Please read the paper carefully. They compared plasma without platelets (PPP, platelet poor plasma) combined with their crafted liposomes to platelet rich plasm

Please read the paper carefully. They compared plasma without platelets (PPP, platelet poor plasma) combined with their crafted liposomes to platelet rich plasma (PRP). Therefore some donored plasma was needed, to have only a difference in the platelet concentraton. Their artificialy synthesized liposomes could then replace the platelets in the study.