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Bioactive Glass/Nanodiamonds system produced by the sol-gel Technique:
Study of Bioactive behaviour
Goudouri O.M. 1 , Stavrev S. 2 , Chatzistavrou X. 1 , Kantiranis N. 3 , Zorba T. 1 ,
Koidis P. 4 and Paraskevopoulos K.M. 1*
1 Solid State Physics Section, Physics Department, 3 Geology Department,
4 School of Dentistry, Department of Fixed Prosthesis and Implant Prosthodontics,
Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
2 Department of Space Materials, Space Research Institute, Bulgarian Academy of Sciences, Sofia, Bulgaria
*kpar@auth.gr
Introduction
A bioactive material is one that elicits a specific physiological response at interfaces with tissues, a property known as
bioactivity. The bone bonding ability occurs through the development of a biological apatite layer (HCAp) when the materials are
exposed to body fluids or Simulated Body Fluids (SBF). The first bioactive material reported was a four-component glass
composed, through the melting process, of SiO 2 , CaO, Na 2 O and P 2 O 5 by Hench et al. in 1971 [1] . Recently, in vitro studies have
shown that simpler compositions such as SiO 2 -CaO-P 2 O 5 , SiO 2 -CaO and pure silica can also develop a HCA layer. Li et al.
showed that SiO 2 -CaO-P 2 O 5 glass powders produced by sol-gel technique are more bioactive than the melt-derived glasses of the
same composition. The higher bioactivity of the sol-gel-derived glasses is related to the textural features of the gels, that is, pore
size and pore volume associated with the large surface area [2] .
The primary disadvantage of bioactive glasses is their mechanical weakness and low fracture toughness due to an amorphous
two-dimensional glass network. This disadvantage in addition to the fact that the tensile bending strength of most compositions is
in the range of 40-60MPa, make them unsuitable for load-bearing applications [3] . In order to improve its mechanical properties
there have been several attempts to produce composites of bioactive glasses and other constituents. Nanodiamonds (ND), on the
other hand, represent a promising material for obtaining superhard composites and are well known for their excellent contribution
in the mechanical behaviour [4] . Each ND particle, like any solid particle, is a supramolecule with a single-crystal diamond core
surrounded by a shell (“coat”) consisting of functional groups. The nature of these functional groups determines the physical and
chemical properties of nanodiamonds [5] .
In the present work, we have produced a bioactive glass/nanodiamond (BG/ND) system by the sol-gel method, in order to
combine the properties of the constituent materials and to investigate how in this mixture is affected the bioactivity of the sol-gelderived
bioactive glass. The sol-gel method was selected, instead of a sintering method, because of the nature of nanodiamonds. It
is well known that nanodiamonds undergo oxidation when treated in air at temperatures about 450 o C, which causes a rapid mass
loss [6] .
Materials and Methods
Nanodiamonds, which have particle size in the range of 3-6nm, are produced by detonation of explosive mixtures and are dry
cleaned in a special furnace with a catalysator mélange. The bioactive glass in system SiO 2 -CaO-P 2 O 5 (60% w.t. SiO 2 , 36%w.t.
CaO and 4%w.t. P 2 O 5 ) is prepared as described by Zhong et al. [7] . During the gelation the mixture was continuously stirred for the
first 3 hours. Finally, the BG/ND system is prepared by the same procedure as pure BG, while in the mixture is added 0.144g
(3%) nanodiamonds. Pure BG and the BG/ND system then were ground into powders with a particle size range 20-40μm. The
powders were then characterized by X-ray diffraction (XRD) and FTIR spectroscopy.
The bioactivity of materials is commonly examined by in vitro procedures involving the dissolution of glasses in aqueous
media that Simulate Body Fluid, like c-SBF, that is prepared as described by Ohtuki et al [8] . In each experiment, 75mg powder of
both the pure BG and the BG/ND system were immersed in 50ml c-SBF for 6, 12 and 24 hours respectively. After filtration, the
powders were rinsed with distilled water, dried and a quantity of 0.002g with 0.2g of KBr was pressed each time in a vacuum
press at 7t in order to produce a pellet with 13mm diameter and 0.8mm thickness. The pellets were then characterized with
Infrared Spectroscopic Analysis (FTIR).
The XRD measurements were carried out using a Philips (PW1710) diffractometer with Ni-filtered CuKα radiation. The
counting statistics of the XRD study were: step size 0.05 o 2θ, start angle 5 o , end angle 85 o and scan sped 0.01 o 2θ/sec. The FTIR
spectra were collected using a Bruker IFS113v FTIR spectrometer, in transmission mode in MIR region (400-4000cm -1 ) and with
a resolution of 2cm -1 .
Results and discussion
In Fig. 1 the XRD pattern of the BG/ND system and that of pure BG and ND are presented. As can be observed, the XRD
diagram of pure BG shows a broad peak between 16-38 ο 2theta a less intense between 10-15 o 2theta. In addition, we can observe
the presence of a crystalline phase that is identified as the phase of dicalsium silicate (Ca 2 SiO 4 ) in percentage of 25% that is
verified by the FTIR spectrum, as mentioned below. In the XRD pattern of pure ND, except for the characteristics peaks of
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