Stimulus-Responsive Contact Lens for IOP Measurement or Temperature-Triggered Drug Release

From lab to wearables: Innovations in multifunctional hydrogel chemistry for next-generation bioelectronic devices

Functional hydrogels have emerged as foundational materials in diagnostics, therapy, and wearable devices, owing to their high stretchability, flexibility, sensing, and outstanding biocompatibility. Their significance stems from their resemblance to biological tissue and their exceptional versatility in electrical, mechanical, and biofunctional engineering, positioning themselves as a bridge between living organisms and electronic systems, paving the way for the development of highly compatible, efficient, and stable interfaces. These multifaceted capability revolutionizes the essence of hydrogel-based wearable devices, distinguishing them from conventional biomedical devices in real-world practical applications. In this comprehensive review, we first discuss the fundamental chemistry of hydrogels, elucidating their distinct properties and functionalities. Subsequently, we examine the applications of these bioelectronics within the human body, unveiling their transformative potential in diagnostics, therapy, and human-machine interfaces (HMI) in real wearable bioelectronics. This exploration serves as a scientific compass for researchers navigating the interdisciplinary landscape of chemistry, materials science, and bioelectronics.

Temperature Self-Compensating Intelligent Wireless Measuring Contact Lens for Quantitative Intraocular Pressure Monitoring

Flexible bioelectronic devices that can perform real-time and accurate intraocular pressure (IOP) monitoring in both clinical and home settings hold significant implications for the diagnosis and treatment of glaucoma, yet they face challenges due to the open physiological environment of the ocular. Herein, we develop an intelligent wireless measuring contact lens (WMCL) incorporating a dual inductor-capacitor-resistor (LCR) resonant system to achieve temperature self-compensation for quantitative IOP monitoring in different application environments. The WMCL utilizes a compact circuitry design, which enables the integration of low-frequency and high-frequency resonators within a single layer of a sensing circuit without causing visual impairment. Mechanically guided microscale 3D encapsulation strategy combined with flexible circuit printing techniques achieves the surface-adaptive fabrication of the WMCL. The specific design of frequency separation imparts distinct temperature response characteristics to the dual resonators, and the linear combination of the dual resonators can eliminate the impact of temperature variations on measurement accuracy. The WMCL demonstrates outstanding sensitivity and linearity in monitoring the IOP of porcine eyes in vitro while maintaining satisfactory measurement accuracy even with internal temperature variations exceeding 10 °C. Overcoming the impact of temperature variations on IOP monitoring from the system level, the WMCL showcases immense potential as the next generation of all-weather IOP monitoring devices.

Contact Lens with pH Sensitivity for On-Demand Drug Release in Wearing Situation

Drug-releasing contact lenses are emerging therapeutic systems for treating ocular diseases. However, their applicability is limited by the burst release of drugs during lens wear and premature drug leakage during packaging, rendering the precise control of release duration or dose difficult. Here, we introduce a pH-sensitive contact lens exhibiting on-demand drug release only during lens wear and negligible premature drug leakage during packaging and transportation, which is accomplished by incorporating drug-loaded mesoporous silica nanoparticles (MSNs) coated with a pH-sensitive polymer into the contact lens. The compositionally optimized pH-sensitive polymer has a lower critical solution temperature (LCST) at >45 °C at pH 7.4, whereas its LCST decreases to <35 °C under acidic conditions (pH ∼ 6.5). Consequently, the MSN-incorporated contact lens sustainably releases the loaded drugs only in the acidic state at 35 °C, which corresponds to lens-wear conditions, through the MSN pores that open because of the shrinkage of polymer chains. Conversely, negligible drug leakage is observed from the contact lens under low-temperature or neutral-pH conditions corresponding to packaging and transportation. Furthermore, compared with the plain contact lens, the pH-sensitive contact lens exhibits good biocompatibility and unchanged bulk characteristics, such as optical (transmittance in the visible-light region), mechanical (elastic modulus and tensile strength), and physical (surface roughness, oxygen permeability, and water content) properties. These findings suggest that the pH-sensitive contact lens can be potentially applied in ocular disease treatment.

Exploring the Potential of Nanoporous Materials for Advancing Ophthalmic Treatments

The landscape of ophthalmology is undergoing significant transformations, driven by technological advancements and innovations in materials science. One of the advancements in this evolution is the application of nanoporous materials, endowed with unique physicochemical properties ideal for a variety of ophthalmological applications. Characterized by their high surface area, tunable porosity, and functional versatility, these materials have the potential to improve drug delivery systems and ocular devices. This review, anchored by a comprehensive literature focusing on studies published within the last five years, examines the applications of nanoporous materials in ocular drug delivery systems (DDS), contact lenses, and intraocular lenses. By consolidating the most current research, this review aims to serve as a resource for clinicians, researchers, and material scientists engaged in the rapidly evolving field of ophthalmology.

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.

