Showing papers by "Mark S. Humayun published in 2008"

Independent Surgical Center

Abstract: A biological tissue cutting and fluid aspiration system provides a plurality of surgical instruments operable independent of an external control console. In some embodiments, each surgical instrument may include all sensors and controls directly applicable to the surgical instrument, and may be used independently. In some embodiments, instruments communicate status information to each other, and adjust operating parameters based on the communications.

Flexible parylene-based multielectrode array technology for high-density neural stimulation and recording

Abstract: Novel flexible parylene-based high-density electrode arrays have been developed for functional electrical stimulation in retinal and spinal cord prosthetics. These arrays are microfabricated according to a single-metal-layer process and a revolutionary dual-metal-layer process that promises to meet the needs of extremely high-density stimulation applications. While in many cases thin-film platinum electrodes in parylene C would be sufficient, high surface-area platinum electroplating has been shown to extend the lifetime of stimulated electrodes to more than 430 million pulses without failing. Iridium electrode arrays with higher charge delivery capacity have also been fabricated using a new high-temperature stabilized parylene variant, parylene HT. In addition, a new heat molding process has been implemented to conform electrode arrays to approximate the curvature of canine retinas, and a chronic implantation study of the mechanical effects of parylene-based electrode arrays on the retina over a 6-month follow-up period has provided excellent results. Retinal stimulation from these parylene-based electrode arrays in an isolated tiger salamander preparation was shown to be comparable to light stimulation in terms of generation of action potentials in the inner retina. Finally, electrode arrays have also been implanted and tested on the spinal cords of murine models, with the ultimate goal of facilitation of locomotion after spinal cord injury; these arrays provide a higher density and better spatial control of stimulation and recording than is typically possible using traditional fine-wire electrodes. Spinal cord stimulation typically elicited three muscle responses, an early (direct), a middle (monosynaptic), and a late (polysynaptic) response, classified based on latency after stimulation. Stimulation at different rostrocaudal levels of the cord yielded markedly different muscle responses, highlighting the need for such high-density arrays.

Microfabricated Implantable Parylene-Based Wireless Passive Intraocular Pressure Sensors

Abstract: This paper presents an implantable parylene-based wireless pressure sensor for biomedical pressure sensing applications specifically designed for continuous intraocular pressure (IOP) monitoring in glaucoma patients. It has an electrical LC tank resonant circuit formed by an integrated capacitor and an inductor coil to facilitate passive wireless sensing using an external interrogating coil connected to a readout unit. Two surface-micromachined sensor designs incorporating variable capacitor and variable capacitor/inductor resonant circuits have been implemented to realize the pressure-sensitive components. The sensor is monolithically microfabricated by exploiting parylene as a biocompatible structural material in a suitable form factor for minimally invasive intraocular implantation. Pressure responses of the microsensor have been characterized to demonstrate its high pressure sensitivity ( > 7000 ppm/mmHg) in both sensor designs, which confirms the feasibility of pressure sensing with smaller than 1 mmHg of resolution for practical biomedical applications. A six-month animal study verifies the in vivo bioefficacy and biostability of the implant in the intraocular environment with no surgical or postoperative complications. Preliminary ex vivo experimental results verify the IOP sensing feasibility of such device. This sensor will ultimately be implanted at the pars plana or on the iris of the eye to fulfill continuous, convenient, direct, and faithful IOP monitoring.[2008-0111].

An electrochemical intraocular drug delivery device

Abstract: A microelectromechanical systems (MEMS) drug delivery device is investigated for the treatment of incurable ocular diseases. Unlike conventional ocular drug delivery devices, this MEMS device is capable of being refilled, features electronic control of the drug regimen, and enables targeted intraocular drug delivery. The refillable design permits long-term drug therapy and avoids repetitive surgeries. Electronic control of dosing is achieved by using electrolysis-actuated pumping to deliver pharmaceuticals directly to the intraocular space. A flexible Parylene transscleral cannula allows targeted delivery to tissues in both the anterior and posterior segments of the eye. This electrochemically driven drug delivery device was demonstrated to provide flow rates suitable for ocular drug therapy (pL/min to μL/min). Both continuous and bolus drug delivery modes were performed to achieve accurate delivery of a target volume of 250 nL. An encapsulation packaging technique was developed for acute surgical studies and preliminary ex vivo drug delivery experiments in porcine eyes were performed.

