Carbon compositional analysis of hydrogel contact lenses by solid-state NMR spectroscopy.

Contact lenses are worn by over 140 million people each year and tremendous research and development efforts contribute to the identification and selection of hydrogel components and production protocols to yield lenses optimized for chemical and physiological properties, eye health and comfort. The final molecular composition and extent of incorporation of different components in contact lenses is routinely estimated after lens production through the analysis of the soluble components that were not included in the lens, i.e. remaining starting materials. Examination of composition in the actual intact materials is always valued and can reveal details that are missed by only examining the non-incorporated components, for example identifying chemical changes to components in lenses during the production process. Solid-state nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for the direct compositional analysis of insoluble and heterogeneous materials and is also uniquely suited to determining parameters of architecture in contact lenses. We utilized 13C cross-polarization magic angle spinning (CPMAS) NMR to examine and compare the carbon composition of soft contact lenses. 13C NMR spectra of individual polymer components enabled the determination of the approximate molecular carbon contributions of major lens components. Comparisons of the conventional etafilcon A hydrogel (1 Day Acuvue MOIST) lenses and silicone hydrogel lenses (Acuvue Oasys, Dailies Total 1, Clariti 1 Day, Biofinity, and Pure Vision) revealed major spectral differences, with considerable variation even among different silicone hydrogel lenses. The solid-state NMR approach provides a direct spectral reporting of carbon types in the hydrogel lens itself. This approach represents a valuable complementary analysis to benefit contact lens research and development and could be extended to isotopically labeled hydrogel lenses to map proximities and architecture between hydrogel components.

Core-shell and asymmetric polystyrene-gold composite particles via one-step Pickering emulsion polymerization.

Core-shell structured polystyrene-gold composite particles are synthesized from one-step Pickering emulsion polymerization. The surface coverage of the core-shell composite particles is improved with increasing gold nanoparticle (AuNP) hydrophobicity and concentration. At high surface coverage, the AuNPs exhibit an ordered hexagonal pattern, likely due to electrostatic repulsion during the emulsion polymerization process. In addition to core-shell structured polystyrene-gold composite particles, an intriguing observation is that at low AuNP concentrations, asymmetric polystyrene-gold nanocomposite particles are simultaneously formed, where a single gold nanoparticle is attached onto each polystyrene particle. It is found that these asymmetric particles are formed via a "seeded-growth" mechanism. The core-shell and asymmetric polystyrene-gold composite particles prove to be efficient catalysts as they successfully catalyze the Rhodamine B reduction reaction with stable performance and show high recyclability as catalysts.

Impact of Closed System Transfer Device (CSTD) Handling Procedure for Low-Transfer-Volume Dose Preparation of Biologic Drug Products.

Many challenges have been identified for ensuring compatibility of closed system transfer devices (CSTDs) with biologic drug products. One challenge is large hold-up volumes (HUVs) of CSTD components, which can be especially problematic with early-stage biologics when low transfer volumes smaller than the nominal fill volume may be used to achieve a wide range of doses with a single drug product configuration. Here, we identified possible CSTD handling techniques during dose preparation of a drug product requiring small volume transfers during reconstitution, intermediate dilution, and dilution in an IV bag, and systematically evaluated the impact of these handling procedures on the ability to deliver an accurate dose to the next step. We show that small changes to CSTD procedures can have a major impact on dose accuracy, depending on both CSTD HUVs and drug product-specific transfer volumes. We demonstrate that it is possible to craft CSTD instructions for use to mitigate these issues, and that the dose accuracy for specific drug product/CSTD combinations can be estimated using theoretical equations. Finally, we explored potential downsides of these mitigations. Our results emphasize key factors for consideration by both drug and CSTD manufacturers when assessing compatibility and providing CSTD instructions for use with biologics requiring low transfer volumes during dose preparation.

Understanding the adsorption and potential tear film stability properties of recombinant human lubricin and bovine submaxillary mucins in an in vitro tear film model.

The wetting and adsorption properties for two glycoproteins, recombinant human lubricin and bovine submaxillary mucins (BSM) were evaluated on hydrophilic and hydrophobic glass dome surfaces in a simplified in vitro tear film model. We show that both recombinant human lubricin (rh-lubricin) and BSM solutions render surfaces hydrophilic and when the fluid films reach 500 nm or less, the fluids resist evaporation-driven breakup through a volumetric flux across the surface, which we believe is due to evaporation-driven solutocapillary flows. rh-Lubricin was able to maintain a wet film without spontaneous breakup for longer periods of time than BSM at lower concentrations, which we attribute to differences in adsorption properties, measured by QCM-D, that result from surface charge and structural differences (confirmed by zeta potential, DLS, and SAXS measurements).

The influence of protein deposition on contact lens tear film stability.

