Integrated nanoreactor systems: triggering the release and mixing of compounds inside single vesicles

We present a method that allows the on-demand release and mixing of zepto- to femtoliter volumes of solutions in the interior of vesicular nanoreactors. The reactors comprise a nested system of lipid vesicles, part of which release their cargo in the interior of the others during a thermotropic phase transition. The performance of individual reactors immobilized on glass is characterized using confocal microscopy and a fluorescent dye that reports dilution during the release. The results confirm the predicted temperature-induced response and reveal a release transition width of 3 degrees C with a half time of approximately 1 min.     

Synthesis of Chemically Asymmetric Silica Nanobottles and Their Application for Cargo Loading and as Nanoreactors and Nanomotors

We report the synthesis of chemically asymmetric silica nanobottles (NBs) with a hydrophobic exterior surface (capped with 3‐chloropropyl groups) and a hydrophilic interior surface for spatially selective cargo loading, and for application as nanoreactors and nanomotors. The silica NBs, which have a “flask bottle” shape with an average diameter of 350 nm and an opening of ca. 100 nm, are prepared by anisotropic sol–gel growth in a water/n‐pentanol emulsion. Due to their chemically asymmetric properties, nanoparticles (NPs) with hydrophilic or hydrophobic surface properties can be selectively loaded inside the NBs or on the outside of the NBs, respectively. A high‐performance nanomotor is constructed by selectively loading catalytically active hydrophilic Pt NPs inside the NBs. It is also demonstrated that these NBs can be used as vessels for various reactions, such as the in situ synthesis of Au NPs, and using Au NP‐loaded NBs as nanoreactors for catalytic reactions.     

Multicompartmental Microcapsules with Orthogonal Programmable Two‐Way Sequencing of Hydrophobic and Hydrophilic Cargo Release

Multicompartmental responsive microstructures with the capability for the pre‐programmed sequential release of multiple target molecules of opposite solubility (hydrophobic and hydrophilic) in a controlled manner have been fabricated. Star block copolymers with dual‐responsive blocks (temperature for poly(N‐isopropylacrylamide) chains and pH for poly(acrylic acid) and poly(2‐vinylpyridine) arms) and unimolecular micellar structures serve as nanocarriers for hydrophobic molecules in the microcapsule shell. The interior of the microcapsule can be loaded with water‐soluble hydrophilic macromolecules. For these dual‐loaded microcapsules, a programmable and sequential release of hydrophobic and hydrophilic molecules from the shell and core, respectively, can be triggered independently by temperature and pH variations. These stimuli affect the hydrophobicity and chain conformation of the star block copolymers to initiate out‐of‐shell release (elevated temperature), or change the overall star conformation and interlayer interactions to trigger increased permeability of the shell and out‐of‐core release (pH). Reversing stimulus order completely alters the release process.     

Encapsulation and Release Mechanisms in Coordination Polymer Nanoparticles

The interplay of guest encapsulation and release mechanisms in nanoscale metal–organic vehicles and its effect on the drug‐delivery kinetics of these materials were investigated through a new multidisciplinary approach. Two rationally‐designed molecular guests were synthesized, which consist of a red‐fluorescent benzophenoxazine dye covalently tethered to a coordinating catechol group and a protected, non‐coordinating catechol moiety. This allowed loading of the guests into compositionally and structurally equivalent coordination polymer particles through distinct encapsulation mechanisms: coordination and mechanical entrapment. The two types of particles delivered their fluorescent cargo with remarkably different kinetic profiles, which could be satisfactorily modeled considering degradation‐ and diffusion‐controlled release processes. This demonstrates that careful selection of the method of guest incorporation into coordination polymer nanoparticles allows selective tuning of the rate of drug delivery from these materials and, therefore, of the time window of action of the encapsulated therapeutic agents.     

