Graphene-Based Hybrid Fillers for Rubber Composites.

Graphene and its derivatives have been confirmed to be among the best fillers for rubber due to their excellent properties, such as high mechanical strength, improved interface interaction, and strain-induced crystallization capabilities. Graphene rubber materials can be widely used in tires, shoes, high-barrier conductive seals, electromagnetic shielding seals, shock absorbers, etc. In order to reduce the graphene loading and endow more desirable functions to rubber materials, graphene-based hybrid fillers are extensively employed, which can effectively enhance the performance of rubber composites. This review briefly summarizes the recent research on rubber composites with graphene-based hybrid fillers consisting of carbon black, silica, carbon nanotubes, metal oxide, and one-dimensional nanowires. The preparation methods, performance improvements, and applications of different graphene-based hybrid fillers/rubber composites have been investigated. This study also focuses on methods that can ensure the effectiveness of graphene hybrid fillers in reinforcing rubber composites. Furthermore, the enhanced mechanism of graphene- and graphene derivative-based hybrid fillers in rubber composites is investigated to provide a foundation for future studies.

Enhanced properties of gelatin films incorporated with TiO2-loaded reduced graphene oxide aerogel microspheres for active food packaging applications.

The synergistic effect of graphene sheets and titanium dioxide nanoparticles (TiO2) hybrid fillers can improve the antibacterial, mechanical, and barrier properties of gelatin (GL), making it more suitable to be used in the food packaging application. However, the uneven dispersion and aggregation of the hybrid fillers restrict its performance for further application. In order to achieve the above superior properties, reduced graphene oxide aerogel microspheres (rGOAMs) loaded with TiO2 (rGOAMs@TiO2) were successfully prepared using one-step hydrothermal process by reducing titanium sulfate into TiO2 on the framework of rGOAMs, followed by effective dispersion in the GL matrix to form nanocomposites (rGOAMs@TiO2/GL) through simultaneous ultrasonication and mechanical stirring, as well as an ultrasonic cell grinder process. Incorporating a mere 0.8 wt% of rGOAMs@TiO2 effectively improved the mechanical, antibacterial, UV light barrier, thermal stability, hydrophobicity, and water vapor barrier properties of the GL. Compared with the composites made of rGOAMs, TiO2, and GL (rGOAMs/TiO2/GL), rGOAMs@TiO2/GL composites showed stronger filler-matrix interactions, better filler dispersion, and lower TiO2 particle aggregation, suggesting superiority compared to rGOAMs/TiO2/GL composites at the same filler content. This innovative method of mixing GL with rGOAMs@TiO2 holds great promise for enhancing the suitability of GL in active food packaging applications.

Surface Wettability-Switchable Janus Fiber Fragments Stabilize Pickering Emulsions for Effective Oil/Water Separation.

Pickering emulsions indicate stronger resistance against droplet coalescence than the surfactant-stabilized emulsions. To resemble the surfactant amphiphilicity, Janus fiber fragments (JFs) were herein prepared through side-by-side electrospinning of poly(styrene-maleic anhydride) (PSMA) derivatives and cryosection of the aligned fibers, followed by conjugation of hydrophobic cetylamine (C16) and hydrophilic poly(N-isopropylacrylamide) (PNIPAm) ligands on the separate sides. Orthogonal analysis table L25(56) was designed to examine the effect of process parameters on the emulsification efficiency and stability index of Pickering emulsions. The emulsification efficiency is dominated by the JF concentration and length, while the emulsion stability could be prolonged through adjusting the JF concentration and hydrophilic graft density. JF-stabilized emulsions exhibit a much higher stability index (96.4%) than that of Janus microparticle counterparts (37.7%). Though there is no apparent effect on the surface wettability, JFs with PNIPAm grafts of about 2200 Da achieve the most stable Pickering emulsions. Superparamagnetic Fe3O4 nanoparticles are inoculated into JFs to collect emulsion droplets under a magnetic field, and the emulsions could be demulsified at an elevated temperature to harvest oil. Meanwhile, the recovered JF emulsifiers could be repeatedly used without loss of the emulsification efficiency. Thus, this study demonstrates surface-switchable JFs to be effective stabilizers of Pickering emulsions and readily recycled for oil harvesting from wastewater.

Fabrication of Multilayered Two-Dimensional Micelles and Fibers by Controlled Self-Assembly of Rod-Coil Block Copolymers.

