Biological Applications
Targeting Functionally Characterized Synaptic Architecture Using Inherent Fiducials and 3D Correlative Microscopy by CI Tomas, MA Ryan, B Scholl, D Guerrero-Given, D Fitzpatrick, and N Kamasawa, Microsc Microanal | doi: 10.1017/S1431927620024757 We established an EM-label-free correlative microscopy
workflow to pair synaptic function with ultrastructural properties in cortical brain tissue. Ca2+
activity in neurons was
captured using GCaMP6s and in vivo 2-photon light microscopy (LM), providing insight into their functional properties during visual stimulation. Conversely, volumetric electron microscopy (EM) provided detailed ultrastructural information of the neuron and subcellular features (that is, dendrites and dendritic spines). We used inherent fiducials, such as blood vessels and cell bodies in the tissue, to correlate: 1) in vivo 2-photon LM, 2) ex vivo confocal LM (that is, aſter fixing and slicing the brain), and 3) serial block face scanning EM. To improve image quality in our correlative workflow for brain tissue, we precisely optimized the sample preparation protocol for visualizing synaptic structures, and we applied improved electron detection hardware in the SEM. 3D EM reconstructions of the neuron could then be mapped back to in vivo functional data, allowing us to analyze functional properties of
individual dendritic spines in the context of their structural characteristics (Figure).
(Top) 2-photon image of a dendritic segment of a cortical pyramidal neuron, imaged using the Ca2+
indicator GCaMP6s. Along the den-
drite are numerous dendritic spines, which are the sites of excitatory synapses onto the neuron. (Bottom) A 3D reconstruction of the same dendrite from SEM data, with the dendrite in blue, spines in green, and presynaptic axon segments in yellow. Correlative matching allows identification and paired function-structure measurements of individ- ual dendritic spines.
Materials Applications
In situ TEM Characterization of Microstructure Evolution and Mechanical Behavior of the 3D-Printed Inconel 718 Exposed to High Temperature by S Koul, L Zhou, O Ahmed, Y Sohn, T Jiang, and A Kushima, Microsc Microanal | doi: 10.1017/S1431927621000052 Understanding
the effect of heat treatment on
microstructure evolution and mechanical property is important for performing postproduction heat treatment of alloys produced by additive manufacturing processes. We performed in situ transmission electron microscopy (TEM) characterization of microstructural evolution in 3D-printed Inconel 718 (IN718) while exposed to elevated temperature and analyzed an associated change in mechanical property. A specially designed specimen shape that enables tensile testing of nano-sized thin films without off-plane deformations was used. Additionally, it allowed seamless transition between in situ heating and tensile experiments, using the same specimen, to elucidate direct correlation of microstructure evolution and mechanical property. A clear transition of the failure mode from ductile to brittle was observed aſter exposing the as-printed IN718 to high temperature, where the residual stress relaxation and the formation of incoherent γ’ precipitates took place (Figure). Ductility was maintained with a full heat treatment with coherent γ’ precipitates.
72
Push-to-pull specimen design that prevents off-plane deformation and allows seamless transition from heating to tensile experiment inside a TEM. Failure mode of the as-printed IN718 changed from ductile to brittle after direct heating.
doi:10.1017/S1551929521000602
www.microscopy-today.com • 2021 May
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