Presentation on theme: "Neurochips a new way of Integration"— Presentation transcript:
1 Neurochips a new way of Integration MAN vs. MACHINENeurochips a new way of IntegrationUniversity of Waterloo - Analytical Instrumentation Chem Dr.KaranassiosAnnie Raditsis
2 building an interface that combines biology and technology The Problembuilding an interface that combines biology and technologyPROsOperates electrically, similar to the brainComputer = e- in a solid ion latticeBrain = ions in polar fluidElectrons within silicon have the mobility of 103 cm2/Vs (voltage*sec)(water within the brain = 10-3 cm2/Vs)CONsLack of adaptability to change within computer versus the plasticity of the brainFunctions are physically separate in a computer, while with a single piece of tissue can carry out a number of different functionsThe sizes of common biological electronics are too large to interface with ions (eg. pacemakers)
3 "Nervenzelle an Chip! Chip an Nervenzelle!" Thanks to the Max Planck Institute for Biochemistry that took the step towards more specific biological-electronic communications with a device that allows a field effect transistor on a silicon chip to sense the electric potential created by a neuron, and the neuron to sense a voltage pulse in the chip.The Neurochippart-mechanical,part-livingelectronic circuitA Neurochip within a Perspex chamberAdvantages:Neurochips have a smooth silicon finish, therefore increasing a neuron’s life span to years instead of 5-6 hours with previous technologyThe photoconductive property of silicon allows for less interference from resistance in conjunction with the neuron. This also betters the control of the frequency induced by experimenterThe chip in general is of higher performance to specific functions with great speed and reliability
4 Here Is How It Is Done 1.The neuron First, one isolates a neural network. A neural network within its own culture is known as a ganglia. Within the ganglia the neurons are connected by electrical synapses.The most common neuron used incorelation with the chip is a snail neuron – Lymnaea stagnalisA biological scheme of a typical neuronThe treatment:1. Soak brains is 25% lysterine2. Additional soak in saline consisting of NaCl, KCl, MgCl2 and Hepes at pH 7.93. Fix onto a Sylgard dish containing antibiotic saline4. Central ganglions are dissected5. Then soak in antibiotic saline and pinned to a Sylgard dish6. Remove outer sheath and soak in colgenase/dipase and trypsin7. Treat with trypsin inhibitor8. Apply a high-osmolarity medium based on glucose9. The ganglia are opened with tungsten microneedle10. Neurons are removed by suction through a micropipette
5 2. The chip ► The Fabrication The Dimensions 4 x 4 array of neuron wells at the center a 9 mm long/ 3mm wide and 20µm thick silicon membrane.2. The chipThe FabricationStarting with an epitaxy/silicon wafer (dia.100nm and resistance 2-4 Ω/cm) with a 16µm lightly-doped layer on to of a 4 µm heavily boron-doped.A composite layer of oxide/nitride insulator and thermal oxide is formed.The Photolithographic step – defines opening in the nitride/oxide layer for electrodes(c) The Plasma & Isotropic Silicon Etching step – etched into the nitride/oxide and silicon substrateThe Semirecessed Process – creates a 1µm oxide step around the electrode openingMetallization – compensates for the stress acting on the chip during usage.Opening the Windows (at the Back of the Wafer) – open bonding pads and etch the alignment on the insulation layer.More Etching – having the alignment to be within 1 µm.Photolithographic steps and Etching on the Side of the Cavities - forms the grillwork in the heavily boron-doped layersThere is also the fabrication of a picket fence made of polymers.It’s purpose is to restrict the movement of the isolated neuron.►
6 growing out of the wells 3. Putting them togetherWe left the neuron last in a micropipette they can now be implanted into the wells of the chip, through the grillwork.They are held to the chip by a capacitive stimulator and a recording transistor.The neuron sits on a gold electrode, which can be coated with platinum to lower the impedance.The neuron is placed in the well, creating the opportunity for growth.This growth occurs within the span of two days, until it forms a good seal with the bottom of the electrode.A live neural networkgrowing out of the wells
7 4. Photoconductive Stimulation For inducing firing onto a neuron, a narrow beam of light isdirected at the specified neuron.The silicon interface of the chip possesses a photoconductive property.This allows the conductivity of the neuron to change.It is the act of change that induces the firing.5. SynapsesThe firing results in an electric signal that travels across the synapse to communicate to adjacent neurons.This process is called Synapses.In essence the electric signal depolarizes the postsynaptic membrane of the neuron.This process in the basis on all neural communication and growth
8 6. Field Effect Transistors (FET) A FET is a type of transistor that has the capability to amplify the humanly undetectable voltages that are produced by a single neuron. It creates an electric field, by supplying an electric charge to a metal plate attached to a battery and a semiconductor, thus drawing out electrons of an atom.The neuron’s ion current flows throughthe membrane, along a narrow gapbetween the neuron and the chip.The gap creates a voltage drop, whichin turn changes the electron flow in thesilicon on the opposite side of the insulating oxide layer.The net current is considered to be the Action Potential of the cell and appears only if the cell membrane is electrically inhomogeneousThe resulting electric signal from synapses is the signal detected by the transistor.It then converts the signal into a voltage, in order to amply to a detectable level.
