Page 60 - IJB-9-1

International Journal of Bioprinting In situ defect detection and feedback control with P-OCT

obtained by comparing the reconstructed result with to the red line in Figure 5C, a cross-sectional image is
the design model of the current layer. The overall displayed in Figure 4D. With the 3D P-OCT datasets
fidelity value was obtained by comparing the overall of the pre-experiment, FS and LT with different
reconstructed results with the overall design model. pressure and velocity inputs are analyzed and plotted in
An ideal 3D design model PT 3D_GCode can be obtained Figure 4E and F, respectively. When the acceptable FS
by traversing the interpolated GCode with the above range was 0.48 ± 0.10 mm and the acceptable LT range
elliptic model. After 3D registration of the design model was 0.33 ± 0.10 mm, suitable pressure and velocity
PT 3D_GCode and the reconstructed result PT P-OCT , fidelity input group can be obtained, as displayed in Figure 4G
can be calculated using the following formulas: with the green boxes. Furthermore, the surface fitting
MatchPT ( POCT− i (), PT 3 DGCode_ ( i ) =) functions of FS and LT can be generated using the
above data with the corresponding material and needle
 1 DisPT ( POCT− (), (ii)) <  conditions, as follows:
i PT

 DisPT ( 3 DGCode_ (5)
i PT,
0 POCT− () 3 DGCode_ i ()) ≥   FS m P= 1 3 + m VP + 2 2 m V P + 3 2 m V + 4 3 m P 2 m VP+ 6

5

1 N MatchPT (  m V+ 7 2 + m P mV+ 9 + m 10
8
Fidelity = ∑ () ( i ) ) 
i PT,
N i=1 POCT− 3 DGCode_  LT n P= 1 3 + n VP + 2 2 n 3 .*V P n V+ 2 4 3 + n P 2 n VP+ 6
5
(6)  2
 + n V + 7 n P nV+ 9 + n 10
8
Where PT P-OCT (i) is the point in the reconstructed
model, and PT 3D_GCode (i) is the point in the design model. (7)
δ is the distance threshold used to judge the matching where V represents the velocity, P represents the
success rate between PT P-OCT (i) and PT 3D_GCode (i) and N pressure, m , m , … , m are coefficients to be solved in the
9
2
was the point number in PT 3D_GCode. This ratio indicates the function of FS, n , n ,… n are coefficients to be solved in
1
1
degree of fidelity. the function of LT. The two fitting surfaces are shown in
2
9
2.4. Pre-built feedback mechanisms Figure 4H and I. The optimum pressure and velocity inputs
were 0.24 MPa and 11 mm/s for the target FS (0.48 mm)
2.4.1. Defects in the straight path and feedback and LT (0.33 mm), respectively.
mechanism
In the straight path section, FS and LT may be 2.4.2. Defects of end points and feedback mechanism
inconsistent with the designed values, which is mainly There were material deposition errors at the start-stop
related to the rheological properties, input pressure, points, as shown in Figure 5A. The left part shows the 3D
and velocity. According to the rheological properties P-OCT results, and the right part shows the registration
of the target material and the target FS and LT values, results of the design model based on GCode nodes and 3D
the feedback mechanism was built through a pre- P-OCT results. There was no material deposition within a
experiment. For example, when the target material is certain distance from the theoretical path starting point
Hap with the target FS (0.48 mm) and LT (0.33 mm), (red dotted line in Figure 4A), and too much material
a nozzle with the inner diameter of 0.41 mm was deposition occurred at the actual path starting point.
selected with different pressure and velocity inputs for Excessive material deposition also occurred at the end of
pre-experiment. Specifically, the pressure range was the path. Armstrong et al. calculated the hysteresis time
set at 0.22 – 0.32 MPa with the interval of 0.02 MPa, by combining the length of the material-free deposition
and the velocity range was set at 6 – 13 mm/s with the at the start point with the printing speed . According
[18]
interval of 1 mm/s. Parts of the printing paths and to the rheological properties of the above target material,
the corresponding input parameters are displayed in the target FS and LT values, the optimum pressure, and
Figure 4A. The length of each filament was set as 8 mm velocity inputs of 0.24 MPa and 11 mm/s were selected
and the overall field was within 19 mm × 19 mm in X-Y for the response hysteresis pre-experiment. Using the Hap
plane, which can be imaged with the wide field function material and printing speed, an average 14.926 mm of
of 3D P-OCT. With different combinations of pressure material deposition length was printed when the designed
and velocity, the pre-experiment was repeated five length was 16 mm. Therefore, a corresponding hysteresis
times and the printed results are shown in Figure 4B. time of 98 ms was calculated. The corresponding results
Figure 4C shows the 3D P-OCT result corresponding to after compensation are shown in Figure 5B; however,
the group in the red box in Figure 5B. Corresponding there were still FS and LT errors (Figure 5B-D). To avoid

Volume 9 Issue 1 (2023) 52 https://doi.org/10.18063/ijb.v9i1.624