Sustained ophthalmic delivery of highly soluble drug using pH-triggered inner layer-embedded contact lens

Harnessing the potential of hydrogels for advanced therapeutic applications: current achievements and future directions

The applications of hydrogels have expanded significantly due to their versatile, highly tunable properties and breakthroughs in biomaterial technologies. In this review, we cover the major achievements and the potential of hydrogels in therapeutic applications, focusing primarily on two areas: emerging cell-based therapies and promising non-cell therapeutic modalities. Within the context of cell therapy, we discuss the capacity of hydrogels to overcome the existing translational challenges faced by mainstream cell therapy paradigms, provide a detailed discussion on the advantages and principal design considerations of hydrogels for boosting the efficacy of cell therapy, as well as list specific examples of their applications in different disease scenarios. We then explore the potential of hydrogels in drug delivery, physical intervention therapies, and other non-cell therapeutic areas (e.g., bioadhesives, artificial tissues, and biosensors), emphasizing their utility beyond mere delivery vehicles. Additionally, we complement our discussion on the latest progress and challenges in the clinical application of hydrogels and outline future research directions, particularly in terms of integration with advanced biomanufacturing technologies. This review aims to present a comprehensive view and critical insights into the design and selection of hydrogels for both cell therapy and non-cell therapies, tailored to meet the therapeutic requirements of diverse diseases and situations.

Recent Advances in Nanomedicine for Ocular Fundus Neovascularization Disease Management

As an indispensable part of the human sensory system, visual acuity may be impaired and even develop into irreversible blindness due to various ocular pathologies. Among ocular diseases, fundus neovascularization diseases (FNDs) are prominent etiologies of visual impairment worldwide. Intravitreal injection of anti-vascular endothelial growth factor drugs remains the primary therapy but is hurdled by common complications and incomplete potency. To renovate the current therapeutic modalities, nanomedicine emerged as the times required, which is endowed with advanced capabilities, able to fulfill the effective ocular fundus drug delivery and achieve precise drug release control, thus further improving the therapeutic effect. This review provides a comprehensive summary of advances in nanomedicine for FND management from state-of-the-art studies. First, the current therapeutic modalities for FNDs are thoroughly introduced, focusing on the key challenges of ocular fundus drug delivery. Second, nanocarriers are comprehensively reviewed for ocular posterior drug delivery based on the nanostructures: polymer-based nanocarriers, lipid-based nanocarriers, and inorganic nanoparticles. Thirdly, the characteristics of the fundus microenvironment, their pathological changes during FNDs, and corresponding strategies for constructing smart nanocarriers are elaborated. Furthermore, the challenges and prospects of nanomedicine for FND management are thoroughly discussed.

Mitigation of pesticide-mediated ocular toxicity via nanotechnology-based contact lenses: a review

The xenobiotic stress exerted by pesticides leads to the deterioration of human and animal health including ocular health. Acute or prolonged exposure to these agricultural toxicants has been implicated in a number of pathological conditions of the eye such as irritation, epiphora or hyper-lacrimation, abrasions on the ocular surface, and decreased visual acuity. The issue is compounded by the fact that tissues of the eye absorb pesticides faster than other organs of the body and are more susceptible to damage as well. However, there is a lacuna in our knowledge regarding the ways by which pesticide exposure-mediated ocular insult might be counteracted. Topical instillation of drugs known to combat the pesticide induced toxicity has been explored to mitigate the detrimental impact of pesticide exposure. However, topical eye drop solutions exhibit very low bioavailability and limited drug residence duration in the tear film decreasing their efficacy. Contact lenses have been explored in this respect to increase bioavailability of ocular drugs, while nanoparticles have lately been utilized to increase drug bioavailability and increase drug residence duration in different tissues. The current review focuses on drug delivery and futuristic aspects of corneal protection from ocular toxicity using contact lenses.

Dexamethasone phosphate and penetratin co-eluting contact lenses: a strategy to enhance ocular drug permeability

Contact lenses (CLs) have been suggested as drug delivery platforms capable of increasing the drug residence time on the cornea and therefore its bioavailability. However, when targeting the posterior segment of the eye, the drug released from CLs still encounters the barrier effect of the ocular tissues, which considerably reduces the efficacy of administration. This work aims at the development of CLs able to simultaneously deliver an anti-inflammatory drug (dexamethasone sodium phosphate) and a cell-penetrating peptide (penetratin), the latter acting as a drug carrier across the tissues. Hydroxyethyl methacrylate (HEMA)-based hydrogels were functionalized with acrylic acid (AAc) and/or aminopropyl methacrylamide (APMA) to serve as CL materials with increased affinity for the drug and peptide. APMA-functionalized hydrogels sustained the dual release for 8 h, which is compatible with the wearing time of daily CLs. Hydrogels demonstrated suitable light transmittance, swelling capacity and in vitro biocompatibility. The anti-inflammatory activity of the drug was not compromised by the presence of the peptide nor by sterilization. The ocular distribution of the drug after 6 h of CL wearing was evaluated in vivo in rabbits and revealed that the amount of drug in the cornea and aqueous humor significantly increased when the drug was co-delivered with penetratin.

