Wet, soft, squishy, and tunable: Hydrogels are highly cross-linked polymer networks that are heavily swollen with water. Hydrogels have been used as dynamic, tunable, degradable materials for growing cells and tissues. Zhang and Khademhosseini review the advances in making hydrogels with improved mechanical strength and greater flexibility for use in a wide range of applications. Science , this issue p. eaaf3627

Bioprinting is an emerging technology with various applications in making functional tissue constructs to replace injured or diseased tissues. In all bioprinting strategies, the bioinks are an essential component. We provide an in-depth discussion of the different bioinks currently employed for bioprinting, and outline some future perspectives in their further development.

Significance: Monitoring human organ-on-a-chip systems presents a significant challenge, where the capability of in situ continual monitoring of organ behaviors and their responses to pharmaceutical compounds over extended periods of time is critical in understanding the dynamics of drug effects and therefore accurate prediction of human organ reactions. In this work, we report a fully integrated modular physical, biochemical, and optical sensing platform, interfaced through a fluidics-routing breadboard with a multi–organ-on-a-chip system to achieve in situ, continual, and automated sensing of microenvironment biophysical and biochemical parameters. It is anticipated that our platform technology that is conveniently compatible with existing organ-on-a-chip models will potentially enhance their performance in drug screening by providing a multitude of sensing data not previously available.