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International Journal of Bioprinting Advancements in 3D printing

cost-efficiency and instigating a fresh industrial paradigm. and demerits in comparison to other molding techniques.
Post-2020, numerous novel 3D bioprinting techniques Among its merits are elevated molding precision, robustness
have emerged, such as in situ printing, suspension of the printed model, and an array of color choices. On the
printing, and digital light processing. Presently, 3D flip side, it harbors shortcomings, including a relatively
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printing boasts wide-ranging applications across domains coarse surface texture on the molded object.
such as biomedicine, aerospace, architectural design,
cultural industries, industrial production, and military 2.3. Direct ink writing
equipment. 16,17 Direct ink writing, also known as robocasting grouting, is
a process involving the controlled extrusion of ink from
In this part, we present and compare four primary types a temperature-regulated barrel through a nozzle onto a
of 3D bioprinting technologies, namely fused deposition substrate using either a screw extrusion or pneumatic
modeling (FDM), direct ink writing (DIW), selective laser pressure control system (Figure 2B). The ink is deposited in
sintering (SLS), and digital light processing (DLP) (Table 1). a layer-by-layer fashion based on the analysis of model slices
Abbreviations: DLP, digital light processing; DIW, direct and the generation of code. Key direct writing parameters
ink writing; FDM, fused deposition modeling; SLS, (pressure, speed) and environmental factors (temperature,
selective laser sintering. direct writing medium) significantly influence the process.
It is crucial to appropriately match the ink with the
2.2. Fused deposition modeling corresponding direct writing parameters and environmental
Fused deposition modeling is a rapid prototyping process conditions to ensure structural stability. DIW displays three
distinct from other techniques as it does not rely on lasers central attributes. 21,22 Firstly, it offers versatility in material
as a formative energy source. Instead, it involves the selection, encompassing metals, ceramics, polymers,
heating and liquefaction of diverse wire-like materials, hydrogels, composites, and even biological cells. Secondly,
such as engineering plastics including polylactic acid the ink exhibits shear-thinning properties and notable
(PLA) and polycarbonate (PC), followed by layer-by-layer viscoelasticity, enabling it to sustain a consistent form and
construction. 18,19 The formative sequence is described as layer stacking without collapsing post-extrusion. Thirdly,
follows (Figure 2A): Controlled by computer algorithms, the ink boasts elevated solid content, thereby mitigating
the heating nozzle maneuvers within the XY plane in line volume and shape alterations during subsequent processing.
with the cross-sectional outline of the desired product. Ink solidification can be accomplished through solvents,
Thermoplastic filament materials are fed into the heating temperature shifts, gelation, or direct writing media, among
nozzle via a wire feeding mechanism. Subsequently, these others. The rheological properties and solid content are
materials are heated, reaching a semi-liquid state within the contingent on the chosen solidification mechanism. Inks
nozzle, and then extruded. Upon extrusion, the material is with slower curing rates require solid content with higher
selectively laid onto the work surface and rapidly cooled, moduli to ensure proper solidification, whereas inks with
yielding a slender profile with a designated thickness. After quicker curing rates can tolerate with solid content of
each cross-sectional layer is generated, the work surface lower moduli. However, DIW does come with certain
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is lowered, and the subsequent layer is deposited. This constraints. Primarily, materials must be carefully designed
iterative process closely resembles the act of “drawing” the to be compatible with direct writing inks and to flow
contour of the cross-section, culminating in the creation of seamlessly through the narrow nozzle, as clogging can occur
a 3D product. Nevertheless, it is crucial to acknowledge otherwise. Secondly, the product’s diameter is often confined
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that FDM, as a molding technology, bears inherent merits by the nozzle’s size, and the pattern deposited is restricted by

Table 1. Comparison of different 3D printing technologies
Methods Materials Fabrication mechanism Typical Applications Cost
resolution
FDM Thermoplastics Heating and extruding solid 50–100 μm Blood vessel, tissue +
filament
DIW Viscoelastic ink Liquid ink is 1–250 μm Organ, tissue +
squeezed through the nozzle
SLS Polymers, ceramics, Melt sintering 1–250 μm Tooth, skeleton ++++
metals, and composites
DLP Optical crosslinking Optical crosslinking 50–200 μm Organ, tissue, delivery +++
material

Volume 10 Issue 2 (2024) 47 doi: 10.36922/ijb.1752