Reversible crosslinking density stimulated diffraction wavelength tuning of hydrogel-encapsulated crystalline colloidal arrays

The reversible variation in the observed stop band of a hydrogel-encapsulated crystalline colloidal array was achieved through the selective formation and destruction of -S-Pb-S- linkages within the hydrogel. A reversible 45 nm stop band shift could be achieved with a cyclical treatment of Pb(2+) and then dithiothreitol solution.     

Multiphase electropatterning of cells and biomaterials

Tissues formed by cells encapsulated in hydrogels have uses in biotechnology, cell-based assays, and tissue engineering. We have previously presented a 3D micropatterning technique that rapidly localizes live cells within hydrogels using dielectrophoretic (DEP) forces, and have demonstrated the ability to modulate tissue function through the control of microscale cell architecture. A limitation of this method is the requirement that a single biomaterial must simultaneously harbor biological properties that support cell survival and function and material properties that permit efficient dielectrophoretic patterning. Here, we resolve this issue by forming multiphase tissues consisting of microscale tissue sub-units in a 'local phase' biomaterial, which, in turn, are organized by DEP forces in a separate, mechanically supportive 'bulk phase' material. We first define the effects of medium conductivity on the speed and quality of DEP cell patterning. As a case study, we then produce multiphase tissues with microscale architecture that combine high local hydrogel conductivity for enhanced survival of sensitive liver progenitor cells with low bulk conductivity required for efficient DEP micropatterning. This approach enables an expanded range of studies examining the influence of 3D cellular architecture on diverse cell types, and in the future may improve the biological function of inhomogeneous tissues assembled from a variety of modular tissue sub-units.     

Diamagnetically trapped arrays of living cells above micromagnets

Cell arrays are of foremost importance for many applications in pharmaceutical research or fundamental biology. Although arraying techniques have been widely investigated for adherent cells, organization of cells in suspension has been rarely considered. The arraying of non-adherent cells using the diamagnetic repulsive force is presented. A planar arrangement of Jurkat cells is achieved at the microscale above high quality microfabricated permanent magnets with remanent magnetization of J(r)≈ 1 T, in the presence of a paramagnetic contrast agent. The cytotoxicity of three Gd based contrast agents, Gd-DOTA, Gd-BOPTA and Gd-HP-DO3A, is studied. Among them, Gd-HP-DO3A appears to be the most biocompatible toward Jurkat cells. In close agreement with analytical simulations, diamagnetically 'suspended' cells have been successfully arrayed above square and honeycomb-like micromagnet arrays, which act as a "diamagnetophobic" surface. Living cell trapping is achieved in a simple manner using concentrations of Gd-HP-DO3A as low as 1.5 mM.     

Photo- and thermochromic spirans

The mechanisms of the valence isomerization of 2H-pyrans and chromene were calculated by means of the MINDO/3 method. A correlation between the magnitude of the barrier of activation of the electrocyclic reaction and the differences in the energies of the bonds of the tautomeric forms was noted. A simple scheme that makes it possible to estimate the magnitude of the activation barrier of the thermochromic transformations of spiropyrans on the basis of quantum-chemical calculations by the Pariser-Parr-Pople (PPP) method is proposed.See [1] for Communication 16.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 172–177, February, 1988.The authors thank V. A. Lokshin and N. A. Voloshin for providing us with data on the barriers of thermochromic transformations of spiropyrans.     

Photo- and thermochromic spirans

New spiropyrans with -acceptor azomethine and ketovinyl substituents in the 8 position were synthesized using the functional possibilities of the carbonyl group. The structures of the compounds obtained and their photochromic properties in 2-propanol at –70°C were studied.For Communication 17 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 176–179, February, 1993.     

Photo- and Ionochromism of Benzoxazolyl-Substituted Spirobenzopyrans

8-Benzoxazolyl-6-formyl-substituted spirobenzopyrans with different acceptor groups in the 5'- position of the indoline moiety have been synthesized. Novel spiropyrans exhibit photochromic properties in an acetone solution at room temperature and form intensely colored complexes with heavy metal cations.     

Photo- and ionochromic properties of new spirobenzochromene-pyranoquinoline

A compound of the new spirobipyran-quinoline series possesses weakly pronounced photochromic properties at room temperature. Its interaction with Co²⁺, Ni²⁺, Zn²⁺ and Cd²⁺ ions leads to intensely colored complexes absorbing in the λ> 600 nm region, which is important for the study of biological objects. Up to three merocyanine molecules are capable of binding one metal ion, which is not typical for the previously studied indoline analogs.     

Photo- and thermochromic 2-amino-2H-chromenes

A number of N-aryl- and N-alkylimines of 2-hydroxy-5,6-benzocinnamaldehyde were synthesized. The cyclic 2-amino-2H-chromene structure in nonpolar solvents was established for them by IR, UV, and PMR spectroscopy. It is shown that the transition to polar solvents leads to the establishment of a tautomeric ring-chain equilibrium. The equilibrium thermal transformations and phototransformations of some N-aryl- and N-alkylimines were studied.Communication 12 from the series Photo- and Thermochromic Spirans. See [1] for Communication 11.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1035–1044, August, 1980.     

