Self-Clearing Catheter

Fig 1. Illustration of hydrocephalus. (a) Normal infant ventricles. (b) Enlarged ventricles with an implanted shunt system [1].

Hydrocephalus is a debilitating neurological disorder for which there is no cure. Patients suffering from hydrocephalus require chronically-implanted shunt systems to control intracranial pressure by diverting excess cerebrospinal fluid from brain (Fig 1). Unfortunately, existing implants have a high rate of failure. Up to 50% of shunt systems are expected to fail within two years of initial implantation. One of the reasons for device failure is cellular obstruction of inlet pores on ventricular catheter. To combat this problem, we are developing micro-fabricated magnetic actuators to be integrated into shunt systems (Fig 2).

Round Unobstructing Magnetic Microactuator

Fig 2. Microfabricated unobstructing magnetic microactuator. Scale bar = 400 μm.

The magnetically-actuated devices facilitate long-term implantation because they do not contain integrated circuit and internal power source. We can design devices to produce large amount of force and deflection required to remove cellular occlusion. Thus far, we have evaluated cell-removal capabilities in static and circulating flow environment, fatigue responses, and MRI compatibility issues of these magnetic microdevices. Prelimary data demonstrate good cell-clearing in both static and circulating environments, excellent mechanical robustness, and no RF-heating concerns (See video below). We are currently developing processing techniques to integrate these microdevices into silicone catheters for in vivo evaluation. In addition, we are looking to integrate wireless pressure sensors to measure intracranial pressure and monitor device functionality.

MEMS-Enabled Medical Devices

Fig 3. Interdigitated magnetic microactuators. This is an example of microdevices that may be integrated into conventional medical device to enhance functionality.

Medical device manufacturers are under constant pressure to deliver high-quality, advanced medical devices with multiple functionalities while cutting cost of overall manufacturing. While there are many examples of microfabricated sensors and actuators that can provide additional functionalities for implants (Fig 3), the packaging standard is lacking for integrating these devices into conventional medical device manufacturing process. We are investigating ways to facilitate integration of microdevices into medical devices by evaluating material safety, packaging process, and connector technologies.

Re-Evaluation of Neurostimulation Safety


Fig 4. Illustration of Shannon plot. Shannon (1992) compiled several in vivo results from previous research to establish “safe” neurostimulation criteria using charge density and total charge per phase parameters.

Platinum-based stimulation electrodes are widely used in the neuromodulation industry. For safe electrical stimulation of nervous tissues, each device has certain charge-injection limit. For years, many companies have adopted the safe charge-injection limit described in Shannon Plot, which is based on several in vivo cortical studies (Fig 4). It is important to evaluate the applicability of Shannon Plot as the gold standard for all neurostimulation application especially with the increasing number of indications (e.g., chronic pain, Parkinson’s disease, hearing and vision impairments, urinary incontinence, obesity, etc.) that target different neural tissues. We are working with collaborators from Medtronic, Boston Scientific, St. Jude Medical, Advanced Bionics, Case Western Reserve University, and FDA to better understand the tissue-electrode charge-transfer process and the impact of electrochemical byproducts to improve the safety and efficacy of neurostimulation.

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