Diapers to Thickeners and Pressure-Sensitive Adhesives: Recycling of Superabsorbers via UV Degradation.

Superabsorbers based on crosslinked sodium polyacrylate polymers cannot be easily recycled, resulting in 2 million tons of superabsorbers being landfilled or burned every year. A fast and efficient strategy to recycle superabsorbers would significantly alleviate environmental pollution and promote a sustainable use of these polymers. Herein, the rapid recycling of crosslinked sodium polyacrylate hydrogels based on their inherent UV degradation is demonstrated without the need for chemicals besides water. A quantitative conversion of crosslinked sodium polyacrylate into soluble sodium polyacrylate is achieved in minutes, almost 200 times faster than a previous approach based on de-esterification. The obtained soluble sodium polyacrylate can be used, for example, as a thickener for aqueous dyes or can be esterified with n-butanol or 2-ethylhexanol to serve as a pressure-sensitive adhesive. The UV photodegradation and esterification of superabsorbers is fast, scalable, safe, and economical and yields polymers with controllable molecular weight in the range of 100-400 kg/mol. It thus offers distinct advantages over the chemical de-crosslinking strategies presented previously.

Inverse Vulcanization of Norbornenylsilanes: Soluble Polymers with Controllable Molecular Properties via Siloxane Bonds.

The inverse vulcanization produces high sulfur content polymers from alkenes and elemental sulfur. Control over properties such as the molar mass or the solubility of polymers is not well established, and existing strategies lack predictability or require large variations of the composition. Systematic design principles are sought to allow for a targeted design of materials. Herein, we report on the inverse vulcanization of norbornenylsilanes (NBS), with a different number of hydrolysable groups at the silicon atom. Inverse vulcanization of mixtures of NBS followed by polycondensation yielded soluble high sulfur content copolymers (50 wt % S) with controllable weight average molar mass (MW ), polydispersity (D), glass transition temperature (TG ), or zero-shear viscosity (η0 ). Polycondensation was conducted in the melt with HCl as a catalyst, abolishing the need for a solvent. Purification by precipitation afforded polymers with a greatly reduced amount of low molar mass species.

A highly selective and sensitive electrochemical sensor for dopamine based on a functionalized multi-walled carbon nanotube and poly(N-methylaniline) composite.

Dopamine (DA) is an important neurotransmitter used for diagnosing various diseases from its abnormal concentrations in human fluids. Herein, an electrochemical sensor based on a composite of re-doped poly(N-methylaniline) (rePNMA) and modified multi-walled carbon nanotubes (fMWCNTs), termed fMWCNT-rePNMA, was developed to measure DA concentration. The successful modification of the fMWCNT surface was confirmed by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Cyclic voltammetry (CV) displayed an excellent electrocatalytic activity of the fMWCNTs-rePNMA composite towards the oxidation of DA. The developed fMWCNTs-rePNMA composite demonstrated a broad linear range from 5 to 90 µmol L-1 with a low limit of detection (LOD) value of 2.23 µmol L-1, and a fast response with a high sensitivity of 251.5 nA µmol-1 L as determined from the calibration curve of the DA determination. In addition, the fMWCNTs-rePNMA composite selectively identified and quantified DA in the presence of ascorbic acid (AA) and uric acid (UA). Therefore, the fMWCNTs-rePNMA composite sensor shows potential to determine the level of DA in human urine.

Miniaturized droplet microarray platform enables maintenance of human induced pluripotent stem cell pluripotency.

The capacity of human induced pluripotent stem cells (hiPSCs) for indefinite self-renewal warrants their application in disease modeling, drug discovery, toxicity assays and efficacy screening. However, their poor proliferation ability, inability to adhere to surfaces without Matrigel coating and tendency to spontaneously differentiate in vitro hinder the application of hiPSCs in these fields. Here we study the ability to culture hiPSCs inside 200 â€‹nL droplets on the droplet microarray (DMA) platform. We demonstrate that (1) hiPSCs can attach to the Matrigel (MG)-free surface of DMA and show good viability after 24 h culture; (2) hiPSC do not spontaneously differentiate when cultured on the MG-free surface of DMAs; (3) culturing of hiPSCs in 200 â€‹nL as compared to 2 â€‹mL culture leads to higher expression of the Nanog pluripotency marker. Overall, the results demonstrate the possibility to culture undifferentiated hiPSCs in 200 â€‹nL droplets on DMA, thereby opening the possibility for high-throughput screenings of hiPSCs with various factors without compromising the results through the involvement of animal-derived materials, such as Matrigel.

