Hydrogel design at anatomical extremes: Lessons learned from ocular and intraperitoneal applications.

Hydrogels are widely used as an effective platform for therapeutic drug delivery, wound healing and corrective vision, among other applications. Their tunability and adaptability, including the choice of natural or synthetic polymers, allow the design of hard or soft hydrogels with variable loading capacity, viscosity, and adhesiveness, tailored for diverse physiological organs and tissues. Common targeted sites include the eye, skin, and joints, whereas the peritoneal cavity remains comparatively less explored. Designing hydrogels for the eye versus the peritoneal cavity share similar challenges, such as biocompatibility, sterility, and injectability, but also distinct challenges, such as transparency, swelling percentage and volume. Although the eye and the peritoneal cavity differ markedly in their anatomy and physiology, both provide suitable environments for hydrogel application, offering an opportunity to identify design principles that extend beyond organ-specific contexts. In this review, we examine how the physiological characteristics of the eye and the peritoneal cavity influence hydrogel formulation and performance. By comparing these two contrasting environments, we also explore whether design strategies developed in one field may be relevant to the other. Finally, we discuss whether a single hydrogel design can realistically meet the requirements for applicability both in the eye and the peritoneal cavity.