Protein deposition on contact lenses: The past, the present, and the future

A self-healable and antifouling hydrogel based on PDMS centered ABA tri-block copolymer polymersomes: a potential material for therapeutic contact lenses

We have prepared an antifouling and self-healable PDMS based hydrogel which consists of a mixture of curcumin loaded zwitterionic PDMS polymersomes and amine functionalized PDMS polymersomes prepared via RAFT polymerization and Schiff-base reaction.

Adhesion of Pseudomonas aeruginosa, Achromobacter xylosoxidans, Delftia acidovorans, Stenotrophomonas maltophilia to contact lenses under the influence of an artificial tear solution

Corneal infection is a devastating sight-threatening complication that is associated with contact lens (CL) wear, commonly caused by Pseudomonas aeruginosa. Lately, Achromobacter xylosoxidans, Delftia acidovorans, and Stenotrophomonas maltophilia have been associated with corneal infection. This study investigated the adhesion of these emerging pathogens to CLs, under the influence of an artificial tear solution (ATS) containing a variety of components commonly found in human tears. Two different CL materials, etafilcon A and senofilcon A, either soaked in an ATS or phosphate buffered saline, were exposed to the bacteria. Bacterial adhesion was investigated using a radio-labeling technique (total counts) and plate count method (viable counts). The findings from this study revealed that in addition to P. aeruginosa, among the emerging pathogens evaluated, A. xylosoxidans showed an increased propensity for adherence to both CL materials and S. maltophilia showed lower viability. ATS influenced the viable counts more than the total counts on CLs.

Contact lens-related corneal infection: Intrinsic resistance and its compromise

Contact lenses represent a widely utilized form of vision correction with more than 140 million wearers worldwide. Although generally well-tolerated, contact lenses can cause corneal infection (microbial keratitis), with an approximate annualized incidence ranging from ~2 to ~20 cases per 10,000 wearers, and sometimes resulting in permanent vision loss. Research suggests that the pathogenesis of contact lens-associated microbial keratitis is complex and multifactorial, likely requiring multiple conspiring factors that compromise the intrinsic resistance of a healthy cornea to infection. Here, we outline our perspective of the mechanisms by which contact lens wear sometimes renders the cornea susceptible to infection, focusing primarily on our own research efforts during the past three decades. This has included studies of host factors underlying the constitutive barrier function of the healthy cornea, its response to bacterial challenge when intrinsic resistance is not compromised, pathogen virulence mechanisms, and the effects of contact lens wear that alter the outcome of host-microbe interactions. For almost all of this work, we have utilized the bacterium Pseudomonas aeruginosa because it is the leading cause of lens-related microbial keratitis. While not yet common among corneal isolates, clinical isolates of P. aeruginosa have emerged that are resistant to virtually all currently available antibiotics, leading the United States CDC (Centers for Disease Control) to add P. aeruginosa to its list of most serious threats. Compounding this concern, the development of advanced contact lenses for biosensing and augmented reality, together with the escalating incidence of myopia, could portent an epidemic of vision-threatening corneal infections in the future. Thankfully, technological advances in genomics, proteomics, metabolomics and imaging combined with emerging models of contact lens-associated P. aeruginosa infection hold promise for solving the problem - and possibly life-threatening infections impacting other tissues.

Localization of full-length recombinant human proteoglycan-4 in commercial contact lenses using confocal microscopy

The aim of this study was to determine the sorption location of full-length recombinant human proteoglycan 4 (rhPRG4) tagged with fluorescein isothiocyanate (FITC) to four silicone hydrogel contact lenses [balafilcon A (PureVision, Bausch + Lomb), senofilcon A (Acuvue Oasys, Johnson & Johnson), comfilcon A (Biofinity, CooperVision), lotrafilcon B (Air Optix, Alcon)] and one conventional hydrogel lens [etafilcon A (Acuvue 2, Johnson & Johnson)], using confocal laser scanning microscopy (CLSM). Lenses (n = 3 each) were incubated under two conditions: (1) FITC-rhPRG4 solution at 300 μg/mL and (2) phosphate-buffered saline, for 1 h at 37 °C in darkness with gentle shaking. The central 4 mm of each lens was removed and viewed with the Zeiss 510 CLSM using an argon laser at 488 nm (FITC excitation 495 nm, emission 521 nm). Depth scans were taken at 1 μm intervals to a maximum depth of 100 μm. All lens materials demonstrated sorption of rhPRG4. Both senofilcon A and balafilcon A revealed FITC-rhPRG4 penetration into the bulk of the lens, generally favoring the surface. rhPRG4 was observed exclusively on the surface of lotrafilcon B, with no presence within the bulk of the lens. rhPRG4 was evenly distributed throughout the bulk of the lens, as well as on the surface, for comfilcon A and etafilcon A. The sorption profile of FITC-rhPRG4 was successfully visualized using CLSM in various contact lens materials. The polymer composition, surface treatment and pore size of the material can influence the sorption of rhPRG4.

