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112
RESEARCH ARTICLE
Powder Loading Effects on the Physicochemical and
Mechanical Properties of 3D Printed Poly Lactic
Acid/Hydroxyapatite Biocomposites
Cyron L. Custodio1,2, Phoebeliza Jane M. Broñola1, Sharyjel R. Cayabyab1, Vivian U. Lagura1,
Josefina R. Celorico1, and Blessie A. Basilia1,2*
1Materials Science Division, Industrial Technology Development Institute, Department of Science and Technology, Bicutan,
Taguig City 1631, Philippines
2School of Graduate Studies, Mapúa University, Manila 1002, Philippines
Abstract: This study presents the physicochemical and mechanical behavior of incorporating hydroxyapatite (HAp) with
polylactic acid (PLA) matrix in 3D printed PLA/HAp composite materials. Effects of powder loading to the composition,
crystallinity, morphology, and mechanical properties were observed. HAp was synthesized from locally sourced nanoprecipitated
calcium carbonate and served as the ller for the PLA matrix. The 0, 5, 10, and 15 wt. % HAp biocomposite laments were
formed using a twin-screw extruder. The resulting laments were 3D printed in an Ultimaker S5 machine utilizing a fused
deposition modeling technology. Successful incorporation of HAp and PLA was observed using infrared spectroscopy and
X-ray diffraction (XRD). The mechanical properties of pure PLA had improved on the incorporation of 15% HAp; from 32.7
to 47.3 MPa in terms of tensile strength; and 2.3 to 3.5 GPa for stiffness. Moreover, the preliminary in vitro bioactivity test
of the 3D printed PLA/HAp biocomposite samples in simulated body uid (SBF) indicated varying weight gains and the
presence of apatite species’ XRD peaks. The HAp particles embedded in the PLA matrix acted as nucleation sites for the
deposition of salts and apatite species from the SBF solution.
Keywords: Hydroxyapatite; Polylactic acid; 3D printing; Simulated body uid
*Correspondence to: Blessie A. Basilia, Materials Science Division, Industrial Technology Development Institute, Department of Science and
Technology, Bicutan, Taguig City 1631, Philippines; basiliablessie@gmail.com
Received: November 6, 2020; Accepted: January 15, 2021; Published Online: January 28, 2021
Citation: Custodio CL, Broñola PJM, Cayabyab SR, et al., 2021, Powder Loading Effects on the Physicochemical and
Mechanical Properties of 3D Printed Poly Lactic Acid/Hydroxyapatite Biocomposites. Int J Bioprint, 7(1):326. http://doi.
org/10.18063/ijb.v7i1.326
1. Introduction
Additive manufacturing, popularly known as
three-dimensional (3D) printing, is a relatively useful
and modern technology that promises excellent
complex architectural control without requiring
molds or templates, and the ability to tailor-t designs
depending on the demands specied by the end-user.
The fabrication technology is mostly used for rapid
prototyping to realize proof of concept ideas before
large scale manufacturing. Another notable use of 3D
printing is in the low-volume production of specic
parts for specialized needs.
Industries where 3D printing has been involved
include aerospace, automotive and transportation[1,2],
military, medicine[3,4], construction[5,6], practical household
items, and even clothing. All 3D printing technology
print the object on some build platform that adjusts in
height equal to the thickness of the layer being printed[7].
The coordinated printing motion relies on a 3D pattern
created with a computer-aided design (CAD) software.
A variety of printing techniques have been available for
research, such as stereolithography (SLA)[8], selective
laser sintering (SLS)[9], and fused deposition modeling
(FDM)[10], to name a few. SLA utilizes ultraviolet (UV)
light to polymerize and cure its liquid photoactive
© 2021 Custodio, et al. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International
License (http://creativecommons.org/licenses/by-nc/4.0/), permitting all non-commercial use, distribution, and reproduction in any medium, provided the
original work is properly cited.
Custodio, et al.
