The chemistry of cross-linked polymeric vesicles and their functionalization towards biocatalytic nanoreactors

Self-assembly of amphiphilic block copolymers into polymersomes continues to be a hot topic in modern research on biomimetics. Their well-known and valued mechanical strength can be increased even further if they are cross-linked. These additional bonds prevent a collapse or disassembly of the polymersomes and open the way towards smart nanoreactors. A variety of chemistries have been applied to obtain the desired cross-linked polymersomes, and therefore, the chemical approaches performed over time will be highlighted in this mini-review. Due to the large number of studies, a selected set of photo-cross-linked and pH-sensitive polymersomes will be specifically highlighted. This system has proven to be a very potent candidate for the formation of nanoreactors and drug delivery systems, and even for the formation of functional multicompartment cell mimics. [Figure not available: see fulltext.]. © 2020, The Author(s)

Thermal annealing to influence the vapor sensing behavior of co-continuous poly(lactic acid)/polystyrene/multiwalled carbon nanotube composites

With the main purpose of being used as vapor leakage detector, the volatile organic compound (VOC) vapor sensing properties of conductive polymer blend composites were studied. Poly(lactic acid)/polystyrene/multi-walled carbon nanotube (PLA/PS/MWCNT) based conductive polymer composites (CPCs) in which the polymer components exhibit different interactions with the vapors, were prepared by melt mixing. CPCs with a blend composition of 50/50 wt% resulted in the finest co-continuous structure and selective MWCNT localization in PLA. Therefore, these composites were selected for sensor tests. Thermal annealing was applied aiming to maintain the blend structure but improving the sensing reversibility of CPC sensors towards high vapor concentrations. Different sensing protocols were applied using acetone (good solvent for PS and PLA) and cyclohexane (good solvent for PS but poor solvent for PLA) vapors. Increasing acetone vapor concentration resulted in increased relative resistance change (Rrel) of CPCs. Saturated cyclohexane vapor resulted in lower response than nearly saturated acetone vapor. The thermal annealing at 150 °C did not change the blend morphology but increased the PLA crystallinity, making the CPC sensors more resistant to vapor stimulation, resulting in lower Rrel but better reversibility after vapor exposure

Organic vapor sensing behavior of polycarbonate/polystyrene/multi-walled carbon nanotube blend composites with different microstructures

With the focus on the use as leakage detectors, the vapor sensing behavior of conductive polymer composites (CPCs) based on polycarbonate/polystyrene/multi-walled carbon nanotube (PC/PS/MWCNT) blends with different blend ratios was studied as well as their morphological and electrical properties. In the melt mixed blend composites, the MWCNTs are preferentially localized in PC. At the PC/PS ratio of 70/30 wt%, the composites showed a sea-island structure, while for blends containing 40 wt% or 50 wt% PS co-continuous structures were developed resulting in a reduction in the MWCNT percolation threshold. The saturated vapors of the selected solvents have good interactions to PS but different interactions to PC. At 0.75 wt% MWCNT, sea-island CPCs showed high relative resistance change (Rrel) but poor reversibility towards moderate vapors like ethyl acetate and toluene, while CPCs with co-continuous structure exhibited lower Rrel and better reversibility. All CPCs showed poor reversibility towards vapor of the good solvent dichloromethane due to strong interactions between polymers and vapor. In the vapor of the poor solvent cyclohexane, CPCs with higher PS content showed increased Rrel. After extraction of the PS component by cyclohexane, the sensing response was decreased and the Rrel of the co-continuous blend even reached negative values

Semi-Interpenetrating Polymer Networks Based on N-isopropylacrylamide and 2-acrylamido-2-methylpropane Sulfonic Acid for Intramolecular Force-Compensated Sensors

Stimulus-responsive hydrogels are swellable polymers that take up a specific volume depending on a measured variable present in solution. Hydrogel-based chemical sensors make use of this ability by converting the resulting swelling pressure, which depends on the measured variable, into an electrical value. Due to the tedious swelling processes, the measuring method of intramolecular force compensation is used to suppress these swelling processes and, thus, significantly increase the sensor's response time. However, intramolecular force compensation requires a bisensitive hydrogel. In addition to the sensitivity of the measured variable the gel has to provide a second sensitivity for intrinsic compensation of the swelling pressure. At the same time, this hydrogel has to meet further requirements, e.g. high compressive strength. Until now, interpenetrating polymer networks (IPN) have been used for such a force-compensatory effective hydrogel, which are complex to manufacture. In order to significantly simplify the sensor design and production, a simpler synthesis of the bisensitive hydrogel is desirable. This paper presents a new bisensitive hydrogel based on semi-interpenetrating polymer networks. It is based on a copolymer network consisting of N-isopropylacrylamide (NiPAAm) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and long PAMPS strands that permeate it. Measurements show, that this hydrogel meets all essential requirements for intramolecular force compensation and is at the same time much easier to synthesize than previously used IPN hydrogels. © 2021 The Author(s)

