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When we enter the enchanting world of electronics we have pleasant routes. The path we have chosen is the union of electronics & medicine. Though many goals could be achieved when passing through those routes we found our routes as a pleasing one. Let us peep inside the real world of MEDICAL ELECTRONICS.
MEMS used in various disciplines of life sciences are referred to as BIO-MEMS. After computers & Information technology, MEMS may be the next technological forte of our country. Bio-MEMS give way to many new concepts like neuron computer interface, minimally invasive surgery, drug delivery at cell level and Neuropharmacology. Now MEMS have penetrated almost all walks of our life. In future use of different types of MEMS sensors and controls can make driverless vehicles a reality.
This paper reveals about a MEMS Neural Implants for freely behaving animals as well as its extension to human brain. A parallel analogue computation strategies that are derived from biology is being used.
Micro-Electro-Mechanical Systems (MEMS) is the integration of mechanical elements, sensors, actuators, and electronics on a common silicon substrate through micro fabrication technology.
MEMS promises to revolutionize nearly every product category by bringing together silicon-based microelectronics with micromachining technology, making possible the realization of complete systems-on-a-chip. MEMS is an enabling technology allowing the development of smart products, augmenting the computational ability of microelectronics with the perception and control capabilities of micro sensors and micro actuators and expanding the space of possible designs and applications.
Microelectronic integrated circuits can be thought of as the "brains" of a system and MEMS augments this decision-making capability with "eyes" and "arms", to allow Microsystems to sense and control the environment. Sensors gather information from the environment through measuring mechanical, thermal, biological, chemical, optical, and magnetic phenomena. The electronics then process the information derived from the sensors and through some decision making capability direct the actuators to respond by moving, positioning, regulating, pumping, and filtering, thereby controlling the environment for some desired outcome or purpose.
MEMS devices are extremely small -- for example, MEMS has made possible electrically-driven motors smaller than the diameter of a human hair (right) -- but MEMS technology is not primarily about size.
MEMS Neural Implants for Freely Behaving Animals
This is a multi-disciplinary research program with the aim of developing the techniques and tools for intracellular recording in live, freely behaving animals. Intracellular recording allows high-fidelity measurements not only of action potentials but also sub -threshold, synaptic interactions between neurons. The goal of this research is to build a self-contained implantable system that can record neuronal signals for several days. Afterwards, the animal is re-captured and the stored data is retrieved.
Towards MEMS Probes for Intracellular Recording
The biological models used in this work. (a) Manduca Sexta is typically 4cm in length, with a 12cm wingspan; at 2.5g, it is among the largest of insect flyers. It can easily carry a test-electronics payload. (b) Tritonia diomedea is typically 20cm in length, and has a readily accessible brain with large and well-characterized neurons.
Simultaneous, multi-site recording from the brain of freely behaving animals will allow neuroscientists to correlate neuronal activity with external stimulation and behavior. This information is critical for understanding the complex interactions of brain cells. Recent interest in microelectromechanical systems (MEMS) and in particular in bio- MEMS research has led to miniaturization of microelectrodes for extra cellular neuronal recording. MEMS technology offers a unique opportunity to build compact, integrated sensors well suited for multi-site recording from freely behaving animals.
These devices have the combined capabilities of silicon-integrated circuit processing and thin-film microelectrode sensing. MEMS probes for intracellular recording may offer significantly improved signal quality. The discussion is on the basic concepts that underlie the construction of intracellular MEMS probes. The basics of neuronal signaling and recording, and the principles of microelectrode technology and techniques is being reviewed, initially.
Tritonia is a marine nudibranch found worldwide with an unusually large species, Tritonia diomedea, indigenous to the Pacific Northwest. Its neuronal cell bodies range from roughly 5Âµm to specialized cells that are approximately 100 times as large. With our existing experimental platform for this animal we can begin experimenting on the large neurons and then gradually scale to cells of smaller size. Cartoon view of the implantable recording system (not to scale). The microprobe and signal amplifier (total size: 2 x 2 x 1 mm3) are attached to the brain tissue of T. diomedea (the animal is about 20cm in length). A thin tether cable connects to a recording unit in the visceral cavity. The micro recorder comprises a semi custom microcontroller, memory, and battery.
