Showing papers by "Mark S. Humayun published in 2006"

Flexible Circuit Electrode Array

Abstract: Polymer materials are useful as electrode array bodies for neural stimulation They are particularly useful for retinal stimulation to create artificial vision, cochlear stimulation to create artificial hearing, or cortical stimulation many purposes The pressure applied against the retina, or other neural tissue, by an electrode array is critical Too little pressure causes increased electrical resistance, along with electric field dispersion Too much pressure may block blood flow Common flexible circuit fabrication techniques generally require that a flexible circuit electrode array be made flat Since neural tissue is almost never flat, a flat array will necessarily apply uneven pressure Further, the edges of a flexible circuit polymer array may be sharp and cut the delicate neural tissue By applying the right amount of heat to a completed array, a curve can be induced With a thermoplastic polymer it may be further advantageous to repeatedly heat the flexible circuit in multiple molds, each with a decreasing radius Further, it is advantageous to add material along the edges It is further advantageous to provide a fold or twist in the flexible circuit array Additional material may be added inside and outside the fold to promote a good seal with tissue

Intraocular retinal prosthesis

Abstract: Retinal prostheses have the potential to restore some level of visual function to blind individuals. While visual prosthetic devices for the optic nerve and visual cortex also have potential application, the retinal approach offers the advantage of relatively accessible retinal neurons in the back of the eye. Biological studies have demonstrated biocompatibility of implantation and stimulation and have investigated retinal response to stimulation. Recent clinical trials have shown that a prototype epiretinal implant, despite having few electrodes contacting the retina, still allows test subjects to perform simple visual tasks. Ongoing engineering research is focusing on the fabrication of a high-resolution implant

In vitro and in vivo evaluation of ultrananocrystalline diamond for coating of implantable retinal microchips

Abstract: In this work, ultrananocrystalline diamond (UNCD) thin films were evaluated for use as hermetic and bioinert coatings for a retinal microchip. These films were deposited on highly conductive Si substrates at different temperatures (from 400 to 800°C), using microwave plasma enhanced chemical vapor deposition with argon-rich Ar/CH4 gas mixtures and different relative amounts of hydrogen (0–20%). Scanning electron microscopy studies showed that all the films are dense and continuous. Results of cyclic voltammetry test revealed that when there was <2% of hydrogen in the plasma, the film obtained renders the surface electrochemically inactive, with very low leakage currents (∼4 × 10−7 A/cm2 at ±5 V). In addition, in vivo tests of the UNCD-coated Si samples were performed by implanting them in the eyes of rabbits for 4–6 months within the eye physiological environment. According to all these results, it was concluded that UNCD is a promising candidate for use as the encapsulating coatings for implantable retinal microelectronic devices. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006

Scalable high lead-count parylene package for retinal prostheses

Abstract: We present the first packaging technology for high lead-count retinal prostheses capable of fully scalable interconnection of a high-density electrode array, a radiofrequency (RF) telemetry coil, and other discrete components, such as chip capacitors, with prefabricated, stand-alone driver circuitry. This parylene-based drop-chip technology enables the application-specific integrated circuit (ASIC) to be directly integrated into the fabrication process of the other system components, such that the resulting device is flexible, facilitating surgical implantation. The ASIC-to-electrode interconnects are patterned using standard photolithography and standard microfabrication techniques, enabling the density of interconnects to scale to the limits of the lithographic equipment used to define the etch holes over the on-chip pads. This scheme also enables the simultaneous integration and interconnection of multiple ASICs with the rest of the system in such a way that the best features of chip-level and wafer-level packaging technologies are combined into a single process. Using this technique, standard photolithography and interconnect fabrication has been performed successfully on 10 chips. Electrical test results verify the efficacy of this cost-effective and high-yield packaging scheme, and pave the way for a monolithic implantable parylene-based retinal prosthesis system as well as other systems requiring the capability to perform microfabrication steps on prefabricated chips.

A dual band wireless power and data telemetry for retinal prosthesis.

