Soft contact lens biomaterials from bioinspired phospholipid polymers

Machine-Learning-Aided Understanding of Protein Adsorption on Zwitterionic Polymer Brushes

Constructing antifouling surfaces is a crucial technique for optimizing the performance of devices such as water treatment membranes and medical devices in practical environments. These surfaces are achieved by modification with hydrophilic polymers. Notably, zwitterionic (ZI) polymers have attracted considerable interest because of their ability to form a robust hydration layer and inhibit the adsorption of foulants. However, the importance of the molecular weight and density of the ZI polymer on the antifouling property is partially understood, and the surface design still retains an empirical flavor. Herein, we individually assessed the influence of the molecular weight and density of the ZI polymer on protein adsorption through machine learning. The results corroborated that protein adsorption is more strongly influenced by density than by molecular weight. Furthermore, the distribution of predicted protein adsorption against molecular weight and polymer density enabled us to determine conditions that enhanced (or weaken) antifouling. The relevance of this prediction method was also demonstrated by estimating the protein adsorption over a wide range of ionic strengths. Overall, this machine-learning-based approach is expected to contribute as a tool for the optimized functionalization of materials, extending beyond the applications of ZI polymer brushes.

Fabrication of a BOC-Protected 2-Hydroxyethyl Methacrylate Brush and Deprotection of the BOC Group to Control the Surface Hydrophilicity

Fabrication of functional surfaces with designed patterns of different hydrophilicity has potential applications in active control of water droplets and water harvesting. For practical applications, the fabrication process needs to be applied to a large area in a cost-effective manner. Herein, we report the fabrication of a polymer brush of 2-(tert-butoxycarbonyloxy)ethyl methacrylate having a BOC-protected hydroxy group. The deprotection of the BOC group converts poly(2-(tert-butoxycarbonyloxy)ethyl methacrylate) (PBHEMA) into poly(2-hydroxyethyl methacrylate) (PHEMA) and hence changes the hydrophilicity. The chemical transformation changes the refractive index and thickness of the brush. This simple chemistry enables easy formation of the boundary of different hydrophilicity. Last, we demonstrate that the shape of the water droplet can be manipulated on the designed surface having different hydrophilicity.

Synthesis of Thermo-Responsive Monofunctionalized Diblock Copolymer Worms

Poly(glycerol monomethacrylate)-block-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) with worm-like morphology is a typical example of reversible addition-fragmentation chain transfer (RAFT) dispersion polymerized thermo-responsive copolymer via polymerization-induced self-assembly (PISA) in aqueous solution. Chain transfer agents (CTAs) are the key component in controlling RAFT, the structures of which determine the end functional groups of the polymer chain. It is therefore of interest to monofunctionalize the polymers via CTA moiety, for bioactive functionality conjugation and in the meantime maintain the precisely controlled morphology of the copolymers and the related property. In this work, a newly designed CTA 5-(2-(tert-butoxycarbonylamino) ethylamino)-2-cyano-5-oxopentan-2-yl benzodithioate (t-Boc CPDB) was synthesized and used for the RAFT polymerization of PGMA45-PHPMA120. Subsequently, PGMA45-PHPMA120 copolymers with primary amine, maleimide, and reduced L-glutathione (a tripeptide) monofunctionalized terminals were synthesized via deprotection and conjugation reactions. These monofunctionalized copolymers maintain worm-like morphology and thermo-responsive property in aqueous solution (10% w/v), as confirmed by the transmission electron microscopy (TEM) images, and the observation of the phase transition behavior in between 4 °C and room temperature (~20 °C), respectively. Summarily, a range of thermo-responsive monofunctionalized PGMA45-PHPMA120 diblock copolymer worms were successfully synthesized, which are expected to offer potential biomedical applications, such as in polymer therapeutics, drug delivery, and diagnostics.

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.

Phosphorylcholine-Based Contact Lenses for Sustained Release of Resveratrol: Design, Antioxidant and Antimicrobial Performances, and In Vivo Behavior

