Introduction: Mesoporous bioactive glasses (MBGs), which combine the textural parameters of ordered mesoporous matrices (i.e. specific surface area up to 800 m2/g, pore size between 2 and 50 nm, large pore volume) with the properties of conventional bioactive sol-gel glasses, have received significant attention as bone-tissue regeneration systems. More recently, the potential of MBGs has moved a big step forward by introducing controllable amount of specific ions in their composition, with the aim to combine their excellent bioactivity with other therapeutic functions, including anti-bacterial activity, as well as stimulation of osteogenesis and angiogenesis.
In this work, binary MBGs based on the SiO2-CaO system and containing different amounts of therapeutic ions Cu2+ were synthesized, fully characterized and tested as antimicrobial agent.
Materials and Methods: Doped-MBGs have been synthesized both by an ultra-sound assisted base-catalyzed sol–gel method and by an aerosol-based spray-drying process. The structural and morphological features of the obtained doped-MBGs have been investigated by several techniques (TEM and FE-SEM coupled to EDS, N2 adsorption-desorption, XPS), as well as their ability to form hydroxyapatite (HA) in vitro by soaking the samples in SBF for 3h, 1, 3, 7 and 14 days. The release profiles of the therapeutic ion have been were measured by inductively coupled plasma-atomic emission spectrometry (ICP-AES).
The antibacterial properties of Cu-containing MBGs have been tested against both Gram-positive (Staphylococcus aureus 8325-4) and Gram-negative (Escherichia colis RB) strains. A suspension of the samples in SBF (1 mg/ml) was incubated in LB and BHI culture medium at 37°C for 3h, 1, 3, 7 and 14 days. In these culture media, 1x103 microorganisms of each strain were seeded for 24 h at 37°C. Culture medium without nanoparticles represented blank sample. An Elisa Reader was used to evaluate antibacterial effect measuring OD600 of the samples.
Results and Discussion: FESEM images of Cu-doped MBGs prepared by ultra-sonication shows spheroidal particles with size of ca 200 nm, without large aggregates (Figure 1, left). For all samples, the elemental analysis by EDS identified the presence of Cu with a concentration very close to the used nominal fraction, suggesting a complete incorporation, and mapping analysis showed that Cu ions are homogeneously distributed throughout the particles (Figure 1, right).
High specific surface area (ca 600 m2/g) and homogeneous pore size distribution, centred at around 3 nm, were obtained by N2 adsorption analyses. FESEM image of Cu-MBG after 3 h of soaking in SBF is reported in Figure 2: particle are covered by newly-formed needle-like HA nanocrystals, mainly composed by calcium and phosphorus as indicated by the EDX analysis, showing that excellent bioactivity is not affected by the incorporation of Cu.
The results of antibacterial tests (Figure 3) evidenced that the incorporation of Cu2+ ions MBG structure induces a strong antibacterial effect, a fundamental function for preventing implant-related infections, or even in avoiding the need for systemically administered antibiotics.
Conclusion: These novel Cu-containing MBGs, characterized by high surface area, fully accessible nanoporosities, excellent bioactivity and antimicrobial properties, can find various applications as therapeutic agent for bone defect filling and for the design of multi-functional scaffolds.
The research leading to these results has received funding from the European Union Horizon 2020 Programme (H2020/2014-2020) under grant agreement n°[685872]-MOZART
References:
[1] Chengtie Wu, Jiang Chang, Journal of Controlled Release 193 (2014) 282–295