New epiretinal implant with integrated sensor chips for optical capturing shows a good biocompatibility profile in vitro and in vivo

BACKGROUND

Retinal degenerative diseases, e.g., retinitis pigmentosa, cause a severe decline of the visual function up to blindness. Treatment still remains difficult; however, implantation of retinal prostheses can help restoring vision. In this study, the biocompatibility and surgical feasibility of a newly developed epiretinal stimulator (OPTO-EPIRET) was investigated. The previously developed implant was extended by an integrated circuit-based optical capturing, which will enable the immediate conversion of the visual field into stimulation patterns to stimulate retinal ganglion cells.

RESULTS

The biocompatibility of the OPTO-EPIRET was investigated in vitro using the two different cell lines L-929 and R28. Direct and indirect contact were analyzed in terms of cell proliferation, cell viability, and gene expression. The surgical feasibility was initially tested by implanting the OPTO-EPIRET in cadaveric rabbit eyes. Afterwards, inactive devices were implanted in six rabbits for feasibility and biocompatibility testings in vivo. In follow-up controls (1-12 weeks post-surgery), the eyes were examined using fundoscopy and optical coherence tomography. After finalization, histological examination was performed to analyze the retinal structure. Regarding the in vitro biocompatibility, no significant influence on cell viability was detected (L929: < 1.3% dead cells; R-28: < 0.8% dead cells). The surgery, which comprised phacoemulsification, vitrectomy, and implantation of the OPTO-EPIRET through a 9-10 mm corneal incision, was successfully established. The implant was fixated with a retinal tack. Vitreal hemorrhage or retinal tearing occurred as main adverse effects. Transitional corneal edema caused difficulties in post-surgical imaging.

CONCLUSIONS

The OPTO-EPIRET stimulator showed a good biocompatibility profile in vitro. Furthermore, the implantation surgery was shown to be feasible. However, further design optimization steps are necessary to avoid intra- and postoperative complications. Overall, the OPTO-EPIRET will allow for a wide visual field and good visual acuity due to a high density of electrodes in the central retina.

Development and in vitro validation of flexible intraretinal probes

The efforts to improve the treatment efficacy in blind patients with retinal degenerative diseases would greatly benefit from retinal activity feedback, which is lacking in current retinal implants. While the door for a bidirectional communication device that stimulates and records intraretinally has been opened by the recent use of silicon-based penetrating probes, the biological impact induced by the insertion of such rigid devices is still unknown. Here, we developed for the first time, flexible intraretinal probes and validated in vitro the acute biological insertion impact in mouse retinae compared to standard silicon-based probes. Our results show that probes based on flexible materials, such as polyimide and parylene-C, in combination with a narrow shank design 50 µm wide and 7 µm thick, and the use of insertion speeds as high as 187.5 µm/s will successfully penetrate the retina, reduce the footprint of the insertion to roughly 2 times the cross-section of the probe, and induce low dead cell counts, while keeping the vitality of the tissue and recording the neural activity at different depths.

Toward a Bidirectional Communication Between Retinal Cells and a Prosthetic Device - A Proof of Concept

Background: Significant progress toward the recovery of useful vision in blind patients with severe degenerative retinal diseases caused by photoreceptor death has been achieved with the development of visual prostheses that stimulate the retina electrically. However, currently used prostheses do not provide feedback about the retinal activity before and upon stimulation and do not adjust to changes during the remodeling processes in the retina. Both features are desirable to improve the efficiency of the electrical stimulation (ES) therapy offered by these devices. Accordingly, devices that not only enable ES but at the same time provide information about the retinal activity are beneficial. Given the above, a bidirectional communication strategy, in which inner retinal cells are stimulated and the output neurons of the retina, the ganglion cells, are recorded using penetrating microelectrode arrays (MEAs) is proposed.

Methods: Custom-made penetrating MEAs with four silicon-based shanks, each one with three or four iridium oxide electrodes specifically designed to match retinal dimensions were used to record the activity of light-adapted wildtype mice retinas and degenerated retinas from rd10 mice in vitro. In addition, responses to high potassium concentration and to light stimulation in wildtype retinas were examined. Furthermore, voltage-controlled ES was performed.

