## 4 Discussion
To the best of our knowledge, no published study compares the three types of PRP considered here in a multi-donor study, even for the state-of-the-art BT activation. Our PRP composition data and BT activation results here for Harvest, EmCyte and Eclipse are not associated with potential clinical efficacy since our study did not involve therapeutic applications and comparisons. Interestingly, Harvest and EmCyte PRPs under PEF stimulation exhibited a narrower range between the minimum and maximum concentrations of PDGF and VEGF for all donors compared to BT release, indicating a smaller donor to donor variability in terms of growth factor release. This narrower range of growth factor release may favor reproducibility of clinical outcomes for PEF-activated PRP compared to BT-activated PRP. Growth factor release is more modest for the Eclipse PRP with BT and PEF; platelet concentration is also lower for Eclipse compared to Harvest and EmCyte. Generally, EGF increased more strongly with donor platelet concentration under PEF activation than with BT activation, VEGF had a weak correlation with donor platelet concentration under both PEF and BT activation, and PDGF had a slightly higher positive correlation for BT activation than PEF activation. Comparing the correlation matrices for PEF A and BT in Table 2 shows that selecting activation methods (i.e., PEF A or BT) or concentration (i.e., Harvest or EmCyte) can tune the correlations between the growth factors. For instance, all four cases reported in Table 2 exhibited positive correlation between PDGF and EGF. Interestingly, only EmCyte and PEF A has a weak negative correlation between VEGF and PDGF, while the other three combinations exhibited strong negative correlations. Similarly, the EmCyte with either PEF A and BT had weak correlation between VEGF and EGF, while the Harvest PRP with both PEF A and BT had strong negative correlations. Even then, the correlation between VEGF and EGF was much stronger for BT (\(r=-0.99\)) than for PEF A (\(r=-0.40\)). Thus, the relationships between certain growth factors after activation can depend strongly on both the platelet concentration and activation methods. While more data is necessary to make a complete assessment based on statistics, these results motivate future work to acquire more data to better assess the statistical significance of this data. Moreover, the overall significance of platelet concentration, or an \"optimum\" platelet concentration, for achieving desirable clinical outcomes for specific applications remains a topic of active research [42]. This proof-of-concept study using biomaterial from four human donors demonstrates that electrical stimulation may be utilized to induce growth factor release without clotting for PRP obtained from various commercially available kits. Future work could entail refining or tailoring the PEF parameters (pulse width, pulse amplitude, number of pulses, and/or repetition rate) for each PRP system to optimize growth factor release. While no CaCl\({}_{2}\) was added prior to electrical activation, our prior studies using the Harvest PRP system [25; 32] suggest that one could experiment with PEFs and limited amounts of added CaCl\({}_{2}\)[28; 29; 32] to further explore growth factor release without clotting for PRP obtained using EmCyte, Eclipse, or other commercial systems with clinical value. While typical injectable clinical workflows utilize non-activated PRPs, PEF activation introduces the opportunity of releasing growth factors without clotting, essentially generating upgraded biological matrices with potential clinical relevance. Moreover, PEF activation facilitates the potential for standardization of activation (researchers can use the same PEF parameters),which could have significant benefits for achieving common efficacy of growth factor release for patient treatment since no activation standard for PRP currently exists. PRP is a complex biological matrix containing numerous cell types besides platelets.