forms used pharmaceutically are polymorphs A and B. PolyMartyn C. Davies,1 Clive J. Roberts,1,4 morph A is easier to handle, particularly in large scale operations Giles H. W. Sanders,1,3 Saul J. B. Tendler,1 due to good flow properties, and lack of adherence making Phillip M. Williams,1 and M. J. Wilkins2 it most suitable for manufacturing tablets (4). Polymorph B

Discrimination of polymorphic forms of a drug product by localized thermal analysis

In chemical processing, it is important to distinguish between and identify polymorphic forms. We demonstrate the novel use of scanning thermal microscopy (SThM) and localized thermal analysis to distinguish and identify polymorphic forms of the drug cimetidine. These forms cannot be resolved by classical bulk thermal analysis. SThM reveals a sample consisting of a 50 : 50 mixture of the polymorphs contains regions of different thermal conductivity, corresponding to the different polymorphs. Localized thermal analysis of small volumes of pure polymorphic samples (approximately 50 µm3) shows that the origin of the thermal conductivity contrast lies, at least in part, with the presence of a surface water layer on the more hydrophilic polymorph.

Molecular patterning on carbon based surfaces through photobiotin activation

We have demonstrated the site-specific adhesion of photobiotin as a method of producing protein micropatterns. These patterns were created by the selective UV irradiation of a thin film of deposited photobiotin. The UV activated areas of photobiotin were then developed using fluorescently labelled avidin. The size of pattern produced is an order of magnitude smaller than those previously reported by this method. The patterns were characterised, using atomic force microscopy (AFM) to determine their microstructure. It was found that the AFM could discriminate between the areas of protein immobilised to the surface through the activated photobiotin, and the bare substrate surface where the inactivated photobiotin had been removed during the washing process. The potential of these patterns as sensing surfaces is demonstrated through the creation of a spatially patterned immunosensing surface. In this case, a biotinylated antibody was bound to the surface and the pattern developed using a second antibody specific to the immobilised biotinylated antibody. This technique could thus provide a simple and efficient method of producing high density immunoassay systems.

A HYDRODYNAMIC AFM FLOW CELL FOR THE QUANTITATIVE MEASUREMENT OF INTERFACIAL KINETICS

A novel liquid flow cell is developed which allows atomic force microscopy images to be obtained under defined and modelled hydrodynamic flow conditions, enabling measured reaction fluxes to be compared with those calculated from proposed heterogeneous reaction mechanisms.