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International Journal of Bioprinting Error assessment and correction AQ7

Figure 2. (A-C) The image data is converted into point cloud data after binarization and centerline calculation according to the Sobel operator. (D-G)
Additional error information and modified reference path information are calculated based on the centerline.

This research focuses on the complex antihelix and helix based hydrogel has excellent mechanical and biological
structure using the Sobel operator and the normal vector properties, and it is widely used in tissue engineering,
approach to reduce the printing error to an acceptable range, including drug delivery , vaccine manufacturing ,
[31]
[32]
thus improving the printing resolution (Figure 1B). A process tissue regeneration , and bioprinting .
[34]
[33]
control method based on computer vision was used in this
study to enable the detection and correction of the path errors 2.3. Image algorithm
of the antihelix and helix. Furthermore, the deviation error was Since the captured image cannot be directly recognized
controlled to an acceptable range to ensure that the accuracy by the correction algorithm, the helix image needs to be
of the helix printing path shows an increasing tendency. pre-processed. Figure 2 illustrates in detail how abstract
image data is converted into spatial point cloud data
2. Methods to be recognized by the correction algorithm. The first
step involves acquiring the antihelix and helix images
2.1. Equipment through a non-contact camera placed above the printing
Based on the initial bioprinting machine, a non-contact platform. Through binarization processing, the image
camera was placed above the printing platform to capture matrix is reduced from three channels to a single channel,
the path of the antihelix and helix after printing. The non- and the gray value in the image matrix is only 0 or 255;
contact camera covered a range of 40 mm × 40 mm rectangle additionally, noise is also removed. The purpose of this step
to ensure that the complete helix could be captured. is to enhance the contour features of the helix and prepare
Two different antihelix and helix structures were for the next step. In the third step, a computer vision-based
designed and counted in this study. Each helix structure method is used to extract the edges of the helix printing
had different antihelix and helix. The purpose of counting image. The Sobel operator is widely used in image edge
the two helix groups was to determine the difference in detection and extraction due to its fast response and high
error values carried by different shapes of helices and prove precision. The Sobel operator usually consists of two 3 ×
that the correction methods are universal. 3 convolution kernels. The two convolution kernels would
respond the most to the horizontal edge and the vertical
2.2. Bioinks edge, respectively. Following the processing of pixels in the
An alginate-based hydrogel system for applications in image matrix by convolution, the Sobel operator outputs
bioink was selected for bioprinting helix [28-30] . The alginate- two images with a horizontal edge and a vertical edge, and

Volume 9 Issue 1 (2023)olume 9 Issue 1 (2023) 301 https://doi.org/10.18063/ijb.v9i1.644
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