Janus particles, colloid-sized particles with two regions of different surface chemical composition, possess energetic interactions that depend not only on their separation but also on their orientation. Research on Janus and colloidal particles that are chemically patchy in even more complicated fashion has opened a new chapter in the colloid research field. This article highlights recent progress in both experiment and theory regarding synthesis and self-assembly of Janus particles, and tentatively outlines some areas of future opportunity.
Clusters in the form of aggregates of a small number of elemental units display structural, thermodynamic, and dynamic properties different from those of bulk materials. We studied the kinetic pathways of self-assembly of "Janus spheres" with hemispherical hydrophobic attraction and found key differences from those characteristic of molecular amphiphiles. Experimental visualization combined with theory and molecular dynamics simulation shows that small, kinetically favored isomers fuse, before they equilibrate, into fibrillar triple helices with at most six nearest neighbors per particle. The time scales of colloidal rearrangement combined with the directional interactions resulting from Janus geometry make this a prototypical system to elucidate, on a mechanistic level and with single-particle kinetic resolution, how chemical anisotropy and reaction kinetics coordinate to generate highly ordered structures.
Dysfunctional endothelium contributes to more disease than any other tissue in the body. Small interfering RNAs (siRNAs) have the potential to help study and treat endothelial cells in vivo by durably silencing multiple genes simultaneously, but efficient siRNA delivery has so far remained challenging. Here we show that polymeric nanoparticles made of low molecular weight polyamines and lipids can deliver siRNA to endothelial cells with high efficiency, thereby facilitating the simultaneous silencing of multiple endothelial genes in vivo. Unlike lipid or lipid-like nanoparticles, this formulation does not significantly reduce gene expression in hepatocytes or immune cells even at the dosage necessary for endothelial gene silencing. It mediates the most durable non-liver silencing reported to date, and facilitates the delivery of siRNAs that modify endothelial function in mouse models of vascular permeability, emphysema, primary tumour growth, and metastasis. We believe these nanoparticles improve the ability to study endothelial gene function in vivo, and may be used to treat diseases caused by vascular dysfunction.
A simple, generalizable, inexpensive method is demonstrated to synthesize Janus colloidal particles in large quantity. At the liquid-liquid interface of emulsified molten wax and water, untreated particles adsorb and are frozen in place when the wax solidifies. The exposed surfaces of the immobilized particles are modified chemically. Finally, wax is dissolved, and the inner surfaces are modified chemically. Gram-sized quantities or more of Janus particles can be synthesized by taking this approach.
A glucose-responsive closed-loop insulin delivery system represents the ideal treatment of type 1 diabetes mellitus. In this study, we develop uniform injectable microgels for controlled glucose-responsive release of insulin. Monodisperse microgels (256 ± 18 μm), consisting of a pH-responsive chitosan matrix, enzyme nanocapsules, and recombinant human insulin, were fabricated through a one-step electrospray procedure. Glucose-specific enzymes were covalently encapsulated into the nanocapsules to improve enzymatic stability by protecting from denaturation and immunogenicity as well as to minimize loss due to diffusion from the matrix. The microgel system swelled when subjected to hyperglycemic conditions, as a result of the enzymatic conversion of glucose into gluconic acid and protonation of the chitosan network. Acting as a self-regulating valve system, microgels were adjusted to release insulin at basal release rates under normoglycemic conditions and at higher rates under hyperglycemic conditions. Finally, we demonstrated that these microgels with enzyme nanocapsules facilitate insulin release and result in a reduction of blood glucose levels in a mouse model of type 1 diabetes.
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