Biology subjects

Poon, J. K. S.

Publications and source records attributed to Poon, J. K. S..

6 recordsLinked to original sources

bioRxiv2024

Foundry-fabricated dual-color nanophotonic neural probes for photostimulation and electrophysiological recording

SignificanceCompact tools capable of delivering multicolor optogenetic stimulation to deep tissue targets with sufficient span, spatiotemporal resolution, and optical power remain challenging to realize. Here, we demonstrate foundry-fabricated nanophotonic neural probes for blue and red photostimulation and electrophysiological recording, which use a combination of spatial multiplexing and on-shank wavelength-demultiplexing to increase the number of on-shank emitters. AimWe demonstrate Si photonic neural probes with 26 photonic channels and 26 recording sites, which were fabricated on 200-mm diameter wafers at a commercial Si photonics foundry. Each photonic channel consists of an on-shank demultiplexer and separate grating coupler emitters for blue and red light, for a total of 52 emitters. ApproachWe evaluate neural probe functionality through bench measurements and in vivo experiments by photostimulating through 16 of the available 26 emitter pairs. ResultsWe report neural probe electrode impedances, optical transmission, and beam profiles. We validated a packaged neural probe in optogenetic experiments with mice sensitive to blue or red photostimulation. ConclusionsOur foundry-fabricated nanophotonic neural probe demonstrates dense dual-color emitter integration on a single shank for targeted photostimulation. Given its two emission wavelengths, high emitter density, and long site span, this probe will facilitate experiments involving bidirectional circuit manipulations across both shallow and deep structures simultaneously.

neuroscience↗

bioRxiv2024

Three dimensionally printed microstructured alginate scaffolds for neural tissue engineering

The integration of scaffolds, signalling cues, and cellular components is essential in tissue engineering to create an in vivo equivalent environment that supports physiological function. Scaffolds provide mechanical reinforcement for cellular proliferation and differentiation while providing cues that instruct the development of cells during culture. Alginate (Alg) is a versatile biopolymer for scaffold engineering. However, due to a lack of intrinsic cell-binding sites, thus far, Alg must be functionalized for cellular adhesion. Here, we demonstrate proof-of-concept, bioactive additive-free, microstructured Alg (M-Alg) scaffolds for neuron culture. The M-Alg scaffold was formed by introducing tetrapod-shaped ZnO (t-ZnO) microparticles as structural templates in the Alg that were subsequently removed. These transparent, porous, additive-free Alg-based scaffolds with neuron affinity are promising for neuroregenerative and organoid- related research. HighlightsTetrapod-shaped ZnO (t-ZnO) microparticles are used as a template for the fabrication of open interconnected channels and textured surfaces in 3D printed microstructured alginate (M-Alg) scaffolds. Primary mouse cortical neurons seeded on the 3D printed M-Alg scaffolds show improved adhesion and maturation with extensive neural projections forming inside the scaffolds.

bioengineering↗

bioRxiv2023

Implantable nanophotonic neural probes for integrated patterned photostimulation and electrophysiology recording

Optogenetics has transformed neuroscience by allowing precise manipulation of neural circuits with light [1-5]. However, a central difficulty has been to deliver spatially shaped light and record deep within the brain without causing damage or significant heating. Current approaches form the light beam in free space and record the neural activity using fluorescence imaging or separately inserted electrodes [6-9], but attenuation limits optical penetration to around 1 mm of the brain surface [10]. Here, we overcome this challenge with foundry-fabricated implantable silicon neural probes that combine microelectrodes for electrophysiology recordings with nanophotonic circuits that emit light with engineered beam profiles and minimal thermal impact. Our experiments reveal that planar light sheets, emitted by our neural probes, excited more neurons and induced greater firing rate fatigue in layers V and VI of the motor and somatosensory cortex of Thy1-ChR2 mice at lower output intensities than low divergence beams. In the hippocampus of an epilepsy mouse model, we induced seizures, a network-wide response, with light sheets without exceeding the[~] 1{whitebullet}C limit for thermally induced electrophysiological responses [11-13]. These findings show that optical spatial profiles can be tailored for optogenetic stimulation paradigms and that the probes can photostimulate and record neural activity at single or population levels while minimizing thermal damage to brain tissue. The neural probes, made in a commercial silicon photonics foundry on 200-mm silicon wafers, demonstrate the manufacturability of the technology. The prospect of monolithically integrating additional well-established silicon photonics devices, such as wavelength and polarization multiplexers, temperature sensors, and optical power monitors, into the probes holds the potential of realizing more versatile, implantable tools for multimodal brain activity mapping.

