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.

Cation exchange: a simple and versatile route to inorganic colloidal spheres with the same size but different compositions and properties.

Abstract: This paper describes a cation exchange approach to the synthesis of metal chalcogenide core−shell particles with the same size but a number of different compositions. This method begins with the preparation of colloidal spheres of amorphous Se (a-Se), followed by their reaction with Ag atoms to form Se@Ag2Se spheres. These core−shell spheres are then converted into Se@MSe (M = Zn, Cd, and Pb) via cation exchange with Zn2+, Cd2+, and Pb2+. All the colloidal spheres prepared using this method are monodispersed in size and characterized by a spherical shape and a smooth surface. Starting from the same batch of Se@Ag2Se, the resultant Se@MSe samples were essentially the same in size. Furthermore, these core−shell colloidal spheres can be easily made superparamagnetic by incorporating Fe3O4 nanoparticles into the a-Se cores. This synthetic approach provides a simple and versatile route to magnetoactive core−shell spheres with the same size but a range of different compositions. This study also implies that it ...

Nanofiber scaffolds with gradients in mineral content for spatial control of osteogenesis.

Abstract: Reattachment of tendon to bone has been a challenge in orthopedic surgery. The disparate mechanical properties of the two tissues make it difficult to achieve direct surgical repair of the tendon-to-bone insertion. Healing after surgical repair typically does not regenerate the natural attachment, a complex tissue that connects tendon and bone across a gradient in both mineral content and cell phenotypes. To facilitate the regeneration of the attachment, our groups have developed a nanofiber-based scaffold with a graded mineral coating to mimic the mineral composition of the native tendon-to-bone insertion. In the present work, we evaluated the ability of this scaffold to induce graded osteogenesis of adipose-derived mesenchymal stem cells (ASCs). Results from 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and proliferating cell nuclear antigen staining indicated that cell proliferation was negatively correlated with the mineral content. In contrast, alkaline phosphatase staining, an indicator of osteogenesis, was positively correlated with the mineral content. Likewise, runt-related transcription factor 2 (an early marker of osteoblast differentiation) and osteocalcin (a late marker of osteoblast differentiation) immunostaining were both positively correlated with the mineral content. These results indicate that a gradient in mineral content on the surface of a nanofiber scaffold is capable of inducing graded differentiation of ASCs into osteoblasts for enthesis repair.

Evaluating the pharmacokinetics and in vivo cancer targeting capability of Au nanocages by positron emission tomography imaging.

Abstract: Gold nanocages have recently emerged as a novel class of photothermal transducers and drug carriers for cancer treatment. However, their pharmacokinetics and tumor targeting capability remain largely unexplored due to the lack of an imaging modality for quick and reliable mapping of their distributions in vivo. Herein, Au nanocages were prepared with controlled physicochemical properties and radiolabeled with 64Cu in high specific activities for in vivo evaluation using positron emission tomography (PET). Our pharmacokinetic studies with femtomolar administrations suggest that 30 nm nanocages had a greatly improved biodistribution profile than 55 nm nanocages, together with higher blood retention and lower hepatic and splenic uptakes. In a murine EMT-6 breast cancer model, the small cages also showed a significantly higher level of tumor uptake and a greater tumor-to-muscle ratio than the large cages. Quantitative PET imaging confirmed rapid accumulation and retention of Au nanocages inside the tumors. Th...

Microfabrication, Microstructures and Microsystems

Abstract: This review gives a brief introduction to materials and techniques used for microfabrication. Rigid materials have typically been used to fabricate microstructures and systems. Elastomeric materials are becoming attractive, and may have advantages for certain types of applications. Photolithography is the most commonly used technique for the fabrication of structures for microelectronic circuits, microelectromechanical systems, microanalytical devices and micro-optics. Soft lithography represents a set of non-photolithographic techniques: it forms micropatterns of self-assembled monolayers (SAMs) by contact printing and generates microstructures of polymers by contact molding. The aim of this paper is to illustrate how non-traditional materials and methods for fabrication can yield simple, cost-effective routes to microsystems, and now they can expand the capabilities of these systems.

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