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An nMgO containing scaffold: Antibacterial activity, degradation properties and cell responses

Escherichia coli (E. coli) compared with chitosan. self-developed SLS system, which consisted mainly of
Yamamoto et al. [19] prepared calcium carbonate/nMgO a CO laser device (SR 10i, Rofin-Sinar Laser GmbH,
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composites via thermal decomposition of dolomite Hamburg, Germany) and a galvanometer scanning
and found the composites exerted high antibacterial system (3D scanhead-300-15D, Beijing Century Sunny
properties towards E. coli and Staphylococcus aureus. Technology Co., Beijing, China). Briefly, the laser
[20]
Ma et al. prepared poly(ʟ-lactide)/nMgO composites selectively sinters the powder layers under the control
and found nMgO neutralized the acidic degradation of the scanning system according to the cross-section
products of poly(ʟ-lactide) and improved its mechanical profiles of the designed parts, forming the solid parts
properties. Nevertheless, studies on MgO-containing in a layer-by-layer manner [22,23] . The primary processing
composites for biomedical applications are still very parameters, i.e., laser power, scanning speed, scanning
lacking, and few papers, to the best of our knowledge, spacing and layer thickness were set as 2 W, 200 mm/s,
have systematically studied their comprehensive 0.1 mm and 0.1 mm, respectively. Five formulations of
performances, especially in the form of scaffolds. PHBV/nMgO scaffolds containing 0, 1, 3, 5 and 7 wt%
In this study, nMgO was incorporated to PHBV nMgO were fabricated, which were denoted as PHBV,
for developing antibacterial bone scaffolds. Three- PHBV/1%nMgO, PHBV/3%nMgO, PHBV/5%nMgO
dimensional porous PHBV/nMgO scaffolds were and PHBV/7%nMgO scaffolds, respectively.
prepared by selective laser sintering (SLS). The
antibacterial activity of the scaffolds was evaluated, 2.3 Microstructures and Mechanical Properties
while the antibacterial mechanisms were analyzed and The phase composition of the PHBV/nMgO scaffolds
discussed. Moreover, the microstructure, mechanical was analyzed by X-ray diffraction (XRD) (Bruker
properties, degradation behaviors and cell responses of D8, German Bruker Co., Karlsruhe, Germany). The
the scaffolds were also assessed. diffraction data were collected from 5 to 70° at a scan

2. Materials and Methods rate of 8°/min using Ni-filtered Cu Kα radiation (λ =
1.5406 Å). The surface morphologies of the PHBV/
nMgO scaffolds were analyzed by scanning electron
2.1 Powders Preparation microscope (SEM) (MIRA3, TESCAN, Brno, Czech
PHBV with 3 mol% of 3-hydroxyvalerate content, 280 Republic) installed with energy dispersive spectroscopy
kDa of molecular weight, 1 µm of average particle size (EDS) (X-Max 20, Oxford Instruments, UK) using
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and 1.25 g/cm of density (the data were provided by secondary electron model under 15 kV accelerating
the manufacturer) was obtained from Tianan Biologic voltage. Before the characterization, the specimens
Materials Co., Ltd. (Ningbo, China). nMgO with average were fixed on copper stubs using electrically conductive
particle size of 50 nm and density of 3.58 g/cm (the adhesives, followed by spurting with platinum to
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data were provided by the manufacturer) was purchased increase their conductivity.
from Shanghai Macklin Biochemical Co., Ltd. (Ningbo, The mechanical properties of the PHBV/nMgO
China). scaf folds were assessed by compression tests using
Five formulations of PHBV/nMgO powders containing a universal testing machine with a 30 kN load cell
0, 1, 3, 5 and 7 wt% nMgO were prepared mainly (MTS Insight 30, MTS Systems Corporation, MN,
[21]
through the following procedures : (a) weighing certain USA). The specimens (cylinder, 12.7 mm in diameter
amounts of PHBV and nMgO powders according to the by 25.4 mm) were compressed to 50% strain at a
designed formulations, and adding them into two beakers rate of 1 mm/min [24,25] . The compressive strength
containing certain amounts of absolute ethyl alcohol, and compressive modulus of the scaffolds were
respectively, followed by magnetically stirring the two determined from the obtained compressive stress-
solutions for 30 min, respectively; (b) adding the nMgO strain curves. Five specimens were tested for each for-
solution into the PHBV solution, and magnetically mulation of the scaffolds. The scaffolds with optimal
stirring the mixed solution for 30 min, followed by compressive properties were then used to characterize
ultrasonically dispersing for 30 min; (c) filtering the their antibacterial activity, degradation properties and
mixed solution to obtain the mixed powders; (d) drying cytocompatibility.
the mixed powders in vacuum drying oven at 60 °C for
24 h; (e) mechanically milling the dried powders with 2.4 Antibacterial Activity
planetary ball mill for 2 h, and finally obtaining the E. coli was used as a model bacterium as it is one of
PHBV/nMgO powders. the most common bacteria causing orthopedic implant-

2.2 Scaffolds Preparation related infections [26] . The antibacterial activity was
evaluated by seeding E. coli ATCC 25922 to the
Three-dimensional porous scaffolds were prepared via a PHBV/5%nMgO scaffolds and then observing the

2 International Journal of Bioprinting (2018)–Volume 4, Issue 1