Design of advanced contact lenses (CLs) demands materials that are safe and comfortable for the wearers and that preserve the normal eye microbiota, avoiding chronic inflammation and biofilm development. This work aimed to combine the natural antibiofouling phosphorylcholine and the antioxidant and prebiotic resveratrol as integral components of CLs that may have the additional performance of preventing oxidative-stress related eye diseases. Different from previous uses of 2-methacryloyloxyethyl phosphorylcholine (MPC) as coating, we explored the feasibility of adding MPC at high proportions as a comonomer of 2-hydroxyethyl methacrylate (HEMA)-based hydrogels while still allowing for the loading of the hydrophobic resveratrol. Homogeneous distribution of MPC along the hydrogel depth (confirmed by Raman spectroscopy) notably increased solvent uptake and the proportion of free water while it decreased Young's modulus. Relevantly, MPC did not hinder the uptake of resveratrol by CLs (>10 mg/g), which indeed showed network/water partition coefficients of >100. Protocols for CLs sterilization and loading of resveratrol under aseptic conditions were implemented, and the effects of tear proteins on resveratrol release rate were investigated. CLs sustained resveratrol release for more than 24 h in vitro, and sorption of albumin onto the hydrogel, although attenuated by MPC, slowed down the release. The combination of MPC and resveratrol reduced P. aeruginosa and S. aureus growth as tested in a novel hydrogel disk-agar interface biofilm growth setup. The developed CLs showed excellent anti-inflammatory properties and biocompatibility in in ovo and rabbit tests and provided higher and more prolonged levels of resveratrol in tear fluid, which favored resveratrol biodistribution in anterior and posterior eye segments compared to eye drops. Correlations between the release profiles of resveratrol in vitro and in vivo were assessed. Relevantly, the CLs preserved the antioxidant properties of resveratrol during the entire 8 h of wearing. In sum, CLs prepared with high proportion in MPC may help address safety and comfort requirements while having drug releasing capabilities.

Zwitterionic Biomaterials

The term "zwitterionic polymers" refers to polymers that bear a pair of oppositely charged groups in their repeating units. When these oppositely charged groups are equally distributed at the molecular level, the molecules exhibit an overall neutral charge with a strong hydration effect via ionic solvation. The strong hydration effect constitutes the foundation of a series of exceptional properties of zwitterionic materials, including resistance to protein adsorption, lubrication at interfaces, promotion of protein stabilities, antifreezing in solutions, etc. As a result, zwitterionic materials have drawn great attention in biomedical and engineering applications in recent years. In this review, we give a comprehensive and panoramic overview of zwitterionic materials, covering the fundamentals of hydration and nonfouling behaviors, different types of zwitterionic surfaces and polymers, and their biomedical applications.

Biomimetic materials based on zwitterionic polymers toward human-friendly medical devices

This review summarizes recent research on the design of polymer material systems based on biomimetic concepts and reports on the medical devices that implement these systems. Biomolecules such as proteins, nucleic acids, and phospholipids, present in living organisms, play important roles in biological activities. These molecules are characterized by heterogenic nature with hydrophilicity and hydrophobicity, and a balance of positive and negative charges, which provide unique reaction fields, interfaces, and functionality. Incorporating these molecules into artificial systems is expected to advance material science considerably. This approach to material design is exceptionally practical for medical devices that are in contact with living organisms. Here, it is focused on zwitterionic polymers with intramolecularly balanced charges and introduce examples of their applications in medical devices. Their unique properties make these polymers potential surface modification materials to enhance the performance and safety of conventional medical devices. This review discusses these devices; moreover, new surface technologies have been summarized for developing human-friendly medical devices using zwitterionic polymers in the cardiovascular, cerebrovascular, orthopedic, and ophthalmology fields.

Safety and Efficacy of a New Water Gradient Biomimetic Monthly Replacement Spherical Contact Lens Material (Lehfilcon A)

Purpose

The objective of this study was to evaluate the safety and performance of the investigational lens, lehfilcon A, when worn in a daily wear modality and replaced monthly as compared to the commercially available comfilcon A contact lens.

Methods

This was a multicenter, prospective, controlled, double-masked, randomized, parallel-group clinical study with bilateral lens wear for 3 months. In all, 115 subjects completed the study (77 with test lehfilcon A and 38 with control comfilcon A contact lenses). Distance visual acuity (VA) was assessed using Snellen VA. Lens performance was assessed by examining lens fit/movement, centration, front surface wettability and front/back surface deposits using slit-lamp biomicroscopy.

Results

At the 3-month follow-up visit, all eyes had a distance VA of 20/20 or better. Further, lens fit/movement was assessed as optimal in 92.9% of the eyes with lehfilcon A and 89.2% with comfilcon A. There were no ratings of unacceptably tight or loose fits for either contact lens material. Lens centration was assessed as optimal in 98.7% of eyes with lehfilcon A and 94.6% with comfilcon A. For front and back surface deposits, both materials showed minimal lens surface deposits. Front surface wettability was assessed as grade 0 or 1 for most of the study lenses in both lens groups across all attended study visits. There were no ocular adverse events related to the study lenses.

Conclusion

Overall, lehfilcon A showed excellent VA, optimal lens fitting characteristics, a clean surface, high wettability, and low risk for adverse events after 3 months of lens wear.

