Micron‐scale anisometric microgels have received increasing attention to replace macromolecule solutions to create injectable 3D regenerative hydrogels. Interlinking these rod‐shaped microgels ...results in microporous constructs, while incorporating magnetic nanoparticles inside the microgels enables their alignment to introduce directionality. This report demonstrates that the angle of microgel alignment in a static external magnetic field can be pre‐programmed, broadening their applicability to artificially assemble into specific architectures. The magnetic rod‐shaped polyethylene glycol microgels are prepared via in mold polymerization. Ellipsoidal maghemite nanoparticles, integrated as responsive fillers are pre‐aligned either parallel or orthogonal to the long axis of the microgel with a weak magnetic field during rod fabrication to implement additional control over their magnetic orientation and allow their precise manipulation and actuation. The magnetic response of the microgels to static and rotating magnetic fields is discussed depending on various process and design parameters, such as magnetic field strength, angular frequency, and pre‐alignment. Finally, the applicability of the approach for tissue engineering is highlighted by growing mouse fibroblasts in three dimensions within Anisogels, i. e., hydrogels containing a mixture of rods with both a parallel and orthogonal orientation, marking a new step toward more advanced functional cell templating for tissue engineering.
Magnetic micrometric rod‐shaped microgels prepared via in mold polymerization are magnetically pre‐programmed using pre‐aligned anisometric maghemite as fillers. Depending on pre‐alignment conditions, the microgel rods can either align parallel or perpendicular to the applied magnetic field. When embedded in Anisogels for cell culture, cell growth can be directed in three dimensions using mixtures of these pre‐programmed microgel rods.
1D fibers of Bombyx mori silk fibroin (SF) and poly(l‐lactide) (SF‐s‐PLLA) with side‐by‐side parallel arrangement of the two components in a single fiber made by electrospinning are presented. The ...side‐by‐side arrangement in both randomly oriented and aligned two‐in‐one fibers was confirmed by scanning electron and confocal laser scanning microscope studies. The molecular orientation and secondary structure of SF and PLLA were dependent on the fiber alignment and annealing conditions. The two sides retained their individual secondary structure before and after annealing without affecting each other in a significant way. The two‐in‐one fibers after post treatment with methanol and heat at 80 °C showed tensile strength 16.5 ± 1.4 MPa, modulus 205 ± 20.6 MPa, and an elongation at break of 53 ± 8%.
Special 1D bio‐composite ductile fibers of silk fibroin and poly(l‐lactide) with side‐by‐side wrap‐up morphology are made by bicomponent electrospinning. Both sides retain their individual secondary structure before and after annealing making them available in future for post‐spinning modifications and applications such as compatibilizers, scaffolds for co‐culture of different cells, and drug carrier with dual release‐profile.
A novel strategy to generate adhesive protein analogues by enzyme‐induced polymerization of peptides is reported. Peptide polymerization relies on tyrosinase oxidation of tyrosine residues to ...Dopaquinones, which rapidly form cysteinyldopa‐moieties with free thiols from cysteine residues, thereby linking unimers and generating adhesive polymers. The resulting artificial protein analogues show strong adsorption to different surfaces, even resisting hypersaline conditions. Remarkable adhesion energies of up to 10.9 mJ m−2 are found in single adhesion events and average values are superior to those reported for mussel foot proteins that constitute the gluing interfaces.
Mussel glue protein mimics: Adhesive mussel‐inspired protein analogues were prepared by an enzyme‐induced polymerization of oligopeptides. The polymers are generated by the formation of cysteinyldopa linkages that contribute to cohesion and adhesion of the protein analogues. Aspects of adhesion properties of mussel foot proteins were mimicked without the need to extract and purify or express native proteins.
