An Experiment to Introduce pH-responsive Hydrogels for Controlled Drug Delivery: Mechanical Testing

In a continuing effort to introduce drug delivery-related experiments for the chemical engineering curriculum, we are developing an experiment to introduce students to pH responsive hydrogels. These hydrogels have been extensively investigated for controlled drug delivery. By responding to the pH environment in the body, which changes depending on location and metabolic state, a pH-sensitive drug dosage form is able to modulate drug delivery patterns to meet physiologic requirements and minimize side effects. In a previous experiment for students, hydrogels were prepared and shown to swell more in the neutral pH environment of the intestines than in the acidic stomach environment. This paper describes an experiment to introduce engineering students in a materials science class to stimuli-responsive polymers for controlled release applications. Students produce a pH-responsive hydrogel using a free-radical solution polymerization and analyze mechanical properties of the gel using tensile testing. The yield stress was greater in the low pH environment simulating the stomach than it was in the higher pH environment which simulated the intestines. Young’s modulus increased with percentage of monomer in the formulation. Such a system would be useful for the oral delivery of a drug that would be damaged by the low pH environment of the stomach, such as insulin, and a future experiment will investigate the drug release characteristics of the hydrogels. In addition to learning about pH-responsive drug delivery, students learned concepts of measurements, material properties, design of experiments, data analysis, and engineering design.