Abstract: Inductive coupling is commonly used for wireless power and data transfer in biomedical telemetry systems. The increasing demand on the performance of medical devices requires high data rate and high power efficiency at the same time. If only one radio frequency carrier is used, it is difficult to achieve both high data rate and high power efficiency due to the competing requirements on carrier frequency and system-Q of the power and data transmission. We propose a dual band telemetry system to implement power and data transmission using different frequencies by allocating lower frequency for power transmission and higher frequency for data transmission. However, the magnetic coupling between the power carrier and data carrier will affect the operation of both links. In this paper, this interference is analyzed and design equations are derived, which are used to design coils to maximize the data signal level received at the implant side. A prototype of dual band telemetry for a retinal prosthetic device has been built and experimental results show that both power and data can be transmitted and high data rate can be achieved without compromising the power transmission efficiency.

Paragraph text reading using a pixelized prosthetic vision simulator: parameter dependence and task learning in free-viewing conditions.

Abstract: PURPOSE. To investigate the feasibility of adequate reading by recipients of future prosthetic visual implants through simulation in sighted observers. METHODS. Four normally sighted subjects used a video headset to view short-story segments at a sixth grade reading level, presented in 6- to 11-word paragraphs through a pixelizing grid defined by five parameters (dot size, grid size, dot spacing, random dropout percentage, and gray-scale resolution). Grid parameters were varied individually, and four character sizes and two contrast levels were used. RESULTS. Reading speeds of 30 to 60 words per minute without errors were recorded for some parameter combinations. In general, reading accuracy and speed were influenced by all parameters. Reading accuracy exceeded 90% if the following conditions were met: At least 3 dots/charwidth were presented, and dropout did not exceed 50%. Reading speed deteriorated below 20 words per minute if accuracy fell below 90% and at low contrast if the grid spanned less than two characters. CONCLUSIONS. It is uncertain whether and to what extent retinal reorganization may limit the perception of multiple phosphenes by blind prosthesis recipients. If distinct phosphenes can be perceived, these results suggest that a 3 X 3-mm 2 prosthesis with 16 X 16 electrodes should allow paragraph reading. The effects of stabilizing the dot grid on the retina must be investigated further.

Retinal prostheses for the blind.

Abstract: Introduction: Using artificial means to treat extreme vision impairment has come closer to reality during the past few decades. The goal of this research has been to create an implantable medical device that provides useful vision for those patients who are left with no alternatives. Analogous to the cochlear implants for some forms of hearing loss, these devices could restore useful vision by converting visual information into patterns of electrical stimulation that excite the remaining viable inner retinal neurons in patients with retinitis pigmentosa or age-related macular degeneration. Methods: Data for this review were selected through a comprehensive literature search. Results: Advances in microtechnology have facilitated the development of a variety of prostheses that can be implanted in the visual cortex, around the optic nerve, or in the eye. Some of these approaches have shown the promise of providing useful visual input to patients with visual impairments. Conclusion: While the development of various retinal prostheses have shown promise in limited clinical trials, there are distinct advantages and disadvantages for each type of prosthesis. This review will focus primarily on the Epiretinal Intraocular Retinal Prosthesis, studied by our group, but will also briefly review other modalities: the subretinal prosthesis, cortical prosthesis, and optic nerve prosthesis. Ann Acad Med Singapore 2006;35:137-44

Unpowered spiral-tube parylene pressure sensor for intraocular pressure sensing

Abstract: This paper presents the first biocompatible, unpowered, micromachined pressure sensor for intraocular pressure (IOP) sensing. This device is designed for implantation in the eye so that IOP can be faithfully measured externally. It features a parylene-based high-aspect-ratio spiral-tube structure fabricated using a buried-channel process. This passive sensor requires no power from other physical (i.e. electrical and/or magnetic) domains and registers pressure variations by changes of a mechanical in-plane spiral rotation that can be gauged by direct and convenient optical observation. The fabricated device has been tested in various media, and a 1 mm-radius device with a 10-turn spiral has successfully demonstrated continuous spiral rotation when immersed in liquids, with 0.22°/mmHg sensitivity in isopropyl alcohol (IPA) and 0.13°/mmHg sensitivity in water. This pressure sensing technology is proposed as a convenient method to monitor in situ IOP in glaucoma patients and to facilitate treatment and scientific study of the disease.

