The influence of protein deposition on contact lens tear film stability

Functionalized Surface Coatings for Rigid Contact Lenses

This research evolves into a comparative study of three different phenolic composites as coatings for rigid contact lenses, with a particular emphasis on enhancing their antifouling properties and hydrophobicity. The primary layer, comprised of diverse phenolic compounds, serves as a sturdy foundation. An exclusive secondary layer, featuring synthetic peptoids, is introduced to further minimize biofouling. Validated through X-ray photoelectron spectroscopy, the surface analysis confirms the successful integration of the polyphenolic layers and the subsequent grafting of peptoids onto the lens surface. The efficacy of the proposed coatings is substantiated through protein adsorption tests, providing definitive evidence of their antifouling capabilities. This research employs a nuanced assessment of coating performance, utilizing the quantification of fluorescence intensity to gauge effectiveness. Additionally, contact angle measurements offer insights into wettability and surface characteristics, contributing to a comprehensive understanding of the coating's practicality.

Impact of the physical properties of contact lens materials on the discomfort: role of the coefficient of friction

Contact Lens Discomfort (CLD) is the main cause in contact lens (CLs) discontinuation, referred in literature as drop-out phenomenon. Despite such evidence was reported in several clinical studies, a relationship between physico-chemical properties of CLs and CLD is not still totally understood. In this regard, the friction of CLs surfaces seems to be related to discomfort feeling events, probably due to an alteration of the lubricate function of the tear film after the CL placement inside the ocular environment. In the last years, many studies have been finalized to the friction measurements of CLs surface, finding conflicting data due to a lack in standardized protocol. The aim of this review is primarily to show evident relationships between CLs surface properties (i.e. wettability, tear evaporation, tear film quality, etc.) and the coefficient of friction (CoF), resulting therefore the most relevant physical quantity in the CLs characterization. In addition, we reported the most recent studies in CLs tribology, which highlight that the introduction of a standard protocol in CoF measurements is necessary to obtain reproducible results, considering the aim to evaluate in a more precise way the relationship between this material surface property and comfort in CLs users.

Biomimetic-Engineered Silicone Hydrogel Contact Lens Materials

Contact lenses are one of the most successful applications of biomaterials. The chemical structure of the polymers used in contact lenses plays an important role in determining the function of contact lenses. Different types of contact lenses have been developed based on the chemical structure of polymers. When designing contact lenses, materials scientists consider factors such as mechanical properties, processing properties, optical properties, histocompatibility, and antifouling properties, to ensure long-term wear with minimal discomfort. Advances in contact lens materials have addressed traditional issues such as oxygen permeability and biocompatibility, improving overall comfort, and duration of use. For example, silicone hydrogel contact lenses with high oxygen permeability were developed to extend the duration of use. In addition, controlling the surface properties of contact lenses in direct contact with the cornea tissue through surface polymer modification mimics the surface morphology of corneal tissue while maintaining the essential properties of the contact lens, a significant improvement for long-term use and reuse of contact lenses. This review presents the material science elements required for advanced contact lenses of the future and summarizes the chemical methods for achieving these goals.

Comparative hydrodynamic and nanoscale imaging study on the interactions of teicoplanin-A2 and bovine submaxillary mucin as a model ocular mucin

Glycopeptide antibiotics are regularly used in ophthalmology to treat infections of Gram-positive bacteria. Aggregative interactions of antibiotics with mucins however can lead to long exposure and increases the risk of resistant species. This study focuses on the evaluation of potential interactions of the last line of defence glycopeptide antibiotic teicoplanin with an ocular mucin model using precision matrix free hydrodynamic and microscopic techniques: sedimentation velocity in the analytical ultracentrifuge (SV-AUC), dynamic light scattering (DLS) and atomic force microscopy (AFM). For the mixtures of teicoplanin at higher doses (1.25 mg/mL and 12.5 mg/mL), it was shown to interact and aggregate with bovine submaxillary mucin (BSM) in the distributions of both sedimentation coefficients by SV-AUC and hydrodynamic radii by DLS. The presence of aggregates was confirmed by AFM for higher concentrations. We suggest that teicoplanin eye drop formulations should be delivered at concentrations of < 1.25 mg/mL to avoid potentially harmful aggregations.

