Biology subjects

Wolfram, U.

Publications and source records attributed to Wolfram, U..

7 recordsLinked to original sources

bioRxiv2025

Crystal interface mechanics of cold-water coral skeletons

Cold-water coral (CWC) skeletons utilise aragonite crystals, which possess exceptional strength (4-6 GPa), to construct a composite skeletal framework that is significantly less strong (~0.5 GPa) yet remarkably resilient. The interfacial processes governing this transition from strong crystal to tough composite remain unclear, suggesting that the organic interfaces between crystals, rather than crystal defects, control the macroscopic mechanical behaviour. We systematise the investigation of this phenomenon by employing Molecular Dynamics simulations, which reproduce experimental elastic constants within 5%. We characterise three limiting interface compositions: dry twin aragonite boundaries, hydrated protein-mediated interfaces, and water interfaces - by applying tensile and shear loading and quantifying their mechanical competence using a three-dimensional failure criterion. Interface composition determines the mechanical hierarchy, spanning nearly an order of magnitude in strength. Dry twin boundaries provide the highest strength, reaching up to 6.5 GPa, through direct crystalline bonding. Conversely, protein-mediated interfaces exhibit the lowest strength (0.5-0.7 GPa) but demonstrate high damage tolerance. Water-mediated hydrogen-bonding networks enable this progressive failure, dissipating energy through sequential bond rupture and reformation rather than catastrophic separation. Water interfaces show thickness-dependent compliance: thin layers (<5[A] ) retain partial electrostatic coupling (>3 GPa), while thick layers allow controlled sliding (~0.8 GPa). These quantitative structure-property relationships provide transferable parameters for multiscale coral modelling, enabling researchers to bridge atomistic mechanisms with mesoscale mechanical response. The findings reveal how skeletal hierarchies integrate strength, stiffness, and energy dissipation, offering potential design princi-ples for biomimetic composites that reproduce the tunable mechanical properties of biomineralised materials. Statement of SignificanceCold-water coral skeletons are built from strong aragonite crystals but fail at much lower stresses than the crystals themselves. We used computer simulations at atomistic scale to understand why. Our study reveals that the interfaces between crystals, rather than the crystals control skeleton strength. We identified three interface types with different behaviours: crystalline twins are strongest and accommodate deformation through boundary migration, proteins with water layers are weaker but absorb energy through progressive failure, and water layers provide tunable properties depending on thickness. These findings explain how natural materials combine strong building blocks with compliant interfaces to achieve toughness. Our quantitative measurements provide design parameters for both predicting coral resilience to environmental stress and creating synthetic materials inspired by this hierarchical architecture.

bioengineering↗

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↗

bioRxiv2024

Regional Variations in Live Proportions of Southwest Pacific Cold-Water Coral Solenosmilia variabilis Reefs

Reef-building cold-water-corals (CWC) form deep-sea habitats that can create biodiversity hotspots. As live coral and dead intact framework provide disparate ecosystem services and are vulnerable to different anthropogenic stressors, it is important to quantify the proportions of each on CWC reefs. We analysed 1,160 images of Solenosmilia variabilis reefs at four sites off New Zealand (Valerie and Forde Guyots at the Louisville Seamount Chain & Ghoul and Gothic Seamounts at the Graveyard Seamount Complex) to determine the ratio of live coral to the whole reef area (termed live:reef). We found live:reef ratios are significantly different between sites at the offshore Louisville Seamount Chain and onshore Graveyard Seamount Complex. This could be driven by reef position relative to the aragonite saturation horizon (ASH) as corals in the Louisville Seamount Chain live below the ASH in colder and deeper waters than those at the Graveyard Seamount Complex, which live above the ASH. In the southwest Pacific, depth is a driver of live:reef ratios, with a larger proportion of live coral at shallow depths and dead intact framework at deeper depths. The live:reef ratios at Gothic Seamount within the Graveyard Seamount Complex remained stable between 2015 and 2020 despite significant differences in live coral, dead intact framework, and reef structure surface area. Our results indicate live:reef ratios can be used to estimate the amount of dead intact framework threatened by shoaling ASH due to ocean acidification at each site, which can help inform which sites could be protected as possible climate change refugia.

ecology↗

bioRxiv2023

QCT-based computational bone strength assessment updated with MRI derived 'hidden' microporosity

