Associate Professor, Knight Campus
Ph.D. Rockefeller University
B.S. Princeton University
Tim Gardner is a highly regarded neuro-engineer with a track record of success in academics and commercialization. He will join the Knight Campus in June 2019.
Most recently, Gardner co-founded the Elon Musk-funded startup, Neuralink, which builds high-resolution brain interfaces for humans. Before Neuralink, he led Boston University's Laboratory of Neural Circuit Formation. There, researchers led by Gardner developed a high-resolution 3D printer and other methods to fabricate ultra-small electrodes to record the neural correlates of birdsong.
Throughout his career, Gardner has worked at the interface of neuroscience and technology and successfully translated his work into a commercial venture, maximizing the impact of his university research.
Gardner holds a bachelor’s degree in physics from Princeton University and earned his doctorate in biology and physics from Rockefeller University. He did post-doctoral fellowships at Rockefeller University and the Massachusetts Institute of Technology. His numerous awards and honors include National Institutes of Health Brain Initiative grants and membership in the National Academy of Inventors.
"I’ve always been interested in maximizing the impact of academic research,” Gardner said. “The Knight Campus and the UO’s Institute of Neuroscience combine to present a very captivating opportunity to develop team-based neuro-technology projects."
Extracting individual neural activity recorded through splayed optical microfibers.
Neurophotonics. 2018 Oct;5(4):045009
Authors: Perkins LN, Devor A, Gardner TJ, Boas DA
Previously introduced bundles of hundreds or thousands of microfibers have the potential to extend optical access to deep brain regions, sampling fluorescence activity throughout a three-dimensional volume. Each fiber has a small diameter ( 8 μ m ) and follows a path of least resistance, splaying during insertion. By superimposing the fiber sensitivity profile for each fiber, we model the interface properties for a simulated neural population. Our modeling results suggest that for small ( < 200 ) bundles of fibers, each fiber will collect fluorescence from a small number of nonoverlapping neurons near the fiber apertures. As the number of fibers increases, the bundle delivers more uniform excitation power to the region, moving to a regime where fibers collect fluorescence from more neurons and there is greater overlap between neighboring fibers. Under these conditions, it becomes feasible to apply source separation to extract individual neural contributions. In addition, we demonstrate a source separation technique particularly suited to the interface. Our modeling helps establish performance expectations for this interface and provides a framework for estimating neural contributions under a range of conditions.
PMID: 30627593 [PubMed]
Amorphous Silicon Carbide Platform for Next Generation Penetrating Neural Interface Designs.
Micromachines (Basel). 2018 Sep 20;9(10):
Authors: Deku F, Frewin CL, Stiller A, Cohen Y, Aqeel S, Joshi-Imre A, Black B, Gardner TJ, Pancrazio JJ, Cogan SF
Microelectrode arrays that consistently and reliably record and stimulate neural activity under conditions of chronic implantation have so far eluded the neural interface community due to failures attributed to both biotic and abiotic mechanisms. Arrays with transverse dimensions of 10 µm or below are thought to minimize the inflammatory response; however, the reduction of implant thickness also decreases buckling thresholds for materials with low Young's modulus. While these issues have been overcome using stiffer, thicker materials as transport shuttles during implantation, the acute damage from the use of shuttles may generate many other biotic complications. Amorphous silicon carbide (a-SiC) provides excellent electrical insulation and a large Young's modulus, allowing the fabrication of ultrasmall arrays with increased resistance to buckling. Prototype a-SiC intracortical implants were fabricated containing 8 - 16 single shanks which had critical thicknesses of either 4 µm or 6 µm. The 6 µm thick a-SiC shanks could penetrate rat cortex without an insertion aid. Single unit recordings from SIROF-coated arrays implanted without any structural support are presented. This work demonstrates that a-SiC can provide an excellent mechanical platform for devices that penetrate cortical tissue while maintaining a critical thickness less than 10 µm.
PMID: 30424413 [PubMed]
Effect of oxidation on intrinsic residual stress in amorphous silicon carbide films.
