Azobenzene as a photoswitchable mechanophore.

Azobenzene has been widely explored as a photoresponsive element in materials science. Although some studies have investigated the force-induced isomerization of azobenzene, the effect of force on the rupture of azobenzene has not been explored. Here we show that the light-induced structural change of azobenzene can also alter its rupture forces, making it an ideal light-responsive mechanophore. Using single-molecule force spectroscopy and ultrasonication, we found that cis and trans para-azobenzene isomers possess contrasting mechanical properties. Dynamic force spectroscopy experiments and quantum-chemical calculations in which azobenzene regioisomers were pulled from different directions revealed that the distinct rupture forces of the two isomers are due to the pulling direction rather than the energetic difference between the two isomers. These mechanical features of azobenzene can be used to rationally control the macroscopic fracture behaviours of polymer networks by photoillumination. The use of light-induced conformational changes to alter the mechanical response of mechanophores provides an attractive way to engineer polymer networks of light-regulatable mechanical properties.

Single-Molecule Force Spectroscopy Reveals Cation-π Interactions in Aqueous Media Are Highly Affected by Cation Dehydration.

Cation-π interactions underlie many important processes in biology and materials science. However, experimental investigations of cation-π interactions in aqueous media remain challenging. Here, we studied the cation-π binding strength and mechanism by pulling two hydrophobic polymers with distinct cation binding properties, i.e., poly-pentafluorostyrene and polystyrene, in aqueous media using single-molecule force spectroscopy and nuclear magnetic resonance measurement. We found that the interaction strengths linearly depend on the cation concentrations, following the order of Li^{+}

Mechanochemical Lithography.

Surfaces with patterned biomolecules have wide applications in biochips and biomedical diagnostics. However, most patterning methods are inapplicable to physiological conditions and incapable of creating complex structures. Here, we develop a mechanochemical lithography (MCL) method based on compressive force-triggered reactions. In this method, biomolecules containing a bioaffinity ligand and a mechanoactive group are used as mechanochemical inks (MCIs). The bioaffinity ligand facilitates concentrating MCIs from surrounding solutions to a molded surface, enabling direct and continuous printing in an aqueous environment. The mechanoactive group facilitates covalent immobilization of MCIs through force-triggered reactions, thus avoiding the broadening of printed features due to the diffusion of inks. We discovered that the ubiquitously presented amino groups in biomolecules can react with maleimide through a force-triggered Michael addition. The resulting covalent linkage is mechanically and chemically stable. As a proof-of-concept, we fabricate patterned surfaces of biotin and His-tagged proteins at nanoscale spatial resolution by MCL and verify the resulting patterns by fluorescence imaging. We further demonstrated the creation of multiplex protein patterns using this technique.

Regulating the Homogeneity of Thiol-Maleimide Michael-Type Addition-Based Hydrogels Using Amino Biomolecules.

Poly(ethylene glycol) (PEG)-based synthetic hydrogels based on Michael-type addition reaction have been widely used for cell culture and tissue engineering. However, recent studies showed that these types of hydrogels were not homogenous as expected since micro domains generated due to the fast reaction kinetics. Here, we demonstrated a new kind of method to prepare homogenous poly(ethylene glycol) hydrogels based on Michael-type addition using the side chain amine-contained short peptides. By introducing such a kind of short peptides, the homogeneity of crosslinking and mechanical property of the hydrogels has been also significantly enhanced. The compressive mechanical and recovery properties of the homogeneous hydrogels prepared in the presence of side chain amine-contained short peptides were more reliable than those of inhomogeneous hydrogels while the excellent biocompatibility remained unchanged. Furthermore, the reaction rate and gelation kinetics of maleimide- and thiol-terminated PEG were proved to be significantly slowed down in the presence of the side chain amine-contained short peptides, thus leading to the improved homogeneity of the hydrogels. We anticipate that this new method can be widely applied to hydrogel preparation and modification based on Michael-type addition gelation.

Engineering hydrogels with homogeneous mechanical properties for controlling stem cell lineage specification.

