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Machine learning in bioprinting
           positioned cells, curved layers, and microstructure   accuracy can be analyzed by machine learning in
           errors in a fabrication process which can monitor   advance, the final fabricated bio-parts can then be
           the whole bioprinting process. Figure 4 shows an    guaranteed in good quality. The process is similar,
           example of using CNN to detect flaws, errors, or    as shown in  Figure  4, while the input data are
           defects in 3D bioprinting. The input data can be    different.
           the images from high-quality cameras during the
           bioprinting process. Then, the data are analyzed    3.4 Material property design or prediction
           by the CNN model  to predict  a defect  or other    In  traditional  3D printing, Gu  et  al.   proposed
                                                                                                  [29]
           objectives.                                         a machine learning-enabled method to design
           3.3 Dimensional accuracy analysis                   hierarchical composites for fabrication, trained
                                                               with  a  database  of  enough  structures  from  finite
           In the traditional 3D printing process, Francis and   element analysis. Hamel  et al.  presented
                                                                                                 [30]
           Bian  developed a deep learning method that can     a machine learning method to design active
               [22]
           accurately predict the distortion of parts in laser-  composite structures where target shape shifting
           based AM. Similarly, Khanzadeh et al.  proposed     responses can be achieved in a 4D printing process.
                                               [23]
           an  unsupervised  machine  learning  approach       Li et al.  proposed a predictive modeling method
                                                                      [31]
           (self-organizing  map) to quantify  the geometric   with machine learning that can predict the surface
           deviations of additively  manufactured  parts in    roughness of  FDM printed parts with high accuracy.
           fused filament fabrication processes. In addition,   Currently, Jiang  et al.  used backpropagation
                                                                                     [32]
           Zhu  et  al.  also  developed  a  strategy  coupled   neural network to analyze and predict printable
                     [24]
           with  machine learning to address the modeling      bridge length  in FDM processes.
                                                                           [38]
           of shape deviations  in  AM.  Tootooni  et al.        Similarly,  machine  learning  can  also be
                                                        [25]
           compared six machine learning techniques (sparse    used to design or analyze material properties
           representation,  k-nearest neighbors, neural        in 3D bioprinting process. For example, tissue-
           network, naïve Bayes, support vector machine,       engineered scaffolds are  very important in 3D
           and  decision  tree)  with  regard  to  the  accuracy   bioprinting, whose structures should be carefully
           of predicting dimensional variation  in fused       designed for successful cell growth and function
           deposition modeling (FDM) printed parts. Based      achievement. For example, if we want to bioprint
           on their study, the sparse representation approach   an organ in the future, the scaffolds should
           has the best classification performance.            have  the  specific  structure  for  the  successful
             In 3D bioprinting, similarly, machine learning    growth of cells to form a functional organ. In
           can be used for analyzing the accuracy of           the case here, what kind of complex scaffold
           fabricated bio-parts. For example, the tissue-      structure is the most suitable? How the properties
           engineered scaffolds are generally very complex     (e.g., density and strength) of the scaffolds will
           because they supporting cell growth in an expected   influence the printed organ function? If machine
           way to achieve corresponding functions. If the      learning can be used to generate these qualified














           Figure 4. An example of using machine learning (convolutional neural network) in three-dimensional
           bioprinting.

           8                           International Journal of Bioprinting (2020)–Volume 6, Issue 1
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