Hydrogels have emerged as versatile platforms for controlled and sustained drug delivery due to their high biocompatibility, tunable mechanical properties, and ability to mimic the natural extracellular matrix. Incorporating functional nanomaterials into hydrogel networks introduces additional structural and functional complexity, enabling stimuli-responsive release, enhanced bioactivity, and synergistic therapeutic effects. This review provides a comprehensive overview of recent advances in the design, fabrication, and characterization of nanomaterial-integrated hydrogels for biomedical applications. Emphasis is placed on nanoparticle synthesis, functionalization strategies, incorporation into hydrogel matrices, physicochemical characterization, and biological aspects, including cytotoxicity, genotoxicity, antioxidative, and antibacterial effects. Emerging approaches for performance optimization, such as preliminary data-driven strategies and machine learning-based modeling, are also discussed. Special attention is given to smart and stimuli-responsive hydrogels and their potential biomedical applications.

Background/Objectives: Chromium (III) oxide nanoparticles possess unique chemical properties, making them increasingly valuable in pharmaceutical applications, which had been neglected until the last few years. However, their use requires stable dispersion and surface functionalization to ensure their biocompatibility. This study aimed to synthesise, characterise, and determine the biocompatibility and antioxidant properties of chromium oxide nanoparticles coated with a natural, plant-derived stabilising agent: chia seed mucilage extract. Methods: The synthesised nanoparticles were characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared (FTIR) spectroscopy, and laser diffraction scattering particle size analysis (LD-PSA). Biological and biochemical assessments were conducted by the DPPH and FRAP assays to quantify antioxidant scavenging abilities and the Artemia salina lethality test for preliminary biocompatibility evaluation. Results: XRD, FTIR, and EDS confirmed the successful synthesis of pure chromium oxide NPs (CrNPs) and their effective coating by the chia mucilage (CM) extract. SEM analysis determined that a 4:1 mass ratio (CrNPs to CM) produced the most consistent morphology and narrowest size distribution, yielding spherical particles approximately 50 nm in diameter. LD-PSA confirmed the coating and identified a hydrodynamic diameter of approximately 0.110 µm. Biological and biochemical assays showed high antioxidant activity, with over 80% free radical scavenging at concentrations of 250 μg/mL and 50 μg/mL. Furthermore, the biocompatibility assessment showed survival rates above 90% across all tested concentrations. Conclusions: The findings confirm that chia seed mucilage extract can serve as an effective, biocompatible coating agent for chromium (III) oxide nanoparticles. The resulting functionalized particles exhibit exquisite biocompatibility and significant antioxidant potential, supporting their further development for pharmaceutical use.