bioengineering↗

bioRxiv2023

3D Printed Ti3C2Tx MXene/PCL Scaffolds for Guided Neuronal Growth and Photothermal Stimulation

The exploration of neural circuitry is essential for understanding the computational mechanisms and physiology of the brain. Despite significant advances in materials and fabrication techniques, controlling neuronal connectivity and response in three dimensions continues to present a formidable challenge. Here, we present a method for engineering the growth of three-dimensional (3D) neural circuits with the capability for optical stimulation. We fabricated bioactive interfaces by melt electrospinning writing (MEW) of 3D printed polycaprolactone (PCL) scaffolds followed by coating with titanium carbide (Ti3C2Tx MXene). Beyond enhancing hydrophilicity, cell adhesion, and electrical conductivity, the Ti3C2Tx MXene coating enabled optocapacitance-based neuronal stimulation due to illumination-induced local temperature increases. This work presents a strategy for additive manufacturing of neural tissues with optical control for functional tissue engineering and neural circuit computation.

bioengineering↗

bioRxiv2022

3D Printed Neural Tissues with in situ Optical Dopamine Sensors

Engineered neural tissues serve as models for studying neurological conditions and drug screening. Besides observing the cellular physiological properties, in situ monitoring of neurochemical concentrations with cellular spatial resolution in such neural tissues can provide additional valuable insights in models of disease and drug efficacy. In this work, we demonstrate the first three-dimensional (3D) tissue cultures with embedded optical dopamine (DA) sensors. We developed an alginate/Pluronic F127 based bio-ink for human dopaminergic brain tissue printing with tetrapodal-shaped-ZnO microparticles (t-ZnO) additive as the DA sensor. DA quenches the autofluorescence of t-ZnO in physiological environments, and the reduction of the fluorescence intensity serves as an indicator of the DA concentration. The neurons that were 3D printed with the t-ZnO showed good viability, and extensive 3D neural networks were formed within one week after printing. The t-ZnO can sense DA in the 3D printed neural network with a detection limit of 0.137 M. The results are a first step toward integrating tissue engineering with intensiometric biosensing for advanced artificial tissue/organ monitoring.

bioengineering↗

bioRxiv2020

Implantable photonic neural probes for light-sheet fluorescence brain imaging

SignificanceLight-sheet fluorescence microscopy is a powerful technique for high-speed volumetric functional imaging. However, in typical light-sheet microscopes, the illumination and collection optics impose significant constraints upon the imaging of non-transparent brain tissues. Here, we demonstrate that these constraints can be surmounted using a new class of implantable photonic neural probes. AimMass manufacturable, silicon-based light-sheet photonic neural probes can generate planar patterned illumination at arbitrary depths in brain tissues without any additional micro-optic components. ApproachWe develop implantable photonic neural probes that generate light sheets in tissue. The probes were fabricated in a photonics foundry on 200 mm diameter silicon wafers. The light sheets were characterized in fluorescein and in free space. The probe-enabled imaging approach was tested in fixed and in vitro mouse brain tissues. Imaging tests were also performed using fluorescent beads suspended in agarose. ResultsThe probes had 5 to 10 addressable sheets and average sheet thicknesses < 16 m for propagation distances up to 300 m in free space. Imaging areas were as large as {approx} 240 m x 490 m in brain tissue. Image contrast was enhanced relative to epifluorescence microscopy. ConclusionsThe neural probes can lead to new variants of light-sheet fluorescence microscopy for deep brain imaging and experiments in freely-moving animals.

bioengineering↗