Approach to Knowledge of the Interaction between the Constituents of Contact Lenses and Ocular Tears: Mixed Monolayers of Poly(methyl methacrylate) and Dipalmitoyl Phosphatidyl Choline

Abstract

Mixed monolayers of poly(methyl methacrylate) (PMMA), the main component of hard contact lenses, and dipalmitoyl phosphatidyl choline (DPPC), a characteristic phospholipidic constituent of ocular tear films, were selected as an in vitro model in order to observe the behavior of contact lenses on the eye. Using Langmuir monolayer and Brewster angle microscopy (BAM) techniques, the interaction between both components was analyzed from the data of surface pressure-area isotherms, compressional modulus-surface pressure, and relative film thickness versus time elapsed from the beginning of compression, together with BAM images. Regardless of the surface pressure at which the molecular/monomer areas (A(m)) were recorded, the A(m) mole fractions of PMMA (X(PMMA)) plots show that the experimental results match the theoretical values calculated from additivity rule A(m) = X(PMMA)A(PMMA) + X(DPPC)A(DPPC). The application of the Crisp phase rule to the phase diagram of the PMMA-DPPC system can explain the existence of a mixed monolayer made up of miscible components with ideal behavior at surface pressures below 25 mN/m. However, at very high surface pressures, when collapse is reached (at 60 mN/m), the single collapsed components are segregated into two independent phases. These results allows us to argue that PMMA hard contact lenses in the eye do not alter the structural characteristics of the phospholipid (DPPC) in tears.

Study of the interaction of GB virus C/Hepatitis G virus fusion peptides belonging to the E2 protein with phospholipid Langmuir monolayers

“…Similarly, the surface pressures of the c-d line, corresponding to the 2D-3D peptide loops formation, vary with the composition of mixtures, and so, a new homogenous surface phase M3 appears in these mixtures above the cited line, formed by coiled peptide molecules and by DPPC molecules with the above described orientation. Similar behaviour was observed in literature for other mixed systems[50][51][52]. Both collapse surface pressures corresponding to the peptide (e-f line) and to DPPC (g-h line) components do not depend on the monolayer composition, and therefore the number of degrees of freedom is F = 0 and q = 3, i.e., three phases in equilibrium coexist in these situations: in the first case the two new phases appearing are formed by the collapsed peptide and by pure DPPC molecules, both separated from one another.…”

Solvent-dependent properties of poly(vinylidene fluoride) monolayers at the air–water interface

“…This phase transition took place because the domains were brought into contact. 35,40 We infer that PVDF molecules in the PVDF Langmuir lms of two kinds occupy the area with different molecular conformations. Therefore, changing solvent properties is effective to modulate molecular aggregation of PVDF at the air-water interface.…”

“…32 The C À1* s of pure pDDA reaches 195.0 mN m À1 at A* ¼ 0.24 nm 2 per monomer (Table 1), which is ascribed to the excellent twodimensional hydrogen bonding network formed in its monolayer at the air-water interface. 34 No report in the relevant literature has described C À1* s > 190.0 mN m À1 for polymer Langmuir lms, although 82.4 and 150.0 mN m À1 have been reported, respectively, for poly(methylmethacrylate) (PMMA) 35 and the oligomer of p-phenylene vinylene. 36 At A < 0.24 nm 2 per monomer, the pDDA monolayer becomes concentrated and the modulus decreases to zero as a consequence of the strong decrease of the available free area at the air-water interface and of the conformational freedom degrees of polymer chains.…”

Polymeric Materials for Eye Surface and Intraocular Applications

“…They typically provide clearer vision and are easier to handle, but they are not as comfortable initially as soft CLs (SCLs). While the first generation of nonglass CLs developed in the 1930s used poly­(methyl methacrylate) (PMMA), , silicone is one of the most common rigid CLs currently on the market . SCLs are typically easier to adjust to, while gas-permeable lenses require an adaptation period for most patients to get comfortable with them.…”