Biomedical Engineering Reference
In-Depth Information
14
In Silico
Study of Hydroxyapatite and
Bioglass®: How Computational Science
Sheds Light on Biomaterials
Marta Corno, Fabio Chiatti, Alfonso Pedone and Piero Ugliengo
Dipartimento di Chimica I.F.M. and NIS, Università di Torino, Torino
Dipartimento di Chimica, Università di Modena & Reggio Emilia, Modena
Italy
1. Introduction
Hydroxyapatite and Bioglass® are two well-known biomaterials, belonging to the vast class
of ceramic supplies, both highly biocompatible and widely applied in the biomedical field.
In spite of a huge research regarding engineering applications of both inorganic materials,
still many aspects of their tissue integration mechanism have not been completely cleared at
a molecular level. Thus,
in silico
studies play a fundamental role in the prediction and
analysis of the main interactions occurring at the surface of these biomaterials in contact
with the biological fluid when incorporated in the living tissue (prevalently bones or teeth).
Hydroxyapatite [HA, Ca
10
(PO
4
)
6
(OH)
2
] owes its relevance and use as a biomaterial since it
constitutes the majority of the mineral phase of bones and tooth enamel in mammalians
(Young & Brown, 1982). For sake of completeness, we mention that hydroxyapatite is also
studied as an environmental adsorbent of metals and a catalyst (Matsumura & Moffat, 1996;
Toulhat et al., 1996). One of the first applications of HA in biomedicine dates back to 1969,
when Levitt
et al.
hot-pressed it in powders for biological experimentations (Levitt et al.,
1969). From then on, several commercial forms of HA have appeared on the market. The
material has also been utilized for preparing apatitic bioceramic, due to its bioresorbability
which can be modulated changing the degree of cristallinity. There are so many examples of
applications, from Mg
2+
-substituted hydroxyapatite (Roveri & Palazzo, 2006) to the
synthesis of porous hydroxyapatite materials by colloidal processing (Tadic et al., 2004),
starch consolidation (Rodriguez-Lorenzo et al., 2002), gel casting (Padilla et al., 2002) and
more. Furthermore, recent applications follow a biologically inspired criterion to combine
HA to a collagen matrix aiming at the improvement of mechanical properties and
bioactivity (Wahl et al., 2007). However, a complete review of all the practical as well as
hypothetical uses of HA in the biomaterial area is outside the scope of this Chapter.
Inside the bone, a highly hierarchical collagen-mineral composite, hydroxyapatite is in the
form of nano-sized mineral platelets (Currey, 1998; Fratzl et al., 2004; Weiner & Wagner,
1998) and contains carbonate ions for the 4-8 weight % (Roveri & Palazzo, 2006). In section
2.1 of this Chapter, two aspects of defects which can be encountered in a synthetic or natural
HA sample will be presented. The first aspect deals with non-stoichiometric surfaces and
