INTELLECTUAL MERIT: Combined atomistic simulations and experimental (X-ray and neutron diffraction) studies will be carried out to obtain refined glass structure models of inorganic bioactive glasses; such models are critical to a better understanding of the bioactivities of these materials. (Bioactivity here denotes the ability of these materials to bond to bone and ultimately to promote bone growth and development, including osteoblast differentiation, proliferation, viability, and mineralization.) The inherent complexity and the lack of long-range order limit our understanding of the structure of multi-component glasses that are important in fields such as biomedical applications. Through development of innovative methodology and integration of experimental and modeling studies, this project attacks two scientifically challenging problems: the structure of the complex multi-component oxide glasses and the dissolution mechanism of these glasses in an aqueous environment. Computer simulation methods such as classical molecular dynamics and Monte Carlo simulations have generated a wealth of information about glass structure, but the results rely heavily on the quality of empirical potential models and validation on experimental results is usually needed. On the other hand, experimental methods such as neutron and X-ray diffraction, EXAFS, and infrared and Raman spectroscopy can probe certain aspects of the structure of glasses but are often limited to averaged short-range structures or mutually overlapping structural information. The novelty of the proposed new method lies in integrating classical or ab initio molecular dynamics simulations with the reverse Monte Carlo algorithm based on scattering data in studying the structure of glass materials, which will generate structural models that have more refined short- and medium-range structures for complex multi-component systems such as bioactive glasses. Based on these structural models, dissolution of bioactive glasses will be studied using kinetic Monte Carlo simulations with input of reaction energy barriers and reaction pathways from ab initio DFT calculations. The structural models and dissolution mechanisms obtained can guide more rational and systematic design of new glass compositions and processes for biomedical applications. This project involves intensive training of graduate and undergraduate students to master skills that combine multiscale materials modeling with state-of-the-art material characterization techniques, and thus prepares students for future careers that involve solving challenging materials problems.
BROADER IMPACTS: Potential applications of refined bioactive glasses in restoration and repair of bone represent an arena in which this research may have an important broader impact. The PI describes a thoughtful commitment to understanding how students learn and to providing the kinds of hands-on experiences that implement this understanding. He has developed a new course in Computational Materials Science based on a series of modules that develop students' understanding of materials phenomena and the underlying mechanisms and experimental methods. He uses multimedia to explain crystal structures through three-dimensional visualization and manipulation, to illustrate crystal dislocations using movies of atomic scale simulations, and to convey the diffusion process through transition state theory and energy barrier calculations. Another important way the PI involves students in advanced courses is to use literature based instruction. Here he focuses on a group of classical and seminal papers, dissecting them and digesting them through class discussions, homework, and exams. This teaches the students how to use the literature effectively to become qualified researchers. The PI also involves undergraduates in his research lab, and the students who prepare the bioactive glass samples will have the opportunity to visit Argonne to participate in the scattering studies. A Materials Day organized by the PI for Dallas-Fort Worth area high school teachers introduces the teachers to state of the art materials processing, characterization, and modeling facilities available on his campus. He also conducts outreach to Latino and Native American students in the Fort Worth School District. He is currently guiding science projects for students in the Texas Advanced Math and Science program, a two year residential early college entrance program for selected high school students.
Normal 0 false false false EN-US ZH-CN X-NONE Final report of NSF DMR 0907593 "Integrated Experimental and Simulation Studies of the Structure and Dissolution Mechanism of Bioactive Glasses" (7/1/2009 – 6/30/2013) PI: Jincheng Du, University of North Texas, Denton, Texas (email: jincheng.du@unt.edu) Bioactive glasses are inorganic glasses made of soda-lime-silicate, like glass window pane or cup, with addition of small amount of phosphorus oxide. These bioactive glasses in their specific composition range show unique bioactivity and can be dissolved and bond to hard or soft tissue. They can be used in biomedical applications such as bone repair, bioactive coatings to metal implants, and scaffolds in tissue engineering. In this project, we use computer simulations namely molecular dynamics to study how the atoms are arranged in these glasses, which are disorder in nature unlike crystalline solids such as salt (NaCl). We also studied the structures of these glasses using neutron and X-ray diffractions studies that help to provide valuable information of the structure of these glasses. The importance of the atomic structure of these glasses is that the dissolution behavior and how these glasses respond in biological environments rely on how the atoms are arranged. However, due to the lack of long range order of these materials, no single or combination of experimental methods alone can provide detailed structure information. Integration of simulations and experiments in an iterative manner help to provide valuable structural information of atomic arrangements of these glasses and thus provide insight of the bioactivity of these glasses. We also studied the addition of strontium ions in the bioactive glasses. Strontium ions are important because they can promote bone growth and inhibit bone absorption thus enhances the bioactivity of these glasses. Through molecular dynamics simulations, we obtained structural information of how strontium substitution influences the atomic arrangement in the glasses. We found that strontium like to sit in locations similar to calcium and increase the density and molar volume of the glasses. In addition, we studied the diffusion of ions in bioactive glasses using simulations. Diffusion is very important in these glasses since dissolution, the first step of bioactivity, starts from ionic diffusion. We found that sodium ions diffuse much faster than calcium and strontium and their diffusion is not influenced by the addition of strontium. The combination of experimental and simulation methods are shown to be an effective way to provide structural information of the complicated bioactive glass materials that lead to further insights of the physical and chemical properties, as well as bioactivity, of these bioactive glasses. Nine papers have been published in peer reviewed scientific journals such as Nature, Chemistry of Materials, Physical Review, and Journal of American Chemical Society to disseminate these findings. In addition, seven invited talks and six contributed talks have been presented at national and international conferences. The project has supported one female PhD students and two undergraduate research assistants. In addition, we have organized two Materials Camp summer camps to high school students in the PI’s department. A module to introduce glass and bioactive glasses to high school students have been developed and used in the camps.
