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Microstructured Calcium Phosphate Ceramics Scaffolds by Material Extrusion
A B

C D E

F

G

Figure 8. (A) Printing of 16 mm diameter scaffold on heated gypsum at v = 1 mm/s. (B) Brushite green body of 16 mm diameter scaffold
next to a coin 18.5 mm in diameter (left). Brushite green body six layers thick resembling part of a bone plate (right). Ruler in centimeters.
(C) Green body of 4-layer tall print on gypsum. Top layer of filaments spans across underlying supports at various distances apart (labeled
in black in mm). d = 0.58 mm, f = 500%. (D) Cross-section of adjacent filaments printed at different infill density I . Scale bar: 200 µm.
f
(E) Deviation of printed green body from design at different infill density. (F) Electron micrograph of dense bulk part printed at infill density
of 50%. Scale bar: 200 µm. (G) Brushite cylindrical shells printed on heated gypsum at d = 1.19 mm, z = z = 0.2 mm, and v = 1 mm/s. Left:
1
2
40 layers tall. Background contains ten microscope slides 10.25 mm tall. Scale bar: 2 mm. Right: 80 layers tall. Scale bar: 5 mm.
mitigated here by the use of a mild heating and cooling generally weakens bulk ceramics exponentially. Notably,
ramp. printing 21 vol% CaP ink at infill density ~50% eliminated
Replacing the 0.58 mm nozzle with a 1.19 mm internal voids, which are inevitable in conventional
nozzle, the layer height is reduced from ~0.5 mm robocasting, while still being sufficiently printable. With
(Figure 7A and B) to just ~0.2 mm (Figure 8G). In this our 3D printing method, it is, therefore, possible to design
way, the vertical resolution and side profile surface finish and print various complex 3D shapes, with well-controlled
may be further improved by adjusting print parameters macroscopic porosity locally.
to reduce the layer height, with potential trade-offs in CaP materials like β-CPP are inherently brittle
horizontal print resolution. in the bulk, monolithic form, despite high stiffness
Our results demonstrate the ability to 3D print of microplatelets at the nano-scale. Debinding and
porous microstructured scaffolds from our CaP ink, which calcination at high temperatures removes all organic
is a desired feature for biomedical applications. The matter, so microstructured CaP scaffolds are fragile
dimensions are comparable to robocast CaP scaffolds, with and brittle due to the absence of intermolecular forces
a layer thickness 0.15~0.35 mm and a macro-pore width or polymer chains bridging the CaP microplatelets.
of 0.1~0.5 mm commonly reported . Closed porosity To induce toughening mechanisms, the residual open
[45]
does not contribute to a scaffold’s nutrient exchange and porosity obtained after calcination could be infiltrated

120 International Journal of Bioprinting (2022)–Volume 8, Issue 2