Biomaterials for Ophthalmic Applications

Ophthalmology is the branch of medicine that deals with diseases of the eye, the organ responsible for vision, and its attachments. Biomaterials can be made with different types of materials and can replace or improve a function or an organ, specifically the eye in the case of ophthalmic biomaterials. Biomaterials are substances that interact with biological systems for a medical purpose, either as a therapeutic (treat, augment, repair, or replace a tissue function of the body) or a diagnostic agent, and have continued to improve over the years, leading to the creation of new biomaterials. With the arrival of new generations, biomaterials have succeeded in reducing complications and toxicity and improving biocompatibilities associated with older generations. With the aging population, eye problems are becoming more prevalent, and biomaterials have helped in recent years to improve or restore vision, improving the quality of life of many patients. This review focuses on the most clinically used ophthalmic biomaterials, including contact lenses, intraocular lenses, artificial tears, inlays and vitreous replacements. Tissue engineering is presented as a new tool that is able to be treat several ophthalmologic disorders.

Structural aspects controlling the mechanical and biological properties of tough, double network hydrogels

Anticipating an increasing demand for hybrid double network (DN) hydrogels in biomedicine and biotechnology, this study evaluated the effects of each network on the mechanical and biological properties. Polyethylene glycol (PEG) (meth)acrylate hydrogels with varied monomer molecular weights and architectures (linear vs. 4-arm) were produced with and without an added ionically bonded alginate network and their mechanical properties were characterized using compression testing. The results showed that while some mechanical properties of PEG single network (SN) hydrogels decreased or changed negligibly with increasing molecular weight, the compressive modulus, strength, strain to failure, and toughness of DN hydrogels all significantly increased with increased PEG monomer molecular weight. At a fixed molecular weight (10 kDa), 4-arm PEG SN hydrogels exhibited better overall mechanical performance; however, this benefit was diminished for the corresponding DN hydrogels with comparable strength and toughness and lower strain to failure for the 4-arm case. Regardless of the PEG monomer structure, the alginate network made a relatively larger contribution to the overall DN mechanical properties when the covalent PEG network was looser with a larger mesh size (e.g., for larger monomer molecular weight and/or linear architecture) which presumably enabled more ionic crosslinking. Considering the biological performance, adipose derived stem cell cultures demonstrated monotonically increasing cell area and Yes-associated protein related mechanosensing with increasing amounts of alginate from 0 to 2 wt.%, demonstrating the possibility for using DN hydrogels in guiding musculoskeletal differentiation. These findings will be useful to design suitable hydrogels with controllable mechanical and biological properties for mechanically demanding applications. STATEMENT OF SIGNIFICANCE: Hydrogels are widely used in commercial applications, and recently developed hybrid double network hydrogels have enhanced strength and toughness that will enable further expansion into more mechanically demanding applications (e.g., medical implants, etc.). The significance of this work is that it uncovers some key principles regarding monomer molecular weight, architecture, and concentration for developing strong and tough hybrid double network hydrogels that would not be predicted from their single network counterparts or a linear combination of the two networks. Additionally, novel insight is given into the biological performance of hybrid double network hydrogels in the presence of adipose derived stem cell cultures which suggests new scope for using double network hydrogels in guiding musculoskeletal differentiation.

Nanoscaled Morphology and Mechanical Properties of a Biomimetic Polymer Surface on a Silicone Hydrogel Contact Lens

Materials taking advantage of the characteristics of biological tissues are strongly sought after in medical science and bioscience. On the natural corneal tissue surface, the highly soft and lubricated surface is maintained by composite structures composed of hydrophilic biomolecules and substrates. To mimic this structure, the surface of a silicone hydrogel contact lens was modified with a biomimetic phospholipid polymer, poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), and the nanoscaled morphology and mechanical properties of the surface were confirmed with advanced surface characterization and imaging techniques under an aqueous medium. Concavities and convexities on the nanometer order were recognized on the surface. The surface was completely covered with a PMPC layer and remained intact even after 30 days of clinical use in a human ocular environment. The mechanical properties of the natural corneal tissue and the PMPC-modified surface were similar in the living environment, that is, low modulus and frictional properties comparable to natural tissues. These results show the validity of material preparation by biomimetic methods. The methodologies developed in this study may contribute to future development of human-friendly medical devices.