The Ionization of Polymeric Materials Accelerates Protein Deposition on Hydrogel Contact Lens Material

Contact lens materials include polymers that are ionized in the ocular pH condition and are susceptible to protein deposition due to their surface characteristics. Herein, we investigated the effect of the electrostatic state of the contact lens material and protein on protein deposition level using hen egg white lysozyme (HEWL) and bovine serum albumin (BSA) as model proteins and etafilcon A and hilafilcon B as model contact lens materials. Only HEWL deposition on etafilcon A showed a statistically significant pH-dependency (p < 0.05); protein deposition increased with pH. HEWL showed a positive zeta potential at acidic pH, while BSA showed a negative zeta potential at basic pH. Only etafilcon A showed a statistically significant pH-dependent point of zero charge (PZC) (p < 0.05), implying that its surface charge became more negative under basic conditions. This pH-dependency of etafilcon A is attributed to the pH-responsive degree of ionization of its constituent methacrylic acid (MAA). The presence of MAA and its degree of ionization could accelerate protein deposition; more HEWL deposited as pH increased despite the weak positive surface charge of HEWL. The highly negatively charged etafilcon A surface attracted HEWL, even overwhelming weak positive charge of HEWL, increasing the deposition with pH.

Phenylboronic acid modified hydrogel materials and their potential for use in contact lens based drug delivery

The use of hydrogel-based contact lens materials holds promise for ophthalmic drug delivery by increasing drug residence time, improving drug bioavailability, reducing administration frequency, and enhancing special site targeting. Issues such as ease of manufacturing, lens comfort and appropriate release kinetics must be considered. Furthermore, the high water content of hydrogel materials can result in rapid and poorly controlled release kinetics. Herein, we modified common hydrogels used in contact lens manufacturing with phenylboronic acid (PBA). PBA addresses these material design issues since boronate esters are easily formed when boron acid and diols interact, opening up a pathway for simple modification of the model lens materials with saccharide based wetting agents. The wetting agents have the potential to improve lens comfort. Furthermore, the hydrophobicity of PBA and the presence of diols can be useful to help control drug release kinetics. In this work, polymerizable 3-(acrylamido)phenylboronic acid (APBA) was synthesized and incorporated into various hydrogels used in contact lens applications, including poly(2-hydroxyethylmethacrylate) (PHEMA), polyvinylpyrrolidone (PVP) and poly(N,N-dimethyl acrylamide) (PDMA) using UV induced free radical polymerization. The APBA structure and its incorporation into the hydrogel materials were confirmed by NMR and FTIR. The materials were shown to interact with and bind wetting agents such as hyaluronan (HA) and hydroxypropyl guar (HPG) by simple soaking in an aqueous solution. The equilibrium water content of the modified materials was characterized, demonstrating that most materials are still in the appropriate range after the introduction of the hydrophobic PBA. The release of three model ophthalmic drugs with varying hydrophilicity, atropine, atropine sulfate and dexamethasone, was examined. The presence of PBA in the materials was found to promote sustained drug release due to its hydrophobic nature. The results suggest that the modification of the materials with PBA was able to not only provide a mucoadhesive property that enhanced wetting agent interactions with the materials, but had the potential to alter drug release. Thus, the modification of contact lens materials with mucoadhesive functionality may be useful in the design of hydrogel contact lenses for ophthalmic drug release and wetting agent binding.

Effect of Recombinant Human Lubricin on Model Tear Film Stability

Purpose

To investigate and quantify the effect of recombinant human lubricin (rh-lubricin) on model tear film stability.

Methods

A custom-built, interferometry-based instrument called the Interfacial Dewetting and Drainage Optical Platform was used to create and record the spatiotemporal evolution of model acellular tear films. Image segmentation and analysis was performed in MATLAB to extract the most essential features from the wet area fraction versus time curve, namely the evaporative break-up time and the final wet area fraction (A10). These two parameters indicate the tear film stability in the presence of rh-lubricin in its unstressed and stressed forms.

