Medical Devices : Neurological devices


‘Smart’ Cerebrospinal Fluid Shunt

UW–Madison neurological surgeons and their collaborators have developed a ‘smart’ shunt that is self-regulating and overcomes the issue of over-drainage associated with all commercially available systems.

The new system features continuous intracranial pressure sensing and a novel valve design actuated by a piezoelectric lever. An external wireless transmitter (e.g., RFID device) connected to a computer enables physicians to control the shunt, to set parameters or thresholds for the valve.

By monitoring intracranial pressure and continuously alternating between opened/closed valve position, the system prevents fluid from constantly draining. This allows the surrounding tissue to rebound from the catheter holes, allows the brain to retain its normal shape, and mitigates blockage concerns.

Improved System for Stroke Therapy and Rehabilitation

UW-Madison researchers have developed an improved system for stroke therapy and rehabilitation.  This system collects movement intention signals from the brain in real-time via EEG and initiates functional electrical stimulation (FES) of the appropriate muscle(s) to assist the neurons in regrowing their connections from the brain to the muscles along the correct pathways.  Additional general sensory stimulation may be added to this therapy to further encourage proper neuron regrowth. 

Improved Neuron Electrode Array Uses Graphene

UW–Madison researchers have designed a new micro-ECoG device that is flexible and transparent over a broad spectrum. The device includes an implantable electrode array made of conductive graphene sheets on a biocompatible substrate.

Both the substrate and the graphene sheets are transparent over a broad range of wavelengths in the UV, IR and visible spectrum. This allows light to be passed through the array and the underlying tissue for imaging purposes or optical stimulation.

The device is called CLEAR (Carbon Layered Electrode Array).

Virtual Reality Rehabilitation for Stroke Victims

UW–Madison researchers have developed a low-cost rehabilitation system that provides a virtual reality environment in which a patient’s depicted hands manipulate simulated structures. Programmed tasks can be designed with increasing difficulty and progress data is reviewable by a therapist.

The Bimanual Rehabilitation Device (BiHRD) uses a depth-sensing camera positioned in a workspace to follow a patient’s hand and finger positions. According to predefined mapping between real and virtual space, a display represents one or both hands in a simulated environment. This display can be a computer screen or eye goggles worn by the patient. Elemental exercises may include grasping and controlling virtual objects.

Gravity- and Pressure-Controlled Valve System for Controlling Cerebrospinal Fluid in the Ventricular System

UW–Madison researchers have developed a system that allows drainage of excess CSF and prevents CSF overdrainage. A key insight is that cardiac pulsations can be transmitted inside the shunt tubing, creating a pulsatile pressure wave that propagates down the tubing. When this pressure wave hits a pressure differential valve, it can force the valve open during the systolic phase of the pressure wave, pumping some CSF through the valve with each systolic phase. In this way, CSF can be pumped across a valve as long as the peak pressure within the shunt tubing exceeds the preset pressure differential threshold for that valve, even if the mean pressure is below that same threshold. Overdrainage then occurs. The improved system and valve design prevent slit ventricle syndrome by addressing both gravity siphon effects and cardiac pulsations.

The improved system consists of tubing that leads from the ventricular system into a valve system that has two arms, a forward flow arm and a return flow arm. A one-way low threshold pressure differential valve is located in the forward flow arm. CSF that passes this first valve can either exit the valve system through a one-way higher threshold exit valve that leads into the peritoneal cavity, or it can flow through the return flow arm via a one-way low threshold valve that returns CSF back to the inlet side of the valve system. By choosing appropriate pressure differentials for the three valves, one can bracket the pressures on the inlet side between a set minimum and maximum value. If the ICP rises above the set maximum, then CSF will flow through the inlet valve and out the exit valve. If the ICP drops below the set minimum, then CSF will flow through the return valve and back towards the inlet side of the valve system, thus preventing overdrainage. The high threshold pressure differential exit valve also incorporates a gravity compensation unit that negates the gravity siphoning effect, regardless of the orientation of the patient. Thus, the net effect is to allow for drainage of excess CSF while preventing overdrainage due to either the cardiac pulsation or gravity siphon effect.