Neural responses elicited by electrical stimulation of the retina.

Abstract: Results: Analysis of EERs revealed distinct early (less than 10 ms) and late (greater than 50 ms) responses. Synaptic blockers abolished the late response but not the early response. For eliciting the early response in normal and rd mice, a square pulse stimulus was more efficient than the sine wave or pulse train. In normal and degenerate canine retina, electrically elicited responses also exhibited early and late phases. EERs in a retinal prosthesis test subject (with retinitis pigmentosa) showed latency similar to the canine, but no evidence of an early response, possibly due to the lack of sensitivity in scalp (human) vs cortical surface (canine) electrode placement. Conclusion: EERs could be elicited from both normal and degenerated retina. Mouse, dog, and human EERs showed common characteristics.

Flexible Parylene Packaged Intraocular Coil for Retinal Prostheses

Abstract: We present a flexible and fully-implantable coil designed for use as a power and data transfer component in retinal prosthesis applications. Compared with traditional hand-made intraocular coils, this microfabricated coil is flexible, with a 9.5 mm outer diameter and 10-mum-thick parylene C as the primary structural and packaging material. A post-fabrication heat treatment was used to improve the parylene package in order to protect the device in harsh corrosive environments such as the human eye. Long-term accelerated-lifetime soak testing in heated saline has been performed, and the mean time to failure (MTTF) of the parylene package extrapolated to 37degC was estimated using the Arrhenius relationship. The electrical failure of this device was also characterized by measuring the DC resistance in saline

Flexible Parylene-based Microelectrode Technology for Intraocular Retinal Prostheses

Abstract: We present the first single metal layer flexible microelectrode arrays designed for intraocular implantation that utilize parylene C as their primary structural and insulating material. These electrodes are fabricated as a key component of an intraocular retinal prosthesis comprising a radio-frequency coil for power and data transfer, a packaged high lead-count telemetry-recovery and driving application-specific integrated circuit (ASIC), and a high-density epiretinal stimulating microelectrode array for the treatment of retinal degenerative blindness in humans. Electrochemical tests have demonstrated that these thin-film platinum electrodes perform as necessary for neuronal stimulation. A novel bioconformal MEMS geometry for a complete intraocular system with capsular retaining-wings that enables all the components of the system to be implanted and retained within the lens capsule and vitreous cavity of the eye is also presented. The efficacy of this geometry when compared with a previous model without capsular retaining-wings has been verified by surgical implantation in animal models.

Fitting a neural prosthesis using impedance and electrode height

Abstract: The invention is a method of automatically adjusting an electrode array to the neural characteristics of an individual subject. The response to electrical neural stimulation varies from subject to subject. Measure of impedance may be used to predict the electrode height from the neural tissue and, thereby, predict the threshold of perception. Alternatively, electrode height may be measured directly to predict the threshold of perception. Also, impedance measurement may be used to quickly identify defective electrodes and proper electrode placement.

Electrical Stimulation in Isolated Rabbit Retina

Abstract: Experiments were conducted to assess the effect of stimulating electrode parameters (size, position, and waveform shape) on electrically elicited ganglion cell action potentials from isolated rabbit retina. Thirty-eight isolated rabbit retinas were stimulated with bipolar stimulating electrodes (either 125 or 25 mum in diameter) positioned on either the ganglion or the photoreceptor side. Recording electrodes were placed between the optic disc and the stimulating electrodes. Cathodic-first, biphasic, current waveforms of varying pulse durations (0.1, 0.5, 1 ms) were used. For the four conditions tested (125- electrode and 25-mum electrode, ganglion cell, and photoreceptor positions) threshold currents ranged from 6.7 to 23.6 muA, depending on location and pulse duration. With 1-ms pulse duration, no statistically significant difference was seen between threshold currents when either size electrode was used to stimulate either the ganglion cell side or the photoreceptor side. For all groups, the threshold currents using the 1-ms pulse were lower than those using 0.1 ms, but the 0.1-ms pulses used less charge. These experiments provide a number of valuable insights into the relative effects of several stimulation parameters critical to the development of an implanted electronic retinal prosthesis

System of fabricating a flexible electrode array

Abstract: An image is captured or otherwise converted into a signal in an artificial vision system. The signal is transmitted to the retina utilizing an implant. The implant consists of a polymer substrate made of a compliant material such as poly(dimethylsiloxane) or PDMS. The polymer substrate is conformable to the shape of the retina. Electrodes and conductive leads are embedded in the polymer substrate. The conductive leads and the electrodes transmit the signal representing the image to the cells in the retina. The signal representing the image stimulates cells in the retina.

