Bone Scaffolds Based on Degradable Vaterite/PEG‐Composite Microgels

Vaterite, a metastable modification of calcium carbonate, embedded in a flexible microgel packaging with adjustable mechanical properties, functionality, and biocompatibility, provides a powerful scaffolding for bone tissue regeneration, as it is easily convertible to bone‐like hydroxyapatite (HA). In this study, the synthesis and physical analysis of a packaging material to encapsulate vaterite particles and osteoblast cells into monodisperse, sub‐millimeter‐sized microgels, is described whereby a systematic approach is used to tailor the microgel properties. The size and shape of the microgels is controlled via droplet‐based microfluidics. Key requirements for the polymer system, such as absence of cytotoxicity as well as biocompatibility and biodegradability, are accomplished with functionalized poly(ethylene glycol) (PEG), which reacts in a cytocompatible thiol–ene Michael addition. On a mesoscopic level, the microgel stiffness and gelation times are adjusted to obtain high cellular viabilities. The co‐encapsulation of living cells provides i) an in vitro platform for the study of cellular metabolic processes which can be applied to bone formation and ii) an in vitro foundation for novel tissue‐regenerative therapies. Finally, the degradability of the microgels at physiological conditions caused by hydrolysis‐sensitive ester groups in the polymer network is examined

Rational Design of Thermoresponsive Microgel Templates with Polydopamine Surface Coating for Microtissue Applications

Functional microgels provide a versatile basis for synthetic in vitro platforms as alternatives to animal experiments. The tuning of the physical, chemical, and biological properties of synthetic microgels can be achieved by blending suitable polymers and formulating them such to reflect the heterogenous and complex nature of biological tissues. Based on this premise, this paper introduces the development of volume-switchable core–shell microgels as 3D templates to enable cell growth for microtissue applications, using a systematic approach to tune the microgel properties based on a deep conceptual and practical understanding. Microscopic microgel design, such as the tailoring of the microgel size and spherical shape, is achieved by droplet-based microfluidics, while on a nanoscopic scale, a thermoresponsive polymer basis, poly(N-isopropylacrylamide) (PNIPAAm), is used to provide the microgel volume switchability. Since PNIPAAm has only limited cell-growth promoting properties, the cell adhesion on the microgel is further improved by surface modification with polydopamine, which only slightly affects the microgel properties, thereby simplifying the system. To further tune the microgel thermoresponsiveness, different amounts of N-hydroxyethylacrylamide are incorporated into the PNIPAAm network. In a final step, cell growth on the microgel surface is investigated, both at a single microgel platform and in spheroidal cell structures