title: Mechanically triggered solute uptake in soft contact lenses.
abstract: Molecular arrangement plays a role in the diffusion of water and solutes across soft contact lenses. In particular, the uptake of solutes in hydrated contact lenses can occur as long as free water is available for diffusion. In this work, we investigated the effect of mechanical vibrations of low frequency (200 Hz) on the solute uptake. Hyaluronan, a polysaccharide of ophthalmic use, was taken as example of solute of interest. For a specific water-hydrated hydrogel material, differential scanning calorimetry experiments showed that a large fraction of the hydration water accounted for loosely-bound water, both before and after one week of daily-wear of the lenses. The size (of the order of magnitude of few hundreds of nanometers) of hyaluronan in aqueous solution was found to be less than the size of the pores of the lens observed by scanning electron microscopy. However, solute uptake in already-hydrated lenses was negligible by simple immersion, while a significant increase occurred under mechanical vibrations of 200 Hz, thus providing experimental evidence of mechanically triggered enhanced solute uptake, which is attributed to the release of interfacial loosely-bound water. Also other materials were taken into consideration. However, the effectiveness of mechanical vibrations for hyaluronan uptake is restricted to lenses containing interfacial loosely-bound water. Indeed, loosely-bound water is expected to be bound to the polymer with bonding energies of the order of magnitude of 10-100 J/g, which are compatible with the energy input supplied by the vibrations.
authors.affiliation: Materials Science Department, University of Milano Bicocca, Via Cozzi 55, I-20125 Milan, Italy. Electronic address: silvia.tavazzi@unimib.it.
authors.forename: Silvia
authors.initials: S
authors.lastname: Tavazzi
authors.affiliation: Materials Science Department, University of Milano Bicocca, Via Cozzi 55, I-20125 Milan, Italy.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Ferraro
authors.affiliation: Materials Science Department, University of Milano Bicocca, Via Cozzi 55, I-20125 Milan, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Fagnola
authors.affiliation: Materials Science Department, University of Milano Bicocca, Via Cozzi 55, I-20125 Milan, Italy.
authors.forename: Federica
authors.initials: F
authors.lastname: Cozza
authors.affiliation: DeFENS, Department of Food, Environmental and Nutritional Sciences, Packaging Division - University of Milan, Via Celoria 2, I-20133 Milan, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Farris
authors.affiliation: Materials Science Department, University of Milano Bicocca, Via Cozzi 55, I-20125 Milan, Italy.
authors.forename: Simone
authors.initials: S
authors.lastname: Bonetti
authors.affiliation: Materials Science Department, University of Milano Bicocca, Via Cozzi 55, I-20125 Milan, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Simonutti
authors.affiliation: Materials Science Department, University of Milano Bicocca, Via Cozzi 55, I-20125 Milan, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Borghesi
mesh_terms: D002152:Calorimetry, Differential Scanning; D003263:Contact Lenses, Hydrophilic; D006801:Humans; D006820:Hyaluronic Acid / Q000737:chemistry* / Q000378:metabolism / Q000493:pharmacokinetics; D057446:Hydrodynamics; D020100:Hydrogels / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D010316:Particle Size; D016062:Porosity; D012833:Siloxanes / Q000737:chemistry; D012996:Solutions / Q000737:chemistry*; D013314:Stress, Mechanical; D013499:Surface Properties; D014732:Vibration; D014867:Water / Q000737:chemistry*
chemical_list: D020100:Hydrogels; D012833:Siloxanes; D012996:Solutions; D014867:Water; D006820:Hyaluronic Acid
keywords: Contact lenses; Controlled release; Hyaluronan; Mechanical vibrations; Water/polymer interface