9 research outputs found
Recommended from our members
Polymerizing Like Mussels Do: Toward Synthetic Mussel Foot Proteins and Resistant Glues
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 10.9â
mJâmâ2 are found in single adhesion events and average values are superior to those reported for mussel foot proteins that constitute the gluing interfaces
CoreâShell Microgels with Switchable Elasticity at Constant Interfacial Interaction
Hydrogels
based on polyÂ(<i>N</i>-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 Youngâs
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 Youngâs
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 coreâshell microgels a promising platform to be
used as building blocks to assemble soft materials with rationally
and independently tunable mechanics
Tuning the Mechanical Properties of Hydrogel CoreâShell Particles by Inwards Interweaving Self-Assembly
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 polyÂ(allylamine)
(PA) and polyÂ(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 coreâshell
particles. The effective elastic modulus of coreâshell particles
was determined from force spectroscopy measurements using the colloidal
probe-AFM (CP-AFM) technique. By varying the shell thickness between
10 and 24 ÎŒm, the elastic modulus of particles can be tuned
in the range of 10â190 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 coreâshell 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 coreâshell
particles for the separation of biomolecules or systemic study of
stiffness-dependent cellular uptake
Supracolloidal Atomium
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 ânodesâ and âlinkersâ. 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 metalâorganic frameworks and in structures engineered at human scale, masterfully represented by the Atomium in Bruxelles
Macroscopic Strain-Induced Transition from Quasi-infinite Gold Nanoparticle Chains to Defined Plasmonic Oligomers
We
investigate the formation of chains of few plasmonic nanoparticlesîžso-called
plasmonic oligomersîžby strain-induced fragmentation of linear
particle assemblies. Detailed investigations of the fragmentation
process are conducted by <i>in situ</i> atomic force microscopy
and UVâvisâNIR 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 limitîžabove which optical
properties show no dependency on chain lengthîžwhile 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 UVâvisâNIR spectroscopy. The
scalable fabrication of oriented, linear plasmonic oligomers opens
up additional opportunities for strain-dependent optical devices and
mechanoplasmonic sensing
Systematic evaluation of different types of graphene oxide in respect to variations in their in-plane modulus
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 <1.5Â ?m by converting the wrinkling frequency. Quite surprisingly, a drastic variation of the in-plane moduli was found spanning the range from 600Â GPa for the best BGO types, which is in the region of chemically derived graphene, all the way down to less than 200Â 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