When contact lenses (CLs) are worn, they are subject to deposition of the surrounding biomolecules found in the tear film (TF) of the eye. There is a correlation between protein deposition on CLs and feelings of discomfort in patients, but it has not been well understood if these feelings of discomfort arise solely from immunogenic reactions to the protein deposits or a physical instability of the tear film on protein-fouled CLs. This study compared two hydrogel CLs: etafilcon A (polyhydroxyethylmethacrylate-based hydrogel) and senofilcon A (silicone hydrogel with internal wetting agent) to elucidate how lysozyme and mucin sorption affect the wettability of CLs and understand the potential impact on TF stability in vivo. Here, we use "wettability" to refer to the stability of a film of phosphate buffered saline on the CL surface. A custom-built platform was used to conduct experiments that monitored the stability of phosphate-buffered saline (PBS) and artificial tear solution (ATS) on clean and fouled CLs. PBS was more stable (wettable) on etafilcon A than senofilcon A, and both CLs showed increased wettability after protein-fouling. However, surface wettability in PBS did not correlate with the stability of ATS on the CLs. The viscoelastic interface of ATS slowed drainage, making evaporation the primary thinning factor, in addition to the presence of a disjoining pressure that stabilized the thin film. From this, we conclude that protein deposition increases CL wettability, but does not alter tear film stability and we predict that CL susceptibility to evaporation is a better predictor of TF stability than wettability.

A highly stretchable, transparent, and conductive polymer.

Previous breakthroughs in stretchable electronics stem from strain engineering and nanocomposite approaches. Routes toward intrinsically stretchable molecular materials remain scarce but, if successful, will enable simpler fabrication processes, such as direct printing and coating, mechanically robust devices, and more intimate contact with objects. We report a highly stretchable conducting polymer, realized with a range of enhancers that serve a dual function: (i) they change morphology and (ii) they act as conductivity-enhancing dopants in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The polymer films exhibit conductivities comparable to the best reported values for PEDOT:PSS, with over 3100 S/cm under 0% strain and over 4100 S/cm under 100% strain-among the highest for reported stretchable conductors. It is highly durable under cyclic loading, with the conductivity maintained at 3600 S/cm even after 1000 cycles to 100% strain. The conductivity remained above 100 S/cm under 600% strain, with a fracture strain of 800%, which is superior to even the best silver nanowire- or carbon nanotube-based stretchable conductor films. The combination of excellent electrical and mechanical properties allowed it to serve as interconnects for field-effect transistor arrays with a device density that is five times higher than typical lithographically patterned wavy interconnects.

Instability and Breakup of Model Tear Films.

PURPOSE: An experimental platform to replicate the human tear film on a contact lens is presented. The influence of interfacial viscoelasticity in stabilizing in vitro model tear films against breakup and dewetting is investigated using this instrument. METHODS: Model tear films consisting of bovine meibomian lipids (meibum) spread on either PBS or artificial tear solution (ATS) are created. The interfacial shear rheology of these films is measured as a function of temperature. The dewetting dynamics of these films is then investigated using the Interfacial Dewetting and Drainage Optical Platform (i-DDrOP) on top of silicone hydrogel (SiHy) contact lenses at 23 and 35°C. The film breakup times are evaluated using two parameters: onset of film breakup, Tonset for thick films (∼100 µm), and tear breakup times, TBU for thin films (∼1 µm). Thin film thinning rates as a result of evaporation are also calculated. RESULTS: The ATS/meibum films have the largest surface rheology and correspondingly show the largest Tonset times at both 23 and 35°C. The parameter TBU is also significantly larger for ATS/meibum (TBU ∼ 40 seconds) compared with that of ATS and PBS/meibum films (TBU ∼ 30 seconds) at room temperature. However, at 35°C, all three model tear films exhibit similar TBU ∼ 17 seconds and average rate of thinning of -4 µm/minute. CONCLUSIONS: Tear film stability is influenced by both surface rheology and evaporation. The in vitro tear breakup times and thinning rates of model tear films at 35°C are in good agreement with in vivo measurements previously reported, highlighting the utility of the i-DDrOP for in vitro tear film breakup research.

Thermo-responsiveness and tunable optical properties of asymmetric polystyrene/PNIPAM-gold composite particles.

Environmentally responsive polystyrene/poly (N-isopropylacrylamide)-gold composite particles are successfully synthesized via a Pickering emulsion polymerization method. It is found that the core-shell and asymmetric structured particles are simultaneously formed during the polymerization. Compared with the core-shell structured composite particles, the asymmetric particles have a higher thermo-responsiveness as a result of differences in morphology and formation mechanism. For asymmetric composite particles, an increase in N-isopropylacrylamide (NIPAAM) content leads to more significant size variation upon temperature changes. From rheology measurements, the viscosity of asymmetric particles suspension greatly decreases as temperature is increased above the lower critical solution temperature (LCST). The large size decrease in asymmetric composite particles gives rise to a significant scattering intensity increase, as a result of increased refractive index contrast between the PNIPAM content and surrounding water. The resulting size decrease also leads to tunable surface plasmon resonance properties.