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           Figure 2. A vision for future bioprinting.

           recently reviewed in Zhang et al. , Schwab et al. . These   huge and diverse, it could be all types of diagnostic images
                                                   [12]
                                     [11]
           mathematical models are useful for construction of virtual   stored in hospital databases, all types of experimental
           bioprinting process. ML models have also been used in   data in worldwide laboratories and research centers, all
           in vitro study for identification of cell signature genes out   the “omics” databases already established in past years,
           of complex gene expression profiles among different cell   or simply the vast scientific literature. Standard and open-
           groups [13,14] . Another in vitro example is virtual histological   access databases with meaningful and valuable training
           staining, which bypasses the lengthy and laborious process   datasets  specifically  targeting  for  bioprinting  must  be
           for tissue preparation. Researchers used deep learning to   created  from Big Data  curation.  A recent  example  is
           transform autofluorescence images of tissue into images   the  construction  of  a  web-based  nanomaterial  database
           equivalent to histologically stained tissue , and achieved   through  Big  Data  curation,  which  contains  705  unique
                                             [15]
           blending of multiple stains by assigning each stain at the   nanomaterials,  and the annotation  of nanostructures
           pixel level [16,17] . Furthermore, mathematical models and   generates 2142 nanodescriptors for modeling and ML, but
                                                                                                            [20]
           ML models, which help us understand the complexities of   more  importantly, the  database  is publicly  available .
           biological systems and extract new biological knowledge   Another example is geoscience databases, which is large
                                                                                                            [21]
           from complex experimental datasets, are expected to   and ideal for ML and automated geoscience analysis .
           bring tissue engineering much closer to clinical reality .   In fact, numerous experimental data and various materials
                                                        [18]
           Collectively, the above evidence of virtual experiments   directly related to bioprinting have been generated over
           in  either  processing  or  post-processing  of  bioprinting   past  years,  making  bioprinting  a  potentially  a  data-
           suggests that we will see more in silico experiments with   driven research, but so far there is limited  database
           ML in bioprinting in future.                        created  specifically  for  bioprinting.  In  future,  we  hope
               However, ML cannot  be performed without Big    to see more developments in this area, in line with the
           Data about modern clinical imaging of organs, histology,   development of databases for 3D printing. Perhaps it may
           immunohistochemistry, biomechanical  properties  of   be even possible to predict new bioprinting discoveries
           tissue and organs, molecular profiles of cell, tissue, and   by exploiting the current literature alone without relying
                                                                                [22]
           organs (genomics and proteomics) function and so on. Big   on experts’ opinions .
           Data can be structured, unstructured or semi-structured   4. Digital twin of human organ
           and it is much more than traditional databases . For ML
                                                 [19]
           purposes, the first step is collection of Big Data or Big   On the other hand, design process in 3D bioprinting must
           Data curation. The sources of big data for bioprinting are   be organized around the concept of digital twins of organs

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