"EFFECT OF ZINC AND STRONTIUM DOPANTS ON THE STRUCTURE AND STABILITY OF HYDROXYAPATITE AT HIGH TEMPERATURES"
Date of Award
Master of Science (MS)
Eric Landahl, PhD
Anuj Sarma, PhD
Gabriela Gonzalez Aviles
Hydroxyapatite (HA) is a bioceramic that synthetically mimics human bone. It is commonly used in medical applications as a filler for damaged bone, and in procedures such as dental implants and hip replacements. Doping of HA with elements such as zinc and strontium is known to increase the bioactivity of HA, as well as increase the retention and adsorption of therapeutic molecules for drug delivery. High-temperature, in-situ X-ray diffraction data were measured on 10 at. % zinc-doped, 10 at. % strontium-doped, and undoped HA powders at the Advanced Photon Source at Argonne National Laboratory. This research studied the temporal and thermal evolution of these samples, which were prepared via wet synthesis. Two dimensional diffraction images were collected as the samples were heated from room temperature up to 800 °C. The crystallographic structures and phase transitions were determined from Rietveld analysis, using programs such as GSAS-II, the FullProf Suite, and Matlab scripts. The undoped HA powder remained single phase throughout the heating cycle. The zinc dopant greatly reduced the temperature for onset of decomposition into a- and b-tricalcium phosphate, which occurred at approximately 690 °C. The strontium-doped sample was more stable, but also exhibited a phase transition with decomposition into a-tricalcium phosphate occurring at 790 °C. Some applications prefer HA which is more biocompatible, while others prefer tricalcium phosphate which is more bioresorbable, in-vivo. It is then sometimes preferable to produce a biphasic material (HA +TCP) which can be obtained by high temperature annealing of Zn- and Sr-doped HA. In clinical applications, Zn and Sr doping amounts would be below 2 at. %, because higher levels could be toxic. Higher doping amounts reveal which phases form more quickly as a function of annealing temperature and provides important information about sample stability in general. Therefore these results provide useful insight on the optimization of Zn- and Sr-doped HA materials for biomedical applications.
Smith, Dylan Correll, ""EFFECT OF ZINC AND STRONTIUM DOPANTS ON THE STRUCTURE AND STABILITY OF HYDROXYAPATITE AT HIGH TEMPERATURES"" (2018). College of Science and Health Theses and Dissertations. 333.