Although
the microfabrication techniques for microwells enabled
to guide physiologically relevant three-dimensional cell spheroid
formation, there have been substantial interests to more closely mimic
nano/microtopographies of in vivo cellular microenvironment.
Here, we developed a versatile fabrication process for nanofibrous
concave microwells (NCMs) with a controllable size and shape. The
key to the fabrication process was the use of an array of hemispherical
convex electrolyte solution drops as the grounded collector for electrospinning,
which greatly improved the degree of freedom of the size, shape, and
curvature of an NCM. A polymer substrate with through-holes was prepared
for the electrolyte solution to come out through the hole and to naturally
form a convex shape because of surface tension. Subsequent electrolyte-assisted
electrospinning process enabled to achieve various arrays of NCMs
of triangular, rectangular, and circular shapes with sizes ranging
from 1000 μm down to 250 μm. As one example of biomedical
applications, the formation of human hepatoma cell line (HepG2) spheroids
was demonstrated on the NCMs. The results indicated that the NCM enabled
uniform, size-controllable spheroid formation of HepG2 cells, resulting
in 1.5 times higher secretion of albumin from HepG2 cells on the NCM
on day 14 compared with those on a nanofibrous flat microwell as a
control.
The endothelialization on the poly (ε-caprolactone) nanofiber has been limited due to its low hydrophilicity. The aim of this study was to immobilize collagen on an ultra-thin poly (ε-caprolactone) nanofiber membrane without altering the nanofiber structure and maintaining the endothelial cell homeostasis on it. We immobilized collagen on the poly (ε-caprolactone) nanofiber using hydrolysis by NaOH treatment and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/sulfo- N-hydroxysulfosuccinimide reaction as a cost-effective and stable approach. NaOH was first applied to render the poly (ε-caprolactone) nanofiber hydrophilic. Subsequently, collagen was immobilized on the surface of the poly (ε-caprolactone) nanofibers using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/sulfo- N-hydroxysulfosuccinimide. Scanning electron microscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, and fluorescence microscopy were used to verify stable collagen immobilization on the surface of the poly (ε-caprolactone) nanofibers and the maintenance of the original structure of poly (ε-caprolactone) nanofibers. Furthermore, human endothelial cells were cultured on the collagen-immobilized poly (ε-caprolactone) nanofiber membrane and expressed tight junction proteins with the increase in transendothelial electrical resistance, which demonstrated the maintenance of the endothelial cell homeostasis on the collagen-immobilized-poly (ε-caprolactone) nanofiber membrane. Thus, we expected that this process would be promising for maintaining cell homeostasis on the ultra-thin poly (ε-caprolactone) nanofiber scaffolds.
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