Thin films of the extracellular matrix protein, collagen, were prepared by adsorbing native or heatdenatured type I collagen onto hexadecanethiol self-assembled monolayers. The resulting films were characterized by atomic force microscopy, ellipsometry, and light microscopy. Denatured collagen formed a topographically smooth ∼3.6 nm thick film, consistent with an adsorbed protein monolayer. In contrast, the native collagen thin film consisted of supramolecular collagen fibrils. The density of the large fibrils could be varied by changing the native collagen concentration in the solution from which the films were prepared. The biomimetic nature of the thin collagen films was partially assessed by examining their effects on vascular smooth muscle cells. Automated quantitative analysis indicated that the morphology of smooth muscle cells on the thin films was dependent on whether the collagen was heat-denatured or was in its native fibrillar form. The area of cells on denatured collagen films was significantly larger than that of cells on thin films of native fibrillar collagen. This response closely mimicked the response of these cells to thick collagen gels. Examination of the relationship between collagen fibril density and cell area indicated that large fibrils play a role in determining how cells respond to collagen. Cells assumed a larger morphology on native collagen films with a lower density of large fibrils. In this study, it is clear that cell morphology on these films is determined by micron-scale interactions between cells and the matrix molecules and is not dependent on the bulk materials properties of collagen gels.

We report a novel combinatorial methodology for characterizing the effects of polymer surface features on cell function. Libraries containing hundreds to thousands of distinct chemistries, microstructures, and roughnesses are prepared using composition spread and temperature gradient techniques. The method enables orders of magnitude increases in discovery rate, decreases variance, and allows for the first time high-throughput assays of cell response to physical and chemical surface features. The technique overcomes complex variable spaces that limit development of biomaterial surfaces for control of cell function. This report demonstrates these advantages by investigating the sensitivity of osteoblasts to the chemistry, microstructure, and roughness of poly(D,L-lactide) and poly(epsilon-caprolactone) blends. In particular, we use the phenomenon of heat-induced phase separation in these polymer mixtures to generate libraries with diverse surface features, followed by culture of UMR-106 and MC3T3-E1 osteoblasts on the libraries. Surface features produced at a specific composition and process temperature range were discovered to enhance dramatically alkaline phosphatase expression in both cell lines, not previously observed for osteoblasts on polymer blends.

A methodology for the preparation of porous scaffolds for tissue engineering using co-extrusion is presented. Poly(epsilon-caprolactone) is blended with poly(ethylene oxide) in a twinscrew extruder to form a two-phase material with micron-sized domains. Selective dissolution of the poly(ethylene oxide) with water results in a porous material. A range of blend volume fractions results in co-continuous networks of polymer and void spaces. Annealing studies demonstrate that the characteristic pore size may be increased to larger than 100 microm. The mechanical properties of the scaffolds are characterized by a compressive modulus on the order of 1 MPa at low strains but displaying a marked strain-dependence. The results of osteoblast seeding suggest it is possible to use co-extrusion to prepare polymer scaffolds without the introduction of toxic contaminants. Polymer co-extrusion is amenable to both laboratory- and industrial-scale production of scaffolds for tissue engineering and only requires rheological characterization of the blend components. This method leads to scaffolds that have continuous void space and controlled characteristic length scales without the use of potentially toxic organic solvents.