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Bioprinting of multimaterials with computer-aided design/computer-aided manufacturing
support material can be a temporary scaffold [57,58] with slight modification . About 10% w/v
[67]
that is either manually remove or dissolved away Gelatin Type A (porcine skin) was dissolved in
(i.e., sacrificial); while support material such as 1× phosphate-buffered saline (PBS) (Vivantis)
poly(epsilon-caprolactone) and poly(lactic-co- stirred at 600 rpm keeping temperature at 60°C
glycolic acid) thermoplastic provides mechanical for 1 h. Methacrylate anhydride was added at
integrity and eventually degrades through 1.4% v/v dropwise into the solution and the
biological process [9,15,59-62] . Pluronic F127 and reaction is continued for 2 h at 50°C. The reaction
gelatin are commonly used in vat-based build/ is quenched by adding pre-warmed 1× PBS at
support printing such that bioink containing cells 40°C. The mixture was transferred into dialysis
are extruded and embedded within the vat of tubing (MWCO: 12400) for dialysis in distilled
support material . water for 4 days at 40°C. Finally, the solution was
[55]
Optimizing build orientation and topology of lyophilized for 7 days to obtain pure GelMA and
support structure aims at reducing support material was stored at −20°C until further use.
usage and total build time. Algorithms have been
developed to design tool path for strategically 3.3 Preparation of bioink (build and support
positioning build parts, minimizing support material)
material wastage, and decreasing both build and The build material contains 5% w/v Gelatin
post-processing time [34,66] . In this article, a novel Type A, 5% w/v GelMA, and 2% w/v sodium
file processing method is introduced. In brief, alginate which were dissolved in 1× PBS.
CAD files used for bioprinting are segmented Photoinitiator containing 10% w/v 2-Hydroxy-
into different sections. Build or support material 4′-(2-hydroxyethoxy)-2-methylpropiophenone
printing reaches a certain z-layer before the (Sigma-Aldrich) was dissolved in ethanol and
printhead is changed for the alternating materials. added to the mixture of build material at 0.02% v/v.
The support material consists of Pluronic F-127
3 Methodology
and 1 M calcium chloride dissolved in 10 mM
3.1 File preparation HEPES buffer.
A series of CAD segmentation method is used 4 Results and discussion
in the novel approach in preparing CAD files for
bioprinting. This method has several advantages Hydrogels that rapidly cross-link are chosen
such as (i) improve structural stability of bioprinted as the complimentary pairs in a build/support
configuration . As such, build material comprising
[25]
construct, (ii) deposit multimaterial, (iii) optimize gelatin methacrylate and sodium alginate is
overall printing time, and (iv) overcome machine coupled with support material comprising of
limitations. Overview of the novel approach
as compared to conventional file segmentation Pluronic F127/calcium chloride. Primary cross-
linking occurs when alginate is in contact with
approach is illustrated in Figure 2. CaCl from the support material. Pluronic F127
To assess the functionality of the novel comprises a hydrophobic core conjugated with
2
file segmentation approach, two models are hydrophilic segments at the two ends . However,
[68]
demonstrated (i) freestanding coil (15 mm) and Pluronic F127 has weak mechanical properties
(ii) left ventricle wall. Regenhu bioprinter with specifically with rapid dissolution when in contact
multi-printhead channels is used for the printing. with aqueous media or biological fluid. Hence,

3.2 Synthesis of gelatin methacrylate it is essential to ensure that support material is
structurally stable before secondary polymerization
All materials are purchased from Sigma-Aldrich of GelMA without being dissolved. A layer of
unless otherwise stated. Gelatin methacrylate alginate hydrogel is formed between the build/
(GelMA) was synthesized as previously described support interface that acts as a barrier to slow the

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