Enhanced in vivo responses of osteoblasts in electrostatically activated zones by hydroxyapatite electrets.

Matured osteoblasts were proved to be located in the bone formation accelerated by induced large surface charges on the electrically polarized hydroxyapatite (HA) ceramics regardless of the charge polarities, whereas the spatial cell distribution patterns were different. Polarized HA ceramic plates with an average electric charge of 3.9 microCcm(-2) were implanted in widely spaced defects of canine femora for 3 and 7 days. The osteoblasts were identified by immunochemical detections of osteocalcin and osteopontin. Expressions of osteocalcin and osteopontin were detected throughout the gaps between the implanted HA plates and the cut cortical bone surfaces, especially in the vicinities of the cut cortical bone surfaces and the osteoids regardless of the polarity of the induced charges. Additionally, the newly formed bone tissue that directly bonded to the negatively charged HA surfaces was lined by an osteoblast layer. As soon as 7 days after the implantation, the presence of well-developed osteoblasts suggested that the electrostatic force of the HA ceramics had conditioned the field in the biointerface zone of the polarized HA surfaces.