Evaluation of the long-term antibiofilm effect of a surface coating with dual functionality of antibacterial and protein-repellent effects

The provision of antibacterial properties to resinous restorative/reconstructive materials by incorporating polymerizable bactericides such as 12-methacryloyloxydodecylpyridinium bromide (MDPB) has been attempted. Previously, MDPB was combined with 2-methacryloyloxyethyl phosphorylcholine (MPC) to fabricate a copolymer coating to increase antibacterial effectiveness by protein repelling. In this study, we assessed the longevity of the protein-repelling, antibacterial, and antibiofilm effects of the MDPB-MPC copolymer. After 28 days of water immersion, MPC-containing copolymers exhibited lower adsorption of bovine serum albumin and salivary proteins; after 24 h of incubation, MDPB-containing copolymers demonstrated antibacterial effects against Streptococcus mutans. The copolymer containing both MDPB and MPC showed thinner biofilm formation with a higher percentage of membrane-compromised bacteria than control. The results were consistent with those before aging, indicating the long-lasting antibacterial, protein-repellent, and antibiofilm effects of this copolymer. The durable copolymer developed in this study can be applied to dental resins to control bacteria in the oral environment.

Progress in drug formulation design and delivery of medicinal substances used in ophthalmology

Due to the very low bioavailability of drugs administered to the surface of the eyeball, issues related to the formulation of an ophthalmic drug pose a technological challenge. The essence of an ophthalmic drug is the selection of an appropriate active substance (API), but also auxiliary substances that determine the desired drug quality and API availability. The ophthalmic drug is not only classic eye drops. Therefore, on the basis of the literature data, the properties and application of auxiliary substances increasing the pharmaceutical availability of API, improving the penetration of API into the eye structures and modifying the viscosity of eye drops were characterized. The possibility of chemical modification of API and the use of prodrugs in ophthalmic drug forms was also noted. Taking into account the progress in the field of ophthalmic drug formulation, the use of multi-compartment systems (lipid particles, nanoparticles, microparticles, liposomes, niosomes, dendrimers) and modern ophthalmic drug delivery systems (inserts, implants, microneedles, contact lenses, ionophoretic systems) have been indicated. Examples of solutions already used by manufacturers, as well as those in the phase of laboratory or clinical trials, were indicated.

Application of Zwitterionic Polymer Hydrogels to Optical Tissue Clearing for 3D Fluorescence Imaging

Zwitterionic polymers have both anion and cation groups in the side chain and have been used in various biomedical applications because of the unique properties. In this study, zwitterionic polymer hydrogels are applied to optical tissue clearing for 3D fluorescence imaging. Polyacrylamide hydrogels have been employed in Clear Lipid-exchanged Acrylamide-hybridized Rigid Imaging/Immunostaining/In situ-hybridization-compatible Tissue-hYdrogel method. Zwitterionic polymer hydrogels are produced using zwitterionic monomers, such as 3-[(3-acrylamidopropyl)dimethylammonio]propane-1-sulfonate (DAPS) and 2-methacryloyloxyethyl phosphorylcholine (MPC), and crosslinkers. The hydrogels made from poly(DAPS-co-acrylamide) and MPC homopolymers afford the most transparent tumor tissues. However, the tissues cleared using DAPS copolymers-containing hydrogels became turbid in a refractive index-matching solution, which are unable to obtain clear 3D fluorescence images. In contrast, the 3D fluorescence imaging is achieved in the MPC polymer-treated 2-mm-thick brain slices after immunostaining. The 3D fluorescence imaging of lung metastasis that is cleared by the MPC hydrogel to demonstrate the possible application to cancer diagnosis is performed. The results indicate the increased potentials of zwitterionic polymer hydrogels, especially MPC polymer hydrogels, in biomedical applications.

Rational synthesis of novel biocompatible thermoresponsive block copolymer worm gels

It is well known that reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA) enables the rational design of diblock copolymer worm gels. Moreover, such hydrogels can undergo degelation on cooling below ambient temperature as a result of a worm-to-sphere transition. However, only a subset of such block copolymer worms exhibit thermoresponsive behavior. For example, PMPC26-PHPMA280 worm gels prepared using a poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC26) precursor do not undergo degelation on cooling to 6 °C (see S. Sugihara et al., J. Am. Chem. Soc., 2011, 133, 15707-15713). Informed by our recent studies (N. J. Warren et al., Macromolecules, 2018, 51, 8357-8371), we decided to reduce the mean degrees of polymerization of both the PMPC steric stabilizer block and the structure-directing PHPMA block when targeting a pure worm morphology. This rational approach reduces the hydrophobic character of the PHPMA block and hence introduces the desired thermoresponsive character, as evidenced by the worm-to-sphere transition (and concomitant degelation) that occurs on cooling a PMPC15-PHPMA150 worm gel from 40 °C to 6 °C. Moreover, worms are reconstituted on returning to 40 °C and the original gel modulus is restored. This augurs well for potential biomedical applications, which will be examined in due course. Finally, small-angle X-ray scattering studies indicated a scaling law exponent of 0.67 (≈2/3) for the relationship between the worm core cross-sectional diameter and the PHPMA DP for a series of PHPMA-based worms prepared using a range of steric stabilizer blocks, which is consistent with the strong segregation regime for such systems.