Results: The spiking activity of retinal ganglion cells (RGCs) was recorded at different depths of penetration inside the retina. Physiological responses during an increase of the extracellular potassium concentration and phasic and tonic responses during light stimulation were captured. Moreover, pathologic rhythmic activity was recorded from degenerated retinas. Finally, ES of the inner retina and simultaneous recording of the activity of RGCs was accomplished.

Conclusion: The access to different layers of the retina with penetrating electrodes while recording at the same time the spiking activity of RGCs broadens the use and the field of action of multi-shank and multi-site penetrating MEAs for retinal applications. It enables a bidirectional strategy to stimulate inner retinal cells electrically and to record from the spiking RGCs simultaneously (BiMEA). This opens the possibility of a feedback loop system to acknowledge the success of ES carried out by retinal prostheses.

Fabrication and Characterization of Bending- Independent Capacitive CMOS Pressure Sensor Stacks

Artificial limbs, equipped with miniaturized tactile sensors, can handle objects with more dexterousness. Next to detecting forces, the sensor devices are also able to measure temperature. With this additional information, the touched objects can be better characterized. As such sensors, active CMOS-based capacitive pressure sensors are used in this work. The Sensors are thinned to 20-30 μm target thickness to make them bendable. One challenge of such thin sensors is the strong dependence of the output signal upon bending. To compensate this dependency, two sensors were mounted back to back. This allows a numerical adjustment of the two characteristic sensor output signals to mechanical stress curves. After electrically contacting of the stacks with a 15 μm thin polyimide foil substrate, the bending dependence of the stacks was characterized with a four-point bending procedure. By this characterization the dependency of the pressure sensor output signal on the height of mechanical stress was determined. Both sensor output signals show an inverted behavior under the same mechanical stress which confirmed prior simulation results with the same setup. Based on this information, a numerical method for compensating the bending dependence was successfully proven.

DRUGAS: implantable telemetric system for measuring the portal venous pressure: assembly aspects

Developing an implantable, telemetric pressure measuring system for venous applications makes a high degree of miniaturization necessary. Thus the influence on the measurement environment is minimized and the risk of thrombosis at small flow blood velocities is decreased. But these systems are limited in terms of accuracy and resolution. The asked system requirements could only be reached by optimising the assembly and encapsulation techniques. To achieve the high degree of miniaturization numerical simulations were performed on the shape and size of the implant and led to the development of a specific metal housing consisting of two main components. A small measuring chamber will be placed into the portal vein and is rigidly fixed to a flat circular part that contains the pressure sensor chip and a transponder board and will be located outside on top of the vein. The main focus of the assembly process was based on a stress-free design and mounting of the components.

[Technological Set-up of Epiretinal Implants]

In blinded patients, visual prostheses can restore visual perception by appropriate electrical stimulation of retinal nerve cells. This article presents the basic technological principles of retinal prostheses, using an epiretinal implantable visual prosthesis as example. An implantable visual prosthesis typically consists of extraocular and intraocular sections. The extraocular section is responsible for detecting the image. The information is derived from this image that is needed for appropriate electrical stimulation of the retinal nerve cells. Together with the necessary energy, these data are transmitted through a magnetic connection to the intraocular section. To ensure reliable transmission, the data are encoded. After transmission, energy and data are separated in the intraocular section, and the data are decoded. In accordance with the transmitted information, biphasic pulses of defined intensity and duration are produced on the simulation electrodes. In this way, ganglia cells are electrically stimulated and react with action potentials, which are transmitted to the visual cortex, where they lead to visual perception.

Development of very large electrode arrays for epiretinal stimulation (VLARS)

BACKGROUND

Retinal implants have been developed to treat blindness causing retinal degenerations such as Retinitis pigmentosa (RP). The retinal stimulators are covering only a small portion of the retina usually in its center. To restore not only central vision but also a useful visual field retinal stimulators need to cover a larger area of the retina. However, large area retinal stimulators are much more difficult to implant into an eye. Some basic questions concerning this challenge should be answered in a series of experiments.

