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Powder Loading Effects on the Physicochemical and Mechanical Properties of 3D Printed Poly Lactic Acid/Hydroxyapatite Biocomposites


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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 filler for the PLA matrix. The 0, 5, 10, and 15 wt. % HAp biocomposite filaments were formed using a twin-screw extruder. The resulting filaments 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 fluid (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
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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;
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.
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 specied 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 specic
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
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original work is properly cited.
Custodio, et al.
International Journal of Bioprinting (2021)–Volume 7, Issue 1 113
monomer resin. The liquid resin solidies 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 benet 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 difculty 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]. Articial 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 modication 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-
modied 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 Scientic), were used without further
purications. 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.
H() ()
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
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 prole 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
2.4. 3D printing of the PLA/HAp composite
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 specically
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 prole, 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 reectance-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
conrm the presence of apatite species and their inuence
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
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 magnication levels,
including the depth prole analysis. The top view of
pure PLA (PLA/0H) was characterized by well-dened
individual print beads, as the grid could be clearly seen
both from 30× to 200× (Figure 2A and B), and even at the
depth prole (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 dened. 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 prole, 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
Parameters Settings
Layer height 0.2 mm
Inll density 100%
Inll 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
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
inuenced 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
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,
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 Scientic 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.
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International Journal of Bioprinting (2021)–Volume 7, Issue 1 117
1181 cm−1, 1127 cm−1, and 1080 cm−1 are identied 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 identied 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.
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
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.
3D Printed PLA/HAp Biocomposites
120 International Journal of Bioprinting (2021)–Volume 7, Issue 1
creating other sites with less material leading to void
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
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.
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.
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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° conrm the growth of apatite species on the
3D printed samples during the immersion bioactivity[18].
Other well-dened 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 conrmed 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.
Conicts of interest
The authors declare that they have no conicts of interest.
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.
1. Najmon JC, Raeisi S, Tovar A, 2019, Review of Additive
Manufacturing Technologies and Applications in the
Aerospace Industry. Additive Manufacturing for the
Aerospace Industry. Elsevier Inc., Amsterdam, Netherlands.
2. Wiese M, Thiede S, Herrmann C, 2020, Rapid Manufacturing
of Automotive Polymer Series Parts: A Systematic Review
of Processes, Materials and Challenges. Addit Manuf,
3. Ng WL, Chua CK, Shen YF, 2019, Print Me An Organ! Why
We Are Not There Yet. Prog. Polym. Sci., 97:101145.
4. Lee JM, Ng WL, Yeong WY, 2019, Resolution and Shape
in Bioprinting: Strategizing Towards Complex Tissue and
Organ Printing. Appl. Phys. Rev., 6:011307.
5. Lao W, Li M, Wong TN, et al., 2020, Improving Surface
Finish Quality in Extrusion-based 3D Concrete Printing
Using Machine Learning-based Extrudate Geometry Control.
Virtual Phys Prototyp, 15:178–93.
6. Ahmed ZY, Bos FP, van Brunschot MCA, et al., 2020, On-
demand Additive Manufacturing of Functionally Graded
Concrete. Virtual Phys Prototyp, 15:194–210.
7. Alizadeh-Osgouei M, Li Y, Wen C. 2019, A Comprehensive
Review of Biodegradable Synthetic Polymer-ceramic
Composites and their Manufacture for Biomedical
Applications. Bioact Mater, 4:22–36.
8. Ng WL, Lee JM, Zhou M, et al., 2020, Vat Polymerization-
based Bioprinting Process, Materials, Applications and
Regulatory Challenges. Biofabrication, 12:022001.
9. Gayer C, Ritter J, Bullemer M, et al., 2019, Development of
a solvent-free polylactide/calcium carbonate composite for
selective laser sintering of bone tissue engineering scaffolds.
Mater Sci Eng C, 101:660–73.
10. Percoco G, Uva AE, Fiorentino M, et al., 2020,
Mechanobiological Approach to Design and Optimize Bone
Tissue Scaffolds 3D Printed with Fused Deposition Modeling:
A Feasibility Study. Materials (Basel), 13: 648.
3D Printed PLA/HAp Biocomposites
122 International Journal of Bioprinting (2021)–Volume 7, Issue 1
11. Hassanajili S, Karami-Pour A, Oryan A, et al., 2019,
Preparation and Characterization of PLA/PCL/HA
Composite Scaffolds Using Indirect 3D Printing for Bone
Tissue Engineering. Mater Sci Eng C, 104:109960.
