title: In situ gel systems as 'smart' carriers for sustained ocular drug delivery.
abstract: BACKGROUND
  In situ gel systems refer to a class of novel delivery vehicles, composed of natural, semisynthetic or synthetic polymers, which present the unique property of sol-gel conversion on receipt of biological stimulus.
  
  
  METHODS
  The present review summarizes the latest developments in in situ gel technology, with regard to ophthalmic drug delivery. Starting with the mechanism of ocular absorption, the review expands on the fabrication of various polymeric in situ gel systems, made up of two or more polymers presenting multi-stimuli sensitivity, coupled with other interesting features, such as bio-adhesion, enhanced penetration or sustained release. Various key issues and challenges in this area have been addressed and critically analyzed.
  
  
  CONCLUSIONS
  The advent of in situ gel systems has inaugurated a new transom for 'smart' ocular delivery. By virtue of possessing stimuli-responsive phase transition properties, these systems can easily be administered into the eye, similar to normal eye drops. Their unique gelling properties endow them with special features, such as prolonged retention at the site of administration, followed by sustained drug release. Despite the superiority of these systems as compared with conventional ophthalmic formulations, further investigations are necessary to address the toxicity issues, so as to minimize regulatory hurdles during commercialization.
authors.affiliation: National Institute of Pharmaceutical Education and Research, Centre for Pharmaceutical Nanotechnology, Department of Pharmaceutics, SAS Nagar, Punjab, 160 062, India.
authors.forename: Ashish Kumar
authors.initials: AK
authors.lastname: Agrawal
authors.forename: Manasmita
authors.initials: M
authors.lastname: Das
authors.forename: Sanyog
authors.initials: S
authors.lastname: Jain
mesh_terms: D000042:Absorption; D000268:Adhesiveness; D060433:Administration, Ophthalmic; D001672:Biocompatible Materials / Q000008:administration & dosage* / Q000737:chemistry / Q000493:pharmacokinetics; D001682:Biological Availability; D002626:Chemistry, Pharmaceutical; D048271:Chitosan / Q000737:chemistry; D003692:Delayed-Action Preparations / Q000008:administration & dosage*; D004337:Drug Carriers / Q000008:administration & dosage* / Q000737:chemistry* / Q000493:pharmacokinetics; D005079:Excipients / Q000008:administration & dosage / Q000493:pharmacokinetics; D005123:Eye / Q000378:metabolism; D005782:Gels; D005936:Glucans / Q000737:chemistry; D006801:Humans; D009883:Ophthalmic Solutions / Q000008:administration & dosage* / Q000737:chemistry / Q000493:pharmacokinetics; D020442:Poloxamer / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D014990:Xylans / Q000737:chemistry
chemical_list: D001672:Biocompatible Materials; D003692:Delayed-Action Preparations; D004337:Drug Carriers; D005079:Excipients; D005782:Gels; D005936:Glucans; D009883:Ophthalmic Solutions; D011108:Polymers; D014990:Xylans; D020442:Poloxamer; C029353:xyloglucan; D048271:Chitosan