METHODS

Large area retinal stimulators were fabricated as flexible multielectrode arrays (MEAs) using silicon technology with polyimide as the basic material for the substrate. Electrodes were made of gold covered with reactively sputtered iridium oxide. Several prototype designs were considered and implanted into enucleated porcine eyes. The prototype MEAs were also used as recording devices.

RESULTS

Large area retinal stimulator MEAs were fabricated with a diameter of 12 mm covering a visual angle of 37.6° in a normal sighted human eye. The structures were flexible enough to be implanted in a folded state through an insertion nozzle. The implants could be positioned onto the retinal surface and fixated here using a retinal tack. Recording of spontaneous activity of retinal neurons was possible in vitro using these devices.

CONCLUSIONS

Large flexible MEAs covering a wider area of the retina as current devices could be fabricated using silicon technology with polyimide as a base material. Principal surgical techniques were established to insert such large devices into an eye and the devices could also be used for recording of retinal neural activity.

Development of a very large array for retinal stimulation

Retina degeneration is one of the leading causes of blindness nowadays and cannot be cured in most cases. It has been shown that electrical stimulation of retinal ganglion cells can generate visual perceptions and therefore implantable electrode arrays can be possible treatment for these patients. Most implants developed for that purpose use electrode arrays with a size of a few millimeters squared and therefore could restore only a very small field of vision and hardly improve orientation in an unknown environment. In this paper we present results of the development of an implantable electrode array covering about 100 mm(2) of retinal tissue.

Stacked planar micro coils for single-sided NMR applications

This paper describes planar micro structured coils fabricated in a novel multilayer assembly for single-sided NMR experiments. By arranging the coil's turns in both lateral and vertical directions, all relevant coil parameters can be tailored to a specific application. To this end, we implemented an optimization algorithm based on simulations applying finite element methods (FEMs), which maximizes the coil's sensitivity and thus signal-to-noise ratio (SNR) while incorporating boundary conditions such as the coil's electrical properties and a localized sensitivity needed for single-sided applications. Utilizing thin-film technology and microstructuring techniques, the planar character is kept by a sub-millimeter overall thickness. The coils are adapted to the Profile NMR-MOUSE® magnet with a homogeneous slice of about 200 μm in height and a uniform depth gradient of about 20T/m. The final design of a coil with 20 turns, separated in four layers with five turns each, and an outer dimension of 4×4 mm(2) is able to measure a sample volume almost five times smaller than that of a state-of-the-art 14×16 mm(2) Profile NMR-MOUSE® coil with the same SNR. This allows for volume-limited measurements with high SNR and enables different future developments. The minimal dead time of 4 μs facilitates further improvements of the SNR by echo adding techniques and the characterization of samples with short T2 relaxation times. Measurements on solid polymers like polyethylene (PE) and polypropylene (PP) with T2 components as short as 200 μs approve the overall beneficial coil properties. Furthermore the ability to perform depth profiling with microscopic resolution is demonstrated.

Flexible multi-electrode array with integrated bendable CMOS-chip for implantable systems

Micro-electrodes and micro-electrode arrays (MEAs) for stimulating neurons or recording action potentials are widely used in medical applications or biological research. For medical implants in many applications like brain implants or retinal implants there is a need for flexible MEAs with a large area and a large number of stimulation electrodes. In this work a flexible MEA with an embedded flexible silicon dummy CMOS-chip facing these challenges has been designed, manufactured and characterized. This approach offers the possibility by connecting and addressing several of these MEAs via a bus system, to increase the number and the density of electrodes significantly. This paper describes the design and fabrication process. Results on the mechanical and electrical behavior will be given and possible improvements for medical applications by this novel approach will be discussed.