The extracellular matrix (ECM) is mechanically inhomogeneous due to the presence of a wide spectrum of biomacromolecules and hierarchically assembled structures at the nanoscale. Mechanical inhomogeneity can be even more pronounced under pathological conditions due to injury, fibrogenesis, or tumorigenesis. Although considerable progress has been devoted to engineering synthetic hydrogels to mimic the ECM, the effect of the mechanical inhomogeneity of hydrogels has been widely overlooked. Here, we develop a method based on host-guest chemistry to control the homogeneity of maleimide-thiol cross-linked poly(ethylene glycol) hydrogels. We show that mechanical homogeneity plays an important role in controlling the differentiation or stemness maintenance of human embryonic stem cells. Inhomogeneous hydrogels disrupt actin assembly and lead to reduced YAP activation levels, while homogeneous hydrogels promote mechanotransduction. Thus, the method we developed to minimize the mechanical inhomogeneity of hydrogels may have broad applications in cell culture and tissue engineering.

Maleimide-thiol adducts stabilized through stretching.

Maleimide-thiol reactions are widely used to produce protein-polymer conjugates for therapeutics. However, maleimide-thiol adducts are unstable in vivo or in the presence of thiol-containing compounds because of the elimination of the thiosuccinimide linkage through a retro-Michael reaction or thiol exchange. Here, using single-molecule force spectroscopy, we show that applying an appropriate stretching force to the thiosuccinimide linkage can considerably stabilize the maleimide-thiol adducts, in effect using conventional mechanochemistry of force-accelerated bond dissociation to unconventionally stabilize an adjacent bond. Single-molecule kinetic analysis and bulk structural characterizations suggest that hydrolysis of the succinimide ring is dominant over the retro-Michael reaction through a force-dependent kinetic control mechanism, and this leads to a product that is resistant to elimination. This unconventional mechanochemical approach enabled us to produce stable polymer-protein conjugates by simply applying a mechanical force to the maleimide-thiol adducts through mild ultrasonication. Our results demonstrate the great potential of mechanical force for stimulating important productive chemical transformations.

Direct Measurement of Length Scale Dependence of the Hydrophobic Free Energy of a Single Collapsed Polymer Nanosphere.

The physics underlying hydrophobicity at macroscopic and microscopic levels is fundamentally distinct. However, experimentally quantifying the length scale dependence of hydrophobicity is challenging. Here we show that the size-dependent hydrophobic free energy of a collapsed polymer nanosphere can be continuously monitored from its single-molecule force-extension curve using a novel theoretical framework. The hydrophobic free energy shows a change from cubic to square dependence of the radius of the polymer nanosphere at a radius of ∼1 nm-this is consistent with Lum-Chandler-Weeks theory and simulations. We can also observe a large variation of the hydrophobic free energy of each polymer nanosphere implying the heterogeneity of the self-assembled structures and/or the fluctuation of the water-polymer interface. We expect that our approach can be used to address many fundamental questions about hydrophobic hydration, which are otherwise inaccessible by ensemble measurements.

Single Molecule Study of Force-Induced Rotation of Carbon-Carbon Double Bonds in Polymers.

Carbon-carbon double bonds (C═C) are ubiquitous in natural and synthetic polymers. In bulk studies, due to limited ways to control applied force, they are thought to be mechanically inert and not to contribute to the extensibility of polymers. Here, we report a single molecule force spectroscopy study on a polymer containing C═C bonds using atomic force microscope. Surprisingly, we found that it is possible to directly observe the cis-to-trans isomerization of C═C bonds at the time scale of ∼1 ms at room temperature by applying a tensile force ∼1.7 nN. The reaction proceeds through a diradical intermediate state, as confirmed by both a free radical quenching experiment and quantum chemical modeling. The force-free activation length to convert the cis C═C bonds to the transition state is ∼0.5 Å, indicating that the reaction rate is accelerated by ∼109 times at the transition force. On the basis of the density functional theory optimized structure, we propose that because the pulling direction is not parallel to C═C double bonds in the polymer, stretching the polymer not only provides tension to lower the transition barrier but also provides torsion to facilitate the rotation of cis C═C bonds. This explains the apparently low transition force for such thermally "forbidden" reactions and offers an additional explanation of the "lever-arm effect" of polymer backbones on the activation force for many mechanophores. This work demonstrates the importance of precisely controlling the force direction at the nanoscale to the force-activated reactions and may have many implications on the design of stress-responsive materials.

