title: Controlling the Mesostructure Formation within the Shell of Novel Cubic/Hexagonal Phase Cetyltrimethylammonium Bromide-Poly(acrylamide-acrylic acid) Capsules for pH Stimulated Release.
abstract: The self-assembly of ordered structures in mixtures of oppositely charged surfactant and polymer systems has been exploited in various cleaning and pharmaceutical applications and continue to attract much interest since their discovery in the late twentieth century. The ability to control the electrostatic and hydrophobic interactions that dictate the formation of liquid crystalline phases in these systems is advantageous in manipulation of structure and rendering them responsive to external stimuli. Nanostructured capsules comprised of the cationic surfactant, cetyltrimethylammonium bromide (CTAB), and the diblock copolymer poly(acrylamide-acrylic acid) (PAAm-AA) were prepared to assess their potential as pH responsive nanomaterials. Crossed-polarizing light microscopy (CPLM) and small-angle X-ray scattering (SAXS) identified coexisting Pm3n cubic and hexagonal phases at the surfactant-polymer interface. The hydrophobic and electrostatic interactions between the oppositely charged components were studied by varying temperature and solution pH, respectively, and were found to influence the liquid crystalline nanostructure formed. The lattice parameter of the mesophases and the fraction of cubic phase in the system decreased upon heating. Acidic conditions resulted in the loss of the highly ordered structures due to protonation of the carboxylic acid group, and subsequent reduction of attractive forces previously present between the oppositely charged molecules. The rate of release of the model hydrophilic drug, Rhodamine B (RhB), from nanostructured macro-sized capsules significantly increased when the pH of the solution was adjusted from pH 7 to pH 2. This allowed for immediate release of the compound of interest "on demand", opening new options for structured materials with increased functionality over typical layer-by-layer capsules.
authors.affiliation: Drug Delivery, Disposition and Dynamics and ARC Centre of Excellence in Convergent Bio-Nano Science and Technology, Monash Institute of Pharmaceutical Sciences, Monash University (Parkville Campus) , 381 Royal Parade, Parkville, Victoria 3052, Australia.
authors.forename: Kristian J
authors.initials: KJ
authors.lastname: Tangso
authors.affiliation: School of Pharmacy, University College London , 29-39 Brunswick Square, London WC1N 1AX, United Kingdom.
authors.forename: Hetika
authors.initials: H
authors.lastname: Patel
authors.affiliation: The Procter and Gamble Company , Corporate Engineering Technical Laboratories Building, Cincinnati, Ohio 45069, United States.
authors.forename: Seth
authors.initials: S
authors.lastname: Lindberg
authors.affiliation: Commonwealth Scientific and Industrial Research Organization , Bag 10, Clayton South, Victoria 3169, Australia.
authors.forename: Patrick G
authors.initials: PG
authors.lastname: Hartley
authors.affiliation: Bragg Institute, Australian Nuclear Science and Technology Organization , Menai, New South Wales 2234, Australia.
authors.forename: Robert
authors.initials: R
authors.lastname: Knott
authors.affiliation: School of Chemical Engineering, University of New South Wales , Sydney, New South Wales 2052, Australia.
authors.forename: Patrick T
authors.initials: PT
authors.lastname: Spicer
authors.affiliation: Drug Delivery, Disposition and Dynamics and ARC Centre of Excellence in Convergent Bio-Nano Science and Technology, Monash Institute of Pharmaceutical Sciences, Monash University (Parkville Campus) , 381 Royal Parade, Parkville, Victoria 3052, Australia.
authors.forename: Ben J
authors.initials: BJ
authors.lastname: Boyd
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D001672:Biocompatible Materials / Q000737:chemistry; D002214:Capsules; D002412:Cations; D000077286:Cetrimonium; D002593:Cetrimonium Compounds / Q000737:chemistry*; D002626:Chemistry, Pharmaceutical / Q000379:methods; D003692:Delayed-Action Preparations / Q000737:chemistry; D004058:Diffusion; D016503:Drug Delivery Systems; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D008027:Light; D049329:Nanostructures / Q000737:chemistry; D010316:Particle Size; D012235:Rhodamines / Q000737:chemistry*; D012542:Scattering, Radiation; D055672:Static Electricity; D013501:Surface-Active Agents / Q000737:chemistry; D013696:Temperature; D014965:X-Rays; D000099166:Polyacrylamides
chemical_list: D000180:Acrylic Resins; D001672:Biocompatible Materials; D002214:Capsules; D002412:Cations; D000077286:Cetrimonium; D002593:Cetrimonium Compounds; D003692:Delayed-Action Preparations; D012235:Rhodamines; D013501:Surface-Active Agents; D000099166:Polyacrylamides; C006903:carbopol 940; C029773:rhodamine B
keywords: Pm3n cubic phase; cetyltrimethylammonium bromide; hexagonal phase; pH responsive; poly(acrylamide-acrylic acid); release studies