Nerve regeneration after injury is a critical medical issue. In previous work, we have developed an oligo(poly(ethylene glycol) fumarate) (OPF) hydrogel incorporated with positive charges as a promising nerve conduit. In this study, we introduced cross-linkable bonds to graphene oxide and carbon nanotube to obtain the functionalized graphene oxide acrylate (GOa) and carbon nanotube poly(ethylene glycol) acrylate (CNTpega). An electrically conductive hydrogel was then fabricated by covalently embedding GOa and CNTpega within OPF hydrogel through chemical cross-linking followed by in situ reduction of GOa in l-ascorbic acid solution. Positive charges were incorporated by 2-(methacryloyloxy)ethyltrimethylammonium chloride (MTAC) to obtain rGOaCNTpega-OPF-MTAC composite hydrogel with both surface charge and electrical conductivity. The distribution of CNTpega and GOa in the hydrogels was substantiated by transmission electron microscopy (TEM), and strengthened electrical conductivities were determined. Excellent biocompatibility was demonstrated for the carbon embedded composite hydrogels. Biological evaluation showed enhanced proliferation and spreading of PC12 cells on the conductive hydrogels. After induced differentiation using nerve growth factor (NGF), cells on the conductive hydrogels were effectively stimulated to have robust neurite development as observed by confocal microscope. A synergistic effect of electrical conductivity and positive charges on nerve cells was also observed in this study. Using a glass mold method, the composite hydrogel was successfully fabricated into conductive nerve conduits with surficial positive charges. These results suggest that rGOa-CNTpega-OPF-MTAC composite hydrogel holds great potential as conduits for neural tissue engineering.
Two-dimensional (2D) materials have
emerged as a new promising
research topic for tissue engineering because of their ability to
alter the surface properties of tissue scaffolds and thus improve
their biocompatibility and cell affinity. Multiple 2D materials, such
as graphene and graphene oxide (GO), have been widely reported to
enhance cell adhesion and proliferation. Recently, a newly emerged
black phosphorus (BP) 2D material has attracted attention in biomedical
applications because of its unique mechanical and electrochemical
characteristics. In this study, we investigated the synergistic effect
of these two types of 2D materials on cell osteogenesis for bone tissue
engineering. BP was first wrapped in negatively charged GO nanosheets,
which were then adsorbed together onto positively charged poly(propylene
fumarate) three-dimensional (3D) scaffolds. The increased surface
area provided by GO nanosheets would enhance cell attachment at the
initial stage. In addition, slow oxidation of BP nanosheets wrapped
within GO layers would generate a continuous release of phosphate,
an important osteoblast differentiation facilitator designed to stimulate
cell osteogenesis toward the new bone formation. Through the use of
3D confocal imaging, unique interactions between cells and BP nanosheets
were observed, including a stretched cell shape and the development
of filaments around the BP nanosheets, along with increased cell proliferation
when compared with scaffolds incorporating only one of the 2D materials.
Furthermore, the biomineralization of 3D scaffolds, as well as cellular
osteogenic markers, was all measured and improved on scaffolds with
both BP and GO nanosheets. All these results indicate that the incorporation
of 2D BP and GO materials could effectively and synergistically stimulate
cell proliferation and osteogenesis on 3D tissue scaffolds.
Chemically crosslinking GOa and CNTpega followed by in situ reduction fabricated a conductive rGOa–CNTpega–OPF hydrogel that strongly stimulated neurite growth.
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