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International Journal of Bioprinting 3D bone: Current & future

Figure 10. Vat polymerization-based 3D bioprinting techniques. Abbreviations: IR: Infrared; NIR: Near-infrared; UV: Ultraviolet. This figure was created
using BioRender.
the next resin layer. Bottom-up printers are based polymerization requires the absorption of two
on the same principle, with the difference that the photons. The light source is typically a high-intensity
optical system is located below the vet, and the ultrashort femtosecond infrared or near-infrared
platform pad descends into the resin from above. laser. The 3D structures are built pointwise, but the
The finished construct is built upside down on the fabrication is not limited to the layerwise method.
platform. SLA is a fast, flexible, and accurate printing Multiple laser beams are directed to the same point
method, but requires supports made from the same and operated simultaneously during printing. When
material for post-processing. 48 the simultaneous energy of two photons exceeds the
(ii) DLP: DLP differs from SLA such that DLP utilizes absorption energy threshold of the photosensitive
light (UV or visible blue light) from a projector. The material, photo-crosslinking occurs. As with
light source remains stationary and simultaneously other vat polymerization techniques, two-photon
cures the resin layer. Depending on the applied polymerization requires post-processing, as the waste
biocompatible resin, the layer height and exposure material must be washed off the structure. However,
time must be controlled to ensure strong interface no support systems can be removed, suggesting its
bonding. The most significant advantage of using suitability to print porous microstructures, vessels,
this technique is the ability to print vessels and and microfluidic systems. The main advantage of
microchannels without a support system. In addition, this technique is the very high resolution, which
blue light damages cells less than UV light, making comes at the expense of printing speed and printing
it even more reliable for printing cell-laden bioinks. volume (limited to a few mm). 48,49
Additionally, DLP features fast printing speed, low 4.1.4. Selective laser sintering
cost, and high accuracy, but the printed construct Selective laser sintering (SLS) is a powder bed fusion
may have poor mechanical properties. 48
3D printing technique that is not commonly used in 3D
(iii) Two-photon polymerization: Two-photon bioprinting but occasionally in bone bioprinting. SLS 3D
polymerization is an ultraprecise micro- or nanoscale printers work on a similar principle to SLA, except that
3D printing technique. While SLA and DLP use a the raw material is in powder form instead of resin, and
single photon to polymerize the resin, two-photon the laser light does not bind the material chemically but

Volume 10 Issue 3 (2024) 158 doi: 10.36922/ijb.2056