Microvortex-induced turbulent mixing for reconstitution of high-density lipoprotein-mimicking nanoparticles with aggregation-prone phosphatidylcholine.

Lipid nanoparticles often contain a phosphatidylcholine with a long chain fatty acid, 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC). However, their preparation often encounters difficulties such as the inability to yield <20 nm nanoparticles due to the aggregation-prone behavior of DSPC. High-density lipoproteins (HDLs) are ∼10 nm protein-bound lipid nanoparticles in our body, and microfluidic preparations of HDL-mimicking nanoparticles (µHDL) have been reported. Herein, we report a new microfluidic mixing mode that enables preparation of µHDL with DSPC in high yield (≥90% on a protein basis). The critical mechanism of this mode is a spontaneous asymmetric distribution of the ethanol flow injected in a symmetric manner followed by turbulent mixing in a simple rectangular parallelepiped-shaped chip.

Arrangement of a nanostructure array to control equilibrium and nonequilibrium transports of macromolecules.

Exploiting the nonequilibrium transport of macromolecules makes it possible to increase the separation speed without any loss of separation resolution. Here we report the arrangement of a nanostructure array in microchannels to control equilibrium and nonequilibrium transports of macromolecules. The direct observation and separation of macromolecules in the nanopillar array reported here are the first to reveal the nonequilibrium transport, which has a potential to overcome the intrinsic trade-off between the separation speed and resolution.

DNA separation in nanowall array chips.

A nanowall array structure was fabricated on a quartz chip as a separation matrix of DNA fragments, and a 30 s separation was realized for a mixture of DNA fragments (48.5 and 1 kbp fragments) by applying the electric voltage. A longer DNA fragment migrates faster than a shorter one in a nanowall array chip, and it is completely different from the separation of DNA based on gel electrophoresis, nanopillar chips, and nanoparticle array chips. Although the result is similar to DNA separation by entropic trapping, it could not be fully explained by entropic trapping phenomena. Direct observation of single-DNA molecular dynamics inside a nanowall array structure indicates that both confined elongation and relaxation recoiling of a DNA molecule occur, and an elongated DNA molecule migrates faster than a recoiled DNA molecule. Numerical fitting of DNA molecular dynamics reveals that the balance between times for the transverse of a DNA molecule in the nanowall array chip and the relaxation-recoiling of a DNA molecule governs the separation of DNA.