Hydrogels based on poly(N-isopropylacrylamide) (pNIPAAm) exhibit a thermo-reversible volume phase transition from swollen to deswollen states. This change of the hydrogel volume is accompanied by ...changes of the hydrogel elastic and Young’s moduli and of the hydrogel interfacial interactions. To decouple these parameters from one another, we present a class of submillimeter sized hydrogel particles that consist of a thermosensitive pNIPAAm core wrapped by a nonthermosensitive polyacrylamide (pAAm) shell, each templated by droplet-based microfluidics. When the microgel core deswells upon increase of the temperature to above 34 °C, the shell is stretched and dragged to follow this deswelling into the microgel interior, resulting in an increase of the microgel surficial Young’s modulus. However, as the surface interactions of the pAAm shell are independent of temperature at around 34 °C, they do not considerably change during the pNIPAAm-core volume phase transition. This feature makes these core–shell microgels a promising platform to be used as building blocks to assemble soft materials with rationally and independently tunable mechanics.
Mechanically Defined Microgels by Droplet Microfluidics Heida, Thomas; Neubauer, Jens W.; Seuss, Maximilian ...
Macromolecular chemistry and physics,
January 2017, 2017-01-00, 20170101, Volume:
218, Issue:
2
Journal Article
Peer reviewed
Over the last two decades, droplet‐based microfluidics has evolved into a versatile tool for fabricating tailored micrometer‐sized hydrogel particles. Combining precise fluid handling down to ...femtoliter scale with diverse hydrogel precursor design, it allows for excellent control over microgel size and shape, but also functionalization and crosslinking density. Consequently, it is possible to tune physicochemical and mechanical properties such as swelling, degradation, stimuli sensitivity, and elasticity by microfluidic droplet templates. This has led to a recent trend in applying microgels as experimental platform in cell culturing, drug delivery, sensing, and tissue engineering. This article highlights advances in microfluidic droplet formation as templates for microgels with tailored physicochemical properties. Special focus is put on evolving design strategies for the synthesis of mechanically defined microgels, their applications, and methods for mechanical characterization on single‐particle level.
Microfluidic emulsion formation combined with hydrogel design via droplet templates has greatly advanced the application of microgels in cell culturing, sensing and actuation. On that account, exact knowledge and control over physicochemical and mechanical properties is crucial. We discuss recent progress in droplet microfluidics‐based design of mechanically defined microgels, their latest applications and characterization methods on single‐particle level.
We investigate the formation of chains of few plasmonic nanoparticlesso-called plasmonic oligomersby strain-induced fragmentation of linear particle assemblies. Detailed investigations of the ...fragmentation process are conducted by in situ atomic force microscopy and UV–vis–NIR spectroscopy. Based on these experimental results and mechanical simulations computed by the lattice spring model, we propose a formation mechanism that explains the observed decrease of chain polydispersity upon increasing strain and provides experimental guidelines for tailoring chain length distribution. By evaluation of the strain-dependent optical properties, we find a reversible, nonlinear shift of the dominant plasmonic resonance. We could quantitatively explain this feature based on simulations using generalized multiparticle Mie theory (GMMT). Both optical and morphological characterization show that the unstrained sample is dominated by chains with a length above the so-called infinite chain limitabove which optical properties show no dependency on chain lengthwhile during deformation, the average chain length decrease below this limit and chain length distribution becomes more narrow. Since the formation mechanism results in a well-defined, parallel orientation of the oligomers on macroscopic areas, the effect of finite chain length can be studied even using conventional UV–vis–NIR spectroscopy. The scalable fabrication of oriented, linear plasmonic oligomers opens up additional opportunities for strain-dependent optical devices and mechanoplasmonic sensing.