Photo- and Redox-Regulated Transmembrane Ion Transporters

Synthetic supramolecular ion transporters find applications as potential therapeutics and as tools for engineering functional membranes. Stimuli-responsive systems enable external control over transport, which is necessary for targeted activation. The Minireview provides an overview of current approaches to developing stimuli-responsive ion transport systems, including channels and mobile carriers, that can be controlled using photo or redox inputs.     

Recent Progress of Photo- and Radiation-Induced Ionic Polymerizations

Photoinduced ionic polymerizations of the monomers α-methylstyrene, cyclohexeneoxide, nitroethylene, and acrylonitrile were carried out in the presence of electron acceptor or donor molecules. These polymerizations are proved to be initiated by ions formed through the dissociation of the photoexcited electron donor-acceptor complex and to proceed by ionic mechanism.

The molecular weight distribution of the polymer and the light intensity dependency on the rate of polymerization indicate that free ionic and ion-pair propagations coexist in the cationic polymerization of α-methylstyrene.

Anionic polymerizations were observed for the nitroethylenetetrahydrofuran and acrylonitrile-dimethylformamide systems.

Radiation-induced cationic polymerizations of styrene and α-methylstyrene were found to proceed by free cationic propagation. The effect of added electron acceptors in these polymerizations was investigated.     

Photo- and Radiation Creep and Durability of Polymers

The creep behavior of polycarbonate, polycaproamide, and polystyrene samples upon simultaneous and successive irradiation by fast electrons and optical-frequency radiation (photo- and radiation impact) was studied. The action of visible light in conjunction with electrons or immediately after electron irradiation leads to a dramatic increase in the creep rate. The absorbed doses of the onset of polymer degradation upon photo- and radiation impact are about an order of magnitude lower than those for electron irradiation alone. Macroradicals and stable radiolytic products absorbing light in a longer wavelength spectral region as compared with the initial polymers are assumed to be responsible for the photo- and radiation creep and durability of the polymers.     

Highly sensitive electrochemical detection of living cells based on diamond microelectrode arrays

The new boron-doped nanocrystalline diamond microelectrode arrays (BNCD-MEAs) with 16 channels were designed to detect biological signals from some activated cancer cells. Upon recordings of the released H₂O₂ from cancer cells stimulated by ascorbic acid (AA), it can readily detect the reactive oxygen species (ROS) released from target cells, which will be helpful for the cancer cell recognition and also beneficial for further studying the cause of relevant disease.     

Three-dimensional microwell arrays for cell culture

We propose the concept of three-dimensional (3D) microwell arrays for cell culture applications and highlight the importance of oxygen diffusion through pores in all three dimensions to enhance cell viability.     

Microtable arrays for culture and isolation of cell colonies

Cell microarrays with culture sites composed of individually removable microstructures or micropallets have proven benefits for isolation of cells from a mixed population. The laser energy required to selectively remove these micropallets with attached cells from the array depends on the microstructure surface area in contact with the substrate. Laser energies sufficient to release micropallets greater than 100 μm resulted in loss of cell viability. A new three-dimensional culture site similar in appearance to a table was designed and fabricated using a simple process that relied on a differential sensitivity of two photoresists to UV-mediated photopolymerization. With this design, the larger culture area rests on four small supports to minimize the surface area in contact with the substrate. Microtables up to 250 × 250 μm were consistently released with single 10-μJ pulses to each of the four support structures. In contrast, microstructures with a 150 × 150-μm surface area in contact with the substrate could not be reliably released at pulse energies up to 212 μJ. Cassie–Baxter wetting is required to provide a barrier of air to localize and sequester cells to the culture sites. A second asset of the design was an increased retention of this air barrier under conditions of decreased surface tension and after prolonged culture of cells. The improved air retention was due to the hydrophobic cavity created beneath the table and above the substrate which entrapped air when an aqueous solution was added to the array. The microtables proved an efficient method for isolating colonies from the array with 100% of selected colonies competent to expand following release from the array.     

