Adjustable Intermolecular Interactions Allowing 2D Transition Metal Dichalcogenides with Prolonged Scavenging Activity for Reactive Oxygen Species.

There is an increasing demand for control over the dimensions and functions of transition metal dichalcogenides (TMDs) in aqueous solution toward biological and medical applications. Herein, an approach for the exfoliation and functionalization of TMDs in water via modulation of the hydrophobic interaction between poly(ε-caprolactone)-b-poly(ethylene glycol) (PCL-b-PEG) and the basal planes of TMDs is reported. Decreasing the hydrophobic PCL length of PCL-b-PEG from 5000 g mol-1 (PCL5000 ) to 460 g mol-1 (PCL460 ) significantly increases the exfoliation efficiency of TMD nanosheets because the polymer-TMD hydrophobic interaction becomes dominant over the polymer-polymer interaction. The TMD nanosheets exfoliated by PCL460 -b-PEG5000 (460-WS2 , 460-WSe2 , 460-MoS2 , and 460-MoSe2 ) show excellent and prolonged scavenging activity for reactive oxygen species (ROS), but each type of TMD displays a different scavenging tendency against hydroxyl, superoxide, and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radicals. A mechanistic study based on electron paramagnetic resonance spectroscopy and density functional theory simulations suggests that radical-mediated oxidation of TMDs and hydrogen transfer from the oxidized TMDs to radicals are crucial steps for ROS scavenging by TMD nanosheets. As-prepared 460-TMDs are able to effectively scavenge ROS in HaCaT human keratinocytes, and also exhibit excellent biocompatibility.

Effective Suppression of Oxidative Stress on Living Cells in Hydrogel Particles Containing a Physically Immobilized WS2 Radical Scavenger.

We report a tungsten disulfide (WS2) nanosheet-immobilized hydrogel system that can inhibit oxidative stress on living cells. First, we fabricated a highly stable suspension of WS2 nanosheets as a radical scavenger by enveloping them with the amphiphilic poly(ε-caprolactone)- b-poly(ethylene oxide) copolymer (PCL- b-PEO) during in situ liquid exfoliation in aqueous medium. After the PCL- b-PEO-enveloped WS2 nanosheets were embedded in three types of hydrogel systems, including carrageenan gum/locust bean gum bulk hydrogels, physically cross-linked alginate microparticles, and covalently cross-linked PEG hydrogel microparticles, they retained their characteristic optical properties. Intriguingly, the WS2 nanosheet-immobilized hydrogel particles exhibited sustainable radical scavenging performance without any deterioration in the original activity of the WS2 nanosheets, even after repeated use. This implies that the hydrogen atoms dissociated from the chalcogen of the WS2 nanosheets effectively scavenged free radicals through the hydrogel mesh. Because of this unique behavior, the coexistence of the WS2 nanosheets with living cells in the hydrogel matrix improved cell viability up to 40%, which demonstrates that the WS2 nanosheets can suppress oxidative stress on living cells.