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

Hydrogel is a three-dimensional hydrophilic polymer network whose dispersed medium is water. The most typical characteristic of hydrogel is that hydrogel is able to change its volume immensely when experiences swelling or deswelling and at the same time keep its shape unchanged. Some hydrogels are sensitive to external environment, such as pH, temperature and ionic concentration. And these hydrogels are called intelligent/smart or stimuli-responsive hydrogels since they can respond to the changes of those environmental factors to swell or deswell. The mechanism of volume change of hydrogel is very similar as the mechanism of size change of single chain of polymer in solvent. In other words, hydrogels or polymer networks deswell in poor solvents while they swell in good solvents. If the nature of the solvent is between good and poor, then the conformation of the polymer network will stay between stretch and collapse. Therefore, volume change can be achieved by changing the nature of the relevant solvent. Hydrogels are not only a kind of smart materials, their nature resembles that of tissues of living creatures, they are soft, and they have excellent biocompatibility and oxygen permeability. These characteristics enable hydrogels to be widely applied in the field of controlled release as outstanding drug earners.In comparison with traditional delivery systems, controlled drug release systems provide more sustained and stable release, even a drug release at a specific location and a desirable rate. On one hand, the duration time of drug is elongated to reduce the frequency of taking medicine; on the other hand, a drug release at a specific location and a desirable rate can achieve the best efficacy of the drug without side effects induced by relatively high drug concentration in plasma.Issues regarding controlled drug release based on hydrogels are multi-disciplinary and nowadays they are focused more and more in medical and pharmaceutical fields. And research about these issues has very important practical significance for treating diseases. Mathematical modeling and numerical simulation play important roles in studying the release mechanisms and predicting the behaviors of controlled drug releases. But mathematical models are generally applicable to specific systems, especially models used to predict release behaviors of some complex systems are not perfect and need to be improved.In this work, drug delivery systems using neutral and polyelectrolyte hydrogels as drug carriers was studied by means of mathematical modeling and finite element simulation. For the neutral hydrogel systems, based on biphasic model and consideration of phenomena of water convection, drug diffusion and polymer network swelling as the factors influencing drug release behavior, a mathematical model was established. By discussing and analyzing evolutions of the main parameters as well as the influences of dominating factors on the drug release processes, the influence of initial drug concentration distribution on drug release was explored. For the polyelectrolyte hydrogel systems, a mathematical model was established based on triphasic model and relevant finite element simulation was implemented. Then influences of ionic concentration and pH on drug release behaviors from polyelectrolyte hydrogels were explored, respectively. Based upon the aforementioned studies, mechanisms of drug release from hydrogels were revealed and the release behaviors were predicted, propelling the development and application of hydrogels as drug carriers in pharmaceutical and biotechnological fields.