Factors affecting perceptual thresholds in epiretinal prostheses.

Abstract: Purpose—The goal was to evaluate how perceptual thresholds are related to electrode impedance, electrode size, the distance of electrodes from the retinal surface, and retinal thickness in six subjects blind as a result of retinitis pigmentosa, who received epiretinal prostheses implanted monocularly as part of a U.S. Food and Drug Administration (FDA)–approved clinical trial. Methods—The implant consisted of an extraocular unit containing electronics for wireless data, power recovery, and generation of stimulus current, and an intraocular unit containing 16 platinum stimulating electrodes (260- or 520-μm diameter) arranged in a 4 × 4 pattern. The electrode array was held onto the retina by a small tack. Stimulation was controlled by a computer-based external system that allowed independent control over each electrode. Perceptual thresholds (the current necessary to see a percept on 79% of trials) and impedance were measured for each electrode on a biweekly basis. The distance of electrodes from the retinal surface and retinal thickness were measured by optical coherence tomography on a less regular basis. Results—Stimulation thresholds for detecting phosphenes correlated with the distance of the electrodes from the retinal surface, but not with electrode size, electrode impedance, or retinal thickness. Conclusions—Maintaining close proximity between the electrode array and the retinal surface is critical in developing a successful retinal implant. With the development of chronic electrode arrays that are stable and flush on the retinal surface, it is likely that the influence of other factors such as electrode size, retinal degeneration, and subject age will become more apparent.

Personal surgical center

Abstract: A personal surgical center embodied as a general purpose computer (e.g. laptop) with wireless technology for monitoring the operation of an independent surgical center and/or handheld instruments. The computer tracks procedures in the operating room and instruments used during those procedures, and accounts for billing, supply management, and payment options. The monitoring of the instruments used during the surgery is conducted by the personal surgical center while actual control of the settings of those instruments is via the independent surgical center or via controls included in the instruments themselves. The monitored information is stored in a log file which is then transmitted to a hospital server for generating reports, inventory control, billing, and the like. Other information generated during the procedure (e.g. doctor notes) is also stored in the log file. The personal surgical center may also access the hospital server or local data storage device for retrieving a surgeon's specific surgery parameters, obtaining patient files, and the like.

Sterile surgical tray

Abstract: A surgical apparatus for use by a surgeon can include a tray and a plurality of surgical instruments. The tray can have a plurality of structures located on an upper side of the tray for receiving the plurality of surgical instruments. The tray can receive a separate control unit. The tray can also have a fluid reservoir receiver for receiving a bottle or container of fluid, such as balanced salt solution. The fluid reservoir receiver can include one or more features, including, a spike, an air vent, and a light. A separate container can be used to place the bottle or container of fluid into the fluid reservoir receiver on the tray. This separate container can include a collapsible section.

An In Vitro Model of a Retinal Prosthesis

Abstract: Epiretinal prostheses are being developed to bypass a degenerated photoreceptor layer and excite surviving ganglion and inner retinal cells. We used custom microfabricated multielectrode arrays with 200-mum-diameter stimulating electrodes and 10-mum-diameter recording electrodes to stimulate and record neural responses in isolated tiger salamander retina. Pharmacological agents were used to isolate direct excitation of ganglion cells from excitation of other inner retinal cells. Strength-duration data suggest that, if amplitude will be used for the coding of brightness or gray level in retinal prostheses, shorter pulses (200 mus) will allow for a smaller region in the area of the electrode to be excited over a larger dynamic range compared with longer pulses (1 ms). Both electrophysiological results and electrostatic finite-element modeling show that electrode-electrode interactions can lead to increased thresholds for sites half way between simultaneously stimulated electrodes (29.4 plusmn 6.6 nC) compared with monopolar stimulation (13.3 plusmn 1.7 nC, < 0.02). Presynaptic stimulation of the same ganglion cell with both 200- and 10- m-diameter electrodes yielded threshold charge densities of 12 plusmn 6 and 7.66 plusmn 1.30 nC/cm2, respectively, while the required charge was 12.5 plusmn 6.2 and 19 plusmn 3.3 nC.

