Preparation of Gradient Surfaces by Using a Simple Chemical Reaction and Investigation of Cell Adhesion on a Two‐Component Gradient

This article describes a simple method for the generation of multicomponent gradient surfaces on self‐assembled monolayers (SAMs) on gold in a precise and predictable manner, by harnessing a chemical reaction on the monolayer, and their applications. A quinone derivative on a monolayer was converted to an amine through spontaneous intramolecular cyclization following first‐order reaction kinetics. An amine gradient on the surface on a scale of centimeters was realized by modulating the exposure time of the quinone‐presenting monolayer to the chemical reagent. The resulting amine was used as a chemical handle to attach various molecules to the monolayer with formation of multicomponent gradient surfaces. The effectiveness of this strategy was verified by cyclic voltammetry (CV), matrix assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) mass spectrometry (MS), MS imaging, and contact‐angle measurements. As a practical application, cell adhesion was investigated on RGD/PHSRN peptide/peptide gradient surfaces. Peptide PHSRN was found to synergistically enhance cell adhesion at the position where these two ligands are presented in equal amounts, while these peptide ligands were competitively involved in cell adhesion at other positions. This strategy of generating a gradient may be further expandable to the development of functional gradient surfaces of various molecules and materials, such as DNA, proteins, growth factors, and nanoparticles, and could therefore be useful in many fields of research and practical applications.     

Mass Spectrometry Assisted Lithography for the Patterning of Cell Adhesion Ligands on Self‐Assembled Monolayers

Pattern of events : A simple and flexible method has been developed for patterning cell adhesion ligands. Locally erasing self‐assembled monolayers with tri(ethyleneglycol) groups on a gold substrate by using a MALDI‐TOF MS nitrogen laser and filling the exposed gold surface with an alkanethiol presenting carboxylic acid groups enables subsequent immobilization of maleimide and a cell adhesion peptide, which can then recognize cells (see scheme).

     

Regulation of Protein Activity and Cellular Functions Mediated by Molecularly Evolved Nucleic Acids

Regulation of protein activity is essential for revealing the molecular mechanisms of biological processes. DNA and RNA achieve many uniquely efficient functions, such as genetic expression and regulation. The chemical capability to synthesize artificial nucleotides can expand the chemical space of nucleic acid libraries and further increase the functional diversity of nucleic acids. Herein, a versatile method has been developed for modular expansion of the chemical space of nucleic acid libraries, thus enabling the generation of aptamers able to regulate protein activity. Specifically, an aptamer that targets integrin alpha3 was identified and this aptamer can inhibit cell adhesion and migration. Overall, this chemical‐design‐assisted in vitro selection approach enables the generation of functional nucleic acids for elucidating the molecular basis of biological activities and uncovering a novel basis for the rational design of new protein‐inhibitor pharmaceuticals.     

Development of a new method for sulfide determination by vapor generator–inductively coupled plasma–mass spectrometry

A new sensitive methodology for the determination of total reduced sulfur species in natural waters and acid volatile sulfides in sediments at low levels (μg L^− 1) is described. Reduced sulfur species were separated from the water matrix in the form of H₂S after reaction with hydrochloric acid in a commercial vapor generator coupled to an inductively coupled plasma quadrupole mass spectrometer (VG–ICP–QMS) equipped with a reaction cell. The method avoided the effect of polyatomic isobaric interferences at m/z 32 caused by ¹⁶O¹⁶O⁺ and ¹⁴N¹⁸O⁺ through the elimination of the aqueous matrix, a source of oxygen. By introducing a mixture of helium and hydrogen gases into the octopole reaction cell, a series of ion-molecule reactions were induced to reduce the interfering polyatomic species. Operating conditions of the octopole reaction cell system and the analyzer were optimized to get the best signal to background ratio for ³²S; a full factorial 2³ experimental design was developed in order to evaluate which variables had a significant effect and a simplex methodology was applied to find the optimum conditions for the variables. The new method was evaluated by comparison to the standard potentiometric method. The analytical methodology developed was applied to the analysis of reduced sulfur species in natural waters and acid volatile sulfides in sea sediments.     

Using an electrical potential to reversibly switch surfaces between two states for dynamically controlling cell adhesion

Smart surfaces presenting both antifouling molecules with a charged functional group at their distal end, and molecules that are terminated by RGD peptides for cell adhesion, were fabricated and characterized (see picture). By applying potentials of +300 or -300?mV, the surfaces could be dynamically switched to make the peptide accessible or inaccessible to cells.     

Determination of ultratrace levels of dissolved metals in seawater by reaction cell inductively coupled plasma mass spectrometry after ammonia induced magnesium hydroxide coprecipitation

A method for the determination of ultratrace amounts of Cr, Fe, Mn, Pb and Zn in seawater has been developed. It combined the low-blank magnesium hydroxide coprecipitation procedure with quadrupole inductively coupled plasma mass spectrometry and used the dynamic reaction cell technique to resolve the polyatomic interferences arising from the residual matrix, the solvent and plasma gases. Detection limits (3σ_B, n = 10) for Cr, Fe, Mn, Pb and Zn were 0.02, 0.10, 0.01, 0.002 and 0.19 nM, respectively, using 50 mL of seawater sample. The accuracy of the analytical procedure was verified by the analysis of the seawater reference materials CASS-4, NASS-5, SAFe D2 and SAFe S. The analytical precision ranged from 3% to 16% (n = 6), with a sample throughput of about 6 samples h⁻¹.     

Switchable phase transition behavior of thermoresponsive substrates for cell sheet engineering

Recently, there are significant interests in the development of biomaterials with nonlinear response to an external stimulus. Thermoresponsive polymers as a well-known class of stimuli-responsive materials represent reversible hydrophilicity/hydrophobicity characteristics around a critical temperature. This switchable behavior applies for nondestructive cellular detachment from cultivation substrates. In this study, poly (N-isopropylacrylamide) (PNIPAAm)-grafted dishes were made up to harvest retinal pigmented epithelial (RPE) and periodontal ligament cell (PDLC) sheets. Wettability assessments verified that all functionalized surfaces were inverted from hydrophilic to hydrophobic state when the temperature rises from lower critical solution temperature (LCST) at 37 °C. Other physicochemical characteristics such as chemical composition, grafting thickness, and surface topography were investigated through attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and atomic force microscopy (AFM). ATR-FTIR results showed typical peaks of amide group corresponding to successful PNIPAAm polymerization. AFM microscopy results also proved creating a rough PNIPAAm layer with thickness of 29.2 nm after grafting process in the mixture of methanol and water. Cell culture experiments showed an irreversible cellular attachment/detachment from modified surfaces upon temperature changes. These results introduced thermoresponsive TCPS to noninvasively harvest RPE and PDLCs sheets especially for application in scaffold-free tissue engineering decorations. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1567–1576