Soft tissues and force fields: advanced 3D synchrotron-based imaging for diagnostics and regenerative medicine

Mechanical stimuli are regulators not only in cells but also in the extracellular matrix activity, with special reference to collagen bundles composition, amount and distribution. Collagen, the major protein in human tissues, contributes to the tissues mechanical properties including ductility under tension and also compressive behavior. However, how mechanical forces in these tissues are translated to mechanotransduction pathways - that ultimately drive the biological response - remains unknown. In this context, 3D imaging methods are necessary to capture the increased complexity that can arise due to high levels of anisotropy and out-of-plane motion, particularly in the disorganized, injured states. An interesting method for 3D imaging and quantitative analysis of collagenous tissues has spread in recent years: it is based on the unique characteristics of synchrotron radiation; it overcome the intrinsic limitations of both histology, achieving only a 2D characterization, and conventional tomographic approaches, poorly resolving the collagenous tissues. In this research, the focus has been placed on our recent researches based on the exploitation of synchrotron-based phase-contrast tomography for the investigation human collagenous tissue physio-pathologies, but also to study the outcome of different tissue-engineering strategies. Encouraging results proved that synchrotron-based imaging is suitable to access and quantify human collagenous tissues. Moreover, with the support of neural networks and deep learning, it is possible to quantify structures in synchrotron phase-contrast images that were not distinguishable before. In particular, collagen bundles can be identified by their orientation and not only by their physical densities, as was made possible using conventional thresholding segmentation techniques. Localised changes in fiber orientation, curvature and strain may involve changes in regional strain transfer and mechanical function, with consequent clinical implications. The comprehension of these kinetics can foster the discovery of therapeutic approaches for the maintaining or re-establishment of correct tissue tensions, as a key to successful and regulated tissues remodeling/repairing and wound healing.