Retinal prosthesis phosphene shape analysis

Abstract: A retinal prosthesis system to restore sight for the blind is under development. The system is analogous to cochlear implants, in which photoreceptor input is bypassed and replaced by direct electrical stimulation of the retinal ganglion cells. Currently, six test subjects have been implanted with a 4×4 electrode array and stimulator. We report here psychophysical clinical data examining how stimulation amplitude affects phosphene shape and repeatability on a single electrode. Phosphene shape data was quantified by a set of numerical descriptors calculated from image moments. Comparison of phosphene descriptors for a single electrode across repeated trials and amplitude levels measured the repeatability within an amplitude group. Our experimental findings show that stimulation of the retina creates repeatable percept shapes and that an increase in stimulation amplitude causes a significant change in size and shape of phosphenes.

A Comparison of Two and Three Dimensional Dipole Antennas for an Implantable Retinal Prosthesis

Abstract: The feasibility is investigated using three dimensional folded dipole antennas as a data-telemetry implantable receiving antenna in a dual-unit retinal prosthesis to restore partial vision to the blind. Three dimensional designs are explored in an effort to enhance certain antenna characteristics such as bandwidth and maximum gain while reducing the planar footprint size in comparison to its two dimensional equivalent. The current vector alignment between the three dimensional layers are examined through folding and rotating the dipole arms with respect to each other to fully optimize the antenna's characteristics. The performance of the 2D and 3D antennas were compared in simulations and further examined by fabricating and characterizing the performance in a transmit/ receive system in air and inside eye phantoms. Results show that three-dimensional antennas can provide larger bandwidth while being physically smaller than the correspondent two-dimensional ones, thus providing larger channel capacity that could lead to a system with an increased number of stimulating electrodes.

A refillable microfabricated drug delivery device for treatment of ocular diseases

Abstract: An implantable manually-actuated microfabricated drug delivery device was demonstrated as a new approach for delivering therapeutic compounds to ocular tissue in acute in vitro, ex vivo, and in vivo studies.

Apparatus and methods for delivering therapeutic agents

Abstract: In various embodiments, a drug-delivery device includes one or more reservoirs that may each contain a therapeutic agent for delivery to a patient.

Vitreous dynamics: vitreous flow analysis in 20-, 23-, and 25-gauge cutters.

Abstract: Purpose: To evaluate porcine vitreous flow and balanced saline solution (BSS) flow rates in different vitrectomy systems. Methods: Porcine vitreous was obtained within 24 hours of slaughter. A high-speed (2 samples/s) balance, precise to 0.01 g, was used. Variable cut rates and vacuum pressures were analyzed in vitreous and BSS. The vitreous was labeled with glass microspheres and triamcinolone acetonide. A high-speed (400 frames/s) camera was used to record cutting for each condition. Results: For all cutters, there was no vitreous flow at zero cut rates (off). In 25-gauge cutters, at 500 mmHg of vacuum, the electric cutter produced higher average flow rates at high cut rates (600 cpm, 0.004 mL/s, and 1500 cpm, 0.013 mL/s) than pneumatic, which demonstrated a decreased flow at speeds higher than 1000 cpm (1000 cpm, 0.015 mL/s, and 1500 cpm, 0.006 mL/s). The percentage of vitreous flow rate/BSS flow rate in different aspiration and cut rates showed an ascending curve. This demonstrates evidence of flow obstruction in 25- (all cut rates), 23- (all cut rates), and 20-gauge (all cut rates). Flow obstruction and surge movements were seen in the high-speed videos. Conclusions: The vitrectomy systems each illustrate different performances of vitreous removal. The physical characteristics of vitreous resulted in nonuniform flow in all vitreous cutters.

