Shephard, J. D. | Search bioRxiv

bioRxiv2025

Micromechanical characterisation of osteoarthritic subchondral bone by micropillar compression

Osteoarthritis (OA) is a multifaceted joint disease which poses significant socioeconomic burdens and remains a significant clinical challenge. Evidence suggests that structural and mechanical changes in subchondral bone influence the pathogenesis and development of OA, leading to diminished bone quality and cartilage degeneration. While changes in microstructure and tissue scale elastic properties are well reported, the tissue yield response of subchondral bone in OA and their correlation with compositional changes have not been investigated. Here, we performed quasistatic micropillar compression and nanoindentation within the subchondral bone plate and trabeculae of hydrated non-diseased (ND) and OA affected specimens retrieved from the distal tibia in vivo. The micropillars, extracted by laser ablation, exhibited a taper angle which mandated the use of an in silico micropillar compression routine to back-calculate elastic modulus and strength of the bone tissue that comprised each micropillar. Elastic modulus remained unchanged between ND and OA subchondral bone, whereas strength increased from 46.0 MPa to 57.3 MPa in OA subchondral trabecular bone but not in the bone plate. Micropillar matched Raman spectroscopy and quantitative backscattered electron imaging revealed mineralisation is the underlying determinant of elastic modulus and strength at the microscale. By combining micromechanical and tissue compositional analyses, we investigated how the mechanical properties are related and how these properties are affected in subchondral bone by OA. Our results may be of value in the development and optimisation of interventions used to alleviate the socioeconomic burdens associated with this debilitating joint disease. Statement of significanceOsteoarthritis imposes significant socioeconomic burden, necessitating ever improving treatment strategies. Abnormal mechanical forces at the joint, such as injury, overloading, or aging are associated with osteoarthritis development. While healthy tissue is well understood, the impact of diseases on tissue mechanical properties needs to be brought on a similar level of understanding. We present in this study the first use of micropillar compression for assessing the tissue scale compressive strength of subchondral bone in osteoarthritis. Strength was increased in osteoarthritis compared to non-diseased tissue only in trabeculae subjacent to the bone plate. Compositional analysis confirmed mineralisation as a key determinant of tissue mechanical properties. This integration of micromechanical and compositional analyses sheds light on tissue properties and how these are affected by osteoarthritis in subchondral bone.

bioengineering↗

bioRxiv2022

The elasto-plastic nano- and microscale compressive behaviour of rehydrated mineralised collagen fibres

The multiscale architectural design of bio-based nanostructured materials such as bone enables them to combine unique structure-mechanical properties that surpass classical engineering materials. In biological tissues, water as one of the main components plays an important role in the mechanical interplay, but its influence has not been quantified at the length scale of a mineralised collagen fibre. Here, we combine in situ experiments and a statistical constitutive model to identify the elasto-plastic micro- and nanomechanical fibre behaviour under rehydrated conditions. Micropillar compression and simultaneous synchrotron small angle X-ray scattering (SAXS) and X-ray diffraction (XRD) were used to quantify the interplay between fibre, mineralised collagen fibrils and mineral nanocrystals. Rehydration led to a 65% to 75% decrease of fibre yield stress and compressive strength, and a 70% decrease of stiffness with a 3x higher effect on stress than strain values. While in good agreement with bone extracellular matrix, the decrease is 1.5-3x higher compared to micro-indentation and macro-compression. Hydration has a higher influence on mineral than fibril strain while the highest difference to the macroscale was observed comparing mineral and tissue levels. Results suggest that the effect of hydration is strongly mediated by ultrastructural interfaces while corroborating the previously reported water-mediated structuring of bone apatite providing insights towards the mechanical consequences. Results show that the missing reinforcing capacity of surrounding tissue is more pronounced in wet than dry conditions when testing an excised array of fibrils, mainly related to the swelling of fibrils in the matrix. Differences leading to higher compressive strength between mineralised tissues do not seem to depend on the rehydration state while fibril mobilisation follows a similar regime in wet and dry conditions. The lack of kink bands point towards the role of water as an elastic embedding, thus, adapting the way energy is absorbed. Statement of significanceCharacterising structure-property-function relationships of biomaterials helps us to elucidate the underlying mechanisms that enables the unique properties of these architectured materials. Experimental and computational methods can advance our understanding towards their complex behaviour providing invaluable insights towards bio-inspired material development. In our study, we present a novel method for biomaterials characterisation. We close a gap of knowledge at the micro- and nanometre length scale by combining synchrotron experiments and a statistical model to describe the behaviour of a rehydrated single mineralised collagen fibre. Results suggest a high influence of hydration on structural interfaces, and the role of water as an elastic embedding. Using a statistical model, we are able to deduce the differences in wet and dry elasto-plastic properties of fibrils and fibres close to their natural hydration state.

bioengineering↗