A novel fully implantable wireless sensor system for monitoring hypertension patients

This paper presents a novel fully implantable wireless sensor system intended for long-term monitoring of hypertension patients, designed for implantation into the femoral artery with computed tomography angiography. It consists of a pressure sensor and a telemetric unit, which is wirelessly connected to an extracorporeal readout station for energy supply and data recording. The system measures intraarterial pressure at a sampling rate of 30 Hz and an accuracy of ±1.0 mmHg over a range of 30-300 mmHg, while consuming up to 300 μW. A special peel-away sheath introducer set was developed to support the implantation procedure. The system delivered stable measurements in initial animal trials in sheep, with results being in good agreement with reference sensor systems.

Implantation and explantation of an active epiretinal visual prosthesis: 2-year follow-up data from the EPIRET3 prospective clinical trial

PURPOSE

The EPIRET3 retinal prosthesis was implanted in six volunteers legally blind from retinitis pigmentosa (RP) and removed after 4 weeks. Two years later, these subjects were re-examined to investigate ocular side effects and potential changes to quality of life.

METHODS

Vision-related quality of life was recorded using the NEI-VFQ-25 questionnaire. Clinical data including interval history, visual acuity, and intraocular pressure were obtained. Anterior and posterior segments of the study eyes were examined and photographed; this included fluorescein angiography and optical coherence tomography (OCT).

RESULTS

Data from five patients could be analysed. Life-quality score was consistent with results obtained at baseline. No unexpected structural alteration could be found in the study eyes. A moderate epiretinal gliosis was present in areas where the epiretinal stimulator had been fixated using retinal tacks. Angiography revealed no leakage or neovascularisation; OCT showed no generalised increase of central retinal thickness.

CONCLUSIONS

Vision-related quality of life is low in patients suffering from end-stage RP. No further deterioration of life quality could however be detected within our monitoring period. Surgery was well tolerated by both patients and their eyes, without adverse events occurring during the follow-up period. Epiretinal gliosis is known to occur with retinal tacks, but seems of no major concern to the integrity of the study eyes. However, it may potentially interfere with functional aspects of active implants. Hence, alternative, possibly biochemical, fixation methods merit further research.

Bioprocess control in microscale: scalable fermentations in disposable and user-friendly microfluidic systems

Background

The efficiency of biotechnological production processes depends on selecting the best performing microbial strain and the optimal cultivation conditions. Thus, many experiments have to be conducted, which conflicts with the demand to speed up drug development processes. Consequently, there is a great need for high-throughput devices that allow rapid and reliable bioprocess development. This need is addressed, for example, by the fiber-optic online-monitoring system BioLector which utilizes the wells of shaken microtiter plates (MTPs) as small-scale fermenters. To further improve the application of MTPs as microbioreactors, in this paper, the BioLector technology is combined with microfluidic bioprocess control in MTPs. To realize a user-friendly system for routine laboratory work, disposable microfluidic MTPs are utilized which are actuated by a user-friendly pneumatic hardware.

Results

This novel microfermentation system was tested in pH-controlled batch as well as in fed-batch fermentations of Escherichia coli. The pH-value in the culture broth could be kept in a narrow dead band of 0.03 around the pH-setpoint, by pneumatically dosing ammonia solution and phosphoric acid to each culture well. Furthermore, fed-batch cultivations with linear and exponential feeding of 500 g/L glucose solution were conducted. Finally, the scale-up potential of the microscale fermentations was evaluated by comparing the obtained results to that of fully controlled fermentations in a 2 L laboratory-scale fermenter (working volume of 1 L). The scale-up was realized by keeping the volumetric mass transfer coefficient k_La constant at a value of 460 1/h. The same growth behavior of the E. coli cultures could be observed on both scales.

Conclusion

In microfluidic MTPs, pH-controlled batch as well as fed-batch fermentations were successfully performed. The liquid dosing as well as the biomass growth kinetics of the process-controlled fermentations agreed well both in the microscale and laboratory scale. In conclusion, a user-friendly and disposable microfluidic system could be established which allows scaleable, fully controlled and fully monitored fermentations in working volumes below 1 milliliter.