Biocompatibility of Nanocellulose-Reinforced PVA Hydrogel with Human Corneal Epithelial Cells for Ophthalmic Applications

Transparent composite hydrogel in the form of a contact lens made from poly(vinyl alcohol) (PVA) and cellulose nanocrystals (CNCs) was subjected to in vitro biocompatibility evaluation with human corneal epithelial cells (HCE-2 cells). The cell response to direct contact with the hydrogels was investigated by placing the samples on top of confluent cell layers and evaluating cell viability, morphology, and cell layer integrity subsequent to 24 h culture and removal of the hydrogels. To further characterize the lens-cell interactions, HCE-2 cells were seeded on the hydrogels, with and without simulated tear fluid (STF) pre-conditioning, and cell viability and morphology were evaluated. Furthermore, protein adsorption on the hydrogel surface was investigated by incubating the materials with STF, followed by protein elution and quantification. The hydrogel material was found to have affinity towards protein adsorption, most probably due to the interactions between the positively charged lysozyme and the negatively charged CNCs embedded in the PVA matrix. The direct contact experiment demonstrated that the physical presence of the lenses did not affect corneal epithelial cell monolayers in terms of integrity nor cell metabolic activity. Moreover, it was found that viable corneal cells adhered to the hydrogel, showing the typical morphology of epithelial cells and that such response was not influenced by the STF pre-conditioning of the hydrogel surface. The results of the study confirm that PVA-CNC hydrogel is a promising ophthalmic biomaterial, motivating future in vitro and in vivo biocompatibility studies.

Nanostructured supramolecular hydrogels: Towards the topical treatment of Psoriasis and other skin diseases

Supramolecular hydrogels were synthesized using a bis-imidazolium based amphiphile, and incorporating chemically diverse drugs, such as the cytostatics gemcitabine hydrochloride and methotrexate sodium salt, the immunosuppressive drug tacrolimus, as well as the corticoid drugs betamethasone 17-valerate and triamcinolone acetonide, and their potential as drug delivery agents in the dermal treatment of Psoriasis was evaluated. The rheological behavior of gels was studied, showing in all cases suitable viscoelastic properties for topical drug delivery. Scanning electron microscopy (SEM) shows that the drugs included have a great influence on the gel morphology at the microscopic level, as the incorporation of gemcitabine hydrochloride leads to slightly thicker fibers, the incorporation of tacrolimus induces flocculation and spherical precipitates, and the incorporation of methotrexate forms curled fibers. ¹H NMR spectroscopy experiments show that these drugs not only remain dissolved at the interstitial space, but up to 72% of either gemcitabine or methotrexate, and up to 38% of tacrolimus, is retained within the gel fibers in gels formed with a 1:1 gelator:drug molar ratio. This unique fiber incorporation not only protects the drug from degradation, but also importantly induces a Two Phase Exponential drug release, where the first phase corresponds to the drug dissolved in the interstitial space, while the second phase corresponds to the drug exiting from the gel fibers, and where the speed in each phase is in accordance with the physicochemical properties of the drugs, opening perspectives for controlled delivery. Skin permeation ex vivo tests show how these gels successfully promote the drug permeation and retention inside the skin for reaching their therapeutic target, while in vivo experiments demonstrate that they decrease the hyperplasia and reduce the macroscopic tissue damage typically observed in psoriatic skin, significantly more than the drugs in solution. All these characteristics, beside the spontaneous and easy preparation (room temperature and soft stirring), make these gels a good alternative to other routes of administration for Psoriasis treatment, increasing the drug concentration at the target tissue, and minimizing side effects.

Synthesis and Characterization of Silicone Contact Lenses Based on TRIS-DMA-NVP-HEMA Hydrogels

In this study, silicone-based hydrogel contact lenses were prepared by the polymerization of 3-(methacryloyloxy)propyltris(trimethylsiloxy)silane (TRIS), N,N-dimethylacrylamide (DMA), 1-vinyl-2-pyrrolidinone (NVP), and 2-hydroxyethylmethacrylate (HEMA). The properties of silicone hydrogel lenses were analyzed based on the methods such as equilibrium water content, oxygen permeability, optical transparency, contact angle, mechanical test, protein adsorption, and cell toxicity. The results showed that the TRIS content in all formulations increased the oxygen permeability and decreased the equilibrium water content, while both DMA and NVP contributed the hydrophilicity of the hydrogels. The maximum value of oxygen permeability was 74.9 barrers, corresponding to an equilibrium water content of 44.5% as well as a contact angle of 82°. Moreover, L929 fibroblasts grew on all these hydrogels, suggesting non-cytotoxicity. In general, the silicone hydrogels in this work exhibited good oxygen permeability, stiffness, and optical transparency as well as anti-protein adsorption. Hence, these silicone hydrogel polymers would be feasible for making contact lens.

Recent Trends in Advanced Contact Lenses

Exploiting contact lenses for ocular drug delivery is an emerging field in the area of biomedical engineering and advanced healthcare materials. Despite all the research conducted in this area, still, new technologies are in their early stages of the development, and more work must be done in terms of clinical trials to commercialize these technologies. A great challenge in using contact lenses for drug delivery is to achieve a prolonged drug release profile within the therapeutic range for various eye-related problems and diseases. In general, desired release kinetics to avoid the initial burst release is the zero-order kinetics within the therapeutic range. This review highlights the new technologies developed to achieve efficient and extended drug delivery. It also provides an overview of the materials and methods for fabrication of contact lenses and their mechanical and optical properties.

