This manuscript investigates the impact of three photoinitiators (PIs)—lithium phenyl (2,4,6-trimethylbenzoyl) phosphinate (LAP), 2-hydroxy-1-(4-hydroxyethyl-phenyl)-2-methyl-1-propanone (I2959), and Eosin Y—on the mechanical properties, pore size, ROS generation, and cell viability of GelMA hydrogels. The study addresses critical aspects for optimizing photoinitiator selection for bioprinting applications, providing experimental evidence on ROS-induced cellular impacts and corresponding hydrogel characteristics. The manuscript presents a systematic experimental approach and provides relevant insights into the biophysical and biological effects of varying photoinitiators. However, the current manuscript significantly lacks comprehensive discussions comparing the experimental outcomes with existing literature. The results are clearly presented, but deeper analysis and integration with prior studies are necessary to justify the novelty and importance of the findings fully.

Specific Comments:

• While the background is adequately presented, it does not sufficiently discuss previous studies on the effects of different photoinitiators on hydrogel properties and cell viability. The manuscript would significantly benefit from a more thorough comparative analysis of existing literature.
• Swelling, degradation, and mechanical characterization results are well-organized and clearly depicted in Figures 2 and 3. However, there is a noticeable absence of discussions comparing these findings with existing literature. This limits the interpretation of how the presented results advance or differ from previous work.
• The manuscript includes swelling ratio measurements over time, which are less informative unless clearly linked to the physical or biological properties of hydrogels. It would be more scientifically meaningful to compare swelling ratios at the saturated stage across different PIs and concentrations, supported by proper statistical analysis.
• Figures 3 and 4 present critical biological data. However, the discussion lacks comparisons with established results in the literature regarding ROS generation and its known effects on MSC viability. Adding comparisons will strengthen the manuscript's discussion and clarify its contribution to the existing body of knowledge.
• The discussion is brief and primarily restates the results without sufficiently integrating previous studies to provide context or highlight the broader implications. An expanded discussion incorporating comparative analysis from the literature is necessary to substantiate the manuscript's conclusions.

The manuscript requires significantly more work to address the substantial gap in comparative analysis with existing literature. After addressing these concerns, the manuscript could be considered again for publication in Biomaterials Science.