Topic:　Biomaterials for Tissue Eng. of Bone and Kidney 

Speaker: Dr. Xing Zhang
　　　　　University of California, San Diego, USA

Date:　9:00-10:00am. ,  Fri. 18, Dec. 2009

Venue: Room 468, Lee Hsun Building

Welcome to Attend!

　 

Biomaterials for Tissue Engineering of Bone and Kidney

by
Xing Zhang
University of California, San Diego

In this presentation, the following two parts will be discussed: (1) preparation and characterization of calcium phosphate ceramics and composites for bone substitutes; (2) in vitro engineering of kidney tissues from cells.

　  In the first part, calcium phosphate ceramics and composites were prepared as bone substitutes, which were studied for their composition, structures and properties. Our research can be divided into three parts: (a) hydrothermal conversion of marine CaCO₃ skeletons to calcium phosphates, (b) creation of dense or porous beta-tricalcium phosphate (b-TCP) ceramics with or without Mg substitution, and (c) preparation of bioresorbable bone-mimicking scaffolds as bone substitutes.

　  Marine CaCO₃ skeletons have tailored architectures created by nature, which give them structural support and other functions. For example, seashells have dense lamellar structures, while coral, cuttlebone and sea urchin spines have interconnected porous structures. In our experiments, seashells, coral and cuttlebone were hydrothermally converted to hydroxyapatite (HAP), and sea urchin spines were converted to Mg–substituted tricalcium phosphate (β-TCMP), while maintaining their original structures.

　  Dense b-TCP and b-TCMP ceramics were produced by pressing green bodies at 100MPa and further sintering above 1100℃ for 2 hours.b-TCMP ceramics ~99.4% relative dense were prepared by sintering green bodies at 1250℃ for 2 hours. Dense b-TCP ceramics have average strength up to 540MPa. Macroporous β-TCMP ceramics were produced either by the extrusion method with sucrose as the porogen or by the replication method using polyurethane sponge.

　　 Bone-mimicking β-TCMP ceramics with porous structures in the center surrounded by dense structures outside were created. The outside dense structures give the scaffold mechanical strength, while the central porous structures enable cells migration and vascular infiltration, and finally in-growth of new bone into the scaffold.

　  In the second part, different approaches were used for in vitro engineering of kidney tissues from cells, including 3-dimensional (3D) tubulogenesis from renal cells, and recellularization of decellularized kidney scaffold.

　  Tubulogenesis and branching morphogenesis, fundamental processes involved in epithelial tissue development, are usually modulated by different extracellular matrices and growth factors. In kidney development, such processes include formation of the collecting duct system from the ureteric bud and formation of the proximal through distal tubules from cells of metanephric mesenchymal origin. In our experiments, cells from both ureteric bud and metanephric mesenchymal origin were cultured in 3D matrix gel to form tubular structures.

　  Scaffolds provide the temporary support for cells, and also stimulate cells to proliferate and differentiate during the developmental process. Because in vivo kidney scaffolds have an extremely complicated architecture, which is hard to recreate using synthetic methods alone, we have been decellularizing rodent kidneys with detergents, while preserving the majority of original extracellular structures. The idea is that renal cells would be injected into the decellularized scaffolds and cultured with slow perfusion of nutrient media. These natural kidney scaffolds preserve most of the original extracellular structures, which can provide renal cells with structural support as well as proper extracellular interactions. By supplying with important growth factors, renal cells are expected to localize, proliferate and differentiate in the scaffold to form kidney tissues.

 

About the presenter: Dr. Xing Zhang (张兴) received his bachelor degree in Materials Science and Engineering from University of Science and Technology of China (中国科学技术大学) in 2003 and then joined in the Ph.D. program of Materials Science and Engineering at University of California, San Diego (UCSD). He completed his Ph.D. study by working on synthetic bone materials with prof. Kenneth S. Vecchio in 2007, and then joined in prof. Sanjay K. Nigam’s lab as a post-doctoral researcher in School of Medicine at UCSD to work on in vitro engineering of kidney tissues from 2008 to present.