Decoding Macrophage Subtypes to Engineer Modulating Hydrogels for the Alleviation of Intervertebral Disk Degeneration

A major pathological basis for low back pain is intervertebral disk degeneration, which is primarily caused by the degeneration of nucleus pulposus cells due to imbalances in extracellular matrix (ECM) anabolism and catabolism. The phenotype of macrophages in the local immune microenvironment greatly influences the balance of ECM metabolism. Therefore, the control over the macrophage phenotype of the ECM is promising to repair intervertebral disk degeneration. Herein, the preparation of an injectable nanocomposite hydrogel is reported by embedding epigallocatechin-3-gallate-coated hydroxyapatite nanorods in O-carboxymethyl chitosan cross-linked with aldehyde hyaluronic acid that is capable of modulating the phenotype of macrophages. The bioactive components play a primary role in repairing the nucleus pulposus, where the hydroxyapatite nanorods can promote anabolism in the ECM through the nucleopulpogenic differentiation of mesenchymal stem cells. In addition, epigallocatechin-3-gallate can decrease catabolism in the ECM in nucleus pulposus by inducing M2 macrophage polarization, which exists in normal intervertebral disks and can alleviate degeneration. The nanocomposite hydrogel system shows promise for the minimally invasive and effective treatment of intervertebral disk degeneration by controlling anabolism and catabolism in the ECM and inhibiting the IL17 signaling pathway (M1-related pathway) in vitro and in vivo.

Construction of Y-Doped BiVO4 Photocatalysts for Efficient Two-Electron O2 Reduction to H2 O2

Photocatalytic hydrogen peroxide (H₂ O₂ ) production on BiVO₄ photocatalysts using water and oxygen as raw materials is a green and sustainable process. However, the photocatalytic efficiency of pristine BiVO₄ is limited by severe charge recombination. In this work, rare earth element Yttrium (Y) doped BiVO₄ photocatalysts were fabricated by the hydrothermal method. In the photocatalytic H₂ O₂ production experiment, the optimized Y-doped BiVO₄ photocatalyst produced 114 μmol g^-1  h^-1 of H₂ O₂ under simulated sunlight (AM1.5) irradiation, which is four times higher than production activity of pure BiVO₄ (26 μmol g^-1  h^-1 ). Density functional theory (DFT) calculation revealed that Y doping can enhance oxygen adsorption on the BiVO₄ photocatalyst surface. Mechanistic investigations suggest that the doping process induces the in situ formation of monoclinic/tetragonal BiVO₄ heterojunction, which further promotes the photogenerated carriers separation efficiency.