Microtube Scaffold for Sensing and Stimulating Nerve Cell Connections

UW-Madison researchers have developed a method to produce a scaffold system for neurons that permits guided growth or interconnection of neurons and sensing or stimulation of neural activity. The method involves growing nerve cells through doped semiconductor microtubes that act as tunable electrodes for sensing and stimulating nerve cell connections. The tubes allow the growth and interconnection of the neurons to be controlled, and sensors and/or stimulating probes incorporated along the length of the tubes can be used to provide precisely located but spatially separated measurements and stimulation.

The tubes are made of semiconducting thin-film nanomembranes, may vary in length and have diameters ranging from one to 100 microns. Cells are placed near the opening of the tube and preferentially grow through the tube. The microtubes form a coaxial probe around the nerve cell growth, effectively coupling an electrode to the neurons. The tube also acts to protect the neuron from a culture solution that may produce ion leakage, affecting signal propagation and introducing signal noise.

Monitoring Consciousness for Improved Anesthesia Delivery

A UW-Madison researcher have developed a method and apparatus for assessing loss of consciousness with the potential for use during anesthesia. The device monitors brain waves in response to stimulation to determine the level of consciousness. It uses EEG sensors to collect electrical signals from firing neurons within a patient’s brain and a neural stimulator to provide localized excitation of neurons within the brain at a certain location and time. A computer receives the electrical signals from the EEG sensor and executes a program to measure neural activity after the excitation of neurons and calculate an indication of consciousness based on the measured activity. The computer determines unconsciousness by noting when the neurons in the brain begin firing in a highly coordinated manner similar to the production of slow waves during deep sleep.

Computational Algorithms for Identifying, Suppressing and Reversing Epilepsy

UW-Madison researchers have developed a protocol that accounts for each of the conditions required for the development of epileptogenesis and determines a treatment to reverse, or “unlearn,” epilepsy.  Because this protocol addresses factors in addition to neuronal hyperexcitability, it may prove more effective than current methods. 

The new technique involves acquiring and analyzing neural activity data from a subject to determine epileptic patterns based on neuronal hyperexcitability, spatial connectivity and temporal connectivity.  Treatment using an electrical stimulus then is focused based on the determined patterns and administered to the subject.

Improved Brain-Computer Interface Technology for Long-Term Cortical Stimulation or Recording

UW-Madison researchers have developed a thin-film microelectrode array that is tailored specifically for long-term, minimally invasive cortical recording or stimulation.  The array includes a new type of electrode, called a “micro-electrocorticographic (μECoG) electrode,” which is significantly smaller, more flexible and less invasive than existing brain recording or stimulating electrodes. 

The microelectrode array is implanted in the cranium of an individual in a contracted configuration.  Then a predetermined stimulus, such as voltage, causes a flexible element to unfurl the electrode structure to its expanded configuration.  An array of contacts, which is linked to a control module, is included on the flexible element.  These contacts engage the cortical surface to record or stimulate brain signals when the microelectrodes are in the expanded position.

A Flow Control Device for the Treatment of Intracranial Aneurysms

UW-Madison researchers have developed a flow control apparatus and method that relieves abnormal hemodynamic forces known to cause aneurysm formation, growth and rupture. The device can be delivered in a compact form endovascularly using standard microcatheters and guidewires. Once it’s delivered to the aneurysm site, the device expands into its final configuration. It is positioned upstream from the aneurysm to effectively divert blood flow and prevent rupture.

A stent-like anchoring element, consisting of a biologically inert material, such as nitinol or stainless steel, stabilizes the device. It is coated with polyurethane or silicon to prevent blood coagulation. To avoid volume flow complications, the device occludes no more than 25 percent of the implant site and comes in a variety of sizes to accommodate the shape and size of an aneurysm. 

