title: Physical hydrogels with self-assembled nanostructures as drug delivery systems.
abstract: BACKGROUND
  As an essential complement to chemically crosslinked hydrogels, drug delivery systems based on physical hydrogels with self-assembled nanostructures are gaining increasing attention, owing to potential advantages of reduced toxicity, convenience of in situ gel formation, stimuli-responsiveness, reversible sol-gel transition, and improved drug loading and delivery profiles.
  
  
  METHODS
  In this review, drug delivery systems based on physical hydrogels are discussed according to their self-assembled nanostructures, such as micelles, layer-by-layer constructs, supramolecular inclusion complexes, polyelectrolyte complexes and crystalline structures. The driving forces of the self-assembly include hydrophobic interaction, hydrogen bonding, electrostatic interaction, π-π stacking and weak van der Waals forces. Stimuli-responsive properties of physical hydrogels, including thermo- and pH-sensitivity, are considered with particular focus on self-assembled nanostructures.
  
  
  CONCLUSIONS
  Fabricating self-assembled nanostructures in drug delivery hydrogels, via physical interactions between polymer-polymer and polymer-drug, requires accurately controlled macro- or small molecular architecture and a comprehensive knowledge of the physicochemical properties of the therapeutics. A variety of nanostructures within hydrogels, with which payloads may interact, provide useful means to stabilize the drug form and control its release kinetics.
authors: Biocompatibles UK Ltd, Chapman House, Farnham, Surrey, UK. Yiqing.Tang@biocompatibles.com
authors: Yiqing
authors: Y
authors: Tang
authors: Clare L
authors: CL
authors: Heaysman
authors: Sean
authors: S
authors: Willis
authors: Andrew L
authors: AL
authors: Lewis