Intraocular epiretinal prosthesis to restore vision in blind humans

Visual sensations in blind patients suffering from retinal degenerations may be restored by electrical stimulation of retinal neurons using implantable microelectrode arrays. The EPI-RET-3 project was initiated to evaluate a wireless intraocular retinal implant system for human use in terms of safety and efficiency. The implant is a remotely controlled fully intraocular prosthesis consisting of a receiver and a stimulator module. The stimulator is placed onto the retina's surface. Data and energy are transmitted via an inductive link from outside the eye to the implant. The EPI-RET-3 device was implanted into six legally blind patients with Retinitis Pigmentosa (RP) for a period of four weeks. The surgery was performed without complications. The implants were activated on days 7, 14 and 27 after implantation. All patients reported visual sensations such as dots, arcs, or lines of different colours and intensities. The required stimulation thresholds were found to be very low. Implantation of the wireless EPI-RET-3 device is safe and the system is suitable to elicit visual sensations in blind RP patients. Major problems in the design and fabrication of a prosthesis for artificial vision could be solved in this approach.

Sputtered iridium oxide for stimulation electrode coatings

This work deals with the reactive RF-powered sputter deposition of iridium oxide for use as the active stimulation layer in functional medical implants. The oxygen gettered by the growing films is determined by an approach based on generic curves. Films deposited at different stages of oxygen integration show strong differences in electrochemical behaviour, caused by different morphologies. The dependence of electrochemical activity on morphology is further illustrated by RF sputtering onto heated substrates, as well as DC sputtering onto cold substrates.

An implantable microsystem as a vision prosthesis

Blindness is often the result of degeneration of the light sensitive rods and cones of the retina in conditions such as retinitis pigmentosa and macula degeneration. An implantable vision prosthesis has been developed that electrically stimulates the retinal ganglion cells in such a way that action potentials in retinal ganglion cells are evoked, causing a visual sensation in the visual cortex. Clinical trials are about to be conducted.

[Epiretinal visual prostheses]

Epiretinal implants consist of a camera chip capturing the scene, a visual processor calculating retina-specific pulse sequences, a transponder for data and energy, and the implant itself. The implant consists of a receiver integrated into a posterior chamber lens, a microcable, and the retina stimulator. The stimulator is fixated onto the retinal surface using retinal tacks. In animal experiments it was shown that the materials being used were tolerated, the data and energy stream did not induce any adverse events, and that the fixation was feasible using retinal tacks. Stimulation of the inner retinal surface yielded a topographically correct activation of visual cortical areas. Even after a long history of blindness, tests in humans disclosed visual percepts.

Iridium sputtered at varying pressures and target-substrate-distances evaluated for use as stimulation electrode material

Iridium was sputtered as the top layer of stimulation electrodes. The coatings were varied in their morphology by adjusting the total deposition pressure and the working distance (WD) of target and substrate. It is shown that the resulting different kinds of morphologies have a strong influence on stimulation characteristics. The combination of high working gas pressure and small WD as well as the combination of medium working gas pressure and larger WD yield the best characteristics on macro-sized test electrodes.

Transponder-based sensor for monitoring electrical properties of biological cell solutions

An inductive passive remote sensor circuit for monitoring fermentation processes is presented. The sensor circuit consists of an interdigital capacitor and a planar coil structured on a glass laminated FR4-printed circuit board. This circuit resonates at frequencies between 2 and 4 MHz. After the resonant sensor circuit is immersed in a fermentation vessel with a cell solution, the resonant frequencies are detected by measuring the impedance of an external loop antenna. A new theory is presented to describe the behavior of the sensor circuit. In combination with a proposed equivalent circuit, the theory enables the calculation of the permittivity and conductivity of the cell solution under test by determining the resonant frequencies of the sensor without the need for any additional fitting functions. The influence of the relaxation behavior of living cells on the sensor signal with respect to the conductivity of the solution is discussed in detail. To prove the new theory, the determined permittivity is compared with the optical density of a cell solution, an indicator of cell concentration. The performed measurements show the expected correlation between the determined permittivity and optical density. The solution under test is a yeast culture in YPG medium.