Controlled biointerfaces with biomimetic phosphorus-containing polymers

Phosphorus is a ubiquitous and one of the most common elements found in living organisms. Almost all molecules containing phosphorus in our body exist as analogs of phosphate salts or phosphoesters. Their functions are versatile and important, being responsible for forming the genetic code, cell membrane, and mineral components of hard tissue. Several materials inspired from these phosphorus-containing biomolecules have been recently developed. These materials have shown unique properties at the biointerface, such as nonfouling ability, blood compatibility, lubricity, mineralization induction capability, and bone affinity. Several unfavorable events occur at the interface of materials and living organisms because most of these materials have not been designed while taking host responses into account. These unfavorable events are directly linked to reducing functions and shorten the usable periods of medical devices. Biomimetic phosphorus-containing polymers can improve the reliability of materials in biological systems. In addition, phosphorus-containing biomimetic polymers are useful not only for improving the biocompatibility of material surfaces but also for adding new functions due to the flexibility in molecular design. In this review, we describe the recent advances in the control of biointerfacial phenomena with phosphorus-containing polymers. We especially focus on zwitterioninc phosphorylcholine polymers and polyphosphoesters.

Evaluation of In Vitro Wettability of Soft Contact Lenses Using Tear Supplements

OBJECTIVE

To evaluate the interaction between tear supplements and soft contact lenses (SCLs), we measured the contact angles (CAs) on the SCLs using commercially available tear supplements.

METHODS

We used four daily disposable conventional hydrogel lenses (etafilcon A, etafilcon A+ polyvinylpyrrolidone, nelfilcon A, and omafilcon A containing 2-methacryloyloxyethyl phosphorylcholine [MPC]) and four silicone hydrogel lenses (narafilcon A, senofilcon A, delefilcon A, and stenfilcon A). The CAs on the SCLs were measured using a sessile drop technique and four different types of sessile drops, including saline, artificial tears, lubricants containing 2-MPC (MPC solution), and 0.1% hyaluronate acid (HA).

RESULTS

The CA values associated with the silicone hydrogel lenses were significantly (P<0.001) lower than those associated with the conventional hydrogel lenses with all four solutions. The mean CA of 0.1% HA was significantly (P<0.01) higher than that of saline. The mean CA of the MPC solution was significantly (P<0.01) lower than that of saline with the conventional hydrogel lenses but significantly (P<0.05) higher than that of saline with the silicone hydrogel lenses.

CONCLUSIONS

The CAs associated with the silicone hydrogel SCLs were higher with the use of the MPC solutions and HA in vitro. The measured CAs may depend on ingredient agents, surface treatment of the CLs, and components of the tear supplements.

Resveratrol-Loaded Hydrogel Contact Lenses with Antioxidant and Antibiofilm Performance

Contact lenses (CLs) are prone to biofilm formation, which may cause severe ocular infections. Since the use of antibiotics is associated with resistance concerns, here, two alternative strategies were evaluated to endow CLs with antibiofilm features: copolymerization with the antifouling monomer 2-methacryloyloxyethyl phosphorylcholine (MPC) and loading of the antioxidant resveratrol with known antibacterial activity. MPC has, so far, been used to increase water retention on the CL surface (Proclear^® 1 day CLs). Both poly(hydroxyethyl methacrylate) (HEMA) and silicone hydrogels were prepared with MPC covering a wide range of concentrations (from 0 to 101 mM). All hydrogels showed physical properties adequate for CLs and successfully passed the hen’s egg-chorioallantoic membrane (HET-CAM) test. Silicone hydrogels had stronger affinity for resveratrol, with higher loading and a slower release rate. Ex vivo cornea and sclera permeability tests revealed that resveratrol released from the hydrogels readily accumulated in both tissues but did not cross through. The antibiofilm tests against Pseudomonas aeruginosa and Staphylococcus aureus evidenced that, in general, resveratrol decreased biofilm formation, which correlated with its concentration-dependent antibacterial capability. Preferential adsorption of lysozyme, compared to albumin, might also contribute to the antimicrobial activity. In addition, importantly, the loading of resveratrol in the hydrogels preserved the antioxidant activity, even against photodegradation. Overall, the designed hydrogels can host therapeutically relevant amounts of resveratrol to be sustainedly released on the eye, providing antibiofilm and antioxidant performance.

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

SIGNIFICANCE

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.

PURPOSE

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.

METHODS

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.

RESULTS

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).

CONCLUSIONS

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.

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.

Therapeutic Properties of PDMS Nanoparticles: A Promising New Drug Delivery Vehicle Against Inflammatory Conditions

BACKGROUND

Over the last few decades, there has been a stupendous change in the area of drug delivery using particulate delivery systems, with increasing focus on nanoparticles in recent times. Nanoparticles helps to improve and alter the pharmacodynamic properties and pharmacokinetics of various types of drug molecules. These features help to protect the drug entity in the systemic circulation, access of the drug to the chosen sites, and to deliver the drug in a controlled and sustained rate at the site of action.