Contact lens as an emerging platform for ophthalmic drug delivery: A systematic review

The number of people with eye diseases has increased with the use of electronics. However, the bioavailability of eye drops remains low owing to the presence of the ocular barrier and other reasons. Although many drug delivery systems have been developed to overcome these problems, they have certain limitations. In recent years, the development of contact lenses that can deliver drugs for long periods with high bioavailability and without affecting vision has increased the interest in using contact lenses for drug delivery. Hence, a review of the current state of research on drug delivery contact lenses has become crucial. This article reviews the key physical and chemical properties of drug-laden contact lenses, development and classification of contact lenses, and features of the commonly used materials. A review of the methods commonly used in current research to create contact lenses has also been presented. An overview on how drug-laden contact lenses can overcome the problems of high burst and short release duration has been discussed. Overall, the review focuses on drug delivery methods using smart contact lenses, and predicts the future direction of research on contact lenses.

Development of corneal contact lens materials and current clinical application of contact lenses: A review

Unlike conventional glasses, corneal contact lenses (CLs) can directly contact the surface of the tear film through the application of biopolymer materials, to achieve therapeutic and cosmetic purposes. Since the advent of polymethylmethacrylate, a material that has gained widespread use and attention, statistically, there are now more than 150 × 106 people around the world who wear corneal contact lenses. However, the associated complications caused by the interaction of contact lenses with the ocular surface, tear film, endogenous and environmental microorganisms, and components of the solution affect nearly one-third of the wearer population. The application of corneal contact lenses in correcting vision and myopia control has been widely recognized. With the development of related materials, corneal contact lenses are applied to the treatment of ocular surface diseases, including corneal bandage lenses, drug-loaded corneal contact lenses, biosensors, and other new products, while minimizing the side effects associated with CL wear. This paper summarized the development history and material properties of CLs, focused on the current main clinical applications and mechanisms, as well as clarified the possible complications in wearing therapeutic contact lenses and the direction for improvement in the future.

Challenges and strategies for ocular posterior diseases therapy via non-invasive advanced drug delivery

Posterior segment diseases, such as age-related macular degeneration (AMD) and diabetic retinopathy (DR) are vital factor that seriously threatens human vision health and quality of life, the treatment of which poses a great challenge to ophthalmologists and ophthalmic scientists. In particular, ocular posterior drug delivery in a non-invasive manner is highly desired but still faces many difficulties such as rapid drug clearance, limited permeability and low drug accumulation at the target site. At present, many novel non-invasive topical ocular drug delivery systems are under development aiming to improve drug delivery efficiency and biocompatibility for better therapy of posterior segment oculopathy. The purpose of this review is to present the challenges in the noninvasive treatment of posterior segment diseases, and to propose strategies to tackle these bottlenecks. First of all, barriers to ocular administration were introduced based on ocular physiological structure and behavior, including analysis and discussion on the influence of ocular structures on noninvasive posterior segment delivery. Thereafter, various routes of posterior drug delivery, both invasive and noninvasive, were illustrated, along with the respective anatomical obstacles that need to be overcome. The widespread and risky application of invasive drug delivery, and the need to develop non-invasive local drug delivery with alternative to injectable therapy were described. Absorption routes through topical administration and strategies to enhance ocular posterior drug delivery were then discussed. As a follow-up, an up-to-date research advances in non-invasive delivery systems for the therapy of ocular fundus lesions were presented, including different nanocarriers, contact lenses, and several other carriers. In conclusion, it seems feasible and promising to treat posterior oculopathy via non-invasive local preparations or in combination with appropriate devices.

