A design framework for in situ-forming medical devices: From drug delivery to tissue regeneration and bioelectronics

In situ -forming (ISF) medical devices are delivered as flowable precursors that assemble into macroscopic, tissue-conformal devices at the target site, enabling minimally invasive implantation. While historically limited to structural or passive roles, next-generation ISF systems must be engineered for multifunctional performance to enable expanded clinical utility. This review presents a design framework in which the device's structure and functionality are governed by precursor composition, phase-transformation mechanism, and transformation stimulus. We examine how this framework guides the development of functional devices across three key domains: drug delivery, tissue regeneration, and bioelectronics. For each, we define critical performance requirements and highlight recent advances addressing these challenges. We conclude with translational considerations and future priorities, including improved geometric control and integration of materials with advanced functionalities, to realize robust, multifunctional ISF systems. By linking materials design to application-specific device performance, this review outlines a path toward next-generation ISF medical technologies.