Results

Our parameters successfully captured the trend of increasing tear film stability with increasing rh-lubricin concentration, and captured differences in rh-lubricin efficacy after various industrially relevant stresses. Specifically, aggregation and fragmentation caused by a 4-week, high temperature stress condition negatively impacted rh-lubricin's ability to maintain model tear film stability. Adsorbed rh-lubricin alone was not sufficient to resist break-up and maintain full area coverage of the model tear film surface.

Conclusions

Our results demonstrate that fragmentation and aggregation can negatively impact rh-lubricin's ability to maintain a stable tear film. In addition, the ability of rh-lubricin to maintain wetted area coverage is due to both freely dispersed and adsorbed rh-lubricin.

Translational Relevance

Our platform and analysis method provide a facile, intuitive, and clinically relevant means to quantify the effect of ophthalmic drugs and formulations intended for improving tear film stability, as well as capture differences between variants related to drug stability and efficacy.

In vitro affinity for nicotine of soft contact lenses of different materials

Smoking is a risk factor for the development of microbial keratitis and corneal infiltrates in contact lens (CL) wearers. It is still unknown if this risk is directly associated with the presence of nicotine in the eye and if adherence of nicotine on the CL can enhance these effects. A better understanding of the interaction between nicotine and CL materials could offer insights to explain this risk associated with smoking. The aim of this work was to compare the affinity of nicotine to different soft CL materials. CLs from FDA groups I, II, IV, and V were incubated in a 2-mM nicotine solution for 24 h and then in a 0.9% saline solution for the next 24 h. The amount of absorbed and released nicotine per CL was deduced as a function of time (t) by ultraviolet (UV) spectrophotometry and normalised to the mass of the hydrated CL. The data were described by the equation y = b -a t^-1, where a and b are constants, and b represents the mass reached at the plateau after ~ 10 min of exposure. Groups IV and V displayed the highest (0.80 ± 0.09 µg) and lowest (0.27 ± 0.08 µg) nicotine absorption per mg of hydrated CL, respectively. The CL affinity for nicotine could be ascribed to the interaction between the positive charge of nicotine pyrrolidine nitrogen and the negative charges of the CLs, especially for the ionic IV group.

CLEAR - Effect of contact lens materials and designs on the anatomy and physiology of the eye

This paper outlines changes to the ocular surface caused by contact lenses and their degree of clinical significance. Substantial research and development to improve oxygen permeability of rigid and soft contact lenses has meant that in many countries the issues caused by hypoxia to the ocular surface have largely been negated. The ability of contact lenses to change the axial growth characteristics of the globe is being utilised to help reduce the myopia pandemic and several studies and meta-analyses have shown that wearing orthokeratology lenses or soft multifocal contact lenses can reduce axial length growth (and hence myopia). However, effects on blinking, ptosis, the function of Meibomian glands, fluorescein and lissamine green staining of the conjunctiva and cornea, production of lid-parallel conjunctival folds and lid wiper epitheliopathy have received less research attention. Contact lens wear produces a subclinical inflammatory response manifested by increases in the number of dendritiform cells in the conjunctiva, cornea and limbus. Papillary conjunctivitis is also a complication of all types of contact lenses. Changes to wear schedule (daily disposable from overnight wear) or lens materials (hydrogel from SiHy) can reduce papillary conjunctivitis, but the effect of such changes on dendritic cell migration needs further study. These changes may be associated with decreased comfort but confirmatory studies are needed. Contact lenses can affect the sensitivity of the ocular surface to mechanical stimulation, but whether these changes affect comfort requires further investigation. In conclusion, there have been changes to lens materials, design and wear schedules over the past 20+ years that have improved their safety and seen the development of lenses that can reduce the myopia development. However, several changes to the ocular surface still occur and warrant further research effort in order to optimise the lens wearing experience.

Metaoptronic Multiplexed Interface for Probing Bioentity Behaviors

Biointerface sensors have brought about remarkable advances in modern biomedicine. To accurately monitor bioentity's behaviors, biointerface sensors need to capture three main types of information, which are the electric, spectroscopic, and morphologic signals. Simultaneously obtaining these three types of information is of critical importance in the development of future biosensor, which is still not possible in the existing biosensors. Herein, by synergizing metamaterials, optical, and electronic sensing designs, we proposed the metaoptronic multiplexed interface (MMI) and built a MMI biosensor which can collectively record electric, spectroscopic, and morphologic information on bioentities. The MMI biosensor enables the real-time triple-monitoring of cellular dynamics and opens up the possibility for powerlessly monitoring ocular dryness. Our findings not only demonstrate an advanced multiplexed biointerface sensor with integrated capacities but also help to identify a uniquely significant arena for the nanomaterials, meta-optics, and nanotechnologies to play their roles in a complementary manner.

