Person:
Xia, Younan

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    Biomimetic Scaffolds for Tissue Repair and Regeneration
    (Georgia Institute of Technology, 2022-09-27) Xia, Younan
    We are seeking to augment rotator cuff repair and peripheral nerve regeneration by developing biomimetic scaffolds capable of recapitulating the compositional, structural, mechanical, and cellular features of the native tissues. Rotator cuff tears are prevalent in the elderly population. Unfortunately, successful repair remains a major clinical challenge, with high post-operative failure rates. At the root of these failures is the poor healing at the repaired tendon-to-bone insertion, and the lack of regeneration of the native attachment structure. We are developing biomimetic scaffolds to augment the surgical repair and healing of the tendon-to-bone attachment. The research is built around the premise that scaffolds can be designed with hierarchical, functionally-graded structures to match the native enthesis for the regeneration of a robust interface between the reattached tendon and bone. When combined with mesenchymal stem cells, the translational potential of the scaffolds in enhancing the formation of a mechanically functional tendon-to-bone insertion are tested in a clinically relevant rotator cuff injury-and-repair model. Peripheral nerve injury is a large-scale problem that annually affects more than one million people in the US. We are developing nerve guidance conduits based on electrospun fibers for the surgical repair of large defects in thick nerves. The conduit facilitates nerve regeneration across a gap by providing a protective environment, limiting the possible directions of axonal sprouting, concentrating neurotrophic factors, and offering physical guidance to neurite extension. Specifically, we are working with conduits featuring a multi-tubular design to recapitulate the fascicles typical of a peripheral nerve while providing good mechanical strength to resist kinking and distortion during surgery. We augment nerve regeneration by leveraging the physical cue arising from the uniaxial alignment of electrospun fibers and nanoscale grooves engraved in the surface of the fibers, in addition to the biological cues provided by Schwann cells and/or encapsulated neurotrophic factors. A combination of in vitro and in vivo models are used to optimize the design and parameters of the conduits for peripheral nerve repair and functional recovery.
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    Symmetry Breaking During the Synthesis of Nanoparticles
    (Georgia Institute of Technology, 2018-04-19) Xia, Younan
    Symmetry breaking is a ubiquitous phenomenon that occurs spontaneously when a system is subjected to variations in size and/or perturbations in terms of thermodynamic parameters. As a stochastic process, even small fluctuations acting on a system can arbitrarily push it downward one of the branches of a bifurcation. In this talk, we will use nanoparticle synthesis to illustrate the concept of symmetry breaking. Our aim is to convey its importance from a mechanistic perspective, by which one can rationally alter the experimental conditions to manipulate the growth pattern (symmetric vs. asymmetric) and thus generate colloidal nanoparticles with controlled shapes, structures, and properties for various applications, including the production of the famous Janus nanoparticles.
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    Simple Chemistry for Complex Nanomaterials
    (Georgia Institute of Technology, 2012-11-13) Xia, Younan
    The first documented synthesis of nanocrystals can be traced back to the beautiful work by Michael Faraday in 1856 when he demonstrated the preparation of gold colloids with a ruby color. Ever since, many different methods have been developed for preparing nanocrystals, but essentially all the products were troubled by problems such as irregular shapes, broad size distributions, and poorly defined morphologies. Only within the last decade has it become possible to generate nanocrystals with the quality, quantity, and reproducibility needed for a systematic study on their properties as a function of size, shape, and structure. I will briefly cover some of these developments in this talk, with a focus on solution-phase syntheses of noble-metal nanocrystals. While the synthetic methods only involve simple redox reactions, we have been working diligently to understand the complex physics behind the simple chemistry – that is, the nucleation and growth mechanisms leading to the formation of nanocrystals with well-controlled sizes, shapes and properties. The success of these syntheses has enabled us to tailor the plasmonic and catalytic properties of noble-metal nanocrystals for a range of applications including photonics, sensing, imaging, biomedicine, catalysis, and fuel cell technology.
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    Putting Chemistry to Work for Nano and Biomedical Research
    (Georgia Institute of Technology, 2012-08-29) Xia, Younan
    Nanomaterials are finding widespread use in many applications, including electronics, photonics, information storage, catalysis, as well as diagnosis and treatment of diseases. Chemistry plays a pivotal role in all these exciting developments because it allows for the synthesis of nanomaterials with well-controlled sizes, shapes, compositions, structures, and properties. In this talk, I will demonstrate this concept using a number of examples from my own research group, including silver/palladium nanocubes, gold nanocages, and platinum nanodendrites. While the synthetic methods mainly involve solution-phase redox chemistry, we have been working diligently to understand the complex physics behind the simple chemistry – that is, the nucleation and growth mechanisms leading to the formation of nanocrystals with specific shapes. For example, we have discovered that the shape of metal nanocrystals are dictated by the crystallinity and structure of the seeds, which are, in turn, controlled by factors such as reduction kinetics, oxidative etching, diffusion, and surface capping. The methodologies we have developed seem to work well for all noble metals including silver, gold, palladium, platinum, and rhodium. The success of these syntheses has enabled us to tailor the electronic, plasmonic, and catalytic properties of noble-metal nanocrystals for a range of applications in catalysis and biomedical research.