Zinc (Zn) shows great potential for biomedical applications due to its unique biodegradability and bi-ocompatibility properties. Although Zn suffers from low mechanical strength and brittleness, pro-gress has been made in recent years in the development of high-strength Zn alloys. The strengthen-ing effect typically depends on the grain size, texture, boundary types, solute elements, or intermetal-lic phases in the material's microstructure. Zn, due to a high c/a ratio of its HCP lattice, exhibits strong anisotropy of mechanical properties, which depends on the initial texture and critical resolved shear stresses (CRSS) of specific deformation modes.

The main goal of this work was to gain insights into the effect of size and crystallographic orientation on the deformation mechanisms and strengthening in Zn micropillars. Many micropillar compression studies follow the principle of "smaller is stronger", meaning that the decrease in specimen size en-tails strain hardening and flow stress increases. Thus, the interplay between micropillar diameter and intrinsic grain size was investigated to understand the strengthening effects at a small-length scale. Single-crystalline and fine-grained Zn micropillars were prepared from annealed and electrodeposited states via FIB milling. EBSD was used for basal- and prismatic slip-oriented grain selection in the an-nealed sample and grain characterisation in the electrodeposited sample. Single slip system activation was predicted based on Schmid Factor calculations, further used for CRSS evaluation. Compression tests conducted using an in situ SEM nanoindentation system showed that the deformation behav-iour depends on the type of slip system, while yield stress and strain hardening depend on the mi-cropillar size. Post-mortem SEM-EBSD and slip trace analysis indicated only basal or prismatic slip ac-tivation in single-crystalline micropillars. A clear effect of intrinsic grain size on the fine-grained mi-cropillar's mechanical response was observed.

Overall, the results are a basis for simulating the mechanical behaviour of currently developed 3D-architected Zn metamaterial structures. Additionally, the calculated CRSS can serve as input data for predicting the mechanical properties and plastic deformation of bioresorbable Zn implant materials.