Effect of Nanoceria Suspension Addition on the Physicochemical and Mechanical Properties of Hybrid Organic-Inorganic Hydroxyapatite Composite Scaffolds

Abstract

In the current study, the synthesis of hydroxyapatite-ceria (HAP-CeO₂) scaffolds is attempted through a bioinspired chemical approach. The utilized colloidal CeO₂ suspension presents antifungal activity against the Aspergillus flavus and Aspergillus fumigatus species at concentrations higher than 86.1 ppm. Three different series of the composite HAP-CeO₂ suspensions are produced, which are differentiated based on the precursor suspension to which the CeO₂ suspension is added and by whether this addition takes place before or after the formation of the hydroxyapatite phase. Each of the series consists of three suspensions, in which the pure ceria weight reaches 4, 5, and 10% (by mass) of the produced hydroxyapatite, respectively. The characterization showed that the 2S series's specimens present the greater alteration towards their viscoelastic properties. Furthermore, the 2S series's sample with 4% CeO₂ presents the best mechanical response. This is due to the growth of needle-like HAP crystals during lyophilization, which-when oriented perpendicular to the direction of stress application-enhance the resistance of the sample to deformation. The 2S series's scaffolds had an average pore size equal to 100 μm and minimum open porosity 89.5% while simultaneously presented the lowest dissolution rate in phosphate buffered saline.

Keywords: CeO2; DMA; antifungal properties; hydroxyapatite scaffolds; mechanical properties.

Figure 1

SEM images of the composite HAP–CeO₂ scaffolds. (a) 1S—4% CeO₂, (b) 1S—5% CeO₂, (c) 1S—10% CeO₂, (d) 2S—4% CeO₂, (e) 2S—5% CeO₂, (f) 2S—10% CeO₂, (g) 3S—4% CeO₂, (h) 3S—5% CeO₂, (i) 3S—10% CeO₂.

Figure 2

TEM images of the composite HAP–CeO₂ scaffolds. (a–c) 1S—4% CeO₂, (d–f) 2S—4% CeO₂ and (g–i) 3S—4% CeO₂.

Figure 3

XRD spectra of the 1S—4% CeO₂, 2S—4% CeO₂, and 3S—4% CeO₂ HAP-CeO₂ composite scaffolds. The identified phases are: B: CaHPO₄·2H₂O (PDF No. 09-0077), H: Ca₅(PO₄)₃(OH) (PDF No. 09-0432) (dashed line circular indications), T: C₄H₁₁NO₃ (PDF No. 33-1699), CC: CaCO₃ (PDF No. 05-0586), CeO₂: CeO₂ (PDF No. 34-0394).

Figure 4

(a) FTIR spectra of the 1S—4% CeO₂ (blue line), 2S—4% CeO₂ (red line) and 3S—4% CeO₂ (green line) HAP-CeO₂ composite scaffolds and of HAP reference scaffold (black line). Magnified regions of interest (b) 3100–2700 cm⁻¹, (c) 1800–750 cm⁻¹, and (d) 850–400 cm⁻¹ from the original FTIR spectra (4000–400 cm⁻¹) are presented separately.

Figure 5

Storage modulus E′ (MPa), loss modulus E″ (MPa), and tanδ graphs of the 1S, 2S, and 3S HAP-CeO₂ composite scaffolds and of the HAP reference scaffold.

Figure 6

Stress (MPa)–strain curves under uniaxial compression for the 1S, 2S, and 3S HAP-CeO₂ composite scaffolds and for the HAP reference scaffold.

Figure 7

Stress (MPa)–strain curves during compressive cyclic loading up to 50% strain for 5 cycles for the 1S, 2S, and 3S HAP-CeO₂ composite scaffolds and for the HAP reference scaffold.

Figure 8

Average values of porosity percentage (%) and density (g/cm³) of the 1S, 2S, and 3S series’ HAP-CeO₂ composite scaffolds and the reference HAP scaffold, obtained using the Archimedes method.

Figure 9

Swelling ratio SR_i (%) of the HAP-CeO₂ composite scaffolds and of HAP reference scaffold, after immersion into PBS solution (pH = 7.4, @37 °C) for i hours (i = 24, 48, 72).

Figure 10

Absorption ratio AR_i (%) of the HAP-CeO₂ composite scaffolds and of HAP reference scaffold, after immersion into PBS solution (pH = 7.4, @37 °C) for i hours (i = 24, 48, 72).

Figure 11

Mass loss ratio D (%) of the HAP-CeO₂ composite scaffolds and of HAP reference scaffold, after immersion into PBS solution (pH = 7.4, @37 °C) for 7 days.