Biomedical Engineering Reference
In-Depth Information
their adsorptive behavior towards simple molecules (water and carbon monoxide). The
second concerns the inclusion of carbonate ions in the pure HA bulk structure to simulate
the apatite bone tissue. These examples of applying sophisticated computational techniques
to the investigation of defects in HA represent a very recent progress achieved in our
laboratory inside this biomedical research area, which has being carried out since 2003. For
the interested reader, a summary of the last years work on simulation of HA in our research
group has been recently published (Corno et al., 2010).
As for bioactive glasses, the first synthesis was performed in 1969-71 by Larry Hench in
Florida (Hench et al., 1971). He had synthesised a silicate-based material containing calcium
and phosphate and had implanted this composition in rats' femurs (Hench, 2006). The result
was a complete integration of the inorganic material with the damaged bone. This very first
composition was called Bioglass® 45S5 (45SiO 2 - 24.5Na 2 O - 24.5CaO - 6P 2 O 5 in wt. % or 46.1
SiO 2 , 24.4 Na 2 O, 26.9 CaO and 2.6 P 2 O 5 in mol %) and has been introduced in clinical use
since 1985. The interest has been then to investigate the steps of the bioactivity mechanism
leading to the formation of a strong bond between the material and the biological tissue. The
most renowned hypothesis is the so-called Hench mechanism and its crucial step resides in
the growth of a thin amorphous layer of hydroxy-carbonated apatite (HCA) (Hench, 1998;
Hench & Andersson, 1993; Hench et al., 1971). Indeed, on that layer biological growth
factors are adsorbed and desorbed to promote the process of stem cells differentiation.
Moreover, before the growth of HCA, several other chemical reactions occur, dealing
particularly with the exchange of sodium and calcium ions present in the Bioglass® with
protons derived from the biological fluid. The influence of the chemical components of the
inorganic material on its bioactivity has recently been object of scientific research and
discussion. For instance, additives such as fluorine (Christie et al., 2011; Lusvardi et al.,
2008a), boron, magnesium (A. Pedone et al., 2008) and zinc (Aina et al., 2011) were
considered in a number of systematic studies. In section 2.2 of this Chapter, the role of
phosphate concentration inside models with the 45S5 composition will be highlighted, since
these changes in content can affect the crucial mechanism of gene activation and modify the
local environment of the silicon framework and of Na and Ca sites, as well as the dissolution
rate of silica (O'Donnell et al., 2009).
The joint use of experimental and theoretical techniques nowadays has reached a very large
diffusion due to the completeness of the derived information. Particularly, in the biological
or biochemical field, computational methods are essential to the investigation of interfacial
mechanisms at a molecular level. Moreover, very often the interplay between experimental
and calculated data allows researchers to improve both methodologies. A huge amount of
examples could be reported, but for sake of brevity here we limit to our own experience of
collaboration with a number of experimentalists. Indeed, in our research papers, dealing
either with HA or with bioactive glasses, there is always a detailed comparison with
measured data, for instance by means of NMR (Pedone et al., 2010), IR and Raman
spectroscopy and of adsorption microcalorimetry (Corno et al., 2009; Corno et al., 2008). In
our computational studies, we refer to quantum-mechanical techniques, which are very
accurate but also quite heavy as for the need of resources. Usually, high parallel computing
systems are required to run the simulations and we have successfully used the
supercomputers of several HPC centers, such as the Barcelona Supercomputing Centre
(Spain) or the CINECA Supercomputing Center (Italy).
The most used theoretical framework in the last decade's literature is the Density Functional
Theory, which grants a good compromise in terms of accuracy of the representation and
Search WWH ::




Custom Search