In-Situ Condition Monitoring of Extrusion-Based 3d Bio-Printing Using Phase-Based Motion Estimation

Abstract The evolution of 3D bio-additive manufacturing holds significant potential to address the growing demand for organ transplants by facilitating the fabrication of complex human organs using bio-compatible material. Ensuring the structural integrity of the 3D bio-constructs is one of the key issues that still remain significantly challenging due to the bioink material being relatively soft, lightweight, and translucent. Traditional methods for structural health assessment generally rely on sensor-based and offline techniques, which often fall short due to the nature of the bio-ink material and geometric constraints of the bio-printed structures. The limited availability of efficient structural health monitoring methods poses a challenge to the broader adoption of this novel additive manufacturing process. Vibration characteristics, such as natural frequencies, operational deflection shapes, are the intrinsic properties of the structure depending on the effective mass distribution and stiffness of the object. Thus, any deviation in the structural integrity of the bio-printed organ from its baseline structure may alter the effective mass and stiffness of the structure, thereby affecting its vibration characteristics. Therefore, determining the vibration characteristics of the structure enables distinguishing healthy and defective structures and contributes to aiding in process optimization, structural integrity monitoring, and the reduction of operational costs and efforts. In this study, a non-contact, non-destructive method using video-based vibrometry has been utilized to assess the structural integrity of the bio-construct under in-situ conditions while being printed. Extrusion based 3D bio-printing was adopted for additively manufacturing human organ structures. The response of the 3D bio-printed organ to ambient excitations was recorded using a high-speed camera. Phase-based motion estimation technique was employed to determine the vibration characteristics of the organ structure. This method can extract the magnified motion, i.e., operational deflection shapes of the object, after magnification at selected frequencies of interest. Material deposition error is one of the key sources of structural inconsistencies in extrusion-based bioprinting. To compare the healthy and defective structures, this type of error was simulated by creating embedded defects in the design through variations in the number of perimeters in vertical layer, and infill density. The responses of both baseline and defective structures to ambient excitation were analyzed during the final layer of printing. A shift in the frequency spectra was found when a defect was introduced in the baseline structure. The findings from this study demonstrate the potential of the proposed video-based method to utilize the vibration characteristics as metrics of defect detection in real-time application for extrusion-based bioprinting. Furthermore, the proposed in-situ evaluation technique can be employed for process optimization by providing insights into structural integrity variations during printing.