Thermally controlled microfluidic back pressure regulator

By using the temperature dependence of viscosity, we introduce a novel type of microfluidic lab-on-a-chip back pressure regulator (BPR) that can be integrated into a micro-total-analysis-system. A BPR is an important component used to gain pressure control and maintain elevated pressures in e.g. chemical extractions, synthesis, and analyses. Such applications have been limited in microfluidics, since the back pressure regularly has been attained by passive restrictors or external large-scale BPRs. Herein, an active microfluidic BPR is presented, consisting of a glass chip with integrated thin-film heaters and thermal sensors. It has no moving parts but a fluid restrictor where the flow resistance is controlled by the change of viscosity with temperature. Performance was evaluated by regulating the upstream pressure of methanol or water using a PID controller. The developed BPR has the smallest reported dead volume of 3 nL and the thermal actuation has time constants of a few seconds. The pressure regulation were reproducible with a precision in the millibar range, limited by the pressure sensor. The time constant of the pressure changes was evaluated and its dependence of the total upstream volume and the compressibility of the liquids is introduced.

Microfluidic active pressure and flow stabiliser

In microfluidics, a well-known challenge is to obtain reproducible results, often constrained by unstable pressures or flow rates. Today, there are existing stabilisers made for low-pressure microfluidics or high-pressure macrofluidics, often consisting of passive membranes, which cannot stabilise long-term fluctuations. In this work, a novel stabilisation method that is able to handle high pressures in microfluidics is presented. It is based on upstream flow capacitance and thermal control of the fluid’s viscosity through a PID controlled restrictor-chip. The stabiliser consists of a high-pressure-resistant microfluidic glass chip with integrated thin films, used for resistive heating. Thereby, the stabiliser has no moving parts. The quality of the stabilisation was evaluated with an ISCO pump, an HPLC pump, and a Harvard pump. The stability was greatly improved for all three pumps, with the ISCO reaching the highest relative precision of 0.035% and the best accuracy of 8.0 ppm. Poor accuracy of a pump was compensated for in the control algorithm, as it otherwise reduced the capacity to stabilise longer times. As the dead volume of the stabiliser was only 16 nL, it can be integrated into micro-total-analysis- or other lab-on-a-chip-systems. By this work, a new approach to improve the control of microfluidic systems has been achieved.

Good Practices of Comirnaty® Vaccine Injection Using Uncrimped Materials

Background In 2020, the first mRNA COVID vaccine was approved by the with six doses from single vial. In the context of material shortages, the aim of the study was to compare different protocols to extract doses using uncrimped materials with good trueness and reproducibility. Methods To optimize the extraction of the sixth dose from a single vial with uncrimped materials, alternative protocols of preparation were tested, derived from the drug information. Results The repeatability of injected volume was acceptable for all protocols (CV<5.3%). To prepare six 0.3mL doses using uncrimped materials, protocols with an air bubble were evaluated to offset the high dead volume inherent to uncrimped materials. Regarding the limited doses observed using long intramuscular needle (92.8% of the reference dose), the air bubble protocol with a liquid volume adjustment at 0.27mL was finally validated to respect the administration of full doses. Conclusion Results highlighted the necessity to adapt the drug information protocol for the preparation and administration of Cominarty®, due to the use of high dead volume materials. Despite the good reproducibility and accuracy of the air bubble protocols, some precautions have therefore to be taken to maintain the integrity of the vaccine suspension for efficient administration.

Meaningful and Physically Consistent Efficiency Definition for Positive Displacement Pumps - Continuation of the Critical Review of ISO 4391 and ISO 4409

ISO 4391:1984 gives the common efficiency definition for positive displacement machines. ISO 4409:2019 uses this efficiency definition to specify the procedure for efficiency measurements. If the machine conditions do not correspond with an incompressible flow due to operation at high pressure levels, the compressibility of the fluid and the dead volume of a pump must be taken into account. On this point, ISO 4391:1984 is physically inconsistent. Achten et. al. address this issue in their paper at FPMC 2019 presenting a critical review of ISO 4409:2007. They introduce new definitions of the overall efficiency as well as the mechanical-hydraulic efficiency. At the same time, they question the validity of the volumetric efficiency definition. Li and Barkei continue on this issue in their paper at FPMC 2020 and give a new efficiency definition based on the introduction of a new quantity Φ which describes the volume specific enthalpy of the conveyed fluid. The motivation of this paper is to contribute to the ongoing and fruitful discussion. Our approach starts with the most general efficiency definition, namely the isentropic efficiency. Subsequently, we make assumptions concerning the fluid properties with respect to the compressibility of the conveyed fluid. On the basis of the ideal cycle of a positive displacement pump and the p-v diagram, we derive physically consistent and more meaningful representations of the overall, the mechanical-hydraulic and the volumetric efficiency that address the inconsistency of ISO 4391:1984. Furthermore, we compare our findings with the existing results of Achten et. al. and Li and Barkei.

Synthesis and crystal structure of the lanthanum cyanurate complex La[H2N3C3O3]3 · 8.5 H2O

Single crystals of La[H2N3C3O3]3 · 8.5 H2O were obtained from stoichiometric amounts of as-precipitated La(OH)3 with cyanuric acid (CYA) [H3N3C3O3]3 in a boiling aqueous solution, followed by slow cooling and evaporation of water under ambient conditions. According to the X-ray structure analysis of the colorless and transparent crystals, La[H2N3C3O3]3 · 8.5 H2O adopts the triclinic space group P1 (no. 1) and exhibits the unit-cell parameters a = 987.24(7), b = 1110.97(8), c = 1179.81(9) pm, α = 113.716(2), β = 97.053(2), γ = 101.502(2)° for Z = 2. The CYA is singly deprotonated to give monoanions [H2N3C3O3]– which are O,N-coordinated to the La3+ cations. These dihdrogencyanurate anions are assembled in ribbons with two crystallographically different La3+ cations coordinating to either one or two different ligands, respectively. The coordination sphere of the La3+ cations is comprised of water molecules, and interstitial water molecules fill the dead volume of the crystals. The anionic ribbons are stacked to maximize the contact between the six-membered rings, showing distances of about 330 pm.