Silicone Hydrogel Contact Lens Materials Research Articles

Sustained Release of a Polymeric Wetting Agent from a Silicone-Hydrogel Contact Lens Material.

Uptake and release kinetics are investigated of a dilute aqueous polymeric-surfactant wetting agent, (ethylene oxide)45—(butylene oxide)10 copolymer, also referred to as poly(oxyethylene)-co-poly(oxybutylene), impregnated into a newly designed silicone-hydrogel lens material. Transient scanning concentration profiles of the fluorescently tagged polymeric surfactant follow Fick’s second law with a diffusion coefficient near 10–11 cm2/s, a value 3–4 orders smaller than that of the free surfactant in bulk water. The Nernst partition coefficient of the tagged polymeric wetting agent, determined by fluorescence microscopy and by methanol extraction, is near 350, a very large value. Back-extraction of the polymeric-surfactant wetting agent releases only ∼20% of the loaded amount after soaking the fully loaded lens for over 7 days. The remaining ∼80% is irreversibly bound in the lens matrix. Reverse-phase liquid chromatography of the lens-loaded and lens-extracted surfactant demonstrates that the released wetting agent is more hydrophilic with a higher polarity. Aqueous poly(oxyethylene)-co-poly(oxybutylene) is hypothesized to attach strongly to the lens matrix, most likely to the lens silicone domains. Strong binding leads to slow transient diffusion, to large uptake, and to significant irreversible retention. These characteristics indicate the suitability of using a poly(oxyethylene)-co-poly(oxybutylene) nonionic polymeric surfactant to maintain enhanced lens wettability over time. Methodology and findings from this study provide useful insights for designing sustained-release contact-lens wetting agents and materials.

Uptake and release of polyhexamethylene biguanide (PHMB) from hydrogel and silicone hydrogel contact lenses using a radiolabel methodology

PurposeThe purpose of this study was to evaluate the uptake and release of radiolabelled polyhexamethylene biguanide (PHMB) on reusable daily wear contact lenses (CLs) over 7 days. MethodsThree silicone hydrogel (SH) contact lens materials (lotrafilcon B, balafilcon A, senofilcon A) and two conventional hydrogel (CH) materials (etafilcon A, omafilcon A) were examined. In experiment 1 (1-day study), CLs were soaked in 2 mL of phosphate buffered solution (PBS) containing radiolabelled 14C PHMB (1 µg/mL) for 8 h. The release kinetics of 14C PHMB from the CLs was measured at t = 0.25, 0.5, 1, 2, 4, 8, and 24 h in fresh 2 mL PBS. In experiment 2 (7-day study), the CLs were soaked in the 14C PHMB (1 µg/mL) solution for 8 h followed by a 16-hour release in 2 mL PBS. The lens cycle was repeated daily for 7 days. After both experiments, the residual amount of PHMB remaining within the lenses was extracted to determine the total uptake of PHMB. ResultsIn experiment 1, the total uptake of PHMB for etafilcon A was significantly greater than senofilcon A (p = 0.01). There were no significant differences in total uptake of PHMB between other lens materials (p > 0.05). Etafilcon A released more PHMB compared to all other lens types over a 24-hr period (p < 0.001). In experiment 2, all CL materials continued to sorb more PHMB over time (p < 0.001). By day 7, the amount of PHMB sorbed by etafilcon A was significantly greater than senofilcon A (p = 0.02). After day 2, the CH materials released significantly more PHMB than the SH materials (p < 0.01). ConclusionThe CL materials continued to sorb PHMB with no signs of saturation after 7 days. All lens materials released a consistent amount of PHMB each day. Radioactive labelling provides a sensitive method of assessing the uptake and release of PHMB from CL materials.

The Impact of Incubation Conditions on In Vitro Phosphatidylcholine Deposition on Contact Lens Materials.

