PSI - Issue 43

Komal P. Malla et al. / Procedia Structural Integrity 43 (2023) 71–76 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

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tabs and coated with platinum. From at least five different positions, the fiber morphology and the average fiber diameter of each scaffold were analyzed. The typical nanofiber morphology of the electrospun scaffolds is exemplary visualized for the neat polymer blend (Fig. 1a) and for the polymer blend with 3 % filler (Fig. 1b). The filler particles were successfully incorporated into the scaffold fibers as shown by the increasing average fiber diameter (from 0 .17 µm to 4.34 µm on the addition of 0 % to 3 % filler, see Fig. 1c). However, as the filler percentage increases (from 3 % to 12 %), it significantly decreases the fiber diameter (from 4.34 µ m to 0.48 µ m), which could be due to an increase in solution conductivity because nano-HAp is a more conducting material than polymers. The physical properties, i.e., the conductivity of the solution, might be affected by the agglomeration of filler inside the fiber and its random distribution during electrospinning, which can result in a gradual decrease of fiber diameter. In contrast to the cast films with macrophase separation easily recognizable with the naked eye, there is no macrophase separation in the electrospun fibers as verified by transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR) (not shown here). From TEM micrographs of the single fibers stained with RuO 4 it has been found that the core of the fibers composed of nano-HAp-filled GEL is surrounded by a shell composed of PCL and/or PLLA. Detailed information about the morphology and the related discussion is given in Malla et al. (2022).

Fig. 1. SEM micrographs of the nano/microfibers for the neat polymer blend (a) and the polymer blend with 3 % filler (b). Average fiber diameter of scaffolds with respect to volume fraction percentage of nano-HAp in polymer blends (c). 3. Tensile Testing and Mechanical Properties The mechanical properties (tensile strength, strain at break, elastic modulus) of the scaffolds (thickness: 0.3 mm) were measured using a uniaxial tensile testing machine Z2.5 (ZwickRoell GmbH & Co KG, Ulm, Germany) according to the standard ISO 527-3. For this, the scaffold samples were cut into 20 mm by 10 mm pieces to provide a 10 mm test gauge length and mounted on rectangular graph paper frames. At least five samples were tested for each scaffold, and the stress – strain curves were calculated from the force – displacement curves. From the solution cast films, small dog-bone-shaped specimens were cut (initial span: 15 mm) and additional stress – strain curves were calculated.

Fig. 2. Typical tensile stress – strain diagrams of the templates for different filler content.