Progress in MEMS technology for neuronal recording is then discussed. Finally, we describe MEMS probes for intracellular recording, viz., and fabrication of micro-machined silicon needles capable of penetrating cell membranes. Using these needles, localized extracellular signals from the hawk moth Manduca sexta is recorded and obtained first recordings with silicon-based micro-probes from the inside of neurons, using an isolated brain of the sea slug Tritonia diomedea.
Evoked extra cellular potentials in the lobula plate of Manduca sexta (hawk moth) plotted versus time.
Spontaneous intracellular potentials in a neuron in the brain of Tritonia diomedea (a sea slug) plotted versus time. The positioning of the probe was controlled via micro-manipulators and an optical microscope.
The neural control group performs basic science and clinical research related to neural control of movement. It focuses mainly at system level of the central nervous system (CNS) as well as the muscular system. This includes understanding CNS plasticity/reorganization as a result of disease and medical intervention, and its relation with functional recovery in evaluating effects of deep brain stimulation on lessening symptoms in Parkinson's disease and the underlying mechanisms using neural-network simulation, and understanding CNS reorganization in stroke and other neurological disorders using neuroimaging and electrophysiological techniques.
Objective fitting of cochlear implants
The increase in the number of young children implanted with cochlear implants (CIs) has spurred the need for an objective aid to assist with the fitting procedure. The electrical stapedius reflex (ESR) threshold has strong correlation with the upper end of the dynamic range of the CI but the traditional non-invasive technique of measuring acoustic impedance has limitations. The use of a new strategy is to record the ESR using electromyogram (EMG) recordings directly from the stapedius muscle. This work successfully characterized the ESR response in a number of animal models, including some awake and unrestrained examples showing that the technique could be clinically useful. This work will hopefully include designing an optimized BioMEMS based chronic stapedial electrode that could be manufactured on a large scale. Improving the accuracy of fitting with objective aids could allow patients to receive greater benefit from their cochlear implant.
Investigations of neural ensemble coding with multi-channel neural recordings
Until recently, much of the literature investigating the neural coding of acoustic environments has been conducted with single electrode penetrations in anesthetized animals probed with simple stimuli. This is similar to the visual cortex, may be specifically designed to detect spectrotemporal features. It has also been hypothesized that cortical neurons dynamically participate in groups or ensembles that multiplex, process, and bind together the key information representing the complex and changing auditory landscape. The studies on that will provide a better understanding of how the brain processes auditory stimuli on a spatio-temporal scale. The plan is to investigate cortical processing of electrical stimuli using electrode arrays that span the auditory cortex. The knowledge gained may be applied to the development of new stimulation protocols that might better recreate natural cortical responses. This may include the development of models for investigating alternative sites of stimulation such as auditory nerve and/or brainstem penetrations that might provide an increased number of independent stimulation channels relative to the traditional cochlear implant electrode. New neural interface designs and stimulation strategies could also be developed in this research.
"A QUESTION INTIMATES THE NEW DEVELOPMENT"
Our interest not only ceases with freely-behaving animals but extends to the physically challenged ones.Inorder to worth the brain, our mission extends with the help of the precious gift of medical electronics ,which is MEMS.In this paper, our concern is mainly on two things that are as follows:
A VISION FOR THE BLIND.
A BOON FOR THE PARALYSED ONE.
A vision for the blind
The aim is to bring a blind person to the point where he or she can read, move around objects in the house, and do basic household chores. The blind won't be able to drive cars, at least in the near future, because instead of millions of pixels, they'll see approximately a thousand. The images will come a little slowly and appear yellow. But people who are blind will see.
The idea of this research is to create 1,000 points of light through 1,000 tiny MEMs electrodes. The electrodes will be positioned on the retinas of those blinded by diseases such as age-related macular degeneration and retinitis pigmentosa. These diseases damage rods and cones in the eye that normally convert light to electrical impulses, but leave intact the neural paths to the brain that transport electrical signals. Eventually the input from rods and cones ceases, but 70 to 90 percent of nerve structures set up to receive those inputs remain intact.