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.

Flow field-based data analysis in interfacial shear rheometry

Developments in interfacial shear rheometers have considerably improved the quality of experimental data. However, data analysis in interfacial shear rheometry is still an active field of research and development due to the intrinsic complexity introduced by the unavoidable contact of the interface with, at least, one supporting bulk subphase. Nonlinear velocity profiles, both at the interface and the bulk phases, pervade the system dynamical behavior in the most usual experimental geometries, particularly in the case of soft interfaces. Such flow configurations demand data analysis schemes based on the explicit calculation of the flow field in both the interface and the bulk phases. Such procedures are progressively becoming popular in this context. In this review, we discuss the most recent advances in interfacial shear rheology data analysis techniques. We extensively review some recently proposed flow field-based data analysis schemes for the three most common interfacial shear rheometer geometries (magnetic needle, double wall-ring, and bicone), showing under what circumstances the calculation of the flow field is mandatory for a proper analysis of the experimental data. All cases are discussed starting at the appropriate hydrodynamical models and using the equation of motion of the probe to set up an iterative procedure to compute the value of the complex Boussinesq number and, from it, the complex interfacial viscosity or, equivalently, the complex interfacial modulus. Moreover, two examples of further extensions of such techniques are proposed, concerning the micro-button interfacial shear rheometer and the potential application of interfacial rheometry instruments, together with adapted flow field-based data analysis techniques, for bulk rheometry, particularly in the case of soft samples.

Deposition of Fluorescently Tagged Lysozyme on Contact Lenses in a Physiological Blink Model

PURPOSE

To visualize the deposition of fluorescein isothiocyanate (FITC) lysozyme on daily disposable contact lenses (CLs) using a novel blink model.

METHODS

Three daily disposable conventional hydrogel CLs (etafilcon A, omafilcon A, and nelfilcon A) and three silicone hydrogel CLs (delefilcon A, senofilcon A, and somofilcon A) were evaluated in the study. The CLs were mounted onto a novel blink model and exposed to an artificial tear solution containing FITC lysozyme for 2 and 10 hr. The flow rate and blink speed were set to 1 μL/min and 6 blinks/min, respectively. After the incubation period, a 5-mm-diameter disc was punched out from the center of the lens and mounted on a microscope slide. The slides were imaged using the Zeiss 510 Meta confocal laser scanning microscope, which scanned the lens from the front to the back surface at 5-μm increments.

RESULTS

There was an increase in deposition of FITC lysozyme for all lens types with increasing incubation time (P<0.05), with the exception of somofilcon A, which did not show statistical significance between 2 and 10 hr (P>0.05). The conventional hydrogel CLs deposited higher amounts of FITC lysozyme than the silicone hydrogel CLs (P<0.001), with etafilcon A depositing the highest at all time points (P<0.05). Interestingly, at the 2-hr incubation time, most CLs showed a higher amount of deposition at the front surface than the back surface of the lens. In particular, etafilcon A showed preferred deposition at the front surface at all time points.

CONCLUSION

The results suggest that there is differential deposition at the front surface of the CL, which is exposed to the prelens tear film, compared with the back surface of the CL, which is exposed to the postlens tear film. Therefore, it may be beneficial to design CL materials with differing surface properties for the front and back surfaces of the CL to enhance interactions with the tear film and ocular surface.

Single bubble and drop techniques for characterizing foams and emulsions

The physics of foams and emulsions has traditionally been studied using bulk foam/emulsion tests and single film platforms such as the Scheludko cell. Recently there has been a renewed interest in a third class of techniques that we term as single bubble/drop tests, which employ isolated whole bubbles and drops to probe the characteristics of foams and emulsions. Single bubble and drop techniques provide a convenient framework for investigating a number of important characteristics of foams and emulsions, including the rheology, stabilization mechanisms, and rupture dynamics. In this review we provide a comprehensive discussion of the various single bubble/drop platforms and the associated experimental measurement protocols including the construction of coalescence time distributions, visualization of the thin film profiles and characterization of the interfacial rheological properties. Subsequently, we summarize the recent developments in foam and emulsion science with a focus on the results obtained through single bubble/drop techniques. We conclude the review by presenting important venues for future research.

