Development of micromachined technologies for neural interfaces

2013-10-29BioMEMS is uniquely positioned to impact the field of neuroscience by advancing neural interface state of the art. Traditional neural interfaces rely on macro-world technologies that can be limited when attempting to interface with neurons on a cellular level. Micromachining enables construction of microengineered devices possessing form factors that are suitable for interfacing with neurons or complex neural networks. Improved tools for neural interfacing can improve neuroscience knowledge by enabling more sophisticated experimental studies or advancing the use of neuroprosthetics. ❧ In this work, three micromachined neural interfaces are developed and described; each addressing a neural interfacing mode; electrical, chemical, and optical. Novel micromachining technologies were developed in order to construct these neural interfaces. ❧ A neural probe in the novel form of a three-dimensional Parylene sheath is first described in chapter 2. This sheath probe was constructed with biocompatible materials and designed to obtain long-term in vivo neural signal recording by promoting neural growth through the sheath structure. Multiple improving sheath probe designs and their fabrication details are described. A Parylene thermoforming process was utilized to shape the sheath. The microfabricated recording electrodes were characterized in vitro and found to possess desirable electrochemical properties for neural recording. Sheath probes were implanted into rat and in vivo neural signals were successfully recorded. ❧ Next, chemical neural interfacing with microdevices is described in chapter 3. A microfluidic platform was first designed and developed to deliver chemicals focally to neurons. This was achieved by micromachining Parylene microchannels that possessed plasma etched pores through which focal delivery could occur. Thermal flow sensors were also embedded in the microchannels which enable real-time sensing of the focal delivery. Many challenges were encountered with the microfluidic platform and so microfluidic modules were designed and constructed to simplify ease of use. Separate microdevice modules separated the challenges of in vitro neural cell culturing and chemical delivery so that each module's packaging requirement was simplified by addressing only one challenge. Soft lithography was utilized to construct μCCM (compartmented culture module), the module for guiding and separating axons and somata in in vitro cultured neurons. Thermocompressive bonding was developed to construct embedded SU-8 microchannels with a Parylene cap for μBAM (biochemical administration module), the module for chemical delivery. μBAM was designed to exploit the principle of passive pumping to self-generate flow and chemical delivery; simplifying packaging requirements. ❧ Finally, optical neural interfacing is explored through the creation of a micromachined mirror array in chapter 4. The mirror array was designed to overcome throughput issues that limit the use of traditional optogenetic or photocaging tools. A novel fabrication process was developed and utilized to construct inclined structures that were then coated with metal to become mirrors. The fabricated optical device was characterized and found to possess acceptable optical properties for optical neural interrogations