Surface modification of model hydrogel contact lenses with hyaluronic acid via thiol-ene "click" chemistry for enhancing surface characteristics

Discontinuation of contact lens wear as a result of ocular dryness and discomfort is extremely common; as many as 26% of contact lens wearers discontinue use within the first year. While patients are generally satisfied with conventional hydrogel lenses, improving on-eye comfort continues to remain a goal. Surface modification with a biomimetic, ocular friendly hydrophilic layer of a wetting agent is hypothesized to improve the interfacial interactions of the contact lens with the ocular surface. In this work, the synthesis and characterization of poly(2-hydroxyethyl methacrylate) surfaces grafted with a hydrophilic layer of hyaluronic acid are described. The immobilization reaction involved the covalent attachment of thiolated hyaluronic acid (20 kDa) on acrylated poly(2-hydroxyethyl methacrylate) via nucleophile-initiated Michael addition thiol-ene "click" chemistry. The surface chemistry of the modified surfaces was analyzed by Fourier transform infrared spectroscopy-attenuated total reflectance and X-ray photoelectron spectroscopy. The appearance of N (1s) and S (2p) peaks on the low resolution X-ray photoelectron spectroscopy spectra confirmed successful immobilization of hyaluronic acid. Grafting hyaluronic acid to the poly(2-hydroxyethyl methacrylate) surfaces decreased the contact angle, the dehydration rate, and the amount of nonspecific sorption of lysozyme and albumin in comparison to pristine hydrogel materials, suggesting the development of more wettable surfaces with improved water-retentive and antifouling properties, while maintaining optical transparency (>92%). In vitro testing also showed excellent viability of human corneal epithelial cells with the hyaluronic acid-grafted poly(2-hydroxyethyl methacrylate) surfaces. Hence, surface modification with hyaluronic acid via thiol-ene "click" chemistry could be useful in improving contact lens surface properties, potentially alleviating symptoms of contact lens related dryness and discomfort during wear.

Impact of a Hyaluronic Acid-Grafted Layer on the Surface Properties of Model Silicone Hydrogel Contact Lenses

The introduction of high oxygen transmissibility silicone hydrogel lenses ameliorated hypoxia-related complications, making them the most prescribed type of contact lens (CL). Despite the progress made over the last 2 decades to improve their clinical performance, symptoms of ocular dryness and discomfort and a variety of adverse clinical events are still reported. Consequently, the rate of CL wear discontinuation has not been appreciably diminished by their introduction. Aiming to improve the interfacial interactions of silicone hydrogel CLs with the ocular surface, a biomimetic layer of hydrophilic glycosaminoglycan hyaluronic acid (HA) (100 kDa) was covalently attached to the surface of model poly(2-hydroxyethyl methacrylate- co-3-methacryloxypropyl-tris-(trimethylsiloxy)silane) (pHEMA- co-TRIS) silicone hydrogel materials via UV-induced thiol-ene "click" chemistry. The surface structural changes after each modification step were studied by Fourier transform infrared spectroscopy-attenuated total reflectance and X-ray photoelectron spectroscopy (XPS). Successful grafting of a homogeneous HA layer to the surface of the model silicone hydrogels was confirmed by the consistent appearance of N (1s) and the significant decrease of the Si (2p) peaks, as determined by low-resolution angle-resolved XPS. The HA-grafted surfaces demonstrated reduced contact angles, dehydration rate, and nonspecific deposition of lysozyme and albumin, while maintaining their optical transparency (>90%). In vitro studies demonstrated that the HA-grafted pHEMA- co-TRIS materials did not show any toxicity to human corneal epithelial cells. These results suggest that surface immobilization of HA via thiol-ene "click" chemistry can be used as a promising surface treatment for silicone hydrogel CLs.

Bioinspired hydrogels for drug-eluting contact lenses

Efficient ocular drug delivery that can overcome the challenges of topical application has been largely pursued. Contact lenses (CLs) may act as light-transparent cornea/sclera bandages for prolonged drug release towards the post-lens tear fluid, if their composition and inner architecture are fitted to the features of the drug molecules. In this review, first the foundations and advantages of using CLs as ocular drug depots are revisited. Then, pros and cons of common strategies to prepare drug-loaded CLs are analyzed on the basis of recent examples, and finally the main section focuses on bioinspired strategies that can overcome some limitations of current designs. Most bioinspired strategies resemble a reverse engineering process to create artificial receptors for the drug inside the CL network by mimicking the human natural binding site of the drug. Related bioinspired strategies are being also tested for designing CLs that elute comfort ingredients mimicking the blinking-associated renewal of eye mucins. Other bioinspired approaches exploit the natural eye variables as stimuli to trigger drug release or take benefit of bio-glues to specifically bind active components to the CL surface. Overall, biomimicking approaches are being revealed as valuable tools to fit the amounts loaded and the release profiles to the therapeutic demands of each pathology. STATEMENT OF SIGNIFICANCE: Biomimetic and bioinspired strategies are remarkable tools for the optimization of drug delivery systems. Translation of the knowledge about how drugs interact with the natural pharmacological receptor and about components and dynamics of anterior eye segment may shed light on the design criteria for obtaining efficient drug-eluting CLs. Current strategies for endowing CLs with controlled drug release performance still require optimization regarding amount loaded, drug retained in the CL structure during storage, regulation of drug release once applied onto the eye, and maintenance of CL physical properties. All these limitations may be addressed through a variety of recently growing bioinspired approaches, which are expected to pave the way of medicated CLs towards the clinics.

Contact Lens Materials: A Materials Science Perspective

More is demanded from ophthalmic treatments using contact lenses, which are currently used by over 125 million people around the world. Improving the material of contact lenses (CLs) is a now rapidly evolving discipline. These materials are developing alongside the advances made in related biomaterials for applications such as drug delivery. Contact lens materials are typically based on polymer- or silicone-hydrogel, with additional manufacturing technologies employed to produce the final lens. These processes are simply not enough to meet the increasing demands from CLs and the ever-increasing number of contact lens (CL) users. This review provides an advanced perspective on contact lens materials, with an emphasis on materials science employed in developing new CLs. The future trends for CL materials are to graft, incapsulate, or modify the classic CL material structure to provide new or improved functionality. In this paper, we discuss some of the fundamental material properties, present an outlook from related emerging biomaterials, and provide viewpoints of precision manufacturing in CL development.