OBJECTIVE

Nanoparticle based targeted delivery of anti-inflammatory drugs/signal modulatory agents to the cytoplasm or nuclei of the targeted cell can significantly enhance the precision and efficacy of intended therapeutic activity. To this end, we report ligand free, enhanced intra-nuclear delivery model of anti-inflammatory therapeutics via PDMS nanoparticles.

METHOD

PDMS nanoparticles were prepared by sacrificial silica template-based approach and details of their characterization for suitability as a nanoparticle-based delivery material is detailed herein.

RESULTS

Biological evaluation for compatibility was carried out and the results showed that the PDMS nanoparticle has no toxicity on RAW 264.7 cells in the concentration range of 10, 20, 40, 60, 80, 100 and 120 μg/mL in culture. Biocompatibility and absence of toxicity was determined by morphological examination and cell viability assays. Drug loading and release kinetics were carried out with the anti-inflammatory drug Diclofenac.

CONCLUSION

In this paper we clearly demonstrate the various aspects of nanoparticle articulation, characterization, effect of their characteristics and their applications as a non-toxic drug delivery molecule for its potential applications in therapeutic delivery of drugs for sustained release.

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.

Lipid-Bilayer Assemblies on Polymer-Bearing Surfaces: The Nature of the Slip Plane in Asymmetric Boundary Lubrication

Phospholipid-macromolecule complexes have been proposed to form highly efficient, lubricating boundary layers at artificial soft surfaces or at biological surfaces such as articular cartilage, where the friction reduction is attributed to the hydration lubrication mechanism acting at the exposed, hydrated head groups of the lipids. Here we measure, using a surface force balance, the normal and frictional interactions between model mica substrates across several different configurations of phosphatidylcholine (PC) lipid aggregates and adsorbed polymer (PEO) layers, to provide insight into the nature of such lubricating boundary layers in both symmetric and especially asymmetric configurations. Our results reveal that, irrespective of the configuration, the slip plane between the sliding surfaces reverts wherever possible to a bilayer-bilayer interface where hydration lubrication reduces the friction strongly. Where such an interface is not available, the sliding friction remains high. These findings may account for the low friction observed between both biological and synthetic hydrogel surfaces which may be asymmetrically coated with lipid-based boundary layers and fully support the hydration lubrication mechanism attributed to act at such boundary layers.

Manufacture of Contact Lens of Nanoparticle-Doped Polymer Complemented with ZEMAX

Many people suffer from myopia or hyperopia due to the refractive errors of the cornea all over the world. The use of high refractive index (RI), Abbe number (ν_d), and visible light transmittance (T%) polymeric contact lenses (CLs) holds great promise in vision error treatment as an alternative solution to the irreversible laser-assisted in situ keratomileusis (LASIK) surgery. Titanium dioxide nanoparticles (TiO₂ NPs) have been suggested as a good candidate to rise the RI and maintain high transparency of a poly(methyl methacrylate) (PMMA)-TiO₂ nanocomposite. This work includes a preparation of TiO₂ NPs using the sol gel method as well as a synthesis of pure PMMA by free radical polarization and PMMA-TiO₂ CLs using a cast molding method of 0.005 and 0.01 w/v concentrations and a study of their effect on the aberrated human eye. ZEMAX optical design software was used for eye modeling based on the Liou and Brennan eye model and then the pure and doped CLs were applied. Ocular performance was evaluated by modulation transfer function (MTF), spot diagram, and image simulation. The used criteria show that the best vision correction was obtained by the CL of higher doping content (p < 0.0001) and that the generated spherical and chromatic aberrations in the eye had been reduced.

Antifouling silicone hydrogel contact lenses via densely grafted phosphorylcholine polymers

