Effect of Al2O3 addition on bioactivity, thermal and mechanical properties of some bioactive glasses
Introduction
Bioactive ceramic was discovered recently, and since then has given rise to new strategies as artificial materials in clinical bone repairs and replacement. The bioactive ceramics spontaneously bond to and integrate with living bone in the body without fibrous tissue forming around them. Hench et al. [1], [2] were the first authors who introduced the idea of firmly bonding bone with synthetic materials through the chemical reactions that take place on a glass surface when it is implanted into a living body.
The characteristic amorphous quality of glass is its open structure arrangement which facilitates the inclusion of cations referred as network modifiers, causing a discontinuity of the glassy network and consequently, non-bridging oxygen is released. This disordered structure, enhanced by the presence of network modifier, gives rise to the high reactivity of glass in aqueous environments. This high reactivity is the main advantage of their application in periodontal repair and bone augmentation. This is due to the reaction [3] products obtained from these types of glasses and physiological fluids resulting in crystallized apatite-like phase similar to the inorganic component of bones in vertebrate species [4].
Bioactive glasses, from their beginnings in the 1970s, have reached a significant level of development, resulting since their discovery in the preparation of different compositions of such kind of glass.
Silicon-free bioactive glasses have the advantage of being close [5] to the composition of natural bone, but their disadvantage lies in their low mechanical strength which limits their applications. Invert phosphate glasses based on the system Na2O/CaO/P2O5 have been developed as resorbable biomaterials which can be considered as regenerator of bony defects, and favored [6] compared with bone substitutes. These resorbable materials can be dissolved after necessary time to fill the defect with new bone, without any toxic effect on the human life. Hydrolytical durability is often an important property required for the glass. However, glasses which are intended to be used in the human body as implant materials and become attached to living tissue must have certain solubility. Also, for long-term implants, it may be important to decrease the solubility as much as possible without losing bioactivity. This in turn requires an understanding of how compositional changes influence the solubility and bioactivity [7]. On the other hand, bio-absorbable materials which degrade and absorb in the human body (phosphate glasses) are useful as suture thread in bone fracture fixation applications and as carriers in drug delivery.
Generally, the addition of Al2O3 improves the long-time stability of the implants needed for bone defect repairing. In this work, phosphate glasses were prepared with different Al2O3 additions to study their effect on the bioactivity, chemical, thermal and mechanical properties of the parent glass.
Section snippets
Preparation of bioactive glasses
Three bioactive glass samples were prepared from Ca(H2PO4)2, CaCO3, Na2CO3 and Al2O3 reagent grades according to the compositions shown in Table 1. The raw materials were mixed and melted in porcelain crucible at 1000–1150 °C for 1 h. All glasses were casted as blocks in heated stainless-steel molds, annealed at 350 °C and cooled to room temperature. Those samples designed as P8, P30 and P31.
Bioactivity studies
To study the bioactivity, each glass sample was soaked in 50 ml of tris-buffered simulated body fluid (SBF)
Results and discussion
It is well known that the phosphate glasses have unique properties and crystallization behavior [8]. These facts make them candidates for a variety of special applications such as biomedical materials. However, so far, to our knowledge, the formation of apatite on phosphate glasses without silica has not been detailed reported. For example, it has been reported that, a calcium phosphate invert glass that contained TiO2 formed a new calcium phosphate apatite layer on its surface after 20 soaking
Conclusion
The effect of slight addition of Al2O3 on the bioactivity behavior of phosphate glass has been studied. The results showed that by gradually addition of Al2O3, the bioactivity increased which could be indicated by the acceleration in the formation of hydroxyl carbonate apatite layer on the surface of immersed glass in simulated body fluid. This is attributed to the increase in glass strength and consequently improvement of mechanical, thermal and chemical properties to the studied bio-glass.
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