International Journal of Bioprinting (2021)–Volume 7, Issue 1 113
monomer resin. The liquid resin solidies on exposure to
a CAD-guided incident light[8]. SLS traces a CAD pattern
using a laser beam onto the powder resin, thus selectively
sintering the powders into a solid object[9]. FDM
extrudes a thermoplastic lament into built materials and
support structures layer by layer[10]. Current commodity
thermoplastic laments that are suitable for FDM printing
include polypropylene, acrylonitrile butadiene styrene,
polystyrene, polyvinyl alcohol, polyamide (PA or nylon),
and polylactic acid (PLA).
PLA has been a common lament for FDM
3D printing, mainly because of its relatively lower
processing temperature, dimensional reliability,
acceptable print quality, and good mechanical
performance. Its monomer, lactic acid, is produced
by fermenting dextrose derived from renewable crop
resources such as corn, starch, and sugarcane. Hence,
PLA is widely known as a sustainable, non-toxic
biocompatible, and biodegrading material. To date,
PLA is often used for biomedical applications, such as
bone tissue engineering[11], scaffolds[12], and implants
fabrication. PLA-based implants benet from the
avoidance of stress shielding effects, which is a known
disadvantage for metal implants. While implanted inside
the body, PLA would also dissolve naturally and is
susceptible to biodegradation, and their by-products are
non-toxic. Although plates and screws made from PLA
have been used to xate jaw fractures without additional
support, PLA still has some inherent drawbacks and
limitations. As compared to more popular bone implant
materials such as stainless steel and alloy metals, PLA
is comparatively inferior by a large margin in terms of
mechanical performance. Another difculty of using
pure PLA is the poor cell attachment and proliferation
on the polymer’s surface. To address these concerns,
the physicochemical properties of pure PLA can be
altered and improved by incorporating biocompatible
ceramic llers and reinforcements.
Ceramic materials, such as calcium phosphates,
silica, and alumina, comprise the human bone tissue. Due
to their biocompatibility, these ceramic compounds have
been synthesized and used as implants for biomedical
applications. Bioactive implants are often coated with
a type of calcium phosphate called hydroxyapatite
(HAp, Ca10(PO4)6(OH)2), a promising bone substitute
mineral. However, HAp is neither used for load-bearing
applications nor in its bulk form due to its inherent
brittleness. Therefore, HAp is mostly used as surface
coating for other biomaterials dedicated for bone grafting.
As a ller or reinforcing material, HAp can act to improve
the matrix material’s biocompatibility[13], stimulate bone
regeneration, and improve the stiffness, compressive, and
bending strengths[14]. Articial implants should mimic
the mechanical properties of the natural bone as close
as possible. The human bone has stiffness in the range
of 17–20 GPa. The integration of hard HAp ceramics
and polymeric PLA matrix allows for bone substitute
materials that are exible and strong[14].
Injection-molded PLA/HAp bioactive composites
have been fabricated to be used as an internal xation
device for cancellous bone regeneration[15]. Micro and
nanoscale-HAp particles have been incorporated to
PLA through electrospinning. Both micro-HAp and
nano-HAp have shown to improve the elastic modulus
of the electrospun mats and acted as nucleating agents.
However, micro-HAp induced brittleness due to the
bigger geometry of the llers which acted as defects
rather than as reinforcements[13]. A study on 3D printed
PLA scaffolds varied the printing orientations (0°, 45°,
and 90°), followed by surface modication using HAp.
The resulting scaffolds’ compressive properties and cell
proliferation were observed. It was found that the optimal
printing orientation was 90° as it produced the highest
compressive strength (53 MPa), while no cell deaths were
observed and all live cells have attached to the scaffold
surface, thus ensuring the non-toxicity of the HAp-
modied 3D printed PLA scaffolds[12].
In this study, Hap-reinforced PLA matrix
biocomposites have been fabricated to determine the
effects of HAp powder loading to the physicochemical
and mechanical properties of the resulting 3D
printed composite (Figure 1). From locally sourced
nanoprecipitated calcium carbonate (NPCC), as-
synthesized HAp powders were mechanically mixed with
PLA at different powder loadings, followed by extrusion
into a lament, and lastly 3D printed. The effect of the
PLA/Hap composition on the crystallinity, morphology,
and mechanical properties was investigated.
