Extracellular vesicles (EVs) represent an emerging class of therapeutics with significant potential and broad applicability. However, a general limitation is their rapid clearance after administration. Thus, methods to enable sustained EV release are of great potential value. Here, we demonstrate that EVs from mesenchymal stem/stromal cells (MSCs) can be incorporated into 3D-printed gelatin methacrylate (GelMA) hydrogel bioink, and that the initial burst release of EVs can be reduced by increasing the concentration of crosslinker during gelation. Further, the data show that MSC EV bioactivity in an endothelial gap closure assay is retained after the 3D printing and photocrosslinking processes. Our group previously showed that MSC EV bioactivity in this assay correlates with pro-angiogenic bioactivity in vivo, thus these results indicate therapeutic potential of MSC EV-laden GelMA bioinks.

We read with interest the recent article titled "Resistance training and its impact on psychological health in participants of corporate wellness programs" by Serra, et al. [1] .We would firstly like to thank the authors for their continued work on frequency of resistance training programs, and notably, in that of a corporate wellness program. This is something that appears to have profound positive influence on general health. However, our examination of the article has produced some questions, and whilst the word constraints of the publication possibly limited the authors, we felt that raising these questions in a public forum allows the authors to elaborate on some specific details in a published response, should they see fit.Firstly, we wanted to ask regarding the significant increases in the general health questionnaire (GHQ) scores for the control group. The data suggests that GHQ scores are not increased to any greater degree for persons engageing in 12-weeks of resistance exercise (RE; pre = 16.5, post = 11.3; p<0.001) compared to participants of a non-exercising control group (CON; pre = 14.0, post = 9.4; p=0.018). The authors report small differences in effect size (ES) in favour of the RE groups; RE = -0.96 vs. CON =-0.74, without statistically significant between-group differences (p=0.727). However, we felt little attention is given to this in the manuscript. The authors state that"a possible justification could be that the possibility of participating in the study voluntarily motivated these individuals to practice physical exercise due to a common work environment" continuing "in this context, the psychological condition of the control group could have been affected by the interaction with their colleagues who trained at the corporate gym." This is certainly an interesting comment -that they spontaneously decided to begin RE because they knew their peers were engaged in a RE program. However, if participants might have engaged in RE or were impacted in any way by the activities of the intervention group, or the occurrence of the study then at a simple scientific level this ceases to be a true control group as they were not unaffected by the training intervention.Secondly, we would like to ask how the corporate wellness program was implemented. There are no details provided within the publication and we believe that this might be impactful to the outcomes. For example, if employees were provided time from their working day as a 'break' to engage in the RE then was a break of equal duration provided for all the other RE groups to match frequency (e.g. did the group only training 2x per week also receive 2 breaks from their work, and did the control group receive 4 such breaks from work to frequency-match the intervention groups, etc.)? If this is the case then having 4 additional breaks from work in the week might be sufficient to improve GHQ scores as the control group did in the present study. However, if the requirement was to participate in RE in a company environment outside of normal office ho...