Cationic Nano-Lipidic Carrier Mediated Ocular Delivery of Triamcinolone Acetonide: A Preclinical Investigation in the Management of Uveitis

The current study was undertaken to evaluate the efficacy of a novel nano-lipoidal eye drop formulation of triamcinolone acetonide (TA) for the topical treatment of uveitis. The triamcinolone acetonide-loaded nanostructured lipid carriers (cTA-NLC) were developed by employing 'hot microemulsion method' using biocompatible lipids, which exhibited a sustained release nature and enhanced efficacy when evaluated in vitro. The in vivo efficacy of this developed formulation was tested on Wistar rats, and a single-dose pharmacokinetic study was conducted in rabbits. The eyes of animals were examined for any signs of inflammation using the 'Slit-lamp microscopic' method. The aqueous humor collected from the sacrificed rats was tested for total protein count and cell count. The total protein count was determined using BSA assay method, while the total cell count was determined by Neubaur's hemocytometer method. The results showed that the cTA-NLC formulation had negligible signs of inflammation, with a clinical score of uveitis 0.82 ± 0.166, which is much less than control/untreated (3.80 ± 0.3) and free drug suspension (2.66 ± 0.405). The total cell count was also found to be significantly low for cTA-NLC (8.73 ± 1.79 × 10⁵) as compared to control (52.4 ± 7.71 × 10⁵) and free drug suspension (30.13 ± 3.021 × 10⁵). Conclusively, the animal studies conducted showed that our developed formulation holds the potential for effective management of uveitis.

Smart Contact Lens Systems for Ocular Drug Delivery and Therapy

Ocular drug delivery and therapy systems have been extensively investigated with various methods including direct injections, eye drops and contact lenses. Nowadays, smart contact lens systems are attracting a lot of attention for ocular drug delivery and therapy due to their minimally invasive or non-invasive characteristics, highly enhanced drug permeation, high bioavailability, and on-demand drug delivery. Furthermore, smart contact lens systems can be used for direct light delivery into the eyes for biophotonic therapy replacing the use of drugs. Here, we review smart contact lens systems which can be classified into two groups of drug-eluting contact lens and ocular device contact lens. More specifically, this review covers smart contact lens systems with nanocomposite-laden systems, polymeric film-incorporated systems, micro and nanostructure systems, iontophoretic systems, electrochemical systems, and phototherapy systems for ocular drug delivery and therapy. After that, we discuss the future opportunities, challenges and perspectives of smart contact lens systems for ocular drug delivery and therapy.

Cellulose Acetate Phthalate-Based pH-Responsive Cyclosporine A-Loaded Contact Lens for the Treatment of Dry Eye

Cyclosporine A (CsA) as an eye drop is an effective treatment for dry eye. However, it has potential side effects and a short ocular residence time. To overcome these obstacles, we developed a cellulose acetate phthalate-based pH-responsive contact lens (CL) loaded with CsA (CsA-CL). The CsA was continuously released from the CsA-CL at physiological conditions (37 °C, pH 7.4) without an initial burst. CsA was well-contained in the selected storage condition (4 °C, pH 5.4) for as long as 90 days. In safety assays, cytotoxicity, ocular irritation, visible light transmittance, and oxygen permeability were in a normal range. CsA concentrations in the conjunctiva, cornea, and lens increased over time until 12 h. When comparing the therapeutic efficacy between the normal control, experimental dry eye (EDE), and treatment groups (CsA eye drop, naïve CL, and CsA-CL groups), the tear volume, TBUT, corneal fluorescein staining at 7 and 14 days, conjunctival goblet cell density, and corneal apoptotic cell counts at 14 days improved in all treatment groups compared to EDE, with a significantly better result in the CsA-CL group compared with other groups (all p < 0.05). The CsA-CL could be an effective, stable, and safe option for inflammatory dry eye.

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.

The Use of Polymer Blends in the Treatment of Ocular Diseases

The eye is an organ with limited drug access due to its anatomical and physiological barriers, and the usual forms of ocular administration are limited in terms of drug penetration, residence time, and bioavailability, as well as low patient compliance. Hence, therapeutic innovations in new drug delivery systems (DDS) have been widely explored since they show numerous advantages over conventional methods, besides delivering the content to the eye without interfering with its normal functioning. Polymers are usually used in DDS and many of them are applicable to ophthalmic use, especially biodegradable ones. Even so, it can be a hard task to find a singular polymer with all the desirable properties to deliver the best performance, and combining two or more polymers in a blend has proven to be more convenient, efficient, and cost-effective. This review was carried out to assess the use of polymer blends as DDS. The search conducted in the databases of Pubmed and Scopus for specific terms revealed that although the physical combination of polymers is largely applied, the term polymer blend still has low compliance.

