Rationalizing the Biodegradation of Glasses for Biomedical Applications Through Classical and Ab-initio Simulations

Abstract

The gradual dissolution of a glass in a living host determines the rate at which processes leading to tissue regeneration can occur, which is of crucial importance for the success of biomedical implants and scaffolds for tissue engineering based on the glass. In-situ radiotherapy applications are also affected-in an opposite way-by the rate at which the glass vector used to deliver radioisotopes will degrade in the bloodstream. This chapter illustrates how a combination of classical and ab-initio simulations techniques, mainly centred on Molecular Dynamics, can shed new light into structural and dynamical features that control the biodegradation of these materials. IntroductionA biomaterial is a material able to elicit a favourable reaction from the human body, leading for instance to the repair of damaged or diseased tissues, including but not limited to bones and soft tissues [1,2]. The high costs and risks associated to autoand allografts for bone replacement have led to large advances in the development and clinical application of synthetic substitutes. For instance, first-generation bioinert materials are metals, alloys and ceramics such as zirconia and alumina, whose application as bone replacement relies on a tight mechanical fit in the implant site. A superior performance can be achieved by second-generation bioactive materials, able to form chemical bonds with the existing issues, which results in better biocompatibility, integration and stability of the implant [1]. The first biomaterials with these desirable bone-bonding properties were the soda-lime phosphosilicate compositions (such as the 45S5 Bioglass ) introduced by Hench in the 70s [3]. Even though several other bioactive materials (such as crystalline calcium phosphates and silicates [4]) able to bond to tissues have been identified thereafter, their performances have A.Tilocca (B)

What Can We Learn from Atomistic Simulations of Bioactive Glasses?

“…These simulations showed that some of these strained surface sites resist hydrolysis long enough to nucleate calcium phosphate precursors, which will then protect them from further reactions [71]. The simulations also suggested that the higher stability of small rings on the bioactive than the pure silica surface is also due to the presence of more favorable absorption sites for water like modifier cations (Na and Ca) and non-bridging oxygens [9].…”

“…Thus, in the last years a fervent computational research activity has been carried out with the aim of supporting in the interpretation of the experimental results. In particular, atomistic computer simulations have shown to provide a detailed picture of the glass structures, and precious information on the structure-properties relationships of complex glasses [5][6][7][8][9]. In fact, the structural and dynamical features that control dissolution and bioactivity cover length and time scales accessible to molecular dynamics (MD) simulations [10][11][12][13][14] Therefore, computational studies have now remarkably advanced the understanding of bioactive glasses, as documented by the numerous reviews and perspective articles published in recent years [9,10,12,13] This chapter reviews the recent efforts to uncover sound relationships among the structure of crucial components and the physico-chemical properties of silicate, phospho-silicate and phosphate glasses with potential bioactive properties.…”