Synthesis of poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) with low polydispersity using ultrasonic irradiation

Poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) having low polydispersity was synthesized in mixed solvent of ethanol and water using ultrasonic irradiation without any chemical polymerization initiator. The effects of the volume fraction of ethanol in the solvent, the molar ratio of two monomers, the monomer concentration and the ultrasonic power intensity on the time courses of the conversion to the polymer, the number average molecular weight, and the polydispersity of synthesized polymer were investigated in order to determine the optimal conditions to synthesize the copolymers with a narrow molecular weight distribution (i.e. low polydispersity). The optimum volume fraction of ethanol in the solvent was 60 vol% to synthesize the copolymers with a low polydispersity. A higher ultrasonic power intensity resulted in a faster polymerization rate and a lower number average molecular weight. The polydispersity was less than 1.5 for all ultrasonic power intensities up to 450 W/dm³ applied in this work. A higher monomer concentration gave a faster polymerization rate and a higher number average molecular weight. The polydispersity was less than 1.5 when the monomer concentration was lower than 0.4 mol/dm³. A higher molar ratio of N-isopropylacrylamide resulted in a higher polymerization rate and a lower number average molecular weight. The copolymers with polydispersity less than 1.5 can be obtained regardless of the molar ratio of N-isopropylacrylamide. The copolymers synthesized by the ultrasonic polymerization method had a high temperature responsibility.

Novel in vitro method to determine pre-lens tear break-up time of hydrogel and silicone hydrogel contact lenses

PURPOSE

To develop an in vitro model to determine pre-lens non-invasive break-up time (NIBUT) and to subsequently use this method to compare the NIBUT over contemporary daily disposable (DD) contact lenses (CL).

METHODS

Three silicone hydrogel (SH) and two conventional hydrogel (CH) DD CLs were incubated in an artificial tear solution (ATS). A model blink cell (MBC) was utilised to mimic intermittent air exposure. CLs were repeatedly submerged for 3 seconds (s) and exposed to air for 10 s over periods of 2, 6, 12, and 16 hours (h). NIBUTs (n = 4) were determined out of the blister pack (T₀) and at the end of each incubation period.

RESULTS

Overall, nesofilcon A showed the longest NIBUTs (p < 0.001). At T₀, CHs revealed significantly longer NIBUTs (p ≤ 0.001) than SHs. After 2 h, nesofilcon A showed the longest NIBUT, however, this was only statistically significant compared with delefilcon A (p ≤ 0.001). After 6 h, nesofilcon A NIBUT was significantly longer than all other CLs (p ≤ 0.001). Etafilcon A showed a significantly longer NIBUT (p ≤ 0.001) after 12 h and delefilcon A had the longest NIBUT (p ≤ 0.001) after 16 h. Statistically significant (p ≤ 0.05) changes of NIBUT within the lens materials varied between time points. After 16 h, all CLs showed significant reductions in NIBUTs (p ≤ 0.001) in comparison to T₀.

CONCLUSION

NIBUT values reduced gradually over time and varying levels of deposition impacted measured pre-lens NIBUTs. While NIBUT of CH materials are longer immediately out of the blister pack, after tear film exposure, the NIBUTs obtained using this methodology became very similar.

Differences between tears of contact lens wearers studied by photon correlation spectroscopy

PURPOSE

The purpose was to evaluate if there are differences between tears of contact lens (CL) wearers of different materials detectable by measuring the hydrodynamic diameter of tear components through photon correlation spectroscopy (PCS).

METHODS

Tears of 59 CL wearers and tears of 39 non-wearers were collected by glass capillary. Wearers were divided into groups depending on the CL material: (i) hydrogels of II FDA group (H-II, 15 subjects), (ii) hydrogels of IV FDA group (H-IV, 13 subjects), (iii) silicone hydrogels (SH, 31 subjects). PCS analyses were performed at 25 °C on samples diluted with deionized water with tear concentration (10 ± 2)% ^V/_W to obtain, for each subject, the average hydrodynamic diameter (d_H,avg) of tear components by analyzing intensity fluctuations in time of scattered light.

RESULTS

Means of d_H,avg calculated on each group were found, on increasing order, to be 256 nm (std dev 18 nm) for non-wearers, 297 nm (std dev 45 nm) for H-II, 360 nm (std dev 76 nm) for SH, and 391 nm (std dev 85 nm) for H-IV with statistical differences between each group of wearers compared to non-wearers and between groups of wearers except between SH and H-IV.

CONCLUSIONS

PCS reveals the differences between tears of CL wearers of different materials, not only between tears of wearers and non-wearers.

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

PURPOSE

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.

MATERIALS AND METHODS

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.

RESULTS

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).

CONCLUSION

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.

Inner layer-embedded contact lenses for ion-triggered controlled drug delivery

Drug leakage during manufacturing and storage process is the main obstacle hindering the application of contact lenses as the carrier for extended ocular drug delivery. In this study, we have designed a novel inner layer-embedded contact lens capable of ion-triggered drug release for extended ocular drug delivery. Using betaxolol hydrochloride as a drug model, drug-ion exchange resin complex dispersed polymer film was used as an inner layer, and silicone hydrogel was used as an outer layer to fabricate inner layer-embedded contact lens. Influence of composition of the inner film and crosslinking degree of the outer hydrogel on drug release profile was studied and optimized for weekly use. The ion-triggered drug eluting property enables the inner layer-embedded contact lens being stable when stored in distilled water at 5 °C for at least 30 days with ignorable drug loss and negligible changes in drug release kinetics. In vivo pharmacokinetic study in rabbits showed sustained drug release for over 168 h in tear fluid, indicating significant improvement in drug corneal residence time. A level A IVIVC was established between in vitro drug release and in vivo drug concentration in tear fluid. In conclusion, this inner layer embedded contact lens design could be used as a platform for extended ocular drug delivery with translational potential for both anterior and posterior ocular disease therapy.

