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Our OCT-based distance sensing approach proved effective in eliminating print quality loss when

printing on a moving target, simulating physiological movements. This finding is particularly
relevant for in vivo bioprinting applications, where the targeted anatomical defect may shift due

to breathing, heartbeat, or unpredictable patient motion 17,41 . Previously developed automation
systems for compensating target motion in 3D bioprinting are primarily machine vision-based

motion 14,41 , and are relatively bulky compared to the miniaturized fiber-based system (0.25 mm

in diameter) developed in this work. These existing systems typically offer millimeter-scale
precision in position tracking, whereas the OCT system presented here achieves micrometer-level

precision. Therefore, this system is well suited for integration with extrusion-based bioprinters,
where the required precision in maintaining the nozzle-to-target distance is an order of magnitude

higher than in DoD systems.

The central mechanism in the LIST printing process is nanosecond laser-induced

thermocavitation—a rapid, localized phenomenon initiated by the interaction of nanosecond laser

pulses with highly-absorbing liquid 42,43 . Ns laser pulses rapidly heat a small volume of liquid,
leading to near-instantaneous vaporization and bubble formation. The bubble expands until its

internal pressure equilibrates with ambient pressure at its maximum radius, after which it collapses

due to compression by the surrounding liquid. The growth and collapse dynamics of these bubbles
are influenced by the physical properties of the liquid medium, particularly its viscosity. In this

work we found that higher ink viscosities slow down bubble dynamics. This is a consistent with
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the fact that in viscous fluids, internal friction resists flow, resulting in slower fluid motion .
When the same amount of energy (e.g., from a laser pulse) is applied, a greater proportion is
dissipated through viscous forces, leaving less energy available for bubble expansion.

Consequently, bubble growth in high-viscosity inks is slower and reaches a smaller maximum

radius compared to low-viscosity fluids 45,46 . We also found that higher viscosities require greater
energy for jet ejection and lead to longer jet pinch-off times. This is primarily because viscous

fluids resist necking flow, allowing the liquid column to sustain elongation for a longer duration
before breaking. This behavior is observed in both inkjet and laser-assisted bioprinting. For

instance, in alginate inkjet printing, increasing the sodium alginate (NaAlg) concentration from
0.15% to 2% (w/v)—and thus increasing viscosity—results in a fourfold increase in droplet pinch-

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off time .

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