Kapok cellulose hydrogels for dermal applications: mechanistic insights into the interplay of cellulose loading and alkali solvent composition

Abstract Cellulose hydrogels offer a promising platform for dermal drug delivery by forming drug reservoirs on the skin. Despite the abundance and cost-effectiveness of kapok fibres, this non-woody biomass remains largely unexplored for advanced biomaterials. This study explores the influence of kapok cellulose content and alkali solvent composition on cellulose solubilisation, hydrogel properties and dermal drug delivery potential. Kapok cellulose (1—3% w/v) was solubilised in alkali solvents containing sodium hydroxide (NaOH) (6—8% w/v) and urea (2—6% w/v) before crosslinking with epichlorohydrin to form hydrogels for characterisation. In vitro skin permeation studies were conducted using hydrogels incorporated with niacinamide solution and hydrogel cytotoxicity was tested. The solubility of cellulose remained relatively unchanged for 1% w/v of cellulose (76—92%) but enhanced with higher solvent content (12—74%) for 2 and 3% w/v cellulose. Hydrogels exhibited increased erosion, swelling and porosity at higher NaOH contents. Yet, this effect was comparatively smaller for hydrogels with higher cellulose loadings due to a denser network structure. The chosen hydrogels are non-cytotoxic and successfully delivered 11—25 µg/cm 2 of niacinamide permeation into the skin in 8 h, demonstrating higher delivery efficiency compared with certain reported solvent-based systems. The current study provides insights into the roles of cellulose and alkali solvent contents in tailoring kapok hydrogel properties for dermal drug delivery and beyond. Graphic abstract