Short-Term Deposition of PM2.5 Particles on Contact Lens Surfaces: Effect on Oxygen Permeability and Refractive Index

PURPOSES

To identify the deposition of fine (≤2.5 μm diameter) particulate matter (PM) particles (PM_2.5) on contact lens surfaces and to investigate the effects of such deposition on the oxygen permeability (OP) and refractive index (RI) of contact lenses.

METHODS

A total of 36 contact lenses, including rigid gas permeable (RGP) lens and soft contact lens (SCL), were investigated. RGP lens (n=12) and SCL (n=12) (experimental group) were incubated in a PM_2.5 solution for 24 h, after which PM_2.5-treated RGP lens (n=6) and SCL (n=6) were further washed for 1 h in phosphate-buffered saline (PBS). All lenses were examined by field emission scanning electron microscopy. OP and RI of all lenses were measured.

RESULTS

Average-sized PM_2.5 particles deposited on RGP contact lens and SCL surfaces after immersion in the PM_2.5 solution were 3.192 ± 1.637 and 2.158 ± 1.187/100 μm², respectively. On RGP lens surfaces, we observed both large (≥2.5 µm diameter) and small (PM_2.5) particles. PM_2.5 particles were deposited in diffuse patterns, primarily along the honeycomb structural border of SCL, while no PM_2.5 particles were found in the honeycomb hole of SCL surfaces. Washing in PBS removed the larger PM particles from RGP lens surfaces, but left copious amounts of PM_2.5 particles. In contrast, nearly all PM particles were removed from SCL surfaces after PBS washing. OP values of RGP lens and SCL appeared to be unchanged by PM_2.5 deposition. RI values increased in both RGP lens and SCL groups after PM_2.5 deposition. However, these increases were not statistically significant, suggesting that PM_2.5 deposition itself does not cause fluctuations in contact lens RI.

CONCLUSIONS

Deposition of PM_2.5 particles on contact lens surfaces varies according to lens material. PM_2.5 particles deposited on SCL, but only large particles on RGP surfaces were able to be removed by washing in PBS and did not appear to alter OP and RI of either lens type.

A comprehensive review on contact lens for ophthalmic drug delivery

With the prevalence of electronic devices and an aging population, the number of people affected with eye disease is increasing year by year. In spite of a large number of eye drops on the market, most of them do not perform sufficiently, due to rapid clearance mechanisms and ocular barriers. To enhance drug delivery to the eye, a number of novel formulations for ocular diseases have been investigated over recent decades, aiming to increase drug retention and permeation while also allowing for sustained drug release over prolonged periods. The contact lens, initially used to correct visual acuity and beautify female eyes, is one such novel formulation with outstanding potential. Recently, contact lenses have been extensively used for ocular drug delivery to enhance ocular bioavailability and reduce side effects, and are particularly suitable for the treatment of chronic diseases, and thus are of interest to ophthalmic scientists. This review summarizes contact lens classification, methods of preparation, strategies for integrating drugs into lenses, in vitro and in vivo studies, and clinical applications. This review also discusses the current state of ocular drug therapy and provides an outlook for future therapeutic opportunities in the field of ocular drug delivery.

Influence of Tear Protein Deposition on the Oxygen Permeability of Soft Contact Lenses

Purpose. To investigate the effect of tear protein deposition on the change in oxygen permeability (Dk) of soft contact lenses (SCL). Methods. Three hydrogel lenses (polymacon, nelfilcon A, and etafilcon A) and two silicon hydrogel lenses (lotrafilcon A and balafilcon A) were investigated. Etafilcon A lenses were incubated in artificial tear solution for 1, 6, 12, and 48 h, whereas the other SCL were incubated for 1, 3, 7, and 14 days. Oxygen permeability was measured using the polarographic method, and lenses were stacked in four layers to correct the boundary effect. Results. The Dk of all investigated SCL was decreased by the protein deposition. Silicone hydrogel lenses showed a smaller deposition of artificial tear proteins than conventional hydrogel lenses. However, their Dk was reduced twofold than those of 3 conventional hydrogel lenses when compared at the same level of protein deposition. Despite a large amount of total deposited protein in etafilcon A lenses, their Dk was more stable than other SCL. Conclusions. From the results, it was revealed that the Dk of SCL is different from the value provided by manufacturers because of the tear protein deposition on surface and/or in pore of SCL; however, the degree of Dk change in SCL was not simply correlated with the amount of tear protein deposition. Thus, it is considered that the correlation between tear protein deposition and properties of lens materials affects Dk change.