In-vitro dewetting properties of planned replacement and daily disposable silicone hydrogel contact lenses

AIM

To compare the in-vitro videokeratoscopic surface dewetting properties of new-generation silicone hydrogel (SiH) planned replacement contact lenses (CL) with those of daily disposable CLs.

METHOD

A chrome coated cornea model was used for the in-vitro evaluation of surface dewetting. Pre-lens and post-lens film layers were formed by instilling a normal preservative-free normal saline solution (PFNs) (0.9 %) before and after the placement of the CL on the model cornea. The tests were carried out on fanfilcon A, lotrafilcon B, samfilcon A, and senofilcon A lenses, as well as such daily disposable lenses as delefilcon, nesofilcon A and senofilcon one day. Using videokeratoscopic methods, images were obtained at 30-second intervals up to 180 s in the lens and control groups and were analyzed by the ImajeJ® program.

RESULTS

The mean measured area of the keratoscopic rings was largest in the fanfilcon group (67.56 mm²), followed by 61.53 mm² in the lotrafilcon A group and 64.60 mm² in the samfilcon group, while the smallest area was measured in the senofilcon A group, at 56.90 mm². The area was measured as 64.33, 63.09 and 68.39 mm² for the delefilcon, nesofilcon and Senofilcon one day CLs, respectively. The dewetting patterns and properties differed in the CL groups (p < 0.05), while no significant differences were found between the measured areas of the planned replacement and daily disposable CL groups (p > 0.05).

DISCUSSION

Videokeratoscopy using in-vitro cornea models has been identified as a reproducible and reliable method for the analysis of the surface dewetting of CLs. The dewetting characteristics of CL groups have been found to differ from each other, despite all being produced from SiH materials. The surface wetting coating has been shown to affect CL dewetting performance.

Correlation between Tribological Properties and the Quantified Structural Changes of Lysozyme on Poly (2-hydroxyethyl methacrylate) Contact Lens

The ocular discomfort is the leading cause of contact lens wear discontinuation. Although the tear proteins as a lubricant might improve contact lens adaptation, some in vitro studies suggested that the amount of adsorbed proteins could not simply explain the lubricating performance of adsorbed proteins. The purpose of this study was to quantify the structural changes and corresponding ocular lubricating properties of adsorbed protein on a conventional contact lens material, poly (2-hydroxyethyl methacrylate) (pHEMA). The adsorption behaviors of lysozyme on pHEMA were determined by the combined effects of protein–surface and protein–protein interactions. Lysozyme, the most abundant protein in tear, was first adsorbed onto the pHEMA surface under widely varying protein solution concentrations to saturate the surface, with the areal density of the adsorbed protein presenting different protein–protein effects within the layer. These values were correlated with the measured secondary structures, and corresponding friction coefficient of the adsorbed and protein covered lens surface, respectively. The decreased friction coefficient value was an indicator of the lubricated surfaces with improved adaptation. Our results indicate that the protein–protein effects help stabilize the structure of adsorbed lysozyme on pHEMA with the raised friction coefficient measured critical for the innovation of contact lens material designs with improved adaptation.

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

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

Hyperspectral imaging for dynamic thin film interferometry

Dynamic thin film interferometry is a technique used to non-invasively characterize the thickness of thin liquid films that are evolving in both space and time. Recovering the underlying thickness from the captured interferograms, unconditionally and automatically is still an open problem. Here we report a compact setup employing a snapshot hyperspectral camera and the related algorithms for the automated determination of thickness profiles of dynamic thin liquid films. The proposed technique is shown to recover film thickness profiles to within 100 nm of accuracy as compared to those profiles reconstructed through the manual color matching process. Subsequently, we discuss the characteristics and advantages of hyperspectral interferometry including the increased robustness against imaging noise as well as the ability to perform thickness reconstruction without considering the absolute light intensity information.