The Effect of Silver and Samarium on the Properties of Bioglass Coatings Produced by Pulsed Laser Deposition and Spin Coating

Abstract

The current study reports the use of silver (Ag) and samarium (Sm) as dopants to improve the properties of standard bioglass in terms of biological performance. This experiment considers thin films of doped bioglass obtained by pulsed laser deposition (PLD) and spin coating (SC). For both methods, some parameters were gradually varied, as the main objective was to produce a bioglass that could be used in biomedical fields. In order to study the morphology, the phase composition and other properties, the samples obtained were subjected to multiple analyses, such as thermal analysis, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Fourier-transform infrared (FT-IR), Raman spectroscopy, and x-ray diffraction (XRD). Furthermore, the in vitro bioactivity of the samples, as assessed through simulated body fluid (SBF) immersion, as well as immunocytochemistry and evaluation of actin filaments, assessed through fluorescence microscopy, are reported. The results confirmed the formation of the designed vitreous target employed as the source of material in the PLD experiments only at sintering temperatures below 800 °C; this vitreous nature was preserved in the grown film as well. The presence of Ag and Ce dopants in the parent glassy matrix was validated for all stages, from powder, to target, to PLD/SC-derived coatings. Additionally, it was demonstrated that the surface topography of the layers can be adjusted by using substrates with different roughness or by modulating the processing parameters, such as substrate temperature and working pressure in PLD, rotation speed, and number of layers in SC. The developed material was found to be highly bioactive after 28 days of immersion in SBF, but it was also found to be a potential candidate for inhibiting the growth of Gram-negative bacteria and a suitable support for cell growth and proliferation.

Keywords: bioglass; coatings; pulsed laser deposition; samarium; spin coating; tissue engineering.

Figure 1

Complex thermal analysis of the dry gel. TGA—thermogravimetric analysis; DrTGA—derivative of the thermogravimetric analysis with respect to time; DTA—differential thermal analysis.

Figure 2

FT-IR spectra of BG gel dried at 80 °C (Sm_80) and powder calcined at 600 °C (Sm_600).

Figure 3

SEM images of BG powder calcined at 600 °C (left) and target sintered at 700 °C (right).

Figure 4

EDX spectra of BG powder calcined at 600 °C (Sm_600) and target sintered at 700 °C (Sm_700).

Figure 5

XRD patterns of BG targets sintered at different temperatures (600, 700, 800 and 900 °C). **—SiO2; *—CaSiO₃; $—Ca₅(PO₄)₂SiO₄; #—Sm₂O₃.

Figure 6

SEM images of BG films obtained by PLD at room temperature and different oxygen pressures: (a) 100 mTorr (PLD_RT_100) and (b) 700 mTorr (PLD_RT_700).

Figure 7

SEM images of BG films obtained by PLD at 400 °C and different oxygen pressures: (a) 100 mTorr (PLD_400_100) and (b) 700 mTorr (PLD_400_700).

Figure 8

EDX spectra of BG films obtained by PLD under different experimental conditions.

Figure 9

RAMAN spectra of BG films obtained by PLD under different experimental conditions.

Figure 10

SEM images of BG films obtained by SC at (a) 5000 rpm (SC_3_5000) and (b) 10,000 rpm (SC_5_10,000).

Figure 11

EDX spectra of BG films obtained by SC under different experimental conditions.

Figure 12

SEM images of the BG target surface (different areas and magnifications) after 28 days of immersion in SBF.

Figure 12

SEM images of the BG target surface (different areas and magnifications) after 28 days of immersion in SBF.

Figure 13

Representative fluorescence images of (a) cells attached to the substrate under control conditions (cells grown on cover slips) and (b) cell cultures on BG film obtained by PLD at 400 °C substrate temperature and 700 mTorr oxygen pressure (PLD_400_700). Nuclei are marked in blue with DAPI; actin filaments are marked in green with phalloidin; FAK is highlighted in red; and the summation image is shown at the end.