Efficient antitumor effect of co-drug-loaded nanoparticles with gelatin hydrogel by local implantation.

Tetrandrine (Tet) could enhance the antitumor effect of Paclitaxel (Ptx) by increasing intracellular Reactive Oxygen Species (ROS) levels, which leads to the possibility of co-delivery of both drugs for synergistic antitumor effect. In the current study, we reported an efficient, local therapeutic strategy employing effective Tet and Ptx delivery with a nanoparticle-loaded gelatin system. Tet- and Ptx co-loaded mPEG-PCL nanoparticles (P/T-NPs) were encapsulated into the physically cross-linked gelatin hydrogel and then implanted on the tumor site for continuous drug release. The drug-loaded gelatin hydrogel underwent a phase change when the temperature slowly increased. In vitro study showed that Tet/Ptx-loaded PEG-b-PCL nanoparticles encapsulated within a gelatin hydrogel (P/T-NPs-Gelatin) inhibited the growth and invasive ability of BGC-823 cells more effectively than the combination of free drugs or P/T-NPs. In vivo study validated the therapeutic potential of P/T-NPs-Gelatin. P/T-NPs-Gelatin significantly inhibited the activation of p-Akt and the downstream anti-apoptotic Bcl-2 protein and also inducing the activation of pro-apoptotic Bax protein. Moreover, the molecular-modulating effect of P/T-NPs-Gelatin on related proteins varied slightly under the influence of NAC, which was supported by the observations of the tumor volumes and weights. Based on these findings, local implantation of P/T-NPs-Gelatin may be a promising therapeutic strategy for the treatment of gastric cancer.

Structure-Dependent cis/trans Isomerization of Tetraphenylethene Derivatives: Consequences for Aggregation-Induced Emission.

The isomerization and optical properties of the cis and trans isomers of tetraphenylethene (TPE) derivatives with aggregation-induced emission (AIEgens) have been sparsely explored. We have now observed the tautomerization-induced isomerization of a hydroxy-substituted derivative, TPETH-OH, under acidic but not under basic conditions. Replacing the proton of the hydroxy group in TPETH-OH with an alkyl group leads to the formation of TPETH-MAL, for which the pure cis and trans isomers were obtained and characterized by HPLC analysis and NMR spectroscopy. Importantly, cis-TPETH-MAL emits yellow fluorescence in DMSO at -20 °C whereas trans-TPETH-MAL shows red fluorescence under the same conditions. Moreover, the geometry of cis- and trans-TPETH-MAL remains unchanged when they undergo thiol-ene reactions to form cis- and trans-TPETH-cRGD, respectively. Collectively, our findings improve our fundamental understanding of the cis/trans isomerization and photophysical properties of TPE derivatives, which will guide further AIEgen design for various applications.

Facile synthesis of brush poly(phosphoamidate)s via one-pot tandem ring-opening metathesis polymerization and atom transfer radical polymerization.

Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA)-based brush poly(phosphoamidate)s are successfully synthesized by a combination of ring-opening metathesis polymerization (ROMP) and atom transfer radical polymerization (ATRP) following either a commutative two-step procedure or a straightforward one-pot process using Grubbs ruthenium-based catalysts for tandem catalysis. Compared with the traditional polymerization method, combining ROMP and ATRP in a one-pot process allows the preparation of brush copolymers characterized by a relatively moderate molecular weight distribution and quantitative conversion of monomer. Moreover, the surface morphologies and aggregation behaviors of these polymers are studied by AFM and TEM measurements.

Near-infrared fluorescence amplified organic nanoparticles with aggregation-induced emission characteristics for in vivo imaging.

