Page 178 - IJB-9-2

International Journal of Bioprinting 3D Printing Multifunctional Orthopedic Biocoatings

4. Discussion improved biological response as compared to the polymers
film alone.
In our past work, direct-write polymeric coatings have
been implemented to retard the corrosion behavior of The VA release data revealed that PCL-ACP composite
magnesium alloy for tracheal stent application. Similarly, films showed slow release compared to PCL film alone.
inkjet printing has provided controlled release coatings This is due to the adsorption of VA molecules on the
for drug-eluting cardiovascular stents. In contrast, in the surfaces of nanosized ACP particles. Moreover, compared
current research, a customized and retrofitted direct-write to other antibiotics, VA did not interfere much with
inkjet method was employed to deposit bioactive organic- osteoblast and skeletal cell growth in vitro and did not
[13]
inorganic composite thin films on Ti alloy substrates. We affect the bone regeneration process in vivo . The ACP
deposited multilayered coatings (10 layers) 3D scaffold powder used in this study had a BET surface area of ~61
printed using composite polymer inks to demonstrate the m /g, which corresponds to spherical particles of ~32 nm
2
fabrication of complex and hierarchical structures. Optimal in size. It is well-established in the literature that these
jetting conditions suitable for both PCL and PLGA polymer nanosized calcium phosphate particles also exhibit surface
types were used for coating multilayer polymeric thin roughness and topographic irregularities on the atomic
films. The biopolymers were blended with nanostructured scale, which favor adsorption, promoting facile formation,
amorphous calcium phosphate and VA drug for promoting and retention of stable aggregates even under relatively
osteoconductivity and preventing bacterial infection intensive agitations in the solution . It is also reported that
52
associated with orthopedic implants. The customized 3D due to the alternation of charged Ca and PO ions on
3−
2+
4
printing process enabled the deposition of multilayered calcium phosphate surfaces, the surfaces adsorb both acidic
coatings with precise control on the thickness of these and alkaline proteins, DNA, and biomolecules, regardless
films to obtain tunable release of the ACP in vitro. Optical of their actual ζ-potential and the net charge [26,52] . Thus, the
microscopy revealed that PCL-ACP coatings had uniform adsorption of VA molecules on the surfaces of nanosized
deposition patterns, whereas the PLGA-ACP coatings ACP particles is highly feasible. On contact with water,
displayed precipitation of ACP patches on the Ti substrate. some of these adsorbed VA molecules diffused out in the
Further SEM analysis of the nanocomposite structure solution and thus resulted in a more sustained release in
within the polymeric coatings revealed a strong binding sample R-3. Presumably, the decrease in the rate of release
between the ACP nanoparticulate and PCL polymer. The of VA over time is partly due to the reduction in easily
FTIR analysis confirmed the presence of both the polymers soluble amorphous content of the powder on the particle
and ACP phases within the multilayered thin films . The surface, combined with the conversion of the ACP phase
[24]
MC3T3 osteoblast cell line showed high cellular viability into hydroxyapatite by dissolution precipitation and
(>90%) after 72 h of proliferation, which was comparable corresponding decrease in the concentration of weakly
to Ti substrate and TCPS controls. The cell attachment and adsorbed drug molecules on the particle surface [2,52] .
live/dead assay confirmed the cell viability data. However,
PLGA coatings had poor cellular attachment (dead cells) The bioactivity of the released VA was confirmed
in certain regions of the substrate. These findings indicate by measuring the zone of inhibition using the disc
the local release of carboxylic acids produced through diffusion method. Thus, the direct-write printing method
degradation of PLGA increases the local acidity . The successfully immobilized therapeutic agents on orthopedic
[50]
presence of ACP in the printed films, however, offers implants for the temporospatial release of drugs. This
some unique advantages other than buffering the local research, therefore, builds the foundation for incorporating
pH. It is known that ACP has the highest solubility bioactive agents within the polymeric coating to efficiently
among the various calcium phosphate phases, and it is regenerate bone structures that interface with orthopedic
expected to dissolve and release calcium and phosphate implants and prevent bacterial infection resulting from
ions in the system. Moreover, the protons generated implantation.
from the released acidic byproducts of PCL and PLGA 5. Conclusions
interact with the ACP particles, leading to an increase
in dissolution of the ACP particles which also causes an In this study, a custom 3D printing method was employed
increase in the soluble Ca and phosphate concentrations to deposit bioactive organic-inorganic composite thin films
2+
in the surrounding media. It is well-established that the on Ti alloy substrates. Optimal jetting conditions suitable
release of calcium and phosphate ions locally improves the for both PCL and PLGA polymer types were used for
osteoclast and osteoblast activity, thereby facilitating bone coating multilayer polymeric thin films. The biopolymers
regeneration . Thus, it is expected that the composite were blended with nanostructured amorphous calcium
[16]
films of PCL-ACP and PLGA-ACP should demonstrate phosphate and VA for promoting osteoconductivity and

Volume 9 Issue 2 (2023) 170 https://doi.org/10.18063/ijb.v9i2.661