Abstract Separation of equally sized particles distinguished solely by material properties remains still a very challenging task. Here a simple separation of differently charged, thermo‐responsive polymeric particles (for example microgels) but equal in size, via the combination of pressure‐driven microfluidic flow and precise temperature control is proposed. The separation principle relies on forcing thermo‐responsive microgels to undergo the volume phase transition during heating and therefore changing its size and correspondingly the change in drift along a pressure driven shear flow. Different thermo‐responsive particle types such as different grades of ionizable groups inside the polymer matrix have different temperature regions of volume phase transition temperature (VPTT). This enables selective control of collapsed versus swollen microgels, and accordingly, this physical principle provides a simple method for fractioning a binary mixture with at least one thermo‐responsive particle, which is achieved by elution times in the sense of particle chromatography. The concepts are visualized in experimental studies, with an intend to improve the purification strategy of the broad distribution of charged microgels into fractioning to more narrow distribution microgels distinguished solely by slight differences in net charge.
Abstract In pH‐responsive drug carriers, the distribution of charges has been proven to affect delivery efficiency but is difficult to control and verify. Herein, we fabricate polyampholyte nanogel‐in‐microgel colloids (NiM−C) and show that the arrangement of the nanogels (NG) can easily be manipulated by adapting synthesis conditions. Positively and negatively charged pH‐responsive NG are synthesized by precipitation polymerization and labelled with different fluorescent dyes. The obtained NG are integrated into microgel (MG) networks by subsequent inverse emulsion polymerization in droplet‐based microfluidics. By confocal laser scanning microscopy (CLSM), we verify that depending on NG concentration, pH value and ionic strength, NiM−C with different NG arrangements are obtained, including Janus‐like phase‐separation of NG, statistical distribution of NG, and core–shell arrangements. Our approach is a major step towards uptake and release of oppositely charged (drug) molecules.
Hydrogels, as well as colloidal hydrogels (microgels), are important materials for a large variety of applications in the biomedical field. Microgels with a controlled pore size (meso- and macropores) are required for efficient nutrient support, modulation of cell adhesion, removal of metabolic products in cell cultures, and probiotic loading. Common microgel fabrication techniques do not provide sufficient control over pore sizes and geometry. In this work, the natural polysaccharide dextran modified with methacrylate groups is used to synthesize highly monodisperse meso- and macroporous microgels in a size range of 100-150 µm via photo cross-linking in microfluidic droplets. The size of mesopores is varied by the concentration of dextran methacrylate chains in the droplets (50-200 g L-1 ) and the size of macropores is regulated by the integration of pH-degradable supramacromolecular nanogels with diameters of 300 and 700 nm as sacrificial templates. Using permeability assays combined with confocal laser scanning microscopy, it is demonstrated that functional dextran-based microgels with uniform and defined pores could be obtained.
Abstract Mechanochemical activations in Rh III ‐ and Au I ‐catalyzed C−H alkynylations lead selectively to C 2 ‐ and C 3 ‐alkynylated indoles. The processes show excellent functional group tolerance, do not require additional heating and proceed under solventless conditions. Compared to solvent‐based standard protocols, the reaction times are shorter and the catalyst quantities lower resulting in high product yields under ambient atmosphere in mixer mills.
Abstract Die Verteilung von Ladungen innerhalb pH‐responsiver Wirkstoffträger beeinflusst nachweislich die Effizienz der Freisetzung, ist aber schwer zu kontrollieren und zu verifizieren. Wir stellen nun polyampholytische Nanogel‐in‐Mikrogel Kolloide (NiM−C) vor und zeigen, dass die Anordnung der Nanogele (NG) abhängig von den Synthesebedingungen ist. Dazu wurden pH‐responsive Polyelektrolyt‐NG durch Fällungspolymerisation synthetisiert und mit Fluoreszenzfarbstoffen markiert. Die NG wurden dann durch inverse Emulsionspolymerisation mittels tropfenbasierter Mikrofluidik in Mikrogel‐Netzwerke (MG) integriert. Mit konfokaler Laser‐Scanning‐Mikroskopie (CLSM) wurde nachgewiesen, dass, je nach NG‐Konzentration, pH‐Wert und Ionenstärke, NiM−C mit unterschiedlichen NG‐Anordnungen, wie Janus‐artiger Phasentrennung, statistischer Verteilung und Kern‐Schale‐Architektur, erhalten werden. Unser Ansatz ist ein Meilenstein auf dem Weg zum simultanen Transport entgegengesetzt geladener Moleküle.
