Recently, self-consistent continuum micromechanics formulations have turned out as particularly effcient and reliable tools to predict (poro-)elasticity and brittle strength of many natural and man-made materials characterized by textured microstructures. Thereby, materials are envisioned as porous polycrystals consisting of an infinite number of non-spherical crystal phases, interacting with a spherical pore phase. In case of hydrated polycrystals, sliding events along very thin (liquid crystalline) water layers forming interfaces between or within the single crystal phases entail ideal plastic behavior of crystals (or clusters thereof). Its occurrence in the extrafibrillar space of bone ultrastructure, together with brittle rupture of collagen, could well explain the strength of different bone samples from different species, ages, and anatomical locations. This explanation, however, required major micromechanical developments, which we refine and extend in the present contribution: The sliding-related elastic-perfectly plastic constitutive law is elaborated for a non-associated Mohr-Coulomb plasticity. Upscaling this elastoplastic behavior from the single crystal to the polycrystal scale is achieved through derivation of concentration and in uence tensors for eigenstressed microheterogeneous materials, which itself is a generalization of the well-known transformation field analysis. The resulting multiscale-multisurface elastoplasticity problema is solved through a new variant of the algorithmic strategy of return-mapping. Then, we consider uids as a source of plastic sliding events of hydrated polycrystals in (bio-)materials, comprising heterogeneous microstructures and uid-filled interfaces at small length scales. By bridging liquid crystal physics with continuum micromechanics, homogenization schemes for eigenstressed heterogeneous materials specialized for the limit case of at interfaces are used to upscale this interface behavior to the much larger composite comprising an isotropic, linear elastic solid matrix of hydroxyapatite, as well as interacting parallel interfaces representing the entity of all uids in a so-called \liquid crystal" state. Next, application examples underpin the relevance of continuum micromechanics tools in medical practice. Herein, chemical information is extracted from Computed Tomographic (CT) data, and converted, via micromechanics laws, into object-speciffic, inhomogeneous and anisotropic material properties. Such CT-tomicromechanics approaches provide a basis for Finite Element Models, and pave the way to patient-speciffic, medical image-based bone fracture risk assessment. Finally, motivated by the success in adapting the polycrystal morphology for 3D (spatial) networks of solid crystal needles, the development of a similar theoretical concept for planar wood fiber networks is tackled. The model is confirmed by various experimental data and deemed as a new support tool in the design of paper production processes.