Multiscale Mechanical Properties of Bone Extracellular Matrix

Swiss Federal Excellence Postdoc Fellowship
Bone is a hierarchically structured bio-composite composed of mineralised collagen fibrils embedded in an extrafibrillar matrix and exhibits various toughening mechanisms from the nano- to the macroscale. This work enriched a former 3D unit-cell finite element model of a mineralised fibril array with cohesive interactions and plasticity, to reproduce the anisotropic post-yield behaviour measured previously in micropillar compression and micro tensile tests.

HR-pQCT based homogenized FEA of multiple sections of the distal radius and tibia

with IS and MGU.
High-resolution peripheral computed tomography (HR-pQCT)-based hFEA of distal radius and tibia becomes an effective method to assess in vivo bone strength. A multi-stack measurement protocol (Fig. 3) was initiated at the University Hospital in Bern and future patients might benefit from this method to detect the progression of bone diseases such as osteoporosis. A cross-sectional clinical study with the University of Basel exploiting this protocol suggested that bone strength at the tibia but not at the radius was significantly reduced in long-standing type I diabetes patients with neuropathy compared to controls after adjustment for age, gender, and BMI. From the methodological point of view, a unified image processing, calibration procedure and hFEA modeling pipeline was integrated and successfully validated with ex vivo mechanical compression tests of both distal radii and tibiae. In longitudinal studies, for instance for evaluation of pharmacological treatment, potential misalignments during scanning may lead to falsified comparisons of bone strength. Accordingly, the unified hFEA pipeline is currently extended with a 3D-registration approach to compensate for these errors.

Double stack and triple stack HR-pQCT scanning protocols in the radius (A, left) and tibia (B, right).

Fracture Risk Estimation of Vertebral Bodies with Metastatic Lesions

with IS.
Vertebral compression fractures (VCF) are a major clinical concern in the management of cancer patients with metastatic spine disease. The aim of this project is to estimate the strength of affected vertebral bodies using quantitative computed tomography (QCT)-based finite element analysis (FEA). As a first step, a reference database of QCT reconstructions of healthy spines acquired at the institute of forensic medicine is established.

Atlas of the Hip and Spine

with IS.
A large dataset of whole-body postmortem CT images containing a calibration phantom (Fig. 3) was used to create atlases of the proximal femur and thora-columbar spine. The first project looked at the evolution of BMD distribution and cortical thickness in the proximal femur with age and BMI. In the second project, the bone strength of ageing thora-columbar vertebral bodies was computed using homogenised finite element analysis.