J Biomed Mater Res B Appl Biomater. 2019 Jul;107(5):1654-1661
Authors: Deku F, Mohammed S, Joshi-Imre A, Maeng J, Danda V, Gardner TJ, Cogan SF
The change in residual stress in plasma enhanced chemical vapor deposition amorphous silicon carbide (a-SiC:H) films exposed to air and wet ambient environments is investigated. A close relationship between stress change and deposition condition is identified from mechanical and chemical characterization of a-SiC:H films. Evidence of amorphous silicon carbide films reacting with oxygen and water vapor in the ambient environment are presented. The effect of deposition parameters on oxidation and stress variation in a-SiC:H film is studied. It is found that the films deposited at low temperature or power are susceptible to oxidation and undergo a notable increase in compressive stress over time. Furthermore, the films deposited at sufficiently high temperature (≥325 C) and power density (≥0.2 W cm-2 ) do not exhibit pronounced oxidation or temporal stress variation. These results serve as the basis for developing amorphous silicon carbide based dielectric encapsulation for implantable medical devices. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1654-1661, 2019.
PMID: 30321479 [PubMed - in process]
High-density microfibers as a potential optical interface to reach deep brain regions.
J Neural Eng. 2018 12;15(6):066002
Authors: Perkins LN, Semu D, Shen J, Boas DA, Gardner TJ
OBJECTIVE: Optical techniques for recording and manipulating neural activity have traditionally been constrained to superficial brain regions due to light scattering. New techniques are needed to extend optical access to large 3D volumes in deep brain areas, while retaining local connectivity.
APPROACH: We have developed a method to implant bundles of hundreds or thousands of optical microfibers, each with a diameter of 8 μm. During insertion, each fiber moves independently, following a path of least resistance. The fibers achieve near total internal reflection, enabling optically interfacing with the tissue near each fiber aperture.
MAIN RESULTS: At a depth of 3 mm, histology shows fibers consistently splay over 1 mm in diameter throughout the target region. Immunohistochemical staining after chronic implants reveals neurons in close proximity to the fiber tips. Models of photon fluence indicate that fibers can be used as a stimulation light source to precisely activate distinct patterns of neurons by illuminating a subset of fibers in the bundle. By recording fluorescent beads diffusing in water, we demonstrate the recording capability of the fibers.
SIGNIFICANCE: Our histology, modeling and fluorescent bead recordings suggest that the optical microfibers may provide a minimally invasive, stable, bidirectional interface for recording or stimulating genetic probes in deep brain regions-a hyper-localized form of fiber photometry.
PMID: 30127101 [PubMed - in process]
Thinking Small: Progress on Microscale Neurostimulation Technology.
Neuromodulation. 2017 Dec;20(8):745-752
Authors: Pancrazio JJ, Deku F, Ghazavi A, Stiller AM, Rihani R, Frewin CL, Varner VD, Gardner TJ, Cogan SF
OBJECTIVES: Neural stimulation is well-accepted as an effective therapy for a wide range of neurological disorders. While the scale of clinical devices is relatively large, translational, and pilot clinical applications are underway for microelectrode-based systems. Microelectrodes have the advantage of stimulating a relatively small tissue volume which may improve selectivity of therapeutic stimuli. Current microelectrode technology is associated with chronic tissue response which limits utility of these devices for neural recording and stimulation. One approach for addressing the tissue response problem may be to reduce physical dimensions of the device. "Thinking small" is a trend for the electronics industry, and for implantable neural interfaces, the result may be a device that can evade the foreign body response.
MATERIALS AND METHODS: This review paper surveys our current understanding pertaining to the relationship between implant size and tissue response and the state-of-the-art in ultrasmall microelectrodes. A comprehensive literature search was performed using PubMed, Web of Science (Clarivate Analytics), and Google Scholar.
RESULTS: The literature review shows recent efforts to create microelectrodes that are extremely thin appear to reduce or even eliminate the chronic tissue response. With high charge capacity coatings, ultramicroelectrodes fabricated from emerging polymers, and amorphous silicon carbide appear promising for neurostimulation applications.
CONCLUSION: We envision the emergence of robust and manufacturable ultramicroelectrodes that leverage advanced materials where the small cross-sectional geometry enables compliance within tissue. Nevertheless, future testing under in vivo conditions is particularly important for assessing the stability of thin film devices under chronic stimulation.
PMID: 29076214 [PubMed - indexed for MEDLINE]
Amorphous silicon carbide ultramicroelectrode arrays for neural stimulation and recording.
J Neural Eng. 2018 02;15(1):016007
Authors: Deku F, Cohen Y, Joshi-Imre A, Kanneganti A, Gardner TJ, Cogan SF
OBJECTIVE: Foreign body response to indwelling cortical microelectrodes limits the reliability of neural stimulation and recording, particularly for extended chronic applications in behaving animals. The extent to which this response compromises the chronic stability of neural devices depends on many factors including the materials used in the electrode construction, the size, and geometry of the indwelling structure. Here, we report on the development of microelectrode arrays (MEAs) based on amorphous silicon carbide (a-SiC).
