Organoapatites: New Materials for Regenerative Artificial Bone
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ORGANOAPATITES: NEW MATERIALS FOR REGENERATIVE ARTIFICIAL BONE Samuel I. Stupp, Jacqueline A. Hanson, Glenn W. Ciegler, G. C. Mejicano, Jo Ann Eurell*, and Ann L. Johnson+ Department of Materials Science and Engineering, *Department of Veterinary Biosciences, +Department of Veterinary Clinical Medicine University of Illinois at Urbana-Champaign INTRODUCTION The objective of this work is to identify synthetic pathways for materials useful in the effective repair of the skeletal system. Ideally a universal artificial bone would be identified that can function as a cementitious, pseudoplastic, or structural material. The cementitious form would be very important for bone adhesives that repair bone fractures and restore bone defects. The pseudoplastic form would aid in the in situ reconstruction of anatomical defects and the structural material could be used to prefabricate prostheses. It is critical of course for all these forms of the artificial bone to have strongly regenerative properties so that as implants they would integrate microscopically with natural bone. In the early 80's our laboratory initiated research on the synthesis of new materials for artificial bone which we termed "organoapatites". These new materials can be best described as apatite mineral networks containing molecularly dispersed organic molecules. The organic component "threads" through the mineral crystal lattice and so its level of dispersion occurs on the level of nanometers to angstroms. This is in great contrast, of course, to conventional composites in which inorganic particles with dimensions in the order of microns are dispersed in a continuous organic matrix. Early reports of our work (1-5) describe the initial efforts on synthesis and biological testing of organoapatites. More recently we have described in more detail the synthesis and characterization of these materials (6). The general approach involves the synthesis of nanosized apatite crystals through nucleation and growth in solutions containing dissolved polypeptides or organic polyelectrolytes. The molecularly dispersed organic component in organoapatites may serve many functions. During synthesis the dissolved organic molecules can induce mineral nucleation and quench crystal growth yielding the desired nanocrystals which simulate mineral crystals in natural bone. Most importantly the use of specific organic molecules in organoapatite synthesis could endow the artificial bone with bioactivity, therapeutic properties and cementitious behavior. Other potential functions of the organic component include toughening of the mineral network and the control of maturation rate in the network's crystals. In fact it is likely that nature does toughen its biominerals such as dental enamel through the dispersion of organic molecules in otherwise brittle ionic lattices. EXPERIMENTAL PROCEDURES Organoapatites are prepared through a liquid phase synthesis and harvested from the mother liquor after one hour of reaction time. Details of the synthetic procedure can be found elsewhere (6). In
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