Nanoscale viscoelastic properties of an aligned collagen scaffold

Localised mechanical properties for aligned collagen scaffolds derived from Type 1 collagen were determined by application of nanoindentation based techniques. It was possible to measure the modulus and hardness with nanometre control over the depth of penetration and quasi-static testing under displacement control yielded average modulus values ranging from 1.71 GPa to 3.31 GPa; a narrower range of values than obtained by other methods. Hardness values of 222 MPa to 256 MPa were recorded and showed little scatter, highlighting the potential of nanoindentation hardness values as a reproducible and accurate measure of soft material properties. Open loop Load-displacement curves for the collagen exhibited the expected shapes for a viscoelastic material and it was thus possible to apply dynamic stiffness measurement at the nano scale. As well as determining the storage modulus (0.71 GPa) and the loss modulus (0.40 GPa) at the sub-micron length and nano depth resolution it was also possible to discriminate between surface and bulk readings allowing surface effects to be discarded if necessary. In addition to being a more accurate indentation method than atomic force microscopy, the localised dynamic mechanical properties of collagen were measured for the first time. These results demonstrate that this nanoindentation technique can serve as a powerful tool for the characterisation of collagen based biomaterials that are used as scaffolds for a variety of engineered tissues, such as artificial skin, skeletal muscle, heart valves and neuroregeneration guides.