Influence of Copper-Strontium Co-Doping on Bioactivity, Cytotoxicity and Antibacterial Activity of Mesoporous Bioactive Glass

Abstract

Mesoporous bioactive glass (MBG) is an extensively studied biomaterial used for the healing of bone defects. Its biological applications can be tailored by introducing metallic ions, such as strontium (Sr) and copper (Cu), which can enhance its functionalities, including osteogenetic, angiogenetic and antibacterial functionalities. In this study, Cu and Sr ions were co-doped (ratio 1:1) with x = 0.5, 1 and 2 mol% each in glass with an intended nominal composition of 80SiO₂-(15-2x)CaO-5P₂O₅-xCuO-xSrO and synthesized with an evaporation-induced self-assembly (EISA)-based sol-gel technique. XRD confirmed the amorphous nature of the glass, while compositional analysis using ICP-OES confirmed the presence of dopant ions with the required amounts. A TEM study of the MBG powders showed fringes that corresponded to the formation of a highly ordered mesoporous structure. The Cu-Sr-doped MBG showed a positive effect on apatite formation when immersed in SBF, although the release of Cu and Sr ions was relatively slow for 1 mol% of each co-dopant, which signified a stable network structure in the glass. The impact of the Cu and Sr ions on the osteoblast-like cell line MG-63 was assessed. At the particle concentrations of 1 wt./vol.% or lower, the cell viability was above 50%. An antibacterial test was conducted against Gram-negative E. coli and Gram-positive S. aureus bacteria. With a sequential increase in the co-doped ion content in the glass, the zone of inhibition for bacteria increased. The results suggest that the doping of MBG with Cu and Sr ions at up to 2 mol% can result in tailored sustained release of ions to enhance the applicability of the studied glass as a functional biomaterial for bone regeneration applications.

Keywords: antibacterial activity; bioactivity; co-doping; cytotoxicity; mesoporous glass.

Figure 1

DTA (a) and TGA (b) plots of as-prepared base glass (80G) and co-doped CS-MBG (1CS, 2CS, 4CS) powders.

Figure 2

Represents the XRD patterns of the base and CS-MBG powders calcined at 700 °C.

Figure 3

N₂ adsorption–desorption isotherm plots of base glass and co-doped MBG.

Figure 4

TEM images with EDX analysis of MBG powders. (a) 80G, (b) 1CS, (c) 2CS and (d) 4CS2.2. In vitro Bioactivity Assessment.

Figure 5

Release profile Si, Ca, P, Cu and Sr ions (mg/L) in SBF and pH measurements for base glass (80G) and co-doped MBG (1CS, 2CS and 4CS).

Figure 6

XRD patterns of SBF soaked MBG powders after (a) 24 h, (b) 7 days, and (c) 14 days; (red star marks indicate possible formation of a new hydroxyapatite (HAp) phase.

Figure 7

FTIR spectra of all MBG powders before and after 0 h, 4 h, 8 h, 24 h, 7 d and 14 d of immersion in SBF.

Figure 8

FESEM images of bare MBG powders and after SBF soaked (7 and 14 days) MBG powders.

Figure 9

Relative cell viability percentage of MG-63 cells cultured with 0.1, 1, 5 and 10 wt./vol.% extract of MBG (n = 9, PC = positive control, NC = Negative control, samples in triplicate, * p < 0.05).

Figure 10

H&E-stained images of MG-63 cells cultured with 0.1 and 1 wt./vol.% extract of MBG along with positive control (PC) and negative control (NC).

Figure 11

Photographic images of MBG pellets treated with Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria using the agar disk diffusion method.