Nanofiber scaffolds influence organelle structure and function in bone marrow stromal cells.

Recent work demonstrates that osteoprogenitor cell culture on nanofiber scaffolds can promote differentiation. This response may be driven by changes in cell morphology caused by the three-dimensional (3D) structure of nanofibers. We hypothesized that nanofiber effects on cell behavior may be mediated by changes in organelle structure and function. To test this hypothesis, human bone marrow stromal cells (hBMSCs) were cultured on poly(ε-caprolactone) (PCL) nanofibers scaffolds and on PCL flat spuncoat films. After 1 day-culture, hBMSCs were stained for actin, nucleus, mitochondria, and peroxisomes, and then imaged using 3D confocal microscopy. Imaging revealed that the hBMSC cell body (actin) and peroxisomal volume were reduced during culture on nanofibers. In addition, the nucleus and peroxisomes occupied a larger fraction of cell volume during culture on nanofibers than on films, suggesting enhancement of the nuclear and peroxisomal functional capacity. Organelles adopted morphologies with greater 3D-character on nanofibers, where the Z-Depth (a measure of cell thickness) was increased. Comparisons of organelle positions indicated that the nucleus, mitochondria, and peroxisomes were closer to the cell center (actin) for nanofibers, suggesting that nanofiber culture induced active organelle positioning. The smaller cell volume and more centralized organelle positioning would reduce the energy cost of inter-organelle vesicular transport during culture on nanofibers. Finally, hBMSC bioassay measurements (DNA, peroxidase, bioreductive potential, lactate, and adenosine triphosphate (ATP)) indicated that peroxidase activity may be enhanced during nanofiber culture. These results demonstrate that culture of hBMSCs on nanofibers caused changes in organelle structure and positioning, which may affect organelle functional capacity and transport. Published 2016. This article is a U.S. Government work and is in the public domain in the USA. J Biomed Mater Res Part B: Appl Biomater, 2016. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 989-1001, 2017.

The support of bone marrow stromal cell differentiation by airbrushed nanofiber scaffolds.

Nanofiber scaffolds are effective for tissue engineering since they emulate the fibrous nanostructure of native extracellular matrix (ECM). Although electrospinning has been the most common approach for fabricating nanofiber scaffolds, airbrushing approaches have also been advanced for making nanofibers. For airbrushing, compressed gas is used to blow polymer solution through a small nozzle which shears the polymer solution into fibers. Our goals were 1) to assess the versatility of airbrushing, 2) to compare the properties of airbrushed and electrospun nanofiber scaffolds and 3) to test the ability of airbrushed nanofibers to support stem cell differentiation. The results demonstrated that airbrushing could produce nanofibers from a wide range of polymers and onto a wide range of targets. Airbrushing was safer, 10-fold faster, 100-fold less expensive to set-up and able to deposit nanofibers onto a broader range of targets than electrospinning. Airbrushing yielded nanofibers that formed loosely packed bundles of aligned nanofibers, while electrospinning produced un-aligned, single nanofibers that were tightly packed and highly entangled. Airbrushed nanofiber mats had larger pores, higher porosity and lower modulus than electrospun mats, results that were likely caused by the differences in morphology (nanofiber packing and entanglement). Airbrushed nanofiber scaffolds fabricated from 4 different polymers were each able to support osteogenic differentiation of primary human bone marrow stromal cells (hBMSCs). Finally, the differences in airbrushed versus electrospun nanofiber morphology caused differences in hBMSC shape where cells had a smaller spread area and a smaller volume on airbrushed nanofiber scaffolds. These results highlight the advantages and disadvantages of airbrushing versus electrospinning nanofiber scaffolds and demonstrate that airbrushed nanofiber scaffolds can support stem cell differentiation.