The initial stages of bioglass dissolution: a Car–Parrinello molecular-dynamics study of the glass–water interface

Abstract

The initial dissolution stages following implantation of a biomaterial in a physiological environment are critical for its bioactive properties. Car-Parrinello molecular-dynamics (CPMD) simulations of the interface between the 45S5 bioglass surface and liquid water have been carried out to investigate these processes. The analysis of a 40 ps CPMD trajectory has highlighted the potential mechanism of Na + /H + exchange, leading to formation of surface silanols through water dissociation. Moreover, by comparing the properties of water layers arranged at different distances from the glass surface, we discuss the way in which the particular structure and composition of the bioglass surface affects the hydrogen-bond network and orientation of water in its close proximity.

Bioactive Glasses—Structure and Properties

“…When silicate glasses come into contact with water, an ion exchange occurs at the glass/water interface between modifier ions,p articularly Na + , and protons from the solution. [69] Thehydrophilic nonbridging oxygen atoms and modifier cations seem to be the active sites,which allow for strong interaction between the bioactive glass surface and water. [69] Thehydrophilic nonbridging oxygen atoms and modifier cations seem to be the active sites,which allow for strong interaction between the bioactive glass surface and water.…”

“…[68] MD simulations showed modifier cations acting as Lewis acids and, through interaction with water molecules,t riggering H 2 Od issociation and stabilizing the hydroxide ions. [69] Thehydrophilic nonbridging oxygen atoms and modifier cations seem to be the active sites,which allow for strong interaction between the bioactive glass surface and water. By contrast, bridging oxygen atoms are more hydrophobic,a nd no significant interaction has been observed.…”

Local structures of mesoporous bioactive glasses and their surface alterations in vitro : inferences from solid-state nuclear magnetic resonance

“…Its first three steps involve reactions at the silicate surface (that will be addressed herein), whereas stages 4 and 5 imply formation of ACP and HCA, respectively. A large number of experimental [1,2,6–14] and numerical [15–19] studies overall validate the HM: yet, many of its details are poorly understood, particularly the optimal silicate surface characteristics and the elementary reactions that initiate ACP formation, as well as details of the ACP→HCA crystallization.

Figure 1.Schematic illustration of the reaction sequence leading to HCA formation according to Hench and co-workers [1,6], here assuming a melt-prepared CaO–SiO 2 glass.

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Molecular Dynamics Simulations of Water Structure and Diffusion in Silica Nanopores

“…(1) determines silica surface charge, an important parameter in the reactivity of silicate glasses and minerals 7,11,72,73 and the design of nanofluidic devices 74,75 . According to bond valence models [76][77][78][79] , the intrinsic pK a value of silanol groups may be sensitive to the number of hydrogen bonds received by the silanol O atom.…”

“…This fundamental question has implications for the utility of synthetic nanoporous silicates such as ordered oxide ceramics (MCM-41, SBA-15) [1][2][3] , controlled pore glasses (CPG, including Vycor glass) 1,4 , mesoporous silica 5,6 , and bioglasses 7 . In geochemistry, it determines the influence of hydrous silica gel coatings on the long-term weathering rates of silicate glasses and minerals 8,9 , these rates being important unknowns in studies of soil formation 10 and global carbon cycling 11 and in predicting the fate of CO 2 12,13 and high-level radioactive waste in geological repositories 14,15 .…”