2. Materials and methods
2.1. Materials
NPCC was locally sourced from the Philippines. PLA
pellets (PLA, NatureWorks LLC, IngeoTM Biopolymer
2003D) were purchased from D&L Polymers & Colors,
Inc. The following chemicals: Phosphoric acid (H3PO4,
RCI Labscan Ltd.), ammonium hydroxide (NH4OH,
Loba Chemie Pvt. Ltd.), and ethanol (CH3CH2OH,
Thermo Fisher Scientic), were used without further
purications. Distilled water was used in preparing the
solutions and for the washing procedures.
2.2. Hydroxyapatite synthesis
Chemical precipitation technique was undertaken using
aqueous solution of calcium hydroxide, Ca(OH)2 and
H3PO4. Before synthesis, Ca(OH)2 was prepared from the
calcination of NPCC to decompose CaCO3 into CaO and O2
(Eq. 2.1). This was followed by slaking to convert CaO into
3D Printed PLA/HAp Biocomposites
114 International Journal of Bioprinting (2021)–Volume 7, Issue 1
Ca(OH)2 (Eq. 2.2). The obtained Ca(OH)2 was dried and
aqueous solution was prepared for the synthesis of HAp.
CaCO CaOCO
32
→+
(2.1)
CaOHOCaOH
+→
22
()
(2.2)
Ca OH HPOCaP
OO
H() ()
()
23410462
+→
(2.3)
HAp was synthesized by mixing 1.5 M Ca(OH)2
and 1 M H3PO4 (Eq. 2.3) at 40–50°C with continuous
stirring. pH was monitored and maintained at 9–10 pH by
dropwise addition of NH4OH to the mixture. The reaction
required a 48-h maturation period, followed by washing
with ethanol, and nally neutralized using deionized
water. Then, the as-synthesized HAp was dried, ball
milled, and then passed through an 80-mesh sieve. Final
drying step was done at 80°C. Finally, the dried HAp
powders were calcined at 1100°C.
2.3. Extrusion of the PLA/HAp composite
lament
HAp powders were mechanically mixed with PLA
pellets at different powder loadings (0, 5, 10, and 15
wt%) before extrusion and were labeled as PLA/0H,
PLA/5H, PLA/10H, and PLA/15H, respectively
(Table 1). A twin-screw extruder (Labtech Engineering
Co. Ltd., Thailand) with a nominal screw diameter of
20 mm was used to composite the PLA/HAp mixture.
Based on the calorimetric data of the PLA precursor, the
input temperature prole of the 10 extruder’s heating
zone blocks was 190°C, 190°C, 190°C, 200°C, 200°C,
200°C, 200°C, 200°C, 190°C, and 180°C, respectively
(Figure 1). The PLA/HAp mixture was fed onto the
hopper, with an 11 rpm feed rate, and the screw speed
set to 130 rpm. On exiting the nozzle, the lament goes
into a water bath for cooling down, followed by passing
through an air blower, before nally consolidating in
a rotating spooler. The desired lament diameter was
achieved by manually controlling the extruder motor
and spooling speeds. Before printing, the PLA/HAp
composite laments were stored in an airtight dry box
at room temperature to reduce the ambient moisture
absorption.
2.4. 3D printing of the PLA/HAp composite
lament
The composited PLA/HAp blends were loaded and fed onto
a 3D printer (Ultimaker S5, Netherlands) which operates
based on a FDM technology. The printing parameters are
listed in Table 2. Basically, the lament feed is re-extruded
through a ruby-tipped CC print core that is specically
designed for composites, which had a 0.6 mm nozzle.
Print core temperature was set at 200°C (±10), while the
build plate was set to 60°C. A CAD le guided the precise
movement of the print core assembly, which includes the
extrusion nozzle. To compensate for any non-uniformity
of the lament diameter and potential under-extrusion,
the material ow rate was adjusted from 100 to 200% to
achieve an acceptable and uniform print quality.
Dumbbell-shaped tensile test specimens were then
3D printed. The specimen dimensions were adopted
from ASTM D638, and the generated 3D model (.stl)
was digitally drafted through a CAD software such as
SolidWorks (Dassault Systemes, France). The (.stl) le
of the design was sliced using the software Cura, an open
source 3D printing slicing application, which converted
the (.stl) le into the printable (.ufp) le format.
2.5. Digital microscopy
The digital microscope VHX-7000 (Keyence
Corporation, Japan) was used to observe the surface
Table 1. Sample nomenclature and composition.