APPROACH: This technology utilizes a-SiC for its chronic stability and employs semiconductor manufacturing processes to create MEAs with small shank dimensions. The a-SiC films were deposited by plasma enhanced chemical vapor deposition and patterned by thin-film photolithographic techniques. To improve stimulation and recording capabilities with small contact areas, we investigated low impedance coatings on the electrode sites. The assembled devices were characterized in phosphate buffered saline for their electrochemical properties.
MAIN RESULTS: MEAs utilizing a-SiC as both the primary structural element and encapsulation were fabricated successfully. These a-SiC MEAs had 16 penetrating shanks. Each shank has a cross-sectional area less than 60 µm2 and electrode sites with a geometric surface area varying from 20 to 200 µm2. Electrode coatings of TiN and SIROF reduced 1 kHz electrode impedance to less than 100 kΩ from ~2.8 MΩ for 100 µm2 Au electrode sites and increased the charge injection capacities to values greater than 3 mC cm-2. Finally, we demonstrated functionality by recording neural activity from basal ganglia nucleus of Zebra Finches and motor cortex of rat.
SIGNIFICANCE: The a-SiC MEAs provide a significant advancement in the development of microelectrodes that over the years has relied on silicon platforms for device manufacture. These flexible a-SiC MEAs have the potential for decreased tissue damage and reduced foreign body response. The technique is promising and has potential for clinical translation and large scale manufacturing.
PMID: 28952963 [PubMed - indexed for MEDLINE]
Carbon fiber on polyimide ultra-microelectrodes.
J Neural Eng. 2018 02;15(1):016010
Authors: Gillis WF, Lissandrello CA, Shen J, Pearre BW, Mertiri A, Deku F, Cogan S, Holinski BJ, Chew DJ, White AE, Otchy TM, Gardner TJ
OBJECTIVE: Most preparations for making neural recordings degrade over time and eventually fail due to insertion trauma and reactive tissue response. The magnitudes of these responses are thought to be related to the electrode size (specifically, the cross-sectional area), the relative stiffness of the electrode, and the degree of tissue tolerance for the material. Flexible carbon fiber ultra-microelectrodes have a much smaller cross-section than traditional electrodes and low tissue reactivity, and thus may enable improved longevity of neural recordings in the central and peripheral nervous systems. Only two carbon fiber array designs have been described previously, each with limited channel densities due to limitations of the fabrication processes or interconnect strategies. Here, we describe a method for assembling carbon fiber electrodes on a flexible polyimide substrate that is expected to facilitate the construction of high-density recording and stimulating arrays.
APPROACH: Individual carbon fibers were aligned using an alignment tool that was 3D-printed with sub-micron resolution using direct laser writing. Indium deposition on the carbon fibers, followed by low-temperature microsoldering, provided a robust and reliable method of electrical connection to the polyimide interconnect.
MAIN RESULTS: Spontaneous multiunit activity and stimulation-evoked compound responses with SNR >10 and >120, respectively, were recorded from a small (125 µm) peripheral nerve. We also improved the typically poor charge injection capacity of small diameter carbon fibers by electrodepositing 100 nm-thick iridium oxide films, making the carbon fiber arrays usable for electrical stimulation as well as recording.
SIGNIFICANCE: Our innovations in fabrication technique pave the way for further miniaturization of carbon fiber ultra-microelectrode arrays. We believe these advances to be key steps to enable a shift from labor intensive, manual assembly to a more automated manufacturing process.
PMID: 28905812 [PubMed - indexed for MEDLINE]
A fast and accurate zebra finch syllable detector.
PLoS One. 2017;12(7):e0181992
Authors: Pearre B, Perkins LN, Markowitz JE, Gardner TJ
The song of the adult male zebra finch is strikingly stereotyped. Efforts to understand motor output, pattern generation, and learning have taken advantage of this consistency by investigating the bird's ability to modify specific parts of song under external cues, and by examining timing relationships between neural activity and vocal output. Such experiments require that precise moments during song be identified in real time as the bird sings. Various syllable-detection methods exist, but many require special hardware, software, and know-how, and details on their implementation and performance are scarce. We present an accurate, versatile, and fast syllable detector that can control hardware at precisely timed moments during zebra finch song. Many moments during song can be isolated and detected with false negative and false positive rates well under 1% and 0.005% respectively. The detector can run on a stock Mac Mini with triggering delay of less than a millisecond and a jitter of σ ≈ 2 milliseconds.
PMID: 28753628 [PubMed - indexed for MEDLINE]