A single-lens polarographic measurement of oxygen permeability (Dk) for hypertransmissible soft contact lenses

Equilibrium water and solute uptake in silicone hydrogels

Equilibrium water content of and solute partitioning in silicone hydrogels (SiHys) are investigated using gravimetric analysis, fluorescence confocal laser-scanning microscopy (FCLSM), and back extraction with UV/Vis-absorption spectrophotometry. Synthesized silicone hydrogels consist of silicone monomer, hydrophilic monomer, cross-linking agent, and triblock-copolymer macromer used as an amphiphilic compatibilizer to prevent macrophase separation. In all cases, immiscibility of the silicone and hydrophilic polymers results in microphase-separated morphologies. To investigate solute uptake in each of the SiHy microphases, equilibrium partition coefficients are obtained for two hydrophilic solutes (i.e., theophylline and caffeine dissolved in aqueous phosphate-buffered saline) and two oleophilic solutes (i.e., Nile Red and Bodipy Green dissolved in silicone oil), respectively. Measured water contents and aqueous-solute partition coefficients increase linearly with increasing solvent-free hydrophilic-polymer volume fraction. Conversely, oleophilic-solute partition coefficients decrease linearly with rising solvent-free hydrophilic-polymer volume fraction (i.e., decreasing hydrophobic silicone-polymer fraction). We quantitatively predict equilibrium SiHy water and solute uptake assuming that water and aqueous solutes reside only in hydrophilic microdomains, whereas oleophilic solutes partition predominately into silicone microdomains. Predicted water contents and solute partition coefficients are in excellent agreement with experiment. Our new procedure permits a priori estimation of SiHy water contents and solute partition coefficients based solely on properties of silicone and hydrophilic homopolymer hydrogels, eliminating the need for further mixed-polymer-hydrogel experiments.

Safety, reliability, and operability of cochlear implant electrode arrays coated with biocompatible polymer

CONCLUSION

Polymer-coated electrodes can reduce surgically-induced trauma associated with the insertion of a cochlear implant (CI) electrode array.

OBJECTIVES

To evaluate if insertion trauma in CI surgery can be reduced by using electrode arrays coated with 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer.

METHODS

We analyzed characteristics of the Contour Advance electrode arrays coated with MPC polymer. To assess surgical trauma during electrode insertion, polymer-coated or uncoated (n = 5 each) animal electrode arrays were implanted in guinea pig cochleae and operability and electrophysiological and histological changes were assessed.

RESULTS

Under light and scanning electron microscopy, polymer-coated electrodes did not appear different from uncoated electrodes, and no change was observed after mechanical stressing of the arrays. Electrode insertion was significantly easier when polymer-coated electrodes were used. Auditory brainstem response (ABR) thresholds did not differ between groups, but p1-n1 amplitudes of the coated group were larger compared with the uncoated group at 32 kHz at 28 days after surgery. The survival of outer hair cells and spiral ganglion cells was significantly greater in the polymer-coated group.

Poly(dimethylsiloxane) (PDMS) surface patterning by biocompatible photo-crosslinking block copolymers

Poly(dimethylsiloxane) (PDMS) surface was patterned by poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC)-containing photo-crosslinking diblock copolymers upon photo-irradiation.

Simple surface treatment using amphiphilic phospholipid polymers to obtain wetting and lubricity on polydimethylsiloxane-based substrates

Simple surface treatment of polydimethylsiloxane (PDMS) substrates was performed using an aqueous-ethanolic solution of amphiphilic phospholipid polymers to reduce the hydrophobic and high friction characteristics of PDMS. The phospholipid polymers, poly(2-methacryloyloxyethyl phosphorylcholine (MPC)-co-2-ethylhexyl methacrylate (EHMA)-co-2-(N,N-dimethylamino)ethyl methacrylate) (PMED) and poly(MPC-co-EHMA) (PMEH) were synthesized, and the effects of the electric charge of the polymer chain on the stability of the attachment to the PDMS surface was investigated. The polymers were dissolved in a mixed solvent of ethanol and water, and the PDMS samples were treated by a simple dipping method using the polymer solution. Pure ethanol as the solvent was ineffective for the attachment of the polymers to the PDMS surface. It was considered that the hydrophobic interactions and electrostatic attraction forces between the polymer chains and the PDMS surface were too weak for efficient interaction in this solvent. On the other hand, the surface wettability and lubricity of PDMS could be improved by treatment with an aqueous-ethanolic solution of PMED. The static contact angle was decreased from 90° to 20° by this treatment, and the dynamic friction coefficient against a Co-Cr ball was decreased by nearly 80% compared with that of the untreated PDMS. The hydrophobic interactions and electrostatic attraction forces generated by PMED were both essential for the stable adsorption of the polymer layer on PDMS. Furthermore, the solubilized state of the polymers affected the adsorption of the polymer. We concluded that the surface of PDMS could be stably modified using aqueous-ethanolic solutions of PMED without the need for pretreatments.

Tear oxygen under hydrogel and silicone hydrogel contact lenses in humans

PURPOSE

To determine the tear oxygen tension under a variety of conventional and silicone hydrogel contact lenses in human subjects.

METHODS

Three hydrogel and five silicone hydrogel lenses (Dk/t = 17 to 329) were coated on the back surface with an oxygen sensitive, bovine serum albumin-Pd meso-tetra (4-carboxyphenyl) porphine complex (BSA-porphine). Each lens type was placed on the right eye of 15 non-contact lens wearers to obtain a steady-state open eye tear oxygen tension using oxygen sensitive phosphorescence decay of BSA-porphine. A closed-eye oxygen tension estimate was obtained by measuring the change in tear oxygen tension after 5 min of eye closure. In separate experiments, a goggle was placed over the lens wearing eye and a gas mixture (PO2 = 51 torr) flowed over the lens to simulate anterior lens oxygen tension during eye closure.

RESULTS

Mean open eye oxygen tension ranged from 58 to 133 torr. Closed eye estimates ranged from 11 to 42 torr. Oxygen tension under the goggle ranged from 8 to 48 torr and was higher than the closed eye estimate for six out of the eight lenses, suggesting that the average closed eye anterior lens surface oxygen tension is <51 torr. For Dk/t >30, the measured tear oxygen tension is significantly lower than that predicted from previous studies.

CONCLUSIONS

The phosphorescence decay methodology is capable of directly measuring the in vivo post lens PO2 of high Dk/t lenses without disturbing the contact lens or cornea. Our data indicate that increasing Dk/t up to and beyond 140 continues to yield increased flux into the central cornea.