Advances in Nanogels for Topical Drug Delivery in Ocular Diseases

Nanotechnology has accelerated the development of the pharmaceutical and medical technology fields, and nanogels for ocular applications have proven to be a promising therapeutic strategy. Traditional ocular preparations are restricted by the anatomical and physiological barriers of the eye, resulting in a short retention time and low drug bioavailability, which is a significant challenge for physicians, patients, and pharmacists. Nanogels, however, have the ability to encapsulate drugs within three-dimensional crosslinked polymeric networks and, through specific structural designs and distinct methods of preparation, achieve the controlled and sustained delivery of loaded drugs, increasing patient compliance and therapeutic efficiency. In addition, nanogels have higher drug-loading capacity and biocompatibility than other nanocarriers. In this review, the main focus is on the applications of nanogels for ocular diseases, whose preparations and stimuli-responsive behaviors are briefly described. The current comprehension of topical drug delivery will be improved by focusing on the advances of nanogels in typical ocular diseases, including glaucoma, cataracts, dry eye syndrome, and bacterial keratitis, as well as related drug-loaded contact lenses and natural active substances.

Application of Convergent Science and Technology toward Ocular Disease Treatment

Eyes are one of the main critical organs of the body that provide our brain with the most information about the surrounding environment. Disturbance in the activity of this informational organ, resulting from different ocular diseases, could affect the quality of life, so finding appropriate methods for treating ocular disease has attracted lots of attention. This is especially due to the ineffectiveness of the conventional therapeutic method to deliver drugs into the interior parts of the eye, and the also presence of barriers such as tear film, blood-ocular, and blood-retina barriers. Recently, some novel techniques, such as different types of contact lenses, micro and nanoneedles and in situ gels, have been introduced which can overcome the previously mentioned barriers. These novel techniques could enhance the bioavailability of therapeutic components inside the eyes, deliver them to the posterior side of the eyes, release them in a controlled manner, and reduce the side effects of previous methods (such as eye drops). Accordingly, this review paper aims to summarize some of the evidence on the effectiveness of these new techniques for treating ocular disease, their preclinical and clinical progression, current limitations, and future perspectives.

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.

Hydrogel-Based Smart Contact Lens for Highly Sensitive Wireless Intraocular Pressure Monitoring

Real-time intraocular pressure (IOP) monitoring plays a crucial role in glaucoma diagnosis and treatment. The wireless smart contact lens based on a flexible inductor-capacitor-resistor (LCR) sensor is chip-free and battery-free, demonstrating excellent application potential for physiological signal monitoring. To promote the use of LCR contact lenses for clinical IOP monitoring, reliable, comfortable contact lens materials should be used and excellent sensitivity needs to be realized. Here, we propose a method for producing hydrogel-based smart contact lenses for wireless IOP monitoring that uses the conformal stacking technique, solving the problems of swelling of the hydrogel and spherical integration of the pyramid-microstructured dielectric elastomer. The IOP of the in vitro porcine eye is successfully monitored owing to the high sensitivity of the spherical pyramid-microstructured capacitive pressure sensor and the hydrogel substrate. In addition, a glasses-integrated impedance-matching tunable reader for remote signal measurement is realized by enhancing the signal amplitude and increasing the reading distance, improving the portability of the signal measurement equipment. With the above improved designs, the wireless contact lens system has application potential for clinical IOP monitoring and shows substantial promise for next-generation daily ocular health management.

Intelligent wireless theranostic contact lens for electrical sensing and regulation of intraocular pressure

Engineering wearable devices that can wirelessly track intraocular pressure and offer feedback-medicine administrations are highly desirable for glaucoma treatments, yet remain challenging due to issues of limited sizes, wireless operations, and wireless cross-coupling. Here, we present an integrated wireless theranostic contact lens for in situ electrical sensing of intraocular pressure and on-demand anti-glaucoma drug delivery. The wireless theranostic contact lens utilizes a highly compact structural design, which enables high-degreed integration and frequency separation on the curved and limited surface of contact lens. The wireless intraocular pressure sensing modulus could ultra-sensitively detect intraocular pressure fluctuations, due to the unique cantilever configuration design of capacitive sensing circuit. The drug delivery modulus employs an efficient wireless power transfer circuit, to trigger delivery of anti-glaucoma drug into aqueous chamber via iontophoresis. The minimally invasive, smart, wireless and theranostic features endow the wireless theranostic contact lens as a highly promising system for glaucoma treatments.