Sample ID % wt of HAp
PLA lled with 0% HAp PLA/0H 0
PLA lled with 5% HAp PLA/5H 5
PLA lled with 10% HAp PLA/10H 10
PLA lled with 15% HAp PLA/15H 15
PLA, polylactic acid; HAp, hydroxyapatite
Figure 1. Schematic diagram of the polylactic acid/hydroxyapatite composite materials development process.
Custodio, et al.
International Journal of Bioprinting (2021)–Volume 7, Issue 1 115
features and textures, depth prole, and fractured cross
section of the 3D printed PLA/HAp composites, as well
as the resulting scaffolds immersed in simulated body
uid (SBF) solutions. The samples were observed from
30× to 500× range.
2.6. Chemical composition
Attenuated total reectance-Fourier transform infrared
(ATR-FTIR) spectra were recorded across the 4000–
600 cm−1 frequency range, with 1–2 µ penetrating depth,
and with 20 scans per sample at room temperature (23°C)
using a Frontier FTIR spectrometer (PerkinElmer, USA).
The synthesized HAp and 3D printed PLA/HAp composites
were subjected to ATR-FTIR scans to determine the
functional groups within the composite material.
2.7. Crystallinity
The diffraction patterns were obtained using a LabX X-ray
diffraction (XRD)-6000 X-ray diffractometer (Shimadzu,
Japan), with a Cu Kα radiation source at 40 kV operating
voltage. The scanned range for all samples was from 2° to
60° (2θ) with a step size of 1°/min. The synthesized HAp,
3D printed PLA/HAp composites, and the biomineralized
scaffolds were subjected to XRD characterization to
conrm the presence of apatite species and their inuence
to the composite.
2.8. Mechanical properties
As adopted from ASTM D638, the tensile tests were
carried out using a universal testing machine (Instron
5585H, USA), with a 10 kN static load cell, at a gauge
length of 50 mm, and a strain rate of 5 mm/min. Tensile
tests were done to determine the elastic modulus and tensile
strength of the 3D printed PLA/HAp biocomposites. Five
trials were tested for each sample, the average values
reported, and the representative samples were plotted.
Width and thickness of the test specimens were measured
using a Mitutoyo digital caliper before testing. The tests
were performed at room temperature and 54% relative
humidity.
2.9. In vitro biomineralization
The bioactivities of the 3D printed scaffolds were
assessed through immersion in SBF. The scaffolds were
immersed in an SBF solution having a composition
similar to what Rodriguez and Gatenholm reported[16], to
determine the effect of increasing HAp powder loading
to their biomineralization activity as a function of time.
A liter of SBF solution was prepared by dissolving the
analytic grade reagents (< 99%) in distilled water in the
following order shown in Table 3.
In preparing the SBF solution, each reagent was
added after the previous reagent has dissolved completely.
The solution was prepared at 36.5°C under constant
stirring. The pH of the solution was also adjusted to pH
7.4 using 1 M HCl solution and was kept refrigerated
at 4°C before usage. The SBF is similar to the human
blood plasma ionic concentration and composition. The
samples were immersed in 15 mL of SBF solution and
placed inside a dedicated oven set at 37°C for 24, 48,
and 72 h to assess the growth and deposition of apatite
species on the scaffold[17,18]. The SBF-immersed samples
were retrieved from the solution and dried in the oven
overnight, and nally characterized through digital
microscopy, gravimetric analysis, and XRD.
3. Results and discussion
3.1. 3D printed PLA/HAp prototype
Figure 2 shows the digital micrographs of the 3D printed
PLA/HAp composites at different magnication levels,
including the depth prole analysis. The top view of
pure PLA (PLA/0H) was characterized by well-dened
individual print beads, as the grid could be clearly seen
both from 30× to 200× (Figure 2A and B), and even at the
depth prole (Figure 2E-F). However, as the HAp loading
was increased from 5 wt% to 15 wt%, the print beads were
slowly disappearing and became less dened. Likewise,
the surface nish oh PLA/5H, PLA/10H, and PLA/15H
were more irregular and rougher than PLA/0H. The same
visual trend could be seen at the depth prole, whereas the
print bead gaps were slowly closing in and disappearing
(Figure 2L, R and X). Hence, the 3D printed PLA/HAp
composites were becoming more irregular as the HAp
loadings were increased. Nonetheless, hydroxyapatite
powders were seen from the composite surface with
increasing frequency in accordance to the increasing
HAp loading, although the distribution were irregular and
agglomeration was present (Figure 2H, J, N, P, T and V).
