The effect of surface chemistry on the formation of thin films of native fibrillar collagen.

In this study, we used well-defined, homogeneous, gradient and patterned substrates to explore the effects of surface chemistry on the supramolecular structure of adsorbed type I collagen. Type I collagen (320microg/mL) was allowed to adsorb onto self-assembled CH(3)-, COOH-, NH(2)- and OH-terminated alkylthiolate monolayers at 37 degrees C. Atomic force microscopy, ellipsometry and phase microscopy indicated that large supramolecular collagen fibril structures (approximately 200nm in diameter, several microns long) assembled only at the hydrophobic CH(3)-terminated surfaces. By varying the surface energy using a mixture of OH- and CH(3)-terminated thiols during monolayer formation, we found that large fibril assembly occurred at surfaces with a water contact angle above 83 degrees , but not on surfaces with a water contact angle below 63 degrees . Examining a surface with a linear hydrophobicity gradient revealed that the assembly of large collagen fibrils requires a hydrophobic surface with a water contact angle of at least 78 degrees . Collagen fibril density increased over a narrow range of surface energy and reached near-maximum density on surfaces with a water contact angle of 87 degrees . These studies confirm that the supramolecular structure of adsorbed collagen is highly dependent on the underlying substrate surface chemistry. We can take advantage of this dependency to pattern areas of fibrillar and non-fibrillar collagen on a single surface. Morphology studies with vascular smooth muscle cells indicated that only collagen films formed on hydrophobic substrates mimicked the biological properties of fibrillar collagen gels.