A modelling study on the degradation of hydroxypropyl cellulose/sodium alginate blend microcapsules for controlled drug delivery

Citation:

Nalzaro PJB, Doctor JNP, Domingo JRC, Madrid LLB, Tumolva TP. A modelling study on the degradation of hydroxypropyl cellulose/sodium alginate blend microcapsules for controlled drug delivery. Basic & Clinical Pharmacology & Toxicology [Internet]. 2019;124 (S3) :12.

Abstract:

Hydrogels are known suitable microencapsulating materials for the controlled delivery of active pharmaceutical ingredients in the body. To ensure biocompatibility and cost- effectiveness, the hydrogel microcapsules can be synthesized using naturally abundant biopolymers such as cellulose and its derivatives, as well as phycocolloids such as alginates that can be derived from locally indigenous seaweeds. This study focuses on a hydrogel developed from blending hydroxypropyl cellulose (HPC) with sodium alginate (NaAlg): with the combined chemical stability of HPC and NaAlg allows for the microcapsules to resist degradation along the digestive pathway up until the entry region of the small intestine, where the active ingredient should be released for optimal bioactivity. It is important to have a better understanding of the degradation phenomenon of the HPC- NaAlg hydrogel microcapsules so they can be more effectively used; hence, mathematical modeling is applied to provide significant insights and a deeper understanding on the blend ' s degradation behavior. In this study, it is desired to analyze the rate of degradation and obtain and validate a hydrogel degradation model by determining the associated kinetic parameters. Hydrogel samples were prepared from 50:50 HPC/NaAlg mixture using aqueous CaCl 2 solution as crosslinking agent. The samples were subjected into a diffusion test under different solutions to simulate the pH conditions throughout the gastrointestinal tract (pH 2, 4, 6 and 7). The diffusion- reaction behavior is mathematically modelled to determine pertinent diffusion kinetic parameters. Results show that only minimal swelling occurs under pH = 2, reaching only about 80.19% weight increase, and the hydrogel does not disintegrate despite the acidity, and there are no significant changes observed over the entire duration of the diffusion. For pH = 4, the weight of the hydrogel increases rapidly initially but slows down over time, with an observed maximum weight increase of 1385% around 70 minutes into the test. For pH = 7, the hydrogel samples are observed to quickly swell until they disintegrate in as early as 7 minutes, reaching around 973.1% in weight increase. Under basic conditions, the crosslinking bonds weaken since the calcium ions are drawn to the alkaline solution to form calcium hydroxide- thus, leading to swelling and disintegration. Using the diffusion data, the pH (concentration) dependence functions of the diffusion coefficient and plateau time parameter for a one- dimensional, combined diffusion and swelling kinetic model is established. These obtained functions are validated by the good agreement of the model with the experimental data taken for diffusion for pH = 6.

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