Microparticles-in-Thermoresponsive/Bioadhesive Hydrogels as a Novel Integrated Platform for Effective Intra-articular Delivery of Triamcinolone Acetonide

Intra-articular (IA) injection of thermoresponsive hydrogels coupled with microparticles (MPs) possess the benefit of sustaining the anti-inflammatory drug effect within the joint cavity for rheumatoid arthritis treatment. Star-shaped thennoresponsive poly(polyethylene glycol) methacrylate [Poly(PEGMA)] copolymers were synthesized using free radical polymerization technique and fully characterized. Triamcinolone acetonide (TA)-loaded PLA/mPEG-PDL MPs, previously optimized, were integrated into the synthesized copolymer solutions at various concentrations and tested for their gelation temperatures. The MPs-in-hydrogel formulations were characterized using scanning electron microscope (SEM), viscosity measurements, ex vivo bioadhesion, and in vitro release studies. The anti-inflammatory effect of integrated systems was assessed in adjuvant-induced monoarthritic rat knee joints and compared to Kenacort and TA-loaded MPs. Two copolymers were successfully synthesized; G-1 = poly(PEGMA(188)-ME-co-PEGMA(475)-ME) and G-2 = poly(PEGMA(246)-EE-co-PEGMA(475)-ME). Using the tube inversion technique, the gel formation was found dependent on copolymer concentration. An irreversible aggregation was obtained at copolymer concentrations <= 10% (w/v), while a gel was formed at 20 and 30% (w/v) of both copolymers upon increasing temperature. The MP-hydrogel formulations were optimized at 20 and 30% (w/v) of G-1 and G-2 with gelation temperatures of 33 and 37 degrees C, respectively. SEM images revealed the porous microstructures of hydrogels and their adsorption on MP surfaces. The integrated formulas showed pseudoplastic behaviors, while the bioadhesion study confirmed their bioadhesiveness on excised cartilage. The in vitro release study confirmed drug sustainment from MPs-hydrogels compared to MPs. In vivo studies proved the superiority of MP-in-hydrogels in treatment of induced arthritis, relative to Kenacort and MPs alone, suggesting the applicability of this integrated platform in IA drug delivery.