Melt-mixed PP/MWCNT composites: Influence of CNT incorporation strategy and matrix viscosity on filler dispersion and electrical resistivity

Small-scale melt mixing was performed for composites based on polypropylene (PP) and 0.5–7.5 wt % multiwalled carbon nanotubes (MWCNT) to determine if masterbatch (MB) dilution is a more effective form of nanofiller dispersion than direct nanotube incorporation. The methods were compared using composites of five different PP types, each filled with 2 wt % MWCNTs. After the determination of the specific mechanical energy (SME) input in the MB dilution process, the direct-incorporation mixing time was adjusted to achieve comparable SME values. Interestingly, the electrical resistivity of MB-prepared samples with 2 wt % MWCNTs was higher than that of those prepared using direct incorporation—despite their better dispersion—suggesting more pronounced MWCNT shortening in the two-step procedure. In summary, this study on PP suggests that the masterbatch approach is suitable for the dispersion of MWCNTs and holds advantages in nanotube dispersion, albeit at the cost of slightly increased electrical resistivity

Self-Replication of Deeply Buried Doped Silicon Structures, which Remotely Control the Etching Process: A New Method for Forming a Silicon Pattern from the Bottom Up

A typical microstructuring process utilizes photolithographic masks to create arbitrary patterns on silicon substrates in a top-down approach. Herein, a new, bottom-up microstructuring method is reported, which enables the patterning of n-doped silicon substrates to be performed without the need for application of etch-masks or stencils during the etching process. Instead, the structuring process developed herein involves a simple alkaline etching performed under illumination and is remotely controlled by the p-doped micro-sized implants, buried beneath a homogeneous n-doped layer at depths of 0.25 to 1 µm. The microstructuring is realized because the buried implants act upon illumination as micro-sized photovoltaic cells, which generate a flux of electrons and increase the negative surface charge in areas above the implants. The locally increased surface charge causes a local protection of the native silicon oxide layer from alkaline etching, which ultimately leads to the microstructuring of the substrate. In this way, substrates having at their top a thick layer of homogeneously n-doped silicon can be structured, reducing the need for costly, time-consuming photolithography steps. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH Gmb

Photo-Cross-Linked Dual-Responsive Hollow Capsules Mimicking Cell Membrane for Controllable Cargo Post-Encapsulation and Release

Multifunctional and responsive hollow capsules are ideal candidates to establish highly sophisticated compartments mimicking cell membranes for controllable bio-inspired functions. For this purpose pH and temperature dual-responsive and photo-cross-linked hollow capsules, based on silica-templated layer-by-layer approach by using poly(N-isopropyl acrylamide)-blockpolymethacrylate) and polyallylamine, have been prepared to use them for the subsequent and easily available post-encapsulation process of proteinlike macromolecules at room temperature and pH 7.4 and their controllable release triggered by stimuli. The uptake and release properties of the hollow capsules for cargos are highly affected by changes in the external stimuli temperature (25, 37, or 45 °C) and internal stimuli pH of the phosphate-containing buffer solution (5.5 or 7.4), by the degree of photo-cross-linking, and the size of cargo. The photo-cross-linked and dual stimuli-responsive hollow capsules with different membrane permeability can be considered as attractive material for mimicking cell functions triggered by controllable uptake and release of different up to 11 nm sized biomolecules

Dendrimere als vielseitige, nano-skalige Objekte für biomimetische, biomedizinische und katalytische Fragestellungen

With their three-dimensional macromolecular structure and shape, and with their tuneable properties in both the inner and outer spheres, dendrimers are ideal model compounds in the nanometre range between 1 and 10 nm. The possibility to combine different properties within one macromolecule destines them for use in various high-end research fields such as medicine, pharmacy, biology, supramolecular chemistry, nanotechnology and material sciences. On the basis of their high end-group density and a compact, highly branched molecular structure, dendrimers are successfully investigated as carrier systems for active substances and metal ions (e.g. contrast agents for the visualisation of blood vessels), as templates for metal nanoparticles, as artificial enzymes with defined functions, and as materials for catalysis.Dendrimere sind aufgrund ihrer dreidimensionalen Makromolekülstruktur und -form und ihrer steuerbaren Eigenschaften sowohl an der Oberfläche als auch im Molekülinneren ideale Modellverbindungen im Nanometerbereich – sie sind zwischen 1 und 10 nm groß –, die vorzugsweise in der Medizin, Pharmazie, Biologie, Supramolekularen Chemie, Nanotechnologie und den Materialwissenschaften eingesetzt werden. Aufgrund ihrer hohen Endgruppendichte und der kompakten, stark verzweigten Molekülform werden Dendrimere unter anderem als Trägermaterialien und Transportsysteme für Wirkstoffe und Metallionen, zum Beispiel als Kontrastmittel zur Visualisierung von Organen und Blutgefäßen, als Template für metallische Nanopartikel, zur Erzeugung künstlicher Enzymfunktionen und in der Katalyse erfolgreich untersucht