Three-dimensional (3D) hydrogel printing enables production of volumetric architectures containing desired structures using programmed automation processes. Our study reports a unique method of resolution enhancement purely relying on post-printing treatment of hydrogel constructs. By immersing a 3D-printed patterned hydrogel consisting of a hydrophilic polyionic polymer network in a solution of polyions of the opposite net charge, shrinking can rapidly occur resulting in various degrees of reduced dimensions comparing to the original pattern. This phenomenon, caused by complex coacervation and water expulsion, enables us to reduce linear dimensions of printed constructs while maintaining cytocompatible conditions in a cell type-dependent manner. We anticipate our shrinking printing technology to find widespread applications in promoting the current 3D printing capacities for generating higher-resolution hydrogel-based structures without necessarily having to involve complex hardware upgrades or other printing parameter alterations.

3D printing has emerged as an enabling approach in a variety of different fields. However, the bulk volume of printing systems limits the expansion of their applications. In this study, a portable 3D Digital Light Processing (DLP) printer is built based on a smartphone‐powered projector and a custom‐written smartphone‐operated app. Constructs with detailed surface architectures, porous features, or hollow structures, as well as sophisticated tissue analogs, are successfully printed using this platform, by utilizing commercial resins as well as a range of hydrogel‐based inks, including poly(ethylene glycol)‐diacrylate, gelatin methacryloyl, or allylated gelatin. Moreover, due to the portability of the unique DLP printer, medical implants can be fabricated for point‐of‐care usage, and cell‐laden tissues can be produced in situ, achieving a new milestone for mobile‐health technologies. Additionally, the all‐in‐one printing system described herein enables the integration of the 3D scanning smartphone app to obtain object‐derived 3D digital models for subsequent printing. Along with further developments, this portable, modular, and easy‐to‐use smartphone‐enabled DLP printer is anticipated to secure exciting opportunities for applications in resource‐limited and point‐of‐care settings not only in biomedicine but also for home and educational purposes.