Fabricating hierarchical nanomaterials by self-assembly of rod-coil block copolymers attracts great interest. However, the key factors that affect the formation of the hierarchical nanomaterials have not been thoroughly researched. Herein, we have synthesized two diblock copolymers composed of poly(3-hexylthiophene) (P3HT) and polyethylene glycol (PEG). Through a heating, cooling, and aging process, a series of multilayered hierarchical micelles and fibers were prepared in alcoholic solutions. The transition from fibers to hierarchical micelles are strictly influenced by the strength of the π-π stacking interaction, the PEG chain length, and solvent. In isopropanol, the P3HT22-b-PEG43 could self-assemble into hierarchical micelles composed of several two-dimensional (2D) laminar layers, driven by the π-π stacking interaction and van der Waals force. The P3HT22-b-PEG43 could not self-assemble into well-defined nanostructures in methanol and ethanol, but could self-assemble into fibers in isobutanol. However, the P3HT22-b-PEG113 with a longer corona block only self-assembled into fibers in four alcoholic solutions, due to the increase in dissolving capacity and steric hindrance. The sizes and the size distributions of the nanostructures both increased with the increase in polymer concentration and the decrease in solvent polarity. This study shows a method to fabricate the hierarchical micelles.

Bacteria-Templated and Dual Enzyme-Powered Microcapsule Motors To Promote Thrombus Penetration and Thrombolytic Efficacy.

Antithrombotic therapy is confronted with short half-lives of thrombolytic agents and high bleeding risks. Challenges remain in the development of drug delivery systems for thorough destruction of thrombi and timely restoration of blood flow while minimizing side effects. Herein, polydopamine capsule-like micromotors with urokinase (uPA) loadings and Arg-Gly-Asp (RGD) grafts (r-u@PCM) were constructed using rod-shaped bacteria as the template, and one single opening was created on each capsule through bacterial ghost (BG) formation. Glucose oxidase and catalase were encapsulated in the large cavity of microcapsules, and their successive oxidation of glucose produced O2 bubbles, which ejected out through the single opening to propel the motion of r-u@PCM. In vitro targeting testing of r-u@PCM shows significant higher accumulations on the activated platelets than those without RGD grafts (u@PCM, 7 folds) or without enzyme loadings (r-u@PC, 11 folds). Compared with the major distribution of r-u@PC on the clot surface, r-u@PCM efficiently penetrates into clots with dense fibrin networks, and near-infrared (NIR) irradiation (r-u@PCM/NIR) promotes thrombus infiltration through increasing uPA release and thermolysis of the networks. Pharmacokinetic study shows that the loading of uPA in r-u@PCM extends the terminal half-life from 24 min to 5.5 h and the bioavailability increased 13 times. In a hindlimb venous thrombosis model, r-u@PCM/NIR treatment promotes uPA accumulations in thrombi and disrupts all the thrombi after 8 h with a full recovery of blood flows. Effective thrombolysis is also achieved even after reducing the uPA dose 5 times. Thus, this is the first attempt to fabricate rod-shaped microcapsule motors through a biologically derived method, including bacterial templating and BG formation-induced opening generation. r-u@PCM/NIR treatment promotes thrombolysis through the photothermal effect, self-propelled infiltration into thrombi, and accelerated local release of uPA, providing a prerequisite for reducing uPA dose and bleeding side effects.

Antibody-based drug delivery systems for cancer therapy: Mechanisms, challenges, and prospects.

In recent years, antibody-based cancer therapy has emerged as one of the efficient therapeutic strategies, such as immune checkpoint inhibitors (ICIs), angiogenesis inhibitors, antibody-drug conjugates (ADCs), multi-specific antibodies, and chimeric antigen receptor T (CAR-T) cells, among others. To date, various drug delivery platforms have been developed to improve the bioavailability, delivery convenience, and reduced toxicity towards increased therapeutic efficacy of antibodies. Herein, we emphasize the clinical manifestations of various antibody-based tumor therapies, highlighting their mechanisms and applications for cancer therapy. Further, based on the problems to be solved in the current clinical application of antibodies, and combined with the advanced drug delivery technologies, we discuss the roles of antibody-based drug delivery systems (DDSs) in cancer therapy, such as enhanced patient compliance and regulating the tumor microenvironment for combined therapy. By expounding the importance of DDSs and discussing the challenges and prospects of their implementation, we suggest that pharmaceutical enterprises and scientists develop appropriate antibody-based delivery platforms.

Bacteria-propelled microtubular motors for efficient penetration and targeting delivery of thrombolytic agents.

