Page 597 - IJB-10-3

International Journal of Bioprinting Five-axis printer for hybrid 3D scaffolds

osteochondral defects. The circumferential pore width and radial pore height deviated by 0.8% and 2%, respectively.
Finally, we inkjet-printed a mesh structure on a free-form surface, which acted as a membrane for palatal implants. In
this case, the pore width deviations were -16% in the printing direction and 2% perpendicular to the printing direction.

Keywords: Hybrid 3D printing; Hybrid scaffolds; Non-planar inkjet printing

1. Introduction for tissue engineering. Altunbek et al. reported the
hybridization of thermoplastic polycaprolactone (hard
Additive manufacturing technologies (AMTs) offer new phase) and polyethylene glycol hydrogels (soft phase) for
opportunities for tissue engineering scaffold fabrication, critical-size bone defects, while Milojevic et al. utilized
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enabling precise replication of natural tissue structural hybrid hydrogel-thermoplastic polymer scaffolds for
properties. Biological structures are an ensemble of various wound dressings. 13
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materials, often with mechanical property gradients
(between soft and hard phases), arranged in multiscale A few studies have reported the combination of
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hierarchical structures with irregular topographies. biomaterial utilization and inkjet printing hybridized with
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Although three-dimensional (3D)-printed scaffolds other AMTs. Stögerer et al. recently reported a hybrid
for hard and soft tissue regeneration have advanced 3D printing device, combining stereolithography and
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significantly, the hybridization of printing technologies and multinozzle inkjet printing, to manufacture composite
printing on curved surfaces to fabricate patient-specific laminates with specific material patterns to mimic the
biomimetic hybrid scaffolds remains largely unexplored, hierarchical structure of marine species. Moreover, Lee
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particularly in the context of equipment and process et al. presented a hybrid process, combining micro-
development. To date, there are limited AMTs available extrusion and single-nozzle inkjet printing, to fabricate
that have demonstrated the capability to effectively print skin equivalents.
dissimilar materials, particularly for high-temperature Apart from hybrid printing, customized 3D printers
sintered ceramics, hydrogels, and photopolymers. Hence, for biomedical applications have emerged, particularly
a sequential hybrid fabrication process between different through adaptions of commercially available desktop
AMTs holds significant promise. Osteochondral and fused filament fabrication (FFF) 3D printers. Jaksa et
maxillofacial defects can be treated using 3D-printed al. demonstrated extrusion printing of multi-material
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hard and soft hybrid scaffolds having different mechanical anatomical structures by combining materials with
properties and could greatly benefit from a sequential different stiffness, namely silicone and polylactic acid
hybrid fabrication process. 5,6 (PLA). Tashman et al. transformed a thermoplastic
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The fabrication landscape of hybrid scaffolds, in terms printer into a bioprinter, and Hinton et al. upgraded a
of the materials and methods used, has undergone several MakerBot Replicator with a custom-built syringe-based
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stages of evolution over the past few decades. Taboas et extruder for hydrogel printing. 19,20 Similarly, Khani et al.
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al. casted hard and soft polymeric-ceramic multi-material presented a multi-material extrusion-based printer for the
scaffolds for osteochondral repair. Similarly, Lantada et al. fabrication of bioinspired structures.
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reported a composite scaffold for osteochondral repair. The Notably, these models are restricted to a linear three-
silicone soft cartilage phase was developed using sponge axis system. For example, rotational axes are required for
scaffold fabrication, whereas the titanium hard bone phase printing on free-form surfaces. Hence, the development of
was developed using selective laser sintering. Besides casting, five-axis printers using different AMTs has recently been
the hybridization of 3D printing technologies has also been reported. Hong et al. successfully printed conductive
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presented in a sequential workflow for vat polymerization, traces on free-form surfaces using a five-axis printer
combining lithographic ceramic manufacturing and two- upgraded from a mono-material three-axis FFF printer.
photon polymerization using zirconia resins. González- Another approach to free-form 3D printing is to use
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Pujana et al. utilized two different AMTs (i.e., filament robotic arms, which is especially interesting for large-
extruding and electrospinning) to develop hybrid scaffolds area printing. Several graphical applications have been
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for bone regeneration. Similarly, Choi et al. constructed reported for inkjet printing on non-planar surfaces.
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hybrid skin substitutes by combining electrospinning and Arango et al. presented a theoretical approach to print on
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3D printing. Additionally, several studies have leveraged single-curved surfaces, followed by printing tests to predict
the combination of thermoplastics and hydrogels droplet position on non-planar substrates. Fechtig
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Volume 10 Issue 3 (2024) 589 doi: 10.36922/ijb.3189