Advances in chip-scale photonic-electronic integration are enabling a new generation of foundry-manufacturable implantable silicon neural probes incorporating nanophotonic waveguides and microelectrodes for optogenetic stimulation and electrophysiological recording in neuroscience research. Further extending neural probe functionalities with integrated microfluidics is a direct approach to achieve neurochemical injection and sampling capabilities. In this work, we use two-photon polymerization 3D printing to integrate microfluidic channels onto photonic neural probes, which include silicon nitride nanophotonic waveguides and grating emitters. The customizability of 3D printing enables a unique geometry of microfluidics that conforms to the shape of each neural probe, enabling integration of microfluidics with a variety of existing neural probes while avoiding the complexities of monolithic microfluidics integration. We demonstrate the photonic and fluidic functionalities of the neural probes via fluorescein injection in agarose gel and photoloysis of caged fluorescein in solution and in fixed brain tissue.
Signal propagation in cardiac cell networks can be modulated by heat stimulation. Here, the response of a connected HL‐1 cardiomyocyte cell network to the application of confined heat stimuli using Ca2+ imaging is investigated. Localized temperature gradients are generated by resistive heating via microwire arrays on a chip surface, which serves as a substrate for growing a confluent cell network. It is demonstrated that upon heat stimulation, the velocity of the propagating Ca2+ wave in the network is locally increased, leading to a deformation of the wavefront. Furthermore, evidence of a change in the signal propagation direction caused by a relocation of the pacemaker cell is shown. This effect might be used in future applications, where heat is employed as an alternative modality for cell stimulation protocols.
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