Effective thrombolysis is critical to rapidly rebuild blood flow for thrombosis patients. Drug delivery systems have been developed to address inadequate pharmacokinetics of thrombolytic agents, but challenges still remain in the timely removal of blood clots regarding the dense fibrin networks. Herein, rod-shaped tubular micromotors were developed to achieve efficient penetration and thorough destruction of thrombi. By using electrospun fiber fragments as the template, urokinase (uPA)-loaded polydopamine (PDA) microtubes with surface decorated fucoidan (FuPDAuPA) were prepared at the aspect ratio of around 2. One E. coli Nissle 1917 (EcN) was assembled into one microtube to construct a FuPDAuPA@EcN hybrid micromotor through PDA adhesion and L-aspartate induction. The pharmacokinetic analysis indicates that the encapsulation of uPA into micromotors extends the half-life from 0.4 to 5.6 h and increases the bioavailability over 10 times. EcN-propelled motion elevates adsorption capacities of FuPDAuPA@EcN for more than four times compared with that of FuPDAuPA. The fucoidan-mediated targeting causes 2-fold higher thrombolysis capacity in vitro and over 10-fold higher uPA accumulation in thrombi in vivo. In the treatment of venous thrombi at mouse hindlimbs, intravenous administration of FuPDAuPA@EcN completely removed blood clots with almost full recovery of blood flows and apparently alleviated tail bleeding. It should be noted that FuPDAuPA@EcN treatment at a reduced uPA dose caused no significant difference in the blood flow rate compared with those of FuPDAuPA. The synergistic action of fucoidan-induced targeting and EcN-driven motion provides a prerequisite for promoting thrombolytic efficacy and reducing uPA dose and bleeding side effect. STATEMENT OF SIGNIFICANCE: The standard treatment to thrombosis patient is intravenous infusion of thrombolytic agents, but the associated bleeding complications and impairment of normal haemostasis greatly offset the therapeutic benefits. Drug delivery systems have been developed to address the limitations of inadequate pharmacokinetics of thrombolytic agents, but challenges still exist in less efficient penetration into dense networks for thorough destruction of thrombi. Up to now only few attempts have been made to construct nano-/micromotors for combating thrombosis and there is no single case that antithrombosis is assisted by bacteria or cells-propelled motors. Herein, bacteria-propelled microtubes were developed to carry urokinase for efficient penetration into blood clots and effective thrombolysis. The synergistic action of bacteria-driven motion and specific ligand-induced targeting holds a promising treatment strategy for life-threatening cardiovascular diseases such as thrombosis and atherosclerosis.

Bacterial navigation for tumor targeting and photothermally-triggered bacterial ghost transformation for spatiotemporal drug release.

Cancer chemotherapy is confronted with challenges regarding the effective delivery of chemotherapeutics into tumor cells after systemic administration. Herein, we propose a strategy to load drugs into probiotic E. coli Nissle 1917 (EcN) for self-guided navigation to tumor tissues and subsequently release the drugs with in situ transformation into bacterial ghosts (BGs). Chemotherapeutic agent 5-fluorouracil (FU) and macrophage phenotype regulator zoledronic acid (ZOL) are loaded into EcN through electroporation, followed by decoration of Au nanorods on the ECN surface to construct EcNZ/F@Au. High loading levels of 5FU (8.8%) and ZOL (10.5%) are achieved as well as high retention rates of bacterial viability (87%) and motion velocity (88%). Under near infrared (NIR) illumination the photothermal effect of Au nanorods elevates the local temperature to induce the transformation of live EcN into BGs. The created transmembrane channels initiate the gradual drug release from BGs, thus representing the first attempt to control the drug release via a biological evolution. An intermittent NIR illumination causes stepwise increases in the BG formation and drug release, which could implement an external on-off control and spatiotemporal drug release. Self-guided motion of EcN promotes efficient extravasation across blood vessels and preferential accumulation of drugs in tumors. In addition to the chemotherapeutic effect of FU, the local release of ZOL from EcNZ/F@Au enhances valid polarization of tumor-associated macrophages toward the M1 phenotype and an effective production of proinflammatory cytokines, leading to a synergistic efficacy on tumor growth inhibition. Thus, this study demonstrates a feasible strategy to integrate chemotherapy, immunotherapy, and photothermal effects in a concise manner for effective cancer treatment with few side effects. STATEMENT OF SIGNIFICANCE: Bacteria are capable to trace and colonize in hypoxic tumor tissues. Bacterial drug carriers indicate limitations in efficient drug loading and effective release modulation. Herein, we propose a strategy to load drugs into bacteria for self-guided delivery and subsequently release the drugs in tumors with in situ transformation into bacterial ghost (BGs). Drugs are loaded into live bacteria through electroporation and Au nanorods are decorated on the bacterial surface, wherein the photothermal effect, chemotherapy, and immunotherapy are integrated in a concise manner. NIR illmumination of Au nanorods elevates the local temparature, induces the BG tranformation, and activates the spatiotemporal drug release, representing the first attempt of release modulation via a biological evolution.

