CHAPTER 18:pH- and Temperature-responsive Hydrogels in Drug Delivery

Stimuli-responsive drug-delivery systems may be therapeutically advantageous over the prolonged release systems, because they offer the possibility of adapting drug levels to the biorhythms and the pathological changes in the body, notably enhancing the efficiency and safety of the treatments. Hydrogels already occupy a prominent position in the drug-delivery field due to their versatile composition and obtaining procedures, high hydrophilicity and tunable mechanical properties. Thus they result in systems suitable for being administered through almost all delivery routes. Adequate selection of ionizable components leads to networks sensitive to the changes in pH that take place under physiological (e.g. in the gastrointestinal tract or inside cell organelles) or pathological (e.g. cancer, inflammation, infection) conditions. On the other hand, monomers that can establish intra-/inter-molecular interactions through hydrophobic or hydrogen bonds endow the hydrogels with temperature-responsive behavior. Combination of both pH- and temperature-sensitive components is also feasible and demonstrated useful to achieve a more selective and precise drug release pattern. The chapter offers an overview of the recent research on pH- and thermo-responsive hydrogels and their applications in controlled drug delivery. Besides micro-sized materials, much attention is paid to hydrogels with nano-sized structure, which have a great potential in stimuli-responsive cell targeting therapies.