Near-infrared (NIR) fluorescence signals are highly desirable to achieve high resolution in biological imaging. To obtain NIR emission with high brightness, fluorescent nanoparticles (NPs) are synthesized by co-encapsulation of 2,3-bis(4-(phenyl(4-(1,2,2-triphenylvinyl)phenylamino)phenyl)fumaronitrile (TPETPAFN), a luminogen with aggregation-induced emission (AIE) characteristics, and a NIR fluorogen of silicon 2,3-naphthalocyanine bis(trihexylsilyloxide) (NIR775) using 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] as the encapsulation matrix. The good spectral overlap between the emission of TPETPAFN and the absorption of NIR775 leads to efficient energy transfer, resulting in a 47-fold enhancement of the NIR775 emission intensity upon excitation of TPETPAFN at 510 nm as compared to that upon direct excitation of NIR775 at 760 nm. The obtained fluorescent NPs show sharp NIR emission with a band width of 20 nm, a large Stokes shift of 275 nm, good photostability and low cytotoxicity. In vivo imaging study reveals that the synthesized NPs are able to provide high fluorescence contrast in live animals. The Förster resonance energy transfer strategy overcomes the intrinsic limitation of broad emission spectra for AIE NPs, which opens new opportunities to synthesize organic NPs with high brightness and narrow emission for potential applications in multiplex sensing and imaging.

Facile synthesis of thiol-functionalized long-chain highly branched ROMP polymers and surface-decorated with gold nanoparticles.

The synthesis of thiol-functionalized long-chain highly branched polymers (LCHBPs) has been accomplished in combination of ring-opening metathesis polymerization (ROMP) and thiol-Michael addition click reaction. A monotelechelic polymer with a terminal acrylate and many pendent thiol groups is first prepared through adding an internal cis-olefin terminating agent to the reaction mixture immediately after the completion of the living ROMP, and then utilized as an ABn -type macromonomer in subsequent thiol-ene reaction between acrylate and thiol, yielding LCHBPs as the reaction time prolonged. Au nanoparticles are then covalently conjugated onto the surface of thiol-functionalized LCHBP to fabricate novel hybrid nanostructures, which is shown as one interesting application of such functionalized metathesis polymers. This facile approach can be extended toward the fabrication of novel nanomaterials with sophisticated structures and tunable multifunctionalities.

Intelligently targeted drug delivery and enhanced antitumor effect by gelatinase-responsive nanoparticles.

AIMS: The matrix metalloproteinase (MMP) 2/9, also known as collagenases IV and gelatinases A/B, play a key role in cancer invasion and metastasis. However, the clinical trials of the MMP inhibitors (MMPIs) ended up with disappointing results. In this paper, we synthesized a gelatinase-responsive copolymer (mPEG-PCL) by inserting a gelatinase cleavable peptide (PVGLIG) between mPEG and PCL blocks of mPEG-PCL for anticancer drug delivery to make use of MMP2/9 as an intelligent target for drug delivery. MATERIALS AND METHODS: mPEG-pep-PCL copolymer was synthesized via ring-opening copolymerization and double-amidation. To evaluate whether Nanoparticles (NPs) prepared from this copolymer are superior to NPs prepared from mPEG-PCL, NPs prepared from mPEG-PCL copolymer were used as positive control. Docetaxel-loading NPs using mPEG-pep-PCL and mPEG-PCL were prepared by nano-precipitation method, mentioned as Gel-NPs and Con-NPs, respectively. The morphologic changes of the NPs after treatment with gelatinases were observed macroscopically by spectrophotometer and microscopically by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The cellular uptake amount and cytotoxicity of Gel-NPs and Con-NPs, respectively, in cell lines with different levels of gelatinase expression were studied. Moreover, the cytotoxicity study on the primary cancer cells isolated from pericardial fluids from a patient with late-stage lung cancer was conducted. RESULTS: The Gel-NPs aggregated in response to gelatinases, which was confirmed macroscopically and microscopically. The cellular uptake amount of Gel-NPs was correlated with the level of gelatinases. The in vitro antitumor effect of Gel-NPs was also correlated with the level of gelatinases and was superior to Taxotere (commercially available docetaxel) as well as the Con-NPs. The cytotoxicity study on the primary lung cancer cells also confirmed the effectiveness of Gel-NPs. CONCLUSION: The results in this study preliminarily demonstrated the effectiveness of gelatinase-responsive targeting strategy and the prospect of this intelligent nano-drug delivery system though further studies are needed.

Enhanced neuroprotective effects of resveratrol delivered by nanoparticles on hydrogen peroxide-induced oxidative stress in rat cortical cell culture.