Microdamage accumulated through sustained periods of cyclic loading or single over-loading events contributes to bone fragility through a reduction in stiffness and strength. Monitoring microdamage in vivo remains unattainable by clinical imaging modalities. As such, there are no established computational methods for clinical fracture risk assessment that account for microdamage that exists in vivo at any specific timepoint. We propose a method that combines multiple clinical imaging modalities to identify an indicative surro-gate, which we term hidden porosity, that incorporates pre-existing bone microdamage in vivo. To do so, we use the third metacarpal bone of the equine athlete as an exemplary model for fatigue induced microdamage, which coalesces in the subchondral bone. N=10 metacarpals were scanned by clinical quantitative computed tomography (QCT) and mag-netic resonance imaging (MRI). We used a patch-based similarity method to quantify the signal intensity of a fluid sensitive MRI sequence in bone regions where microdamage coa-lesces. The method generated MRI-derived pseudoCT images which were then used to de-termine a pre-existing damage (Dpex) variable to quantify the proposed surrogate and which we incorporate into a nonlinear constitutive model for bone tissue. The minimum, median, and maximum detected Dpex of 0.059, 0.209, and 0.353 reduced material stiffness by 5.9%, 20.9%, and 35.3% as well as yield stress by 5.9%, 20.3%, and 35.3%. Limb-specific voxel-based finite element meshes were equipped with the updated material model. Lateral and medial condyles of each metacarpal were loaded to simulate physiological joint loading dur-ing gallop. The degree of detected Dpex correlated with a relative reduction in both condylar stiffness (p = 0.001, R2 > 0.74) and strength (p < 0.001, R2 > 0.80). Our results illustrate the complementary value of looking beyond clinical CT, which neglects the inclusion of micro-damage due to partial volume effects. As we use clinically available imaging techniques, our results may aid research beyond the equine model on fracture risk assessment in human diseases such as osteoarthritis, bone cancer, or osteoporosis.

bioengineering↗

bioRxiv2022

Towards modelling cold-water coral reef-scale crumbling: Including morphological variability in mechanical surrogate models

The structural complexity of cold-water corals is threatened by ocean acidification. Increased porosity and weakening of structurally critical parts of the reef framework may lead to rapid physical collapse on an ecosystem scale, reducing their potential for biodiversity support. We can use computational models to describe the mechanisms leading to reef-crumbling. How-ever, the implementation of such models into an efficient predictive tool that allows us to determine risk and timescales of reef collapse is missing. Here, we identified possible surrogate models to represent the branching architecture of the cold-water coral species Lophelia pertusa. For length scales greater than 13 cm, a continuum finite element mechanical approach can be used to analyse mechanical competence whereas at smaller length scales, mechanical surrogate models need to explicitly account for the statistical differences in the structure. We showed large morphological variations between L. pertusa colonies and branches, as well as dead and live skeletal structures, which need to be considered for the development of rapid monitoring tools for predicting risk of cold-water coral reefs crumbling. This will allow us to investigate timescales of changes, including the impact of exposure times to acidified waters on reef-crumbling.

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↗

bioRxiv2022

Nonlinear micro finite element models based on digital volume correlation measurements predict early microdamage in newly formed bone

Bone regeneration in critical-sized defects is a clinical challenge, with biomaterials under constant development aiming at enhancing the natural bone healing process. The delivery of bone morphogenetic proteins (BMPs) in appropriate carriers represents a promising strategy for bone defect treatment but optimisation of the spatial-temporal release is still needed for the regeneration of bone with biological, structural, and mechanical properties comparable to the native tissue. Nonlinear micro finite element (FE) models can address some of these challenges by providing a tool able to predict the biomechanical strength and microdamage onset in newly formed bone when subjected to physiological or supraphysiological loads. Yet, these models need to be validated against experimental data. In this study, experimental local displacements in newly formed bone induced by osteoinductive biomaterials subjected to in situ X-ray computed tomography compression in the apparent elastic regime and measured using digital volume correlation (DVC) were used to validate FE models. Displacement predictions from homogeneous linear FE models were highly correlated to DVC-measured local displacements, while tissue heterogeneity capturing mineralisation differences showed negligible effects. Nonlinear FE models improved the correlation and showed that tissue microdamage occurs at low apparent strains. Microdamage seemed to occur next to large cavities or in biomaterial-induced thin trabeculae, independent of the mineralisation. While localisation of plastic strain accumulation was similar, the amount of damage accumulated in these locations was slightly higher when including material heterogeneity. These results demonstrate the ability of the nonlinear FE model to capture local microdamage in newly formed bone tissue and can be exploited to improve the current understanding of healing bone and mechanical competence. This will ultimately aid the development of BMPs delivery systems for bone defect treatment able to regenerate bone with optimal biological, mechanical, and structural properties.

bioengineering↗