Liquid Wells as Self-Healing, Functional Analogues to Solid Vessels.

Liquids are traditionally handled and stored in solid vessels. Solid walls are not functional, adaptive, or self-repairing, and are difficult to remove and re-form. Liquid walls can overcome these limitations, but cannot form free-standing 3D walls. Herein, a liquid analogue of a well, termed a "liquid well" is introduced. Water tethered to a surface with hydrophobic-hydrophilic core-shell patterns forms stable liquid walls capable of containing another immiscible fluid, similar to fluid confinement by solid walls. Liquid wells with different liquids, volumes, and shapes are prepared and investigated by confocal and Raman microscopy. The confinement of various low-surface-tension liquids (LSTLs) on surfaces by liquid wells can compete with or be complementary to existing confinement strategies using perfluorinated surfaces, for example, in terms of the shape and height of the confined LSTLs. Liquid wells show unique properties arising from their liquid aggregate state: they are self-healing, dynamic, and functional, that is, not restricted to a passive confining role. Water walls can be easily removed and re-formed, making them interesting as sacrificial templates. This is demonstrated in a process termed water-templated polymerization (WTP). Numerical phase-field model simulations are performed to scrutinize the conditions required for the formation of stable liquid wells.

Inverse Vulcanization of Styrylethyltrimethoxysilane-Coated Surfaces, Particles, and Crosslinked Materials.

Sulfur as a side product of natural gas and oil refining is an underused resource. Converting landfilled sulfur waste into materials merges the ecological imperative of resource efficiency with economic considerations. A strategy to convert sulfur into polymeric materials is the inverse vulcanization reaction of sulfur with alkenes. However, the materials formed are of limited applicability, because they need to be cured at high temperatures (>130 °C) for many hours. Herein, we report the reaction of elemental sulfur with styrylethyltrimethoxysilane. Marrying the inverse vulcanization and silane chemistry yielded high sulfur content polysilanes, which could be cured via room temperature polycondensation to obtain coated surfaces, particles, and crosslinked materials. The polycondensation was triggered by hydrolysis of poly(sulfur-r-styrylethyltrimethoxysilane) (poly(Sn -r-StyTMS) under mild conditions (HCl, pH 4). For the first time, an inverse vulcanization polymer could be conveniently coated and mildly cured via post-polycondensation. Silica microparticles coated with the high sulfur content polymer could improve their Hg2+ ion remediation capability.

Design and Applications of Photoresponsive Hydrogels.

Hydrogels are the most relevant biochemical scaffold due to their tunable properties, inherent biocompatibility, and similarity with tissue and cell environments. Over the past decade, hydrogels have developed from static materials to "smart" responsive materials adapting to various stimuli, such as pH, temperature, chemical, electrical, or light. Light stimulation is particularly interesting for many applications because of the capability of contact-free remote manipulation of biomaterial properties and inherent spatial and temporal control. Moreover, light can be finely adjusted in its intrinsic properties, such as wavelength and intensity (i.e., the energy of an individual photon as well as the number of photons over time). Water is almost transparent for light in the photochemically relevant range (NIR-UV), thus hydrogels are well-suited scaffolds for light-responsive functionality. Hydrogels' chemical and physical variety combined with light responsiveness makes photoresponsive hydrogels ideal candidates for applications in several fields, ranging from biomaterials, medicine to soft robotics. Herein, the progress and new developments in the field of light-responsive hydrogels are elaborated by first introducing the relevant photochemistries before discussing selected applications in detail.