Surface‐Triggered In Situ Gelation for Tunable Conformal Hydrogel Coating of Therapeutic Cells and Biomedical Devices

Abstract Hydrogel coatings have been proposed as a promising strategy to improve the biocompatibility of therapeutic cells and biomedical devices. However, developed coating methods are only applicable for simple geometries, typical sizes, and limited substrates. In addition, its applications in therapeutic cell encapsulation are hampered by inadequate construction of the hydrogel capsules such as off‐center encapsulation, immense volume, and lack of control over the thickness of capsules. Here, a method called surface‐triggered in situ gelation (STIG) for universal hydrogel coating of multiscale objects ranging from single cells to mini‐organs to biomedical devices with arbitrary shapes and heterogeneous components is reported. By covering cells or devices with calcium carbonate particles, progressive propagation of alginate hydrogel from their surface under the stimulation of GDL is achieved. The thickness of the hydrogel layers can be easily controlled from several micrometers to hundreds of micrometers by adjusting the gelation time and the release rate of calcium ions. Importantly, STIG facilitates accurate, complete, and individual cell encapsulation, which potentially overcomes the pitfalls of conventional strategies. It is further proven that the low‐cost and facile method can potentially lead to advances in different fields by rendering precisely controlled microscale alginate layers on a wide variety of biomedical substrates.