Biomedical Engineering Reference
In-Depth Information
bone grafts due to their high biocompatibility and proper mechanical strength. Polylactic acid (PLA),
polyglycolic acid (PGA), poly(ε-caprolactone) (PCL), and their copolymers are the most common
polymers used for tissue engineering. It has been reported that ceramic/polymer composites represent
improved biological and mechanical properties. Incorporation of synthetic nanocomposites along with
a proper micro- and macrostructural design can further enhance the performance of bone grafts. Higher
surface area and higher grain boundaries can improve the toughness and mechanical properties of the
structures significantly. Additionally, nanocomposites provide enhanced osteoblast cell adhesion and
proliferation. There are many reports on the development of ceramic, polymeric, and metallic nano-
composites for load-bearing applications. However, manufacturing of porous structures with proper
interconnectivity and strength is still challenging and needs more in-depth investigation.
11.6.2
AM OF NANOCOMPOSITES: SEVERAL TECHNIQUES,
LIMITATIONS AND OPPORTUNITIES
Zhou et al. (
Zhou et al. 2008
) reported the synthesis of PLLA/HA nanocomposite with the HA particle
size of around 20 nm. The scaffolds were built using SLS at the layer thickness of 100
m
m. It was
shown that using inappropriate laser power, part bed temperature (PBT) and scan spacing (SS) can
lower the resolution and quality of 3D printed structures.
In vitro
cell culture experiments indicated
promising results in regards to osteoconductivity and proliferation of osteoblast cells.
Heo et al. (
Heo et al., 2009
) studied layer-by-layer manufacturing of HA/PCL composite fabricated
with nano (n-HPC) and micro HA (m-HPC) particles, respectively, prepared through a solvent casting
method. 3D-printed scaffolds were freeze-dried after immersion in distilled water. The SEM images of the
n-HCP and m-HCP scaffolds reveal that the n-HCP scaffolds have a smooth surface while that of m-HCP
is rough with less consistency. It was also shown that the attachment of cells, alkaline phosphatase activity,
calcium content, and mechanical strength were higher in n-HPC compared to that of m-HPC scaffolds.
In another study, calcium phosphate /poly(hydroxybutyrateco-hydroxyvalerate) (PHBV) and
HA/PLLA nanocomposites were synthesized and 3D-printed into scaffolds using SLS (
Duan and
Wang 2010a, 2010b
;
Duan et al., 2010
,
2011
). Osteoconductivity and biodegradability are provided
by calcium phosphate and polymer matrix, respectively. Proximal femoral condyle sintered scaffolds
show high quality prints compared to the model. The mechanical properties of the nanocomposite scaf-
folds were shown to be higher than their polymeric counterparts in dry state. It was also reported that
SaOS-2 osteoblast cell adhesion, proliferation, and ALP activity of the structures were significantly
improved using the nanocomposite.
Poly-lactide-co-glycolide acid (PLGA) and nanotitania particles are also known as biocompatible
materials. Liu et al. (
Liu and Webster, 2011
) fabricated titania/PLGA nanocomposite dispersion via a
solvent casting technique and used aerosol-based M3D™ 3D printing system (M3D™ developed by
OPTOMEC) to produce 3D scaffolds of titania/PLGA nanocomposite. The results indicated better
mechanical properties and biological performance than PLGA control samples.
Graphene has been reported to improve mechanical properties and osteoblast cell adhesion and pro-
liferation significantly (
Zhang et al., 2013; Zanin et al., 2013; Marques et al., 2012; Biris et al., 2011;
Ma et al., 2012; Liu et al., 2012; Rodríguez-Lorenzo, 2009
). Azhari et al. (
Azhari et al., 2014
) investi-
gated the AM of graphene/hydroxyapatite nanocomposite using layer-by-layer 3D-printing technique.
As illustrated in
Figure 11.9
, the rotating roller spread a layer of powder onto the building bed where an
aqueous binder is injected to adhere particles based on the sliced CAD model. The process is iterated
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