Theoretical calculations and performance results of a PZT thin film actuator

High piezoelectric coupling coefficients of PZT-based material systems can be employed for actuator functions in micro-electro-mechanical systems (MEMS) offering displacements and forces which outperform standard solutions. This paper presents simulation, fabrication, and development results of a stress-compensated, PZT-coated cantilever concept in which a silicon bulk micromachining process is used in combination with a chemical solution deposition (CSD) technique. Due to an analytical approach and a finite element method (FEM) simulation for a tip displacement of 10 microm, the actuator was designed with a cantilever length of 300 microm to 1000 microm. Special attention was given to the Zr/Ti ratio of the PZT thin films to obtain a high piezoelectric coefficient. For first characterizations X-ray diffraction (XRD), scanning electron microscopy (SEM), hysteresis-, current-voltage I(V)- and capacitance-voltage C(V)-measurements were carried out.

Transponder system for non-invasive measurement of intravascular pressure

Monitoring of blood pressure and pulse rate offers diagnostical and therapeutical opportunities in hypertension disease and arrhythmia, respectively. This paper presents an intravascular pressure monitoring system consisting of an implantable silicone capsule, which can be placed in an arterial system via a catheter. The capsule contains a pressure sensor and signal conditioning circuits for wireless data and energy transfer using 6.78 MHz transponder technology.

Vascular capsule for telemetric monitoring of blood pressure

PURPOSE

Development and experimental evaluation of an intravascular monitoring system for telemetric measurement of blood pressure and heart rate.

MATERIALS AND METHODS

The monitoring system consists of an implantable silicone capsule (diameter 2.3 mm), containing a dedicated microchip with pressure sensors and signal-processing circuits as well as an antenna for wireless data and energy transfer using 6.78 MHz transponder technology. Three self-expanding legs at one end of the capsule served as a mechanism to lock the capsule at an arterial branch. A flow model, driven by a ventricular assist system, was used for testing and optimizing the implantation equipment, for checking the anchoring mechanism and for ensuring transmission of the measured pressure to the readout unit. In-vivo experiments were performed in 8 minipigs (weight 25 to 30 kg), with three capsules placed in each minipig via the femoral artery using a dedicated 8-F sheath/pusher system. Follow-up was by CT angiography for up to 6 months after implantation.

RESULTS

Flow model tests revealed a maximum deviation of pressure and heart rate measurements of 5% from the reference measurements. Signal transmission was reliable over a distance of 3 to 4 cm. Fluoroscopically guided in-vivo implantation of the capsules was simple and straightforward. In arteries with a diameter of 5 to 6 mm, the capsules were permanently fixed with one or two legs interlocked in side branches and without occlusion within 6 months. Three capsules developed a small non-occlusive appositional thrombus attached to the downstream (leg) part of the capsule.

CONCLUSION

Our in-vitro and in-vivo experiments demonstrate the feasibility of wireless transmission from a capsule with a sufficient resolution of the sensor output signals to determine blood pressure and pulse rate. As long as the vessel diameter is wide enough, arterial fixation of the capsule does not induce thrombotic occlusion of the parent artery. With respect to future clinical applications, further refinements of the transmission technology are needed to extend the transmission distance between capsule and reader antenna. The technology of intelligent implants has further implications, such as monitoring of other physiological parameters, and the design of a control loop, which may be used for therapeutic feedback.

Development of a completely encapsulated intraocular pressure sensor

A completely encapsulated intraocular pressure (IOP) sensor equipped with telemetric signal and energy transfer is introduced integrated into a silicone disc for implantation into the eye. After implantation into enucleated pig eyes and into rabbit eyes in vivo, the IOP was recorded and compared to established techniques of IOP measurement. Pressure chamber tests showed that the sensor functioned correctly after biocompatible encapsulation in polydimethylsiloxane. In vivo and in vitro tests in rabbit and pig eyes demonstrated that the implanted system worked with the same precision as established techniques for IOP determination. The correlation between the measurements with the implanted device and pneumotonometry in several experiments was between 0.9 and 0.99. This device serves as a functioning model for the realization of a telemetric IOP sensor for integration into an artificial intraocular lens. Such a device will open new perspectives, not only in the management of glaucoma, but also in basic research for mechanisms of glaucoma.