We introduce a novel concept for mechanosensitive hydrogel microparticles, which translate deformation into changes in fluorescence and can thus function as mechanical probes. The hydrogel particles ...with controlled polymer network are produced via droplet microfluidics from poly(ethylene glycol) (PEG) precursors. Förster resonance energy transfer donors and acceptors are coupled to the PEG hydrogel network for reporting local deformations as fluorescence shifts. We show that global network deformations, which occur upon drying/rehydration, can be detected via a characteristic fluorescence shift. Combined characterization with confocal laser scanning microscopy and atomic force microscopy (AFM) shows that also local deformation of the particles can be detected. Using AFM, the mechanical properties of the particles can be quantified, which allows linking strain with stress and thus force sensing in a three-dimensional environment. Microfluidic material design allows for precisely varying the size of our hydrogel microparticles as well as their mechanical properties and polymer network structure with regard to the choice of the macromolecular precursors and their functionalization with fluorophores. Thus, concomitant changes in mechanical properties and mechanosensitivity qualify these hydrogel microparticles as an adjustable material platform for force sensing in structural mechanics or cell culturing.
Nature suggests that complex materials result from a hierarchical organization of matter at different length scales. At the nano- and micrometer scale, macromolecules and supramolecular aggregates ...spontaneously assemble into supracolloidal structures whose complexity is given by the coexistence of various colloidal entities and the specific interactions between them. Here, we demonstrate how such control can be implemented by engineering specially customized bile salt derivative-based supramolecular tubules that exhibit a highly specific interaction with polymeric microgel spheres at their extremities thanks to their scroll-like structure. This design allows for hierarchical supracolloidal self-assembly of microgels and supramolecular scrolls into a regular framework of “nodes” and “linkers”. The supramolecular assembly into scrolls can be triggered by pH and temperature, thereby providing the whole supracolloidal system with interesting stimuli-responsive properties. A colloidal smart assembly is embodied with features of center-linker frameworks as those found in molecular metal–organic frameworks and in structures engineered at human scale, masterfully represented by the Atomium in Bruxelles.
Graphene oxide samples prepared in various laboratories following a diversity of synthesis protocols based on Brodie's (BGO) and Hummers/Offeman's (HGO) methods were compared in respect of their ...in-plane moduli. A simple wrinkling method allowed for a spatial resolution <1.5 μm by converting the wrinkling frequency. Quite surprisingly, a drastic variation of the in-plane moduli was found spanning the range from 600 GPa for the best BGO types, which is in the region of chemically derived graphene, all the way down to less than 200 GPa for HGO types. This would suggest that there are no two equal GO samples and GO should not be regarded a compound but rather a class of materials with very variable physical properties. While large differences between Brodie's and Hummers/Offeman's types might have been expected, even within the group of Hummers/Offeman's types pronounced differences are observed that, based on 13C solid-state NMR, were related to over-functionalization versus over-oxidation.
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Mechanical properties of hydrogel particles are of importance for their interactions with cells or tissue, apart from their relevance to other applications. While so far the majority of works aiming ...at tuning particle mechanics relied on chemical cross-linking, we report a novel approach using inwards interweaving self-assembly of poly(allylamine) (PA) and poly(styrenesulfonic acid) (PSSA) on agarose gel beads. Using this technique, shell thicknesses up to tens of micrometers can be achieved from single-polymer incubations and accurately controlled by varying the polymer concentration or incubation period. We quantified the changes in mechanical properties of hydrogel core–shell particles. The effective elastic modulus of core–shell particles was determined from force spectroscopy measurements using the colloidal probe-AFM (CP-AFM) technique. By varying the shell thickness between 10 and 24 μm, the elastic modulus of particles can be tuned in the range of 10–190 kPa and further increased by increasing the layer number. Through fluorescence quantitative measurements, the polymeric shell density was found to increase together with shell thickness and layer number, hence establishing a positive correlation between elastic modulus and shell density of core–shell particles. This is a valuable method for constructing multidensity or single-density shells of tunable thickness and is particularly important in mechanobiology as studies have reported enhanced cellular uptake of particles in the low-kilopascal range (<140 kPa). We anticipate that our results will provide the first steps toward the rational design of core–shell particles for the separation of biomolecules or systemic study of stiffness-dependent cellular uptake.
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