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Streszczenie:
The current work studies the electrospun poly (vinyl alcohol) (PVA) nanofibers and its nanocomposites including nanohydroxy apatite (nHAp) and nHAp/cellulose nanofibers (CNFs), emphasizing the impact of nanofillers on the toughness of nanofibers. PVA nanofibers were incorporated with 10 wt% of nHAp and then various amounts of CNF were added to subsequent PVA/nHAp fibrous nanocomposites. The morphology of nonwoven mats was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). While neat PVA nanofibers were smooth and uniform in thickness, the nanofiller loading resulted in thinner fibers with less uniformity. Furthermore, the thermal properties of the nonwoven network of fibers were characterized employing thermogravimetric analysis (TGA). Although the maximum loss mass temperature of PVA was partially reduced upon addition of nanofillers, the onset of decomposition was not altered. The mechanical characterizations were performed using static tensile and dynamic mechanical analysis (DMA). Compared to neat PVA mats, the tensile test of nanocomposites mats demonstrated the significant increase in Young's modulus; however, strain at break was dramatically reduced. In addition, the fracture work was assessed from the area under the stress-strain curve, which showed brittleness of fibrous nanocomposites due to the nanofiller incorporation. Field emission SEM (FE-SEM) was employed to scan the fracture surface of stretched fibers. The increase in modulus of electrospun mats was also shown by DMA in frequency mode. In parallel, both tensile test and DMA confirmed the change in fracture of PVA fibers from a tough to brittle mode, due to the nanofiller addition.

Słowa kluczowe:
electrospun nanocomposites, nanofillers, toughness, mechanical properties

Streszczenie:
The present study aims to theoretically model and verify the mechanical behavior of electrospun fibers of poly(vinyl alcohol) (PVA) reinforced by nanohydroxy apatite (nHAp) and cellulose nanofibers (CNF), the three composites designated as PVA/nHAp, PVA/CNF, and PVA/nHAp/CNF. Tensile tests and AFM nanoindentation studies were used to measure tensile modulus of electrospun scaffolds and single fibers respectively. Halpin–Tsai and Ouali models were applied to predict the stiffness of electrospun mats. Theoretical analysis according to the Halpin–Tsai model showed that CNF have no preferred orientation in the electrospun fibers, particularly at higher filler content. Additionally, this model provided a better prediction than Ouali model, especially at lower filler content. Theoretical models based on the geometry of an unit cell in open-cell structure such as honeycomb, tetrakaidecahedron and cube models simulate electrospun scaffolds. Among the structural models for analysis of porous scaffolds, the honeycomb model showed the best prediction, tetrakaidecahedron model—a moderate one, and cube model was the worst. In general, it was proved by both experiment and theory that the porous structure of electrospun mat caused significant modulus reduction of nanocomposites.

Słowa kluczowe:
Nanocomposites, Cellulose nanofibers, Electrospinning, Modulus

Streszczenie:
The article is focused on the role of nanohydroxy apatite (nHAp) and cellulose nanofibers (CNFs) as fillers in the electrospun poly (vinyl alcohol) (ES-PVA) nanofibers for bone tissue engineering (TE). Fibrous scaffolds of PVA, PVA/nHAp (10 wt.%), and PVA/nHAp(10 wt.%)/CNF(3 wt.%) were successfully fabricated and characterized. Tensile test on electrospun PVA/nHAp10 and PVA/nHAp10/CNF3 revealed a three-fold and seven-fold increase in modulus compared with pure ES-PVA (45.45 ± 4.77). Although, nanofiller loading slightly reduced the porosity percentage, all scaffolds had porosity higher than 70%. In addition, contact angle test proved the great hydrophilicity of scaffolds. The presence of fillers reduced in vitro biodegradation rate in PBS while accelerates biomineralization in simulated body fluid (SBF). Furthermore, cell viability, cell attachment, and functional activity of osteoblast MG-63 cells were studied on scaffolds showing higher cellular activity for scaffolds with nanofillers. Generally, the obtained results confirm that the 3-componemnt fibrous scaffold of PVA/nHAp/CNF has promising potential in hard TE.

Słowa kluczowe:
electrospinning, PVA bionanocomposites, scaffolds, bone tissue engineering, cell culture

Streszczenie:
This study aims to explore crystallinity variations of polyvinyl alcohol (PVA) as a result of electrospinning, filler addition, and heat treatment. Pure PVA and PVA nanocomposite fibers containing only nanohydroxy apatite (nHAp) and together with cellulose nanofibers (CNF) were electrospun. Electrospun nanofibers were heat treated at 180°C for 8 h. The morphology of electrospun fibers was evaluated by scanning electron microscopy (SEM) while Fourier transform infrared spectroscopy, differential scanning calorimetry, and wide angle X-ray scattering were used to analyze nanofibers crystallinity. Un-treated electrospun nanofibers were shrank and lost their porous structure in water, while heat treatment of nanofibers caused stabilization of fibrous mats in boiling water. It was concluded that the crystallinity of electrospun PVA were considerably reduced compared to PVA powder due to formation of metastable—small and/or defective crystals. Adding small content (1 wt%) of nHAp led to increase in electrospun nanofibers crystallinity. However, incorporation of higher content of nHAp and CNF caused reduction of crystallinity most probably due to possible interactions among components which interrupt the orientation of macromolecules. All analyzing methods proved the crystallinity enhancement of nanofibers upon heat treatment which can be attributed mostly to water evaporation from electrospun fibers structure.

Słowa kluczowe:
Polyvinyl alcohol, Crystallinity, Electrospinning, Nanofiber, Nanofiller, Heat treatment

Streszczenie:
The aim of the present study was preparation, optimization, and systematic characterization of electrospun bionanocomposite fibers based on polyvinyl alcohol (PVA) as matrix and nanohydroxy apatite (nHAp) and cellulose nanofibers (CNF) as nanoreinforcements. The presence of nHAp and nHAp-CNF affected the morphology of electrospun mats and reduced fiber diameter, particularly at a higher content of nanofillers. The obtained results of FTIR, DSC, and WAXS proved the crystallinity reduction of electrospun nancomposites. Both nHAp and nHAp-CNF addition led to a significant increase of Young modulus with the highest stiffness for nanocomposite fibers at 10 wt% of nHAp and 3 wt% of CNF.

Słowa kluczowe:
Bionanocomposite, cellulose nanofibers, electrospinning, nanohydroxy apatite

Streszczenie:
In the present study, a full bionanocomposite scaffold from poly (vinyl alcohol) (PVA), nanohydroxy apatite (nHAp) and cellulose nanofibers (CNF) was fabricated by electospinning and its potential application for bone tissue engineering was investigated. Morphology of the electrospun scaffolds was seen by field emission scanning electron microscope (FE-SEM). Both nHAp and CNF enhanced the tensile modulus of the scaffolds; however, both tensile strength as well as slongation at break showed reduced behaviour. Porosity measurement showed that scaffolds had porosity more than 70% which is appropriate for tissue engineering scaffolds. Contact angle test proved high hydrophilicty of electrospun mats while nanofiller incorporation promoted hydrophilicity. Biodegradability was investigated in phosphate buffer saline (PBS). In vitro biomineralization in simulated body fluid (SBF) and MTT cytotoxicity analysis showed that addition of nHAp and CNF increased bioactivity and cell viability of the scaffolds. The obtained results offered a 3-component promising scaffold for bone tissue engineering.

Słowa kluczowe:
Bionanocomposite, Scaffold, Electrospinning, Poly (vinyl alcohol) and Bone tissue engineering