12. Mondal S, Phuoc T, Pham VH, et al., 2019, Hydroxyapatite
Nano Bioceramics Optimized 3D Printed Poly Lactic Acid
Scaffold for Bone Tissue Engineering Application. Ceram
Int, 46:1–13.
13. Lopresti F, Pavia FC, Vitrano I, et al., 2020, Effect of
Hydroxyapatite Concentration and Size on Morpho-
mechanical Properties of PLA-based Randomly Oriented
and Aligned Electrospun Nanobrous Mats. J Mech Behav
Biomed Mater, 101:103449.
14. Pietrzykowska E, Mukhovskyi R, Chodara A, et al., 2019,
Composites of Polylactide and Nano-Hydroxyapatite Created
by Cryomilling and Warm Isostatic Pressing for Bone
Implants Applications. Mater Lett, 236:625–8.
15. Prasad A, Bhasney S, Katiyar V, et al., 2017, Biowastes
Processed Hydroxyapatite lled Poly (Lactic acid) Bio-
Composite for Open Reduction Internal Fixation of Small
Bones. Mater Today Proc, 4:10153–7.
16. Rodríguez K, Renneckar S, Gatenholm P, 2011, Biomimetic
Calcium Phosphate Crystal Mineralization on Electrospun
Cellulose-based Scaffolds. ACS Appl Mater Interfac, 3:681–9.
17. Hamzah MSA, Ng C, Zulkarnain NI, et al., 2020, Entrapment
of Collagen on Polylactic Acid 3D Scaffold Surface as a
Potential Articial Bone Replacement. Mater Today Proc,
18. Alam F, Varadarajan KM, Kumar S, 2020, 3D Printed
Polylactic Acid Nanocomposite Scaffolds for Tissue
Engineering Applications. Polym Test, 81:106203.
19. Nawawi AN, Alqap SF, Sopyan I, 2011, Recent Progress on
Hydroxyapatite-based Dense Biomaterials for Load Bearing
Bone Substitutes. Recent Patents Mater Sci, 4:63–80.
20. Lizundia E, Vilas JL, León LM, 2015, Crystallization,
Structural Relaxation and Thermal Degradation in Poly(l-
lactide)/Cellulose Nanocrystal Renewable Nanocomposites.
Carbohydr Polym, 123:256–65.
21. Xu C, Chen J, Wu D, et al., 2016, Polylactide/Acetylated
Nanocrystalline Cellulose Composites Prepared by a
Continuous Route: A Phase Interface-property Relation
Study. Carbohydr Polym, 146:58–66.
22. Gazzotti S, Farina H, Lesma G, et al., 2017, Polylactide/
Cellulose Nanocrystals: The in situ Polymerization Approach
to Improved Nanocomposites. Eur Polym J, 94:173–84.
23. Bhasney SM, Bhagabati P, Kumar A, et al., 2019, Morphology
and Crystalline Characteristics of Polylactic Acid [PLA]/
Linear Low Density Polyethylene [LLDPE]/Microcrystalline
Cellulose [MCC] Fiber Composite. Compos Sci Technol,
... Using a simple desktop 3D printer, PLA's excellent mechanical qualities, chitosan's bioactivity, and HAp's osteogenic capabilities are combined to build composite scaffolds where the solvent used was formic acid for making PLA/CS/HAp composites to prepare stable chitosan/HAp dispersions [28]. In the SBF solution, the PLA matrix's HAp particles served as nucleation sites for salt and apatite species deposition [29]. ...
... The influence of the extrusion process was particularly noticeable in PLA, where the prominent PLA peak at 2h = 16.9 diminishes thereby indicating amorphity in the polymer matrix during the extrusion process [207,208]. Figure 11 shows the XRD spectra of PLA/HAp composites prepared by Custodio et al. at varying HAp loading [29]. Lizundia et al. pointed out that the peaks and functional groups arising from PLA were found at 2996 cm -1 and 2945 cm -1 , respectively (CH 3 stretching) wherein the backbone of PLA ester groups is recognised as peaks at 1748 cm -1 , 1181 cm -1 , 1127 cm -1 , and 1080 cm -1 , respectively [209]. ...
... In a study conducted by Soufiani et al. involving PLA/HAp with regenerate cellulose microfibres, TGA examination of samples were taken at various places along the films revealed the distribution of the HAp and Figure 11 XRD spectra of PLA/HAp composites. Reproduced with permission [29]. Copyright 2021, Whioce. ...
