Advances in our understanding of structure, its role in biological processes and in the functioning of high performance materials, require techniques which can probe that structure. We are particularly interested in the hierarchical organisation (composition, orientation, and interaction) of materials and tissues over the nanometre to millimetre scales. Our main tools to probe structure and properties over these scales use harmonic generation, vibrational spectroscopy, and scanning probe techniques.
Second harmonic generation (SHG) has emerged as a label-free and non-destructive method for characterising the organisation of noncentrosymmetric structures such as collagen. By combining polarised imaging with a vectorial Green’s function model of SHG from collagen, we can quantitatively relate images to the underlying, tens of nanometre scale, structure within the focal volume. Through this model we can probe the early structural changes in diseases such as osteoarthritis and tendonopathy. Further, our development of interferometric SHG allows the orientation of χ(2) / piezoelectric domains to be determined, providing insights into cell signalling and mechanical behaviour, as well as a performance indicator in collagen-based piezosupercapacitors.
Spectroscopy provides a means to study the concentration and arrangement of the major components of musculoskeletal tissues and materials. Scattering and absorbance of NIR and UV-Vis light are being studied in healthy and diseased tissue configurations, and analysis techniques developed to relate optical profiles to tissue state. With Raman spectroscopy in particular, we are examining the response of materials under loading to explore not only how they work, but how they work together.
Scanning probe techniques such as piezoresponse force microscopy, Kelvin probe microscopy and AMFM nanomechanical mapping provide insight into the relationships between structural and functional properties on the nanometre to micron scales. This is complemented by techniques such as dynamic force spectroscopy with functionalised tips to estimate patterns of kinetic and energetic parameters of adhesion and bonding. By applying multiple techniques to the sample, and at different scales, structural interactions can be determined on the fundamental scales at which biological materials function.