Microstructure-elasticity relations for bone tissue engineering scaffolds are key to rational biomaterial design. As a contribution thereto, we here report comprehensive length measuring, weighing, and ultrasonic tests at 0.1MHz frequency, on porous baghdadite (Ca3ZrSi2O9) scaffolds. The resulting porosity-stiffness relations further confirm a formerly detected, micromechanically explained, general relationship for a great variety of different polycrystals, which also allows for estimating the zero-porosity case, i.e. Young modulus and Poisson ratio of pure (dense) baghdadite. These estimates were impressively confirmed by a physically and statistically independent nanoindentation campaign comprising some 1750 indents. Consequently, we can present a remarkably complete picture of porous baghdadite elasticity across a wide range of porosities, and, thanks to the micromechanical understanding, reaching out beyond classical elasticity, towards poroelastic properties, quantifying the effect of pore pressure on the material system behavior.

Optimizing thermal and mechanical properties of clay block masonry requires detailed knowledge on the microstructure of fired clays. We here identify the macro-and microporosity stemming from the use of three different poreforming agents (expanded polystyrene, sawdust, and paper sludge) in different concentrations. Micro-CT measurements provided access to volume, shape, and orientation of macropores, and in combination with X-ray attenuation averaging and statistical analysis, also to voxel-specific microporosities. Finally, the sum of micro-and macroporosity was compared to corresponding data gained from two statistically and physically independent methods (namely from chemical analysis in combination with weighing, and from mercury intrusion porosimetry). Satisfactory agreement of all these independently gained experimental data renders our new concept for identifying the pore spaces of fired clay as a very promising tool supporting the further optimization of clay blocks.

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While the quest for understanding and even mimicking biological tissue has propelled, over the last decades, more and more experimental activities at the micro and nanoscales, the appropriate evaluation and interpretation of respective test results has remained a formidable challenge. As a contribution to tackling this challenge, we here describe a new method for identifying, from nanoindentation, the elasticity of the undamaged extracellular bone matrix. The underlying premise is that the tested bovine bone sample is either initially damaged (i.e. exhibits micro-cracks a priori) or that such micro-cracks are actually induced by the nanoindentation process itself, or both. Then, (very many) indentations may relate to either an intact material phase (which is located sufficiently far away from micro-cracks), or to differently strongly damaged material phases. Corresponding elastic phase properties are identified from the statistical evaluation of the measured indentation moduli, through representation of their histogram as a weighted sum of Gaussian distribution functions. The resulting undamaged elastic modulus of bovine femoral extracellular bone matrix amounts to 31 GPa, a value agreeing strikingly well both with direct quasi-static modulus tests performed on SEM-FIB-produced micro-pillars (Luczynski et al., 2015), and with the predictions of a widely validated micromechanics model (Morin and Hellmich, 2014). Further confidence is gained through observing typical indentation imprints under Scanning Electron Microscopy (SEM), which actually confirms the existence of the two types of micro-cracks as described above.

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