Resveratrol (RES) has recently been reported as a potential antioxidant in treatment of ischemia/reperfusion injury through attenuating oxidative stress and apoptosis. However, application of RES is limited for its insolubility and short half-time. Latest evidence raises the possibility of developing nanoparticle-based delivery systems with improved solubility, stability and cytotoxicity of lipophilic drug. Here, we reported first a simple way to produce RES-loaded nanoparticles (RES-NPs) based on poly(N-vinylpyrrolidone)-b-poly(ε-caprolactone) polymer and further evaluated the protective effect of RES-NPs on hydrogen peroxide-induced oxidative stress and apoptosis in rat cortical cell culture. The controlled release pattern of RES-loaded nanoparticles was characterized by in vitro release experiments. Cytotoxicity tests proved cytocompatibility of these nanoparticles with neurons. Shown by coumarin-6 loaded nanoparticles, the uptake of nanoparticles by neurons was considered through endocytosis, which could lead to higher uptake efficiency at lower concentration. Thereby, the hypothesis is raised that RES-NPs could demonstrate enhanced neuroprotection compared to an equivalent dose of free RES at lower concentration, especially. It was further supported by enhanced reduction of LDH release, elimination of ROS and MDA, and attenuation of apoptosis signal (ratio of Bax/Bcl-2, activation of caspase-3). RES-NPs could be a potential treatment needing intensive research for ischemia/reperfusion related disorder including stroke.

Photodynamic effect of 5-aminolevulinic acid-loaded nanoparticles on bladder cancer cells: a preliminary investigation.

OBJECTIVE: The aim of this study was to assess the photodynamic effect of nanoparticles loaded with a photosensitizing nanomedicine, 5-aminolevulinic acid (5-ALA), on T24 bladder cancer cells in vitro. MATERIAL AND METHODS: The nanoprecipitation technique was successfully used to prepare the drug-loaded polymeric nanoparticles. The drug loading rate and the drug loading efficiency were determined by ultraviolet spectrophotometry. The size and morphology of nanoparticles were detected using dynamic light scattering (DLS) and transmission electron microscopy. Cytotoxicity to T24 bladder cancer cells was assessed by coincubating 5-ALA-loaded nanoparticles of different concentrations with T24 bladder cancer cells. The cell growth inhibitory rate was measured after irradiation by a 650 nm wavelength diode laser. RESULTS: The drug loading rate of 5-ALA-loaded nanoparticles was 7% with a loading efficiency of 85%. The T24 cell growth inhibitory rates after incubation with 5.0, 10.0, 25.0 and 50.0 µg/ml 5-ALA-loaded nanoparticles were 73.19%, 79.95%, 83.86% and 89.74%, respectively, which demonstrated significantly higher cytotoxicity than those in the empty nanoparticle groups and 5-ALA free drug groups (p < 0.05). CONCLUSIONS: 5-ALA-loaded nanoparticles were successfully prepared and had a significantly enhanced photodynamic tumoricidal effect on bladder cancer cells in vitro.

Enhanced in vitro and in vivo therapeutic efficacy of codrug-loaded nanoparticles against liver cancer.

Paclitaxel (Ptx), one of the most widely used anticancer agents, has demonstrated extraordinary activities against a variety of solid tumors. However, the therapeutic response of Ptx is often associated with severe side effects caused by its nonspecific cytotoxic effects and special solvents (Cremophor EL(®)). The current study reports the stable controlled release of Ptx/tetrandrine (Tet)-coloaded nanoparticles by amphilic methoxy poly(ethylene glycol)-poly(caprolactone) block copolymers. There were three significant findings. Firstly, Tet could effectively stabilize Ptx-loaded nanoparticles with the coencapsulation of Tet and Ptx. The influence of different Ptx/Tet feeding ratios on the size and loading efficiency of the nanoparticles was also explored. Secondly, the encapsulation of Tet and Ptx into nanoparticles retains the synergistic anticancer efficiency of Tet and Ptx against mice hepatoma H22 cells. Thirdly, in the in vivo evaluation, intratumoral administration was adopted to increase the site-specific delivery. Ptx/Tet nanoparticles, when delivered intratumorally, exhibited significantly improved antitumor efficacy; moreover, they substantially increased the overall survival in an established H22-transplanted mice model. Further investigation into the anticancer mechanisms of this nanodelivery system is under active consideration as a part of this ongoing research. The results suggest that Ptx/Tet-coloaded nanoparticles could be a potential useful chemotherapeutic formulation for liver cancer therapy.

