The effect of urea on the phase transition of PNIPAM was studied using differential scanning calorimetry (DSC). For a certain urea concentration, the enthalpy change of phase transition of poly(N-isopropylacrylamide) (PNIPAM) aqueous solution increases with the number of DSC cycles, presumably due to the displacement of water molecules bound to the amide groups of PNIPAM by urea molecules at the temperature higher than the lower critical solution temperature (LCST) of PNIPAM and causes the decrease in the absolute value of the exothermic heat related to the dehydration of hydrophilic groups and interactions of hydrophilic residues to around 0. Moreover, the enthalpy change decreases with the urea concentration during the heating process of the first DSC cycle, indicating the replacement of water molecules around the apolar isopropyl groups by urea molecules at the temperature lower than LCST, and the endothermic heat caused by the dehydration of apolar groups decreases. Furthermore, the urea molecules which replace the water molecules at high temperature can be replaced again by water molecules at the temperature lower than LCST, but this process needs several days to complete.

Fluorescent carbon dots (CDs) have been increasingly used in fluorescence detection and imaging based on their tunable fluorescence (FL) and resistance to photobleaching. However, the fast and reliable design of fluorescent CDs with specific optical properties involves a number of factors, such as the concentration of precursors, reaction time, and solvents. Therefore, it is usually considered difficult to design CDs with favorable optical properties. Herein, we report an extreme gradient boosting (XGBoost) model for guiding the fabrication of CDs with high FL intensity and tunable emission from p-benzoquinone (PBQ) and ethylenediamine (EDA) in different solvents at room temperature. Among a variety of studied machine learning models, XGBoost shows the best performance in the field of material synthesis, with a prediction coefficient of determination (R 2) higher than 0.96. The XGBoost model can effectively predict the optical properties of CDs, including the maximum FL intensity and emission centers. Guided by the XGBoost model, various green or blue fluorescent CDs with adjustable emission centers and solubility properties are designed and fabricated accurately. These CDs are successfully applied for Fe3+ detection, sustained drug release, whole-cell imaging, and poly­(vinyl alcohol) (PVA) film preparation. These results suggest the great potential of the combination of machine learning and CD synthesis as an effective strategy to help researchers realize accurate selection of reasonable CDs with individual customized properties to achieve different goals.

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Cell polarization exists in a variety of tissues to regulate cell behaviors and functions. Space constraint (spatially limiting cell extension) and adhesion induction (guiding adhesome growth) are two main ways to induce cell polarization according to the microenvironment topographies. However, the mechanism of cell polarization induced by these two ways and the downstream effects on cell functions are yet to be understood. Here, space constraint and adhesion induction guiding cell polarization are achieved by substrate groove arrays in micro and nano size, respectively. Although the morphology of polarized cells is similar on both structures, the signaling pathways to induce the cell polarization and the downstream functions are distinctly different. The adhesion induction (nano‐groove) leads to the formation of focal adhesions and activates the RhoA/ROCK pathway to enhance the myosin‐based intracellular force, while the space constraint (micro‐groove) only activates the formation of pseudopodia. The enhanced intracellular force caused by adhesion induction inhibits the chromatin condensation, which promotes the osteogenic differentiation of stem cells. This study presents an overview of cell polarization and mechanosensing at biointerface to aid in the design of novel biomaterials.

The combination of high desalination efficiency, negligible draw-solute leakage, nontoxicity, ease of regeneration, and effective separation to produce liquid water makes the smart draw agents developed here highly suited for forward-osmosis desalination.

The theory and practice of thermal field-flow fractionation (thermal FFF) as a tool for characterizing the molecular weight distribution of polymers are reviewed and a number of advantages with respect to size exclusion chromatography (SEC or GPC) are summarized. Retention values are measured and tabulated for linear polystyrenes in THF in the molecular weight range 5.1 X 104 to 20.6 X 106. For calibration purposes, it is shown that a plot of the logarithm of the product of retention parameter X and temperature drop AT vs. the logarithm of molecular weight is linear for this entire experimental range with a slope of -0.53. To demonstrate fractionation and the absence of shear degradation in the higher molecular weight range, a fraction was cut from the 20.6M peak, reinjected, and observed to elute as a narrow peak centered near the position of the cut. Calculations based on nonequilibrium theory show that column band broadening for a 20.6M peak eluted at AT = 8 °C contributes only about 10% to the plate height, the remainder arising from the fractionation of the molecular weight distribution. Thus a molecular weight distribution curve was obtained. We found the latter to be characterized by Mw/Mn s 1.52. We conclude that thermal FFF is applicable to ultrahigh molecular weight polymers but that other FFF subtechniques, especially flow FFF and sedimentation FFF, may also work in this molecular weight range.

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