Previous in vitro measurements of contact lenses commonly investigate the impact of nonpolar tear film lipids (i.e., sterols). Polar lipids, however, are equally important stabilizing components of the tear film. This research explores and presents further knowledge about various aspects of polar lipid uptake that may impact contact lens performance. This study evaluated the impact of incubation time, lipid concentration, and replenishment of an artificial tear solution (ATS) on the uptake of phosphatidylcholine (PC) onto conventional hydrogel (CH) and silicone hydrogel (SH) contact lens materials. Four SHs and two CH lens materials (n = 4) were soaked in a complex ATS containing radioactive 14C-PC as a probe molecule. Phosphatidylcholine uptake was monitored at various incubation time points (1, 3, 7, 14, and 28 days), with different ATS lipid concentrations (0.5×, 1×, 2×) and with and without regular replenishment of the ATS. Phosphatidylcholine was extracted from the lenses, processed, and counted by a β counter, and accumulated PC (μg/lens) was extrapolated from standard lipid calibration curves. All materials exhibited increasing PC deposition over time. Conventional hydrogel materials showed significantly lower PC uptake rates (P < .001) than any of the SH materials. Increasing lipid concentration in the ATS resulted in increased PC binding onto the contact lens materials (P < .001). Replenishing the ATS every other day, however, impacted the PC deposition differently, showing increased binding (P < .001) on CHs and reduced PC deposition for SH materials (P < .001). Length of incubation, lipid concentration in the ATS, and renewal of the incubation solution all influenced the amount of PC that sorbed onto various lens materials and therefore need to be considered when conducting future in vitro deposition studies.

In vitro analysis of the interaction of tear film inflammatory markers with contemporary contact lens materials

PurposeSeveral clinical studies have suggested that reusable silicone hydrogel contact lens materials exhibit a two-times increased rate of corneal infiltrative events compared to reusable hydrogels. One potential factor contributing to this complication relates to the differential uptake of tear film-based pro-inflammatory cytokines. The purpose of this study was to use an in vitro assay to investigate whether four pro-inflammatory cytokines differed in their uptake onto six contemporary contact lens materials. MethodsConventional hydrogel (etafilcon A, omafilcon A) and silicone hydrogel (balafilcon A, comfilcon A, senofilcon A, somofilcon A) contact lens materials were soaked in solutions containing pro-inflammatory cytokines IL-1β, IL-6, IL-8 and TNF-α. Samples of the soaking solutions were collected over various time points and analyzed using the Meso Scale Discovery system, which served as a measurement of cytokine uptake onto the contact lens materials. ResultsBoth conventional hydrogels (etafilcon A, omafilcon A) and two of the four silicone hydrogels tested (balafilcon A, comfilcon A), exhibited some uptake of IL-1β, IL-8 or TNF-α (p < 0.05). Senofilcon A and somofilcon A did not exhibit uptake of any of these cytokines (p > 0.05). There was no uptake of IL-6 onto any of the contact lens materials investigated (p > 0.05). ConclusionThe contact lens materials tested did not exhibit any uptake of IL-6 and furthermore, did not exhibit more than 10 ± 3 % to 25 ± 12 % uptake of IL-1β, IL-8 or TNF-α. Numerous factors could contribute to the reported increase in corneal infiltrative events with reusable silicone hydrogel materials, however, based on these results, it appears that uptake of these four cytokines are unlikely to contribute to this finding.

Antifouling Silicone Hydrogel Contact Lenses with a Bioinspired 2-Methacryloyloxyethyl Phosphorylcholine Polymer Surface.

Inspired by the cell membrane surface as well as the ocular tissue, a novel and clinically applicable antifouling silicone hydrogel contact lens material was developed. The unique chemical and biological features on the surface on a silicone hydrogel base substrate were achieved by a cross-linked polymer layer composed of 2-methacryloyloxyethyl phosphorylcholine (MPC), which was considered important for optimal on-eye performance. The effects of the polymer layer on adsorption of biomolecules, such as lipid and proteins, and adhesion of cells and bacteria were evaluated and compared with several conventional silicone hydrogel contact lens materials. The MPC polymer layer provided significant resistance to lipid deposition as visually demonstrated by the three-dimensional confocal images of whole contact lenses. Also, fibroblast cell adhesion was decreased to a 1% level compared with that on the conventional silicone hydrogel contact lenses. The movement of the cells on the surface of the MPC polymer-modified lens material was greater compared with other silicone hydrogel contact lenses indicating that lubrication of the contact lenses on ocular tissue might be improved. The superior hydrophilic nature of the MPC polymer layer provides improved surface properties compared to the underlying silicone hydrogel base substrate.