Implantable Unpowered Parylene MEMS Intraocular Pressure Sensor

Abstract: This paper presents the first implantable, unpowered, parylene-based micro-electro-mechanical-systems (MEMS) pressure sensor for intraocular pressure (IOP) sensing. From in situ mechanical deformation of the compliant structures, this sensor registers pressure variations without power consumption/transduction. Micromachined high-aspect-ratio thin-walled tubes in different geometric layouts are exploited to obtain a high-sensitivity pressure response. An integrated packaging method has been successfully developed to realize suture-less implantation of the device. In vitro testing results have demonstrated that the IOP sensor can achieve 0.67 degree/mmHg angular sensitivity with a spiral-tube design, 3.43 mum/mmHg lateral sensitivity with a long-armed-tube design, and 0.38 mum/mmHg longitudinal sensitivity with a serpentine-tube design. This IOP sensor is designed to be implanted in the anterior chamber of the eye and anchored directly on the iris so that, under incident visible light, the pressure response of the implant can be directly observed from outside the eye, which enables faithful and unpowered IOP monitoring in glaucoma patients

Batch-fabricated flexible intraocular retinal prosthesis systems and methods for manufacturing the same

Abstract: Intraocular retinal prosthesis systems and methods for fabricating the same are provided. In one aspect, fabrication of all or multiple components of a prosthesis device or system are combined into a single monolithic fabrication process. Also, many such entire systems can be fabricated simultaneously in a single microfabrication processing run. A prosthesis device includes a cable region that connects an electrode array region with a power and data management region. The electrode array region includes one or more arrays of exposed electrodes, and the power and data management region includes various power and control elements. The power and data management elements, in one aspect, include an RF coil or coils and circuit arrangements and/or chips configured to provide drive signals to the electrodes via a cable and receive power and signals from the RF coil or coils. Each region includes elements fabricated on or in a single polymer layer during the same fabrication process.

A transcutaneous data telemetry system tolerant to power telemetry interference.

Abstract: � Abstract—Minimally-invasive implanted devices usually transmit both power and data through inductive coupling. By separating power and data carriers into different frequency bands, a high data rate can be transmitted without affecting power link efficiency. However in a dual band approach, the electromagnetic field from the power link interferes with data transmission. This paper presents a high data rate Differential Phase Shift Keying (DPSK) telemetry designed to tolerate interference without electromagnetic shielding or a high-order filter. On the transmitter side, by analyzing the nature of the interference, "frequency pre-distortion" is introduced to maintain the maximum efficiency. On the receiver side, a differential scheme is employed to provide inherent interference rejection. Using subsampling and novel analog demodulation, the scheme also eliminates the requirement of carrier recovery, thus reducing circuit complexity. The receiver achieves a 1Mbps data rate and can be upgraded to 2Mbps.

A Passive Refillable Intraocular MEMS Drug Delivery Device

Abstract: This paper presents the first passive implantable microelectromechanical systems (MEMS) device for targeted intraocular delivery of therapeutic compounds. In particular, this device addresses the treatment of chronic, difficult to reach diseases that affect the retina including retinitis pigmentosa, age-related macular degeneration, diabetic retinopathy, and glaucoma. The device is composed of three structural polymethyldisiloxane (PDMS) layers that are irreversibly bonded without the use of any adhesives. These layers form an integrated drug delivery device consisting of a refillable reservoir, tube, check valve, and suture tabs. This device requires a single implantation surgery and is capable of repeated delivery of multiple drugs. Characterization of the refillable reservoir and check valve performance is presented. Preliminary surgical implantation results of a mechanical test structure are also presented.