Lab-on-a-Contact Lens: Recent Advances and Future Opportunities in Diagnostics and Therapeutics

The eye is one of the most complex organs in the human body, containing rich and critical physiological information (e.g., intraocular pressure, corneal temperature, and pH) as well as a library of metabolite biomarkers (e.g., glucose, proteins, and specific ions). Smart contact lenses (SCLs) can serve as a wearable intelligent ocular prosthetic device capable of noninvasive and continuous monitoring of various essential physical/biochemical parameters and drug loading/delivery for the treatment of ocular diseases. Advances in SCL technologies and the growing public interest in personalized health are accelerating SCL research more than ever before. Here, the current status and potential of SCL development through a comprehensive review from fabrication to applications to commercialization are discussed. First, the material, fabrication, and platform designs of the SCLs for the diagnostic and therapeutic applications are discussed. Then, the latest advances in diagnostic and therapeutic SCLs for clinical translation are reviewed. Later, the established techniques for wearable power transfer and wireless data transmission applied to current SCL devices are summarized. An outlook, future opportunities, and challenges for developing next-generation SCL devices are also provided. With the rise in interest of SCL development, this comprehensive and essential review can serve as a new paradigm for the SCL devices.

Bibliometric and visualized analysis of ocular drug delivery from 2001 to 2020

OBJECTIVE

To perform a bibliometric analysis in the field of ocular drug delivery research to characterize the current international trends and to present visual representations of the past and emerging trends on ocular drug delivery research over the past decade.

METHOD

In this cross-sectional study, a bibliometric analysis of data retrieved and extracted from the Web of Science Core Collection (WoSCC) database was performed to analyze evolution and theme trends on ocular drug delivery research from January 1, 2001, to December 31, 2020. A total of 4334 articles on ocular drug delivery were evaluated for specific characteristics, such as publication year, journals, authors, institutions, countries/regions, references, and keywords. Co-authorship analysis, co-occurrence analysis, co-citation analysis, and network visualization were constructed by VOSviewer. Some important subtopics identified by bibliometric characterization were further discussed and reviewed.

RESULTS

From 2001 to 2020, the annual global publications increased by 746.15%, from 52 to 440. International Journal of Pharmaceutics published the most manuscripts (250 publications) and produced the highest citations (9509 citations), followed by Investigative Ophthalmology & Visual Science (202 publications) and Journal of Ocular Pharmacology and Therapeutics (136 publications). The United States (1289 publications, 31,512 citations), the University of Florida (82 publications, 2986 citations), and Chauhan, Anuj (52 publications, 2354 citations) were the most productive and impactful institution, country, and author respectively. The co-occurrence cluster analysis of the top 100 keywords form five clusters: (1) micro/nano ocular drug delivery systems; (2) the treatment of inflammation and posterior diseases; (3) macroscopic ocular drug delivery systems/devices; (4) the characteristics of drug delivery systems; (5) and the ocular drug delivery for glaucoma treatment. Diabetic macular edema, anti-VEGF, ranibizumab, bevacizumab, micelles and latanoprost, were the latest high-frequency keywords, indicating the emerging frontiers of ocular drug delivery. Further discussions into the subtopics were provided to assist researchers to determine the range of research topics and plan research direction.

CONCLUSIONS

Over the last two decades there has been a progressive increase in the number of publications and citations on research related to ocular drug delivery across many countries, institutions, and authors. The present study sheds light on current trends, global collaboration patterns, basic knowledge, research hotspots, and emerging frontiers of ocular drug delivery. Novel solutions for ocular drug delivery and the treatment of inflammation and posterior diseases were the major themes over the last 20 years.

Cellulosic Polymers for Enhancing Drug Bioavailability in Ocular Drug Delivery Systems

One of the major impediments to drug development is low aqueous solubility and thus poor bioavailability, which leads to insufficient clinical utility. Around 70–80% of drugs in the discovery pipeline are suffering from poor aqueous solubility and poor bioavailability, which is a major challenge when one has to develop an ocular drug delivery system. The outer lipid layer, pre-corneal, dynamic, and static ocular barriers limit drug availability to the targeted ocular tissues. Biopharmaceutical Classification System (BCS) class II drugs with adequate permeability and limited or no aqueous solubility have been extensively studied for various polymer-based solubility enhancement approaches. The hydrophilic nature of cellulosic polymers and their tunable properties make them the polymers of choice in various solubility-enhancement techniques. This review focuses on various cellulose derivatives, specifically, their role, current status and novel modified cellulosic polymers for enhancing the bioavailability of BCS class II drugs in ocular drug delivery systems.

