Advances in Materials Physics and Chemistry, 2012, 2, 239-248 http://dx.doi.org/10.4236/ampc.2012.24036 Published Online December 2012 (http://www.SciRP.org/journal/ampc) In Silico Experiments of Carbon Dioxide Atmosphere and Buffer Type Effects on the Biomimetic Coating with Simulated Body Fluids Gustavo M. Platt 1 , Ivan N. Bastos 1 , Mônica C. Andrade 1 , Glória D. A. Soares 2 1 State University of Rio de Janeiro, Nova Friburgo, Brazil 2 Federal University of Rio de Janeiro, Rio de Janeiro, Brazil Email: gmplatt@iprj.uerj.br Received September 29, 2012; revised October 29, 2012; accepted November 14, 2012 ABSTRACT The formation of calcium phosphate phases is extremely important in a biomedical engineering context. These phos- phates are used in many applications, such as grafts, drug-delivery processes and evaluation of the bioactivity of metal- lic surfaces. Considering this scenario, it is useful to evaluate the thermodynamic conditions for the precipitation of phosphates of biomedical interest, mainly hydroxyapatite. In this work, we investigate the effects of two important fac- tors using a thermodynamic framework: 1) carbon dioxide partial pressure; and 2) buffer type (2-Amino-2-hydroxy- methyl-propane-1,3-diol, known as TRIS and 2-[4-(2-hydroxyethyl)piperazin-1-yl] ethanesulfonic acid, also called HEPES), on the driving force behind the precipitation of calcium phosphates in simulated body fluids. The in silico results show that the pH value is governed by carbon dioxide content, as expected to occur in vivo. Moreover, the buff- ers can deplete the free calcium available in solution and, consequently, can cause difficulties in the calcium phosphate precipitation. Keywords: Hydroxyapatite; Thermodynamic Modelling; Carbon Dioxide, HEPES and TRIS Buffers; In Silico Experiments 1. Introduction Hydrogen potential (pH) is a parameter of prime rele- vance in aqueous liquid phases, either with in vivo or in vitro situations. Therefore, species that are able to control their pH values deserve special attention in these systems. In the context of fluids that simulate those of body solu- tions, two chemicals are very important: carbon dioxide and buffers. In spite of this situation, few studies focus on the thermodynamic aspects of these chemicals in the precipitation of calcium phosphates. Carbon dioxide partial pressure affects the pH of aqueous solutions and can promote an increase/decrease of carbonate/bicarbonate content in the liquid phase. In- deed, its partial pressure plays a key role in in vivo pH regulation. The use of buffers is advisable in order to maintain the pH of aqueous systems within narrow ranges and, thus, several chemical reactions can take place under con- trolled physico-chemical conditions. However, besides protonation/deprotonation reactions of buffers, in some cases, several complexation reactions can occur, mainly with alkaline-earth ions. In these cases, the availability of specific ions is diminished, influencing all chemical equilibrium reactions, as well as the driving force to the precipitation of phosphate phases when these ions take part. In the specific case of calcium phosphates of bio- medical interest, the quantity of free calcium ions in an aqueous system is extremely important because this pa- rameter affects the stoichiometry of solid phases (such as hydroxyapatite). For example, using BISTRIS buffer, we noted a drastic depletion of calcium ion concentrations in simulated body fluids [1]. In the same context, Nakon and Krishnamoorthy [2] showed that, among 20 buffers known as “Good’s buffers”, three of them showed com- plexation reactions with metal ions, interfering particu- larly in protein analysis. In this paper, we analyze the depletion of calcium ions in the presence of TRIS buffer, comparing the results with HEPES buffer. Besides, the determination of the carbon dioxide effects on calcium phosphate precipitation was performed. To evaluate the buffers and carbon dioxide in simu- lated body fluids, we choose a thermodynamic analysis, also known as in silico experiments, due to the scarcity of works that use a similar theoretical approach. Copyright © 2012 SciRes. AMPC