In situ forming polymeric formulations drug delivery systems is in sol form before administration in the body, but once administered, undergoes gelation in situ to form a gel. The formulation of gel depends upon factors like temperature modulation, pH changes, presence of ions and ultra-violet irradiation, from which drug gets released in a sustained and controlled manner
http://informahealthcare.com/doi/abs/10.1517/17425247.2013.734806