Intracellular bacteria destruction via traceable enzymes-responsive release and deferoxamine-mediated ingestion of antibiotics.

Intracellular bacteria (ICBs) are among the most life-threatening causes of drug resistance. Challenges remains in the intracellular drug release specific to ICB-infected cells and efficient uptake into ICBs. In this study, mannose-grafted polymers containing enzymes-responsive and tetraphenylethylene segments (mPET) are assembled into nanoparticles with loading complexes of deferoxamine-ciprofloxacin conjugates with Fe3+ (DFeC). The aggregation-induced emission (AIE) of tetraphenylethylene segments is overlapped with DFeC absorptions, leading to fluorescence resonance energy transfer (FRET)-caused quenching of mPET@DFeC nanoparticles. Nanoparticles are efficiently acquired by infected macrophages via mannose mediation, and the DFeC release is triggered by intracellular lipase and alkaline phosphatase specific to ICB-engulfed macrophages, followed by deferoxamine-mediated ingestion of ciprofloxacin into ICBs. The gradual alleviation of FRET effect and the concurrent restoration of AIE activity demonstrate capabilities of dynamically tracking the drug release and ICB treatment outcome. The mPET@DFeC treatment inhibits the hematological, hepatic and nephric toxicities caused by ICB infections, and all the infected mice survive with dramatic reductions of bacterial levels in livers (over 430 folds), spleens (over 240 folds) and kidneys (5.6 × 104 folds). Thus, this study has provided a feasible strategy to achieve intracellular enzymes-responsive and traceable release of antibiotics and then deferoxamine-mediated bacterial ingestion for ICB destruction.

Fibrous testing papers for fluorescence trace sensing and photodynamic destruction of antibiotic-resistant bacteria.

The increasing prevalence of antibiotic-resistant bacteria needs rapid identification and efficient destruction routes. This study proposes testing paper derived from electrospun fibrous mats and aggregation-induced emission (AIE) probes for trace sensing and simultaneous destruction of antibiotic-resistant E. coli. Aptamers are conjugated on fibers for selective capture of E. coli, and the capture capability can be regenerated via rinsing with salt solution. Hydroxyl tetraphenylethene (TPE) is linked with two cephalosporin molecules to construct TPE-Cep probes, and the fluorescence emission is turned on specifically in the presence of ß-lactamase, which is a critical marker for screening resistant bacteria. Fibrous mats are lit up only in the presence of antibiotic-resistant bacteria, and the fluorescence intensity changes could be statistically fitted into an equation for quantitative analysis. Fibrous strips display apparent color changes from blue to green for a visual readout of bacterial levels, and the limit of detection (LOD) is much lower than those of previous paper substrates. In addition, the TPE-Cep probes could produce reactive oxygen species (ROS) under room light illumination to kill the captured bacteria. Thus, the integration of aptamer-grafted electrospun fibers and functional AIE probes provides potential for selective capture, trace imaging and photodynamic destruction of antibiotic-resistant bacteria.

Macrophage Spheroids with Chronological Phenotype Shifting To Promote Therapeutic Angiogenesis in Critical Limb Ischemia.

