## 1 Introduction  
Platelet rich plasma (PRP) is an autologous biological matrix containing growth factors and proteins that are important for the wound healing cascade and tissue regeneration [1; 2; 3; 4; 5; 6]. Clinical workflows leveraging PRP for wound healing use either the topical path or the injectable path. Both workflows entail drawing whole blood from the patient and separating the PRP, typically using a commercially available kit. The topical path involves activation with a mix of thrombin and calcium chloride. While bovine thrombin (BT) is most commonly utilized in the clinic, other alternatives exist, such as recombinant thrombin, human thrombin from donor plasma, and autologous thrombin. Thrombin triggers growth factor release and clotting. Injectable treatments typically use non-activated PRP. To date, clinical exploration using PRP includes diabetic foot ulcers [3], cardiac surgery [4], orthopedics and sports medicine [7], and, increasingly, cosmetic applications [8; 9; 10; 11; 12]. For diabetic foot ulcers, activated and clotted PRP (\"platelet gel\") is typically applied on the wound, while most orthopedic, sports medicine, and cosmetic applicationsuse injectable, non-activated PRP. It is hypothesized that in injectable workflows, platelets are activated by the collagen at the site of the injury. Various challenges with bovine thrombin activation [13; 14; 15; 16; 17], including lack of standardization, expense, potential side effects, and workflow complexity, have motivated exploration into alternative ex vivo platelet activation methods. Pulsed electric fields (PEFs), which have been applied for multiple applications in cancer treatment [18] and microorganism inactivation [19], have also been proposed for platelet activation [18] with promising results [19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32]. PEFs can facilitate growth factor release from PRP with or without clotting [25; 28; 29; 32]--a unique capability that cannot be matched by thrombin. Another exciting discovery has been the ability to tune the level of growth factor release [28; 29; 32; 33] and the mechanical properties of the clot when clotting with growth factor release was desired [28]. PEFs also provide the capability to tune the serotonin release from platelet dense granules [32] and induce differential growth factor release during PEF activation [28]. PEFs facilitate physiological activation of platelets and not just mechanical fragmentation of platelets [28]. Since there is no current standardization for bovine thrombin activation, an instrument-based PEF platelet activator [22; 23; 24; 27] would provide the first standardized PRP activation method, which could facilitate clinical protocols for the numerous topical and injectable applications described above. PEF platelet activation was successfully tested for in vitro cell proliferation assays [23; 24; 26] and in animal wound healing studies [34; 35; 36]. It should be mentioned that electrical ex-vivo activation of platelets is currently explored not only for wound healing and tissue regeneration, but also for cell culture [37]. Most previous work in PEF platelet activation used Harvest PRP [21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 32] or whole blood [31], which was tested since some clinicians have started to inject whole blood instead of non-activated PRP to achieve comparable clinical benefits [38; 39; 40; 41]. Since there are many PRP separation devices available commercially, it is of great interest to test the activation of other types of biological matrices besides the Harvest PRP or whole blood. In this paper, we report the first experimental demonstration of PEF activation of three different types of PRP, separated from the whole blood of four human donors by three commercial kits (Harvest, Eclipse and EmCyte). Some of the most interesting clinical application of platelets use injectable non-activated PRP for orthopedic or cosmetic applications.