Preparation and evaluation of dual modified Ethiopian yam (Dioscorea abyssinica) starch for sustained release tablet formulations
Starch has been intensively studied over decades due to the fact that native starches are diverse, biodegradable, amenable to modifications and have enormous applications. In this study, Dioscorea abyssinica starch has been chemically dual modified by cross-linking using sodium hexametaphosphate (SHMP) followed by acetylation with acetic anhydride (AA). The physicochemical and tablet forming properties of the modified starches were investigated to determine potential usages in sustained release (SR) applications. Moisture sorption and swelling properties of the native starch (NS) were improved by the dual modification. The reduction observed in viscosity values indicated the effectiveness of cross-linking in reducing swelling of the NS. On the basis of powder properties analysis, it was evident that acetylation improved the poor flow property of NS. The starch acetylated at starch:AA ratio of 1:2 was found to be free flowing with angles of repose of 23.02o and flow rate 10.54 g/sec. The Hausner ratio and Carr’s index also confirmed the same, 1.25 and 20.24, respectively. Tablets were prepared and evaluated for hardness, tensile strength, friability, and disintegration time. Results indicated that both cross-linking and acetylation processes improved tablet forming properties of the NS with more significant effect in the dual modified starches. Matrix tablets containing Ac-CLS-F, where cross-linked starch (CLS – at 15% SHMP) reacted in a 1:2 ratio with AA, loaded with 20, 30 and 40% theophylline released 80% of theophylline in about 10.62, 9.35, and 8.18 h, respectively. From the foregoing, it can be concluded that Ac-CLS-F could have a potential for use as a sustained release excipient.
Keywords: Dioscorea abyssinica, cross-linking, acetylation, dual modification, sustained release