Nanocoated Converted Coral Meets High Structural Strength Requirement for Load-Bearing Bone Graft Applications
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Nanocoated Converted Coral Meets High Structural Strength Requirement for Load-Bearing Bone Graft Applications Current bone graft materials are largely made of natural coral that has been converted to coralline hydroxyapatite [Ca10(PO4)6(OH)2] (HAp). From a mechanical and structural perspective, commercial coralline products are associated with two significant problems. One is incomplete conversion of the aragonite (calcium carbonate) to HAp, with the inner core remaining as unconverted CaCO3. This limits control of the biodegradation of the graft because the solubility rates of the two materials differ. Uncontrolled dissolution in the physiologic environment compromises the durability, tissue integration, and ultimately the long-term success of prostheses that are intended to be load-bearing. A second problem originates in the porosity of the converted material. Although coralline HAp has a favorable macroporous structure consisting of a network of interconnecting channels (150–500 µm in diameter) that allow tissue in-growth (see Figure 1), the spine (interpore solid structure) is laced with a system of very fine interconnecting nanoand micropores (40 120% hole mobility enhancement >50 500% hole mobility enhancement >70 700% hole mobility enhancement 100 Ge detectors on Si; Lasers on Si; Optical links on Si
New Heating Techniques and Ceramic Crucibles Make Melting and Casting of Metals MicrowaveCompatible Placing a metal fork or aluminum foil in a home microwave oven can cause arcing and electrical damage to the oven. However, by controlling the microwaves to uniformly heat a ceramic crucible containing the metal, the electric field surrounding the metal is sufficiently reduced to avoid arcing. Researchers at Microwave Technology Inc. in Tennessee have developed microwave processes for melting and casting a variety of metals— including aluminum, superalloys, and high-level metal scrap—at melt temperatures well above 2000°C without generating plasma about the metal. Thermally, microwave heating is an efficient process. Heated uniformly, the ceramic crucibles transfer heat to the metal. This minimizes thermal shock when the ceramics are heated and cooled. An advantage of microwave heating over induction heating is that efficient heating does not require a large single block of metal or molten metal at the bottom of the crucible. The system can readily be used for different metals and crucibles. In addition, microwaves do not require water-cooled coils, which further reduces the possibility of water leaks and contamination. The researchers’ development of nonwetting, microwave-compatible ceramic materials for melting and casting reduces the contamination often found in commercial processes that use molds coated with refractory paints. Painted coatings tend to erode, crack, and flake into the
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melt, leaving inclusions in the cast metals. The exposed areas of the (typically graphite) crucible can then react with some metals, also adding to the impurity and inclusion content. Inclusions and im
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