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The field of tissue engineering involves various methodologies employed to improve or replace biological tissues with extracellular matrices (ECMs). Significant progress has been made, particularly in the fabrication of three-dimensional (3D) scaffolds for replacing damaged tissues or organs. The current review broadly focuses on the various research works carried out involving the use of biomaterials (biopolymers, bio-ceramics and dopants) in this area. A detailed discussion on several scaffold-making modern technologies has also been provided, along with a demonstration of different characterization techniques. Though a number of review papers have been published on biomaterials and fabrication techniques, a very small number focuses on the clinical trials carried out and the commercialization of scaffolds in the biomedical field. Thus, a critical analysis and detailed discussion of some of the clinical trials, market growth, and future demands have been presented in this paper. Graphical Abstract
... There is, finally, a property of PLA of particular interest in relation to the 3D-FDM technology: its low glass transition temperature (55-65 • C) [14]. This property makes it deformable under high temperatures (190-220 • C), providing the versatility sought in the manufacture of the scaffold [11,[15][16][17]. ...
... In relation to 3D-printed PLA, numerous studies have been found in the literature reviewed where PLA has been combined with HA by the surface modification of 3D-printed parts [4,22] or by manufacturing a filament prior to the printing process [16,[23][24][25]. However, obtaining this single pre-fabricated filament requires a laborious process, especially when the materials to combine are formulated in different sizes. ...
... Thus, as it can be observed, the value of Young's modulus (dark gray) obtained for the PLA0HA scaffolds was 4.57 ± 0.06 GPa, which is in agreement with the literature [41]. Moreover, it is shown that this elasticity modulus is affected by the incorporation of HA into the scaffold, being higher as the HA wt.% increases, which was also noted by other authors for PLA biocomposites with 5, 10 and 15 wt.% of HA, by 3D printing with previously extruded filaments [16]. This tendency is interpreted as an increase in the material's stiffness as the bioceramic particle concentration increases. ...
Full-text available
The reconstruction or regeneration of damaged bone tissue is one of the challenges of orthopedic surgery and tissue engineering. Among all strategies investigated, additive manufacturing by fused deposition modeling (3D-FDM printing) opens the possibility to obtain patient-specific scaffolds with controlled architectures. The present work evaluates in depth 3D direct printing, avoiding the need for a pre-fabricated filament, to obtain bone-related scaffolds from direct mixtures of polylactic acid (PLA) and hydroxyapatite (HA). For it, a systematic physicochemical characterization (SEM-EDS, FT-Raman, XRD, micro-CT and nanoindentation) was performed, using different PLA/HA ratios and percentages of infill. Results prove the versatility of this methodology with an efficient HA incorporation in the 3D-printed scaffolds up to 13 wt.% of the total mass and a uniform distribution of the HA particles in the scaffold at the macro level, both longitudinal and cross sections. Moreover, an exponential distribution of the HA particles from the surface toward the interior of the biocomposite cord (micro level), within the first 80 µm (10% of the entire cord diameter), is also confirmed, providing the scaffold with surface roughness and higher bioavailability. In relation to the pores, they can range in size from 250 to 850 µm and can represent a percentage, in relation to the total volume of the scaffold, from 24% up to 76%. The mechanical properties indicate an increase in Young’s modulus with the HA content of up to ~50%, compared to the scaffolds without HA. Finally, the in vitro evaluation confirms MG63 cell proliferation on the 3D-printed PLA/HA scaffolds after up to 21 days of incubation.
... Additive manufacturing (also known as 3D printing), developed in the second half of the 20th century, is a technology that enables the construction of three-dimensional objects out of digital data (a 3D model) [2][3][4]. The recent development of AM technologies has enabled tailored patient treatment and several uses for in medicine (anatomical models, dental appliances, medical devices, pharmaceuticals, organs, tissue, and testing models) [5,6]. alone can increase the mechanical resistance of the products by enhancing compression and elasticity resistance. ...
... Additionally, as a direct consequence of the synthesis technology [45], the HA particles acquired a microporous surface, which is considered to be beneficial for a more intimate contact and adhesion to other materials used as matrix for composite filaments (e.g., polymeric materials) [43]. When addressed differently, this feature of the ceramic particles is sometimes challenging and rather difficult to achieve [5,27]. ...
