Page 118 - IJB-7-1

3D Printed PLA/HAp Biocomposites

Figure 1. Schematic diagram of the polylactic acid/hydroxyapatite composite materials development process.

Ca(OH) (Eq. 2.2). The obtained Ca(OH) was dried and Table 1. Sample nomenclature and composition.
2
2
aqueous solution was prepared for the synthesis of HAp. Sample ID % wt of HAp
PLA filled with 0% HAp PLA/0H 0
CaCO → CaOCO+ 2 (2.1) PLA filled with 5% HAp PLA/5H 5
3
PLA filled with 10% HAp PLA/10H 10
CaOH O+ 2 → CaOH( ) 2 (2.2) PLA filled with 15% HAp PLA/15H 15
PLA, polylactic acid; HAp, hydroxyapatite
Ca OH( ) + HPO → Ca ( PO ) ( OH) 2 (2.3)
4 6
10
3
4
2
and spooling speeds. Before printing, the PLA/HAp
HAp was synthesized by mixing 1.5 M Ca(OH) composite filaments were stored in an airtight dry box
2
and 1 M H PO (Eq. 2.3) at 40–50°C with continuous at room temperature to reduce the ambient moisture
3
4
stirring. pH was monitored and maintained at 9–10 pH by absorption.
dropwise addition of NH OH to the mixture. The reaction 2.4. 3D printing of the PLA/HAp composite
4
required a 48-h maturation period, followed by washing
with ethanol, and finally neutralized using deionized filament
water. Then, the as-synthesized HAp was dried, ball The composited PLA/HAp blends were loaded and fed onto
milled, and then passed through an 80-mesh sieve. Final a 3D printer (Ultimaker S5, Netherlands) which operates
drying step was done at 80°C. Finally, the dried HAp based on a FDM technology. The printing parameters are
powders were calcined at 1100°C. listed in Table 2. Basically, the filament feed is re-extruded
through a ruby-tipped CC print core that is specifically
2.3. Extrusion of the PLA/HAp composite designed for composites, which had a 0.6 mm nozzle.
filament Print core temperature was set at 200°C (±10), while the
HAp powders were mechanically mixed with PLA build plate was set to 60°C. A CAD file guided the precise
pellets at different powder loadings (0, 5, 10, and 15 movement of the print core assembly, which includes the
wt%) before extrusion and were labeled as PLA/0H, extrusion nozzle. To compensate for any non-uniformity
PLA/5H, PLA/10H, and PLA/15H, respectively of the filament diameter and potential under-extrusion,
(Table 1). A twin-screw extruder (Labtech Engineering the material flow rate was adjusted from 100 to 200% to
Co. Ltd., Thailand) with a nominal screw diameter of achieve an acceptable and uniform print quality.
20 mm was used to composite the PLA/HAp mixture. Dumbbell-shaped tensile test specimens were then
Based on the calorimetric data of the PLA precursor, the 3D printed. The specimen dimensions were adopted
input temperature profile of the 10 extruder’s heating from ASTM D638, and the generated 3D model (.stl)
zone blocks was 190°C, 190°C, 190°C, 200°C, 200°C, was digitally drafted through a CAD software such as
200°C, 200°C, 200°C, 190°C, and 180°C, respectively SolidWorks (Dassault Systemes, France). The (.stl) file
(Figure 1). The PLA/HAp mixture was fed onto the of the design was sliced using the software Cura, an open
hopper, with an 11 rpm feed rate, and the screw speed source 3D printing slicing application, which converted
set to 130 rpm. On exiting the nozzle, the filament goes the (.stl) file into the printable (.ufp) file format.
into a water bath for cooling down, followed by passing 2.5. Digital microscopy
through an air blower, before finally consolidating in
a rotating spooler. The desired filament diameter was The digital microscope VHX-7000 (Keyence
achieved by manually controlling the extruder motor Corporation, Japan) was used to observe the surface

114 International Journal of Bioprinting (2021)–Volume 7, Issue 1