Photo-, thermally, and pH-responsive microgels

Microgels with photo-, thermally, and pH-responsive properties in aqueous suspension have been synthesized and characterized using dynamic light scattering and UV-visible spectroscopy. The new route involved first preparing poly(N-isopropylacrylamide) (PNIPAM)-allylamine copolymer microgels and a spiropyran photochrome (SP) bearing a carboxylic acid group. Then the functionalized spiropyran was coupled to the microgel via an amide bond. The dark-equilibrated gel particles feature spiropyran molecules in the polar, merocyanine form. After irradiation of visible light, the particle size becomes smaller because spiropyran changes to the relatively nonpolar, closed spiro form. The PNIPAM-SP microgels undergo a volume phase transition in water from a swollen state to a collapsed state with increasing temperature under all light conditions. However, the transition temperature range of the PNIPAM-SP is much broader than that for the PNIPAM without SP. The PNIPAM-SP microgels are monodisperse and self-assemble into a crystalline lattice while in suspension. The UV-visible spectra of an aqueous suspension of PNIPAM-SP microgel in the dark-adapted, merocyanine form showed both an absorption peak around 512 nm due to the merocyanine (giving a reddish color to the suspension) and two sharp peaks from Bragg diffraction of colloidal crystallites. Upon visible irradiation, the 512-nm band bleached significantly due to spiropyran photoisomerization. The spiropyran photoisomerization and accompanying color changes of the suspension were reversible upon alternating dark, UV, and visible light irradiation. Due to the residues of amine groups, the swelling capability of PNIPAM-SP microgels reduces as the pH value is changed from 7 to 10.     

Polyoxometalate-Based Compounds for Photo- and Electrocatalytic Applications

Photo/electrocatalysis of water (H₂O) splitting and CO₂ reduction reactions is a promising strategy to alleviate the energy crisis and excessive CO₂ emissions. For the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and CO₂ reduction reaction (CO₂RR) involved, the development of effective photo/electrocatalysts is critical to reduce the activation energy and accelerate the sluggish dynamics. Polyoxometalate (POM)-based compounds with tunable compositions and diverse structures are emerging as unique photo/electrocatalysts for these reactions as they offer unparalleled advantages such as outstanding solution and redox stability, quasi-semiconductor behaviour, etc. This Minireview provides a basic introduction related to photo/electrocatalytic HER, OER and CO₂RR, followed by the classification of pristine POM-based compounds toward different catalytic reactions. Recent breakthroughs in engineering POM-based compounds as efficient photo/electrocatalysts are highlighted. Finally, the advantages, challenges, strategies and outlooks of POM-based compounds on improving photo/electrocatalytic performance are discussed.     

A steady-state and flow-through cell for screen-printed eight-electrode arrays

An electrochemical cell has been developed enabling amperometric steady-state- and flow-injection measurements with screen-printed arrays consisting of eight working electrodes (Ø = 1 mm) arranged radially around a printed Ag/AgCl reference electrode in the centre. The cell contained a rotator, providing similar hydrodynamics over all the working electrodes in the array, which was manually centered under the rotator. The reproducibility of steady-state measurements with eight-electrode platinum or gold arrays in this cell was studied by measuring and comparing currents from ferricyanide reduction at each electrode in the array. It was found that the relative standard deviation (R.S.D.) for the currents at different electrodes on one array was below 5%. Similar R.S.D. was found if measurements were compared between several arrays. This indicates that manual insertion/positioning of the eight-electrode array in the cell and hydrodynamics at the electrodes provided measurement reproducibility similar to the reproducibility of manufacturing eight-electrode platinum or gold arrays by screen-printing. A comparative study was performed between screen-printed and through mask sprayed carbon arrays. It was found that the reproducibility of the sprayed arrays was similar to that of the platinum or gold screen-printed arrays, with R.S.D. values below 6% regarding the variation between electrodes within the same array and the variation between different arrays. To enable flow-injection measurements, a tube (0.4 mm inner diameter) was inserted into a hole drilled through the centre of the steady-state cell rotator. This construction made it possible to inject the solution into the cell through the tube (not rotating), while the rotator was spinning over the eight-electrode array. It was found that this combination of flow-injection and mixing by a rotator provided a uniform current response over the array electrodes and that, at optimum conditions, the R.S.D. values between the eight electrodes in the array were nearly the same as in case of the steady-state measurements, i.e., below 5%.     

High-density microfluidic arrays for cell cytotoxicity analysis

In this paper, we report on the development of a multilayer elastomeric microfluidic array platform for the high-throughput cell cytotoxicity screening of mammalian cell lines. Microfluidic channels in the platform for cell seeding are orthogonal to channels for toxin exposure, and within each channel intersection is a circular chamber with cell-trapping sieves. Integrated, pneumatically-actuated elastomeric valves within the device isolate the microchannel array within the device into parallel rows and columns for cell seeding and toxin exposure. As a demonstration of the multiplexing capability of the platform, a microfluidic array containing 576 chambers was used to screen three cell types (BALB/3T3, HeLa, and bovine endothelial cells) against a panel of five toxins (digitonin, saponin, CoCl(2), NiCl(2), acrolein). Evaluation of on-chip cell morphology and viability was carried out using fluorescence microscopy, with outcomes comparable to microtiter plate cytotoxicity assays. Using this scalable platform, cell seeding and toxin exposure can be carried out within a single microfluidic device in a multiplexed format, enabling high-density parallel cytotoxicity screening while minimizing reagent consumption.