Full-text available
Additive manufacturing or 3D printing technologies might advance the fabrication sector of personalised biomaterials with high-tech precision. The selection of optimal precursor materials is considered the first key-step for the development of new printable filaments destined for the fabrication of products with diverse orthopaedic/dental applications. The selection route of precursor materials proposed in this study targeted two categories of materials: prime materials, for the polymeric matrix (acrylonitrile butadiene styrene (ABS), polylactic acid (PLA)); and reinforcement materials (natural hydroxyapatite (HA) and graphene nanoplatelets (GNP) of different dimensions). HA was isolated from bovine bones (HA particles size < 40 μm, <100 μm, and >125 μm) through a reproducible synthesis technology. The structural (FTIR-ATR, Raman spectroscopy), morphological (SEM), and, most importantly, in vitro (indirect and direct contact studies) features of all precursor materials were comparatively evaluated. The polymeric materials were also prepared in the form of thin plates, for an advanced cell viability assessment (direct contact studies). The overall results confirmed once again the reproducibility of the HA synthesis method. Moreover, the biological cytotoxicity assays established the safe selection of PLA as a future polymeric matrix, with GNP of grade M as a reinforcement and HA as a bioceramic. Therefore, the obtained results pinpointed these materials as optimal for future composite filament synthesis and the 3D printing of implantable structures.
... The HAP particle embedded in the PLA matrix could serve as nucleation sites to facilitate the nucleation of apatite. 32 Otherwise Ca 2+ ion released from HAP particle could interact with the PO 4 3ions in the SBF solution to promote the growth and maturity of apatite. HAP particle enhance the formation and deposition of apatite on the PLA matrix. ...
In this study, biocomposites as feedstock material for 3D printing were produced by poly (lactic acid) (PLA) as a polymer matrix and Hydroxyapatite (HAP) as reinforcing filler for potential use in biomedical applications. Biocomposites filament from PLA and different HAP content varying from 1–10 wt% were prepared from extrusion and then injection moulding process. The impact of HAP loading on the properties of biocomposites was investigated for crystallinity, density, hardness, tensile, impact, flexural, melt flow index (MFI), thermal properties and biomineralization studies. The formation of PLA/HAP biocomposites was confirmed by fourier transform infrared spectroscopy (FTIR). The hydrophilicity of the biocomposites was studied by contact angle analysis. Dispersion of HAP into PLA matrix was confirmed by scanning electron microscopy (SEM) and optical microscopy. The HAP addition increased the density of the composites. From mechanical analysis PLA/HAP composites containing 1–5 wt% showed an increase in tensile modulus. The Shore D hardness of the composites increased with increase in wt% of HAP content. The maximum hardness was achieved for 10 wt% of HAP content i.e., 87 ± 0.1, which is about 6.1% more than neat PLA. The MFI increased with rise in HAP content that gives a positive opinion of reinforcing PLA composites without deteriorating the processability. The hydrophilicity of the biocomposites was slightly increased after the addition of HAP. From thermal analysis it was concluded that the thermal stability of the biocomposites increased when compared with neat PLA. From the Biomineralization studies formation of apatite layer on PLA composites was confirmed by SEM analysis.
... The fundamental justification for why polylactic acid can be utilized as a 3printing material is that it has great biocompatibility, sparkle and straightforwardness, mechanical properties, degradability, low softening point, and low thickness [86,87]. While it has imperfections like more noteworthy weakness and unfortunate effect resistance [88]. ...
Full-text available
Bone and articular cartilage degeneration and damage are the most common causes of musculoskeletal disability. 3D bioprinting can help regenerate these structures. Autologous/allogeneic bone and cartilage transplantation, vascularized bone transplantation, autologous chondrocyte implantation, mosaicplasty, and joint replacement are all common clinical and surgical procedures. In vitro layer-by-layer printing of biological materials, living cells, and other biologically active substances using 3D bio printing technology is anticipated to replace the aforementioned repair methods. With the ability to prepare various organs and tissue structures, 3D bio printing has largely solved the issue of insufficient organ donors. Researchers use biomedical materials and cells as discrete materials. Bioprinting cell selection and its use in bone and cartilage repair are the primary topics of discussion in this paper.
