Surface transformation of bioactive glass in bioreactors simulating microgravity conditions. Part I: Experimental study

Surface modified bioactive glass with surface properties akin to those of t he bone mineral phase is an attractive candidate for use as a microcarrier material for 3-D growth of bone-like tissue in rotating wall vessel bioreac tors (RWVs). The critical surface properties of this material are the resul t of reaction in solution. Because an RWV environment is completely differe nt from conditions previously employed for bioactive glass testing, a detai led study of the surface reactions is warranted. Under properly chosen cond itions, RWVs can also provide a simulated microgravity environment for the bioactive glass (BG) particles. In this sense, this study is also a report on the behavior of a bioactive material under microgravity conditions simul ated on earth. A high aspect ratio vessel (HARV) and carefully selected exp erimental conditions enabled the simulation of microgravity in our laborato ry. A complimentary numerical study was simultaneously conducted to ascerta in the appropriateness of the experimental parameters (particle size, parti cle density, medium density, medium viscosity, and rotational speed) that e nsure simulated microgravity conditions for the glass particles in the HARV . Physiological solutions (pH 7.4) with and without electrolytes, and also with serum proteins, were used to study the change in surface character res ulting from simulated microgravity. Control tests at normal gravity, both s tatic and dynamic, were also conducted. Solution and surface analyses revea led major effects of simulated microgravity. The rates of leaching of const ituent ions (Si-, Ca-, and P-ions) were greatly increased in all solutions tested. The enhanced dissolution was followed by the enhanced formation of bone-like minerals at the BG surface. This enhancement is expected to affec t adsorption of serum proteins and attachment molecules, which, in turn, ma y favorably affect bone cell adhesion and function. The findings of the stu dy are important for the use of bioactive materials as microcarriers to gen erate and analyze 3-D bone-like tissue structures in bioreactors under micr ogravity conditions or otherwise. (C) John Wiley & Sons, Inc.