Silicone hydrogel contact lenses (CLs) permit increased oxygen permeability through their incorporation of siloxane functional groups. However, contact lens biofouling can be problematic with these materials; surface modification to increase lens compatibility is necessary for acceptable properties. This work focuses on the creation of an antifouling CL surface through a novel grafting method. A polymer incorporating 2-methacryloyloxyethyl phosphorylcholine (MPC), well known for its antifouling and biomimetic properties, was grafted to the model lens surfaces using surface-initiated atom transfer radical polymerization (SI-ATRP). The SI-ATRP modification generated a unique double-grafted polymeric architecture designed to resist protein adsorption through the presence of a surrounding hydration layer due to the PC groups and steric repulsion due to the density of the grafted chains. The polymer was grafted from model silicone hydrogel CL using a four-step SI-ATRP process. Attenuated total reflectance-Fourier transform infrared spectroscopy and XPS were used to confirm the surface chemical composition at each step of the synthesis. Both the surface wettability and equilibrium water content of the materials increased significantly upon polyMPC modification. The surface water contact angle was as low as 16.04 ± 2.37° for polyMPC-50 surfaces; complete wetting (∼0°) was observed for polyMPC-100 surfaces. A decrease in the protein adsorption by as much as 83% (p < 0.000 36) for lysozyme and 73% (p < 0.0076) for bovine serum albumin was observed, with no significant difference between different polyMPC chain lengths. The data demonstrate the potential of this novel modification process for the creation of extremely wettable and superior antifouling surfaces, useful for silicone hydrogel CL surfaces.

On-Chip Detection of the Biomarkers for Neurodegenerative Diseases: Technologies and Prospects

Alzheimer's disease (AD), Parkinson's disease (PD) and glaucoma are all regarded as neurodegenerative diseases (neuro-DDs) because these diseases are highly related to the degeneration loss of functions and death of neurons with aging. The conventional diagnostic methods such as neuroimaging for these diseases are not only expensive but also time-consuming, resulting in significant financial burdens for patients and public health challenge for nations around the world. Hence early detection of neuro-DDs in a cost-effective and rapid manner is critically needed. For the past decades, some chip-based detection technologies have been developed to address this challenge, showing great potential in achieving point-of-care (POC) diagnostics of neuro-DDs. In this review, chip-based detection of neuro-DDs' biomarkers enabled by different transducing mechanisms is evaluated.

Phospholipid Polymer Hydrogel Matrices with Dually Immobilized Cytokines for Accelerating Secretion of the Extracellular Matrix by Encapsulated Cells

Construction of 3D tissues by various types of cells with specific characteristics is an important and fundamental technology in tissue reconstruction medicine and animal-free diagnosis system. To do so, an excellent extracellular matrix (ECM) is needed for encapsulation of cells and maintaining cell activity. Spontaneously forming hydrogel matrix is used by complexation between two water-soluble polymers, 2-methacryloyloxyethyl phosphorylcholine polymer bearing phenylboronic acid groups and poly(vinyl alcohol). Two cytokines for cell proliferation are immobilized in the hydrogel matrix to control the activities of the encapsulated cells. The cytokine-immobilized hydrogel matrix can encapsulate both L929 fibroblasts and normal human dermal fibroblasts under mild condition. The physical properties of the hydrogel matrix can follow the proliferation process of the encapsulated cells. The encapsulated cells secrete ECM in the polymer hydrogel networks upon 3D culturing for 7 days. Consequently, the tissue-mimicking ECM hybrid hydrogels are fabricated successfully.

Novel anti-biofouling and drug releasing materials for contact lenses

Contact lens users very often become patients of allergic conjunctivitis, which is caused by protein and bacteria adsorption to the eye, because contact lenses easily adsorb proteins and bacteria. However, even if contact lens users develop eye diseases such as allergic conjunctivitis, most of them continue to use contact lenses to avoid interference to daily life or a decrease in their quality of life. If novel contact lenses able to prevent and additionally cure eye diseases can be manufactured, they could improve the quality of life of contact lens users worldwide. Thus, we aim to develop a novel material for contact lenses to prevent diseases by incorporating a zwitterionic polymer with the ability to suppress protein and bacteria adsorption. In addition, we also aim to effectively introduce and release a drug against allergic conjunctivitis from the contact lens material. Because the poorly water-soluble drug for allergic conjunctivitis (pranoprofen) forms a rigid crystal structure, we developed the novel "hot-melt press method" to construct a contact lens able to effectively release it. In the present study, polymer sheets containing carboxymethyl betaine (a kind of zwitterionic monomer), 2-hydroxyethyl methacrylate, and 1-vinyl-2-pyrrolidone were prepared using three different procedures. The sheets were hydrophilic and showed a strong resistance against protein and bacteria adsorption. The sheets prepared by the hot-melt press method were transparent and seemed to have potential as a material for contact lenses. In addition, the drug introduced into the sheets during preparation was observed to release at a practically appropriate dose. Therefore, it is expected that the sheets could possibly be used as a material for contact lenses which not only protect against the development of eye trouble due to protein and bacterial adsorption, but also heal allergic conjunctivitis.

