Tapioca starch graft copolymers and Dome Matrix® modules assembling technology. I. Effect of module shape on drug release

This paper studies the Riboflavin release from compressed disc modules of Dome Matrix® technology using tapioca starch–ethylmethacrylate (TSEMA) and tapioca hydroxypropylstarch–ethylmethacrylate (THSEMA), graft copolymers produced by two different drying methods. The comparison with the release behaviour of similar HPMC modules was performed. Two different shape modules have been made, identified as female and male modules, in order to obtain their assemblage by interlocking the disc bases. HPMC matrices showed quasi-linear Riboflavin release in case of both female and male modules, with faster drug release than TSEMA modules. In the case of THSEMA modules, a faster release was observed compared to HPMC modules. Furthermore, matrices obtained with TSEMA copolymers remained nearly intact after dissolution process, while matrices containing HPMC experimented a complete dissolution of the modules. Combining these results with the release curve analysis using the Korsmeyer and Peppas exponential equation, HPMC modules controlled the drug release by polymer relaxation or erosion. For TSEMA and THSEMA, the drug release mechanism was controlled mainly by drug diffusion. The pronounced faster releases for the matrices containing THSEMA copolymers compared with the ones with TSEMA were due to a more important erosive support; however, the main structure of the matrix remains coherent. Porosity and tortuosity values and the shape of the modules explained the drug release observed.