Color images available online atwww.liebertonline.com/ten. The effects of PCL fiber diameter and alignment on differentiation of NPs were assessed by counting TUJ1+ cells from ten randomly selected fields of NP cultures on various types of fibrous matrices (Fig. meshes, human NPs adopt polarized cell morphology with processes extending along the axis of the fiber, whereas NPs on simple tissue culture surfaces or random fiber substrates form nonpolarized neurite networks. Under differentiation conditions, human NPs cultured on aligned fibrous substrates show a higher rate of neuronal differentiation than other matrices; 62% and 86% of NPs become TUJ1 (+) early neurons on aligned micro- and nanofibers, respectively, whereas only 32% and 27% of NPs acquire the same fate on random micro- and nanofibers. Metabolic cell activity/viability studies reveal that fiber alignment and diameter also have an effect on NP viability, but only in the presence of mitogens. Our findings demonstrate that fibrous substrates serve as an artificial extracellular matrix and provide a microenviroment that influences key aspects of the neuronal differentiation of ES-derived NPs. == Introduction == Neural stem cellspresently utilized for transplantation are derived from human embryonic stem (ES) cells that are differentiatedin vitrointo the neural lineage or from neural precursors (NPs) isolated from your fetal or the adult nervous system.13As recently demonstrated, neural stem cells can be also derived from somatic cells reprogrammed to pluripotency with combinations of transcription factors.46At this juncture, human ES cells may symbolize the best solution for transplantation therapies as they can provide a potentially unlimited source of human neural stem cells for single or repeated administrations in the nervous system.7The substantial plasticity and broad differentiation potential of human ES cells have been exhibited in severalin vitrostudies where these cells were induced to specific neuronal and glial lineages, including motor8and dopaminergic9,10neurons as well as oligodendrocytes.11 One of the ways to control the growth and differentiation of grafted neural stem cells is the use of suitable scaffolding materials serving as three-dimensional microenvironments for the cells to attach and grow and also functioning as temporary extracellular matrix (ECM). Fibrous matrices are particularly useful in neural tissue engineering as they can be designed to have high porosity, high surface-to-volume ratio, and high spatial interconnectivity,12all physical properties that can promote cellular adhesion and proliferation.13,14Fibrous substrates of desired sizes and dimensions can be easily prepared using electrospinning,1517that is usually, a convenient fabrication process to produce random or aligned fibrous matrices with fiber diameters ranging from tens of nanometers to several microns.1820The topography of electrospun nanofibers resembles that of the fibrous ECM proteins.21Various studies have shown that this alignment of micro-to-nano topography can significantly influence the morphology, proliferation rate, phenotype, and function of various cell types,2224as well as adult and ES cell types.25,26For HYRC example, when cultured on aligned microgrooves, human keratinocytes tend to elongate and their longitudinal axis is co-aligned with the grooves.27Surface-aminated electrospun nanofibers have been shown to promote the adhesion and proliferation of umbilical cord blood hematopoietic stem/progenitor cells.28These adaptations are believed to involve rearrangement of cytoskeletal constituents, a process that in turn can influence cell phenotype and function via established links with intracellular signaling pathways. Some of the above principles have been recently found to be useful in controlling neural stem cell differentiation for the purpose of neural tissue engineering. For example, aligned poly-L-lactic acid (PLLA) SB 743921 nanofibrous substrates support the adhesion of immortalized neural stem cell-like C17.2 cells and cause extensive neurite outgrowth along the longitudinal axis of nanofibers.12,29Mouse neural SB 743921 stem cells show increased rate of differentiation on nanofibers than on microfibers; and aligned electrospun fibers further promote neurite outgrowth.12,30Fiber diameter of electrospun polymer nanofiber matrix can also influence the proliferation and differentiation of neural stem cells derived from the rat hippocampus.31 In this study, SB 743921 fiber matrices of different diameter (nanofibers and microfibers) and orientation (aligned and random) were prepared by electrospinning and functionalized with ECM molecules to create an environment biocompatible with human ES cell-derived NPs. The effects of topography around the morphology, viability, and differentiation of human ES cell-derived NPs were examined. Our findings suggest that fiber diameter and orientation SB 743921 can impact the adhesion and viability of human NPs and that cells seeded on aligned fibrous substrates appear to have the best viability. Aligned fiber.