15 research outputs found
Hydrophobic Modification on Surface of Chitin Sponges for Highly Effective Separation of Oil
A highly hydrophobic and oleophilic
chitin sponge was synthesized, for the first time, via a freeze-dried
method and then by using a thermal chemical vapor deposition of methyltrichlorosilane
(MTCS) at different relative humidity. Fourier-transform infrared,
energy-dispersive X-ray spectra, and scanning electron microscopy
confirmed that the silanization occurred on the pore wall surface
of the chitin sponge. The MTCS-coated chitin sponge had interconnected
open-cell structures with the average pore size from 20 to 50 ÎŒm,
and the MTCS nanofilaments immobilized on the chitin matrix, leading
to the high hydrophobicity, as a result of the existence of a solid/air
composite rough surface. Cyclic compression test indicated that the
hydrophobic chitin sponges exhibited excellent elasticity and high
mechanical durability. The sponges could efficiently collect organics
both on the surface and bottom from the water with the highest 58
times of their own weight absorption capacities through the combination
of the particular wettability and great porosity. Furthermore, the
biodegradation kinetics of the chitin sponge forecasted that the chitin
could be completely biodegraded within 32 days by the microorganisms
in the soil. This work provided a new pathway to prepare the chitin-based
materials for highly effective removal of oil from water, showing
potential application in the pollutant remediation field
Chitinous Bioplastic Enabled by Noncovalent Assembly
Natural polymeric-based bioplastics usually lack good
mechanical
or processing performance. It is still challenging to achieve simultaneous
improvement for these two usual trade-off features. Here, we demonstrate
a full noncovalent mediated self-assembly design for simultaneously
improving the chitinous bioplastic processing and mechanical properties
via plane hot-pressing. Tannic acid (TA) is chosen as the noncovalent
mediator to (i) increase the noncovalent cross-link intensity for
obtaining the tough noncovalent network and (ii) afford the dynamic
noncovalent cross-links to enable the mobility of chitin molecular
chains for benefiting chitinous bioplastic nanostructure rearrangement
during the shaping procedure. The multiple noncovalent mediated network
(chitinâTA and chitinâchitin cross-links) and the pressure-induced
orientation nanofibers structure endow the chitinous bioplastics with
robust mechanical properties. The relatively weak chitinâTA
noncovalent interactions serve as water mediation switches to enhance
the molecular mobility for endowing the chitin/TA bioplastic with
hydroplastic processing properties, rendering them readily programmable
into versatile 2D/3D shapes. Moreover, the fully natural resourced
chitinous bioplastic exhibits superior weld, solvent resistance, and
biodegradability, enabling the potential for diverse applications.
The full physical cross-linking mechanism highlights an effective
design concept for balancing the trade-off of the mechanical properties
and processability for the polymeric materials
Biodegradable Theranostic Plasmonic Vesicles of Amphiphilic Gold Nanorods
We have developed surface-initiated organocatalytic ring-opening polymerization on functional nanocrystals and synthesized amphiphilic gold nanorods carrying well-defined mixed polymer brushes of poly(ethylene glycol) and polylactide. Self-assembly of the amphiphilic gold nanorods affords biodegradable plasmonic vesicles that can be destructed by both enzymatic degradation and near-infrared photothermal heating. When tagged with Raman probes, strongly coupled gold nanorods in the self-assembled vesicles give rise to highly active SERS signals. The biodegradable plasmonic vesicles exhibit a unique combination of optical and structural properties that are of particular interest for theranostic applications. We have demonstrated that bioconjugated SERS-active plasmonic vesicles can specifically target EpCAM-positive cancer cells, leading to ultrasensitive spectroscopic detection of cancer cells. Furthermore, integration of photothermal effect of gold nanorods and large loading capacity of the vesicles provides opportunities for localized synergistic photothermal ablation and photoactivated chemotherapy, which have shown higher efficiency in killing targeted cancer cells than either single therapeutic modality. The versatile chemistry of organocatalytic ring-opening polymerization, in conjugation with recent development in synthesizing functional nanocrystals with tailored optical, electronic, and magnetic properties opens the possibilities for constructing multifunctional biodegradable platforms for clinical translation
Hair-Inspired Crystal Growth of HOA in Cavities of Cellulose Matrix via HydrophobicâHydrophilic Interface Interaction
As one of the most ordinary phenomena
in nature, numerous pores on animal skins induce the growth of abundant
hairs. In this study, cavities of a cellulose matrix were used as
hard templates to lead the hair-inspired crystal growth of 12-hydroxyoctadecanoic
acid (HOA) through hydrophobicâhydrophilic interface interaction,