Enhanced antitumor efficacy, biodistribution and penetration of docetaxel-loaded biodegradable nanoparticles.

To investigate the antitumor effect, biodistribution and penetration in tumors of docetaxel (DOC)-loaded polyethylene glycol-poly(caprolactone) (mPEG-PCL) nanoparticles on hepatic cancer model, DOC-loaded nanoparticles (DOC-NPs) were prepared with synthesized mPEG-PCL by nano-precipitated method with satisfactory encapsulation efficiency, loading capacity and size distribution. The fabricated nano-drugs were effectively transported into tumoral cells through endocytosis and localized around the nuclei in the cytoplasm. In vitro cytotoxicity test showed that DOC-NPs inhibited the murine hepatic carcinoma cell line H22 in a dose-dependent manner, which was similar to Taxotere, the commercialized formulation of docetaxel. The in vivo biodistribution performed on tumor-bearing mice by NIRF real-time imaging demonstrated that the nanoparticles achieved higher concentration and longer retention in tumors than in non-targeted organs after intravenous injection. The immunohistochemical analysis demonstrated that the nanoparticles located not only near the tumoral vasculatures, but also inside the tumoral interior. Therefore, DOC-NPs could penetrate into tumor parenchyma, leading to high intratumoral concentration of DOC. More importantly, the in vivo anti-tumor evaluation showed that DOC-NPs significantly inhibited tumor growth by tumor volume measurement and positron emission tomography and computed tomography (PET/CT) imaging observation. Taken together, the reported drug delivery system here could shed light on the future targeted therapy against hepatic carcinoma.

[Assessment of lymph node metastasis in gastric cancer: status quo, recent advances and new perspectives].

The precondition of accurate gastric cancer surgery is precise assessment of lymph node metastasis. To date, no imaging modality achieves both high sensitivity and high specificity in detecting lymph node metastasis in gastric cancer. Intraoperative sentinel node tracing and biopsy are the most popular method to identify the localization of tumor cell, but is limited to early gastric cancer. Nano-composite materials, designed for tumor imaging and tracing, show us a newly emerging domain for tumor detection in gastric cancer. The function of these nano-composite materials to detect lymph node metastasis in gastric cancer relies on the effective backflow of lymph system. However, the lymph vessels can be obstructed by tumor cells in advanced gastric cancer, which may restrain the application of these nanoparticles. Therefore, more methods to detect lymph node metastasis in gastric cancer should be explored. This review summarizes the characteristic of the targeted nanosphere. Based on the reported studies, a novel idea is conceived that targeted multifunctional nanosphere may be a potential method to achieve precise assessment of lymph node metastasis in gastric cancer.

Tumor accumulation, penetration, and antitumor response of cisplatin-loaded gelatin/poly(acrylic acid) nanoparticles.

In this report, the cisplatin (CDDP)-loaded gelatin/poly(acrylic acid) (GEL-PAA) nanoparticles with a spherical shape and drug loading content of 24.6% were prepared. In vivo near-infrared fluorescence (NIRF) imaging and ex vivo gamma scintillation counting analyses reveal that CDDP-loaded GEL-PAA nanoparticles have prominent passive tumor-targeting ability and the nontarget nanoparticles can be readily excreted from the body. Further, it is demonstrated that the CDDP-loaded nanoparticles have the ability to penetrate the tumor after their extravasation through the leaky vessels and distribute in a distance of about 20 µm from the vessels at 24 h postinjection. The in vivo antitumor responses reveal that the nanoparticle formulation exhibits significantly superior in vivo antitumor effect than free CDDP by the comparison of tumor volume and the examinations of cell apoptosis and proliferation in tumor tissues through proliferating cell nuclear antigen (PCNA) and terminal deoxynucleotidyl-transferase-mediated nick end labeling (TUNEL) methods.