Zein is an insoluble, yet swellable, biopolymer that has been extensively studied for its\napplications in drug delivery. Here, we screened the effect of co-excipients on the swelling and drug\nrelease of zein tablets. All throughout the study the behavior of zein was benchmarked against that\nof hydroxypropyl methylcellulose (HPMC) and ethylcellulose (EC). Tablets containing either zein,\nHPMC, or EC alone or in combination with co-excipients, namely lactose, dicalcium phosphate\n(DCP), microcrystalline cellulose (MCC), polyvinylpyrrolidone (PVP), or sodium lauryl sulfate\n(SLS) were prepared by direct compression. Matrix swelling was studied by taking continuous\npictures of the tablets over 20 h, using a USB microscope connected to a PC. The overall size change\nand the axial and radial expansion of the tablets were automatically extrapolated from the pictures\nby image analysis. Moreover, drug release from tablets containing ternary mixtures of zein, coexcipients\nand 10% propranolol HCl was also studied. Results showed that zein matrices swelled\nrapidly at first, but then a plateau was reached, resulting in an initial rapid drug burst followed by\nslow drug release. HPMC tablets swelled to a greater extent and more gradually, providing a more\nconstant drug release rate. EC did not practically swell, giving a nearly constant drug release\npattern. Among the additives studied, only MCC increased the swelling of zein up to nearly threefold,\nand thus suppressed drug burst from zein matrices and provided a nearly constant drug\nrelease over the test duration. Overall, the incorporation of co-excipients influenced the swelling\nbehavior of zein to a greater extent compared to that of HPMC and EC, indicating that the molecular\ninteractions of zein and additives are clearly more complex and distinct.
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