New Method That Allows Unsupervised Cluster Analysis

UW-Madison researchers have developed a method of analyzing N-dimensional data using proximity in N-dimensional space to group data into an unknown number of clusters. First, a processor measures the similarities between all data points based on N-dimensional distance where N is the number of parameters recorded. The point in closest proximity to a number of other points is then selected as the index point for one cluster. If the distance from the index point to its nearest neighbor falls within a predetermined, statistically significant value, it becomes a member of that cluster. The distance from the cluster to the next nearest neighbor is then evaluated, and so forth until a point fails to be significantly close. The points from the completed cluster are removed from the data set and the process is repeated to find the next cluster.

Bioactive Device for Improved Vascular Aneurysm Occlusion and Healing

UW-Madison researchers have developed an endovascular device for occluding a cerebral or vascular aneurysm. The device is composed of a single nickel-titanium coil surrounded by a bioactive polymer shell.  Nickel-titanium is a shape memory alloy that allows minimally invasive delivery of the coil. The polymeric shell component overcomes the problem of coil compaction by supporting the coil, and also forms a barrier blocking blood flow into the aneurysm. Furthermore, the shell is composed of elastic, blood-compatible and bioactive material that stimulates regrowth and healing of the vessel wall. 

When deployed, the device fills the aneurysm and causes contact between the wire stent and surrounding tissue. The bioactive polymer shell provides an isolated biological environment to promote accelerated and complete wound healing. The device allows for more precise, controlled aneurysm blockage as well as time-efficient device delivery, thus decreasing the fatality rate associated with traditional coiling treatments.

Improved Endovascular Aneurysm Occlusion Device

UW-Madison researchers have developed an aneurysm occlusion device that consists of a polymeric shell, which is filled in situ with a liquid embolic agent. This polymeric shell addresses some of the shortcomings of previous methods by providing liquid embolic agent containment.

The polymer shell is composed of an elastic, hemocompatible, bioactive polyurethane-based material that stimulates blood vessel growth and native wound healing through the bioactive component. Upon delivery of the device in the aneurysm, the shell is filled with liquid embolic agents that gel/cross-link when mixed or stimulated. This containment approach allows a variety of liquid embolic agents to be used.

Once filled, the bioactive shell initiates a cascade of wound healing events to stimulate repair of the aneurysm, improving patient outcomes. This device should allow for more precise, controlled aneurysm occlusion, leading to a decrease in the mortality rate associated with cerebral aneurysm rupture.

Drug-Free Method and Device for Promoting Restorative Sleep

A UW-Madison researcher has developed a drug-free method of enhancing sleep quality and efficiency in humans. The method relies on a device that induces or promotes slow-wave activity in the brain of a resting person through targeted transcranial magnetic stimulation (TMS). Low frequency TMS increases slow-wave activity, which is associated with the restorative aspects of sleep.

In addition to the magnetic stimulator, the device includes EEG electrodes for measuring brain waves. The measurements from the EEG trigger the device to stimulate the brain to produce large slow waves. These waves, which are in every respect similar to the largest ones observed spontaneously in the deepest sleep, keep the person in a profound, restorative sleep. When slow waves fall to normal as detected by the EEG, the brain is stimulated again. This process can be repeated for hours to provide the user with a short, but high-quality period of sleep. When it is time for the user to wake, the device can simply be turned off, or it may shut down after a specified period of time.

Nanoscale and Microscale Wireless Stimulating Probes Precisely Deliver Electrical Current to Cells

UW-Madison researchers have developed freely dispersable microscale and nanoscale probes that can be activated without a direct wired connection.  Instead, these probes can be triggered remotely by electromagnetic radiation from a laser or other source.

The probes consist of small tubes of strained semiconductor material that overlaps to form a heterojunction semiconductor device.  The overlap region may comprise n and p type doped regions to form a versatile p-n junction, such as a photodiode, which is capable of absorbing electromagnetic radiation. 