Porosity and density are also some physical
properties that must be considered, especially with polymer
matrix composites. These properties can provide useful
information in the prediction of the material’s behavior,
for instance, under mechanical stimuli. A denser material
is usually a stronger one, and a porous material is usually
Table 2. 3D printing parameters for FDM printing of PLA/HAp
composites.
Parameters Settings
Layer height 0.2 mm
Inll density 100%
Inll pattern Grid (45°, −45°)
Printing temperature 210°C
Build plate temperature 60°C
Print speed 45 mm/s
Extrusion width (nozzle diameter) 0.6 mm
PLA, polylactic acid; HAp, hydroxyapatite; FDM, fused deposition
modeling.
3D Printed PLA/HAp Biocomposites
116 International Journal of Bioprinting (2021)–Volume 7, Issue 1
mechanically inferior. The experimental density and true
porosity are presented in Figures 3A and B, respectively.
We can see that as the HAp loading was increased, in an
opposite manner the composites’ density decreased. On
the other hand, the porosity kept increasing, which means
that more voids were forming as more HAp was added.
Perhaps the tendency of HAp particles to agglomerate
inuenced the composites’ microstructure and developed
two kinds of sites that were agglomerated and areas that
were porous as well. The true porosity was calculated
using the following equation:
%
()
=− ×P1 100
experimental
theoretical
(3.1)
Where P refers to the true porosity (in percent),
ρexperimental refers to experimental density, and ρtheoretical
refers to theoretical density. The literature theoretical
densities of ρPLA and ρHAp are 1.43 g•cm−3 and 3.16 g•cm−3,
respectively[19].
3.2. Chemical composition
The changes in absorbance or absence of certain peaks
in the FTIR spectra are presented in Figure 4. These
absorption peaks can be attributed to functional groups
that are present in HAp, in pure PLA, or in the composite
material. Peaks and functional groups originating from
PLA were located approximately at 2996 cm−1 and
2945 cm−1 (CH3 stretching). The peaks at 1748 cm−1,
Table 3. Reagents and composition of the simulated body uid solution.
Chemical reagent Formula
weight (g/mol)
Weight (g or mL
in 1 L solution)
Sodium chloride NaCl, Univar 58.44 7.996 g
Sodium bicarbonate NaHCO3, Loba Chemie 84.01 0.350 g
Potassium chloride KCl, TPC 74.55 0.224 g
Potassium phosphate dibasic anhydrous K2HPO4, Loba Chemie 174.18 0.228 g
Magnesium chloride hexahydrate MgCl·6H2O, Loba Chemie 203.3 0.305 g
Hydrochloric acid (1 M) HCl, LabScan 36.458 40 mL
Calcium chloride dihydrate CaCl2·2H2O, TPC 147.02 0.278 g
Sodium sulfate anhydrous Na2SO4, Fisher Scientic 142.02 0.071 g
Tris buffer NH2C(CH2OH)3 Loba Chemie 121.14 6.057 g
Figure 2. Digital micrographs of 3D printed polylactic acid (PLA)/hydroxyapatite: (A-F) PLA/0H; (G-L) PLA/5H; (M-R) PLA/10H; and
(S-X) PLA/15H.
D
L
H
P
C
K
G
O
B
J
F
N
A
I
E
M
TX
SW
R
V
Q
U
Custodio, et al.
International Journal of Bioprinting (2021)–Volume 7, Issue 1 117
1181 cm−1, 1127 cm−1, and 1080 cm−1 are identied as
the backbone of ester groups of PLA[20]. Furthermore,
1748 cm−1 pertains to C=O stretching vibrations[21], the
peak at 1045 cm−1 for the OH bending, while the 1200–
1000 cm−1 refers to C-O stretching[22].
