Effects Of Microgravity On Collagen Fibrosis And Crystal Growth Of Hydroxyapatite

Obvious changes of physiological state will happen in space microgravity environment, such as serious bone loss. The main components of bone are inorganic minerals, such as hydroxyapatite (HAP), and biological macromolecules. The mineralization of bone is completed under the regulation of cells such as osteoblasts and biological macromolecules. Biological macromolecules influence the mineralization process by regulating the nucleation of inorganic minerals on the inorganic/organic interfaces. However, the mechanism of bone loss in space is still unclear.In this work, in order to clarify the mechanism of bone loss, firstly, we focused on the changes of structure of three-dimensional (3D) collagen gel formed under simulated microgravity condition and subsequent changes of HAP crystallization process in vitro.3D collagen gel was prepared by three-dimensional rotation method and thin layer method, respectively. After that,3D collagen gel was immersed in simulated body fluid and cultured HAP crystals. Secondly, according to the requirements of experiments in space microgravity environment, we developed the modular, highly reliable, miniaturized prototype system to study mass transport processes of crystallization.In case of 3D collagen gel prepared by three-dimensional rotation method, we mainly studied the influences of simulated microgravity on 3D collagen gel structures by observation of morphology of HAP crystals and statistical analysis of collagen porosity. Results showed that the amount of pores inside 3D collagen that were formed at different concentrations under simulated microgravity condition was significantly larger than that under normal gravity condition. With increasing collagen concentration, the amount of pores inside 3D collagen decreased. Moreover, 3D collagen formed at different concentrations had different affect on HAP crystal growth. We found that, with increasing collagen concentration, the affect of 3D collagen on HAP crystals gradually decreased. The properties of HAP crystals were studied by XRD, EDS, FT-IR and other methods. Results showed that 3D collagen gel formed under simulated microgravity condition decreased the growth rate of HAP crystals.In case of 3D collagen gel prepared by thin layer method, we also studied the influences of simulated microgravity on 3D collagen gel structures and statistical analysis of collagen porosity. Results showed that morphology of 3D collagen formed by thin layer method was completely different with that under normal gravity condition. Under simulated microgravity condition,3D collagen gel appeared fibrillar structure and had microscopic pores. However, under normal gravity conditions,3D collagen gel had layer structure and uneven pores. With increasing the collagen concentration, the amount of pores inside 3D collagen gel decreased. We studied the affect on HAP crystals modulated by 3D collagen gel formed by thin layer method and under normal gravity condition, respectively. Results showed that 3D collagen gel formed by thin layer method obviously affected the growth of HAP crystals. We found that, only amorphous calcium phosphate grown on the surface of 3D collagen formed by thin layer method after 1-3 days and HAP crystals grown on the surface of 3D collagen after 5 days. However, square bulk crystals appeared on the surface of 3D collagen formed under normal gravity conditions after 1-3 days. After 7 days, the crystallization degree of HAP crystals grown on the surface of 3D collagen that were formed under normal gravity was significantly lower than that under simulated microgravity by thin layer method.We have developed the prototype system for studying mass transport processes of crystallization, which have three optical observation technologies. We tested its accuracy and reliability by observing the structure of candle flame, combined with the observation of ground and microgravity drop tower. Our results showed that the prototype system could be used for observing physical process and had a high reliability in microgravity environment. In future, the prototype system will study mass transport processes during the growth process of HAP crystals in space.