Soft Gel-Based Transformative Structured Engineering Design

Soft gels, a category of soft materials, consist of polymer networks with small molecules, such as water or other solvents. They possess mechanical flexibility and softness along with tunable physical and chemical functionalities. These gels are capable of responding to external stimuli, such as temperature, pH, light, and electric and magnetic fields, making them highly suitable for applications in drug delivery, tissue engineering, sensors, and soft robotics. As many advantages as soft gels have, there are many more mechanisms to be understood to bridge clear structure-function relationships. There is also a continuous need to facilitate these new functionalities into the device or product technologies. In this Account, we aim to provide an overview of recent progress in functional soft gels with a focus on structural design and innovative fabrication techniques. We start with exploring how structural design can impart diverse functionalities to soft gels. This is followed by a discussion of mechanics with an emphasis on elastic instabilities that are deliberately introduced and controlled to achieve shape morphing. The multilength scale instabilities will be linked with local to global surface deformation and/or macroscopic deformation of gel objects. We then examine how chemical modificationsespecially cross-linking and network formationcontribute to the architecture and functionality of soft gels. These chemical modifications have been harnessed to enrich the designability of the gel to enable extra function or provide dedicated controllability. Manufacturing techniques also play a vital role in establishing structural varieties that enable programmable responses to external stimuli for specific applications. We offer a quick scan on the frontier technologies on fabricating soft gel-based devices with an alignment to the advanced manufacturing trend with novelty structural design. Finally, the applications of functional soft gels were selectively scoped in areas such as sensing, energy and sustainable materials, and biomedical devices. They are well-suited for both diagnostic and therapeutic functions. All the above applications will be enabled by the novel structural design with realization of unique structure-property relationships. Designed structures can be programmed to exhibit specific mechanical behaviors, which, in turn, enable responsive and functional soft gels. Importantly, when a stimulus activates the designated trigger points, the engineered structure responds in the manner that we designed. This interplay within the gel ultimately manifests as a controllable response, highlighting how transformative structural engineering serves as the foundation for achieving multifunctionality. We conclude by highlighting the current challenges and future directions in the development of high-performance functional soft gels through structure-based design.