Portable handheld illumination system

Abstract: Illumination systems are described that can include one or more light sources, which can include LEDs, one or more lenses, and one or more optical fibers. A handheld, portable, and surgical intraocular illumination system is disclosed that is disposable, low-cost, and efficient. A surgeon can have direct control of turning the illuminator on and off and adjusting the intensity via a simple control ergonomically placed on the handpiece and/or voice activated control. A coupling is provided, such as through an endo-probe, which is coupled to the one or more light sources. A user input device can be included that is operable to transmit to a feedback controller a first signal based on a user-selected light intensity. The feedback controller can, in response to the first signal, transmit a second signal to the power source for altering the power provided by the power source to the illumination system.

Implantable parylene-based wireless intraocular pressure sensor

Abstract: This paper presents a novel implantable, wireless, passive pressure sensor for ophthalmic applications. Two sensor designs incorporating surface-micromachined variable capacitor and variable capacitor/inductor are implemented to realize the pressure sensitive components. The sensor is monolithically microfabricated using parylene as a biocompatible structural material in a suitable form factor for increased ease of intraocular implantation. Pressure responses of the microsensor are characterized on-chip to demonstrate its high pressure sensitivity (> 7000 ppm/mmHg) with mmHg level resolution. An in vivo animal study verifies the biostability of the sensor implant in the intraocular environment after more than 150 days. This sensor will ultimately be implanted at the pars plana or iris of the eye to fulfill continuous intraocular pressure (IOP) monitoring in glaucoma patients.

The Dependence of Spectral Impedance on Disc Microelectrode Radius

Abstract: As microelectrodes gain widespread use for electrochemical sensing, biopotential recording, and neural stimulation, it becomes important to understand the dependence of electrochemical impedance on microelectrode size. It has been shown mathematically that a disc electrode, coplanar in an insulating substrate and exposed to a conducting media, exhibits an inhomogeneous current distribution when a potential step is applied. This distribution is known as the primary distribution, and its derivation also yielded an analytic solution for electrical resistance of the conducting media (Rs), between the disc surface and a distant ground, which is inversely proportional to disk radius [Rs = 1/(4Kr), where k is media conductivity and r is disk radius]. The dependence of spectral impedance on microelectrode radius, however, has not been explored. We verify the analytical solution for resistance using high-frequency (100 kHz) electrochemical impedance data from microelectrodes of varying radius (11-325 mum). For all disc radii, as we approach a lower frequency (rarr 10 Hz), we observe a transition from radial to area dependence (e.g., 1/r rarr 1/r2). We hypothesize that this transition is driven by the fact that the derivation of the primary distribution ignores concentration gradients, but that these gradients cannot be ignored at lower frequencies.

Flexible Circuit Electrode Array with Wire or Film Support

Abstract: The disclosure relates to a flexible circuit electrode array comprising: a polymer base layer; metal traces deposited on said polymer base layer, including electrodes suitable to stimulate neural tissue; a polymer top layer deposited on said polymer base layer and said metal traces; and at least one support embedded in said array. The disclosure further relates to a flexible circuit electrode array comprising: a polymer base layer; metal traces deposited on said polymer base layer, including electrodes suitable to stimulate neural tissue; a polymer top layer deposited on said polymer base layer and said metal traces; and a folded flexible circuit cable connecting the electrode array with an interconnection pad. The disclosure further relates to a method of making a flexible circuit electrode array comprising: depositing a polymer base layer; depositing metal on said polymer base layer; patterning said metal to form metal traces; depositing a polymer top layer on said polymer base layer and said metal traces; heating said flexible circuit electrode array in a mold to form a three dimensional shape in said flexible circuit electrode array, embedding a support at least in the base layer, top layer or between the base and top layer, and/or folding a flexible circuit cable at least once connecting the electrode array with an interconnection pad the array.

