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± 113 µm to 119 ± 57 µm at 3 mm. This suggests that mechanical instability and vibrations in the

robotic arm play an important role in accuracy limitations. This issue could potentially be mitigated
by using a robotic arm that is less susceptible to vibration, or by employing a separate end-effector

dedicated to z-positioning, thus decoupling vertical adjustments from general motion.

In experiments conducted without Z-position adjustment, the mobile LIST printer operated

smoothly at frequencies up to 30 Hz, which corresponds to the maximum repetition rate of our

current laser system. Based on the observed pinch-off times, frequencies as high as 800 Hz appear
to be theoretically feasible, although this has yet to be experimentally confirmed.

We employed an FDA-approved dye to enhance the model ink’s absorption coefficient at 532 nm.
While effective for energy absorption, this dye imparts a red coloration to the printed constructs.

The dye does not pose biocompatibility concerns 26-28,34,35 , but the coloration may not be entirely

washable from some matrices. This may limit the use of this approach in applications that require
high optical transparency. One potential solution is to shift to mid-infrared laser sources, where

water exhibits a much higher absorption coefficient 52,53 . These wavelengths have already been
successfully applied in donor-free LIFT bioprinting 54,55 , suggesting a promising path forward for

dye-free LIST.

5. Conclusion

In conclusion, we successfully developed and validated a mobile, laser-assisted DoD printing head
integrated with a robotic arm and an optical distance sensor. Printing volumes for model inks with

viscosities up to 165 cP were in the nanoliter range. Higher viscosities required increased laser
energy and resulted in longer jet pinch-off times. Our results highlight that maintaining a printing

head-to-target distance below 3 mm is essential for preserving print quality, and that our dynamic

distance compensation effectively mitigates printing quality loss on targets simulating
physiological motion. This compact, mobile DoD system can facilitate in situ bioprinting

applications in dynamic physiological environments.

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