... 32 The continuous increase in the impact strength of the PLA nanocomposites observed as the NHA loading increased suggests the PLA became less brittle upon adding NHA. 33 With the addition of only 0.01 wt% of GNP, the impact strength of the PLA-mNHA-GNP nanocomposite was increased by 22.1% (neat PLA) and 7.9% (PLA-5wt%mNHA(APTES)). This can be accredited to the mNHA-GNP nanofiller absorbing the energy and acting as crack deflectors and crack bridging mechanisms at a lower loading. ...
Full-text available
In this study, poly-lactic acid (PLA), nanohydroxyapatite (NHA), and graphene nanoplatelets (GNP) were compounded to attain a suitable nanocomposite for load-bearing bone implants with strain sensing prospects. Biocompatibility of the nanocomposites (PLA, PLA-NHA, PLA-mNHA, and PLA-mNHA-GNP) was investigated using in-vitro analysis. The nanocomposites were attached with MG63 cells to proliferate and differentiate within 7 days and 21 days of incubation, respectively. In comparison to cells cultivated on clean PLA, those on the PLA-5wt%NHA nanocomposite spread to a greater extent. In comparison to PLA-5wt%NHA, PLA-5wt%mNHA (APTES) nanocomposite was able to promote the highest rate of cell proliferation at day 7. Field-emission scanning electron microscope observation of the cells-nanocomposites and the MTT and Alkaline Phosphatase assays results confirmed that the nanocomposites were biocompatible with the MG63 cells. In addition to biocompatibility, the tensile properties and impact strength of PLA-NHA nanocomposite have been studied as it is one of the favourable properties of biomechanical implants with strain sensing application prospects. In comparison to 0.01wt% GNP, an increase in GNP loading caused the impact strength to decrease by 7.9% (0.05wt% GNP) and 25.7% (0.1wt% GNP). The biocompatibility of the prepared nanocomposites was determined based on their ability to, thus allowing the cell perfoliation.
... For PLA/HAp composites, the XRD pattern exhibits some characteristic peaks of HAp powder at approximately 25°, 31° and 33°, which are assigned to the (002), (211) and (300) reflections, respectively. Furthermore, there is also an increase in the peak intensity with increasing the HAp content, as reported in the literature [44]. In Figure 8, the XRD spectrum of the PLA/HAp composite, loaded at 5 wt%, displays two sharp diffraction peaks, the first one is located at 2θ = 16.6° and the other at 19.8°, which correspond respectively to the plans (110)/(200) and (203)/(113). ...
Full-text available
The effect of hydroxyapatite (HAp) synthesized by the chemical precipitation process on the morphology and properties of composites based on poly(lactic acid) (PLA) was investigated at various filler content ratios, i.e., 5, 10 and 15 wt%. Both neat PLA and PLA-based composites were first prepared using the solvent casting method, followed by melt compounding in an internal mixer, whereas tensile specimens were obtained by thermo-compression. The study revealed that the addition of 5 wt% of HAp into the PLA led to a slight improvement in both the thermal stability and tensile properties of the composite material in comparison with neat PLA and other composite samples. Indeed, the values of the tensile strength and modulus increased from approximately 61 MPa and 2.9 GPa for the neat PLA to almost 64 MPa and 3.057 GPa for the composite sample, respectively. Moreover, the degradation temperature at a 5 wt% mass loss also increased by almost 5 °C compared to other samples, due probably to a finer dispersion of the HAp particles in the PLA, as observed under a scanning electron microscope. Furthermore, the FT-IR spectra displayed some changes in the chemical structure of the PLA/HAp (5 wt%), indicating the occurrence of filler-matrix interactions. At a higher filler content ratio, a decrease in the properties of the PLA/HAp composites was observed, being more pronounced at 15 wt%. The PLA composite containing 5 wt% HAp presents the best compromise among the investigated properties. The study highlighted the possibility of using HAp without any prior surface treatment as a reinforcement in PLA composite materials.
... The inclusion of CaP particles, like hydroxyapatite (HA) and/or β-tricalcium phosphate (β-TCP) in the PLA matrix, could be a solution to address these limitations, by improving mechanical and thermal properties and accelerating the biodegradation rate [8][9][10]. This type of composite materials has recently been explored in the production of filaments as feedstock for scaffolds fabrication through Fused Filament Fabrication (FFF) [8,[11][12][13][14][15][16]. ...
