Silicon microsystems for neuroscience and neural prostheses.

Silicon-based microsystems are being developed to interface with the central nervous system (CNS) at the cellular level. Dense three-dimensional (3-D) microelectrode arrays with as many as several hundred sites permit acute and semichronic single-unit recording and stimulation, while on-chip circuitry for site selection, amplification, and multiplexing reduces noise and limits the number of output leads to manageable levels. Hybrid implant-mounted circuitry can be used to separate single units from baseline noise and provide simultaneous wireless access to more than a hundred information channels. This article focuses on the technology for electronically interfacing with the CNS at the cellular level. Devices based on silicon-on-insulator technology and silicon array structures not based as directly on the planar processes of ICs are given notice. Tissue interface and cabling problems still exist for long-term applications but the basic technology platform is robust and should allow engineering solutions to be developed over time. Present technology is consistent with real breakthroughs in our understanding of the brain at the circuit/system level during the coming decade though detailed mapping that has been impossible in the past. Such mapping could also serve as a basis for prosthetic devices for treating some of mankind's most debilitating disorders.     

Evaluation of command algorithms for control of upper-extremity neural prostheses

Five new command control algorithms were created to enable increased control over grasp force in upper-extremity neural prostheses. Most of these algorithms took advantage of the ability to lock or assign a steady command value to the hand neural prosthesis. Five able-bodied subjects tested the algorithms by using a shoulder controller that controlled a video-simulated hand to repeatedly complete a consistent evaluation task. A generalized estimating equations-based linear model was used to analyze the data. The algorithms were ranked via contrast analyses between the coefficient values from the linear model of the proportional control with lock algorithm, which is the algorithm presently used in neural prostheses, and each of the other algorithms. The algorithms that allowed adjustment of the command value after the hand was locked as well as algorithms that allowed a decrease in controller gain after the hand was locked performed better than the proportional control with lock algorithm. Algorithms that changed command as a function of time performed worse than the proportional control with lock algorithm. Further, the computer-based video simulator proved to be useful as a first-pass evaluation tool for neural prosthesis control.     

A 128‐channel discrete cosine transform‐based neural signal processor for implantable neural recording microsystems

A 128‐channel neural signal processor for implantable neural recording microsystems is presented. The processor compresses the neural information of 128 simultaneous recording channels using discrete cosine transform, achieving a compression factor of 69 at the expense of a 5.6% root mean square error. The proposed processor is implemented on register transfer level and synthesized in a 65‐nm complementary metal‐oxide semiconductor process. The post‐layout simulated power consumption at 1.2 V is 33.06 μW (258 nW per channel) at an area cost of 0.46 mm². Copyright © 2013 John Wiley & Sons, Ltd.     

Microelectronic packaging for retinal prostheses.

An innovative parylene-based high-density chip-level integrated interconnect (CL-I/sup 2/) packaging system for retinal implants id discussed. The implications of this CL-I/sup 2/ technology for retinal prosthesis packaging effort are far-reaching. This technology obviates the need for a technician to create electrical and mechanical connections one by one. Instead, the technology is limited only by standard photolithography and standard microfabrication techniques, providing the capability for a reduction of an order of magnitude or more in the center-to-center pad distances that can be accommodated in the process. High-density electrode arrays are thereby feasible, because the fabrication process places no limit on the number of output pads that can reasonably be connected to the array.     

The optimal controller delay for myoelectric prostheses.

A tradeoff exists when considering the delay created by multifunctional prosthesis controllers. Large controller delays maximize the amount of time available for EMG signal collection and analysis (and thus maximize classification accuracy); however, large delays also degrade prosthesis performance by decreasing the responsiveness of the prosthesis. To elucidate an "optimal controller delay" twenty able-bodied subjects performed the Box and Block Test using a device called PHABS (prosthetic hand for able bodied subjects). Tests were conducted with seven different levels of controller delay ranging from nearly 0-300 ms and with two different artificial hand speeds. Based on repeted measures ANOVA analysis and a linear mixed effects model, the optimal controller delay was found to range between approximately 100 ms for fast prehensors and 125 ms for slower prehensors. Furthermore, the linear mixed effects model shows that there is a linear degradation in performance with increasing delay.     

