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International Journal of Bioprinting Five-axis printer for hybrid 3D scaffolds

Figure 5b displays the cylinder positioned on the printer. linear axis carries the mass of hardware components. The
The printing parameters are summarized in Table 2. rotational axis allows for higher acceleration since it has to
move a smaller mass, resulting in increased accuracy when
The design features nine open channels, covering half
the circumference of the cylinder. Pore width (w ) and printing on single-curved surfaces.
p
pore height (h ) were set to 1 mm, while strut width (w ) 3.3. Inkjet printing on free-form surfaces for
s
p
and strut height (h ) were measured at 3 and 1.5 mm, palatal defects
s
respectively. A total of 120 and 60 layers of model and Finally, we printed a thin membrane on a free-form
support materials were printed for the porous structure, surface resembling a palatal implant. A palatal defect is
due to different layer heights. Moreover, an additional 20 an abnormal opening in the roof of the mouth that can
layers of the model material were printed to seal the pores significantly affect speech, eating, hearing, and breathing
from the top. The sample, both before and after support functions. The defect can vary in size and severity, affecting
removal, is presented in Figure 5c. either the soft palate (posterior cleft palate) or both the soft
Notably, a periodic wavy pattern appeared on the top and hard palate (complete cleft palate). The state-of-the-
layer, attributed to the rotation of the cylinder during art treatment to close the defect is palatoplasty, which also
printing. The rotation caused material flow in the direction often results in scarring and subsequently widens the gap
of rotation, leading to the accumulation and formation of and restricts maxillary growth as the patient grows into
a small hill (Figure 5c-ii). This behavior aligns with the an adult. 43,44 These complications could be addressed by
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findings described by Thalheim et al. After the curing placing a resorbable palatal bone implant adapted to the
process, this hill remained intact, leading to the wavy patient’s defect. A potential innovative development in
surface. Additionally, decreasing φ and increasing N points the production of such PSIs may involve the integration
could potentially diminish the observed effect, with the of a soft membrane, printed conformally onto a patient-
disadvantage of prolonged printing time. specific hard phase. In the context of palatal bone implants,
the incorporation of a guided tissue regeneration (GTR)
We conducted accuracy measurements of struts and membrane can enhance post-surgical tissue regeneration.
pores in both the radial and circumferential directions GTR membranes serve as barriers, selectively allowing the
(Figure 5d). A minor mismatch of -2.21 ± 3.53% for growth of desired bone cells while preventing the migration
circumferential struts, 0.37 ± 3.21% for radial struts, 0.8 of undesirable epithelial cells into the healing site, 45-47
± 8.07% for circumferential pores, and 2.06 ± 5.63% for and are commonly employed in periodontal surgeries to
radial pores (n = 9 measured pores and struts) from the facilitate bone regeneration. A GTR membrane should
intended design was observed (Figure 5e). The printing ideally cover both the nasal and oral surfaces of the hard
parameters employed are detailed in Table 2. phase and maintain a thickness of approximately 150 µm.
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The accuracy of the printed model seems to improve This can be achieved using inkjet printing, a non-contact
significantly when using only the rotational axis and AMT, to print a GTR membrane-inspired structure with a
not involving the linear movement of the linear axis for photopolymer on a free-from palatal implant.
printing. This improvement may be due to the rotational The workflow for inkjet printing on a free-form surface,
axis rotating only the part to be printed on, while the focusing on the bony part of a PSI for a palatal defect,
is presented in Figure 6a. We first define the use case to
Table 2. Printing parameters for 3D inkjet printing on a single- fabricate a GTR-like structure on a palatal hard phase
curved surface (Figure 6a-1i). Due to the anatomical situation of the palate,
Printing parameter Value a PSI exhibits non-zero Gaussian curvature. Hence, prior
Angular velocity, ω (deg/s) 10 to path planning, anatomical landmarks of the topology
are identified using primitives, including points and
Jetting frequency, ƒ (Hz) 555 curves, to set the boundary conditions of the movement.
Resolution, ϕ (dpi) 8100
The landmarks include global maxima, inflection points,
Number of discretization points, 9 and principal curvatures (Figure 6a-1ii). Considering
N (-) the dimensions of the printing block from Figure 2, our
Arc length between discretization 3.49 approach is viable for convex and low-curvature concave
points, Δs (mm) surfaces and involves approximating free-form surfaces
Angle between discretization 20 as double-curved surfaces, where at least one of the
points, φ (deg) principal curvatures is dominant (κ >> κ ), effectively
1
2
Radius of the cylinder, r (mm) 10 treating free-form surfaces as single-curved surfaces.
Volume 10 Issue 3 (2024) 597 doi: 10.36922/ijb.3189