Fuente: WIPO "biotechnology" The present invention generally relates to calcium-containing structures and methods of making and using the structures. In one aspect, hollow calcium containing microstructures are used in conjunction with bone tissues/by-products to augment bone defects and extend the supply of bone tissues/by-products for bone augmentation. Bonding agents, such as calcium cements, are also used in the preparation of the hollow calcium microstructures combined with bone tissues/by-products or for use in preparing the hollow microstructures. The calcium-containing microstructures of the present invention are also useful as delivery vehicles of nitric oxide and/or nitric oxide containing or producing compounds for a variety of in vitro and in vivo uses. Calcium containing contoured substrates upon which cells/tissues can be grown in vitro for replacement and repair of tissues in vivo that conform in size and shape to the tissue surface to be replaced are also provided.