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International Journal of Bioprinting                                    Machine learning and 3D bioprinting



            Table 1. Summary of ML algorithms in bioprinting
             Application area  Tasks                                 ML methods                         Ref.
             Image analysis-  Identify cone mode in scaffold fabrication process in EHD   CNN           [14]
             based in situ   jetting
             monitoring   Identify deposit fibers’ continuity, uniformity, and regularity in   Four-layer CNN, ResNeXt-50 network, linear SVM   [25]
                          EBB                                        classifier
                          Extract the flow pattern and droplet evolution in DBB  Deep recurrent neural network (DRNN)  [29]
             Printing parameter  Predict the electrospun diameter of PCL/Gt nanofibers  Multiple regression, multilayer perceptron ANN   [24]
             optimization  Identify suitable printing conditions for PPF scaffold in EBB  Random forest classifiers (RFc), random forest   [26]
                                                                     regression (RFr)
                          Optimize ink composition and printing parameters in EBB  SVM classifier       [27]
                          Predict the droplet diameter in EHD inkjet printing  Statistical regression analysis, GA-NN, BPNN  [28]
                          Optimize printing parameters for GelMA and HAMA bioinks  Bayesian optimization (BO)  [30]
                          Optimize the droplet size and printing frequency in EHD inkjet  Desirability function analysis  [31]
             Biomaterial/bioink  Achieve high shape fidelity in EBB  Inductive logic programming, multiple regression   [32]
             optimization  Achieve ideal linewidth and shape fidelity in EBB  Hierarchical machine learning  [33]
                          Predict filament diameter in EBB           RFr, linear regression, intrastudy linear regression  [34]
             Cell performance   Predict cell viability               SVM regression, linear regression, RFr, SVM classi-  [34]
             analysis                                                fier, RFc, logistic regression classifier
                          Detect the impact of scaffold morphology on cell shape pheno-  SVM classifier  [35]
                          types
                          Analyze cell-scaffold interaction          AD-GAN                             [36]
                          Predict cell-material interactions in fibrous scaffold  RFr model             [37]
                          Associate cell morphologies with diverse microenvironment   SVM classifier    [38]

            and available dataset. Moreover, multiple methods have
            been compared to identify a competitive model with better
            performance [24,25] . One task can also be organized into
            either a classification or regression model, and then solved
            accordingly based on data processing strategies [26,30-34] .
               These studies aimed to enhance the reliability and
            stability of the bioprinting process as well as the mechanical
            and biological performance of bioprinted constructs. In the
            following section, ML methods are discussed with regard
            to application areas.

            2.1. Image-based in situ process monitoring
            To maintain the stability and reliability of bioprinting in   Figure 4. Image-based in situ process monitoring.
            large-scale and long-term fabrication, the development of
            in situ process monitoring is necessary. As such, the quality   for identification purposes. The extrusion parameters were
            of  bioprinted  constructs  relies on  intelligent  printing   adjusted based on model outputs. Similarly, the deposited
            process control rather than operator experience.
                                                               images can be compared with predefined patterns using the
               Similar to the manufacturing process, bioprinting   extracted features to depict the fiber quality and pattern.
            process monitoring often collects real-time extrusion and   The identification model built using such features can be
            deposition images, as shown in  Figure 4. Subsequently,   directly linked to the adjustment strategy for the deposition
            image preprocessing methods are utilized to extract key   parameters. Generally, extrusion and deposition images
            features from the captured images, which are the inputs of             [15]     [25]
            the corresponding ML models. These features reflect the   are used to monitor EHD  and EBB , respectively.
            difference between the standard cone and identified cone   Both traditional ML and DL methods can be used to
            in EHD and deliver critical information to the ML model   analyze the collected images. The former extracts image

            Volume 9 Issue 4 (2023)                         52                           https://doi.org/10.18063/ijb.717
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