Natural course of experimental retinal vein occlusion in rabbit; arterial occlusion following venous photothrombosis

Abstract: Background Retinal vein occlusion (RVO) is the second leading cause of vascular eye disease. Currently there is no definite treatment for this condition. Animal models could be potentially helpful in developing new treatments; however, it is essential to understand the differences these models may have with human RVO. The aim of our study was to examine the course of experimentally created retinal vein occlusion (RVO) in rabbits.

Surgical pack and tray

Abstract: A surgical pack includes a platform having a plurality of recesses configured to function as a surgical tray. A plurality of surgical instruments are contained in a corresponding recess of the platform. The recess may have the shape of the surgical instrument that it is designed to receive. The recess may also include safety mechanisms to protect the tips of certain instruments and to lower the risk of injury caused by them. A packaging or covering holds the platform and the plurality of surgical instruments in a substantially sterile condition.

Treatment of consumption disorders with biostimulation

Abstract: Nerves that carry taste sensations to the brain are stimulated in order to diminish (or, depending on the application, augment) the pleasure ordinarily associated with consumption behavior to be modified.

Saliency-Based Apparatus And Methods For Visual Prostheses

Abstract: Saliency-based apparatus and methods for visual prostheses are disclosed. A saliency-based component processes video data output by a digital signal processor before the video data are input to the retinal stimulator. In a saliency-based method, an intensity stream is extracted from an input image, feature maps based on the intensity stream are developed, plural most salient regions of the input image are detected and one of the regions is selected as a highest saliency region.

A reversible thermosensitive adhesive for retinal implants: in vivo experience with plasma-deposited poly(N-isopropyl acrylamide).

Abstract: Purpose:To study the in vivo effects of a thermosensitive retinal adhesive, plasma-polymerized N-isopropyl acrylamide (ppNIPAM), in rabbit eyes.Methods:Parylene C(poly(monochloro-p-xylylene)) (20 μm) and poly(dimethyl siloxane) (PDMS) (≥200 μm) coated with ppNIPAM were used as implant materials. Fol

Port geometry and its influence on vitrectomy.

Abstract: Purpose:To determine the influence of port geometry on water and vitreous flow rates and test novel vitreous cutter tips in specific surgical situations.Methods:Custom 20-gauge and 25-gauge vitreous cutter tips with different sized ports were evaluated through porcine vitreous and water flow rates.

On the Thermal Elevation of a 60-Electrode Epiretinal Prosthesis for the Blind

Abstract: In this paper, the thermal elevation in the human body due to the operation of a dual-unit epiretinal prosthesis to restore partial vision to the blind affected by irreversible retinal degeneration is presented. An accurate computational model of a 60-electrode device dissipating 97 mW power, currently under clinical trials is developed and positioned in a 0.25 mm resolution, heterogeneous model of the human head to resemble actual conditions of operation of the prosthesis. A novel simple finite difference scheme combining the explicit and the alternating-direction implicit (ADI) method has been developed and validated with existing methods. Simulation speed improvement up to 11 times was obtained for the the head model considered in this work with very good accuracy. Using this method, solutions of the bioheat equation were obtained for different placements of the implant. Comparison with in-vivo experimental measurements showed good agreement.

Floating-disk parylene microvalve for self-regulating biomedical flow controls

Abstract: A novel self-regulating parylene micro valve is presented in this paper with potential applications for biomedical flow controls. Featuring a free-floating bendable valve disk and two-level valve seat, this surface-micromachined polymeric valve accomplishes miniature pressure/flow rate regulation in a band-pass profile stand-alone without the need of power sources or active actuation. Experimental data of underwater testing results have successfully demonstrated that the microfabricated in-channel valve can regulate water flow at 0-80 mmHg and 0-10 muL/min pressure/flow rate level, which is perfectly suitable for biomedical and lab-on-a-chip applications. For example, such biocompatible microvalve can be incorporated in ocular implants for control of eye fluid drainage to fulfill intraocular pressure (IOP) regulation in glaucoma patients.

