Conversion of Flat to Cylindrical Hydrogel Structures by Asymmetric Crosslinking and Ionic Exchange

The similarity of hydrogels with human soft tissues serves a two-fold purpose: they are convenient, humane tissue substitutes for biomedical testing, while they are also a reliable platform for the development of biocompatible implantable devices and organoids. However, these assets come with challenges with reproducible processing of stable hollow structures that are common transducers of liquids in living organisms, from twodimensional polymeric precursors. Here, we describe a protocol for film-to-tube transformation that is devoid of templates, catalysts, 3D printing, heating, and light, and can be used to prepare hollow hydrogel structures. The resulting hydrogel tubes have tensile strength of up to 45 MPa, turning these materials into the most robust hydrogel materials reported to date. The flexibility and elasticity favor the resulting hydrogel tubes for catheterization of artificial intestinal demonstrating the potential for medical applications. The approach can be applied to prepare structure/function-mimetic organoids such as branched blood vessels and nephrons with higher resolution than additive manufacturing. Then hollow structures are degradable in alkaline solution, and the solution can be recycled to recover the tubular structures. The convenience of the approach described overcomes some of the most challenging aspects of preparation of hollow hydrogel elements.