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 homogenisation 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 homogenisation yielded particles within a submicron range (150–200 nm). Produced nano-suspensions formed significantly thinner films (p < 0.01), at lower plasticiser concentrations, than films cast from micro-suspensions (differences in thickness up to 100 µm); 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 plasticisation. 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 plasticiser.
Highlights
The rationale behind coating of oral tablets is multifaceted, yet may be encompassed under two categories, functional and aesthetic
Nano-suspension based products have been often employed in coating (e.g. Eudragit L30- D55 and Aquacoat ECD), they are either dependent upon the use of copious quantities of alkalinising agen, which partially dissolve the enteric polymers in their suspensions, or organic solvents used in their manufacture (Carlin and Li 2008; Skalsky and Petereit 2013)
The ability of the homogenisation process to generate nano-suspensions may be attributed to the brittle nature of the methacrylate polymer i.e. their associated high Glass transition temperature (Tg) values, which allows for the polymer to withstand the high temperature inside the homogeniser unit (>150 C)
Summary
The rationale behind coating of oral tablets is multifaceted, yet may be encompassed under two categories, functional and aesthetic. Differences in uniformity can be attributed to the mechanism of film formation i.e. polymer-dispersed as particles in aqueous solvents, as opposed to dissolved in organic solvents. Nano-suspension based products have been often employed in coating (e.g. Eudragit L30- D55 and Aquacoat ECD), they are either dependent upon the use of copious quantities of alkalinising agen, which partially dissolve the enteric polymers in their suspensions, or organic solvents used in their manufacture (Carlin and Li 2008; Skalsky and Petereit 2013). The impact of reducing particle size to the nano-scale on film formation and resultant film properties for the methacrylate polymer; Eudragit S100 has been investigated This polymer is commercially used in the oral tablet products targeting ileocaecal site e.g. Asacol and Mezavant (EMC 2021a, 2021b)
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