The Effect of Simulated Microgravity Environment of Rwv Bioreactors on Surface Reactions and Adsorption of Serum Proteins on Bone-bioactive Microcarriers

Biomimetically modified bioactive materials with bone-like surface properties are attractive candidates for use as microcarriers for 3-D bone-like tissue engineering under simulated microgravity conditions of NASAdesigned rotating wall vessel (RWV) bioreactors. The simulated microgravity environment is attainable under suitable parametric conditions of the RWV bioreactors. Ca-P containing bioactive glass (BG), whose stimulatory effect on bone cell function had been previously demonstrated, was used in the present study. BG surface modification via reactions in solution, resulting formation of bone-like minerals at the surface and adsorption of serum proteins is critical for obtaining the stimulatory effect. In this paper, we report on the major effects of simulated microgravity conditions of the RWV on the BG reactions surface reactions and protein adsorption in physiological solutions. Control tests at normal gravity were conducted at static and dynamic conditions. The study revealed that simulated microgravty remarkably enhanced reactions involved in the BG surface modification, including BG dissolution, formation of bone-like minerals at the surface and adsorption of serum proteins. Simultaneously, numerical models were developed to simulate the mass transport of chemical species to and from the BG surface under normal gravity and simulated microgravity conditions. The numerical results showed an excellent agreement with the experimental data at both testing conditions.1, 2 Introduction Studies from space flights over the last two decades have demonstrated that there are basic physiological changes in humans during space flight, including severe loss of calcium and mineralized bone.3 Microgravity has been noted to modify the function of the bone cells and disturb metabolism.4 With the planned long duration space travel and stay, there is a great need to gain a fundamental understanding of the effect of microgravity on human bone cell function. Several aspects of microgravity conditions of outer space can be simulated on earth using NASA designed Rotating Wall Vessel (RWV) bioreactors.5 In the RWVs, cells may be seeded on suitable microcarriers and their function determined in comparison to the function under normal gravity conditions. An important aspect is the development of a “suitable” microcarrier to successfully enable the study of this problem in simulated microgravity. In this study we hypothesize that studies focusing on understanding bone loss are conducted in a near optimal way if the microcarriers have properties akin to those of the bone mineral phase.