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3D-printed borate glass scaffolds for bone repair
non-loading bone repair and increase the bone A cross-head speed of 0.5 mm/min was used
regeneration in a critical-sized bone defect. To test during the compression tests with a mechanical
this hypothesis, we compared the structural and load frame (Instron 4469, Norwood, MA). Five
mechanical properties of the borate glass scaffolds samples in each set were used and the average
with five different architectures, namely, cubic, values were reported with standard deviation.
spherical, x, gyroid, and diamond. Degradation X-ray diffraction (XRD) analysis (Philips X-Pert,
of scaffolds in SBF was assessed. Subsequently, Westborough, MA) was performed on the as-
cubic and diamond architecture scaffolds were received borate glass powder, sintered scaffolds,
chosen to evaluate the bone regeneration in a as well as the dried scaffolds after soaking in the
rat calvarial defect model. Cubic architecture SBF to confirm the crystalline-like formations
represented a traditional lattice design whereas on the scaffold surface, the amorphous nature
diamond architecture represented a biomimetic of borate glass, and its conversion. Scanning
architecture that mimics natural bone, which electron microscopy (SEM) (S-570, Hitachi Co.,
has previously been shown to promote cell Tokyo, Japan) was used to analyze the surface
proliferation in vitro . The treatment groups morphology of the scaffold.
[34]
included borate glass scaffolds with or without
bone morphogenetic protein-2 (BMP-2), an 2.3 Degradation tests
established osteogenesis inducing protein in this An established protocol was used to prepare the SBF
study. solution . Samples were ultrasonically cleaned
[36]
3 times using ethanol and then dried in an oven
2 Materials and methods overnight before kept in the SBF solution (100 ml

2.1 Scaffold fabrication of solution was used for 1 g of the scaffold). The
scaffolds were soaked in an incubator maintained
Bioactive borate glass (13-93B3 glass; nominal at 37°C. To evaluate the scaffold degradation,
composition in wt % – 56.6% B O , 5.5% Na O, compression tests were conducted on soaked
2
3
2
11.1% K O, 4.6% MgO, 18.5% CaO, 3.7% P O ) scaffolds in their wet condition. At least three
2
2
5
with an average particle size of ~12 µm was used samples in each set were used and the average
in this research. Borate glass particles were mixed values with standard deviations were reported.
with a polymeric binder and then dry ball-milled to
obtain the feedstock powder for the SLS machine 2.4 Scaffold preparation before implantation
(DTM Sinterstation 2000). The binder content, For in vivo tests, cubic and diamond scaffolds were
feedstock preparation, and scaffold fabrication grinded to the required dimensions (~1.5 mm thick
parameters established previously for silicate glass disks having 4.6 mm in diameter), ultrasonically
(laser power – 5 W, scan speed – 508 mm/s, scan washed thrice (5 min each) with ethanol, dried in
spacing – 0.23 mm, layer thickness – 76.2 µm, air and then heat sterilized overnight at 250°C. Six
15 wt % binder) were adopted in this study . animals were used for each treatment group and
[35]
The fabricated parts were heat treated in a furnace scaffolds with ~50% porosity were used for this
(Vulcan Benchtop, York, PA) to remove the study. Experiments were carried out with or without
polymeric binder and sintered at 570°C for 1 h. the use of BMP-2. Animals were randomized to

2.2 Scaffold assessment different types of scaffold, based on the presence
or absence of BMP-2. Scaffolds were soaked in
Scaffolds measuring 5 × 5 × 5 mm were used SBF for 6 h and then dried at room temperature
3
for compression tests and scaffolds measuring overnight before loading BMP-2 to roughen the
10 × 10 × 10 mm were used to measure porosity surface for improved protein adhesion. BMP-2
3
using Archimedes method. The scaffold’s pore was dissolved in citric acid (10 µg in 100 µl) and
size was measured using an optical microscope. 10 µl of the solution was loaded on each scaffold

84 International Journal of Bioprinting (2020)–Volume 6, Issue 2