Multiscale structure-functional modeling of musculoskeletal mineralized tissues

• Applicants: Dr. Alf Gerisch; Professor Dr. Kay Raum
• Subject Area: Biomaterials ; Biophysics ; Mathematics ; Theoretical Chemistry: Molecules, Materials, Surfaces
• Term: from 2009 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 127651561

Musculoskeletal mineralized tissues (MMTs) are examples of natural materials achieving unique combinations of stiffness and strength. MMTs are able to adapt to different functional demands by different structural arrangements of one common building block, the mineralized collagen fibril, at several levels of hierarchical organization. This project combines multi-scale and multi-modal experimental assessment of tissue properties with numerical modeling and homogenization approaches from the nanoscale to the macroscale to describe the tissue elastic behavior of various MMTs. This bottom-up approach allows the decoupling of tissue composition, structure, and material properties at various spatial scales and hence the systematic evaluation of their relative impacts on the macroscopic elastic function. In the previous funding periods, experimental data of heterogeneous elastic and structural parameters of MMTs at several length scales (from the nanometer to the centimeter scale) have been assessed systematically with respect to tissue type, anatomical location, and ageing in human and ovine cortical bone samples. This led to the discovery of new plywood arrangements in lamellar bone. Moreover, a survey of mineralized turkey leg tendons (MTLT) has been the basis for the development of a hierarchical model of uni-axially aligned mineralized collagen fibril composites. Based on the experimental data of MTLT we have established an improved and validated a numerical homogenization model for the analysis of unidirectional hierarchical composites. A global sensitivity analysis identified the most important parameters in this model. However, an additional stiffening mechanism in old tissue has been observed that cannot be explained by established mean-field homogenization methods. Finally, new insights into the interplay of structure and functional adaptation at the macroscale have been observed by the implementation of micro- and mesoscale data into a macroscopic Finite-Element based musculoskeletal loading model.Two major findings revealed during the first two funding periods define our future research hypotheses. First, an interlocking of mineral crystals in old bone tissue leads to a stiffening mechanism that is not apparent in conventional indentation testing and cannot be explained by the reinforcement of the organic matrix by mineral crystals, as modeled by mean field homogenization methods. Second, the new orientation patterns revealed by novel high-fidelity imaging techniques (X-ray phase nanotomography, polarized Raman) in lamellar bone will be systematically investigated and implemented into our models to unravel their impact on the mechanical function. Moreover, a network of collaborations with partners of the SPP1420, but also with external groups working in the field of biomimetic research could be established and the initiated joint projects on biological and artificial hierarchical mineralized compounds will be continued.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1420: Biomimetic Materials Research: Functionality by Hierarchical Structuring of Materials
• International Connection: France, Sweden
• Participating Persons: Professor Dr. Quentin Grimal; Professorin Hanna Isaksson, Ph.D.; Professor Dr. Jens Lang; Privatdozentin Francoise Peyrin, Ph.D.