Effect Of Silicon Hydrogel Contact Lens Materials On Tear Film Stability And Central Corneal Radius Of Curvature: A Comparative Study Of Balafilcon A And Lotrafilcon B

The keratometer was adjusted and focused on the right eye. With the mires in focus, the subject was asked to blink once and refrain from blinking. A stopwatch was started immediately after the last complete blink. At the first appearance of any distortion of the focusing mire, the stopwatch was stopped and the time noted. If subject blinks between measurements, the test is halted, and then repeated after several blinks. The interval between the last blink and the doubling/distortion of mires was recorded in seconds as the NIBUT. Five measurements were taken for each subject and the average of three closest NIBUT values was taken as the mean value.Contact Lens Materials and Corneal Radius of Curvature: -The corneal curvature of the subject was measured immediately after NIBUT assessment. The distorted mire was sharply focused with the focusing knob. The corneal curvature was converted to corneal radius of curvature (in millimetres) by dividing 337.5 by the dioptric power of the flatter meridian.RESULTS:25 subjects (50 eyes) were participated in this study. The corneal radius of curvature (CRC) and non-invasive tear break-up time (NIBUT) were assessed with the Bausch and Lomb Keratometer H-135A.Participants were allocated RE with BALAFILCON A and LE with LOTRAFILCON B, Single Blinded – (Patient). The difference in mean NIBUT between pre-insertion,8thday ,15thday ,22th day and 29thday of BALAFILCON A and LOTRAFILCON B Contact Lens wear was statistically significant where p value is <0.05 with paired T test. The difference in mean CRC between pre-insertion,8thday ,15thday ,22 thday and 29thday of BALAFILCON A and LOTRAFILCON B Contact Lens wear was statistically not significant where p value is> 0.05 with paired T test.CONCLUSION:Balafilcon A having greater corneal tearfilm stability compare to Lotrafilcon B. The corneal curvature was not significantly affected by any of the Silicone Hydrogel Contact Lens materials during the period under study.

Surface characterization of a silicone hydrogel contact lens having bioinspired 2-methacryloyloxyethyl phosphorylcholine polymer layer in hydrated state

A silicone hydrogel contact lens material, with a unique chemical and physical structure has been designed for long-term ocular performance. Enhancement of this silicone hydrogel contact lens material was achieved through surface modification using a cross-linkable bioinspired 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer, which creates a soft surface gel layer on the silicone hydrogel base material. The surface properties of this MPC polymer-modified lens were characterized under hydrated condition revealing, inter alia, its unique polymer structure, excellent hydrophilicity, lubricity, and flexibility. Analysis of the MPC polymer layer in a hydrated state was performed using a combination of a high-resolution environmental scanning electron microscopy and atomic force microscopy. Compared to the silicone hydrogel base material, this surface had a higher captive bubble contact angle, which corresponds to higher hydrophilicity of the surface. In addition, the hydrated MPC polymer layer exhibited an extremely soft surface and reduced the coefficient of friction by more than 80 %. These characteristics were attributed to the hydration state of the MPC polymer layer on the surface of the silicone hydrogel base material. Also, interaction force of protein deposition was lowered on the surface. Such superior surface properties are anticipated to contribute to excellent ocular performance.

In vitro Evaluation of the Location of Cholesteryl Ester Deposits on Monthly Replacement Silicone Hydrogel Contact Lens Materials.

PurposeThe deposition profile of cholesteryl ester on the surface and throughout the matrix of silicone hydrogel contact lens (CL) materials was determined under conditions that mimic a daily wear regimen.MethodsIn this in vitro study, four SiHy CL materials (senofilcon C, lotrafilcon B, comfilcon A and samfilcon A) were incubated in an artificial tear solution (ATS) for up to 30 days. CL incubation was alternated between the ATS (16 hours) and a multipurpose care regimen (8 hours). The ATS included fluorescently tagged cholesteryl ester (5-cholesten-3ß-ol 6-[(7-nitro-2-1,3-benzoxadiazol-4-yl)amino]caproate; CE-NBD) and confocal laser scanning microscopy visualized the distribution of the lipid through the CLs.ResultsThe distribution of CE-NBD was homogenous from the anterior to posterior surface in senofilcon C and comfilcon A, at all time points. For lotrafilcon B and samfilcon A, CE-NBD localization was heterogeneous, with greater amounts on the surfaces on Day 1 and Day 14 compared to the lens matrix; however, differences in concentration between the surface and bulk diminished by Day 30.ConclusionThe distribution of the non-polar lipid CE-NBD varied with lens material chemistry. While some lens materials deposited the lipid primarily on the surface after 16 hours of exposure, all materials exhibited a homogenous distribution after one month.

