https://imechanica.org/files/Qiu_environmental_sensitive_hydrogel.pdf

Environment-sensitive hydrogels for drug delivery

Microfabricated integrated circuits revolutionized computation by vastly reducing the space, labor, and time required for calculations. Microfluidic systems hold similar promise for the large-scale automation of chemistry and biology, suggesting the possibility of numerous experiments performed rapidly and in parallel, while consuming little reagent. While it is too early to tell whether such a vision will be realized, significant progress has been achieved, and various applications of significant scientific and practical interest have been developed. Here a review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena. Specifically, this review explores the Reynolds number Re, addressing inertial effects; the Peclet number Pe, which concerns convective and diffusive transport; the capillary number Ca expressing the importance of interfacial tension; the Deborah, Weissenberg, and elasticity numbers De, Wi, and El, describing elastic effects due to deformable microstructural elements like polymers; the Grashof and Rayleigh numbers Gr and Ra, describing density-driven flows; and the Knudsen number, describing the importance of noncontinuum molecular effects. Furthermore, the long-range nature of viscous flows and the small device dimensions inherent in microfluidics mean that the influence of boundaries is typically significant. A variety of strategies have been developed to manipulate fluids by exploiting boundary effects; among these are electrokinetic effects, acoustic streaming, and fluid-structure interactions. The goal is to describe the physics behind the rich variety of fluid phenomena occurring on the nanoliter scale using simple scaling arguments, with the hopes of developing an intuitive sense for this occasionally counterintuitive world.

/pdf/microfluidics-fluid-physics-at-the-nanoliter-scale-4bpahtd8qa.pdf

Microfluidics: Fluid physics at the nanoliter scale

Advances in determination of polymer structure and in preservation of structure for electron microscopy provide the best view to date of how polysaccharides and structural proteins are organized into plant cell walls. The walls that form and partition dividing cells are modified chemically and structurally from the walls expanding to provide a cell with its functional form. In grasses, the chemical structure of the wall differs from that of all other flowering plant species that have been examined. Nevertheless, both types of wall must conform to the same physical laws. Cell expansion occurs via strictly regulated reorientation of each of the wall's components that first permits the wall to stretch in specific directions and then lock into final shape. This review integrates information on the chemical structure of individual polymers with data obtained from new techniques used to probe the arrangement of the polymers within the walls of individual cells. We provide structural models of two distinct types of walls in flowering plants consistent with the physical properties of the wall and its components.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-313X.1993.tb00007.x

Structural models of primary cell walls in flowering plants: consistency of molecular structure with the physical properties of the walls during growth

▪ Abstract Most prokaryotic signal-transduction systems and a few eukaryotic pathways use phosphotransfer schemes involving two conserved components, a histidine protein kinase and a response regul...

Two-component signal transduction

Thermo- and pH-responsive polymers in drug delivery.

An infinitesimal change in electric potential across a polyelectrolyte gel produces a discrete, reversible volume change. The volume of the collapsed gel can be several hundred times smaller than that of the swollen gel.

https://science.sciencemag.org/content/sci/218/4571/467.full.pdf

Collapse of Gels in an Electric Field

We sequenced the 274-nucleotide intercistronic glnA-glnL region of Escherichia coli to localize regulatory regions postulated from genetic evidence. The transcriptional start of glnLp, identified by S1 nuclease mapping, preceded the structural gene by 32 bases. NR1, the glnG gene product and a repressor of glnLp, protected from DNase digestion a region of DNA between -12 and +15 from the transcriptional start. A mutation rendering glnLp insensitive to NRI was within the protected region in a-TGCA- sequence found in all nitrogen-regulated operons, providing evidence for involvement of this sequence in interactions with NRI. We also observed in the intercistronic region a potential rho-independent terminator preceding glnLp and a sequence previously found in other intercistronic regions. Images

https://jb.asm.org/content/jb/160/1/379.full.pdf

Identification and regulation of the glnL operator-promoter of the complex glnALG operon of Escherichia coli.

Mutations in the glnG gene of Escherichia coli that result in increased activity of nitrogen regulator I (NRI), the product of glnG, were obtained by two different selection procedures. The mutant proteins were purified and characterized. The concentrations of mutant proteins needed to activate transcription at the glnAp2 promoter were three to four times lower than that of the wild-type NRI. The rate of phosphorylation of these proteins and the stability of mutant NRI phosphate were found to be similar to those of the wild-type NRI. In one of the mutants, the site of the mutation was localized in the DNA region specifying the central domain of NRI. Images

Mutations in the glnG gene of Escherichia coli that result in increased activity of nitrogen regulator I.

We purified the product of glnL (ntrB), NRII, and the product of a mutant glnL allele, NRII2302. In vitro transcription of the nitrogen-regulated promoter glnAp2 by purified components of Escherichia coli required NRII or NRII2302 when the template DNA was linear.

Purification of nitrogen regulator II, the product of the glnL (ntrB) gene of Escherichia coli.

We identified the portion of the glnALG operon that contains the promoter and operator of the glnLG suboperon and showed that the product of glnG represses transcription initiated at glnLp.

Shizue Ueno-Nishio

Papers

Collapse of Gels in an Electric Field

Identification and regulation of the glnL operator-promoter of the complex glnALG operon of Escherichia coli.

Mutations in the glnG gene of Escherichia coli that result in increased activity of nitrogen regulator I.

Purification of nitrogen regulator II, the product of the glnL (ntrB) gene of Escherichia coli.

Regulation at the glnL-Operator-Promoter of the Complex glnALG Operon of Escherichia coli