Abstract Temperature‐responsive microgels find widespread applications as soft materials for designing actuators in microfluidic systems, as carriers for drug delivery or catalysts, as functional coatings, and as adaptable sensors. The key property is their volume phase transition temperature, which allows for thermally induced reversible swelling/deswelling. It is determined by the gel's chemical structure as well as network topology and cannot be varied easily within one system. Here a paradigm change of this notion by facilitating a light‐triggered reversible switching of the microgel volume in the range between 32 and 82 °C is suggested. Photo‐sensitivity is introduced by photosensitive azobenzene containing surfactant, which forms a complex with microgels consisting of poly(N‐isopropylacrylamide‐co‐acrylic acid) (PNIPAM‐AAc) chains when assuming a hydrophobic trans‐state, and prefers to leave the gel matrix in its cis‐state. Using a similar strategy, it is demonstrated that at a fixed temperature, for example, 37 °C, one can reversibly change the microgel radius by a factor of 3 (7–21 µm) by irradiating either with UV (collapsed state) or green light (swollen state). It is envisaged that the possibility to deploy a swift external means of adapting the swelling behavior of microgels may impact and redefine the latter's application across all fields.
We demonstrate a novel method to synthesize aqueous microgels with supramolecular redox-cleavable crosslinks. The redox-cleavable crosslinker was synthesized on the basis of host–guest interactions using methacrylate-modified β-cyclodextrin (host) and vinylferrocene (guest). A series of microgels with variable contents of a redox-cleavable crosslinker were synthesized via precipitation polymerization. Synthesized supramolecular microgels exhibit hydrodynamic radii in the size range 100–200 nm in the swollen state at 20 °C. The increase of the temperature induces a volume-phase transition, leading to the deswelling of microgels. This temperature-induced swelling/deswelling is completely reversible and does not lead to the degradation of microgels. Using the combination of characterization methods such as light scattering and electron microscopy, we demonstrate that the obtained microgels can be degraded using chemical oxidants (FeCl3 or H2O2) or oxidation during bulk electrolysis. The degradation rate was studied by tracing the hydrodynamic radius, scattering intensity, and turbidity as a function of time. Furthermore, we could also demonstrate efficient loading and release of anticancer drug (doxorubicin) with UV–vis spectroscopy.
We report on triggering of p(NIPAM-AA) microgels' photo-responsiveness by making complexes with a spiropyran (SP) containing surfactant. Being dissolved in water, the SP surfactant in its merocyanine state bears three charges, while irradiation with UV and vis light leads to the partial or complete reversal of the SP state. The complexation of the photo-responsive amphiphile with swollen anionic microgels results in charge compensation within the gel interior and as a consequence its size reduces and the volume phase transition temperature (VPTT) decreases down to 32 °C. Under irradiation the MC form photo-isomerizes to a ring closed SP state generating a more hydrophobic surfactant with one positive charge at the head. The increase in the hydrophobicity of the surfactant and thus of the interior of the gel results in the reversible size change of the microgel. We investigate the photo-responsivity of the microgel as a function of wavelength and irradiation intensity, as well as of surfactant concentration and charge density of the microgel. We show that the change in the size and VPTT of the microgels during irradiation occurs through a combination of two processes: heating of the solution during light absorption by the surfactant (more pronounced in the case of UV irradiation) and the change in the hydrophobicity of the surfactant.