Therapeutic angiogenesis becomes an essential approach to rescue ischemia and the cell-based therapy facilitates ischemia recovery via stimulation of paracrine signals or replacement of damaged cells. Macrophages participate in multiple processes of tissue repair, and the M1 and M2 phenotypes play distinct roles in the sequential stages of healing initiation, angiogenesis stabilization, and tissue maturation. In this study, macrophage spheroids (MøSs) are proposed to promote therapeutic angiogenesis in critical limb ischemia (CLI) via chronological shifting from M1 to M2 phenotypes. Uniform-sized MøSs are prepared by using electrosprayed microcapsules as the confined growth template, and fiber fragments are inoculated to achieve a local release of chrysin for macrophage phenotype manipulation. The macrophage polarization shifting is confirmed from the decreased CD86 expressions (M1 marker) from 64.7 to 31.7% and the concurrent increase in CD206 expressions (M2 marker) from 39.3 to 72.4%. Meanwhile, the tumor necrosis factor-α secretion from M1 is downregulated by around threefold, whereas the levels of interleukin-10 and transforming growth factor-ß1 from M2 increase by around threefold. The incubation with conditioned media from the MøS culture could promote the proliferation and migration of endothelial cells (ECs), showing a high healing rate of EC layers. The local treatment of hind-limb ischemia leads to a full recovery from ischemic to normal limbs with a high blood perfusion rate. Histological analysis shows few muscle degeneration and fibrosis areas and high capillary densities. As far as we know, this is the first attempt to develop uniform-sized MøSs and to undergo dynamic phenotypic shifting from early M1 to later M2 for angiogenesis promotion in the CLI treatment.

3D spheroids generated on carbon nanotube-functionalized fibrous scaffolds for drug metabolism and toxicity screening.

The mechanical and electrical stimuli have a profound effect on the cellular behavior and function. In this study, a series of conductive nanofibrous scaffolds are developed by blend electrospinning of poly(styrene-co-maleic acid) (PSMA) and multiwalled-carbon nanotubes (CNTs), followed by grafting galactose as cell adhesion cues. When the mass ratios of CNTs to PSMA increase up to 5%, the alignment, Young's modulus and conductivity of fibrous scaffolds increase, whereas the average diameter, pore size and elongation at break decrease. Primary hepatocytes cultured on the scaffolds are self-assembled into 3D spheroids, which restores the hepatocyte polarity and sufficient expression of drug metabolism enzymes over an extended period of time. Among these conductive scaffolds, hepatocytes cultured on fibers containing 3% of CNTs (F3) show the highest clearance rates of model drugs, offering a better prediction of the in vivo data with a high correlation value. Moreover, the drug metabolism capability is maintained over 15 days and is more sensitive towards the inducers and inhibitors of metabolizing enzymes, demonstrating the applicability for drug-drug interaction studies. Thus, this culture system has been demonstrated as a reliable in vitro model for high-throughput screening of metabolism and toxicity in the early phases of drug development.

Janus micromotors for motion-capture-lighting of bacteria.

The rapid and sensitive identification of bacteria has long been a major challenge in quality control, environmental monitoring and food safety. In the current study, the "motion-capture-lighting" strategy is proposed via integration of motion-enhanced capture of bacteria and capture-induced fluorescence turn-on of micromotors. Compared with the commonly used microtubes and microparticles, micromotors of flexible fiber rods could offer multiple interactions with the bacterial surface with less steric hindrance. Janus fiber rods (JFRs) are prepared by cryocutting of aligned fibers prepared by side-by-side electrospinning. Catalase is grafted on one side of JFRs to produce oxygen bubbles for propulsion of Janus micromotors (JMs), and mannose is conjugated on the other side for specific recognition of FimH proteins from fimbriae on the bacterial surface. The biphasic Janus structure of JFRs and the separate grafting of catalase and mannose on the opposite sides of JMs are confirmed after fluorescent labelling. JMs with aspect ratios of 0.5, 1, 2 and 4 are fabricated, and the aspect ratios of JMs show significant effects on the tracking trajectories and motion speed. JMs with the aspect ratio of 2 exhibit significantly higher magnitudes of mean square displacement (MSD) with a directional motion trajectory, leading to higher bacterial capture and larger fluorescence intensity changes. The bacteria capture leads to lighting up of JMs due to the aggregation-induced emission (AIE) effect of tetraphenylethene (TPE) derivatives. Under an ultraviolet lamp, the fluorescence color of JM suspensions turns from blue to bluish-green and to green after incubation with E. coli of 102 and 105 CFU mL-1, respectively. The fluorescence intensities of JM suspensions could be fitted to an equation versus bacterial concentrations, and the limit of detection (LOD) was around 45 CFU mL-1 within 1 min. Thus, this study demonstrates a motion-capture-lighting strategy for visual, rapid and real-time detection of bacteria without complicated sample pretreatment, expensive apparatus, and trained operators.

Uniform field electrospinning for 3D printing of fibrous configurations as strain sensors.

