Surface Crystal and Degradability of Shape Memory Scaffold Essentialize Osteochondral Regeneration.

The minimally invasive deployment of scaffolds is a key safety factor for the regeneration of cartilage and bone defects. Osteogenesis relies primarily on cell-matrix interactions, whereas chondrogenesis relies on cell-cell aggregation. Bone matrix expansion requires osteoconductive scaffold degradation. However, chondrogenic cell aggregation is promoted on the repellent scaffold surface, and minimal scaffold degradation supports the avascular nature of cartilage regeneration. Here, a material satisfying these requirements for osteochondral regeneration is developed by integrating osteoconductive hydroxyapatite (HAp) with a chondroconductive shape memory polymer (SMP). The shape memory function-derived fixity and recovery of the scaffold enabled minimally invasive deployment and expansion to fill irregular defects. The crystalline phases on the SMP surface inhibited cell aggregation by suppressing water penetration and subsequent protein adsorption. However, HAp conjugation SMP (H-SMP) enhanced surface roughness and consequent cell-matrix interactions by limiting cell aggregation using crystal peaks. After mouse subcutaneous implantation, hydrolytic H-SMP accelerated scaffold degradation compared to that by the minimal degradation observed for SMP alone for two months. H-SMP and SMP are found to promote osteogenesis and chondrogenesis, respectively, in vitro and in vivo, including the regeneration of rat osteochondral defects using the binary scaffold form, suggesting that this material is promising for osteochondral regeneration.

Facet Engineering of Pd Nanocrystals for Enhancing Photocatalytic Hydrogenation: Modulation of the Schottky Barrier Height and Enrichment of Surface Reactants.

Metal cocatalyst loading is one of the most widely explored strategies in promoting photocatalytic solar energy conversion. Engineering surface-active facets of metal cocatalyst and exploring how they modulate the reactivity is crucial for the further development of advanced photocatalysts. In this work, through controlled hybridization of two-dimensional (2D) TiO2 nanosheets with well-designed Pd nanocube (Pd NC) with exposed {100} facet and Pd nano-octahedron (NO) with exposed {111} facet, we unravel the distinct crystal facet effect of Pd cocatalyst in promoting the selective hydrogenation of nitroarenes to amines of TiO2 photocatalyst. The activity tests show that the Pd NO with {111} facet is a more efficient cocatalyst than the Pd NC with exposed {100} facet. The prepared TiO2-Pd NO composite displays a 900% enhancement of photocatalytic hydrogenation rate in comparison with bare TiO2, while the TiO2-Pd NC sample only shows a 200% photoactivity enhancement. Microscopic mechanism study discloses that the distinctive photoactivity improvement of Pd NO is ascribed to the concurrent modulation of the Schottky barrier height and enrichment of surface reactants: (i) the Pd NO with a lower Fermi level could result in steeper band bending of TiO2 (i.e., higher Schottky barrier) than the Pd NC, which is more efficient in boosting interfacial separation and inhibiting the recombination of photoexcited charge pairs; and (ii) the {111} facet of Pd has higher nitroarenes adsorption ability and especially stronger hydrogen enrichment capability, thus accelerating the surface hydrogenation process and contributing to a higher reaction rate. This work emphasizes the rational facet control of cocatalysts for enhancing the photocatalytic hydrogenation performance.

New insights into the oleate flotation response of feldspar particles of different sizes: Anisotropic adsorption model.

The anisotropic adsorption of sodium oleate (NaOL) on feldspar surfaces was investigated to elucidate the different flotation properties of feldspar particles of four different size ranges. Microflotation experiments showed that the feldspar flotation recovery of particles with sizes spanning different ranges decreased in the order 0-19>19-38>45-75>38-45µm. Zeta potential and FTIR measurements showed that NaOL was chemically adsorbed on the Al sites of the feldspar surface. The anisotropic surface energies and broken bond densities estimated by density functional theory calculations showed that, although feldspar mostly exposed (010) and (001) surfaces, only the (001) surfaces contained the Al sites needed for NaOL adsorption. The interaction energies calculated by molecular dynamics simulations confirmed the more favorable NaOL adsorption on (001) than (010) surfaces, which may represent the main cause for the anisotropic NaOL adsorption on feldspar particles of different sizes. SEM measurements showed that the main exposed surfaces on coarse and fine feldspar particles were the side (010) and basal (001) ones, respectively. A higher fraction of Al-rich (001) surfaces is exposed on fine feldspar particles, resulting in better floatability compared with coarse particles. XPS and adsorption measurements confirmed that the Al content on the feldspar surface varied with the particle size, explaining the different NaOL flotation of feldspar particles of different sizes. Therefore, the present results suggest that coarsely ground ore should be used for the separation of feldspar gangue minerals. Further improvements in the flotation separation of feldspar from associated valuable minerals can be achieved through selective comminution or grinding processes favoring the exposure of (010) surfaces.