In this article, we reported a new and sensitive method for characterizing rapid rotational and translational diffusion of gold nanoparticles (GNPs) and gold nanorods (GNRs) by resonance light scattering correlation spectroscopy (RLSCS). The RLSCS is a new single nanoparticle method, and its principle is based on measuring the resonance light scattering fluctuations in a highly focused volume due to Brownian motion of single particles, which resembles fluorescence correlation spectroscopy (FCS). On the basis of the theory of FCS, we first developed a model for rotational and translational diffusion and aspect ratio of nanoparticles in the RLSCS system. Then, we investigated the effects of certain factors such as the wavelength of illumination light and viscosity of solution using GNPs and GNRs as model samples and discovered that the polarization anisotropy and the scattering light intensity of GNPs and GNRs were significantly dependent on the wavelengths of illumination light. Using the 632.8 nm He-Ne laser as a light source, which was close to the resonance scattering band, we successfully obtained the translational and rotational diffusion coefficients and aspect ratios of anisotropic nanoparticles by the RLSCS method. The results obtained by this new method were in good agreement with transmission electron microscopy and theoretical calculation. Furthermore, the homogeneous sandwich immunoreaction was investigated using the antibody-modified GNPs as the probes. The changes in translational diffusion behaviors and aspect ratios of GNPs in immunoreaction were observed by the RLSCS method. By these changes, we can develop a new homogeneous immunoassay. Our preliminary results illustrated that the RLSCS method was a powerful tool for characterizing rapid rotational and translational diffusion behaviors of anisotropic nanoparticles in solution. We believe that the RLSCS method exhibits the wide applications in biological science especially in vivo study on the interaction of nanoparticles and biomolecules.

Mesenchymal stem cells (MSCs) are multipotent stem cells that have attracted increasing interest in the field of regenerative medicine. Previously, the differentiation ability of MSCs was believed to be primarily responsible for tissue repair. Recent studies have shown that paracrine mechanisms play an important role in this process. MSCs can secrete soluble molecules and extracellular vesicles (EVs), which mediate paracrine communication. EVs contain large amounts of proteins and nucleic acids, such as mRNAs and microRNAs (miRNAs), and can transfer the cargo between cells. The cargoes are similar to those in MSCs and are not susceptible to degradation due to the protection of the EV bimolecular membrane structure. MSC-EVs can mimic the biological characteristics of MSCs, such as differentiation, maturation, and self-renewal. Due to their broad biological functions and their ability to transfer molecules between cells, EVs have been intensively studied by an increasing number of researchers with a focus on therapeutic applications, especially those of EVs secreted by MSCs. In this review, we discuss MSC-derived EVs and their therapeutic potential in tissue regeneration.

In the past decade, mesenchymal stem cells (MSCs) have been widely used for the treatment of osteoarthritis (OA), and extracellular vesicles (EVs) may play a major role in the efficacy of this treatment. Hypoxia can change the cargo and biological functions of MSC-derived EVs (MSC-EVs). The aim of the present study was to determine whether the effects of hypoxia-preconditioned MSC-EVs on OA cartilage repair are superior to normoxia-preconditioned MSC-EVs. By using in vitro and in vivo OA models, we verified that hypoxia-preconditioned MSC-EVs improved chondrocyte proliferation and migration and suppressed chondrocyte apoptosis to a greater extent than normoxia-preconditioned MSC-EVs. Furthermore, we found that hypoxia altered the microRNA expression in MSC-EVs and identified four differentially expressed microRNAs: hsa-miR-181c-5p, hsa-miR-18a-3p, hsa-miR-376a-5p, and hsa-miR-337-5p. Bioinformatics analysis revealed that hypoxic pretreatment may promote cartilage repair by stimulating chondrocyte proliferation and migration and suppressing chondrocyte apoptosis through the miRNA-18-3P/JAK/STAT or miRNA-181c-5p/MAPK signaling pathway. Therefore, hypoxia-preconditioned EVs may be a novel treatment for OA.