ABSTRACT
Maintaining constant drug levelswithin therapeutic window at the target site for extended period of time is a challenging task.Of the many controlled drug release technologies, in situ forming implant (ISFI) systems have gained in popularity for a range of biomedical applications including drug delivery. There are numerous methods by which implants may form in situ. ISF process sees a free flowing system solidify once introduced into the physiological environment, thereby overcoming issues surrounding surgically implanted hydrogel systems. Depending upon their mechanism of implant formation the ISF implants can be categorised into different types such as pH, temperature, and phase separation systems. This chapter focuses on solvent induced phase inversion (SPI)-based ISF hydrogel implants, which has gained significant popularity due to its simplicity in formulation and non-dependence upon external stimuli (e.g. pH or temperature) in forming an implant upon injection. Here we have discussed a wide of polymeric materials, solvents and drug molecules studied in the formulation of SPI-ISF hydrogel implants. It also covers mechanism of drug release and biodegradation of these injectable hydrogel implants and methods to modify the drug release. A brief discussion on currently marketed products and challenges associated to further improve these types of hydrogel-based controlled drug delivery systems is also presented.
