Computer Simulations of Responsive Nanogels at Lipid Membrane.

The swelling and collapse of responsive nanogels on a planar lipid bilayer are studied by means of mesoscopic computer simulations. The effects of molecular weight, cross-linking density, and adhesion strength are examined. The conditions for collapse-mediated engulfing by the bilayer are found. In particular, the results show that at low hydrophobicity level the increase in the nanogel softness decreases the engulfing rate. On the contrary, for stronger hydrophobicity level the trend changes to the opposite one. At the same time, when the cross-linking density is too low or the adhesion strength is too high the nanogel deformation at the membrane suppresses the engulfing regardless of the network swelling ratio. Finally, for comparative reasons, the behavior of the nanogels is also studied at the solid surface. These results may be useful in the design of soft particles capable of tuning of their elasticity and porosity for successful intracellular drug delivery.

What is the maximum charge uptake of Lindqvist-type polyoxovanadates in organic-inorganic heterostructures?

One of the striking characteristics of the tris(alkoxo)-ligated Lindqvist-type polyoxovanadates [VV6O13{(OCH2)3CR}2]2- in highest oxidation state in solution is the ease of their chemical post-functionalization via the R group. On surfaces it is their conductivity as a function of individual V(3d) redox states. In both cases, the structural stability of the fully-oxidized dianion is enabled by charge-balancing counterions. In this Article, we explore the charge stability and the charge distibution across the molecular Lindqvist-type hexavanadate structure regarding the R functionality (R = OC2H4N3, CH2N3, and O3C29H36N5) and the different type of countercations (Cat = K+, Li+, NH4+, H+, or Mg2+). We show that the hexavanadate core can accept in its vacant V(3d) orbitals at least four and, in some cases, up to nine additional electrons if the negative charge is offset by the corresponding cation(s), without electron leakage to the covalently attached R groups. Remarkably, the maximum number of accepted electrons strongly depends on the type of cation(s) and is independent on the type of the remote R group exploited herein. The (Cat)n[VV6O13{(OCH2)3CR}2] complexes exibit the structural integrity in all studied charged states. Our study demonstrates the importance of the countercations of multistate polyoxovanadate nanoswitches for the development of multi-charge based molecular memories and/or batteries.

Tuning the Elasticity of Nanogels Improves Their Circulation Time by Evading Immune Cells.

Peptide receptor radionuclide therapy is used to treat solid tumors by locally delivering radiation. However, due to nephro- and hepato-toxicity, it is limited by its dosage. To amplify radiation damage to tumor cells, radiolabeled nanogels can be used. We show that by tuning the mechanical properties of nanogels significant enhancement in circulation half-life of the gel could be achieved. We demonstrate why and how small changes in the mechanical properties of the nanogels influence its cellular fate. Nanogels with a storage modulus of 37 kPa were minimally phagocytosed by monocytes and macrophages compared to nanogels with 93 kPa modulus. Using PET/CT a significant difference in the blood circulation time of the nanogels was shown. Computer simulations affirmed the results and predicted the mechanism of cellular uptake of the nanogels. Altogether, this work emphasizes the important role of elasticity even for particles that are inherently soft such as nano- or microgels.

Amphiphilic PVCL/TBCHA microgels: From synthesis to characterization in a highly selective solvent.

Thermoresponsive copolymer microgels based on the biocompatible monomer N-vinylcaprolactam (VCL) and the hydrophobic comonomer 4-tert-butylcyclohexylacrylate (TBCHA) with highly tunable comonomers ratio were for the first time synthesized by miniemulsion polymerization. Their physical properties in aqueous solution and at the solid interface were characterized using dynamic light scattering (DLS), atomic force microscopy (AFM) and dissipative particle dynamics (DPD) simulations. The results show a significant decrease of the swelling rate of the obtained microgels with an increase of the amount of the hydrophobic comonomer. In the case when the fraction of TBCHA is equal or higher than the fraction of VCL, the microgels become almost insensitive to the temperature changes, and the amount of water inside the microgels appeared to be diminishingly small. In the opposite case, if the VCL fraction is major, the copolymer microgels preserve their softness and deformability while being adsorbed onto a solid surface. At the same time, all samples have shown a good colloidal stability and a low polydispersity in size. Thus, the presented polymerization technique is applicable for the fabrication of microgels using hydrophobic monomers, which are not accessible by conventional precipitation polymerization. We demonstrate that the mechanical properties and the temperature-responsiveness of the copolymer microgels can be precisely adjusted by the content of the hydrophobic comonomer.