Page 286 - IJB-10-1

International Journal of Bioprinting Scaffolds manufacturing by fused deposition modeling

Figure 1. Geometries employed in this work: (a) tensile test specimens with different raster angles and (b) scaffolds.

from the slope of the tensile test curve. On the other hand, 700°C. The heating rate was set at 20°C/min, and the tests
compression test values were taken from the yield point were performed in a nitrogen atmosphere.
(the point where the curve starts to decrease) to obtain the For the rheological measurements, cylinders with 25-
stress at yield point and the deformation at yield point. mm diameter and 1-mm height after each processing stage
DSC tests were performed over a pellet obtained from [dual screw extruding (E), filament (F) and 3D-printed
the dual screw extruding process before the filament sample (3D)] were obtained for rheological measurements
fabrication (E), a small piece from the obtained filament (F), by means of compression molding in a hot-plate press at
and a small piece of a 3D-printed sample (3D) in a Mettler 160°C and 300 bar for 1 min. The rheological behavior
Toledo 821 from Mettler-Toledo Inc. (Schwerzenbach, was measured in an oscillatory rheometer AR G2 from
Switzerland). First, a heating-cooling cycle was performed TA Instruments (New Castle, USA). The rheometer
to remove the thermal history of the material by means configuration was plate-plate (diameter of 25 mm) using
of heating from 30°C to 200°C and cooling down to a gap of 0.5 mm to allow the sample insertion. Frequency
−40°C. The third heating scan went from −40°C to 200°C. sweep experiments were carried out at a fixed strain of
Heating and cooling rates were set at 10°C/min, using a 0.1%. The storage modulus (G′), loss modulus (G″), and the
nitrogen atmosphere with a flow rate of 66 mL/min. The complex viscosity (η*) were determined from rheological
DSC test provided the melting temperature (T ), the cold measurements. The angular frequencies were swept from
m
crystallization temperature (T ), the melting enthalpy 100 to 0.01 Hz with five points per decade at 170°C.
cc
(ΔH ), and the cold crystallization enthalpy (ΔH ).
cc
m
Crystallinity was calculated from the enthalpies, the mass 2.5. Characterization of scaffolds
fraction of hydroxyapatite (w) and the normalized enthalpy Prior to immersion in the PBS, scaffolds were numbered
values (∆H ), as reported in Equation I. and weighed to obtain the initial mass (W ). The scaffolds
0
0
m were then placed in individual bottles containing PBS
H H
% H m 1 w 100 (I) and kept at 37°C for 8 weeks. The PBS was replaced every
m
cc
0
c
characterization purposes.
The ∆H values for a theoretical pure crystalline P(3HB- week, and three scaffolds were taken out every 2 weeks for
0
m
co-3HHx) were noted as 146 J/g. 55
The total porosity of scaffolds was determined by
TGA was performed using samples with an average gravimetry according to Equation II, where ρ scaffold is the
weight of 15–25 mg in a PT1000 from Linseis (Selb, density of the scaffold calculated from the apparent volume
Germany). The nanocomposites were placed in 70-µL and the scaffold weight, and ρ material is the density of each
alumina crucibles and subjected to a heating from 30°C to nanocomposite, which was determined in a densitometer
Volume 10 Issue 1 (2024) 278 https://doi.org/10.36922/ijb.0156