Hierarchical patterning of hydrogels by replica molding of impregnated breath figures leads to superoleophobicity

The surface chemistry and topography govern the spreading of liquids on a solid. When an oil drop makes a contact angle, θ > 90° on a solid surface, the solid is termed as oleophobic. Adding roughness to an inherently oleophobic surface enhances its oil dewetting and can lead to superoleophobicity when θ > 150°. In this study, we introduce the concept of a two-tier hierarchical roughness on the surface of soft materials such as hydrogels by forming the patterned inverse replica of breath figure polymer films impregnated with nanoparticles. The directed deposition of nanoparticles in the breath figure pores is accomplished by an aerosol assisted technique that exclusively leads to deposition within the pores and filling of the pores. The inverse replica of such impregnated films exhibits a close packed hexagonally structured second tier of surface roughness which directly leads to a superoleophobic surface. Since these structures have well defined geometries, it is possible to estimate the contact angle by assuming a partial wetting of the oil drop in a 'fakir' state on the rough surface. The estimation is in good agreement with the experimental contact angle value. While the work demonstrates a facile method to impart superoleophobicity to a hydrogel surface, it also demonstrates new methods to imbue breath figure pores with functional materials that can be easily transferred to the pores of the inverse replica.

"Click" Chemistry-Tethered Hyaluronic Acid-Based Contact Lens Coatings Improve Lens Wettability and Lower Protein Adsorption

Improving the wettability of and reducing the protein adsorption to contact lenses may be beneficial for improving wearer comfort. Herein, we describe a simple "click" chemistry approach to surface functionalize poly(2-hydroxyethyl methacrylate) (pHEMA)-based contact lenses with hyaluronic acid (HA), a carbohydrate naturally contributing to the wettability of the native tear film. A two-step preparation technique consisting of laccase/TEMPO-mediated oxidation followed by covalent grafting of hydrazide-functionalized HA via simple immersion resulted in a model lens surface that is significantly more wettable, more water retentive, and less protein binding than unmodified pHEMA while maintaining the favorable transparency, refractive, and mechanical properties of a native lens. The dipping/coating method we developed to covalently tether the HA wetting agent is simple, readily scalable, and a highly efficient route for contact lens modification.

A contact-lens-on-a-chip companion diagnostic tool for personalized medicine

We present a novel, microfluidic platform that integrates human tears (1 μL) with commercial contact lens materials to provide personalized assessment of lens care solution performance. This device enabled the detection of significant differences in cleaning and disinfection outcomes between subjects and between biofilms vs. planktonic bacteria.

Hydrogel Inverse Replicas of Breath Figures Exhibit Superoleophobicity Due to Patterned Surface Roughness

The wetting behavior of a surface depends on both its surface chemistry and the characteristics of surface morphology and topography. Adding structure to a flat hydrophobic or oleophobic surface increases the effective contact angle and thus the hydrophobicity or oleophobicity of the surface, as exemplified by the lotus leaf analogy. We describe a simple strategy to introduce micropatterned roughness on surfaces of soft materials, utilizing the template of hexagonally packed pores of breath figures as molds. The generated inverse replicas represent micron scale patterned beadlike protrusions on hydrogel surfaces. This added roughness imparts superoleophobic properties (contact angle of the order of 150° and greater) to an inherently oleophobic flat hydrogel surface, when submerged. The introduced pattern on the hydrogel surface changes morphology as it swells in water to resemble morphologies remarkably analogous to the compound eye. Analysis of the wetting behavior using the Cassie-Baxter approximation leads to estimation of the contact angle in the superoleophobic regime and in agreement with the experimental value.

Deposition of a hydrophilic nanocomposite-based coating on silicone hydrogel through a laser process to minimize UV exposure and bacterial contamination

Silicone hydrogel used as contact lens is deposited a nanocomposite coating by a matrix assisted pulsed laser evaporation (MAPLE), which can protect eyes from UV exposure, and against bacterial contamination.

Tear film proteins deposited on high water content contact lenses identified with two-dimensional gel electrophoresis and mass spectrometry

PURPOSE

Tear film proteins adhere to the surface of contact lenses (CLs). While the proteins in the tears have been extensively studied with various proteomic techniques, adhered proteins to CLs are less studied. In this pilot study, we have separated proteins with 2D gel electrophoresis prior to the conventional mass spectrometry (MS) in order to analyse the deposited proteins on hydrogel CLs from myopic patients.

METHODS

pHEMA and PVA hydrogel CLs worn by 3 patients for different time lengths were analysed. After wear, the CLs were frozen at -20°C. Proteins were extracted in lysis buffer, separated on 12% polyacrylamide gels and silver-stained. Protein spots were excised and identified with liquid chromatography - tandem MS.

RESULTS

Deposited proteins were extracted with a yield of 26-66 μg and separated by 2D gel electrophoresis. The silver-stained gels showed similar protein patterns independent of the patient, hydrogel type and wear time. Seventy-two spots were analysed with MS, representing at least 12 different tear film proteins or protein fragments.

CONCLUSIONS

Deposited tear film proteins from a single set of CLs worn for 1 day can successfully be analysed first with 2D gel electrophoresis and subsequently with MS, thus making examination of individual patients possible. The protein composition appeared homogeneous between the test persons which is a necessity for additional comparison analysis. The molecular masses of the identified proteins indicate that protein degradation occurs only as a minor event. Myopic patients were investigated in this pilot study, but the combined techniques can easily be applied to other eye diseases.

