Oligo(ethylene glycol)-sidechain microgels prepared in absence of cross-linking agent: Polymerization, characterization and variation of particle deformability

Abstract

We present a systematic study of self-cross-linked microgels formed by precipitation polymerization of oligo ethylene glycol methacrylates. The cross-linking density of these microgels and, thus, the network flexibility can be easily tuned through the modulation of the reaction temperature during polymerization. Microgels prepared in absence of any difunctional monomer, i.e. cross-linker, show enhanced deformability and particle spreading on solid surfaces as compared to microgels cross-linked with varying amounts of poly(ethylene glycol diacrylate) (PEG-DA) in addition to self-crosslinking. Particles prepared at low reaction temperatures exhibit the highest degree of spreading due to the lightly cross-linked and flexible polymer network. Moreover, AFM force spectroscopy studies suggest that cross-linker-free microgels constitute of a more homogeneous polymer network than PEG-DA cross-linked particles and have elastic moduli at the particle apex that are ~5 times smaller than the moduli of 5 mol-% PEG-DA cross-linked microgels. Resistive pulse sensing experiments demonstrate that microgels prepared at 75 and 80°C without PEG-DA are able to deform significantly to pass through nanopores that are smaller than the microgel size. Additionally, we found that polymer network flexibility of microgels is a useful tool to control the formation of particle dewetting patterns. This offers a promising new avenue for build-up of 2D self-assembled particle structures with patterned chemical and mechanical properties.

Platelet-like particles dynamically stiffen fibrin matrices and improve wound healing outcomes

“…Each force map was fitted by applying the Hertz model, which is commonly used for biological samples, to the linear region of the force curve to obtain the Young's modulus of the clot, as done in similar works. 26 The model was fitted to the linear region of the curve because the Hertz model assumes that a measured sample is isotropic and linear elastic. It also assumes that the indenter (cantilever tip) is not deformable and that the indentation into the sample is negligible in comparison to sample thickness.…”

Nanoparticle Properties Modulate Their Attachment and Effect on Carrier Red Blood Cells

“…A number of methods have been developed to prolong circulation time of nanocarriers/nanoparticles (NPs) and avoid uptake by the reticuloendothelial system (RES), such as PEG surface coatings, modification of NP shape (e.g. elongated), and increased mechanical flexibility of NPs 4 – 25 . More recently, improved circulation time was achieved through the adsorption of NPs onto the surface of red blood cells (RBCs) 21 , 22 , 26 – 32 .…”

Functional Microgels for the Decoration of Biointerfaces

“…The control of the crosslink density distribution is still very challenging, since the majority of synthesized microgels exhibit more crosslinks in the core and less in the coronae, due to the higher reactivity of crosslinking agents compared to monomers in precipitation polymerization . A low amount of crosslinking, however, results in soft, deformable microgels, while a high amount of crosslinker results in stiff microgels with characteristics gradually approaching those of hard spheres . Other factors such as the structure of the monomers (presence of bulky groups in close proximity to the vinyl group) used also affect the stiffness of the resulting microgels.…”

“…[20] A low amount of crosslinking, however, results in soft, deformable microgels, [21] while a high amount of crosslinker results in stiff microgels with characteristics gradually approaching those of hard spheres. [22] Other factors such as the structure of the monomers (presence of bulky groups in close proximity to the vinyl group) used also affect the stiffness of the resulting microgels. However, arguably, the crosslinker has the most dramatic impact on the mechanical properties of microgels.…”

“…Temperature responsivity at pH 3 of microgel solutions and microgel films fabricated using traditional microgels with charge distribution throughout the network (C). Percent transmittance curve at pH 3 of a mixed microgel film where microgels containing NIPAm:NIPMAm in the molar ratios 66 : 22 (1) and 0 : 88 (2) respectively, were deposited alternatively. Red lines indicate the deswelling temperatures for films composed of either microgel type 1 or 2 only (D).…”