Peaks coming from HAp are generally from phosphate
groups, such as 1090 cm−1, 1030 cm−1, 600 cm−1, and
565 cm−1 (PO4 bending), and 960 cm−1 (PO4 stretching).
Carbonate ions were faintly present at 870 cm−1[11,13].
The high calcining temperature of 1100°C in the HAp
synthesis has caused the removal of water (as suggested
by the absence of 3600–3200 cm−1 OH stretch). The
visibility of the structuring OH was identied at 635 cm−1
ngerprint region, indicating a better powder-polymer
Figure 4. Fourier transform infrared spectra of hydroxyapatite (Hap), polylactic acid (PLA), and the 3D printed PLA/HAp composite
(15 wt. %).
Figure 3. (A) Experimental density and (B) true porosity of the 3D printed polylactic acid /hydroxyapatite composites.
B
A
3D Printed PLA/HAp Biocomposites
118 International Journal of Bioprinting (2021)–Volume 7, Issue 1
adhesion. However, the high calcination temperature
might have also caused aggregation which prevented good
dispersion of HAp powders in the PLA matrix[14]. The few
prominent peaks of HAp were observed to be overlapped
by the more intense peaks of PLA, approximately around
1100–900 cm−1. Moreover, no new covalent bonds formed
within the PLA/HAp composites, suggesting that the HAp
llers were embedded in the polymer matrix through
mechanical manner rather than by chemical means.
3.3. Crystallinity
XRD of HAp, PLA, and the printed PLA/HAp
biocomposites is shown in Figure 5. The HAp
diffractogram displayed the crystalline nature of the
powder. Prominent peaks and their corresponding planes
were noted at approximately 26° (002), 33° (112), 47°
(222), and 49° (213). The (211) plane at ca. 32° is inherent
to and characteristic of pure HAp[12].
Pure PLA (PLA/0H) exhibited a broad spectrum
indicating the amorphous structure of the polymer[23].
The composite samples exhibited diffraction peaks
characterized by the presence of HAp in the polymer
matrix. The peak intensity increases as a function of the
increase in HAp powder loading.
3.4. Mechanical properties
The tensile stress-strain curve of PLA/HAp biocomposites
is shown in Figure 6A. The HAp indeed had a reinforcing
effect, as the elastic moduli and tensile strengths both
increased compared to pure PLA. As the powder loading
was increased, the elastic modulus increased compared
to pure PLA (2.3–~3.5 GPa), but the modulus remained
consistent despite the further increase in HAp loading
(Figure 6B). Unsurprisingly, the tensile strength decreased
at 15 wt% HAp loading as the powder loading increased.
This may be primarily due to the HAp agglomeration and
poor dispersion, as well as the formation of macro voids
between neighboring lament beads. Nevertheless, HAp
has shown to improve the strength of pure PLA (32.7–
47.3 MPa). HAp might also act as nucleation sites where
PLA molecule chains could have entangled itself through
mechanical interlocking effects.
The stiffness of both PLA/10H and PLA/15H
similarly generated 3.5 GPa elastic modulus which is
within the range of the human cancellous bone tissue[15];
hence, these formulations have the potential for the repair
of smaller bone tissues.
The fracture surface after the uniaxial tensile
testing of PLA/HAp biocomposites are shown in
Figure 5. X-ray diffractograms of hydroxyapatite (HAp), and varying powder loading in 3D printed polylactic acid/HAp composites
(0–15 wt. %).
Custodio, et al.
International Journal of Bioprinting (2021)–Volume 7, Issue 1 119
Figure 7. Fracture surfaces can provide knowledge
and insight on the interaction between the matrix
and reinforcement upon the application of force. The
tensile-tested PLA/HAp composites exhibited linear,
brittle fractures (Figure 7D, G and J), contrary to
the somewhat irregular, moderately ductile fracture
from the PLA/0H sample (Figure 7A). Furthermore,
at higher magnifications (Figure 7B, E and H, K) the
individual print beads were slowly disappearing as the
HAp loading was increased. Evolution of macro voids
or pores were also noticeable at higher magnifications
(Figure 7 I and L). These macro voids account
for the decreasing density and likewise increasing
porosity from Figure 3. A plausible explanation can
be attributed to the agglomeration of HAp particles,[15]
which causes some areas to be denser and consequently
Figure 6. (A) Tensile stress-strain graph, (B) elastic moduli, and (C) tensile strength of the 3D printed polylactic acid/hydroxyapatite
composites.
