Mechanically Tunable Thin Films of Photosensitive Artificial Proteins: Preparation and Characterization by Nanoindentation

Thin films of controlled elastic modulus were made by photo-cross-linking artificial extracellular matrix (aECM) proteins containing the photosensitive amino acid p -azidophenylalanine ( p N 3 Phe). The elastic moduli of the films were calculated from nanoindentation data collected by atomic force microscopy (AFM) using a thin-film Hertz model. The modulus was shown to be tunable in the range 0.3−1.0 MPa either by controlling the irradiation time or by varying the level of p N 3 Phe in the protein. Tensile measurements on bulk films of the same proteins and finite-element simulation of the indentation process agreed with the thin-film modulus measurements from AFM. Substrates characterized by spatial variation in elastic modulus were created by local control of the irradiation time.