A stretchable platform with spherical-shaped electronics based on thermo- plastic polyurethane (TPU) is introduced for soft smart contact lenses. The low glass transition temperature of TPU, its relatively low hardness, and its proven biocompatibility (i.e., protection of exterior body wounds) fulfill the essential requirements for eye wearable devices. These requirements include optical transparency, conformal fitting, and flexibility comparable with soft contact lenses (e.g., hydrogel-based). Moreover, the viscoelastic nature of TPU allows planar structures to be thermoformed into spherical caps with a well-defined curvature (i.e., eye’s curvature at the cornea: 9 mm). Numerical modeling and experimental validation enable fine-tuning of the thermo - forming parameters and the optimization of strain-release patterns. Such tight control is proven necessary to achieve oxygen permeable, thin, nonde- velopable, and wrinkle-free contact lenses with integrated electronics (silicon die, radio-frequency antenna, and stretchable thin-film interconnections). This work paves the way toward fully autonomous smart contact lenses potentially for vision correction or sensing applications, among others

handling into the eye. The cornea, which is the environment where the CL is worn, is the first layer of the eye to which we have direct access and plays an important role in monitoring the health of the ocular surface. A soft contact lens with graphenebased electrodes has been demonstrated to perform local electroretinogram which can monitor in real time the electrophysiology of the corneal surface. [8] Although, this device was tested in animal models, optical power correction (found in conventional contact lenses) was not included. Additionally, the parylene support layer in direct contact with the eye lid could introduce discomfort while blinking (since parylene is commonly known as hydrophobic). [9,10] Tear fluid, originated at the lacrimal gland and drained by the lacrimal ducts, [11] covers the corneal surface (for protection and moist) allowing the CL to float and at the same time to have a direct interaction with its physiology. [12] This thin fluid layer, divided in lipid (outer), aqueous (middle) and mucin (inner) containing all the physiologically active substances present in blood, [13] is commonly known as colorless and transparent blood. Different studies have been reported on the elucidation of the causal relationship between the presence (quantity/ frequency) of certain biomarkers (e.g., cancer biomarkers) and systemic diseases. [14,15] With this in mind, attempts to monitor the differentiation and abnormalities of systemic diseases have been actively researched in recent years by introducing a system capable of measuring a specific substance from within a contact lens, [16-20] or measuring a physical quantity (i.e., temperature, pressure, etc.). [21,22] Regarding biosensors focused on the tear fluid, different approaches have been demonstrated either embedded inside of a contact lens [4,23] or by means of an external device temporarily in contact with the tears. These techniques aim to develop noninvasive and continuous monitoring solutions. Although not inside a contact lens, a flexible and biocompatible amperometric glucose sensor in contact with the eye and with an external readout system was tested in animal models and compared with glucose levels measured in blood. [24] The results show a delay between 40 to 60 min after the oral administration of glucose, which could present a risk factor for patients in need of reliable and fast glucose measurements. In parallel, a glucose sensor Nowadays, smart contact lenses (SCLs) display interesting features for healthcare monitoring; however, their comfort and practical usability strongly depend on the outermost material in contact with the eye. In this publication, the embedding of a custom-made and thermoformed Near-Field Communication based circuit in a conventional soft CL is presented. The circuit is composed of gold tracks on polyimide between thermoplastic polyurethane layers (insert), while the lens is based on industry standard double-molding process of poly(2-hydroxyethyl methacrylate) with proven compatibility with corneal tissue. The lens ...

An electrochemical smart contact lens (ESCL) capable of real-speed spatiotemporal electrochemical sensing across the surface of the eye is demonstrated. Four microelectrode arrays, each comprising 33 gold microdiscs of 30 µm diameter, and a distributed common gold counter electrode, are integrated into a soft smart contact lens platform based on polyimide and thermoplastic polyurethane. Using a novel fast-switching chronoamperometric method, an electrochemical 'video' of concentration variation in a model eye under flow conditions is produced, in which the introduction, progress, mixing and drainage of fluid of varying concentration can be observed. The device builds on previous work towards a platform suitable for clinical use and has proven to be robust under expected use conditions, with sensing performance remaining unchanged after thermoforming and repeated mechanical deformation. This work represents a significant step forward in ESCL design, and constitutes significant progress towards a technology with real clinical utility.

We demonstrate a real-speed spatiotemporal electrochemical map showing both time-and position-varying concentration of an analyte in contact with a flexible microelectrode array. A polymer-based device of 11 μm in thickness comprising patterned gold metallisation on a polyimide substrate was fabricated, with eight individually addressable working electrodes (diameter 30 μm) and an integrated counter electrode. We performed a repeated sequence of high-speed chronoamperometric measurements at each electrode and processed the data to generate a spatiotemporal concentration map, in which a number of fluid effects, including bulk flow, diffusive mixing and homogenisation of two miscible fluids of different concentration were observed. This device was fabricated using processes compatible with an existing smart contact lens platform, with a view to develop integrated sensors in future work. We believe this technique has significant potential in the field of electrochemical smart contact lenses, both in introducing new functionality and in improving our ability to draw accurate and clinically-relevant conclusions from measurements made in the tear film.

This paper presents the simulated performance assessment of an artificial iris embedded on a scleral contact lens using real data from an aniridia patient. The artificial iris is based on guest-host liquid crystal cells (GH-LCD) in order to actively modify the transmittance of the lens and effective pupil size. Experimental validation of the GH-LCD spectrum and iris contrast (determined to be 1:2.1) enabled the development of optical models that include the effect of a small pupil on image quality and visual quality on an optical system with aniridia characteristics. Visual simulations at different light conditions (high/low photopic and mesopic) demonstrated the theoretical capacity of the customized artificial iris smart contact lens to expand the depth-of-focus and decrease the optical aberrations (in particular, the spherical aberration). The visual modelling suggests a maximum depth-of-focus value for a 2-mm pupil diameter for both eyes as follows: 3D (1,000 cd/m 2), 2D (10 cd/m 2) and 0.75D (1 cd/ m 2). This work demonstrates the beneficial optical effects of an active artificial iris, based on visual simulations in response to different light levels, and enables further experimental investigation on patients to validate the dynamic light attenuation and visual performance of smart contact lenses with GH-LCD. A smart contact lens is a device with integrated electronics in direct contact with the eye, which provides sensing, actuation and wireless communication 1,2 and offers both remarkable opportunities and challenges in a wide range of ocular applications: (1) active vision correction 3-8 , (2) biomedical sensing 9-11 and (3) augmented reality 5,12. These applications can be attained thanks to important breakthroughs in miniaturized stretchable systems and hybrid integration of a variety of components onto flexible platforms 13-19. Liquid crystal cells (LC) are particularly attractive as an active electro-optical component 20,21 for presbyopia correction (the age-related loss of the ability to dynamically focus near and far objects) 22,23 or a solution for iris defects (such as aniridia, the partial or complete absence of iris) 8. The artificial iris solution is based on the so-called guest-host liquid crystal (GH-LCD) 24,25. GH-LCD is composed by liquid crystal, chiral dopant and dichroic dye, and is capable of producing transmittance variations when an electric field is applied between its parallel electrodes, due to the combination of chirality and double absorption profiles of the mix 4. The GH-LCD electrodes can be partitioned in independent rings that mimic the functionality of the natural iris when actuated in the correct sequence. Controlled transmittance changes of every ring make the GH-LCD technology an interesting approach to create an active artificial iris embedded within a contact lens; opening extraordinary possibilities in patients with aniridia by attenuating the light intensity through the ocular media and offering new options for presbyopia correction by expanding depth-of-focus with a...