Altering the release of tobramycin by incorporating poly(ethylene glycol) into model silicone hydrogel contact lens materials

Delivery of drugs from contact lens materials is attractive for a number of reasons. However, the controlled delivery of hydrophilic drugs can be difficult to achieve due to the burst release of drug that is associated with materials of high water content, such as hydrogels. Silicone hydrogels have significant potential for drug delivery due to their increased hydrophobicity and the tortuous nature of the pores, overcoming some of the limitations associated with conventional hydrogel materials. The aim of this study was to examine the potential of model poly(ethylene glycol) (PEG) containing silicone hydrogels for delivery of hydrophilic aminoglycoside antibiotics. It was hypothesized that PEG, a polymer that has seen extensive use in biomedical applications, will provide in addition to hydrophilicity and protein repulsion, a mechanism for controlling the delivery of this hydrophilic antibiotic. PEG was combined with the macromer TRIS to create the model silicone hydrogel materials. The optical and physical properties of the novel TRIS-co-PEG silicone hydrogels exhibited excellent transparency, appropriate refractive index and high transmittance indicating minimal phase separation. Desirable properties such as wettability and protein repulsion were maintained across a wide range of formulations. The water content was found to be highly correlated with the ethylene oxide content. Drug release could be influenced through PEG content and was found to fit Higuchi-like kinetics. Overall, the study demonstrates that incorporation of PEG into a model silicone hydrogel could be used to control the release of a hydrophilic compound. Data suggests this is related to the unique structure and properties of PEG, which alter the types of water found in each formulation and the water content.

Comparing Pre-Lens Non-invasive TBUT with Two Different Silicone Hydrogel Contact Lens Materials

Purpose : To compare pre-lens non-invasive tear break-up time(NITBUT) and subjective ocular symptoms with two different silicone hydrogel lens materials. Methods : Samfilcon A and Comfilcon A lenses were worn on the right and left eyes of 32 (23.5± 2.92 years, female: 24, male: 8), respectively. After Each subjects attended three visits (on day 1 after 3 hours: on days 1 and 7 after 9 hours of wear), visual acuity using high (100%) and low (10%) contrast chart and pre-lens NITBUT using Keratograph 5M were measured. The subjects were surveyed with questionnaire for subjective ocular symptoms in terms of discomfort, dryness, changeable vision, closing eyes and removing lenses. Results : High and low contrast visual acuity, and pre-lens NITBUT values were not significantly different between Samfilcon A and Comfilcon A. There was no significant difference in visual acuity and NITBUT change during 7 days of wearing each lens. The relative frequency of subjective symptoms of 5 items related to wearing contact lenses was not significantly different in all items, the responses of the wearers in terms of lens preference were not statistically different (40.6%, 37.5%, respectively). Conclusion : The study demonstrates similar clinical results for pre-lens NITBUT and subjective ocular symptoms with Samfilcon A and Comfilcon A. The two silicone hydrogel lenses could not find the difference between the two lenses in the lens wearer despite difference lens materials and manufacturers.

Efficacy of Contact Lens Care Solutions in Removing Cholesterol Deposits From Silicone Hydrogel Contact Lenses.

