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

and photocuring-based bioprinting. Extrusion-based monitoring and 3D imaging detection of internal defects
bioprinting employs pneumatic, mechanical or ram in 3D bioprinting. Simeunović and Hoelzle developed
extruders to dispense materials, and other biological non-linear and linearized models of extrusion-based
molecules. Using extrusion-based bioprinters, various printing dynamics to avoid adversely impacting flow
biopolymers and multiple cell types encapsulated in rate and achieve accurate material delivery at start-stop
hydrogels can be deposited in a defined trajectory to points . Armstrong et al. presented an iteration-to-
[13]
fabricate constructs with specific biological features . iteration process monitoring system that enabled direct
[7]
Extrusion-based bioprinting has been widely used with the process feedback in material deposition based on the
main advantages of a wide selection of biomaterials, low- laser displacement scanner integrated to the printing
cost equipment, and the ability to maintain great control of platform [6,18] . They modified the spatial material placement
porosity and pore interconnectivity, which are important error and the material width error, and developed process
for proper cell growth in scaffolds . Tissue scaffolds play control strategies based on the measured errors to adjust
[8]
an very important role in the process of tissue engineering control inputs and ultimately eliminate material deposition
for the growth of new or repairs of defected tissue . errors. However, the laser displacement scanner can only
[7]
However, researchers face some challenges in maintaining provide surface profile information without penetration
the desired 3D structure due to the system assembly error, and 3D structural reconstruction; quantification and
nozzle calibration error, unstable material rheological overall fidelity evaluation of large constructs were not
properties, and unstable environmental control errors. In provided. With 3D-DIC, Holzmond et al. monitored the
this study, we focus on the material deposition error due to surface geometry of a printed part to detect and locate
the lack of online monitoring and feedback control, which defects in parts produced by a fused filament fabrication
limits the implementation of high-fidelity structures. 3D printer . They produced a point cloud model using
[17]
Material deposition errors result in deviations in the a visualization toolkit based on GCode originally sent to
material path, filament size (FS), layer thickness (LT), pore the printer. Errors were detected and located by comparing
size (PS), volume porosity (VP), and porosity connectivity the 3D-DIC measurement data with the reference point
(PC) between the printed structure and design model. In cloud model. The measured errors and defect locations are
tissue-engineering scaffolds, specific PS values are required prerequisites for subsequent feedback control and defect
to accommodate cell growth and tissue regeneration [8,9] . 3D repair. In situ defect detection and quantitative analysis,
porous interconnected structures can facilitate cell growth feedback control, and defect repair are the main challenges
and the transport of nutrients and metabolic waste, which in high-fidelity 3D printing.
is beneficial for large-size tissue repair [9,10] . High-fidelity In the previous work, 3D extrusion-based bioprinter-
structures can ensure that the constructs perfectly match associated optical coherence tomography (3D P-OCT) has
the tissue defect site and provide sufficient mechanical been proposed . OCT is a non-destructive, label-free,
[19]
[11]
support, particularly for bone defect repair . Moreover, high-resolution, and fast tomographic imaging technique
low fidelity can affect the consistency between drug that are widely used in the biomedical and industrial
screening and disease models . Insufficient product quality testing fields [20,21] . OCT enables 3D volumetric imaging
[12]
assurance could lead to increased lead-times, operational with micron-scale resolution over centimeter length scales
costs, and part waste. Therefore, an increasing number of and 3D P-OCT enables large-field full-depth imaging to
researchers have become aware of the significance of high- meet the imaging requirements of large structures. 3D
fidelity structures and the importance of precise material P-OCT can provide in situ process monitoring and multi-
deposition . Material deposition errors usually lead to parameter evaluation layer by layer during extrusion-
[13]
low structural fidelity, poor consistency of constructs, and based bioprinting including LT, FS, layer fidelity, and 3D
insufficient functional characteristics, which are mainly structure quantitative analysis, including material volume,
caused by the mismatch between the material extrusion VP, and PC . This study mainly focuses on in situ defect
[19]
and the three-axis mechanical movement. detection and timely feedback control for print parameter
The incorporation of sensing and feedback control compensation and defect repair.
in extrusion bioprinting is one way to reduce material In this study, three types of defects related to material
deposition errors and improve the fidelity of the deposition were considered, including material deposition
constructs. At present, X-ray CT [14,15] , MRI , industrial path, FS, and LT. Moreover, the improved quantification
[16]
camera , and 3D digital image correlation (3D-DIC) methods using 3D P-OCT reconstructed results were
[17]
[13]
are the main detection technologies commonly used in 3D proposed for defect detection and location. On this basis,
printing; however, there are some limitations for in situ a pre-built feedback mechanism was developed for timely

Volume 9 Issue 1 (2023) 48 https://doi.org/10.18063/ijb.v9i1.624