Two‐Phase Emulgels for Direct Ink Writing of Skin‐Bearing Architectures

Direct ink writing (DIW) provides programmable and customizable platforms to engineer hierarchically organized constructs. However, one‐step, facile synthesis of such architectures via DIW has been challenging. This study introduces inks based on two‐phase emulgels for direct printing and in situ formation of protecting layers enveloping multicomponent cores, mimicking skin‐bearing biological systems. The emulgel consists of a Pickering emulsion with an organic, internal phase containing poly(lactic acid) stabilized by chitin/cellulose nanofibers and a continuous, cross‐linkable hydrogel containing cellulose nanofibers and any of the given solid particles. The shear during ink extrusion through nozzles of low surface energy facilitates the generation of the enveloped structures via fast and spontaneous phase separation of the emulgel. The skin‐bearing architectures enable control of mass transport as a novel configuration for cargo release. As a demonstration, a hydrophilic molecule is loaded in the hydrogel, which is released through the core and skin, enabling regulation of diffusion and permeation phenomena. This 3D‐printed functional material allows independent control of strength owing to the hierarchical construction. The new method of fabrication is proposed as a simple way to achieve protection, regulation, and sensation, taking the example of the functions of skins and cuticles, which are ubiquitous in nature.