Abstract
Zein is an insoluble, yet swellable, biopolymer that has been extensively studied for its applications in drug delivery. Here, we screened the effect of co-excipients on the swelling and drug release of zein tablets. All throughout the study the behavior of zein was benchmarked against that of hydroxypropyl methylcellulose (HPMC) and ethylcellulose (EC). Tablets containing either zein, HPMC, or EC alone or in combination with co-excipients, namely lactose, dicalcium phosphate (DCP), microcrystalline cellulose (MCC), polyvinylpyrrolidone (PVP), or sodium lauryl sulfate (SLS) were prepared by direct compression. Matrix swelling was studied by taking continuous pictures of the tablets over 20 h, using a USB microscope connected to a PC. The overall size change and the axial and radial expansion of the tablets were automatically extrapolated from the pictures by image analysis. Moreover, drug release from tablets containing ternary mixtures of zein, co-excipients and 10% propranolol HCl was also studied. Results showed that zein matrices swelled rapidly at first, but then a plateau was reached, resulting in an initial rapid drug burst followed by slow drug release. HPMC tablets swelled to a greater extent and more gradually, providing a more constant drug release rate. EC did not practically swell, giving a nearly constant drug release pattern. Among the additives studied, only MCC increased the swelling of zein up to nearly three-fold, and thus suppressed drug burst from zein matrices and provided a nearly constant drug release over the test duration. Overall, the incorporation of co-excipients influenced the swelling behavior of zein to a greater extent compared to that of HPMC and EC, indicating that the molecular interactions of zein and additives are clearly more complex and distinct.
Highlights
Zein is the main storage protein of corn
The swelling of compacts made of pure hydroxypropyl methylcellulose (HPMC), EC, and zein was first determined using the imaging technique described earlier
Considering that the USB microscope used for collecting the images can be purchased for only $35 and that the image analysis software is open access, we anticipate that this technique could be adopted in the future studies, as a direct readout of swelling of controlled release polymer matrices
Summary
Zein is the main storage protein of corn. In the last few years, zein has gained tremendous popularity as a novel biocompatible and biodegradable material, produced from sustainable sources. While most pharmaceutical homo- and co-polymers have highly repetitious structures, zein is a sequence of many different monomers (i.e., amino acids), with several domains and regions, which are variable at the level of primary, secondary, and tertiary structure of the protein [14]. Due to this heterogenous and complex physico-chemical composition, the molecular interactions of zein with neighboring compounds could be distinct and unpredictable
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