Assessing Collagen Nanoscale Thin Films Heterogeneity by AFM Multimode Imaging and Nanoindetation for NanoBioMedical Applications

Collagen due to its filamentous shape and unique properties is a very promising molecule for the development of nanostructures, scaffolds, cell culture platforms and nanobiomaterials. Furthermore, collagen thin films are of great interest as they can cover non-biological surfaces in medical devices and sensors so as to offer them biocompatibility. Since surface nanotopography and mechanical properties can influence cell-biomaterial interactions it is of crucial im- portance to nano-characterize collagen surface and heterogeneity. Nano-characterization can be performed with Atomic Force Microscopy (AFM), which operates in a variety of modes/techniques and can offer a wide range of information, from topography to mechanical properties. In this paper it was sought to gain insights of structural and mechanical hetero- geneity of collagen fibers in thin films by combining AFM multimode-imaging, including phase imaging, with quantita- tive measurements through nanoindentation. The results demonstrated that the overlap-gap regions on collagen fibers (D-periodicity) yield a significant phase contrast, due to different mechanical properties. In addition, phase contrast was also demonstrated in collagen 'kinks', which provides evidence that collagen fiber shell and core possess different properties. The mechanical heterogeneity of the collagen fibers in the kink areas was confirmed by AFM-nanoindentation and the obtained quantitative measurements. In addition, AFM multimode imaging performance was demonstrated on fibroblasts cultured on collagen thin films. The correlation between the heterogeneous structure and the mechanical properties of collagen fibers in thin films will enable the design and development of biomaterials and tissue scaffolds with improved properties.