Polymer Fiber–Hydrogel Hybrid Systems for Controlled Delivery of Bioactive Compounds: From Structure to Release

Polymeric fiber–hydrogel hybrids combine the structural organization and mechanical reinforcement of fibrous scaffolds with the high water content, permeability, and biological compatibility of hydrogels. However, the relationships between hybrid architecture, material properties, and bioactive-compound release remain fragmented across application-specific studies. This review examines how polymer selection, fabrication strategy, and the spatial organization of fibrous and hydrogel phases govern morphology, surface properties, swelling, degradation, mechanical stability, and molecular transport. Strategies involving hydrogel-infiltrated scaffolds, layered and core–shell constructs, injectable short-fiber composites, and additively manufactured systems are compared. Particular attention is given to loading compounds into fibers, hydrogels, separate compartments, or intermediate nanocarriers. Current evidence indicates that release behavior arises from the coupled effects of payload localization and properties, hydrogel crosslinking and swelling, fiber wettability and degradation, interfacial transport, and environmental conditions. Compartmentalized architectures can reduce initial burst release, protect labile biomolecules, and enable staged or sequential delivery. Common kinetic models are critically discussed, emphasizing that model fitting should be supported by physicochemical characterization and biological-activity assessment. Applications in wound healing, tissue regeneration, and localized therapy demonstrate the versatility of these systems. An architecture-centered design framework is proposed to guide the development of more predictable and clinically relevant delivery platforms.