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Composite Bioprinting for Bio-fabrication
resolution camera is used to position the nozzle while the the bio-CAD/CAM system and realizes the use of bio-
z-axis sensor can accurately control the height between CAM processing for fabricating structures which could
the nozzle and the receiving platform. Lu et al. used CAD not be modeled in the CAD processing was put forward
software to design the 3D model of the internal micropore (Figure 5) .
[79]
structure of the bionic bone scaffold and fabricated it In summary, for tissue engineering scaffold
based on the path planned by an independently developed printing, the CAD/CAM system for 3D bioprinting
path planning software . Yan et al. put forward the low- is the same as the traditional 3D printing system if the
[73]
temperature 3D bioprinting technology and equipment scale of the printing structure is single or common and
and made a number of achievements in the preparation the material used is suitable for the current mainstream
of bone scaffolds . Liu et al. introduced the inertial 3D printing technology and system. Otherwise, if the
[74]
force injection (AVIFJ) and extrusion printing composite goal of printing is to assemble components such as cells,
forming system, which can achieve precise deposition of drugs, biomaterials, etc., both path planning strategy and
droplets containing a single cell and the printing of cell- process control can become more complex. Hence, it
laden hydrogel . Xie et al. introduced a printing system, is necessary to add a process management module in a
[75]
which integrates extrusion printing and electrospinning traditional CAD/CAM system and supplement with more
for forming structures with micro-nano scale features. information reflecting component gradient in the path
The system had a micro-level printing resolution to meet planning strategy. Besides, it should be pointed out that
the requirements of forming exquisite complex cross- at present, the 3D composite bioprinting system proposed
scale structures . Liu et al. proposed and preliminarily by different institutions involves different processes,
[76]
provided the test platform of the bio-CAD/CAM/3D so there will be differences in the scope of applicable
composite printing technology, abbreviated as a composite materials and specific application objects. As for the index
forming test platform [77,78] . advantage analysis from the engineering and technology
It can be found that combining the process with micro- perspectives, the detailed parameter comparison is not
nano forming precision and 3D bioprinting effectively available at present because most of the systems are not
solves the problem of limited precision and the inability commercial.
of forming micro-scale structures inside the structure,
which are evident in the formation process of traditional 4. Discussion and prospects
3D printing. This feature makes the corresponding bio- According to the researches and demands for tissue
CAD/CAM process different from the traditional CAD/ engineering and regenerative medicine, the core issue
CAM, that is, the biological CAM process needs to of the regeneration of tissue and organ by biofabrication
merge the scale information that cannot be modeled in technologies lies in the effective assembly and behavior
the CAD process with the information from the CAD regulation of cells. A typical way of cell assembly is
process. In addition, the composite forming process, using the biodegradable scaffolds with autologous stem
which combines printing technology and micro-nano cells seeded and then co-cultured on it in vitro. After that,
forming technology, often integrates multiple physical the scaffold can be planted in vivo to repair the injured
fields, cross-linked reaction, and other effects so as to tissue and organ. In this context, to ensure the effective
effectively regulate the interface effect in the composite adhesion of the inoculated cells and further realize the
structure which make the prepared scaffold satisfy the accurate positioning and reasonable distribution of cells
requirements of cell attachment and growth while taking or cell clusters, the solution of precisely controlling the
into account the structural controllability and mechanical components and microstructures of scaffolds as required
properties. These also call out challenges upon the has become an important goal of the development of 3D
corresponding printing system and the designation of the printing technologies and equipment. Another route is the
CAD/CAM function module. To solve these problems, technology of direct assembly of cells which is capable
Liu Yuanyuan et al. from Shanghai University proposed of precisely depositing living cells in the spatiotemporal
a type of a composite forming system consisting of dimension. Although great progress has been made
multiple functional subsystems with which the bio-CAD/ in this field in obtaining a 3D biological structure, its
CAM software system was studied. The system designed shortcomings still lie in the manufacturing efficiency,
the automatic processing flow and detail implementer achievable scale, and complexity of the structure; these
method that encompass the following: Obtaining STL problems pose new challenges to the biological printing
models of injury tissue from manual designs or medical process and equipment technology.
imaging modalities reconstruction, generating printing In such a context, the research interest in 3D
path information and drive file containing processing composite bioprinting based on the integration of two
information by post-processing. Importantly, an approach or more printing processes with different forming
of adding process management module which innovates principles is gradually intensifying (Table 1). 3D

14 International Journal of Bioprinting (2021)–Volume 7, Issue 1