To determine the efficacy of multipurpose solutions (MPSs) on the removal of cholesterol deposits from silicone hydrogel (SH) contact lens materials using an in vitro model. Five SH lens materials: senofilcon A, comfilcon A, balafilcon A, lotrafilcon A, and lotrafilcon B were removed from the blister pack (n=4 for each lens type), incubated for 7 days at 37°C in an artificial tear solution containing C radiolabeled cholesterol. Thereafter, lenses were stored in a preserved saline solution control (Sensitive Eyes Saline Plus) or cleaned with 1 of the 5 MPSs incorporating different preservatives (POLYQUAD/ALDOX, polyquaternium-1/alexidine, polyquaternium-1/PHMB, and 2 based on PHMB alone) using a rub and rinse technique, according to the manufacturer's recommendations, and stored in the MPS for a minimum of 6 hr. Lenses were then extracted with 2:1 chloroform:methanol, analyzed in a beta counter, and μg/lens of cholesterol was determined. Balafilcon A and senofilcon A lens materials showed the highest amounts of accumulated cholesterol (0.93±0.02 μg/lens; 0.95±0.01 μg/lens, respectively), whereas lotrafilcon A and lotrafilcon B deposited the lowest amounts (0.37±0.03 μg/lens; 0.47±0.12 μg/lens, respectively). For all lens materials, the MPS preserved with POLYQUAD/ALDOX removed more deposited cholesterol than any other test solution; however, the amount of removed cholesterol contamination from the individual contact lenses was only statistically significant for balafilcon A and senofilcon A (P=0.006 and P=0.042, respectively). Sensitive eyes and the other evaluated MPSs showed no significant effect on cholesterol removal (P>0.05). Cholesterol-removal efficacy varies depending on the combination of lens material and solution. Only 1 MPS showed a statistically significant reduction of cholesterol deposit for only 2 of the 5 tested lens materials.

Randomized crossover trial of silicone hydrogel contact lenses

PurposeThe aim of the current study is to assess, using new technologies, the interaction of four monthly silicone hydrogel contact lenses on the ocular surface and the comfort over 15 days of use. MethodsProspective cross-over, randomized and double-masked study including four materials (lotrafilcon-B, samfilcon-A , comfilcon-A and filcom-V3). Clinical examination was performed in the following order: tear meniscus height, first break-up of the tear film, the average time of all tear film breakup incidents, bulbar redness, limbal redness (Keratograph 5M ,Oculus, Germany); central corneal thickness (Pentacam, Oculus, Germany), thermography values (FLIR A325; FLIR Systems Inc., USA), and slit-lamp evaluations, including ocular surface staining. Finally, subjective comfort was obtained from Contact Lens Dry Eye Questionnaire-8. ResultsThe impact of contact lens wear on the ocular surface didn’t show statistically significant changes over time except for corneal and conjunctival staining grades on day 15 compared to day 1 for the comfilcon A group (P = .003 and P = .01, respectively). Contact lens stability and impact on the ocular surface during contact lens wear didn’t show statistically significant changes over time except in the case of the comfilcon A material with respect to the irritation item (P = .01). ConclusionsThese results suggest that the impact of monthly silicone hydrogel contact lens materials on the ocular surface after and during contact lens wear, contact lens stability over time, and subjective comfort did not reveal any significant changes over 15 days of use for any of the materials.

Lubricity comparison of a silicone hydrogel contact lens material, the human cornea, and a wetting agent

Purpose: Narafilcon A (daily disposable, silicone hydrogel) has been previously shown to be equivalent to no lens wear after one year in several key areas of physiology including corneal staining and papillary changes (Morgan et al., CLAE 2013). The material contains a high molecular weight wetting agent, polyvinylpyrrolidone (PVP), which has individual repeating units similar in function to ocular mucins in providing a lubricious (low friction) surface. It is hypothesized this lubricious interface helps to minimize the interaction between the contact lens (CL) and the eye. The purpose of this study was to evaluate the coefficient of friction (CoF) of PVP, narafilcon A and human corneal tissue in vitro to help elucidate the previously published clinical performance findings.

Visualization of a hyaluronan network on the surface of silicone-hydrogel materials.

