Page 168 - IJB-9-2

International Journal of Bioprinting 3D Printing Multifunctional Orthopedic Biocoatings

coating techniques and offers numerous advantages as 2.2. Coating solution preparation
discussed by Cooley et al. as, “Inkjet-based deposition Two types of printing solutions were formulated depending
[48]
requires no tooling, is non-contact, and is data driven; no on the type of study or characterization to be performed.
masks or screens are required; the printing information is These include solutions of ACP only (polymer_ACP only)
created directly from CAD information stored digitally. within the polymer and a combination of both ACP and
Being data driven, it is flexible. As an additive process with VA (polymer_ACP_VA) in the polymer solution. Different
no chemical waste, it is environmentally friendly and cost formulations of each type of coating “ink solution” were
effective.”
prepared by dissolving certain amounts of PLGA or PCL
In this work, the custom 3D printing method was in TFE solvent and stirring for 2 h. The concentrations
employed to achieve precision deposition of uniform of both PLGA and PCL solutions were fixed at 1 wt. %
multilayer coatings. The biofunctional coatings consisted polymer in the solvent. These biopolymer solutions were
of ACP and VA formulations mixed within a biodegradable further blended with ACP at 0.5 – 1% w/v concentrations
polymeric matrix. VA is a glycopeptide antibiotic which based on the coating to be evaluated (Table 1). The
is used to treat serious infections of many Gram-positive resultant polymer/ACP solution was mixed, stirred for 2 h,
bacteria [58,59] . It was hypothesized that the steady release and further ultrasonicated for 4 h to obtain a completely
of antibiotics would eliminate the bacterial infection on homogeneous mixture. All printing solutions were filtered
the titanium implant surfaces, whereas the presence of (30 µm – mesh) to remove large ACP and VA particulates
ACP would aid in osseointegration and wound healing to prevent them from clogging the printing nozzles.
process. Titanium samples coated with this printing solution were
used for materials characterizations and in vitro studies.
2. Materials and methods Printing solutions consisting of VA were prepared from an
Nanoparticles of ACP were synthesized by controlled initial 1 wt. % PCL in TFE solvent. The polymeric solution
precipitation using water-soluble calcium and phosphate was further homogeneously blended with 1 – 2% w/v VA
salts. Biodegradable poly(D, L-lactic-co-glycolic) based on the coating to be evaluated (Table 2). Titanium
acid (PLGA 50:50) and polycaprolactone (PCL Mn alloy substrates coated with these printing solutions were
~2,000) polymers were obtained from Sigma-Aldrich. used for antibiotic release measurements and antibiotic
2,2,2-trifluoroethanol (TFE) obtained from Aldrich, activity studies.
St. Louis, MO, was used as a solvent for dissolution. VA
(vancomycin hydrochloride, Alfa Aesar, USA) was used as a 2.3. Printing procedure
model antibiotic known for its efficacy in treating bacterial A customized hybrid inkjet system was employed for this
infections associated with orthopedic implants [15,16,18,60,61] . research. A printing nozzle with an orifice dimension of
Mechanically polished thin titanium (Ti) alloy coupons 50 µm was used for all the printing procedures. A motion
(10 mm × 10 mm × 1 mm) were used as the substrates for controller printing script was coded for uniformly coating
depositing the embedded polymeric materials. each Ti alloy substrate. The substrate temperature was
controlled at 20°C. Uniform coatings of 10 or 20 layers were
2.1. Substrate cleaning procedure printed on the Ti substrates. Figure 1 shows the custom
Titanium alloy coupons (substrates) underwent a 3D printing equipment and schematic for depositing the
cleaning procedure. The pre-cleaning treatment of
Ti coupon substrates involved an initial rinsing of the Table 1. Experimental design and ink composition for
coupon substrates with ethanol to remove organic in vitro cellular viability and cytocompatibility assessments
surface impurities followed by further rinsing with
distilled water. The rinsed Ti substrates were then Sample Polymer ACP concentration No. of
type
(% w/v)
layers
code
dipped and washed in 3 mol L of nitric acid in water for
−1
degreasing. After that, the substrates were washed with 1 PCL 0.5 20
excess deionized water to remove the acids at the surface 2 PCL 0.5 10
and then were air-dried. In the mechanical polishing 3 PLGA 0.5 20
process, a 1200 grit size SiC paper was used to eliminate 4 PLGA 0.5 10
surface adhered impurities. Polishing was performed on 5 PCL 1 20
both surfaces of the Ti substrates. The polished surfaces 6 PCL 1 10
were then finally rinsed using deionized water and the
samples were subsequently air-dried and stored in a 7 PLGA 1 20
Class 1000 cleanroom. 8 PLGA 1 10

Volume 9 Issue 2 (2023) 160 https://doi.org/10.18063/ijb.v9i2.661