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Osteoblast, fibroblast, and endothelial cell adhesion on nanophase (that is, materials with grain sizes less than 100 nm) alumina, titania, and hydroxyapatite (HA) was investigated using in vitro cellular models. Osteoblast adhesion was significantly (p < 0.01) greater after 4 h on nanophase alumina, titania, and HA than it was on conventional formulations of the same ceramics. In contrast, compared to conventional alumina, titania, and HA, after 4 h fibroblast adhesion was significantly (p < 0.01) less on nanophase ceramics. Examination of the underlying mechanism(s) of cell adhesion on nanophase ceramics revealed that these ceramics adsorbed significantly (p < 0.01) greater quantities of vitronectin, which, subsequently, may have contributed to the observed select enhanced adhesion of osteoblasts. Select enhanced osteoblast adhesion was independent of surface chemistry and material phase but was dependent on the surface topography (specifically on grain and pore size) of nanophase ceramics. The capability of synthesizing and processing nanomaterials with tailored (through, for example, specific grain and pore size) structures and topographies to control select subsequent cell functions provides the possibility of designing the novel proactive biomaterials (that is, materials that elicit specific, timely, and desirable responses from surrounding cells and tissues) necessary for improved implant efficacy.

Experimental measurements of the viscosity of silica (SiO2) are critically examined; the best measurements show an activation energy of 515 kJ/mole above 1400 °C and 720 kJ/mole below this temperature. The diffusion of silicon and oxygen in silica have temperature dependencies close to that of the high temperature viscosity. Mechanisms of viscous flow and diffusion of silicon and oxygen in silica are proposed that involve motion of SiO molecules. Viscous flow is proposed to result from the motion of line defects composed of SiO molecules At temperatures below 1400 °C the fraction of SiO molecules in line defects changes with temperature. The relaxation of this fraction to an equilibrium value depends on the time. These proposed mechanisms are consistent with experimental measurements of silica viscosity.

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The optical absorption of dispersions of gold particles is studied as a function of particle size, temperature, and method of preparation. The absorption spectra for gold sols in glass and water with small spread in particle size are compared to spectra calculated from Mie theory and the most reliable of recently measured optical constants of gold. The comparisons indicate that the real part of the dielectric constant ε1 for particles from 85 to 200 Å in diameter is the same as for bulk gold, and that the imaginary part ε2 is similar for particles and bulk, although some discrepancies exist. Gold sols in glass have optical properties closer to bulk gold than sols in water, probably because of defects and adsorbed material on the particles in water. Between wavelengths of about 0.40 and 0.45 μ the optical properties of the particles in glass are unchanged down to particles containing very few atoms. The optical absorption peak at 0.525 μ is unaffected by particle size down to a particle diameter of about 85 Å, showing that this absorption cannot be described by the simple free-electron model. This inadequacy of the model in this wavelength region was also deduced from the bulk optical constants. Below a diameter of about 85 Å the absorption peak is proportional to the particle diameter, as required by the free electron theory for particles much smaller than the mean free path of the electrons, but quantitative agreement with this theory is lacking. The absorption peak is shifted slightly with temperature because of the small change in electron concentration, and the peak is broadened as the temperature is increased for particles both larger and smaller than 85 Å in diameter.

A new process is described for preparing dense, polycrystalline hydroxylapatite. This material has close to theoretical density and is free of fine pores and second phases. The best material has an average compressive strength of 917 MN m -2 (133 • 103 psi), and polished samples have an average tensile strength of 196 MN m-2 (28.4 • 103 psi). The material is highly translucent, and the degree of translucence depends upon processing conditions. The relationship between processing variables and microstructure, strength, and translucence is described. This dense hydroxylapatite has good promise for bone implants and dental applications.

Responses of neonatal rat calvarial osteoblasts to a variety of orthopedic implant materials were examined in vitro. Attachment, proliferation, and collagen synthesis of a well-characterized line of osteoblasts with 316L stainless steel, Ti-6Al-4V, Co-Cr-Mo, PMMA, hydroxyapatite, borosilicate glass, and tissue culture polystyrene were studied. Cell adhesion and growth were similar on nonapatitic materials. In contrast, attachment and growth of osteoblasts were significantly lower and slower, respectively, on hydroxyapatite. Collagen synthesis per cell and relative collagen synthesis, however, were comparable on all the materials tested.

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