Novel Hybrid Composites Based on PVA/SeTiO2 Nanoparticles and Natural Hydroxyapatite for Orthopedic Applications: Correlations between Structural, Morphological and Biocompatibility Properties

By Simona Cavalu et al.

The aim of our work was to develop and characterize a novel composition based on PVA reinforced with Se-doped TiO2 nanoparticles and natural hydroxyapatite (HA), for possible orthopedic applications. The PVA/Se-doped TiO2 composites with and without HA were structurally investigated by FTIR and XRD, in order to confirm the incorporation of the inorganic phase in the polymeric structure, and by SEM and XRF, to evidence the ultrastructural details and dispersion of nanoparticles in the PVA matrix. Both the mechanical and structural properties of the composites demonstrated a synergic reinforcing effect of HA and Se-doped TiO2 nanoparticles. Moreover, the tailorable properties of the composites were proved by the viability and differentiation potential of the bone marrow mesenchymal stem cells (BMMSC) to osteogenic, chondrogenic and adipogenic lineages. The novel hybrid PVA composites show suitable structural, mechanical and biological features to be considered as a promising biomaterial for articular cartilage and subchondral bone repair. (Copyright Simona Cavalu et al.)

SEM micrographs of hydroxyapatite (HA) crystals (a) and Se-doped TiO2 nanoparticles obtained from a TiO2 precursor calcinated at 400 (c), 600 (d) and 800 °C (e) along with the corresponding EDX spectra (b,f).
XRD pattern of precursor TiO2 particles calcinated at different temperatures (400 °C, 600 °C and 800 °C) (a) and corresponding Se-doped TiO2 particles (b). The symbols are: A—anatase, R—rutile, Se—elemental selenium, T—reduced titanate. Copyright Simona Cavalu et al.
Photographic images of poly(vinyl alcohol)/Se-doped TiO2 composites with and without HA and the reference PVA specimen (10%). The inset images present the powder of Se-doped TiO2 particles prepared from TiO2 precursor after calcination at 400, 600 and 800 °C, respectively. Copyright Simona Cavalu et al.
FTIR spectra of PVA/Se-doped TiO2 composites (a) and PVA/HA/Se-doped TiO2 composites (b). Copyright Simona Cavalu et al.
XRD patterns of PVA composites: (a) PVA-based composites with Se-doped TiO2 particles incorporated; (b) PVA-based composites with HA and Se-doped TiO2 particles incorporated. Copyright Simona Cavalu et al.
SEM images (cross section) of the PVA composites reinforced with Se-doped TiO2 nanoparticles and HA, with different details: (a) PVA 10%; (b,c) PVA HA; (d) PVA 400; (e,f) PVA 400HA; (g) PVA 600; (h,i) PVA 600HA; (j) PVA 800; (k,l) PVA 800HA.
Copyright Simona Cavalu et al.
Load–displacement curves recorded for the PVA samples with (right) and without (left) HA. Copyright Simona Cavalu et al.
Differentiation potential of bone marrow mesenchymal stem cells (BMMSCs) to adipogenic, osteogenic and chondrogenic lineages, after 72 h incubation time, in the presence of PVA-based composites. Copyright Simona Cavalu et al.
MTT assay of BMMSCs after 72 h incubation with PVA-based composites.
Copyright Simona Cavalu et al.

In our paper, Se-doped TiO2 nanoparticles were used as nanofiller, with the main goal of possible multiple advantages, such as osteogenic, anticancer and antimicrobial properties.We succeeded in preparing Se-doped TiO2 nanoparticles via a hydrothermal reaction, characterized by XRD and SEM, emphasizing their morphology and crystallinity. Depending on the calcination temperature of the TiO2 precursor, the morphology of the nanoparticles turns from nanorods to nanowires, while Se nanoparticles preserve their spherical shape.The morphology of the composites evidenced a good dispersion of both Se-doped TiO2 and HA particles within the polymeric hydrogel, resulting in a reinforced fibrous structure. Se-doped TiO2 nanoparticles were deeply embedded in the polymeric network, while the larger HA particles filled the porous architecture. It is obvious that the presence of HA particles influences the porosity of the PVA matrix. As an overall behavior, it seems that all the composites show better performance for the osteogenic and chondrogenic differentiation rather than for the adipogenic one. BMMSCs had fibroblast-like morphologies, maintaining their normal spindle shape in the early passages, while at later passages, exhibiting less concordant cell morphologies, with some cells characterized by an irregular flattened geometry and enlarged size. Particularly, the chondrogenic stimulation exhibited a distinct extracellular cartilage matrix stained with Alcian Blue (Sigma-Aldrich). At the same time, for osteogenic differentiation, Alizarin (Sigma-Aldrich) staining showed the formation of calcium oxalates on the differentiated BMMSCs, which was not observed in the undifferentiated cells. Intracellular lipid droplets staining using Oil Red-O (Sigma-Aldrich) proved the adipogenesis of BMSCs. Comparing the results obtained for different composites, it seems that PVA800 with or without HA shows the lowest differentiation potential in terms of adipogenic, osteogenic and chondrogenic stimulation. (Copyright Simona Cavalu et al.).

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