The effect of crystallinity on hydroxyapatite‐induced production of reactive oxygen metabolites by polymorphonuclear leukocytes

To assess the role of crystallinity in biological response, we quantitated the generation of reactive oxygen metabolites in human polymorphonuclear leukocytes (PMN) with a chemiluminescence assay using three hydroxyapatite preparations with sintering temperatures of 1,200 degrees C and 900 degrees C and a drying temperature of 110 degrees C on the basis of equal weights (1 mg/ml). These crystals have almost the same average diameters and similar average zeta potentials. The crystals prepared at higher temperatures have higher crystallinity, or larger domain sizes, which were calculated by X-ray diffraction line broadening. The production of reactive oxygen metabolites by PMN in hydroxyapatite of 1,200 degrees C was 10-times that by PMN in hydroxyapatite of 900 degrees C and more than 50-times greater than that in hydroxyapatite of 110 degrees C. A single linear correlation was observed for a plot of log (peak chemiluminescence levels) vs. a plot of log (domain sizes). These results clearly show that the maximal effect of crystallinity on hydroxyapatite-induced production of reactive oxygen metabolites by human PMN was seen at higher crystallinity.