Design of stimuli-responsive drug delivery hydrogels

Abstract

Stimuli-responsive hydrogels have become popular in medicine and polymer science as useful ‘smart’ devices due to their various properties such as overall biocompatibility, high drug loading capacity, and controlled molecule delivery. By tuning the polymer side chains and degree of crosslinking, these gels may exhibit swelling/shrinking behaviour in response to environmental stimuli such as light, pH, chemicals, temperature, mechanical strain, and electrical field. Sensitivity of these hydrogels enables precise control over fundamental material properties such as physical structure, porosity, swelling behaviour, mechanical strength and drug permeability. Temperature and pH alterations are examples of physiological deviations that are commonly considered for the design of responsive hydrogels, specifically for site-specific controlled drug delivery. A class of hydrogels known as multi-responsive hydrogels can respond to more than one stimuli which make them tunable and controllable with improved biomimetic properties well-suited for controlled and site specific drug delivery. Despite all these attractive properties of stimuli-responsive hydrogels, slow response time may cause some limitations in practical applications. Reduced hydrogel thickness may decrease the response time of the gel to a stimulus; however, this 2may lead to mechanically fragile hydrogel structures. Therefore, practical applications need significant improvement in hydrogel design to improve response time considering mechanical properties, biocompatibility, and biodegradability. This chapter highlights recent progress in the field of stimuli-responsive hydrogels, focusing primarily on drug delivery vehicles.