Increased osteoblast functions on theta plus delta nanofiber alumina

Nanophase materials, or materials with grain sizes less than 100 nm in at least one direction, are promising materials for various implant applications since our tissues are composed of nanometer components (i.e., proteins and/or inorganics). Specifically, bone is comprised of nanostructured hydroxyapatite and collagen fibers which continuously provide an extracellular matrix surface to bone-forming cells (osteoblasts) with a high degree of nanometer roughness. Despite this fact, materials currently utilized for orthopedic implants, whether metallic or ceramic, have constituent grain sizes in the non-biologically inspired micron regime. For this reason, the objective of the present in vitro study was to determine osteoblast functions on one classification of nanomaterials for orthopedic applications: nanofiber alumina. Various crystalline forms of nanofiber alumina were tested in this study. To obtained different crystalline structured nanofiber alumina, boehmite nanofiber alumina was sintered at either 400degreesC, 600degreesC, 800degreesC, 1000degreesC, or 1200degreesC for 2 h in air. X-ray diffraction results provided evidence that boehmite nanofiber alumina remained boehmite when sintered at 400degreesC but changed crystalline phases to gamma, gamma + delta, theta + delta, and alpha when sintered at 600degreesC, 800degreesC, 1000degreesC, and 1200degreesC, respectively. Moreover, compared to any other alumina formulation tested in this study, osteoblast functions (as measured by alkaline phosphatase activity and calcium deposition) were the greatest on theta + delta crystalline phase nanofiber alumina after 14 days of culture. Boehmite had the next greatest amount of calcium deposition by osteoblasts followed by gamma + delta. Gamma crystalline phase then followed and was greater than alpha crystalline phase nanofiber alumina which promoted osteoblast functions the least of all the compacts with the exception of borosilicate glass (reference substrate). For this reason, this study suggests that theta + delta nanofiber alumina should be further investigated in orthopedic applications. (C) 2004 Elsevier Ltd. All rights reserved.