2 research outputs found
Strong Adhesion and Friction Coupling in Hierarchical Carbon Nanotube Arrays for Dry Adhesive Applications
The adhesion and friction coupling of hierarchical carbon
nanotube
arrays was investigated with a hierarchical multiscale modeling approach.
At device level, vertically aligned carbon nanotube (VA-CNT) arrays
with laterally distributed segments on top were analyzed via finite
element methods to determine the macroscopic adhesion and friction
force coupling. At the nanoscale, molecular dynamics simulation was
performed to explore the origin of the adhesion enhancement due to
the existence of the laterally distributed CNTs. The results show
interfacial adhesion force is drastically promoted by interfacial
friction force when a single lateral CNT is being peeled from an amorphous
carbon substrate. By fitting with experiments, we find that under
shearing loadings the maximum interfacial adhesion force is increased
by a factor of ∼5, compared to that under normal loadings.
Pre-existing surface asperities of the substrate have proven to be
the source of generating large interfacial friction, which in turn
results in an enhanced adhesion. The critical peeling angles derived
from the continuum and nano- levels are comparable to those of geckos
and other synthetic adhesives. Our analysis indicates that the adhesion
enhancement factor of the hierarchically structured VA-CNT arrays
could be further increased by uniformly orienting the laterally distributed
CNTs on top. Most importantly, a significant buckling of the lateral
CNT at peeling front is captured on the molecular level, which provides
a basis for the fundamental understanding of local deformation, and
failure mechanisms of nanofibrillar structures. This work gives an
insight into the durability issues that prevent the success of artificial
dry adhesives
Natural Particulates Inspired Specific-Targeted Codelivery of siRNA and Paclitaxel for Collaborative Antitumor Therapy
The
effective combination of drugs promoting antiangiogenesis and
apoptosis effects has proven to be a promising collaborative tumor
antidote; and the codelivery of small interfering RNA (siRNA) and
chemotherapy agents within one efficient vehicle has gained more attention
over single regimen administration. Herein, vascular endothelial growth
factor specific siRNA (siVEGF) and paclitaxel (PTX) were introduced
as therapeutic companions and coencapsulated into naturally mimic
high-density lipoproteins (rHDL/siVEGF-PTX), so that various mechanisms
of treatment can occur simultaneously. The terminal nanoparticles
share capacity of specific-targeting to tumor cells overexpressed
scavenger receptor class B type I (SR-BI) and deliver siVEGF and PTX
into cytoplasm by a nonendocytosis mechanism. By exchanging HDL core
lipids with hydrophobic therapeutics, rHDL/siVEGF-PTX possessed particle
size of ∼160 nm, surface potential of ∼−20 mV,
and desirable long-term storage stability. <i>In vitro</i> results confirmed that the parallel activity of siVEGF and PTX displayed
enhanced anticancer efficacy. The half-maximal inhibitory concentration
(IC<sub>50</sub>) of rHDL/siVEGF-PTX toward human breast cancer MCF-7
cell is 0.26 μg/mL (PTX concentration), which presents a 14.96-fold
increase in cytotoxicity by taking Taxol as comparison. Moreover, <i>in vivo</i> results further demonstrated that rHDL/siVEGF-PTX
performed enhanced tumor growth inhibition via natural targeting pathway,
accompanied by remarkable inhibition of neovascularization <i>in situ</i> caused by siVEGF silencing in down-regulation of
VEGF proteins. On the premise of effective drug codelivery, rHDL/siVEGF-PTX
demonstrated high tumor targeting for collaborative antitumor efficacy
without side effects after systemic administration, and this bioinspired
strategy could open an avenue for exploration of combined anticancer
therapy