Hierarchically heterogeneous materials Micro-structure-related size effects Natural bone tissue Bio-resorbable material Bone resorption and synthesis Load-induced replacement of artificial material with natural bone tissue Numerical simulationsWe propose a second gradient, two-solids, continuum mixture model with variable masses to describe the effect of micro-structure on mechanically-driven remodelling of bones grafted with bio-resorbable materials. A one-dimensional numerical simulation is addressed showing the potentialities of the proposed generalized continuum model. In particular, we show that the used second gradient model allows for the description of some micro-structure-related size effects which are known to be important in hierarchically heterogeneous materials like reconstructed bones. Moreover, the influence of the introduced second gradient parameters on the final percentages of replacement of artificial bio-material with natural bone tissue is presented and discussed.

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Linear actuation is a basic need in robotized manipulation of surgical instruments, that must comply with a challenging environment in terms of safety, compactness and now often compatibility with imaging modalities like CT or MRI. In this paper, we focus on needle manipulation for interventional radiology. We propose a needle driver, i.e. a linear actuator for needle insertion, based on the inchworm principle combined with pneumatic energy. Our first contribution is to propose, model and implement the device using a so-called auxetic structure. Its use increases achievable displacement under pressure and provides sufficient off-axis stiffness to use the actuator without additional guidance. Simplified modeling is introduced for the actuator synthesis. Our second contribution is to implement the actuator with multimaterial additive manufacturing combining rigid and flexible materials to increase compactness. As a third contribution, initial assessment of component sterilization and compatibility with X-ray and MRI imaging modalities is presented.

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A first application of a Stewart platform used as a multiaxial testing machine is presented. A specific case study is chosen, namely the so‐called Nooru‐Mohamed experiment, which is a tension‐shear test on a notched concrete specimen. The calibration, analysis of performances, and a validation test are investigated. The results confirm that the hexapod can be used to apply multiaxial loadings under small displacements, and allow also the measurement of the six components of forces and torques. Additional digital image correlation procedures are implemented at two scales of observation. Global measurements show the effect of the compliance of the device. Local measurements around the crack tip, necessary due to the small deformation of the specimen, give quantitative information about crack nucleation and propagation and will allow for future accurate numerical model validations.