Implantable transducer for two-degree of freedom joint angle sensing.

An implantable joint angle transducer (IJAT) was developed to provide command-control and feedback-control information for chronic use with functional neuromuscular stimulation (FNS) neuroprostheses. The IJAT uses Hall effect sensors to transduce joint angle. A titanium encapsulated array of Hall effect sensors and support circuitry is surgically implanted in one bone, and a similarly encapsulated permanent magnet in an opposing bone, across a joint. The IJAT provides consistent, reliable, high quality signals that reflect joint movement from midsized two-degree-of-freedom joints. IJAT's were implanted using a chronic in vivo dog model to demonstrate the feasibility of implantation and periodic measurement techniques, and to validate modeling techniques used for prediction of function and calibration. The flexion resolution ranged from 0.4 to 3.0 degrees over a range of 115 degrees. The maximum deviation from a linear response was 9 degrees. The resolution and linearity depend on several transducer and joint geometry parameters, and can be predicted prior to implantation and calibrated after implantation. The results of this study 1) defined the most appropriate hermetic capsule designs for the IJAT sensor and magnet, 2) defined the best orientation of the magnetic field to optimize device function, 3) provided a computer model of the IJAT to aid in placement, calibration, and evaluation of the device, 4) verified the surgical techniques used to implant the device, and 5) verified the long-term functionality and the biocompatibility of the device.     

Implantable biomimetic microelectronic systems design.

In this article, design examples will be presented for a biomimetic microelectronic system for a retinal prosthesis that electrically stimulates the retinal neurons. The system replaces the functionality of vision in blind patients affected by retinitis pigmentosa and age-related macular degeneration. The components and signal processing needed for a cortical prosthesis are described. Integration of all the components of a wireless biomimetic microelectronic system, such as input signal conditioning, power telemetry, data telemetry, stimulation amplifier and control circuitry (microstimulator), and a neural recording and processing device, into a single chip or a package is a tremendous challenge, requiring innovative approaches at both circuit and system levels and consideration of the multiple trade-offs between size, power consumption, flexibility in functionality, and reliability of the microelectronics. The chips described in this paper are prototypes for testing their implemented functionalities. The die sizes do not reflect the actual size of the implant. When the microelectronics are finally integrated, the circuits will be optimized to minimize the area. The use of submicron CMOS technology will also help reduce the die area. It should be noted that the biocompatible package encapsulating the electronics will increase the implant size.     

Studies of MEMS Acoustic Sensors as Implantable Microphones for Totally Implantable Hearing-Aid Systems

There is a need for high-quality implantable microphones for existing semiimplantable middle-ear hearing systems and cochlear prosthesis to make them totally implantable, thus overcoming discomfort, inconvenience, and social stigma. This paper summarizes and compares the results of an in-vitro study on three design approaches and the feasibility of using microelectromechanical system acoustic sensors as implantable microphones to convert the umbo vibration directly into a high-quality sound signal. The requirements of sensors were selected including the ability to withstand large body shocks or sudden changes of air pressure. Umbo vibration characteristics were extracted from literature and laboratory measurement data. A piezoelectric vibration source was built and calibrated to simulate the umbo vibration. Two laboratory models of the acoustic sensor were studied. The model-A device, using electrets-microphone as the sensor, was designed and tested in the laboratory and on temporal bones. The results verify that the laboratory measurement is consistent with the temporal bone characterization and achieves a near flat frequency response with a minimum detectable signal of a 65-dB sound-pressure-level (SPL) at 1 kHz. The model-B sensor was then designed to increase the sensitivity and provide an easy mounting on umbo. The model-B device can detect 40-dB SPL sound in the 1-2 kHz region, with 100-Hz channel bandwidth. The results of model-A and model-B displacement sensors and the acceleration sensor are summarized and compared. A preliminary design of the implantable displacement sensor for totally implantable hearing-aid systems is also presented.     