Electrospinning is becoming an efficient method to produce fibers in the submicron range, but the bending instability of conventional electrospinning system (CES) brings limitations in the distinctive deposition of electrospun fibers. Herein, we proposed a strategy to update the electrospinning system through establishment of a uniform electric field, realizing 3D printing of electrospun fibers with well-controlled, low-cost, and template-free manners. The uniform field electrospinning (UFES) apparatus is configured by inserting the electrospinning nozzle into the center of an aided metal plate. The electric field simulation of UFES indicates a uniform distribution between the aided metal plate and the collector, while a diverging and weaker electric field is produced by CES. The collector of UFES is mounted on a translation stage, which moves along x and y axes under computer control. The distinctive deposition of electrospun fibers produces fibrous mats with rectangular patterns of different grid sizes, and butterfly and TaiJi figures with high resolutions are directly written by UFES. The layer-by-layer deposition of electrospun fibers under UFES produces microscale Mongolian yurts with distinct hollow structure. Fibrous blocks with an average width of 120 µm and height of 630 µm were printed by UFES from conductive polymer composites and constructed into strain sensors. The electric current strength of fibrous microblocks changes sharply in response to the finger bending and release, indicating the capability to monitor human motions. Thus, this study demonstrates that the UFES becomes an easy-handling strategy for 3D printing of electrospun fibers to create complex geometries.

Bacterial biofilm destruction by size/surface charge-adaptive micelles.

Biofilms formed by pathogenic bacteria are one of the most important reasons for multidrug resistance. One of the major limitations in the biofilm treatment is the existence of intensive matrices, which greatly block the diffusion of antimicrobial agents. In the current study, we designed poly(aspartamide)-derived micelles self-assembled from cationic copolymers with azithromycin-conjugated and pH-sensitive copolymers, followed by loading cis-aconityl-d-tyrosine (CA-Tyr) via electrostatic interactions. In response to the acidic microenvironment of the biofilm matrix, the hydrophilic transition of the pH-sensitive copolymers and the removal of CA-Tyr led to a sharp decrease in micelle size from 107 nm to 54 nm and a rapid shift in their zeta potential from -11.7 mV to +26.4 mV, which facilitated the penetration of the micelles into biofilms. The acid-labile release of d-tyrosine disintegrated the biofilm matrix, and the lipase-triggered release of azithromycin eradicated the bacteria in the biofilms. An in vitro test was performed on pre-established P. aeruginosa biofilms in microwells, while biofilms grown on catheters were surgically implanted in rats for in vivo evaluation. The results demonstrated the capabilities of the size/surface charge-adaptive micelles in the intensive infiltration in the biofilm matrix and spatiotemporal release of biofilm dispersion and antibacterial agents for the comprehensive treatment of biofilm-relevant infections.

Synergistic antitumor efficacy of hybrid micelles with mitochondrial targeting and stimuli-responsive drug release behavior.

The term synergism means that the overall therapeutic benefits should be greater than the sum of the effects of individual agents and that the optimal therapeutic efficacy can be achieved at reduced doses. Micellar systems usually fail to deliver multiple drugs to target sites at synergistic doses and thus are not able to maximize the antitumor efficacy. In the current study, we demonstrate a strategy to coordinate the release of camptothecin (CPT) and α-tocopheryl succinate (TOS) from hybrid micelles for nucleus and mitochondrion interferences. TOS is decorated with cationic triphenylphosphonium (TPP) to promote the targeting capability of TOS-TPP to mitochondria. The combination of CPT and TOS-TPP shows strong synergistism with a combination index of 0.186. Hyaluronic acid (HA) is conjugated with CPT or TOS-TPP via disulfide linkages for tumor cell targeting and intracellular reduction-triggered release. Both conjugates either separately self-assemble into MC and MT micelles, or are blended at different ratios to form MC-T hybrid micelles. In response to elevated intracellular glutathione levels, the coordinated release of CPT and TOS-TPP from MC-T results in a combination index of 0.26 and the dose-reduction indexes of CPT and TOS are 7.7 and 3.4, respectively. Compared with MC and MT, MC-T micelles with 5 fold lower doses exhibit higher intracellular reactive oxygen species (ROS) levels, comparable tumor growth inhibition and animal survival, indicating no hematologic and intestinal toxicities. Moreover, the HA conjugates of MC-T are linked to polylactide via acid-labile linkages and electrospun into short fibers (MC-T@SF) as an injectable depot to release MC-T in response to the acidic tumor microenvironment. At a predetermined synergistic ratio, MC-T@SF with 5 fold lower doses achieves antitumor profiles comparable to those of individual micelle-loaded short fibers. Therefore, the hybrid micelles and micelle-releasing short fibers represent a feasible strategy to synergistically enhance the therapeutic efficacy and enable significant reduction in effective doses of chemotherapeutic agents.

