Synthetic Optimization of Gelatin-Oleic Conjugate and Aqueous-Based Formation of Self-Assembled Nanoparticles without Cross-Linkers

Amphiphilically-modified gelatin has the ability to form self-assembled NPs which own hydrophobic inner core for water-insoluble drugs loading and gelatin layer for circulation extension and biocompatibility. Gelatin-oleic acid conjugates (GOC) was synthesized from oleic acid (OA) and gelatin, using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS) in 60% ethanol. The effect of various gelatin concentrations, oleic acid-gelatin molar ratio and reaction time on the substitution of GOC was evaluated. Fourier transform infrared (FT-IR) spectroscopy and proton nuclear magnetic resonance (H-1 NMR) revealed the successful synthesis of GOC. The ratio of oleic acid-reacted amino groups within gelatin was above 50% as quantified using the 2,4,6-trinitrobenzene sulfonic acid (TNBS) method. Based on the physicochemical changes of GOC upon the modification of various synthesis factors, the optimized process for the GOC synthesis was well established. Self-assembled gelatin-oleic acid nanoparticles (GON) were fabricated simply by the desolvation method using dialysis membrane, without adding a cross-linker. GON was formed at a lower critical micelle concentration (CMC) in water, 0.3 mg/mL. GON has a homogenous size of 100-300 nm, which was showed in the electrophoretic light scattering (ELS) results, scanning electron microscope (SEM) and transmission electron microscope (TEM) images. The zeta potential of GON indicated a slightly negative surface charge (-6 mV). The GON showed no toxicity in human embryonic kidney cells (HEK 293) and significantly improved coumarin loading in adenocarcinomic human alveolar basal epithelial cells (A549). The current GOC and GON could provide versatile strategies to deliver cargo into the body by acting as a safe and biocompatible nanoparticulate carrier.