Biotechnology for biomedical engineers

Biotechnology is poised to have a major impact on the delivery of health care, through the development of new drugs and products for diagnosis and monitoring. It is providing and will continue to provide new and exciting research opportunities for Biomedical Engineering. Biotechnology has grown into an important area in which many significant engineering and scientific challenges exist. Vital research in biotechnology is identified especially as they relate to areas in which biomedical engineers could contribute, i.e., in biosensing, control, signal analysis, and computer applications     

Balance prostheses for postural control

There is a clear need for a prosthesis that improves postural stability in the balance impaired. Such a device would be used as a temporary aid during recovery from ablative inner-ear surgery and as a permanent prosthesis for those elderly prone to falls. Research using a one-axis device that estimates body tilt and displays it to vestibulopathic subjects via an array of tactile vibrators has demonstrated feasibility. The noninvasive, vibrotactile display of body tilt helped the balance-impaired subjects to reduce their body sway during standardized tests. The motion sensor array is comprised of three MEMS linear accelerometers and three MEMS rate gyros whose sensitive axes are aligned along three orthogonal directions to provide six-degree-of-freedom (dof) motion information.     

Implantable electrode lead in a growing limb.

An implantable electrode leadwire system used to provide limb function for individuals with spinal cord injuries (SCI's) was evaluated in a series of growing dogs to determine whether it could maintain its performance in the presence of growth. Thirty implantable electrodes (15 epimysial and 15 intramuscular) were implanted in the forelimb muscles of six young dogs. The electrodes' leads were tunneled subcutaneously and anchored proximally in the shoulder with excess lead incorporated into the subcutaneous space to accommodate growth. Six of the leads had some of this excess placed in pouches made from surgical membrane while the other 24 leads had excess placed freely within the subcutaneous space. Motor responses to the electrodes were tested before and after growth with tendon force transducers and were compared to the performance of new electrodes implanted to the same muscles of the mature dog during the explant procedure. Measured were the pulse duration at which a measurable force is first produced (threshold) and the percentage of the maximum force that could be attained from the target muscle before activation of adjacent muscles (usable force range). An analysis of variance indicated that there was no difference in the usable force range (p = 0.62) of the original electrodes before and after growth and that of the new electrodes placed at maturity. There was a difference in the threshold (p = 0.001) which can be attributed to an increase in the values measured from the original electrodes after growth. However, the increase in threshold with growth averaged 6 micros which is not clinically significant and can be accommodated through stimulation programming. Growth of the limb and unwinding of excess lead were quantified by radiograph. Extension of the freely placed excess lead was comparable to growth so that the pouch enclosures were found to be unnecessary for facilitating lead expansion. By radiograph and surgical observations, only two of 30 electrodes (both intramuscular) appeared to have been subjected to lead tension, although they continued to provide adequate motor responses. Insufficient excess lead was judged to be the cause of dislodgment for one of these electrodes. Results of this study suggest that for this implantable leadwire system, excess lead placed in the subcutaneous space can unwind on demand with limb growth such that an electrode will remain in position and provide a stable motor response.     

Optical tomography for biomedical applications

Nonionizing optical tomography is a new and active research field although projection-light imaging was investigated as early as 1929. The optical properties of normal and diseased tissues are usually different despite the large variation of values in optical properties of the normal tissues alone. Therefore, it is possible to detect some breast cancers based on measurements of optical properties. In summary, optical techniques have the following advantages: (1) the use of nonionizing radiation, (2) the capability of measuring functional (physiological) parameters, (3) the potential high sensitivity to pathologic state of biological tissues, and (4) low cost. However, biomedical optics is a challenging research field requiring the participation of many diverse, talented scientists and engineers     

Standards for biomedical signal databases

This article presents some requirements imposed on data format specifications derived from different biosignal recording environments. This is followed by a review of four particularly interesting data formats and some notes about other specifications. Finally, the merits of different formats are discussed and some views about future developments are given     

CMOS imaging for biomedical applications

CMOS photodetectors and imaging systems have shown that they possess adequate performance characteristics to replace CCDs or PMTs in some biomedical applications, thereby providing low power, portable, and cheap integrated bioimaging systems. Some advanced solutions, like novel active pixel sensors that detect ultra-low light levels, and avalanche photodiodes that are integrated in CMOS and perform single photon detection, are addressed in this paper.