Antibacterial Micelles with Vancomycin-Mediated Targeting and pH/Lipase-Triggered Release of Antibiotics.

Antibiotic delivery systems play an important role in increasing the efficacy while reducing the off-target toxicity and antibiotic resistance. Though bacterial infections share pathophysiological pathways similar to tumor tissues, few delivery systems have achieved bacterial targeting and on-demand release of antibiotics. In the current study, amphiphilic poly(ethylene glycol)-poly(ε-caprolactone) (PECL) copolymers are conjugated with vancomycin (VAN) as targeting ligands via pH-cleavable hydrazone bonds to obtain micelle carriers (Van-hyd-PECL). Subsequently, ciprofloxacin (CIP) is encapsulated to obtain Van-hyd-PECL/Cip micelles with an average size of 77 nm and a CIP loading amount of 4.5%. The poly(ethylene glycol) shells and the extension of VAN moieties on the micelle surface enhance the blood circulation and selective recognition of bacteria. The deshielding of VAN shells under acidic conditions disrupts the hydrophobic/hydrophilic balance leading to an increase in micelle sizes, which facilitates the degradation of poly(ε-caprolactone) by lipase overexpressed in the infection site and the release of encapsulated CIP for bacterial destruction. The micelle treatment has improved the survival of Pseudomonas aeruginosa-infected mice and reduced the bacterial burdens and alveolar injuries in lungs, compared with free drugs and micelles without inoculation of VAN moieties. Three doses of Van-hyd-PECL/Cip micelles further extend the animal survival, decrease the bacterial colonization in lungs, and almost restore the normal alveolar microstructure. In this regard, this study has demonstrated a strategy to enhance the bacterial targeting of micelles via an antibiotic (VAN) and to sequentially trigger the release of antibiotics (VAN and CIP) at the infection site.

Bacterial microbots for acid-labile release of hybrid micelles to promote the synergistic antitumor efficacy.

Bacteria have inherent properties of self-propelled navigation and specific infiltration into solid tumors. In the current study, we investigate a novel type of bacterial microbots for delivery of hybrid micelles to promote the synergistic antitumor efficacy. Escherichia coli Nissle 1917 (EcN) is used as a bacterial carrier to immobilize amphiphilic copolymers through acid-labile 2-propionic-3-methylmaleic anhydride (CDM) linkers. Doxorubicin (DOX) and α-tocopheryl succinate (TOS) are conjugated with poly(ethylene glycol) through disulfide linkers to obtain amphiphilic promicelle polymers (PMTOS and PMDOX). Tetrazine and norbornene terminals are grafted on EcN and PMTOS/PMDOX copolymers, respectively, and the mild and site-specific bioorthogonal reaction between them maintains the viability, motion ability, and tumor accumulation capability of the conjugated EcN. The PMTOS/PMDOX copolymers are released from bacterial microbots in response to the slightly acidic tumor microenvironment, followed by in situ formation of these copolymers as hybrid micelles (MD/T). The self-assembled micelles from PMTOS/PMDOX with a ratio of 1:2 demonstrate the most significant synergistic efficacy, and the released MD/T hybrid micelles exhibit cellular uptake efficiency, glutathione (GSH)-sensitive drug release, and cytotoxicities similar to those exhibited by micelles prepared by solvent evaporation. Because of the consecutive process of the self-propelling nature of bacteria and preferential accumulation of EcN in tumors, in situ formation of MD/T hybrid micelles, and intracellular drug release, bacterial microbots have shown remarkable antitumor efficacy with regard to animal survival, tumor growth, and apoptosis induction in tumor cells. Therefore, we demonstrate a feasible strategy for the construction of bacterial microbots to achieve tumor accumulation and on-demand release of multiple therapeutic agents for synergistic antitumor efficacy. STATEMENT OF SIGNIFICANCE: Challenges remain in the targeted delivery of nanoparticles to solid tumors and the realization of synergistic efficacy in cancer chemotherapy. In the current study, we explore a novel class of bacterial microbots to load, deliver, and release hybrid micelles. Escherichia coli Nissle 1917 (EcN) is used as a bacterial carrier to immobilize amphiphilic copolymers through acid-labile linkers, and the released copolymers are self-assembled into micelles. The resulting bacterial microbots integrate self-propelling bacteria and self-assembling amphiphilic polymers into micelles and realize pH-responsive release of promicelle polymers from bacterial microbots and glutathione-responsive intracellular release of drugs. A synergistic antitumor efficacy is achieved using hybrid micelles, which release both doxorubicin and α-tocopheryl succinate to display toxicities in the nucleus and mitochondria, respectively.

