4 research outputs found
High Strength Chitosan Hydrogels with Biocompatibility via New Avenue Based on Constructing Nanofibrous Architecture
Breaking
the limitation of traditional acid dissolving methods
for chitosan by creating an alkali/urea hydrogen-bonded chitosan complex,
a new solvent (4.5 wt % LiOH/7 wt % KOH/8 wt % urea aqueous solution)
was used to successfully dissolve chitosan via the freezing–thawing
process, for the first time. Subsequently, high strength hydrogels
with unique nanofibrous architecture were constructed from the chitosan
alkaline solution. The results from <sup>13</sup>C NMR, laser light
scattering, atomic force microscopy, transmission electron microscopy,
and scanning electron microscopy confirmed that chitosan easily aggregated
in the solution and could self-assemble in parallel to form perfect
regenerated nanofibers induced by heating. At elevated temperature
and concentration, the regenerated chitosan nanofibers could entangle
and cross-link with each other through hydrogen bonds to form hydrogels.
The novel chitosan hydrogels exhibited homogeneous architecture and
high strength as a result of the strong networks woven with the compact
nanofibers. The compression fracture stress of the chitosan hydrogels
was nearly 100 times that of the chitosan hydrogels prepared by the
traditional acid dissolving method, revealing that the nanofibrous
network microstructures contributed greatly to the reinforcement of
the hydrogels. Furthermore, the chitosan hydrogels exhibited excellent
biocompatibility and safety as well as a smart controlled drug release
behavior triggered by acid. Therefore, we opened up a completely new
avenue to construct high strength chitosan hydrogels for applications
in biomedicine
Fast Contact of Solid–Liquid Interface Created High Strength Multi-Layered Cellulose Hydrogels with Controllable Size
Novel onion-like and multi-layered
tubular cellulose hydrogels
were constructed, for the first time, from the cellulose solution
in a 7% NaOH/12% urea aqueous solvent by changing the shape of the
gel cores. In our findings, the contacting of the cellulose solution
with the surface of the agarose gel rod or sphere loaded with acetic
acid led to the close chain packing to form immediately a gel layer,
as a result of the destruction of the cellulose inclusion complex
by acid through inducing the cellulose self-aggregation. Subsequently,
multi-layered cellulose hydrogels were fabricated via a multi-step
interrupted gelation process. The size, layer thickness and inter-layer
space of the multi-layered hydrogels could be controlled by adjusting
the cellulose concentrations, the gel core diameter and the contacting
time of the solid–liquid interface. The multi-layered cellulose
hydrogels displayed good architectural stability and solvent resistance.
Moreover, the hydrogels exhibited high compressive strength and excellent
biocompatibility. L929 cells could adhere and proliferate on the surface
of the layers and in interior space, showing great potential as tissue
engineering scaffolds and cell culture carrier. This work opens up
a new avenue for the construction of the high strength multi-layered
cellulose hydrogels formed from inner to outside via a fast contact
of solid–liquid interface
High-Strength Films Consisted of Oriented Chitosan Nanofibers for Guiding Cell Growth
Chitosan
has biocompatibility and biodegradability; however, the
practical use of the bulk chitosan materials is hampered by its poor
strength, which can not satisfy the mechanical property requirement
of organs. Thus, the construction of highly strong chitosan-based
materials has attracted much attention. Herein, the high strength
nanofibrous hydrogels and films (CS-E) were fabricated from the chitosan
solution in LiOH/KOH/urea aqueous system via a mild regenerating process.
Under the mild condition (ethanol at low temperature) without the
severe fluctuation in the system, the alkaline-urea shell around the
chitosan chains was destroyed, and the naked chitosan molecules had
sufficient time for the orderly arrangement in parallel manner to
form relatively perfect nanofibers. The nanofibers physically cross-linked
to form CS-E hydrogels, which could be easily oriented by drawing
to achieve a maximum orientation index of 84%, supported by the scanning
electron microscopy and two-dimensional wide-angle X-ray diffraction.
The dried CS-E films could be bent and folded arbitrarily to various
complex patterns and shapes. The oriented CS-E films displayed even
ultrahigh tensile strength (282 MPa), which was 5.6× higher than
the chitosan films prepared by the traditional acid dissolving method.
The CS-E hydrogels possessed hierarchically porous structure, beneficial
to the cell adhesion, transportation of nutrients, and removal of
metabolic byproducts. The cell assay results demonstrated that the
CS-E hydrogels were no cytotoxicity, and osteoblastic cells could
adhere, spread, and proliferate well on their surface. Furthermore,
the oriented CS-E hydrogels could regulate the directional growth
of osteoblastic cells along the orientation direction, on the basis
of the filopodia of the cells to extend and adhere on the nanofibers.
This work provided a novel approach to construct the oriented high
strength chitosan hydrogels and films
Robust and Low-Cost Flame-Treated Wood for High-Performance Solar Steam Generation
Solar-enabled
steam generation has attracted increasing interest
in recent years because of its potential applications in power generation,
desalination, and wastewater treatment, among others. Recent studies
have reported many strategies for promoting the efficiency of steam
generation by employing absorbers based on carbon materials or plasmonic
metal nanoparticles with well-defined pores. In this work, we report
that natural wood can be utilized as an ideal solar absorber after
a simple flame treatment. With ultrahigh solar absorbance (∼99%),
low thermal conductivity (0.33 W m<sup>–1</sup> K<sup>–1</sup>), and good hydrophilicity, the flame-treated wood can localize the
solar heating at the evaporation surface and enable a solar-thermal
efficiency of ∼72% under a solar intensity of 1 kW m<sup>–2</sup>, and it thus represents a renewable, scalable, low-cost, and robust
material for solar steam applications