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bioinks. LIST has been successfully tested for printing primary cells, including human umbilical

vein endothelial cells and sensory neurons, while maintaining high post-printing viability 26,27 . The
latest version of LIST employs continuous bioink perfusion through a glass capillary with a laser-

machined hole serving as a nozzle and utilizes focused, low-energy nanosecond laser pulses for
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droplet ejection . However, all previous implementations of LIST have relied on a bulky free-
space beam delivery system, preventing the mobility of the printing head.

Here, we introduced and validated a mobile printing head based on the LIST technique. Central to
our approach is the replacement of a bulky free-space beam delivery system with a fiber-based

alternative. The mobile printing system was mounted on a robotic arm, and a model ink (with
viscosity up to 165 cP), along with a time-resolved imaging setup, was used to study printability

and printing dynamics. We investigated how variations in the distance between the printing head
and the target substrate affect printing quality. Finally, we developed and validated an automated

distance-tracking system based on a fiber-optic sensor to compensate for quality degradation when

printing on moving substrates that mimic physiological motion in patients.

2. Materials and methods

2.1. Model ink

A water-glycerol mixture was used as a model ink with different mixing ratios, producing a
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viscosity range from 2.8 cP to 165 cP . We used a single viscosity (18 cP) to test printability on
moving substrates, while the full viscosity range was applied in the second part of the study to

investigate the effects of viscosity on bubble formation, jetting dynamics, and printing volume.
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Due to the transparency of water in the visible range , a biocompatible food dye, Allura Red AC
(10 mM) (458848 100G, Sigma-Aldrich), was added to the ink to increase its absorption

coefficient at 532 nm.

2.2. Microjet and bubble imaging

We used a time-resolved imaging approach to capture bubble and jet dynamics. The imaging
system comprises a high-speed camera (Chronos 1.4; Kron Technologies), an achromatic lens

(AC254-150-A-ML, Thorlabs), an objective lens (RMS4X, Thorlabs), and an LED light source

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