Preconditioning of Acellular Vascular Regeneration Templates by Neutrophils: Regulation and Potential Consequences

Immediately upon implantation of any vascular graft, blood proteins absorb on the graft structural surfaces. This protein-coated graft structure then invokes a response by the innate immune system. Neutrophils are the... [ view full abstract ]

Immediately upon implantation of any vascular graft, blood proteins absorb on the graft structural surfaces. This protein-coated graft structure then invokes a response by the innate immune system. Neutrophils are the sentinels of the innate immune system and their adaptability to microenvironmental cues and ability to synthesize and release an array of factors (cytokines and metalloproteinases (MMPs)) with multifaceted physiological effects including angiogenesis and regeneration have been demonstrated (i.e. tumor biology). However, no studies have been conducted regarding regeneration template modulation of the initially interacting human neutrophils. Hypothesis: Electrospun template architecture and composition can be engineered to modulate interacting neutrophil phenotype (inflammatory, N1 vs. angiogenic/regenerative, N2) and degree of NETosis (neutrophil form of death which results in the extrusion of chromatin nanofibers). This study examined the human peripheral blood neutrophil functional response and degree of NETosis upon interacting with electrospun templates of defined architectures (large and small fiber diameter/pore (LD and SD)) and composition (polydioxanone (PDO) and collagen at 100:0, 90:10, and 0:100 PDO:collagen ratios). The results indicate that the LD templates regulate a N2 functional phenotype (i.e. increased MMP-9 secretion) and significantly less NETosis (in vitro and in vivo). Additionally, the SD templates support a N1 functional phenotype and significantly more NETosis. In conclusion, this is the first data to indicate that human neutrophil phenotype, functionality, and NETosis can be regulated by template design and more importantly can be engineered to direct/enhance in situ, neutrophil-guided template regeneration (i.e. transmural angiogenesis and regeneration needed for clinical success).