Younan Xia

Bio: Younan Xia is an academic researcher from The Wallace H. Coulter Department of Biomedical Engineering. The author has contributed to research in topics: Nanocages & Nanowire. The author has an hindex of 216, co-authored 943 publications receiving 175757 citations. Previous affiliations of Younan Xia include Washington University in St. Louis & University of Texas at Dallas.

Tissue-engineering strategies for the tendon/ligament-to-bone insertion

Abstract: Injuries to connective tissues are painful and disabling and result in costly medical expenses. These injuries often require reattachment of an unmineralized connective tissue to bone. The uninjured tendon/ligament-to-bone insertion (enthesis) is a functionally graded material that exhibits a gradual transition from soft tissue (i.e., tendon or ligament) to hard tissue (i.e., mineralized bone) through a fibrocartilaginous transition region. This transition is believed to facilitate force transmission between the two dissimilar tissues by ameliorating potentially damaging interfacial stress concentrations. The transition region is impaired or lost upon tendon/ligament injury and is not regenerated following surgical repair or natural healing, exposing the tissue to risk of reinjury. The need to regenerate a robust tendon-to-bone insertion has led a number of tissue engineering repair strategies. This review treats the tendon-to-bone insertion site as a tissue structure whose primary role is mechanical and discusses current and emerging strategies for engineering the tendon/ligament-to-bone insertion in this context. The focus lies on strategies for producing mechanical structures that can guide and subsequently sustain a graded tissue structure and the associated cell populations.

Synthesis and Characterization of Ru Cubic Nanocages with a Face-Centered Cubic Structure by Templating with Pd Nanocubes

Abstract: Nanocages have received considerable attention in recent years for catalytic applications owing to their high utilization efficiency of atoms and well-defined facets. Here we report, for the first time, the synthesis of Ru cubic nanocages with ultrathin walls, in which the atoms are crystallized in a face-centered cubic (fcc) rather than hexagonal close-packed (hcp) structure. The key to the success of this synthesis is to ensure layer-by-layer deposition of Ru atoms on the surface of Pd cubic seeds by controlling the reaction temperature and the injection rate of a Ru(III) precursor. By selectively etching away the Pd from the Pd@Ru core-shell nanocubes, we obtain Ru nanocages with an average wall thickness of 1.1 nm or about six atomic layers. Most importantly, the Ru nanocages adopt an fcc crystal structure rather than the hcp structure observed in bulk Ru. The synthesis has been successfully applied to Pd cubic seeds with different edge lengths in the range of 6-18 nm, with smaller seeds being more favorable for the formation of Ru shells with a flat, smooth surface due to shorter distance for the surface diffusion of the Ru adatoms. Self-consistent density functional theory calculations indicate that these unique fcc-structured Ru nanocages might possess promising catalytic properties for ammonia synthesis compared to hcp Ru(0001), on the basis of strengthened binding of atomic N and substantially reduced activation energies for N2 dissociation, which is the rate-determining step for ammonia synthesis on hcp Ru catalysts.

Transformation of Pd Nanocubes into Octahedra with Controlled Sizes by Maneuvering the Rates of Etching and Regrowth

Abstract: Palladium octahedra with controlled edge lengths were obtained from Pd cubes of a single size. The success of this synthesis relies on a transformation involving oxidative etching and regrowth. Because the {100} side faces of the Pd nanocubes were capped by Br– ions, Pd atoms were removed from the corners during oxidative etching, and the resultant Pd2+ ions could be reduced and deposited back onto the nanocubes, but preferentially on the {100} facets. We could control the ratio of the etching and regrowth rates (Retching and Rregrowth) simply by varying the amount of HCl added to the reaction solution. With a large amount of HCl, etching dominated the process (Retching ≫ Rregrowth), resulting in the formation of Pd octahedra with an edge length equal to 70% of that of the cubes. In contrast, with a small amount of HCl, all of the newly formed Pd2+ ions could be quickly reduced and deposited back onto the Pd cubes. In this case, Retching ≈ Rregrowth, and the resultant Pd octahedra had roughly the same vol...

Probing the surface-enhanced Raman scattering properties of Au–Ag nanocages at two different excitation wavelengths

Abstract: The surface-enhanced Raman scattering (SERS) properties of bimetallic Au–Ag nanocages has been thoroughly investigated by changing the nanocage composition, localized surface plasmon resonance (LSPR) peak position and excitation wavelength. We found a significant dependency on excitation wavelength for the Au–Ag nanocages, independent of the underlying LSPR, which can be extended to other bimetallic SERS substrates. While it is well-understood that plasmon damping can occur for Au nanoparticles when their LSPR peaks are close to interband transition frequencies and thereby attenuate SERS intensities, this study probes an additional aspect and shows that SERS intensities are reduced when the excitation light source is near interband transition frequencies regardless of the LSPR location.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology.

Abstract: Although gold is the subject of one of the most ancient themes of investigation in science, its renaissance now leads to an exponentially increasing number of publications, especially in the context of emerging nanoscience and nanotechnology with nanoparticles and self-assembled monolayers (SAMs). We will limit the present review to gold nanoparticles (AuNPs), also called gold colloids. AuNPs are the most stable metal nanoparticles, and they present fascinating aspects such as their assembly of multiple types involving materials science, the behavior of the individual particles, size-related electronic, magnetic and optical properties (quantum size effect), and their applications to catalysis and biology. Their promises are in these fields as well as in the bottom-up approach of nanotechnology, and they will be key materials and building block in the 21st century. Whereas the extraction of gold started in the 5th millennium B.C. near Varna (Bulgaria) and reached 10 tons per year in Egypt around 1200-1300 B.C. when the marvelous statue of Touthankamon was constructed, it is probable that “soluble” gold appeared around the 5th or 4th century B.C. in Egypt and China. In antiquity, materials were used in an ecological sense for both aesthetic and curative purposes. Colloidal gold was used to make ruby glass 293 Chem. Rev. 2004, 104, 293−346