9 7. Neuroelectronic signal transmission First output is the burst of voltage pulses at the stimulatorSecond output is the intracellular voltage from within the neuron Third is the extracellular voltage form the transistorThe resulting voltage change can be expressed by the difference of the specific ion conductance in the attached and free membrane.The shapes of the postsynaptic records differ significantly from the intracellularvoltages.This delay is distinct suggesting a role of differing chemicals within the neuron (eg. potassium channels)
10 SoThis is the fundamental step in neuro-manipulation, in its combination of culturing neurons on an inert surface of a microelectronically active substrate, isolating individual neurons without any disruption of migration, and noninvasive electronic interfacing for stimulation and recordingThese methods are suitable for long-term studies on synaptic modulation in small networks of invertebrate neurons that are connected by chemical synapses and contribute an astonishing amount to the world of science and technology.From the world of NASANASA SCIENTISTS USE HANDS-OFF APPROACH TO LAND PASSENGER JETImagine being able to land a jumbo jet without ever taking control of the stick. NASA scientists recently demonstrated the ability to control a 757 passenger jet simulation, using only human muscle-nerve signals linked to a computer.Neuroelectric control uses "neural net" software that "learns" patterns that can slowly change and evolve with time, as well as combining many patterns together to generate a response.October 2000To the Medical WorldSevered optical nerves can be made to grow again One of the most significant advances in nerve regeneration in a decade. After severing an optic nerve in rats, neurologists have found a way to reconnect it to the brain so that it once again transmits normal electrical signals.05 December 01Advanced within this field have only started to progress within the past 20 years and predictions are more advances as soon as the next 5 years
11 The Latest There has been development on a multi-neuron chip This chip consist of two layers of 64 neurons, which have the ability of spiking neurons and dynamic synapses.Dynamic synapses provides a short-term plasticity (depression or facilitation). Therefore these neurons can be stimulated by an excitatory synapse, a depressing synapse and inhibitory synapse.Each layer has 63 excitatory neurons and1 global inhibitory neuron.The excitatory neurons excite the globalinterneuron which in return, inhibits theexcitatory neurons.Connections between the excitatory neuronscan be configuredIt is a building block for a multi-chip spike-based system that can be used to explorespike-based models.
12 ReferencesBonifazi, Paolo and Fromherz, Peter. Silicon Chip for Electronic Communication between Nerve Cells by Noninvasive Interfacing and Analog-Digital Processing. AdvancedMaterial.ca (2002)Jenkner, Martin. Muller, Bernt. And Fromherz, Peter. (2001) Interfacing a silicon chip to pairs of snail neurons connected by electrical synapses. Vol. 84, # 4. ppJohnson, Colin. Neurochips detect brain’s reaction to learning. EE times. January 2,Locklear, Fred. Learning visualized in “neurochips’ December, 12, 2001Max Planck Institute for Biochemistry, Department of Membrane and Neurophysics. Neuroelectronic Interfacing: Semiconductor Chips with Ion Channels, Nerve Cells and Brain. BerlinNeurochips Detect Brain’s Reaction to Learning. Artificialintelligence.ai-depot.comVedantam, Shankar. Brain Cells, Silicon Chips Are Linked Electronically. Wastingon Post. Tuesday, August 28, pp.A03