Mechanical modeling of mechanosensitive insect strain sensors as a tool to investigate exoskeletal interfaces.

During walking, sensory information is measured and monitored by sensory organs that can be found on and within various limb segments. Strain can be monitored by insect load sensors, campaniform sensilla (CS), which have components embedded within the exoskeleton. CS vary in eccentricity, size, and orientation, which can affect their sensitivity to specific strains. Directly investigating the mechanical interfaces that these sensors utilize to encode changes in load bears various obstacles, such as modeling of viscoelastic properties. To circumvent the difficulties of modeling and performing biological experiments in small insects, we developed 3-dimensional printed resin models based on high-resolution imaging of CS. Through the utilization of strain gauges and a motorized tensile tester, physiologically plausible strain can be mimicked while investigating the compression and tension forces that CS experience; here, this was performed for a field of femoral CS inDrosophila melanogaster. Different loading scenarios differentially affected CS compression and the likely neuronal activity of these sensors and elucidate population coding of stresses acting on the cuticle.

Remote laser ablation electrospray ionization mass spectrometry for non-proximate analysis of biological tissues.

RATIONALE: We introduce remote laser ablation electrospray ionization (LAESI), a novel, non-proximate ambient sampling technique. Remote LAESI allows additional analytical instrumentation to be incorporated during sample analysis. This work demonstrates the utility of remote LAESI and, when combined with optical microscopy, allows for the microscopy-guided sampling of biological tissues. METHODS: Rapid prototyping using a 3D printer was applied to produce various ablation chamber geometries. A focused 5 ns, 2.94 µm laser pulse kept at 10 Hz ablated the sample within the chamber, remote to the mass spectrometer inlet. Ablated particulates were carried through a transfer tube by N2 gas, delivered to the electrospray plume and ionized. A long-distance microscope was used to capture images of tissues before, during and after ablation. RESULTS: Optimized remote LAESI was found to have a 27% transport efficiency compared with conventional LAESI, sufficient for many applications. A comparable molecular coverage was obtained with remote LAESI for the analysis of plant tissue. Proof-of-principle experiments using a pansy flower and a maple leaf indicated the functionality of this approach for selecting domains of interest for analysis by optical microscopy and obtaining chemical information from those selected regions by remote LAESI-MS. CONCLUSIONS: Remote LAESI is an ambient non-proximate sampling technique, proven to detect metabolites in biological tissues. When combined with optical microscopy, remote LAESI allows for the simultaneous acquisition of morphological and chemical information. This technique has important implications for histology, where chemical information for specific locations within a tissue is critical.