Advances and challenges in the nanoparticles-laden contact lenses for ocular drug delivery

The delivery of drugs that target ocular tissues is challenging due to the physiological barriers of the eye like tear dilution, nasolacrimal drainage, blinking, tear turnover rate and low residence time Drug-laden contact lenses can be a possible solution to overcome some of these challenges. Nanoparticles are being extensively studied as novel systems for loading drugs into therapeutic contact lenses. The versatile features of the organic and inorganic nanoparticles and their diverse physicochemical properties make it possible to load and sustain drug release from the contact lenses. Nevertheless, several issues remains to be solved before its clinical application and commercialization such as changes in contact lens swelling (water content), transmittance, protein adherence, surface roughness, tensile strength, ion and oxygen permeability and drug leaching during contact lens manufacture. However, clinical studies demonstrated the potential of therapeutic contact lenses to manage the scientific, commercial and regulatory challenges to make its place in the market. This review highlights the different methodologies used to fabricate nanoparticle-laden contact lenses and highlights the major advances and challenges to commercialization.

Pharmaceutical-loaded contact lenses as an ocular drug delivery system: A review of critical lens characterization methodologies with reference to ISO standards

Therapeutic contact lenses for ocular drug delivery have received considerable interest as they can potentially enhance ocular bioavailability, increase patient compliance, and reduce side effects. Along with the successful in vitro and in vivo studies on sustained drug delivery through contact lenses, lens critical properties such as water content, optical transparency and modulus have also been investigated. Aside from issues such as drug stability or burst release, the potential for the commercialization of pharmaceutical-loaded lenses can be limited by the alteration of lens physical and chemical properties upon the incorporation of therapeutic or non-therapeutic components. This review outlines advances in the use of pharmaceutical-loaded contact lenses and their relevant characterization methodologies as a potential ocular drug delivery system from 2010 to 2020, while summarizing current gaps and challenges in this field. A key reference point for this review is the relevant ISO standards on contact lenses, relating to the associated characterization methodologies. The content of this review is categorized based on the chemical, physical and mechanical properties of the loaded lens with the shortcomings of such analytical technologies examined.

Intellective and stimuli-responsive drug delivery systems in eyes

Stimuli-responsive drug delivery systems have attracted widespread attention in recent years since they can control drug release in a spatiotemporal manner and can achieve tunable drug release according to patient's physiological or pathological condition. In this review, we briefly introduce the drug delivery barriers and drug delivery systems in the anterior and posterior segment of eyes, and collect the recent advances in stimuli-responsive drug delivery systems in eyes for controlled drug release in response to exogenous stimuli (ultrasound, magnetic stimulus, electrical stimulus, and light) or endogenous stimuli (enzyme, active oxygen species, temperature, ions, and pH). In addition, the design and mechanisms of the stimuli-responsive drug delivery systems have been summarized in this review, and the advantages and limitations are also briefly discussed.

In vivo drug delivery via contact lenses: The current state of the field from origins to present

Over the past half century, contact lenses have been investigated for their potential as drug delivery devices for ocular therapeutics. Hundreds of studies have been published in the pursuit of the most effective and efficient release strategies and methods for contact lens drug delivery. This paper provides a thorough overview of the various contact lens drug delivery strategies, with a specific, comprehensive focus on in vivo studies that have been published since the field began in 1965. Significant accomplishments, current trends, as well as future strategies and directions are highlighted. In vivo study analysis provides a straightforward perspective and assessment of method success and commercialization potential in comparison to benchtop, in vitro studies. Analysis of the majority of published work indicates in vitro and in vivo studies do not correlate with a correlation coefficient of 0.25, with many in vitro studies grossly overestimating drug release duration and not showing appreciable drug release control. However, there has been an increase in activity in the last decade, and some methods have generated promising results exhibiting controlled release with commercialization potential. Clinical translation of drug releasing lenses is on the horizon and has high potential to impact a large number of patients providing efficacious treatment compared to current topical treatments.

Hydrogels-based ophthalmic drug delivery systems for treatment of ocular diseases

An increasing number of people worldwide are affected by eye diseases, eventually leading to visual impairment or complete blindness. Conventional treatment involves the use of eye drops. However, these formulations often confer low ocular bioavailability and frequent dosing is required. Therefore, there is an urgent need to develop more effective drug delivery systems to tackle the current limitations. Hydrogels are multifunctional ophthalmic drug delivery systems capable of extending drug residence time and sustaining release of drugs. In this review, common ocular diseases and corresponding therapeutic drugs are briefly introduced. In addition, various types of hydrogels reported for ophthalmic drug delivery, including in-situ gelling hydrogels, contact lenses, low molecular weight supramolecular hydrogels, cyclodextrin/poly (ethylene glycol)-based supramolecular hydrogels and hydrogel-forming microneedles, are summarized. Besides, marketed hydrogel-based opthalmic formulations and clinical trials are also highlighted. Finally, critical considerations regarding clinical translation of biologics-loaded hydrogels are discussed.