Biotrue multipurpose solution (MPS) is a bioinspired disinfecting and conditioning solution that includes hyaluronic acid (HA) as a natural wetting agent. Previous studies demonstrated that HA sorbed from Biotrue MPS on both conventional and silicone hydrogel (SiHy) contact lens materials; an in vitro simulated-wear test validated the presence of HA on the lens surfaces for as long as 20 hours. In this study, the morphology and distribution of HA sorbed from both Biotrue and pure HA solution on SiHy contact lens surfaces was examined. Atomic force microscopy imaging was used to illustrate the topography of fresh SiHy contact lens materials before and after incubation with 0.1% (w/v) HA solution. The distribution, as well as fine details of the HA network, were resolved by first staining HA with Gram’s safranin, then imaging with confocal laser-scanning microscopy and differential interference-contrast microscopy. In this approach, SiHy materials take up the dye (safranin) nonspecifically, such that the resultant safranin–HA complex appears dim against the fluorescent lens background. Balafilcon A was chosen as the representative of glassy SiHy lenses that require postpolymerization plasma treatment to increase wettability. Senofilcon A and samfilcon A were chosen as representatives of SiHy materials fabricated with an internal wetting agent. A confluent and dim HA–safranin network was observed adhered to balafilcon A, senofilcon A, and samfilcon A lens surfaces incubated with either 0.1% (w/v) HA solution or Biotrue MPS. Therefore, the conditioning function provided by Biotrue MPS may be in part explained by the presence of the HA humectant layer that readily sorbs on the various types of SiHy contact lens materials.

Reduction in ionic permeability of a silicone hydrogel contact lenses after one month of daily wear

Purpose. To compare the ionic permeability using the ionoflux method of new and worn samples of a silicone hydrogel contact lens material. Methods. An ionoflux experimental setup was established to measure the ionic permeability (NaCl) of soft contact lenses. Samples of a silicone hydrogel lens (Comfilcon A, Coopervision, Pleasanton, CA) with optical powers of −1.00, −1.50 and −4.75 diopters (D) were used in this study. Three samples of each power were measured after being worn for one month on a daily wear basis. Lenses were cleaned and disinfected every night using multipurpose disinfecting solutions. Three samples of new lenses from the same batch and the same optical power were also measured to evaluate the effect of lens wear on the ionic permeability of the lens material. Before measurement, the lenses were equilibrated with a 1 M NaCl solution during one week before of each measurement. Results. Lens power had minimal effect on the ionic permeability of a modern silicone hydrogel contact lens with the −1.00 lens having a 15% lower permeability compared to the other two lenses. After one month of lens wear the apparent ionic permeability for lenses with −1.50 D decreased by 15%. In the case of −1.00 and −4.75 D lenses there was a decrease of 26%. Conclusions. The ionic permeability of silicone hydrogel lenses of different optical powers was not significantly different. Worn lenses present a significant reduction of the ionic permeability after a month of wear. The potential effect this reduction on lens movement and discomfort associated to lens wear should be further evaluated.

Timolol maleate release from hyaluronic acid-containing model silicone hydrogel contact lens materials.

This study was designed to assess the impact of a releasable wetting agent, such as hyaluronic acid (HA), on the release profile of timolol maleate (TM) from model silicone hydrogel contact lens materials. Polyvinylpyrrolidone (PVP) was used as an alternative wetting agent for comparison. The model lenses consisted of a hydrophilic monomer, either 2-hydroxyethyl methacrylate or N,N-dimethylacrylamide and a hydrophobic silicone monomer of methacryloxypropyltris (trimethylsiloxy) silane. The loading of the wetting and the therapeutic agent occurred during the synthesis of the silicone hydrogels through the method of direct entrapment. The developed materials were characterized by minimal changes in the water uptake, while lower molecular weight of HA improved their surface wettability. The transparency of the examined silicone hydrogels was found to be affected by the miscibility of the wetting agent in the prepolymer mixture as well as the composition of the developed silicone hydrogels. Sustained release of TM from 4 to 14 days was observed, with the drug transport occurring presumably through the hydrophilic domains of the silicone hydrogels. The release profile was strongly dependent on the hydrophilic monomer composition, the distribution of hydrophobic (silane) domains, and the affinity of the therapeutic agent for the silicone hydrogel matrix. Noncovalent entrapment of the wetting agent did not change the invitro release duration and kinetics of TM, however the drug release profile was found to be controlled by the simultaneous release of TM and HA or PVP. In the case of HA, depending on the HA:drug ratio, the release rate was decreased and controlled by the release of HA, likely due to electrostatic interactions between protonated TM and anionic HA. Overall, partitioning of the drug within the hydrophilic domains of the silicone hydrogels as well as interactions with the wetting agent determined the drug release profile.

