Chemically defined serum-free medium has been shown to maintain the mechanical integrity of articular cartilage explants better than serum-supplemented medium during long-term in vitro culture, but little is known about its effect on cellular mechanisms. We hypothesized that the chemically defined culture medium can regulate the spontaneous calcium signaling of in situ chondrocytes, which may modulate the cellular metabolic activities. Bovine cartilage explants were cultured in chemically defined serum-free or serum-supplemented medium for four weeks. The spontaneous intracellular calcium ([Ca2+]i) signaling of in situ chondrocytes was longitudinally measured together along with the biomechanical properties of the explants. The spontaneous [Ca2+]i oscillations in chondrocytes were enhanced at the initial exposure of serum-supplemented medium, but were significantly dampened afterwards. In contrast, cartilage explants in chemically defined medium preserved the level of calcium signaling, and showed more responsive cells with higher and more frequent [Ca2+]i peaks after one to four week culture in comparison to those in serum medium. Regardless of the culture medium that the explants were exposed, a positive correlation was detected between the [Ca2+]i responsive rate and the stiffness of cartilage (Spearman's rank correlation coefficient = 0.762). A stable pattern of [Ca2+]i peaks was revealed for each chondrocyte, i.e., the spatiotemporal features of [Ca2+]i peaks from a cell were highly consistent during the observation period (15 minutes). This study showed that the beneficial effect of chemically defined culture of cartilage explants is associated with the spontaneous [Ca2+]i signaling of chondrocytes in cartilage.
Our recent research efforts on the synthesis of nonplanar nanographenes bearing tribenzotriquinacene or fenestrindane skeleton are summarized. Wizard hat-shaped or saddle-shaped nanographenes could be prepared using a non-classical Scholl-type cycloheptatriene formation or 19-membered ring macrocyclization. The key to the success of these transformation relies on the proper installation of the electron rich aryl functional groups in the bay areas of these molecular motifs. The three-dimensional structures of some of the nanographenes were determined by X-ray crystallography. Furthermore, these carbon-rich π-conjugated molecules are also showed to have interesting photophysical, self-assoication and host-guest complexation properties.
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