Hybridization of a phospholipid polymer hydrogel with a natural extracellular matrix using active cell immobilization

Three-dimensional tissue organization is still an obstacle in the field of tissue engineering, which generally involves cell immobilization, proliferation, and organization. As an artificial extracellular matrix (ECM) for providing a suitable environment of cells to construct tissues, combination of cytocompatible polymer hydrogels and natural ECM produced by the immobilized cells was considered. In this research, we designed a spontaneously forming hydrogel system between two water-soluble polymers for the immobilization of cells. These polymers were poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate-co-p-vinylphenylboronic acid-co-N-succinimidyloxycarbonyl tetra(ethylene glycol)methacrylate) (PMBVS) and poly(vinyl alcohol) (PVA) to form a PMBVS/PVA hydrogel in a cell culture medium under mild conditions. Basic fibroblast growth factor (bFGF) was conjugated with PMBVS (PMBV-bFGF). To enhance the growth of the immobilized cells, mouse fibroblast L929 cells were immobilized in the PMBVS/PVA hydrogel and the PMBV-bFGF/PVA hydrogel, and their proliferation and secretion of the ECM under stimulation with bFGF was observed. The ECM infiltrated and replaced the hydrogel, resulting in the formation of a hybrid hydrogel with the ECM and laden cells.

Blood-Compatible Surfaces with Phosphorylcholine-Based Polymers for Cardiovascular Medical Devices

For the acquisition of blood-compatible materials, various hydrophilic polymers for surface modification have been examined. Among them, polymers with a representative phospholipid polar group, the phosphorylcholine (PC) group, are a successful example. These polymers were designed from inspiration of the cell membrane surface and provide protein adsorption resistance even following contact with plasma. This important property is based on the unique hydration state of water molecules surrounding hydrated polymer; in other words, water molecules weakly interact with the polymers and maintain their favorable cluster structure through hydrogen bonding. These polymers are not only hydrophilic, but also electrically neutral, important characteristics which make hydrogen bonding with water molecules less likely to occur and avoid hydrophobic interactions. Phosphorylcholine groups and other zwitterionic structures are significant as hydrophilic functional groups meeting these important requirements. In this review, blood compatibility of a polymer having a PC group is introduced in relation to its hydration structure, followed by a description of the applications of this polymer to cardiovascular medical devices.

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.

Multidisciplinary Perspectives for Alzheimer's and Parkinson's Diseases: Hydrogels for Protein Delivery and Cell-Based Drug Delivery as Therapeutic Strategies

This review presents two intriguing multidisciplinary strategies that might make the difference in the treatment of neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. The first proposed strategy is based on the controlled delivery of recombinant proteins known to play a key role in these neurodegenerative disorders that are released in situ by optimized polymer-based systems. The second strategy is the use of engineered cells, encapsulated and delivered in situ by suitable polymer-based systems, that act as drug reservoirs and allow the delivery of selected molecules to be used in the treatment of Alzheimer's and Parkinson's diseases. In both these scenarios, the design and development of optimized polymer-based drug delivery and cell housing systems for central nervous system applications represent a key requirement. Materials science provides suitable hydrogel-based tools to be optimized together with suitably designed recombinant proteins or drug delivering-cells that, once in situ, can provide an effective treatment for these neurodegenerative disorders. In this scenario, only interdisciplinary research that fully integrates biology, biochemistry, medicine and materials science can provide a springboard for the development of suitable therapeutic tools, not only for the treatment of Alzheimer's and Parkinson's diseases but also, prospectively, for a wide range of severe neurodegenerative disorders.

Direct Intranuclear Anticancer Drug Delivery via Polydimethylsiloxane Nanoparticles: in Vitro and in Vivo Xenograft Studies

Direct delivery of anticancer drugs to nuclei of tumor cells is required to enhance the therapeutic activity, which can be achieved by a nuclear localization signal (NLS) or peptide-decorated nanovehicles. However, NLS/peptide-based approaches may create certain undesirable immunological responses and the utilized synthesis processes are generally labor intensive. To this end, we report ligand-free, enhanced intranuclear delivery of Doxorubicin (Dox) to different cancer cells via porous polydimethylsiloxane (PDMS) nanoparticles (NPs). PDMS NPs were prepared by sacrificial silica template-based approach and Dox was loaded into the pores of PDMS NPs. These Dox-loaded PDMS NPs show enhanced cytotoxicity and reduce the IC50 values by 84 and 54% for HeLa and PC-3, respectively, compared to free Dox. Further, DNA damage in HeLa cells was estimated using comet assay suggesting enhanced DNA damage (72%) with Dox-loaded PDMS NPs as compared to free Dox (12%). The therapeutic efficiency of PDMS-Dox drug delivery system was tested in prostate cancer (PC-3) xenografts in NOD/SCID mice which showed enhanced tumor reduction (∼66%) as compared to free Dox. Taken together, our PDMS-Dox delivery system shows efficient and enhanced transportation of Dox to tumor cells which can be harnessed to develop advanced chemotherapy-based approaches to treat prostate and other cancers.