A drawing of retinal prosthesis implant shows the imaging camera at bottom, transmitting power and information via loop antenna to modules within the eyeball.
Ultimately, the modules will be connected to retinal nerves, where electrical stimulation will be processed by the brain. The plan is to use a tiny camera and radio-frequency transmitter lodged in the frame of a patient's glasses to transmit information and power to modules placed within the eyeball. The modules will be linked to retinal nerves that will send electrical impulses to the brain for processing.
The approach is to attach a MEMs chip on the retina - that is, within the vitreous humor of the eyeball - made of LIGA and surface micro machined silicon parts. The idea is to directly stimulate some of the nerve endings within the retina to produce images good enough to read large print and to distinguish between objects in a room.
The main aim is to build retinal implants in the form of electrode arrays that sit on the retina and stimulate the nerves that the eye's rods and cones formerly served. The size of cones and rods, as well as nerve connections, are in the micron range .Integrating micro devices into the human eye is incredibly challenging because of the need for high-reliability operation over decades in a saline environment. BioMEMs interfaces and biocompatibility issues drive much of the effort, particularly in the packaging of the micro system." 'Packaging' refers to sealing and securing a micro device in place and linking it electronically and physically with its environment. The rods and cones of the retina lie beneath nerves, not above them, which makes it slightly easier to connect directly to the nerves. The problem is the retina can't handle much pressure. To curb this problem, spring-loaded electrodes that insure good electrode contact with minimal force is used. Also, protein fouling can mess up delicate interfaces intended to transmit electrical impulses. Other problems include biocompatibility, the problem of rejection of alien matter by the body and long-term reliability.
A Boon for the Paralyzed One
The aim is to develop an electrode brain implant that is allowing speech-impaired patients to communicate through a computer. This is referred to as "cognitive engineering," developed and patented the neurotrophic brain implants.
Cognitive engineering has potential for helping many different kinds of patients. This development will open up a tremendous amount of opportunity for patients who have lost the ability to move and talk because of stroke, spinal cord injury or diseases like Lou Gehrig's disease. Though the brain implant could someday be used to help paralyzed patients move limbs or prosthetic devices, current focus has been on patients who are "locked-in"-unable to communicate with the world around them.
The neurotrophic electrode is implanted into the motor cortex of the brain using a tiny glass encasing. Neurotrophic growth factors are implanted into the glass, and the cortical cells grow into the electrode and form contacts. It takes several weeks for the cortical tissue to grow into the electrode. The neurons in the brain transmit an electronic signal when they "fire." Recording wires are placed inside the glass cone to pick up the neural signals from the ingrown brain tissue and transmit them through the skin to a receiver and amplifier outside of the scalp.
This figure shows the schematic drawing of the electrode showing the glass conical shaped tip in which the peripheral nerve is placed just prior to implantation. The glass cone contains gold recording wires and is placed below the surface of the cortex. The connecting pins are cemented in place and the electronic devices are plugged in and cemented to the skull. The scalp is closed in layers. There is no battery. The transmitted signals are picked up by the receiving coil placed within 10 inches of the scalp.
Before the device is implanted, physicians examine the brain with an MRI to learn precisely the areas that control muscle movements. When the patient thinks about moving an arm, for example, the MRI shows the increased activity in certain areas: blood flow increases and the brain cells "fire," or conduct impulses.
Figure. (A) Axial functional MR image obtained while the patient imagined movements of the left hand, indicating active neurons in the right motor area 4. (B) Corresponding MR image obtained prior to surgery.
Neural signals are used to drive the computer cursor in the same way a computer mouse is moved back and forth. The recorded neural signals are connected to the computer and are used as a substitute for the mouse cursor. The patient learns to control the strength and pattern of the electric impulses being produced in the brain, and after some training is able to 'will' a cursor to move and then stop on a specific point on the computer screen. The researchers are hopeful that the new technology will eventually allow patients to communicate smoothly and accomplish tasks such as turning on light switches and sending email. They also plan to try connecting the neural signals to a muscle stimulator in a patient's paralyzed limb so the patient can move the limb using the same principle used to move the computer cursor.