A Meta-Analysis of Wearable Contact Lenses for Medical Applications: Role of Electrospun Fiber for Drug Delivery

In recent years, wearable contact lenses for medical applications have attracted significant attention, as they enable continuous real-time recording of physiological information via active and noninvasive measurements. These devices play a vital role in continuous monitoring of intraocular pressure (IOP), noninvasive glucose monitoring in diabetes patients, drug delivery for the treatment of ocular illnesses, and colorblindness treatment. In specific, this class of medical devices is rapidly advancing in the area of drug loading and ocular drug release through incorporation of electrospun fibers. The electrospun fiber matrices offer a high surface area, controlled morphology, wettability, biocompatibility, and tunable porosity, which are highly desirable for controlled drug release. This article provides an overview of the advances of contact lens devices in medical applications with a focus on four main applications of these soft wearable devices: (i) IOP measurement and monitoring, (ii) glucose detection, (iii) ocular drug delivery, and (iv) colorblindness treatment. For each category and application, significant challenges and shortcomings of the current devices are thoroughly discussed, and new areas of opportunity are suggested. We also emphasize the role of electrospun fibers, their fabrication methods along with their characteristics, and the integration of diverse fiber types within the structure of the wearable contact lenses for efficient drug loading, in addition to controlled and sustained drug release. This review article also presents relevant statistics on the evolution of medical contact lenses over the last two decades, their strengths, and the future avenues for making the essential transition from clinical trials to real-world applications.

Trends in Outpatient Prescribing Patterns for Ocular Topical Anti-Infectives in Six Major Areas of China, 2013-2019

Topical anti-infectives are important in the management of ocular infections, but little is known about their current status and trends in their use in China. Thus, we carried out a prescription-based, cross-sectional study using the database of Hospital Prescription Analysis Projection of China, and aimed to analyze the trend in the use of ocular topical anti-infectives for outpatients of the ophthalmology department from 2013 to 2019. A total of 2,341,719 prescriptions from 61 hospitals located in six major areas written by ophthalmologists for outpatients were identified, and 1,002,254 of the prescriptions contained at least one anti-infective. The yearly anti-infective prescriptions increased continuously from 126,828 prescriptions in 2013 to 163,434 prescriptions in 2019. The cost also increased from 4,503,711 Chinese Yuan (CNY) in 2013 to CNY 5,860,945 in 2019. However, the use rate of anti-infectives decreased slightly from 46.5% in 2013 to 41.1% in 2019. Patients aged between 19 and 45 years old had the highest anti-infective use rate. Levofloxacin was the most frequently used anti-infective and kept on increasing among all age groups, occupying 67.1% of the total cost at the end of the study. Tobramycin was more frequently used in pediatric patients than in adults, but the use still decreased. Ganciclovir was the preferred anti-viral drug over acyclovir. In conclusion, the prescriptions and cost of ocular topical anti-infectives for outpatients both increased progressively. The increasingly widespread use of levofloxacin raised concerns regarding safety in pediatrics and resistance development. The observed trends can lead to the more efficient management of ocular anti-topical anti-infectives in China.

Effect of Carbon Chain Length, Ionic Strength, and pH on the In Vitro Release Kinetics of Cationic Drugs from Fatty-Acid-Loaded Contact Lenses

This paper explores the use of fatty acids in silicone hydrogel contact lenses for extending the release duration of cationic drugs. Drug release kinetics was dependent on the carbon chain length of the fatty acid loaded in the lens, with 12-, 14- and 18-carbon chain length fatty acids increasing the uptake and the release duration of ketotifen fumarate (KTF) and tetracaine hydrochloride (THCL). Drug release kinetics from oleic acid-loaded lenses was evaluated in phosphate buffer saline (PBS) at different ionic strengths (I = 167, 500, 1665 mM); the release duration of KTF and THCL was decreased with increasing ionic strength of the release medium. Furthermore, the release of KTF and THCL in deionized water did not show a burst and was significantly slower compared to that in PBS. The release kinetics of KTF and THCL was significantly faster when the pH of the release medium was decreased from 7.4 towards 5.5 because of the decrease in the relative amounts of oleate anions in the lens mostly populated at the polymer–pore interfaces. The use of boundary charges at the polymer–pore interfaces of a contact lens to enhance drug partition and extend its release is further confirmed by loading cationic phytosphingosine in contact lenses to attract an anionic drug.

In Vivo Efficacy of Contact Lens Drug-Delivery Systems in Glaucoma Management. A Systematic Review

Adherence is crucial in medical glaucoma therapy, although half of the patients skip eyedrops. In recent years alternative drug-delivery systems have been developed. One of the most promising seems the contact lens (CL). This systematic review aims to present the in vivo efficacy of different CL drug-delivery systems. A total of 126 studies were identified following a literature search adhering to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. After full-text evaluation, 19 studies about CL drug-delivery systems were included. To date, the following drug-delivery systems have been investigated in vivo: drug-soaked CL, CL with physical barriers (vitamin E), molecularly imprinted CL, CL with implants, and nanoparticle-loaded CL. Nanoparticle-loaded CL and CL with implants seem the most promising drug-delivery systems, although initial burst drug release and patient acceptance may limit their widespread use in current practice. Clinical trials are warranted to understand the role of CL as a drug-delivery system in improving glaucomatous patient care.

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.