A methodological framework for nanomechanical characterization of soft biomaterials and polymers

Nanoindentation utilizes a hard indenter probe to deform the sample surface in order to measure local properties, such as indentation modulus and hardness. Initially intended for characterization of elastic and elastic-plastic materials, nanoindentation has more recently been utilized for viscoelastic solids as well as hydrated and soft biological materials. An advantage to nanoindentation is the ability to determine the nano- and microscale properties of materials with complex microstructures as well as those of limited sample dimension. Nanoindentation finds utility in the characterization of structural tissues, hydrogels, polymers and composites. Nevertheless, testing complexities such as adhesion and surface detection exist in nanoindentation of compliant viscoelastic solids and hydrated materials. These challenges require appropriate modifications in methodology and use of appropriate contact models to analyze nanoindentation data. A full discussion of protocol adjustments has yet to be assembled into a robust nanoindentation testing framework of soft biomaterials and polymers. We utilize existing nanoindentation literature and testing expertise in our laboratories to (1) address challenges and potential errors when performing indentations on soft or hydrated materials, (2) explore best practices for mitigating experimental error, and (3) develop a nanoindentation framework that serves researchers as a primer for nanoindentation testing of soft/hydrated biomaterials and polymers.