The effect of albumin and cholesterol on the biotribological behavior of hydrogels for contact lenses

The irritation/discomfort associated with the use of contact lenses (CLs) is often related to the eyelid-lens friction. Although the use of such devices is widespread, the information about the influence of the lacrimal fluid biomolecules on the tribological behavior of the CLs hydrogels is scarce. In this work, we investigated the effect of the presence of albumin and cholesterol in the lubricant medium, on the frictional response of two model hydrogels for CLs: a hydroxyethylmethacrylate based hydrogel, HEMA/PVP, and a silicone based one, TRIS/NVP/HEMA. Tribological experiments were done in a nanotribometer, in water and in the presence of solutions of those biomolecules. It was observed a significant increase of the friction coefficient (μ) for HEMA/PVP when the lubricant contains cholesterol, and for TRIS/NVP/HEMA when it contains albumin. Solid-state NMR and DSC analysis revealed that HEMA/PVP hydrated in cholesterol solution has a lower amount of free and loosely bound water than the hydrogel hydrated in water. Therefore, a smaller amount of water shall be released into the contact region during the friction tests with cholesterol solution, leading to a thinner film in the contact zone, and consequently to a higher μ. Concerning TRIS/NVP/HEMA, QCM-D studies showed that this hydrogel adsorbs less albumin than HEMA/PVP and that the formed film is more rigid, which can explain the increase of μ. The obtained results contribute to understand the influence of lacrimal fluid composition on the tribological behavior of CLs materials, being relevant for the selection and optimization of these devices.

STATEMENT OF SIGNIFICANCE

Understanding the tribological behavior of contact lenses (CLs) materials in contact with the lacrimal fluid and the role of its components is of major importance to optimize the comfort and overall success of these devices. Nevertheless, the available information on this subject in the literature is scarce. In this work, the effect of albumin and cholesterol (two of the main components of the lacrimal fluid) on the frictional response of distinct types of hydrogels suitable for CLs, is compared, for the first time. Significant differences were observed with the two molecules, depending on the material, stressing the need to further study this issue to understand, predict and optimize the in vivo performance of CLs.

Atomic force microscopy and Langmuir-Blodgett monolayer technique to assess contact lens deposits and human meibum extracts

PURPOSE

The purpose of this exploratory study was to investigate the differences in meibomian gland secretions, contact lens (CL) lipid extracts, and CL surface topography between participants with and without meibomian gland dysfunction (MGD).

METHODS

Meibum study: Meibum was collected from all participants and studied via Langmuir-Blodgett (LB) deposition with subsequent Atomic Force Microscopy (AFM) visualization and surface roughness analysis. CL Study: Participants with and without MGD wore both etafilcon A and balafilcon A CLs in two different phases. CL lipid deposits were extracted and analyzed using pressure-area isotherms with the LB trough and CL surface topographies and roughness values were visualized using AFM.

RESULTS

Meibum study: Non-MGD participant meibum samples showed larger, circular aggregates with lower surface roughness, whereas meibum samples from participants with MGD showed more lipid aggregates, greater size variability and higher surface roughness. CL Study: Worn CLs from participants with MGD had a few large tear film deposits with lower surface roughness, whereas non-MGD participant-worn lenses had many small lens deposits with higher surface roughness. Balafilcon A pore depths were shallower in MGD participant worn lenses when compared to non-MGD participant lenses. Isotherms of CL lipid extracts from MGD and non-MGD participants showed a seamless rise in surface pressure as area decreased; however, extracts from the two different lens materials produced different isotherms.

CONCLUSIONS

MGD and non-MGD participant-worn CL deposition were found to differ in type, amount, and pattern of lens deposits. Lipids from MGD participants deposited irregularly whereas lipids from non-MGD participants showed more uniformity.

In Vitro Spoilation of Silicone-Hydrogel Soft Contact Lenses in a Model-Blink Cell

PURPOSE

We developed an in vitro model-blink cell that reproduces the mechanism of in vivo fouling of soft contact lenses. In the model-blink cell, model tear lipid directly contacts the lens surface after forced aqueous rupture, mirroring the pre-lens tear-film breakup during interblink.

METHODS

Soft contact lenses are attached to a Teflon holder and immersed in artificial tear solution with protein, salts, and mucins. Artificial tear-lipid solution is spread over the air/tear interface as a duplex lipid layer. The aqueous tear film is periodically ruptured and reformed by withdrawing and reinjecting tear solution into the cell, mimicking the blink-rupture process. Fouled deposits appear on the lenses after cycling, and their compositions and spatial distributions are subsequently analyzed by optical microscopy, laser ablation electrospray ionization mass spectrometry, and two-photon fluorescence confocal scanning laser microscopy.

RESULTS

Discrete deposit (white) spots with an average size of 20 to 300 μm are observed on the studied lenses, confirming what is seen in vivo and validating the in vitro model-blink cell. Targeted lipids (cholesterol) and proteins (albumin from bovine serum) are identified in the discrete surface deposits. Both lipid and protein occur simultaneously in the surface deposits and overlap with the white spots observed by optical microscopy. Additionally, lipid and protein penetrate into the bulk of tested silicone-hydrogel lenses, likely attributed to the bicontinuous microstructure of oleophilic silicone and hydrophilic polymer phases of the lens.

CONCLUSIONS

In vitro spoilation of soft contact lenses is successfully achieved by the model-blink cell confirming the tear rupture/deposition mechanism of lens fouling. The model-blink cell provides a reliable laboratory tool for screening new antifouling lens materials, surface coatings, and care solutions.

Prevention and removal of lipid deposits by lens care solutions and rubbing

PURPOSE

Despite the prevalence of silicone hydrogel (SiHy) contact lenses, there are relatively few studies that evaluate the efficacy of multipurpose lens care solutions (MPSs) in reducing lipid deposition on these lenses and the effect of rubbing on the removal. Therefore, we used an in vitro soaking and rubbing model to compare the effectiveness of borate buffered saline (BBS) and two commercial MPSs, PureMoist and Biotrue, in preventing sorption of representative polar and nonpolar lipids.

