Upconversion Photoluminescence to Monitor Local Heat Release During Femtosecond Direct Laser Writing of Bioinks In...

Area of Science:

• Materials Science
• Biotechnology
• Optical Engineering

Background:

• Photopolymerization processes, particularly femtosecond direct laser writing, generate heat.
• Understanding and controlling this exothermic heat is critical for applications involving sensitive materials like bioinks.
• Existing thermometry methods may lack the precision or real-time capability needed for these dynamic processes.

Purpose of the Study:

• To develop and validate a real-time thermometry technique for monitoring heat signatures during femtosecond direct laser writing.
• To investigate the influence of process parameters (scan speed, laser power, photoinitiator concentration) on local heating.
• To identify thermal runaway effects and establish optimal conditions for laser-assisted bioprinting.

Main Methods:

• Utilized NaYF4:Yb3+/Er3+ upconversion nanoparticle (UCNP) photoluminescence for temperature sensing.
• Employed a collinear lithography and thermometry laser configuration for in-situ monitoring.
• Implemented statistical short-pass filtering to enhance temperature calibration accuracy.

Main Results:

• Achieved high thermometry performance with relative sensitivity of 0.89-1.58% K−1 and uncertainty of 0.2-0.4 K.
• Observed significant thermal effects, including transient temperature spikes exceeding 120-140°C, linked to process parameters.
• Identified that physiological conditions were maintained only at scan speeds of 20 µm/s.

Conclusions:

• The developed UCNP-based thermometry provides a powerful tool for real-time thermal monitoring in laser writing.
• Findings highlight the necessity of managing thermal load to prevent detrimental effects in bioinks.
• This work enables improved process control for laser-assisted bioprinting and related advanced manufacturing technologies.