Impact of Nanosizing on the Formation and Characteristics of Polymethacrylate Films: Micro- versus Nano- suspensions

Abstract

Aqueous based film coating suspensions are associated with reliance on alkalinising reagents and poor film formation. The impact of particle size in this process and resultant film properties remains unclear. This study offers the first direct comparison of film formation properties between aqueous micro- and nano-suspensions of the enteric polymer Eudragit S100. High pressure homogenization was employed to produce nano-suspensions of the enteric polymer. Formed enteric suspensions (micro- and nano-) were evaluated in terms of size, morphology and ability to form film; with resultant films analysed in terms of; film thickness, mechanical and thermoplastic properties, water uptake, weight loss and drug permeability in acidic medium. High pressure homogenization yielded particles within a submicron range (150-200nm). Produced nano-suspensions formed significantly thinner films (p < 0.01), at lower plasticizer concentrations, than films cast from micro-suspensions (differences in thickness up to 100µm); however, exhibited comparative gastro-resistant properties (p > 0.05) in terms of water uptake (∼25% w/w), weight loss (<16% w/w) and drug permeability (<0.1%). Interestingly, nano-suspension based films exhibited lower glass transition temperatures (Tg) (p < 0.01), when compared to films cast from micro-suspensions (∼7-20 °C difference), indicating enhanced plasticization. This was reflected in film mechanical properties; where nano-suspension based films demonstrated significantly lower tensile strength (p < 0.01) and higher percentage elongation (p < 0.05), suggesting high elasticity. Thinner, highly elastic films were formed from nano- suspensions, compared to films cast from micro-suspensions, exhibiting comparative properties; obviating the need for alkalinising agents and high concentrations of plasticizer.