This work aims the manufacture of injection molded polylactic acid (PLA)-based magnetic biocomposites, presenting an alternative approach to enhance the magnetic susceptibility of PLA-based biocomposites without resorting to the exclusive incorporation of magnetic nanoparticles whose long-term side effects are still unclear. Magnetic biocomposites were obtained by incorporating 5 wt% of iron doped biphasic calcium phosphate (FeBCP) powders into the PLA matrix and compared with similar composites containing 2 and 5 wt% of non-doped BCP powder, as well as neat PLA. The chemical, thermal, mechanical, and magnetic performances were evaluated. Biodegradability according to two sterilization methods used and cytotoxicity were also assessed. The composites with FeBCP exhibited a typical ferromagnetic-like behavior and presented a superior tensile strength even with low concentrations of FeBCP, when compared to PLA or non-doped composites, besides being cytocompatible. The presented proof of concept paves the way for future developments of new magnetic PLA-based biocomposites for biomedical applications.
Exosome-based strategies constitute a promising tool for therapeutics, avoiding potential immunogenic and tumorigenic side-effects of cell therapies. However, the collection of a suitable exosome pool, and the need for high doses with conventional administration approaches, hamper their clinical translation. To overcome these challenges, versatile exosome collection strategies together with advanced delivery platforms may represent major progress in this field. Microfluidics enables large-scale gathering of both natural and synthetic exosomes for their implementation into bioinks, while 3D-bioprinting holds great promise in regenerative medicine with the use of exosome-loaded scaffolds that mimic the target tissue with controlled pharmacokinetics and pharmacodynamics. Hence, the combination of both strategies might become the key for the translation of exosome therapies to clinical practice.
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The rapid development of additive manufacturing of cementitious materials has enabled the emergence of a new design paradigm, namely functional grading of material properties by location. Target performance parameters could be material weight and insulation value or (particularly important) ductility. A generic concept to achieve this, is through the selective addition of fibres or aggregates. In 3D concrete printing (3DCP), this concept can be developed into two strategies: by adding particles (i) to the bulk mixture through a second stage mixing process at the printer head (Simultaneous Process, SP), or (ii) in between the layers of deposited cementitious filament (Repetitive Sequential Process, RSP). The present paper presents the development of specific equipment required to obtain on–demand functional grading of the printed material. Subsequently, the application of these systems in print trials is shown. The current study focussed on ductility by creating fibre–reinforced 3D printed concrete through both strategies. The mechanical performance of the obtained material has been established through compressive, flexural, and crack–mouth opening displacement tests. To underline the generic nature of the strategies, a trial with lightweight aggregates has also been performed. It was shown that particularly the SP is capable of achieving improvements in ductility and self–weight.
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In spite of the rather large use of the fused deposition modeling (FDM) technique for the fabrication of scaffolds, no studies are reported in the literature that optimize the geometry of such scaffold types based on mechanobiological criteria. We implemented a mechanobiology-based optimization algorithm to determine the optimal distance between the strands in cylindrical scaffolds subjected to compression. The optimized scaffolds were then 3D printed with the FDM technique and successively measured. We found that the difference between the optimized distances and the average measured ones never exceeded 8.27% of the optimized distance. However, we found that large fabrication errors are made on the filament diameter when the filament diameter to be realized differs significantly with respect to the diameter of the nozzle utilized for the extrusion. This feasibility study demonstrated that the FDM technique is suitable to build accurate scaffold samples only in the cases where the strand diameter is close to the nozzle diameter. Conversely, when a large difference exists, large fabrication errors can be committed on the diameter of the filaments. In general, the scaffolds realized with the FDM technique were predicted to stimulate the formation of amounts of bone smaller than those that can be obtained with other regular beam-based scaffolds.
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Over the years, the field of bioprinting has attracted attention for its highly automated fabrication system that enables the precise patterning of living cells and biomaterials at pre-defined positions for enhanced cell-matrix and cell-cell interactions. Notably, vat polymerization (VP)-based bioprinting is an emerging bioprinting technique for various tissue engineering applications due to its high fabrication accuracy. Particularly, different photo-initiators (PIs) are utilized during the bioprinting process to facilitate the crosslinking mechanism for fabrication of high-resolution complex tissue constructs. The advancements in VP-based printing have led to a paradigm shift in fabrication of tissue constructs from cell-seeding of tissue scaffolds (non-biocompatible fabrication process) to direct bioprinting of cell-laden tissue constructs (biocompatible fabrication process). This paper, presenting a first-time comprehensive review of the VP-based bioprinting process, provides an in-depth analysis and comparison of the various biocompatible PIs and highlights the important considerations and bioprinting requirements. This review paper reports a detailed analysis of its printing process and the influence of light-based curing modality and PIs on living cells. Lastly, this review also highlights the significance of VP-based bioprinting, the regulatory challenges and presents future directions to transform the VP-based printing technology into imperative tools in the field of tissue engineering and regenerative medicine. The readers will be informed on the current limitations and achievements of the VP-based bioprinting techniques. Notably, the readers will realize the importance and value of highly-automated platforms for tissue engineering applications and be able to develop objective viewpoints towards this field.
