Page 246 - IJB-9-3

International Journal of Bioprinting Multi-material bioprinting with OCT imaging

applications of bioprinting, including the development and imaging results to achieve improved printing accuracy. For
improvement of bio-ink , relevant bio-structure , and example, Zhou et al. proposed a model for silica gel material,
[4]
[5]
methods to achieve biological function using printed which can predict and control the filament size between
structures . To pave the way for real application of the critical moving speed and the limit moving speed .
[25]
[6]
printed structures, it is of great significance to simulate Considering the distinguished properties difference
human organs or tissues with complex structures and between various materials in multi-material bioprinting,
heterogeneous properties. To achieve this, multi-material the same printing parameters used for different materials
bioprinting is essential. would generate matching errors between the printed
Bioprinting have various categories, including structures, such as layer thicknesses deviation or filament
vat polymerization , material jetting , and material sizes difference between different materials, resulting in
[8]
[7]
extrusion . Among them, material extrusion is the most crack or collapse of the overall printed structure.
[9]
used method, and its advantages include flexible control Especially, extrusion-based biological 3D printing has
of printing parameters and low requirements on the been the simplest and popular bio-printing technique
material. It also avoids the use of photo-initiators in vat among the multi-material printing methods. This method
polymerization that may affect the cell growth, and is usually uses multi-nozzle for different materials, and
easier to realize complicated structure as compared with mechanically switches nozzles to change the material. In
material jetting [10-12] . In addition, by using multi-nozzles this way, different materials can be deposited in the same
and bio-inks with live cells, extrusion-based bioprinting or different layers . Errors are easily produced in the
[26]
can establish a bio-model that remains biologically active, printing process, such as the problem of under-extrusion
which can better mimic the real tissue or organ both and over-extrusion. To improve the extrusion-based
morphologically and biologically. However, high-precision printing process, Hoelzle et al. adopted compression
registration of the print structure and the target structure dynamic model which proposed that the system presents
is the basis for the function of the artificial organ or tissue. response hysteresis at both the start and end positions .
[27]
Thus, applications of multi-material bioprinting impose However, efficiency suffers from their manual error
higher requirements on printing accuracy compared with correction method. Armstrong et al. employed the process
the single-material bioprinting. For example, the printing monitoring method to determine the time to reduce the
structure should perfectly match the suture defect to pressure input signal to correct the error and make ensure
provide correct and sufficient mechanical support in the that material was deposited in the correct position [28,29] .
application of bone defect repair . In the field of cell However, the method Armstrong et al. proposed failed to
[13]
containers, high-precision registration of four printing solve the problem of separation or overlapping of extruded
supports with four materials can be used to simultaneously materials at the connection point between different nozzles.
culture four types of cells in a non-contact way . In order to improve printing accuracy in multi-material
[14]
Therefore, some studies related with the optimization extrusion-based bioprinting process, efficient imaging
of the printing path before printing were reported to technology are required to evaluate the state of 3D-printed
ensure printing accuracy. Sodupe-Ortega et al. studied models to correct printing errors for high-precision
the influence of the main parameters of multi-material 3D structure construction. It was reported that Almela et al.
bioprinting and proposed two main calibration models used micro-CT technology to analyze the porosity and
to adjust the positions of multiple print heads to improve connectivity of printed bone scaffolds . Gerdes et al. used
[30]
printing accuracy . Naghavi et al. studied the deviation camera imaging to quantify the effect of process variables on
[15]
between the as-designed and as-built matrices, and the exactness of the dimension and shape of the deposited
designed compensation strategy before the fabrication of strand . However, these technologies mentioned above are
[31]
scaffolds, which can improve the printing accuracy .
[16]
limited by the imaging results with relatively low resolution
Among all contributing factors, the properties of and ability of only providing 2D structural information.
printing materials and the printing parameters are primary To overcome these disadvantages, optical coherence
factors that influence printing accuracy [17,20] . The material tomography (OCT) is utilized to facilitate the structural
properties include physical properties , viscoelasticity, observation in label-free, noninvasive 3D imaging of
[21]
thixotropic property , and fluidity , and the printing printing structure. For example, Joshua et al. developed a
[23]
[22]
parameters include the pressure applied during printing, multi-material bioprinting platform with integrated OCT,
the moving speed and the temperature of the platform, which can enable quantitative 3D volumetric imaging with
and the printing nozzle . Normally, for the same material, micron resolution over centimeter length scales, the ability
[24]
the relationship between the printing parameters and the to detect a range of print defect types within a 3D volume,
filament size of the printed filaments is studied by later and real-time imaging of the printing process at each print
Volume 9 Issue 3 (2023) 238 https://doi.org/10.18063/ijb.707