Ultrasound and microbubbles in ocular diagnostics and therapies

Abstract: The present disclosure described methods, systems, and techniques for applying contrast-enhanced ultrasound to locate areas of blockage within retinal vessels and to break up clots that are causing damage. In addition to identifying the damaged area, the researchers anticipate that the initial image may serve as a baseline for monitoring the effect of treatment on the vessel, which may be achieved in multiple ways. The vibration effect of the ultrasound itself may suffice to dislodge clots. The microbubbles may also be coated or filled with medication, with ultrasonic shock waves activating the coating or causing mini explosions to release the medicine. Loading the microbubbles with a therapeutic agent, visualizing their presence at the diseased site using the ultrasound diagnostic mode, and then activating the microbubbles to release their contents at the targeted lesion could be a powerful and effective way to reverse occlusion without harming other areas of the eye or body.

Selectable stroke cutter

Abstract: Apparatus, systems, and devices are described that utilize an adjustable biological tissue cutting handpiece that is based on selectable settings. The biological tissue cutting handpiece includes a cutter tip that allows multiple duty cycles as well as multiple port configurations. For example, when working next to the retina, the port could be adjusted to be a smaller size, allowing delicate membrane dissection. When working near or in less sensitive tissue, e.g. the center of the eye, the port could be wide open. The port aperture size can be independent of cut speed, allowing a surgeon to work at high speed both next to the retina and away from the retina. High speeds have been shown to have increased tissue (e.g., vitreous) removal, e.g., in 25 and 23-gauge instruments. Duty cycle is not necessarily dependent on cut speed, allowing high cutter performance and varied flow characteristics.

Thrombolysis In Retinal Vessels With Ultrasound

Abstract: Systems and methods are described providing for the use of ultrasound energy to effect the dislodging of one or more blood clots inside blood vessels. Such clots can include those inside retinal vessels, especially in patients with central retinal vein occlusion. Embodiments of the present disclosure may be used for any retinal arterial or venous occlusion. In exemplary embodiments, a small probe can be inserted into the eye of a patient and placed over the retinal vessels. Acoustic streaming created by the probe can be directed to an area or region including targeted blood vessels, resulting in increased flow in one or more retinal veins and facilitating or effecting mechanical dislodging of one or more blood clots in the targets blood vessels. Exemplary embodiments can utilize ultrasonic energy produced at a frequency of approximately 44 MHz to 46 MHz with pulse repetition frequencies of approximately 100 Hz to 100 kHz.

Functional abiotic nanosystems

Abstract: The invention relates to imparting photoreactivity to target cells, e.g., retinal cells, by introducing photoresponsive functional abiotic nanosystems (FANs), nanometer-scale semiconductor/metal or semiconductor/semiconductor hetero-junctions that in this case include a photovoltaic effect. The invention further provides methods of making and using FANs, where the hetero-junctions bear surface functionalization that localizes them in cell membranes. Illumination of these hetero-junctions incorporated in cell membranes generates photovoltages that depolarize the membranes, such as those of nerve cells, in which FANs photogenerate action potentials. Incorporating FANs into the cells of a retina with damaged photoreceptor cells reintroduces photoresponsiveness to the retina, so that light creates action potentials that the brain interprets as sight.

Method and apparatus for treating ischemic diseases

Abstract: The present invention relates to the treatment of ischemic diseases, and more particularly, to treatment of diabetic retinopathy and ischemia of the retinal and choroidal tissues. The treatment, which will work in vitrectomized eyes as well as non-vitrectomized eyes, is based on selective and fractional electrolysis of the vitreous humor to produce oxygen and optionally active chlorine while simultaneously controlling pH. Oxygen or active chlorine can suppress or reverse the onset of diabetic retinopathy, other retinovascular diseases, and choroidal neovascularization.