Therapeutic Ophthalmic Lenses: A Review

An increasing incidence of eye diseases has been registered in the last decades in developed countries due to the ageing of population, changes in lifestyle, environmental factors, and the presence of concomitant medical conditions. The increase of public awareness on ocular conditions leads to an early diagnosis and treatment, as well as an increased demand for more effective and minimally invasive solutions for the treatment of both the anterior and posterior segments of the eye. Despite being the most common route of ophthalmic drug administration, eye drops are associated with compliance issues, drug wastage by lacrimation, and low bioavailability due to the ocular barriers. In order to overcome these problems, the design of drug-eluting ophthalmic lenses constitutes a non-invasive and patient-friendly approach for the sustained drug delivery to the eye. Several examples of therapeutic contact lenses and intraocular lenses have been developed, by means of different strategies of drug loading, leading to promising results. This review aims to report the recent advances in the development of therapeutic ophthalmic lenses for the treatment and/or prophylaxis of eye pathologies (i.e., glaucoma, cataract, corneal diseases, or posterior segment diseases) and it gives an overview of the future perspectives and challenges in the field.

Extended Delivery of Pirfenidone with Novel, Soft Contact Lenses In Vitro and In Vivo

Purpose: The aim of this study was to fabricate pirfenidone (PFD)-loaded soft contact lenses (SCLs), explore their characteristics, and evaluate their efficiency on extended delivery of PFD in vitro and in vivo. Methods: PFD-loaded SCLs were fabricated by embedding an insert of PFD and polyvinyl alcohol (PVA) into 2 layers of silicone elastomer. The optical transparency, water content, and protein deposition were measured. Transformed human corneal epithelial cells were used to test the cytotoxicity of SCLs. The release rate of PFD by SCLs in vitro was evaluated by an ultraviolet-visible spectrophotometer. Toxicity of SCLs was assessed by inspection of ocular surface irritation in rabbits before and after contact lens wear. The concentrations of PFD in tears and aqueous humor of rabbits' eyes as a function of time were determined by high-performance liquid chromatography for SCLs and 30 μL of 0.5% PFD eye drops. Results: SCLs possessed good light transmittance. Blank SCLs had poor water content (0.548% ± 0.330), and an improved water content was found in PVA film-loaded SCLs (11.022% ± 1.508, P = 0.010). No lysozyme and human serum albumin were found in SCLs. There was no significant toxicity of SCLs in vitro and in vivo. SCLs prolonged the residence time of PFD in tears and aqueous humor of rabbit eyes by 5 times compared with the eye drop instillation while around 1/10 of the eye drop dosage was loaded in SCLs. Conclusions: PFD-loaded SCLs can significantly prolong the residence time of PFD and may be a promising ocular drug delivery system.

In Situ Gelling Systems Using Pluronic F127 Enhance Corneal Permeability of Indomethacin Nanocrystals

We previously designed an ophthalmic dispersion containing indomethacin nanocrystals (IMC-NCs), showing that multiple energy-dependent endocytoses led to the enhanced absorption of drugs from ocular dosage forms. In this study, we attempted to prepare Pluronic F-127 (PLF-127)-based in situ gel (ISG) incorporating IMC-NCs, and we investigated whether the instillation of the newly developed ISG incorporating IMC-NCs prolonged the precorneal resident time of the drug and improved ocular bioavailability. The IMC-NC-incorporating ISG was prepared using the bead-mill method and PLF-127, which yielded a mean particle size of 50–150 nm. The viscosity of the IMC-NC-incorporating ISG was higher at 37 °C than at 10 °C, and the diffusion and release of IMC-NCs in the IMC-NC-incorporating ISG were decreased by PLF-127 at 37 °C. In experiments using rabbits, the retention time of IMC levels in the lacrimal fluid was enhanced with PLF-127 in the IMC-NC-incorporating ISG, whereby the IMC-NC-incorporating ISG with 5% and 10% PLF-127 increased the transcorneal penetration of the IMCs. In contrast to the results with optimal PLF-127 (5% and 10%), excessive PLF-127 (15%) decreased the uptake of IMC-NCs after instillation. In conclusion, we found that IMC-NC-incorporating ISG with an optimal amount of PLF-127 (5–10%) resulted in higher IMC corneal permeation after instillation than that with excessive PLF-127, probably because of the balance between higher residence time and faster diffusion of IMC-NCs on the ocular surface. These findings provide significant information for developing ophthalmic nanomedicines.

