Soo-Hyung Choi

Highly stable Au nanoparticles with double hydrophilic block copolymer templates: correlation between structure and stability

We herein report a facile synthetic method for preparing gold nanoparticles (Au NPs) with superior colloidal stability using a series of double hydrophilic block copolymers (DHBC), poly(ethylene oxide)-block-poly(acrylic acid) (PEO-b-PAA), as a template (Au@DHBC NPs). Due to the presence of a well-defined polymeric shell around the Au NPs, this DHBC-based synthetic method provides superior stability when compared to conventional citrate-based synthesis. We have investigated NP performance by systematically varying the molecular weight of the interacting PAA block from 5000 g mol−1 to 27 000 g mol−1. Interestingly, the size of the Au NPs did not significantly depend on the molecular weight of the PAA block and the density of DHBC present around a single NP decreased upon an increase in the molecular weight of the PAA block. Cyanide etching of Au@DHBC NPs further confirmed the presence of DHBC with different densities around the NPs, resulting in tunable stability. Considering the structural variability of DHBCs, it is expected that the approach presented in this study will offer a new means for creating Au NPs with enhanced colloidal stability for potential biological and biomedical applications.

Effect of urea on heat-induced gelation of bovine serum albumin (BSA) studied by rheology and small angle neutron scattering (SANS)

This paper reports the effects of urea on the heat-induced gelation of bovine serum albumin (BSA), which was studied by the tube inversion method, rheological measurements, and small-angle neutron scattering (SANS). An increase in the urea concentration accelerated the rate of gelation because the protein molecules have already been unfolded to some extent during sample preparation in the urea solution. In addition, the BSA solution in the presence of urea underwent a sol-gel-sol transition during the time sweep test at a constant temperature of 80oC. On the other hand, the BSA solution without urea turned into a hard and brittle gel that did not return to the solution state during isothermal heating at a constant temperature of 80oC. Aggregation and re-bonding of the denatured and unfolded protein chains led to gel formation. Urea added to the protein denatures its tertiary and secondary structures by simultaneously disrupting the hydrogen bonds, hydrophobic interactions, and altering the solvent properties. Furthermore, urea induces thermoreversible chemical interactions in BSA solutions leading to the formation of a gel with dynamic properties under these experimental conditions.

The power of the ring: a pH-responsive hydrophobic epoxide monomer for superior micelle stability

Despite the growing interest in amphiphilic block copolymers for their application in micelles as ideal drug delivery carriers, there remain some challenges related to biocompatibility, stability, degradability, and loading efficiency of the micelles. Herein, we report a novel hydrophobic, pH-responsive epoxide monomer, tetrahydropyranyl glycidyl ether (TGE). Anionic ring-opening polymerization affords the controlled synthesis of a series of its homopolymers (PTGE) and amphiphilic polymers, poly(ethylene glycol)-block-poly(tetrahydropyranyl glycidyl ether) (PEG-b-PTGE). Interestingly, these block copolymers with cyclic TGE moieties showed superior stability in biological media, high loading capacity, tunable release, and controllable degradation compared to the block copolymers with its acyclic analogue, 1-ethoxyethyl glycidyl ether (EEGE), widely employed in polyether, which satisfy all the required design principles and address the challenges in drug delivery systems. The superior biocompatibility coupled with the high stability of the novel functional epoxide monomer is anticipated to lead to the development of a versatile platform for smart drug delivery systems.