For more than half of a century, many studies have been conducted in order to find a reasonable candidate for the reconstruction and repair of the defective bone tissues which were mainly caused by accidental injuries and various bone illnesses such as tumors, trauma or infection (osteomyelitis) [1, 2]. One of the main strategies proposed to eliminate these bone defects has been the application of a variety of biological materials such as ceramic-based implants and scaffolds. Bioceramics are synthetic materials with excellent biocompatibility towards living tissue and therefore can be used in medicine to repair defects and replace damaged tissues [3, 4].
Among the bioceramics, bioactive glasses (BGs) are recognized as the favorable biomaterials in the field of bone tissue engineering since they can quickly form a bond with both hard and soft tissues [5, 6]. The capability of BGs in the formation of a bone bonding was investigated in many researches in which the researchers located the bioactive glasses in contact with the biological media. They have reported that the main reason for the bonding ability was the creation of a hydroxyapatite (HA) layer at the interfacial surface of bioactive glasses and the biological fluids [7–9].
It is known that Prof. Larry Hench was the inventor of bioactive glasses, who synthesized the first ones using the melt-quenching process in 1969 at the University of Florida. Later, his fabricated bioactive glass was named 45S5 Bioglass® due to its composition in weight percent (45% SiO2, 24.5% CaO, 24.5% Na2O and 6% P2O5) [10]. Another technique for the preparation of bioactive glasses was presented in 1991 by Li et al [11]. That named as the sol-gel method. This bottom-up procedure is done at considerably lower temperatures compared to conventional melt-quenching and constitutes two key reactions of glass precursors namely hydrolysis and condensation [12].
Sol-gel derived inherently porous bioactive glasses can be synthesized in different morphologies among which the nanoparticles have attracted the particular attention of many researchers due to their premium features like great specific surface area and small particle size [13, 14]. In fact, the larger specific surface area of nano-sized bioactive glasses compared to that of micro particles may lead to the enhancement in the hydroxyapatite deposition process and also the formation of tighter bone bonding because more active sites at the interface will be present for osteoblast to attach [15].
It can be found in the literature that some researchers incorporated different metal oxides (MO) like Calcium Oxide, Zinc Oxide and Magnesium Oxide in the structure of SiO2–CaO–P2O5 based bioactive glasses and fabricated BG-MO nano composites to enhance the bioactivity and antibacterial activity of sol-gel derived bioactive glass nanoparticles [16–18]. Due to the significant function of Magnesium element in the human bone metabolism, such as osteoblast differentiation and osteogenic gene expression, [19, 20]. This element based oxides are considered as an appropriate alternative to be applied in the structure of bioactive glasses for the improvement of bioactivity.
It is worth mentioning that magnesium oxide has been incorporated in the preparation of bioactive glasses in different ways. In most of those studies, Magnesium Oxide (MgO) was usually added, as a new component to the composition of common ternary (SiO2–CaO–P2O5) [21–26] or quaternary (SiO2–Na2O-CaO–P2O5) [27–29] bioactive glasses. In these surveys, the researchers used some sources for MgO like Magnesium nitrate hexahydrate in the composition of bioactive glasses and did not use MgO directly as a starting material in sol-gel method. In fact, magnesium oxide was substituted for one of the main constituents (usually calcium oxide) in the formula of bioactive glasses like 58S (58SiO2–33CaO–9P2O5 (wt. %)). For instance, Prabhu et al. [23] decreased the weight percent of CaO and instead added MgO with the weight percent of 10 and 20 to the aforementioned composition of 58S so that the obtained 58SiO2–23CaO–9P2O5–10MgO and 58SiO2–13CaO–9P2O5–20MgO nano bioactive glasses exhibited better in vitro bioactivity compared to common 58S and did not reveal significant antibacterial activity. In another work, [25] the molar composition of CaO was changed by the addition of a different mole percent of MgO in the range of 0–10. In that survey, it was revealed that the bioactivity of synthesized bioactive glasses was firstly increased with an increase in mole percent of MgO and then decreased so that the composition of 60SiO2-4P2O5-31CaO-5MgO (mole %) had the highest formation rate of hydroxyapatite.
In another point of view, some researchers have focused on the direct incorporation of metal oxide nanoparticles into bioglass and fabricated bioactive glass-metal oxide nanocomposites due to the great characteristics of nano bioactive glasses, such as great antibacterial behavior, [30] osteoblast cell adhesion, and proliferation [31]. As an example, Saqaie et al. [32] synthesized bioactive glass-forsterite nanocomposites by adding the various weight percent of forsterite (Mg2SiO4) to the 58S bioactive glass powders and studied its effect on the bioactivity of the prepared samples. They concluded that the sample containing 20 wt. % of forsterite exhibited the highest bioactivity by the formation of a hydroxyl-carbonate apatite layer (HCA) on the nanocomposite surface.
According to above mentioned explanations, it is clear that different results were reported on the effect of the MgO contents in bioglass composition on the in vitro rate of HA formation [33, 34]. Moreover, to the best of our knowledge, there is no research reporting the effect of direct impregnation of MgO nanoparticles, with a good number of active sites for HA nucleation, into 58S bioactive glass on the bioactivity of resulting nano composites. The main goal of this research is to prepare a novel bioactive glass-magnesium oxide nanocomposite by impregnating different weight percent of magnesium oxide nanoparticles into 58S bioactive glass material. Moreover, the effect of MgO nanoparticles content present in the nanocomposites structure on the bioactivity of nanocomposite powders were evaluated through immersion of samples in the simulated body fluid at different time intervals of 14 and 28 days. Finally, the nanocomposite sample with the highest bioactivity was determined by comparing the bioactivity results obtained from characterization tests. Moreover, antibacterial activity of the produced bioactive nanocomposites against Methicillin-resistant Staphylococcus aureus (MRSA) bacteria is investigated.