Smart biodegradable hydrogels with applications in drug delivery and tissue engineering

C. ELVIRA; G.A. ABRAHAM; A. GALLARDO; J. SAN ROMÁN

Biodegradable Systems in Tissue Engineering and Regenerative Medicine

CRC Press

Lugar: Boca Raton, FL, USA; Año: 2005; p. 493 - 508

Hydrogels are hydrophilic three-dimensional networks, crosslinked by chemical or physical bonds, swollen by water. It is well-known their applications as biomaterials because of their permeability to small molecules, soft consistency, low interfacial tension, facility of purification and mainly high equilibrium water content which make their physical properties similar to those of living tissues. Hydrogels can be applied as artificial skin, as contact lenses, as an interface between bone and an implant, as blood contact materials and in controlled release applications for the delivery of bioactive compounds such as enzymes, contraceptives, anticoagulants, etc. Stimuli-responsive or smart hydrogels are polymers that respond with dramatic property changes to small changes in the environment. These polymers undergo fast changes in microstructure from a hydrophobic to a hydrophilic state (sol to gel, or collapsed to expanded morphology), triggered by environmental changes, being observed at macroscopic level as in size or swelling degree. These changes can be also reversible as the systems return to their initial state when the stimulus is removed. The common stimuli applied are changes in pH or temperature which induce neutralization of opposite charged groups or changes in the efficiency of hydrogen bonding respectively, which can expand or collapse the corresponding hydrogels. Recent advances in the design of stimuli responsive polymers have created opportunities for novel biomedical applications. Stimuli-responsive changes in shape, surface characteristics, solubility, formation of an intricate molecular self-assembly, and sol-gel transition have enabled several new applications in the delivery of therapeutics, tissue engineering, cell culture, bioseparations and sensor actuator systems. In this sense, it has to be pointed out that hydrogels with applications in tissue engineering and drug delivery are usually proven in both fields due to their intimate ties to biomaterials. This chapter describes different stimuli-responsive hydrogels attending to the type of stimuli applied: temperature, pH, glucose concentration and others such as electric fields, magnetic field and ultrasound. Also new systems are described as the applications of all of them in drug delivery and tissue engineering, paying special attention to biodegradable or partially biodegradable systems.