C
B
A
Figure 7. Fracture surfaces of the tensile-tested 3D printed polylactic acid (PLA)/hydroxyapatite composites. (A-C) PLA/0H; (D-F)
PLA/5H; (G-I) PLA/10H; and (J-L) PLA/15H.
D
H I
JKL
C
G
B
F
A
E
3D Printed PLA/HAp Biocomposites
120 International Journal of Bioprinting (2021)–Volume 7, Issue 1
creating other sites with less material leading to void
formation.
3.5. In vitro biomineralization
A preliminary in vitro bioactivity test was done by
immersing the 3D printed PLA/HAp composite samples
in SBF solutions for 24, 48, and 72 h, and the digital
micrograph results are shown in Figure 8, while the
percent weight gain and X-ray diffractograms are
shown in Figure 9A and B, respectively. As seen on the
digital micrographs, the 3D printed pure PLA (PLA/0H)
exhibited an etching response to soaking in SBF. This
was supported by the mass loss in Figure 9A. Pure PLA
remains to be partly hydrophilic, and hence subjecting it
to an aqueous immersion resulted to some PLA dissolving
away.
The PLA/HAp composites reported varying weight
gains, with the trend that was increasing. HAp particles
Figure 8. Digital micrographs of 3D printed polylactic acid/hydroxyapatite scaffolds immersed for 72 h in simulated body uid for
biomineralization activity.
D
L
H
C
K
G
B
J
F
A
I
E
Figure 9. (A) Weight gain (%) and (B) X-ray diffractograms of the 3D printed polylactic acid/hydroxyapatite composites after the 72-h
immersion test in SBF.
B
A
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International Journal of Bioprinting (2021)–Volume 7, Issue 1 121
embedded within the PLA matrix served as nucleation
sites for the deposition of calcium salts and apatite species
present from the SBF solution. X-ray diffractograms
shown in Figure 9B report of the evolution of peaks after
the immersion in SBF for 72 h. The characteristic peak
at 2θ ~32° conrm the growth of apatite species on the
3D printed samples during the immersion bioactivity[18].
Other well-dened peaks could be attributed to other salt
species present in the SBF solution being deposited onto
the 3D printed substrates.
4. Conclusion
The HAp used in this study was successfully synthesized
as conrmed by the FTIR and XRD spectra. Pure PLA
exhibited a broad infrared spectrum indicating the
amorphous structure of the polymer. The 3D printed
PLA/HAp composite samples exhibited XRD diffraction
peaks characterized by the presence of HAp with the
peak intensity increasing as a function of HAp powder
loading. Moreover, composites’ density decreases as
the HAp loading was increased. The elastic modulus
increased from 2.3 to 3.5 GPa and the tensile strength
increased from 32.7 to 47.3 MPa with 15% HAp loading.
The preliminary in vitro bioactivity test of the 3D printed
PLA/HAp composite samples in SBF solutions for 24, 48,
and 72 h indicated varying weight gains progressively as
well as the evolution of XRD peaks. These indicate that
HAp particles embedded within the PLA matrix served
as nucleation sites for the deposition of calcium salts and
apatite species present from the SBF solution.
Author contributions
B.A.B. led the project and edited the paper. J.R.C., C.L.C.,
and P.J.M.B. designed the study. P.J.M.B. and S.R.C.
performed the HAp synthesis and biomineralization,
respectively. P.J.M.B. and C.L.C. performed the lament
extrusion. C.L.C. performed most experiments, 3D
printing, characterizations, data analysis, and wrote the
paper with help from V.U. L. and J.R.C.
Conicts of interest
The authors declare that they have no conicts of interest.
Acknowledgments
We acknowledge the funding of this research project from
the Department of Science and Technology – Grants-In-
Aid (Department of Science and Technology [DOST]-
GIA). We are also grateful for the technical support
provided by the Advanced Device and Materials Testing
Laboratory, and the Standards and Testing Division of
the Industrial Technology Development Institute of the
DOST, Philippines.
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