An in situ Gelling System Based on Methylcellulose and Tranilast Solid Nanoparticles Enhances Ocular Residence Time and Drug Absorption Into the Cornea and Conjunctiva

We previously developed ophthalmic formulations containing tranilast nanopartaicles (ophthalmic TL-NPs formulations), and found them to show high uptake into ocular tissues. In this study, we aimed to design an in situ gel incorporating TL-NPs with 0.5–3% methylcellulose (MC, type SM-4) to ensure long residence time of the drug at the ocular surface. The ophthalmic TL-NPs formulations were prepared by the bead mill method, which yielded a mean particle size of ~93 nm with or without MC (0.5–3%). Although the dispersibility of TL particles in ophthalmic formulations increased with the MC content, the diffusion behavior of TL particles in the dispersion medium decreased with MC content. In an in vivo study using rats, the TL content in the lacrimal fluid was enhanced with MC content in the ophthalmic TL-NPs formulations, and the optimum amount of MC (0.5–1.5%) enhanced the TL content in the cornea and conjunctiva, and an anti-inflammatory effect of TL in rats instilled with ophthalmic TL-NPs formulations was observed. On the other hand, excessive MC (3%) prevented the corneal uptake of TL-NPs after instillation, and the anti-inflammation effect of TL was lower than that of ophthalmic TL-NPs formulations with optimum MC (0.5–1.5%). In conclusion, we found that gel formulations of TL-NPs with 0.5 and 1.5% MC provided a prolonged pre-corneal and pre-conjunctival contact time of TL, and resulted in higher TL contents in the cornea and conjunctiva following instillation in comparison with TL-NPs with or without 3% MC. This is probably due to the balance between the higher residence time and faster diffusion of TL-NPs on the ocular surface. These findings provide significant information that can be used to design further studies aimed at developing ophthalmic nanomedicines.

Ophthalmic In Situ Gelling System Containing Lanosterol Nanoparticles Delays Collapse of Lens Structure in Shumiya Cataract Rats

We attempted to prepare ophthalmic in situ gel formulations containing lanosterol (Lan) nanoparticles (LA-NPs/ISG) and investigated the characteristics, delivery pathway into the lens, and anti-cataract effects of LA-NPs/ISG using SCR-N (rats with slight lens structure collapse) and SCR-C (rats with a combination of remarkable lens structure collapse and opacification). LA-NPs/ISG was prepared by bead milling of the dispersions containing 0.5% Lan powder, 5% 2-hydroxypropyl-β-cyclodextrin, 0.5% methylcellulose, 0.005% benzalkonium chloride, and 0.5% mannitol. The particle size distribution of Lan was 60–250 nm. The LA-NPs/ISG was gelled at 37 °C, and the LA-NPs/ISG was taken into the cornea by energy-dependent endocytosis and then released to the intraocular side. In addition, the Lan contents in the lenses of both SCR-N and SCR-C were increased by the repetitive instillation of LA-NPs/ISG (twice per day). The space and structure collapse in the lens of SCR-N with aging was attenuated by the instillation of LA-NPs/ISG. Moreover, the repetitive instillation of LA-NPs/ISG attenuated the changes in cataract-related factors (the enhancement of nitric oxide levels, calpain activity, lipid peroxidation levels, Ca²⁺ contents, and the decrease of Ca²⁺-ATPase activity) in the lenses of SCR-C, and the repetitive instillation of LA-NPs/ISG delayed the onset of opacification in the SCR-C. It is possible that the LA-NPs/ISG is useful in maintaining lens homeostasis.

Comparison of thermosensitive in situ gels and drug-resin complex for ocular drug delivery: In vitro drug release and in vivo tissue distribution

Conventional ophthalmic eye drops are limited by their rapid elimination rate and short time of action. Ion exchange resin has been used to achieve sustained ocular drug delivery but the high selectivity of drug molecules restricts its broad application. In situ gel system seems to be a good strategy to address these problems but the influence of in situ gel type on the sustained release behavior and tissue distribution after ocular application is unclear. Therefore, in this study, using betaxolol hydrochloride as a model drug, poloxamer 407 and methylcellulose as the carriers, two thermosensitive in situ gel systems were prepared and characterized. Influence of formulation composition type and concentration on in vitro drug release was studied. Tissue distribution after ocular delivery of two different thermosensitive in situ gels was studied and compared with commercial BH eye drop (Betoptic S®). In vitro studies demonstrated that addition of 4% HPMC 606W in 15% P407 solution and 5% PEG4000 in 2% MC solution obtained gels with appropriate gelation temperature and similar sustained drug release rate. In vivo tissue distribution study indicated that they presented similar drug concentration in cornea, iris-ciliary and aqueous humor irrespective of gel type, with higher drug concentration achieved after 4 h compared to the commercial resin suspension eye drops. The AUC and MRT of the two in situ gel eye drops were 2 times higher than that of the commercial resin suspension eye drops in cornea. In conclusion, the two thermosensitive in situ gels have prolonged drug release after ocular drug delivery compared with ion exchange resin eye drops, implying their potential applications in clinic with broad drug adoptability.