In this study, biodegradable polylactic acid (PLA) and PLA nanocomposite scaffolds reinforced with magnetic and conductive fillers, were processed via fused filament fabrication additive manufacturing and their bioactivity and biodegradation characteristics were examined. Porous 3D architectures with 50% bulk porosity were 3D printed, and their physicochemical properties were evaluated. Thermal analysis confirmed the presence of ~18 wt% of carbon nanostructures (CNF and GNP; nowonwards CNF) and ~37 wt% of magnetic iron oxide (Fe2O3) particles in the filaments. The in vitro degradation tests of scaffolds showed porous and fractured struts after 2 and 4 weeks of immersion in DMEM respectively, although a negligible weight loss is observed. Greater extent of degradation is observed in PLA with magnetic fillers followed by PLA with conductive fillers and neat PLA. In vitro bioactivity study of scaffolds indicate enhancement from ~2.9% (PLA) to ~5.32% (PLA/CNF) and ~ 3.12% (PLA/Fe2O3). Stiffness calculated from the compression tests showed decrease from ~680 MPa (PLA) to 533 MPa and 425 MPa for PLA/CNF and PLA/Fe2O3 respectively. Enhanced bioactivity and faster biodegradation response of PLA nanocomposites with conductive fillers make them a potential candidate for tissue engineering applications such as scaffold bone replacement and regeneration.
A new potential biomimetic polymeric 3D scaffold is fabricated using collagen entrapment and 3D printed polylactic acid scaffold. The modified scaffold was characterized by compressive modulus, degree of swelling, water contact angle (WCA), and Fourier Transform Infrared Spectroscopy (FTIR). The findings show that sample PLA/col40 with 40 s entrapment duration is the optimum composition that meets the requirement for artificial bone tissue replacement. In vitro biomineralization using simulated body fluid (SBF) demonstrates that the PLA/collagen 3D scaffold is able to promote the growth of hydroxyapatite (HA) after 7 days which will subsequently improve the osteoconductive and osteoinductive properties of the 3D scaffold. The overall results suggest the potential of the 3D PLA/collagen scaffold as a prospective material for bone tissue engineering applications.
3D Concrete Printing (3DCP) has been gaining popularity in the past few years. Due to the nature of line-by-line printing and the slump of the material deposition in each extruded line, 3D printed structures exhibit obvious lines or marks at the layer interface, which affects surface finish quality and potentially affect bonding strength between layers. This makes it necessary to control the extrudate formation in 3DCP. However, it is difficult to directly analyse the extrudate formation process because the extrudate shape depends on many parameters. In this paper, a machine learning technique is applied to correlate the formation of the extrudate to the printing parameters using an Artificial Neural Network model. The training data for the model development was obtained from extrudates printed in 3DCP experiments. The performance of the trained model was experimentally validated and the predicted extrudate geometry resulting from the developed model showed good agreement to the actual extrudate geometry. Subsequently, the developed model was used to find proper nozzle shapes to produce designated extrudate geometries. Significant improvement on the printing quality was demonstrated using nozzle shapes generated from the model on 3D printed objects consisting a vertical wall, an inclined wall and a curved part.
To achieve optimum functionality and mechanical properties of advanced manufacturing-based scaffolds for biomedical application, it is important to study their mechanical strength by 3D-printing at different orientations. This study examined the effects of printing at different orientations on the mechanical properties of synthesized 3D-polylactic acid (PLA) and hydroxyapatite-modified PLA (PLA-HAp) scaffolds. A total number of 30 samples were printed in three orientations on the XY plane: 0°, 45°, and 90°. Finite element modeling and simulation was employed to identify the strongest scaffold in terms of compression strength, which is the primary criterion for load bearing bone tissue scaffolds. These findings indicate that 3D-printing at an orientation of 90° on the XY plane resulted in a scaffold with the highest compression strength. Moreover, the fabricated PLA scaffolds showed very poor cell attachment and proliferation on their surface, which is not suitable for their biomedical application. This study additionally showed the optimization of a very simple post-fabrication modification technique with nano HAp for better cell attachment and proliferation with enhanced mechanical properties. The post-fabrication modification of PLA scaffolds by nano-HAp results in excellent cell attachment property with enhanced mechanical strength and stability of up to 47.16% for 90° 3D-printed PLA-HAp scaffolds.
