Gellan gum-montmorillonite nanocomposite films as tablet coatings for sustained-release drug delivery: simultaneous burst suppression and extended release duration

Controlling the early burst and the later diffusion phase at the same time, and with a single coating layer, is a persistent difficulty in oral sustained-release design. Here we examined gellan gum (GG) films loaded with montmorillonite (MMT) as such a coating. Films were cast at four MMT levels (0-2.0% w/w relative to GG) and characterized, and propranolol HCl tablets were then coated to 3% or 5% weight gain and tested sequentially in 0.1 M HCl and PBS (pH 6.8). FTIR showed shifts in the OH and Si-OH regions consistent with hydrogen bonding between GG and the clay, and XRD showed that the MMT basal spacing was retained near 12 Å rather than expanding-evidence that the clay sits at the GG surface rather than intercalating, while crystallinity rose from 19.1% to 63.1%. Mechanically, puncture strength increased 11.2-fold with MMT. In permeability testing the films slowed drug transport in an MMT-dependent way, lowering the apparent permeability coefficient of propranolol by 87%. On coated tablets, lower burst was tied to longer release: across the formulation set, Q₅ burst and T₅₀ were strongly and inversely correlated (Spearman ρ = -0.967, p < 0.0001). Burst fell from 4.6% to 0.5% (an 89% reduction) and T50 lengthened from 92.3 to 316.6 min (a 243% increase). GG-MMT films therefore offer a simple, composition-tunable route to sustained-release coatings in which burst suppression and release prolongation are achieved together.