Triamcinolone acetonide loaded-cationic nano-lipoidal formulation for uveitis: Evidences of improved biopharmaceutical performance and anti-inflammatory activity

Topical administration of corticosteroids is the cornerstone treatment of anterior uveitis, but poor corneal penetration and retention cause hindrance in their therapeutic utility. The conventional eye drops are less valuable in conditions where inflammation reaches deeper regions of the eye. Therefore, there is a clear need for an effective drug delivery system, which can increase corticosteroid penetration after topical application. To address this, cationic nanostructured lipid carriers of the drug triamcinolone acetonide (cTA-NLC) were prepared. The cTA-NLC were prepared by a hot microemulsion method and evaluated for drug release, permeation, cell uptake, cytotoxicity, anti-inflammatory activity and ocular irritancy. The cTA-NLC are nanometric in size (< 200 nm), with a zeta potential of about +35 mv and % drug EE of 88 %. The nanocarriers exhibited slow and sustained release of around 84 % in 24 h and transcorneal drug permeation of 51 % in 8 h. The nanocarriers exhibited no cytotoxicity (% cell viability of>90 %). The cell uptake study showed that nanocarriers could retain inside the cells for 24 h. The developed formulation could significantly reduce the TNF-α level in LPS induced inflamed cells. The studies indicated that cTA-NLC could be a promising option for the topical treatment of uveitis.

S, Akshara MR, N. K, Zaidi ZS, Iqbal SF, Misra SK. Advances in chemistry and composition of soft materials for drug releasing contact lenses

Ocular drug delivery has always been a challenging feat to achieve in the field of medical sciences. One of the existing methods of non-invasive ocular drug delivery is the use of eye drops. However, drugs administered through these formulations have low bioavailability in the ocular system. This limitation can been overcome by using contact lenses as drug delivery vehicles. According to USA FDA definitions they can be categorized into two main categories-hard and soft contact lenses. Based on the material properties, hard contact lenses are mostly produced from polymers of acrylate monomers such as MMA (methyl methacrylate). These have the least water retention capacity, thereby, having minimal ability to diffuse oxygen into the corneal layer and are not ideal for long term use. Soft material contact lenses are flexible and are mainly hydrogel based. They have higher water retention capacities as compared to rigid contact lenses, which gives them the ability to transmit oxygen to the corneal layer. These hydrogel based soft materials are mainly produced from polymers of acrylate monomers such as HEMA (hydroxyethyl methacrylate) and found to be better for drug delivery contact lenses. These polymer-based soft materials have been efficiently modified in terms of their chemistry to achieve diverse physicochemical properties to produce efficient ocular drug delivery systems. However, complications such as drug leaching during storage and distribution, sterilisation, preservation of integrity of the lens and the possibility of surface roughness due to the incorporated drug molecules still need to be optimised. This review highlights the chemistries of various polymeric molecules through which physicochemical properties can be modified to achieve optimum drug loading and sustained release of the drug for application in the ocular system.

Contact lens as controllable route for ocular drug delivery.

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.

Hydrogels and Their Applications in Targeted Drug Delivery

Conventional drug delivery approaches are plagued by issues pertaining to systemic toxicity and repeated dosing. Hydrogels offer convenient drug delivery vehicles to ensure these disadvantages are minimized and the therapeutic benefits from the drug are optimized. With exquisitely tunable physical properties that confer them great controlled drug release features and the merits they offer for labile drug protection from degradation, hydrogels emerge as very efficient drug delivery systems. The versatility and diversity of the hydrogels extend their applications beyond targeted drug delivery also to wound dressings, contact lenses and tissue engineering to name but a few. They are 90% water, and highly porous to accommodate drugs for delivery and facilitate controlled release. Herein we discuss hydrogels and how they could be manipulated for targeted drug delivery applications. Suitable examples from the literature are provided that support the recent advancements of hydrogels in targeted drug delivery in diverse disease areas and how they could be suitably modified in very different ways for achieving significant impact in targeted drug delivery. With their enormous amenability to modification, hydrogels serve as promising delivery vehicles of therapeutic molecules in several disease conditions, including cancer and diabetes.

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.