ABSTRACT
Three different implants, bare Ti-6Al-4V alloy, Ti-6Al-4V alloy coated with plasma-sprayed hydroxyapatite (PSHA), and Ti-6Al-4V alloy coated with electrochemically deposited hydroxyapatite (EDHA), were implanted into canine trabecular bone for 6 h, 7, and 14 days, respectively. Environmental scanning electron microscopy study showed that PSHA coatings had higher bone apposition ratios than those exhibited by bare Ti-6Al-4V and EDHA coatings after 7 days; however, at 14 days after implantation, EDHA and PSHA coatings exhibited similar bone apposition ratios, much higher than that for bare Ti-6Al-4V. The ultrastructure of the bone/implant interface observed by transmission electron microscope showed that the earliest mineralization (6 h-7 days) was in the form of nano-ribbon cluster mineral deposits with a Ca/P atomic ratio lower than that of hydroxyapatite. Later-stage mineralization (7-14 days) resulted in bone-like tissue with the characteristic templating of self-assembled collagen fibrils by HA platelets. Though adhesion of EDHA coatings to Ti-6Al-4V substrate proved problematical and clearly needs to be addressed through appropriate manipulation of electrodepositon parameters, the finely textured microstructure of EDHA coatings appears to provide significant advantage for the integration of mineralized bone tissue into the coatings.
Subject(s)
Bone and Bones/physiology , Coated Materials, Biocompatible , Durapatite , Titanium , Alloys , Animals , Bone and Bones/ultrastructure , Dogs , Electrochemistry , Prostheses and Implants/ultrastructureABSTRACT
Technetium-99m-methylene-diphosphonate (Tc-99m-MDP) labeling was used to quantify mineralization of cultures of MC3T3 osteoblast-like cells in vitro. MC3T3 cells were cultured on tissue culture polystyrene (TCPS) in mineralizing and non-mineralizing media, and then labeled by Tc-99m-MDP. The gamma signal from labeled samples was imaged with a gamma camera and compared with the calcium content in the same samples determined by inductively coupled plasma. The high correlation (coefficient of determination, 0.88) between these two values validated the radiotracer uptake method as a quantitative analytical tool for certain mineralization studies in vitro. There was an association between mineralization and radionuclide uptake in the MC3T3 cultures on titanium alloy, but the attenuation of the gamma photons by the metal resulted in a less robust correlation. The results warrant implementation of this scintigraphic method for quantitative studies of osteoblast-mediated mineralization in vitro.
Subject(s)
Calcification, Physiologic , Osteoblasts/cytology , Polystyrenes/chemistry , Technetium Tc 99m Pyrophosphate/chemistry , Titanium/chemistry , 3T3 Cells , Alloys , Animals , Mice , Tissue Culture TechniquesABSTRACT
The success of clinical results obtained with many hydroxyapatite (HA)-coated prosthetic designs has deflected attention from the need to extend the life of the HA coating on the device. In the current study the percentages of HA and titanium surfaces to which bone was bonded, on HA-coated and non-coated titanium femoral stems retrieved from human subjects, were evaluated. Plasma-sprayed hydroxyapatite (PSHA)-coated devices demonstrated wide variability in the percentage of the PSHA coating remaining on the stems. The coating was missing from a substantial portion of a stem after only about 6 months of implantation. The percentage of revealed metal to which bone was bonded was significantly less than the percentage of the HA coating demonstrating such bonding. The revealed metal to which bone was bonded was comparable to the same value for a separate group of non-PSHA-coated titanium stems. If HA-coatings degrade over time precipitous decline in performance may occur even after several functional years. Many ultrastructural features of the bone bonded to the HA coatings on these implants from human subjects were comparable to those found on HA-coated devices implanted in a canine model.
Subject(s)
Coated Materials, Biocompatible/chemistry , Durapatite/chemistry , Femur/surgery , Femur/ultrastructure , Hip Prosthesis , Osseointegration , Titanium/chemistry , Autopsy , Cadaver , Cell Adhesion , Equipment Failure Analysis , Humans , In Vitro Techniques , Materials TestingABSTRACT
Topologically modeled amorphized silica structures have been refined using a molecular dynamics simulation technique. Several metastable structures with substantially different medium-range connectivities, as characterized by primitive ring statistics, were obtained. Whereas the total correlation function is insensitive to these differences, the first step diffraction peak derived from energy-filtered electron diffraction shows a promising correlation to medium-range structure.
