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Materials Science in Additive Manufacturing Fibrous silk in biomedicine

transparent vinyl substrates in parallel line patterns. shear-thickening behavior at shear rates above 100 s due
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Human MSCs seeded on these patterns aligned along to β-sheet transitions, which can lead to nozzle clogging.
the FS lines and differentiated into osteoblasts, with cell To address this, materials with shear-thinning properties
bridging observed between lines spaced <1.25 mm apart are preferred. To mitigate shear-thickening during
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after 4 weeks. the printing process, researchers have explored various
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rheological modifications. Chawla et al. developed FS–
However, inkjet printing faces significant limitations
in 3D bioprinting, primarily due to the narrow nozzle gelatin composites with optimized flow properties, while
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diameter and strict viscosity requirements of the bioinks. Das et al. screened multiple FS–gelatin formulations to
These constraints pose challenges for efficient cell loading identify those that balance flowability with rapid gelation,
and can result in thermal or mechanical stress, reducing minimizing clogging under high shear conditions.
cell viability. Consequently, the range of suitable bioinks A critical concern in extrusion-based 3D printing is
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for inkjet printing remains limited. While FS’s naturally low whether functional additives introduced into FS bioinks
viscosity allows it to be printed without prior modification, compromise cell viability. Zheng et al. addressed this
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post-treatment is typically required to stabilize the printed concern by incorporating low molecular weight PEG
architecture. Rider et al. developed an FS-based dental 400 to promote β-sheet formation, thereby stabilizing FS
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barrier membrane using inkjet printing and methanol bioinks. Their findings demonstrated that the modified
treatment to induce rapid β-sheet formation. However, bioink maintained biosafety without adversely affecting cell
methanol exhibited cytotoxic, making it unsuitable for viability. Furthermore, FS–PEG 400 composites co-printed
direct cell encapsulation. with hMSCs supported sustained cell proliferation within
To overcome this issue, Compaan et al. introduced the 3D constructs for up to 15 days. In another study, Jose
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a methanol-free crosslinking strategy, combining FS with et al. enhanced the stability of FS bioinks by incorporating
alginate to produce a low-viscosity bioink. Calcium ions glycerol and calendula alcohol during the printing process,
were used to induce temporary alginate gelation, followed achieving excellent cellular viability. Similarly, Rodriguez
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by horseradish peroxidase-mediated covalent crosslinking et al. developed a novel freeform printing strategy using
of FS, resulting in stable 3D scaffolds. This method enabled a PEG 400–laponite support bath. In this system, PEG
successful cell encapsulation and proliferation, significantly 400 facilitated β-sheet formation, while synthetic laponite
enhancing the feasibility of FS-based inkjet bioprinting. stabilized the ink and maintained structural integrity.
Despite being one of the earliest bioprinting methods, the Notably, synthetic laponite exhibited no cytotoxicity and
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use of FS bioinks in inkjet printing remains limited due to supported over 90% cell viability.
functional crosslinking challenges and nozzle-induced cell Collectively, these studies demonstrate that
viability concerns. functionalized and additive-enriched FS bioinks can retain
high biocompatibility, validating their utility in cell-laden
5.2. Extrusion 3D printing extrusion-based 3D bioprinting.
Extrusion-based 3D printing is a widely used method for
fabricating both non-biological and biological structures, 5.3. Light-based 3D printing
particularly due to its compatibility with bioinks across Light-based bioprinting has recently emerged as an
a broad viscosity range. This technique often involves innovative technique in the field of 3D bioprinting,
co-printing two materials: a highly viscous component garnering significant attention from materials science
for mechanical support and a low-viscosity component researchers due to its ability to fabricate structures with
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to foster cell growth and proliferation. The printing high spatial resolution and accuracy. This technique
process entails loading the bioink or printing solution into involves the use of a light source within the printer to cure
a reservoir connected to a nozzle, from which the material photosensitive resins, allowing for layer-by-layer or point-
is extruded layer by layer under controlled temperature by-point construction of 3D models. 209-211 The two principal
conditions and solidified on the printing platform. Similar light-based 3D printing techniques currently employed are
to inkjet printing, rapid and controlled solidification is laser-induced forward transfer (LIFT) and DLP.
required to maintain the structural integrity of the printed LIFT operates through single-pulse laser irradiation
constructs. 202 that triggers photochemical crosslinking within

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Ghosh et al., from the group led by Lewis, was bioinks and ejects individual droplets onto a receiving
among the first to apply extrusion-based printing to FS, substrate. In contrast, DLP projects patterned light
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successfully printing 28% – 30% FS solutions into square through a digital micromirror device to initiate spatially
and mesh-like architectures. However, FS solutions exhibit controlled photopolymerization. In LIFT, the laser pulse
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Volume 4 Issue 2 (2025) 14 doi: 10.36922/MSAM025130020