The growing demand for nanofibrous biocomposites able to provide peculiar properties requires systematic investigations of processing-structure-property relationships. Understanding the morpho-mechanical properties of an electrospun scaffold as a function of the filler features and mat microstructure can aid in designing these systems. In this work, the reinforcing effect of micrometric and nanometric hydroxyapatite particles in polylactic acid-based electrospun scaffold presenting random and aligned fibers orientation, was evaluated. The particles incorporation was investigated trough Fourier transform infrared spectroscopy in attenuated total reflectance. The morphology of the nanofibers was analyzed through scanning electron microscopy and it was correlated with the viscosity of polymeric solutions studied by rheological measurements. Scaffolds were mechanical characterized with tensile tests in order to find a correlation between the preparation method and the strength of the mats. The influence of hydroxyapatite particles on the crystallinity of the composites was investigated by differential scanning calorimetry. Finally, cell culture assays with pre-osteoblatic cells were conducted on a selected composite scaffold in order to compare the cell proliferation and morphology with that of polylactic acid scaffolds. Based on the results, we can prove that polylactic acid/hydroxyapatite composites can be one of the biomaterials with the greatest potential for bone tissue regeneration.
Bioprinting offers a highly-automated and advanced manufacturing platform that facilitates the deposition of bio-inks (living cells, biomaterials and growth factors) in a scalable and reproducible manner, a process that is lacking in conventional tissue engineering approaches. There are significant improvements in the field of bioprinting over the last two decades; an in-depth analysis of current improvement in the bioprinting techniques, progress in bio-ink development, implementation of new bioprinting and tissue maturation strategies are presented. In this review, we highlight how the progress in polymer sciences complements 3D bioprinting in overcoming some of the major impediments in the field of organ printing. We provide a concise overview of the anatomy and physiology of different tissues/organs, followed by important design considerations to better facilitate the fabrication of biomimetic tissues/organs for tissue engineering and regenerative medicine (TERM). Lastly, a realistic overview of current progress in organ bioprinting by presenting the current limitations and achievements in bioprinted tissue-engineered constructs, followed by an outlook. We strongly believe that with the advances in polymer sciences, it will be an impending reality for on-demand bioprinting of patient-specific tissues/organs. Here's the Share Link – a personalized URL providing 50 days' free access to our article (until September 29, 2019).
3D printing-based technologies can fabricate scaffolds offer great precision to control internal architecture and print complicated structures based upon the defect site. However, the materials used in the direct printing are restricted depending on the printing technology used and the indirect one can overcome this limitation. In the present study, indirect 3D printing approach was used to develop bone scaffolds from polylactic acid/ polycaprolactone/ hydroxyapatite (PLA/PCL/HA) composites. Casting of the composite suspensions was done into a dissolvable 3D printed negative mold, in order to achieve simultaneous macro- and micro-porous composites, using freeze drying/particle leaching method. To evaluate morphology, functional groups, and elemental analysis of the scaffolds, scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and energy dispersive spectroscopy (EDS) were respectively used. Scaffolds' porosity was measured with the aid of liquid replacement technique. Also, the mechanical strength of scaffolds was examined by compression test and measuring the compressive modulus Considering the microstructure, porosity and pore size as well as mechanical property, the scaffold composed of PLA/PCL 70/30 w/w and 35% HA was more favorable. The PLA/PCL/HA 70/30-35% scaffold presented a porosity of 77%, an average pore size of 160 μm, and Young's modulus of 1.35 MPa. Cell adhesion, viability and mineral deposits formation for PLA/PCL/HA scaffolds at PLA/PCL ratios of 70/30, 50/50 and 30/70 and the fixed amount of HA (35%) were also studied in vitro by the means of MG63 cells. The cytotoxicity assessment showed that the cells could be viable and proliferate on the scaffolds. The results indicated that composite scaffold with the PLA/PCL weight ratio of70/30 accomplished more favorable properties in terms of biocompatibility, viability, and osteoinduction property.