Improved affordances offered
The primary goal of the brain implant is to re-connect the "locked-in" patient with the world around her by offering her a means of communicating. The new affordances are not truly "new", but rather "regained". Recovered actions include interactions with a computer, communication with the outside world, and control of the patient's nearby surroundings. The brain implant affords the expression of mental desire taken for granted by most able-bodied people.
New interaction styles and metaphors to brain implants
The brain implant seeks to link the brain to computer actions by associating neuron firing with mouse movement. The technology is referred to as "a mental mouse" that allows the patient to move the cursor as if he held a computer mouse in his hand. At this level, the obvious metaphor is one which allows direct manipulation of objects on a screen-like a mouse or basic hand movements. Thinking about moving the hand and foot may make the cursor move up and down for one patient. The trick is teaching the patient to control the strength and pattern of the electric impulses being produced in the brain. After some training, the patient is able to 'will' a cursor to move and then stop on a specific point on the computer screen. As the technology improves, controlling movement or speaking will become more and more automatic for patients.
In this respect, the interaction has the potential to become quite literally invisible. A computer user rarely attends to the hand and mouse that move the cursor on the screen. Likewise, the user of the brain implant will not attend to the relearned mental activity that has translated "move my hands" into "move the mouse vertically." The invisibility is achieved more so, since mental activity alone accomplishes the task.
Some of the technical constraints that are limiting the development are:
The patients who have the greatest need for the brain implant are often terminally ill. This poses problems for long-term development. The first recipient of the brain implant, for instance, died within three months of her operation due to complications from ALS. The second recipient also had physical set-backs that limited his control of the implant. The mind doesn't work well when one is sick, and the target user will never be in perfect health.
The technology is inherently dangerous and complicated, involving advanced elements of neurology, electrical engineering, computer science, and surgery. It is a far more complex system than the computers that read the eye movements of paralyzed patients.
Financial support has always been a constraint for technology aiding the disabled.
Fundamental Problem of Implantable Microelectrode Arrays
Brain often encapsulates the device with scar tissue
Normal brain movement may cause micro-motion at the tissue-electrode interface
Proteins adsorb onto device surface
Useful neural recordings are eventually lost
Development of BioMEMS based neural interfacing devices
Central to the above thrust is the necessity of a neural interface. The neural interfacing technology developed thus far has provided an exciting view into the operation of neural circuits. However, if this technology is ever to have clinical impact, devices should bio-integrate and yield stable communication channels with ever increasing numbers of neurons for significant amounts of time. This problem can be overcome by polymer based electrodes. Flexible polymer-based BioMEMS have the potential of better matching the mechanical properties of brain tissue while at the same time surfaces can be engineered to enhance biocompatibility.
In thin film processing and microelectronics to create such optimal and reliable neural interfacing device structures can be readily produced. This provides potential surface modifications or neural culturing techniques that might further enhance long-term biocompatibility. Finally, while flexible structures are desirable to reduce potential micro-damage in chronically implanted devices they are more difficult to implant.
Desired properties for neural implants
Bio Active Coatings
Controlled Biological Response
The other research thrusts provide a vast "test-bed" for the development of this technology and will in turn receive great benefit from it. Bio-robotics and direct brain-machine interface research is very new and exciting. Some of these efforts may lead not only to clinically viable technologies, but may also usher in a new generation of robotics that have the processing power and adaptive properties of living systems by employing neural tissue as an adaptive micro-controller.
Advantages of polymer based electrodes
low moisture uptake
low dielectric constant and
easy surface modification.
The applications of the brain implant aim to free the most "trapped" members of society and are an excellent example of technology's ability to improve the quality of human life. Not only will handicapped individuals be freed from the physical constraints that have isolated them from others, but they will be able to become active members of society, potentially changing the social stigma associated with being handicapped. But, people are generally afraid of brain implants, as they conjure up science fiction plots, mind control, and robotic take-over. The direct correspondence of thought to action inhibits a "filter" system that prevents rash behavior in most people. The implications of systems that enable such impulse behavior are truly frightening.