and short hair-like HOA crystals with a smooth surface were formed
on cellulose films. In our findings, by using solvent evaporation
induced crystallization, hydrophobic HOA grew along the hydrophilic
cellulose pore wall to form regular vertical worm-like and pillar-like
crystals with an average diameter of about 200 nm, depending on the
experimental conditions and HOA concentration. The formation mechanism
of the short hair-like HOA crystals as well as the structure and properties
of the cellulose/HOA submicrometer composite films were studied. The
pores of the cellulose matrix supplied not only cavities for the HOA
crystals fixation but also hydrophilic shells to favor the vertical
growth of the relatively hydrophobic HOA crystals. The cellulose/HOA
submicrometer composite films exhibited high hydrophobicity, as a
result of the formation of the solid/air composite surface. Furthermore,
4-(1,2,2-triphenylethenyl) benzoic acid, an aggregation-induced emission
luminogen, was used to aggregate on the cellulose surface with HOA
to emit and monitor the HOA crystal growth, showing bifunctional photoluminscence
and self-cleaning properties. This work opens up a novel one-step
pathway to design bio-inspired submicrometer materials by utilizing
natural products, showing potential applications in self-cleaning
optical devices
Intermolecular Interaction and the Extended Wormlike Chain Conformation of Chitin in NaOH/Urea Aqueous Solution
The
intra- and intermolecular interactions of chitin in NaOH/urea
aqueous system were studied by a combination of NMR measurements (including <sup>13</sup>C NMR, <sup>23</sup>Na NMR, and <sup>15</sup>N NMR) and differential
scanning calorimetry. The results revealed that the NaOH and chitin
formed a hydrogen-bonded complex that was surrounded by the urea hydrates
to form a sheath-like structure, leading to the good dissolution.
The optimal concentration range, in which chitin was molecularly dispersed
in NaOH/urea aqueous, was found to investigate the chain conformation
in the dilute solution with a combination of static and dynamic light
scattering. The weight-average molecular weight (<i>M</i><sub>w</sub>), radii of gyration (âš<i>R</i><sub>g</sub>â©<sub><i>z</i></sub>), and hydrodynamic radii
(âš<i>R</i><sub>h</sub>â©<sub><i>z</i></sub>) values of chitin were determined, and the structure-sensitive
parameter (Ï) and persistent length (<i>L</i><sub>p</sub>) were calculated to be >2.0 and âŒ30 nm, respectively,
suggesting an extended wormlike chain conformation. The visualized
images from TEM, cryo-TEM, and AFM indicated that, chitin nanofibers
were fabricated from the parallel aggregation of chitin chains in
NaOH/urea system. This work would provide a theoretical guidance for
constructing novel chitin-based nanomaterials via âbottom-upâ
method at the molecular level
Hair-Inspired Crystal Growth of HOA in Cavities of Cellulose Matrix via HydrophobicâHydrophilic Interface Interaction
As one of the most ordinary phenomena
in nature, numerous pores on animal skins induce the growth of abundant
hairs. In this study, cavities of a cellulose matrix were used as
hard templates to lead the hair-inspired crystal growth of 12-hydroxyoctadecanoic
acid (HOA) through hydrophobicâhydrophilic interface interaction,
and short hair-like HOA crystals with a smooth surface were formed
on cellulose films. In our findings, by using solvent evaporation
induced crystallization, hydrophobic HOA grew along the hydrophilic
cellulose pore wall to form regular vertical worm-like and pillar-like
crystals with an average diameter of about 200 nm, depending on the
experimental conditions and HOA concentration. The formation mechanism
of the short hair-like HOA crystals as well as the structure and properties
of the cellulose/HOA submicrometer composite films were studied. The
pores of the cellulose matrix supplied not only cavities for the HOA
crystals fixation but also hydrophilic shells to favor the vertical
growth of the relatively hydrophobic HOA crystals. The cellulose/HOA
submicrometer composite films exhibited high hydrophobicity, as a
result of the formation of the solid/air composite surface. Furthermore,
4-(1,2,2-triphenylethenyl) benzoic acid, an aggregation-induced emission
luminogen, was used to aggregate on the cellulose surface with HOA
to emit and monitor the HOA crystal growth, showing bifunctional photoluminscence
and self-cleaning properties. This work opens up a novel one-step
pathway to design bio-inspired submicrometer materials by utilizing
natural products, showing potential applications in self-cleaning
optical devices
SERS-Encoded Nanogapped Plasmonic Nanoparticles: Growth of Metallic Nanoshell by Templating Redox-Active Polymer Brushes
We
report a new strategy to synthesize coreâshell metal
nanoparticles with an interior, Raman tag-encoded nanogap by taking
advantage of nanoparticle-templated self-assembly of amphiphilic block
copolymers and localized metal precursor reduction by redox-active
polymer brushes. Of particular interest for surface-enhanced Raman
scattering (SERS) is that the nanogap size can be tailored flexibly,
with the sub-2 nm nanogap leading to the highest SERS enhancement.
