Analysis and modeling of radial water up-take in pure HPMC tablets
Multi-scale and/or multi-disciplinary approach to process-product innovation
Controlled Release of the Active Ingredient: Mechanisms, Devices & Analysis (T3-2)
Keywords: controlled release systems, swelling, erosion, HPMC
Serafina Chirico, Gaetano Lamberti*, Valentina Nunziata, Giuseppe Titomanlio
Department of Chemical and Food Engineering - University of Salerno
Via Ponte Don Melillo - 84084 Fisciano - www.dica.unisa.it
*glamberti@unisa.it Tel. +39089964077
This work deals with the analysis of transport phenomena involved in controlled drug delivery systems. In particular the attention is focused on the swelling and the erosion kinetics of pure hydroxypropylmethylcellulose (HPMC) tablets.
The hydrogel used in these experiments is HPMC K15M, kindly supplied by Colorcon. The HPMC is commonly used in extended release formulation of systems for oral drug delivery.
Tablets were made by compressing pure polymer powder with a tabletting machine having a 13 mm flat-faced punch, applying a force of 50 kN for 5 minutes. All tablets, shaped as discs, were 2.2 mm in thickness and they were made up of 350 mg of pure HPMC.
In order to study the swelling and erosion behavior of the HPMC tablets, they have been clamped between two square glass slabs, allowing the water up-take only by radial direction. These sandwiches were immersed in vessels filled with distilled and stirred water kept at 37°C. By a video camera, programmed to capture one frame per minute, digital movie were collected. Subsequently several frames for each movie were analyzed providing the light intensity as function of tablet radius at different time of immersion. The analysis allows the identification of the erosion fronts. Furthermore, the light intensity profile was related to the water mass concentration profile.
To confirm the data obtained by image analysis, a checking method was pointed out. Some swollen tablet, after a given immersion time, were cut by annular punches of different size, obtaining several annuli, and one core disc. The different amounts of partially hydrated polymer in different annuli were carefully weighted, dried, weighted once more. In this way it was possible to determine the mean concentration of water in each annulus, i.e. as function of tablet radius. A satisfactory agreement was found between the light intensity analysis and the cut-and-weight technique.
Then, a model able to describe the transport phenomena (water diffusion, gel swelling and polymer erosion), taking place during drug release from swelling devices has been developed. Since the water up-take and the polymer erosion occurs only in the radial direction, the confined matrix has been treated as it was an infinite cylinder. The model prediction well agree with the evolution of water profiles and radial erosion determined experimentally.
Presented Tuesday 18, 11:40 to 12:00, in session Controlled Release of the Active Ingredient: Mechanisms, Devices & Analysis (T3-2).
