Injectable gellan gum hydrogel with PLGA-LDH microspheres for controlled alendronate release and bone regeneration

Injectable Gellan Gum-Gelatin hydrogel (GG/gelatin hydrogel) with PLGA-LDH composite microspheres (Gel-PMA) was developed for controlled alendronate (ALN) release and enhanced bone regeneration. Manganese-Zinc Layered Double Hydroxide (LDH) nanoparticles (∼142 nm) were synthesized, loaded with ALN (ALN-LDH, about 25 %), and encapsulated in poly (d,l-lactide-co-glycolide) (PLGA) microspheres (∼120 μm) via a solid-in-oil-in-water (S/O/W) double-emulsion technique. Microspheres (10 wt%) were incorporated into a GG/gelatin hydrogel and crosslinked with CaCl₂. Physicochemical and morphological analyses confirmed successful fabrication of LDH, ALN-LDH, ALN-LDH-loaded PLGA microspheres, and composite hydrogels. Mechanical testing showed that incorporating PLGA microspheres increased compressive strength from 30 to 170 kPa. Gel-PMA enabled sustained ALN release (∼95 % in 28 days), significantly improving ALN cumulative released amount (drug availability) over previous studies. Gel-PMA also exhibited excellent biocompatibility (>90 % cell viability). In vitro studies demonstrated osteogenic potential of Gel-PMA through increased ALP activity (0.0062 to 0.022 μmol/min/mg), calcium deposition (0.0125 to 0.022 μg/μl), and Alizarin Red staining over 28 days. ARS and MT assays, alongside upregulated ALP, Col I, and OCN gene expression, further confirmed osteogenic differentiation. These findings highlight Gel-PMA as a promising injectable scaffold for bone tissue engineering, offering controlled drug release, enhanced mechanical properties, and superior osteogenic potential.