Hydrogel microspheres, beads, and capsules of uniform size, differing in their chem. compn., have been prepd. by electrostatic complex formation of sodium alginate with divalent cations and polycations. These have served as model spheres to study the influence of the chem. compn. on both surface characteristics and bulk mech. properties. Resistance to compression expts. yielding the compression work clearly identified differences as a function of the compn., with forces at maximal compression in the range of 34-455 mN. The suitability and informative value of at. force microscopy have been confirmed for the case where surface characterization is performed in a liq. environment equiv. to physiol. conditions. Surface imaging and mech. response to indentation revealed different av. surface roughness and Young's moduli for all hydrogel types ranging from 0.9 to 14.4 nm and from 0.4 to 440 kPa, resp. The hydrogels exhibited pure elastic behavior. Despite a relatively high std. deviation, resulting from both surface and batch heterogeneity, nonoverlapping ranges of Young's moduli were reproducibly identified for the selected model spheres. The findings indicate the reliability of contact mode at. force microscopy to quantify local surface properties, which may have an impact on the biocompatibility of alginate-based hydrogel materials of different compn. and conditions of prepn. Moreover, it seems that local elastic properties and bulk mech. characteristics are subject to analogous compn. influences. [on SciFinder (R)]