Finite Element Simulation Of Swelling And Drug Release Processes Using Weak Polyelectrolyte Hydrogels As Drug Carriers

Polyelectrolyte hydrogels whose dispersed medium is water, has a kind of three-dimensional network structure. Moreover, it can change its volume immensely when swelling or deswelling and keep its outline unchanged at the same time. Factors that can influence the macro-size and shape of hydrogels mainly include internal factors which cover the crosslink density of polymer and degree of substitution and external factors consisting of temperature, pH, solvent compositions and ionic strength. Generally, the intelligent responsiveness can be achieved through the regulation of these factors to control the changes between swelling and collapsed states.The polymer networks of weak polyelectrolyte hydrogels carry with ionized groups that can be ionized into fixed ions surrounded by free ions which carry with opposite charges under the action of electrostatic force. The amount of fixed ions of strong polyelectrolyte hydrogels in the process of water-absorption swelling or water-losing collapse keeps unchanged. On the contrary, because of the ionized groups of weak polyelectrolyte hydrogels carrying on partial ionizing, the ionization degree of ionized groups will alter with the change of the ionic strength and pH. Besides, its swelling and collapse states alter with the variation of external condition and the drug release ratio of hydrogel will also be changed. Therefore weak polyelectrolyte hydrogels are particularly sensitive to the outside environment and especially suitable for the material of drug controlled release preparation.Drug slow release system can reduce the dosing frequency to relieve the pain of the patients, strengthen the drug efficacy and reduce the drug side effects. The swelling drug release process is a complicated procedure which possesses the characteristics of multi-disciplinary crossing. Therefore, building mathematic model to intensively study the drug release mechanism is of great significance.Aiming at the ionic strength and pH responsiveness of weak polyelectrolyte hydrogel, a mathematical model was built through the finite element simulation. Then the swelling and drug release process were studied. The effects of pH value and ionic strength on drug release were discussed to illuminate the drug release mechanisms and the operation mechanisms of drug controlled release process. Besides, the theories of multiphase model were established to reveal moving mechanism of water phase, polymer network phase and free ionic phase during the drug release process. Furthermore, the concentration of fixed ions and free hydrogen ions of polymer networks were calculated by Langmuir isothermal adsorption equation. The aforementioned studies of weak polyelectrolyte hydrogel act as drug carriers are of great importance during the application in slow controlled release drug preparation field.