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Objective: Nanofiber scaffolds with amino groups conjugated to fiber surface through different spacers (ethylene, butylenes, and hexylene groups, respectively) were prepared and the effect of spacer length on adhesion and expansion of umbilical cord blood hematopoietic stem/ progenitor cells (HSPCs) was investigated., Materials and Methods: Electrospun polymer nanofiber scaffolds were functionalized with poly(acrylic acid) grafting, followed by conjugation of amino groups with different spacers. HSPCs were expanded on aminated scaffolds for 10 days. Cell proliferation, surface marker expression, clonogenic potential, and nonobese diabetic (NOD)/severe combined immunodeficient (SCID) repopulation potential of the expanded cells were evaluated following expansion culture., Results: Aminated nanofiber scaffolds with ethylene and butylene spacers showed high-expansion efficiencies (773- and 805-fold expansion of total cells, 200- and 235-fold expansion of CD34+CD45' cells, respectively). HSPC proliferation on aminated scaffold with hexylene spacer was significantly lower (210-fold expansion of total cells and 86-fold expansion of CD34+CD45+ cells), but maintained the highest CD34+CD45+ cell fraction (41.1%). Colony-forming unit granulocyte-erythrocyte-monocyte-megakaryocyte and long-term culture-initiating cell maintenance was similar for HSPCs expanded on all three aminated nanofiber scaffolds; nevertheless, the NOD/SCID mice engraftment potential of HSPCs expanded on aminoethyl and aminobutyl conjugated nanofibers was significantly higher than that on aminohexyl conjugated nanofibers., Conclusion: This study demonstrated that aminated nanofibers are superior substrates for ex vivo HSPC expansion, which was correlated with the enhanced HSPC adhesion to these aminated nanofibers. The spacer, through which amino groups were conjugated to nanofiber surface, affected the expansion outcome. Our results highlighted the importance of scaffold topography and cell-substrate interaction to regulating HSPC proliferation and self-renewal in cytokine-supplemented expansion.

Interaction between hematopoietic stem/progenitor cells (HSPCs) and their extra cellular matrix components is an integral part of the signaling control for HSPC survival, proliferation and differentiation. We hypothesized that both substrate topographical cues and biochemical cues could act synergistically with cytokine supplementation to improve ex vivo expansion of HSPCs. In this study, we compared the ex vivo expansion of human umbilical cord blood CD34(+) cells on unmodified, hydroxylated, carboxylated and aminated nanofibers and films. Results from 10-day expansion cultures showed that aminated nanofiber mesh and film were most efficient in supporting the expansion of the CD34(+)CD45(+) cells (195-fold and 178-fold, respectively), as compared to tissue culture polystyrene (50-fold, p<0.05). In particular, aminated nanofiber meshes supported a higher degree of cell adhesion and percentage of HSPCs, as compared to aminated films. SEM imaging revealed the discrete colonies of cells proliferating and interacting with the aminated nanofibers. This study highlights the potential of a biomaterials approach to influence the proliferation and differentiation of HSPCs ex vivo.