Page 260 - IJB-9-3

International Journal of Bioprinting Multi-material bioprinting with OCT imaging

Figure 12. Printing design and experimental results of different trajectories. (A) The printing trajectory and strategy for a circle. (B) Printing results
before optimization of nozzle control parameters for the circle. (C) Printing results after optimization of nozzle control parameters for the circle. (D) The
printing trajectory and strategy for a triangle. (E) Printing results before optimization of nozzle control parameters for the triangle. (F) Printing results after
optimization of nozzle control parameters for the triangle.

related control model), which provides control parameters layer thickness, and a good match of the layer thicknesses
for multi-material printing, achieving improved printing of different materials in the same plane was obtained, as
accuracy of multi-material 3D-printed scaffolds. shown in Figures 9E and 10E.
In this study, we used an extrusion-based multi-nozzle The smooth transition of the connection points
printer to establish printing model in the OCT monitoring between different materials is one of the key problems in
printing process. Compared with the conventional multi-material printing. To solve this problem, we studied
machine vision method , OCT imaging technology the extrusion delay property of the nozzles at the starting
[37]
not only quantifies the error in the print plane, but also and ending point in the multi-nozzle printing process. We
detects the defects in the depth direction, which allows established a time-related control model, monitoring the
for a more accurate evaluation of the fracture degree and results of different nozzle printing strategies using OCT and
material accumulation at the connection points in our optimizing the control parameters of each nozzle in one or
pre-experimental model, as shown in Figures 7 and 8. two cycles. The above experimental results showed that the
In addition, OCT imaging enables different layers of the materials extruded by different nozzles were closely and
scaffold to be distinguished during printing and allows smoothly connected in the connection points, the problem
the 3D evaluation of the printing result, as shown in of stress concentration in this area was alleviated, and the
Figures 9–11. overall accuracy of the printing scaffold was improved, as
shown in Figure 8.
In a previous study on the complex relationship
between printing parameters and filament size, main To investigate the feasibility of the connection
attention has been paid to optimize the printing parameter registration method using nozzle control parameters in
of a single material , but in this study, we focused more a general condition, a circle trajectory with a radius of
[38]
on the registration between the filament metrics (filament 4 mm and a triangle with 8 mm bottom edge and height
size and layer thickness) with different materials. In the was designed and printed. The designed trajectories and
multi-material static model, we found that the filament the printing strategies are illustrated in Figure 12A and
size and the layer thickness of different materials with D, respectively. The pressure is set to 0.30 Mpa and the
the same needle cannot be guaranteed to be the same by speed is 6 mm/s to obtain a 0.28 mm filament size from the
adjusting the printing parameters, as shown in Figure 2. static model. For each printing condition, two connection
However, according to the characteristics of multi-material points were evaluated using OCT. The printing results
printing, the key is to keep the same layer thickness of without the proposed method (i.e., AET = 0 and ATEP =
printed filaments of different materials on the same plane. 0) are shown in Figure 12B and E. For the circle trajectory,
Therefore, the printing parameters were selected and a gap of 0.146 mm exists in area 1 and obvious material
were optimized in corner area according to the target accumulation occurs in area 2. For the triangle trajectory,

Volume 9 Issue 3 (2023) 252 https://doi.org/10.18063/ijb.707