The concept of co-processing as a particle engineering technique has been used as a tool to improve the functionality of many existing excipients. This study was designed to improve the functionality of cassava starch as excipient for direct compression by co-processing with gelatin and colloidal silicon dioxide.

The Design of Experiment (DoE) approach was employed to optimize the percentage ratios of the primary excipients for the co-processed excipient. Fourteen experimental formulations containing varying proportions of the primary excipients were prepared by the method of co-fusion and twelve tablets each weighing 400 mg each were produced for each formulation using the Hydraulic Carver Press. The compressed tablets were kept for 24 h in the desiccator and evaluated for tensile strength and disintegration time. The data obtained from the tablets were suitably analysed using the Design Expert software and fitted to a special quartic model that correlated the effect of varying the proportions of the excipients in the different formulations on tablet properties.The composition of the co-processed excipient that produced tablets of desirable characteristics after optimization was found to be cassava starch (90 %), gelatin (7.5 %) and colloidal silicon dioxide (2.5%).

The optimized co-processed excipient subsequently known as “StarGelaSil” (SGS) was prepared in large quantities and stored in an airtight container for further studies. Solid-state characterization was conducted on SGS to determine its particle size, shape, distribution, surface morphology, degree of crystallinity, hygroscopicity, compatibility etc using established analytical techniques. Powder properties of SGS were also determined by measuring its flowability using the angle of repose, bulk and tapped densities, porosity, dilution potential, lubricant sensitivity ratio etc. The compaction behaviour of SGS was analysed using Heckel and Kawakita equations and the vii

compressibility, tablet ability, compact ability (CTC) profile was determined in comparison to the physical mixture of the primary excipients (SGS-PM). Tablets were formulated by direct compression using Ibuprofen as the drug of choice and compared with tablets produced using Prosolv® and StarLac® as reference standards.

The results revealed that co-processed particles of SGS were largely amorphous and spherical in shape with rough surfaces. There was no incompatibility between the excipients used for co-processing and between drug and co-processed excipient. Flow properties were enhanced as a result of co-processing. A superior CTC profile was obtained for SGS when compared with SGS-PM. The tablets produced by SGS conformed to the specifications of USP (2009) and compared well with those of the reference excipients in terms of tensile strength, disintegration time and drug-release profile.

This study concluded that co-processing was able to improve the functionality of cassava starch as excipient for direct compression. Hence, the excipient can be developed for use in pharmaceutical industry as a choice material for direct compression.