Our results have further demonstrated that surface functionalization
of the nanogapped Au nanoparticles with aptamer targeting ligands
allows for specific recognition and ultrasensitive detection of cancer
cells. The general applicability of this new synthetic strategy, coupled
with recent advances in controlled wet-chemical synthesis of functional
nanocrystals, opens new avenues to multifunctional coreâshell
nanoparticles with integrated optical, electronic, and magnetic properties
Construction of Chitin/PVA Composite Hydrogels with Jellyfish Gel-Like Structure and Their Biocompatibility
High
strength chitin/polyÂ(vinyl alcohol) (PVA) composite hydrogels
(RCP) were constructed by adding PVA into chitin dissolved in a NaOH/urea
aqueous solution, and then by cross-linking with epichlorohydrin (ECH)
and freezingâthawing process. The RCP hydrogels were characterized
by field emission scanning electron microscopy, FTIR, differential
scanning calorimetry, solid-state <sup>13</sup>C NMR, wide-angle X-ray
diffraction, and compressive test. The results revealed that the repeated
freezing/thawing cycles induced the bicrosslinked networks consisted
of chitin and PVA crystals in the composite gels. Interestingly, a
jellyfish gel-like structure occurred in the RCP75 gel with 25 wt
% PVA content in which the amorphous and crystalline PVA were immobilized
tightly in the chitin matrix through hydrogen bonding interaction.
The freezing/thawing cycles played an important role in the formation
of the layered porous PVA networks and the tight combining of PVA
with the pore wall of chitin. The mechanical properties of RCP75 were
much higher than the other RCP gels, and the compressive strength
was 20Ă higher than that of pure chitin gels, as a result of
broadly dispersing stress caused by the orderly multilayered networks.
Furthermore, the cell culture tests indicated that the chitin/PVA
composite hydrogels exhibited excellent biocompatibility and safety,
showing potential applications in the field of tissue engineering
Hierarchical Microspheres Constructed from Chitin Nanofibers Penetrated Hydroxyapatite Crystals for Bone Regeneration
Chitin exists abundantly
in crab and shrimp shells as the template
of the minerals, which inspired us to mineralize it for fabricating
bone grafting materials. In the present work, chitin nanofibrous microspheres
were used as the matrix for in situ synthesis of hydroxyapatite (HA)
crystals including microflakes, submicron-needles, and submicron-spheres,
which were penetrated by long chitin nanofibers, leading to the hierarchical
structure. The shape and size of the HA crystals could be controlled
by changing the HA synthesis process. The tight interface adhesion
between chitin and HA through the noncovanlent bonds occurred in the
composite microspheres, and HAs were homogeneously dispersed and bounded
to the chitin nanofibers. In our findings, the inherent biocompatibilities
of the both chitin and HA contributed the bone cell adhesion and osteoconduction.
Moreover, the chitin microsphere with submicron-needle and submicron-sphere
HA crystals remarkably promoted in vitro cell adhesion and in vivo
bone healing. It was demonstrated that rabbits with 1.5 cm radius
defect were almost cured completely within three months in a growth
factor- and cell-free state, as a result of the unique surface microstructure
and biocompatibilities of the composite microspheres. The microsphere
scaffold displayed excellent biofunctions and an appropriate biodegradability.
This work opened up a new avenue to construct natural polymer-based
organicâinorganic hybrid microspheres for bone regeneration
Micro- and Macromechanical Properties of Thermoelectric Lead Chalcogenides
Both
n- and p-type lead telluride (PbTe)-based thermoelectric (TE) materials
display high TE efficiency, but the low fracture strength may limit
their commercial applications. To find ways to improve these macroscopic
mechanical properties, we report here the ideal strength and deformation
mechanism of PbTe using density functional theory calculations. This
provides structureâproperty relationships at the atomic scale
that can be applied to estimate macroscopic mechanical properties
such as fracture toughness. Among all the shear and tensile paths
that are examined here, we find that the lowest ideal strength of
PbTe is 3.46 GPa along the (001)/âš100â© slip system.
This leads to an estimated fracture toughness of 0.28 MPa m<sup>1/2</sup> based on its ideal stressâstrain relation, which is in good
agreement with our experimental measurement of 0.59 MPa m<sup>1/2</sup>. We find that softening and breaking of the ionic PbâTe bond
leads to the structural collapse. To improve the mechanical strength
of PbTe, we suggest strengthening the structural stiffness of the
ionic PbâTe framework through an alloying strategy, such as
alloying PbTe with isotypic PbSe or PbS. This point defect strategy
has a great potential to develop high-performance PbTe-based materials
with robust mechanical properties, which may also be applied to other
materials and applications