The main component of the payload is the 3D-printed micropot. The overall micropot concept was recently developed by Kawa et al. as a novel tool for the real-time monitoring of seed growth and biological potential assessment experiments with integrated force sensors [12 (link)]. Our previous work showed the possibility of performing biological experiments with a semi-automatic system and under 1 g gravity. In the case of microgravity experiments, the micropot and the fluid-based nutrition circuit had to be redesigned to meet all the above conditions of a closed-loop fluid flow in microgravity, and gas exchange in a closed payload container. The printed micropot contains four main components: a seed sample socket, a microfluidic nutrition supply system, a semi-permeable air supply membrane, and two calibrated force sensors (Figure 2 ).
The micropot was fabricated in a single printing process with a ProJet3510 inkjet printer (3D Systems Inc., Rock Hill, South Carolina, United States) configured to high-definition printing mode. The resolution was 650 × 650 dpi with a 16 µm layer thickness. VisiJet M3 crystal was used as a building material and the wax-like VisiJet S300 as a support material. Postprocessing included four steps. First, the support material was melted away in the oven (60 °C, 2.5 h). Second, the structures were cleaned with mineral oil at 60 °C with ultrasonic agitation (~15 min). Third, the micropots were washed with deionised water (15 MΩcm) and dried in a stream of nitrogen (N2). The final step was rising with isopropyl alcohol and drying, which was performed immediately before placing the seeds in the sockets.
The 3D-printed device was equipped with calibrated force sensors [12 (link)]. When the root and stalk develop properly, they come into contact with the force sensors. The seed socket has an aperture that, under 1 g gravity conditions, guide the root towards the force sensor. The sensors were calibrated with deflection-force characteristics. Thus, the measurement of the sensor beam deflection can be used to determine the force generated by the root/stalk, and as a result, the biological potential of the seed can be determined. The deflection scale is integrated into the micropot structure, and the displacement is measured with dedicated image analysis software, which automatically tracks the tip of the beam [12 (link)]. The micropot was designed to hold a specific kind of seed, which was cress seeds (Lepidium sativum). Nevertheless, the 3D printing fabrication process enables the free modification of the seed socket size and the performing of experiments on most small grains.
In order to ensure the gas exchange between the inside volume of the micropot and the tight payload container, the micropot has a semi-permeable air supply membrane made of Parafilm® M, and is located on the top of the micropot. Additionally, the whole device was designed and successfully tested as a robust system able to sustain vibration and overloads of launching into Earth’s orbit.
The micropot was fabricated in a single printing process with a ProJet3510 inkjet printer (3D Systems Inc., Rock Hill, South Carolina, United States) configured to high-definition printing mode. The resolution was 650 × 650 dpi with a 16 µm layer thickness. VisiJet M3 crystal was used as a building material and the wax-like VisiJet S300 as a support material. Postprocessing included four steps. First, the support material was melted away in the oven (60 °C, 2.5 h). Second, the structures were cleaned with mineral oil at 60 °C with ultrasonic agitation (~15 min). Third, the micropots were washed with deionised water (15 MΩcm) and dried in a stream of nitrogen (N2). The final step was rising with isopropyl alcohol and drying, which was performed immediately before placing the seeds in the sockets.
The 3D-printed device was equipped with calibrated force sensors [12 (link)]. When the root and stalk develop properly, they come into contact with the force sensors. The seed socket has an aperture that, under 1 g gravity conditions, guide the root towards the force sensor. The sensors were calibrated with deflection-force characteristics. Thus, the measurement of the sensor beam deflection can be used to determine the force generated by the root/stalk, and as a result, the biological potential of the seed can be determined. The deflection scale is integrated into the micropot structure, and the displacement is measured with dedicated image analysis software, which automatically tracks the tip of the beam [12 (link)]. The micropot was designed to hold a specific kind of seed, which was cress seeds (Lepidium sativum). Nevertheless, the 3D printing fabrication process enables the free modification of the seed socket size and the performing of experiments on most small grains.
In order to ensure the gas exchange between the inside volume of the micropot and the tight payload container, the micropot has a semi-permeable air supply membrane made of Parafilm® M, and is located on the top of the micropot. Additionally, the whole device was designed and successfully tested as a robust system able to sustain vibration and overloads of launching into Earth’s orbit.
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