Acid-Labile Degradation of Injectable Fiber Fragments to Release Bioreducible Micelles for Targeted Cancer Therapy.

Cancer chemotherapy is confronted with difficulties enhancing the tumor accumulation, improving the bioavailability, and relieving the adverse effect of chemotherapeutic agents. To address the challenges, this study proposes a feasible strategy to realize a sustained release of drug-loaded micelles from fiber fragments after intratumoral injection. Camptothecin (CPT) is grafted on hyaluronic acid (HA) via 3,3'-dithiodipropionic acid to obtain reduction-sensitive promicelle polymers (PMCPT), which are conjugated with poly(d,l-lactide) via 2-propionic-3-methylmaleic anhydride (CDM) to obtain acid-labile copolymers for the preparation of injectable fiber fragments. Fiber fragments show remarkable acid-sensitive degradation, and the released PMCPT are spontaneously self-assembled into micelles, followed by subsequent HA-mediated internalization into tumor cells and reduction-sensitive release of drugs in the cytosol. Compared to fresh micelles prepared by ultrasonication, the micelles released via the degradation of fiber fragments display similar behaviors, such as the size and morphology, glutathione-sensitive drug release, cellular uptake efficiency, and cytotoxicity. Taking advantage of the aggregation-induced emission (AIE) effect of tetraphenylethene (TPE), the micelle release, cellular uptake, and tumor accumulation have been elucidated from the self-assembly induced fluorescence light-up in vitro and after intratumoral injection. Compared to the intratumoral injection of free micelles, sustained micelle release from fiber fragments resulted in significantly higher antitumor efficacy with respect to the inhibition of tumor growths, prolonging of animal survivals, and induction of cell apoptosis in tumor tissues. Thus, the micelle-releasing fiber fragments integrated with double targeting capabilities and double stimuli responsiveness have demonstrated a superior capacity to sustainably deliver chemotherapeutic agents directly within tumor cells.

An implantable depot capable of in situ generation of micelles to achieve controlled and targeted tumor chemotherapy.

Camptothecin (CPT)-containing promicelle polymers (PMCPT) based on 4-armed poly(ethylene glycol) (PEG) were developed previously to self-assemble into folate-targeted and glutathione (GSH)-sensitive micelles (MCPT). To address severe systemic toxicity and lack of tumor specificity implicated in the intravenous administration of MCPT, a micelle-generating depot has been developed by blend electrospinning of PEG-poly(lactide) (PELA) copolymers, PMCPT and polyethylene oxide (PEO). Upon implantation of the depot onto a tumor, PMCPT are sustainably released to self-assemble into MCPT on the tumor site. The release of PMCPT is adjusted by varying PEO/PELA ratios and reaches in the range of 23-92% after 30 days of incubation. By making use of the aggregation-induced emission (AIE) features of tetraphenylethylene (TPE) derivatives, the release process of TPE-containing promicelle polymers (PMTPE) from the depot and the spontaneous formation of micelles (MTPE) have been monitored from the self-assembly-induced fluorescence light-up both in vitro and in vivo. Compared with intravenous injection of MCPT, the micelle-generating depot has significantly enhanced micelle accumulation in the tumor for an extended period of time and resulted in stronger tumor inhibitory efficacy, reduced systemic toxicity and more effective inhibition of tumor metastasis, demonstrating great potential for targeted cancer therapy with sustained efficacy. STATEMENT OF SIGNIFICANCE: The promicelle polymer-co-electrospun fibers are developed to form a micelle-generating depot after implantation onto the tumor. The promicelle polymers are continuously released and simultaneously self-assemble into folate-targeted and glutathione-sensitive micelles, ensuring sustained micelle delivery for more than 30 days. The process of micelle formation in the tumor tissue is visualized in vivo for the first time based on the mechanism of aggregation-induced emission. This in situ micelle formation also prevents premature drug release and rapid clearance from the bloodstream. In addition, these fibers deliver anti-cancer agents directly within tumor cells via dual selectivity (i.e. spatially selective accumulation in tumor tissues via implantation and selective internalization into tumor cells via folate receptor-mediated endocytosis) and on-demand drug release in response to cytosol GSH. They exhibit superior tumor inhibitory efficacy with minimal systemic toxicity, and prevent from malignant metastasis of cancer cells.