Vitreous Substitutes in Vitreoretinal Surgery: From Native Vitreous Physiology to Bioengineered Experimental Replacements.

The vitreous body is not only a transparent filling material of the posterior segment; it is a soft, hydrated, and biologically active matrix that supports structural, optical, and biochemical homeostasis. Vitrectomy therefore leaves a functional deficit that current substitutes only partly address. Intraocular gases, silicone oils, and perfluorocarbon liquids remain essential surgical tools, but they mainly provide mechanical tamponade and do not reproduce native viscoelasticity, diffusion control, or protection against oxidative and inflammatory stress. This review considers vitreous replacement as a functional biomaterials challenge. We discuss native vitreous physiology, the limitations of present tamponade agents, and emerging bioengineered substitutes designed to create a more physiological intravitreal environment. Particular attention is given to hydrogel and polymer-based systems, especially hyaluronic acid-based and in situ crosslinked platforms, which are being developed to combine optical clarity, injectability, soft mechanical support, controlled degradation, and favorable tissue interaction. We also emphasize the need for standardized preclinical testing of swelling, enzymatic stability, drug diffusion, rheology, and long-term biocompatibility. Although next-generation materials may move the field beyond passive space filling, manufacturing reproducibility, regulatory validation, chronic safety, and cautious early-phase trials remain major translational barriers.