Method of fabricating an integrated intraocular retinal prosthesis device

Abstract: Intraocular retinal prosthesis devices and methods for fabricating the same. A prosthesis device includes a cable region that connects an electrode array region with a power and data management region. The electrode array region includes one or more arrays of exposed electrodes, and the power and data management region includes various power and control elements. The power and data management elements, in one aspect, include an RF coil or coils and circuit arrangements and/or chips configured to provide drive signals to the electrodes via a cable and receive power and signals from the RF coil or coils. Each region includes elements fabricated on or in a single polymer layer during the same fabrication process.

Micromachined tissue anchors for securing implants without sutures

Abstract: Systems and methods for attaching an implant device to tissue by mechanically (and non-invasively) anchoring the device to the tissue. The systems and methods provide a safe, practical way to attach an implant device to tissue in a non-invasive, or less invasive manner. According to the present invention, an implant device includes one or more protruding anchor-like structures for securely attaching to tissue. One or more device features, such as sensing elements, may be incorporated on the implant device. The anchor structures are configured and arranged to match the topology and features of the tissue environment where implant is to occur.

Methods and systems for enhanced medical procedure visualization

Abstract: The present invention employs image intensification for medical procedures within the human body. Methods and systems of the invention utilize infrared radiation (e.g. greater than about 750 nm) illumination and visualization of a surgical treatment area Preferred methods and systems of the invention incorporate use of an infrared radiation visualization system which may be known as “night vision” systems.

One-year results of a pilot study using oral 13-cis retinoic acid as a treatment for subfoveal predominantly occult choroidal neovascularization in patients with age-related macular degeneration.

Abstract: PURPOSE To evaluate the safety and evidence of efficacy for oral 13-cis retinoic acid as a treatment for patients with subfoveal occult choroidal neovascularization (CNV) due to age-related macular degeneration (ARMD). METHODS Patients with active, subfoveal occult CNV with no prior treatment of the subfoveal component were eligible for inclusion. Patients received 40 mg of 13-cis retinoic acid twice daily for 5 months, stopped treatment for 2 months, and then resumed treatment for 5 months. Patients were observed monthly with Early Treatment Diabetic Retinopathy Study (ETDRS) visual acuity (VA), clinical examination, fluorescein angiography, and laboratory testing. RESULTS Eleven patients, aged 64 to 88 years, were enrolled and followed for 1 year. Initial VA ranged from 55 (20/40) to 5 (20/400) ETDRS letters (median 48 letters). Mild drug-related side effects (dry skin, chapped lips) occurred in all 11 patients. Three patients experienced more severe side effects (muscle aches, mood swings) and did not resume treatment after the drug holiday. Moderate VA loss occurred in 36% at both 6 and 12 months. CONCLUSIONS Oral 13-cis retinoic acid is too toxic to be useful in patients with ARMD. Oral 13-cis retinoic acid did not improve vision although it may have slowed visual acuity loss in patients with ARMD with occult subfoveal CNV.

Enucleated eye model for intraocular retinal prosthesis implantation.

Abstract: An enucleated porcine eye model was developed to assess intraocular retinal prosthesis implantation surgery. The surgical technique consists of corneal and crystalline lens removal, keratoprosthesis replacement, and vitrectomy. To test the eye model, the scleral incision was increased to 5 mm and a 10-mm wide retinal prosthesis folded and inserted. One retinal tack was used to fix the prosthesis to the retina. A retinal prosthesis array was inserted without significant damage to the array and conformed to the curvature of the eye. Fundus photography and optical coherence tomography were performed at the end of surgery.

Towards a Modular 32 x 32 Pixel Stimulator for Retinal Prosthesis

Abstract: Future retinal prosthesis requires more stimulation sites to restore vision to the level of independent mobility, large print reading and facial recognition. This paper presents a modular design of a 1024 pixel retinal stimulator. The individual module consists of 64 drivers, chosen to optimize the system. The circuit design and the layout of the 64-driver module are presented. The chip is currently under fabrication in 0.35-?m CMOS. The digital controller block for the chip is currently being designed and will be integrated with this driver chip in the future.