METHODS

Radiolabeled cholesterol (CH) and dipalmitoylphosphatidylcholine (DPPC) were sorbed on two SiHy lenses (senofilcon A and balafilcon A) from an artificial tear fluid. Deposition and removal were evaluated by quantitative solvent extraction and scintillation counting.

RESULTS

The efficiencies of the MPSs in reducing lipid deposition are somewhat dependent on lens material. Both DPPC and CH sorption on senofilcon A are greater when lenses are preconditioned in BBS compared with preconditioning in either MPS (p < 0.05). However, neither MPS affects lipid sorption on balafilcon A lenses (p > 0.05). As for removal of presorbed lipids, neither PureMoist, Biotrue, nor BBS removed CH in the absence of rubbing. When a simulated rubbing protocol was used, minimal but detectible CH was removed (p < 0.05) from senofilcon A and balafilcon A lenses (likely only from the lens surface). These commercial solutions were not substantially better than BBS in removing DPPC, with or without rubbing (p > 0.05).

CONCLUSIONS

These data suggest that MPSs do not appreciably alter lipid sorption. Rubbing lenses removes a small amount of sorbed lipids. Yet, we recommend that MPSs be used as they may disinfect SiHy lenses and may clean their surfaces of large particles.

Dexamethasone diffusion across contact lenses is inhibited by Staphylococcus epidermidis biofilms in vitro

PURPOSE

This study was designed to measure the impact of bacterial biofilms on diffusion of an ocular therapeutic through silicone hydrogel bandage lenses in vitro.

METHODS

An assay was designed to study the passage of a commonly used steroid, dexamethasone, through silicone hydrogel soft contact lenses. Diffused dexamethasone was measured using a spectrophotometer over a period of 18 hours and quantified using a standard curve. This assay was performed with control and Staphylococcus epidermidis biofilm-coated contact lenses comprised of lotrafilcon A and methafilcon. Biofilms were formed in brain heart infusion broth supplemented with D-glucose.

RESULTS

The presented data validate a simple in vitro model that can be used to measure the penetration of a topical therapeutic through silicone hydrogel soft contact lenses. Using this model, we measured a reduction in dexamethasone diffusion up to 88% through S. epidermidis biofilm-coated silicone hydrogel lenses compared with control lenses.

CONCLUSIONS

The results of this in vitro study demonstrate that bacterial biofilms impede dexamethasone diffusion through silicone hydrogel contact lenses and warrant future studies regarding the clinical benefit of using ocular therapeutics in the setting of bandage contact lens use for corneal epithelial defects.

Fluorescent solute-partitioning characterization of layered soft contact lenses

Partitioning of aqueous packaging, wetting, and care-solution agents into and out of soft contact lenses (SCLs) is important for improving wear comfort and also for characterizing lens physico-chemical properties. We illustrate both features of partitioning by application of fluorescent-solute partitioning into DAILIES TOTAL1® (delefilcon A) water-gradient SCLs, which exhibit a layered structure of a silicone-hydrogel (SiHy) core sandwiched between thin surface-gel layers. Two-photon fluorescence confocal laser-scanning microscopy and attenuated total-reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) characterize the lens and assess uptake profiles of six prototypical fluorescent solutes. Comparison of solute uptake in a SiHy-core prototype lens (i.e., O2OPTIX(TM)) validates the core SiHy structure of DAILIESTOTAL1®. To establish surface-layer charge, partition coefficients and water contents are obtained for aqueous pH values of 4 and 7.4. Solute fluorescence-intensity profiles clearly confirm a layered structure for the DAILIES TOTAL1® lenses. In all cases, aqueous solute partition coefficients are greater in the surface layers than in the SiHy core, signifying higher water in the surface gels. ATR-FTIR confirms surface-layer mass water contents of 82±3%. Water uptake and hydrophilic-solute uptake at pH 4 compared with that at pH 7.4 reveal that the surface-gel layers are anionic at physiologic pH 7.4, whereas both the SiHy core and O2OPTIX™ (lotrafilcon B) are nonionic. We successfully confirm the layered structure of DAILIES TOTAL1®, consisting of an 80-μm-thick SiHy core surrounded by 10-μm-thick polyelectrolyte surface-gel layers of significantly greater water content and aqueous solute uptake compared with the core. Accordingly, fluorescent-solute partitioning in SCLs provides information on gel structure and composition, in addition to quantifying uptake and release amounts and rates.

Surface modification of intraocular lenses with hyaluronic acid and lysozyme for the prevention of endophthalmitis and posterior capsule opacification

Posterior capsule opacification is one of the complications of cataract surgery caused by the adhesion and reproduction of residual human lens epithelial cells (HLECs) on the posterior capsule.

Antibiofouling polymer interfaces: poly(ethylene glycol) and other promising candidates

This review highlights antibiofouling polymer interfaces with emphasis on the latest developments using poly(ethylene glycol) and the design new polymeric structures.

Contact lenses as drug reservoirs & delivery systems: the successes & challenges

Although conventional eye drops comprise over 90% of the marketed ocular dosage forms, they do have limitations, such as poor ocular drug bioavailability and systemic side effects; contact lenses are amongst the new delivery systems and devices that could overcome some of these problems. The most common approach to load drug molecules into contact lenses includes soaking in a drug solution. This approach had some success, but failed to achieve controlled/sustained drug release to the eye. On the other hand, nanoreservoir systems comprising nanoparticles, cyclodextrins, liposomes or surfactant aggregates being incorporated into the contact lenses could offer a plausible solution. This review highlights the status quo with contact lenses as ocular drug-delivery carriers and identifies possible future directions.