The probes receive electromagnetic radiation, such as light, which they then convert to a local electrical potential and subsequently to an electrical current flow.  The current flow could be used to directly stimulate neural cells.  Alternatively, it could be used to trigger the chemical or mechanical release of compounds held by the probes, or to activate a biological system, such as an ion channel.

Medical Shunt and Valve for Regulating Bodily Fluids, Especially Cerebral Spinal Fluid

UW-Madison researchers have now created a shunt with a new type of ventriculoperitoneal valve that does not allow undesired siphoning of CSF. The shunt includes an inlet port, an outlet port and a fluid channel in between. It also contains a valve located between the two ports and a valve-actuating member, such as a piston, which holds the valve closed.

As CSF accumulates, it puts pressure on the piston, which is held in place by a circumferential rubber skirt that acts as a spring. When the pressure reaches a predetermined level, a channel within the piston aligns with the fluid channel, allowing CSF to flow from the head through a catheter. The valve is designed so that the piston responds to the build-up of CSF, but not to changes in CSF flow due to gravity. Thus, the valve opens only in response to intracranial pressure, eliminating the problem of gravity-induced siphoning seen in conventional shunts.

Methods for Identifying Neuronal Spikes

UW-Madison researchers have developed a software package designed to automate identification of neuronal spikes and sort them by neuron virtually independent of human intervention. Electrode probes are inserted into the brain and advanced by the software until they read the firing of neurons. That firing is then recorded as spikes of activity. The spikes vary by shape, amplitude, frequency, and period. The software compares spikes to templates based on previously recorded spikes, eliminates spikes from non-neuronal sources, and creates a map of brain activity.

Neural Probe Array for Stable, Reliable Long-Term Implant Function

UW-Madison researchers have developed an improved neural probe array that is designed for reliable and stable long-term implant function. The new design is more biocompatible than previous neural interfaces.

The array can be subdurally implanted in the brain to record intracranial field potentials in animals or humans and then transmit that information to an external device. Also, several apertures are located between the two sides of the array for drug delivery. They can be used to enhance the device’s biocompatibility or to treat neurological disorders.

Implantable Intracranial Neural Interface System

UW-Madison researchers have developed an implantable intracranial neural interface node, which provides an integrated and minimally invasive microsystem for neural recording, stimulation and delivery of chemical or biological substances. This system supports cross-modal neural interfaces to the cerebrum and other associated structures in the central nervous system.

The implant consists of a cylindrical chamber that is inserted into the cranium through a burr hole. The cylindrical housing contains electrical components for instrumentation and signal processing and fluidic components for the delivery of therapeutic substances. Microscale neuroprobe assemblies are connected to the electronic and fluidic processing elements via a flexible, multi-wire ribbon cable. The probe assemblies are inserted into the brain to provide electrical and chemical interfaces to specific brain regions, allowing for neural recording, electrical stimulation, sensing and sampling of chemicals, and delivery of chemicals, cells and genetic material.

An Improved Stent for the Treatment of Hydrocephalus Offering Lower Failure Rates and Fewer Risks

A UW-Madison researcher has developed a stent designed to drain CSF by holding the third ventricle hole open, analogous to ear tubes used to treat fluid in the middle ear. No such stent is commercially available.

The stent can be deployed down a side channel of an endoscope, a tool commonly used to make the third ventricle hole. A blunt probe inserted through a channel of the endoscope can make an opening in the floor of the third ventricle in the brain. After the opening is made, the stent is inserted to keep the opening permanent.

The stent device is composed of two winged anchors. Before being inserted into the third ventricle hole, the device has a tubular appearance with the membrane located at the center or “waist.” After lining up the membrane with the hole opening, the anchors are flared up, sandwiching the tissue between the anchors on either side of the opening. This final configuration secures the membrane from moving and gives it an eyelet appearance. This new stent design forces the hole to remain open and lacks the common problems associated with other techniques.