Background: Chitosan (CS) crosslinked with genipin (GNP) provides a mild, non-toxic route to generate nanogels (NGs) with enhanced integrity and colloidal stability. Objectives: To develop and characterise CS-GNP NG as a novel platform for targeted cellular delivery, optimising design through physicochemical characterisation and biocompatibility evaluation. Methods: NGs were synthesised under optimised conditions by adjusting the pH of the CS solution, followed by high-intensity ultrasound (HIUS) to achieve disaggregation. Physicochemical characterisation was carried out using UV-Vis spectroscopy, FTIR, dynamic light scattering (DLS), and scanning electron microscopy (SEM). Rheological studies and SAXS analysis assessed structural properties. Biocompatibility was evaluated via MTT assay, and internalisation was monitored by fluorescence microscopy on mammalian cell lines. Results: NG formation was highly pH-dependent, with optimal configuration at pH 4.5, yielding stable, uniformly sized particles (~200 nm, ζ-potential +29 mV). Kinetic modelling showed a sigmoidal formation pattern, suggesting nucleation, growth, and stabilisation. FTIR confirmed covalent bonding between CS and GNP via primary amide bonds and Schiff bases. Rheology indicated pseudoplastic behaviour, and SAXS revealed a compact network formation. Biocompatibility assays confirmed non-cytotoxicity below 100 µg/mL and efficient cellular uptake. Conclusions: This study presents a rapid, reproducible protocol for generating colloidally stable, biocompatible NGs suitable for drug delivery.

Background/Objectives: Magnetically responsive biomaterials have emerged as promising platforms for tissue engineering as they allow remote stimulation of cells and improved control over tissue regeneration. Although gelatin–alginate hydrogels incorporating iron oxide nanoparticles have been reported, the use of U-type hexaferrite particles, particularly Al³⁺-substituted compositions, remains largely unexplored. This study aimed to develop and characterize extrusion-based 3D-printed gelatin–alginate scaffolds containing U-type hexaferrite particles and to evaluate the influence of particle composition and loading on the rheological, physicochemical and magnetic properties of the resulting biomaterials, as well as their in vitro compatibility with macrophages. Methods: Gelatin–alginate inks containing two U-type hexaferrite compositions (Ba₄Co₂Fe₃₆−_xAl_xO₆₀; x = 0.0 and x = 1.0) at two particle loadings (20 and 200 mg) were prepared and processed by extrusion-based 3D printing. The scaffolds were characterized by rheological analysis, SEM-EDS, FTIR, swelling measurements, magnetic responsiveness, and in vitro biological evaluation using RAW264.7 macrophages. Results: The inks exhibited suitable shear-thinning behavior and viscoelastic properties for extrusion-based printing. Increasing particle loading enhanced the thermal resistance of the network, whereas Al³⁺ substitution modified the viscoelastic response of the polymeric network. The 3D scaffolds successfully responded to an external magnetic field and SEM-EDS confirmed the homogeneous incorporation of hexaferrite particles. The magnetic scaffolds did not compromise macrophage metabolic activity. Conclusions: U-type hexaferrite particles provide an effective strategy for producing 3D-printed magnetically responsive scaffolds with tunable rheological properties without inducing an inflammatory response. The combined modulation of particle composition and loading represents a versatile approach for designing multifunctional inks with potential applications in tissue engineering.