Kinetics of Competitive Adsorption between Lysozyme and Lactoferrin on Silicone Hydrogel Contact Lenses and the Effect on Lysozyme Activity

Purpose: To determine the effect of competitive adsorption between lysozyme and lactoferrin on silicone hydrogel contact lenses and the effect on lysozyme activity.Methods: Three commercially available silicone hydrogel contact lens materials (senofilcon A, lotrafilcon B and balafilcon A) were examined, for time points ranging from 10 s to 2 h. Total protein deposition was determined by I125 radiolabeling of lysozyme and lactoferrin, while the activity of lysozyme was determined by a micrococcal activity assay.Results: Senofilcon A and balafilcon A did not show any relevant competitive adsorption between lysozyme and lactoferrin. Lotrafilcon B showed reduced protein deposition due to competitive adsorption for lactoferrin at all time points and lysozyme after 7.5 min. Co-adsorption of lactoferrin and lysozyme decreased the activity of lysozyme in solution for senofilcon A and lotrafilcon B, but co-adsorption had no effect on the surface activity of lysozyme for all lens types investigated.Conclusions: Competition between lysozyme and lactoferrin is material specific. Co-adsorption of lysozyme and lactoferrin does not affect the activity of surface-bound lysozyme but can reduce the activity of subsequently desorbed lysozyme.

Extended latanoprost release from commercial contact lenses: in vitro studies using corneal models.

In this study, we compared, for the first time, the release of a 432 kDa prostaglandin analogue drug, Latanoprost, from commercially available contact lenses using in vitro models with corneal epithelial cells. Conventional polyHEMA-based and silicone hydrogel soft contact lenses were soaked in drug solution ( solution in phosphate buffered saline). The drug release from the contact lens material and its diffusion through three in vitro models was studied. The three in vitro models consisted of a polyethylene terephthalate (PET) membrane without corneal epithelial cells, a PET membrane with a monolayer of human corneal epithelial cells (HCEC), and a PET membrane with stratified HCEC. In the cell-based in vitro corneal epithelium models, a zero order release was obtained with the silicone hydrogel materials (linear for the duration of the experiment) whereby, after 48 hours, between 4 to 6 of latanoprost (an amount well within the range of the prescribed daily dose for glaucoma patients) was released. In the absence of cells, a significantly lower amount of drug, between 0.3 to 0.5 , was released, (). The difference observed in release from the hydrogel lens materials in the presence and absence of cells emphasizes the importance of using an in vitro corneal model that is more representative of the physiological conditions in the eye to more adequately characterize ophthalmic drug delivery materials. Our results demonstrate how in vitro models with corneal epithelial cells may allow better prediction of in vivo release. It also highlights the potential of drug-soaked silicone hydrogel contact lens materials for drug delivery purposes.

In vitro and in vivo evaluation of novel ciprofloxacin-releasing silicone hydrogel contact lenses.

The purpose of this study was to evaluate ciprofloxacin-releasing silicone hydrogel contact lens materials in vitro and in vivo for the treatment of microbial keratitis. Model silicone hydrogel contact lens materials were manufactured using a molecular imprinting technique to modify ciprofloxacin release kinetics. Various contact lens properties, including light transmission and surface wettability, were determined, and the in vitro ciprofloxacin release kinetics elucidated using fluorescence spectrophotometry. The materials then were evaluated for their ability to inhibit Pseudomonas aeruginosa growth in vitro and in an in vivo rabbit model of microbial keratitis. Synthesized lenses had similar material properties to commercial contact lens materials. There was a decrease in light transmission in the shorter wavelengths due to incorporation of the antibiotic, but over 80% light transmission between 400 and 700 nm. Modified materials released for more than 8 hours, significantly longer than unmodified controls (P < 0.05). In vivo, there was no statistically significant difference between the number of colony-forming units (CFU) recovered from corneas treated with eye drops and those treated with one of two modified contact lenses (P > 0.05), which is significantly less than corneas treated with unmodified control lenses or those that received no treatment at all (P < 0.05). These novel contact lenses designed for the extended release of ciprofloxacin may be beneficial to supplement or augment future treatments of sight-threatening microbial keratitis.

In vitro efficiency of contact lens care solutions in removing cholesterol deposits from silicone hydrogel contact lenses

Purpose: To determine the efficiency of multi- purpose solutions (MPS) and saline in removing cholesterol deposits from silicone hydrogel (SH) contact lens materials using an in vitro model.