Mono‐allyloxylated Cucurbit[7]uril Acts as an Unconventional Amphiphile To Form Light‐Responsive Vesicles

Serendipitously, mono‐allyloxylated cucurbit[7]uril (AO₁CB[7]) was discovered to act as an unconventional amphiphile which self‐assembles into light‐responsive vesicles (AO₁CB[7]VC) in water. Although the mono‐allyloxy group, directly tethered on the periphery of CB[7], is much shorter (C4) than the hydrophobic tails of conventional amphiphiles, it played an important role in vesicle formation. Light‐activated transformation of the allyloxy group by conjugation with glutathione was exploited as a remote tool to disrupt the vesicle. The vesicle showed on‐demand release of cargo upon irradiation by a laser, after they were internalized into cancer cells. This result demonstrated the potential of AO₁CB[7]VC as a new type of light‐responsive intracellular delivery vehicle for the release of therapeutic cargo, within cells, on demand.     

Multistimuli responsive micelles formed by a tetrathiafulvalene-functionalized amphiphile

An electroactive tetrathiafulvalene (TTF)-functionalized amphiphile 1 was designed and synthesized to investigate its self-assembling behavior in water. Dynamic light scattering (DLS), (1)H NMR, fluorescence spectrum, and cryogenic transmission electron microscopy (cryo-TEM) studies revealed that amphiphile 1 can form micelle-like aggregates via direct dissolution into water, and the micellar architectures could be disrupted either by addition of chemical oxidant Fe(ClO(4))(3) or by complexation with electron-deficient cyclobis(paraquat-p-phenylene) tetracation cyclophane (CBPQT(4+)) to release encapsulated hydrophobic dye Nile Red from the interior of micelles.     

Enzyme‐Responsive Silica Mesoporous Supports Capped with Azopyridinium Salts for Controlled Delivery Applications

The preparation of a new capped silica mesoporous material, Rh‐Azo‐S , for on‐command delivery applications in the presence of target enzymes is described. The material consists of nanometric mesoporous MCM‐41‐like supports loaded with Rhodamine B and capped with an azopyridine derivative. The material was designed to show “zero delivery” and to display a cargo release in the presence of reductases and esterases, which are usually present in the colon, mainly due to intestinal microflora. The opening and cargo release of Rh‐Azo‐S in vitro studies were assessed and seen to occur in the presence of these enzymes, whereas no delivery was noted in the presence of pepsine. Moreover, Rh‐Azo‐S nanoparticles were used to study controlled Rhodamine B dye delivery in intracellular media. HeLa cells were employed for testing the “non”‐toxicity of nanoparticles. Moreover, delivery of the dye in these cells, through internalization and enzyme‐mediated gate opening, was confirmed by confocal microscopy. Furthermore, the nanoparticles capped with the Azo group and loaded with a cytotoxic camptothecin ( CPT ) were also prepared (solid CPT‐Azo‐S ) and used as delivery nanodevices in HeLa cells. When this solid was employed, the cell viability decreased significantly due to internalization of the nanoparticles and delivery of the cytotoxic agent.     

A Polymeric Bowl for Multi‐Agent Delivery

This paper describes a simple system for multi‐agent delivery. The system consists of a biodegradable polymer particle with a hollow interior, together with a hole on its surface that can be completely or partially sealed via thermal annealing. A hydrophobic dye, Nile‐red, entrapped within the shell of hollow particles presents a sustained release behavior while methylene blue, a hydrophilic model agent, encapsulated in the hollow interior shows a fast release manner. The release profiles of the probes can be further independently controlled by encapsulating methylene blue‐loaded polymer nanoparticles, instead of free dye, in the hollow particle with a small hole on its surface.

     

Size‐Selective Encapsulation of Hydrophobic Guests by Self‐Assembled M4L6 Cobalt and Nickel Cages

Subtle differences in metal–ligand bond lengths between a series of [M₄L₆]^4? tetrahedral cages, where M=Fe^II, Co^II, or Ni^II, were observed to result in substantial differences in affinity for hydrophobic guests in water. Changing the metal ion from iron(II) to cobalt(II) or nickel(II) increases the size of the interior cavity of the cage and allows encapsulation of larger guest molecules. NMR spectroscopy was used to study the recognition properties of the iron(II) and cobalt(II) cages towards small hydrophobic guests in water, and single‐crystal X‐ray diffraction was used to study the solid‐state complexes of the iron(II) and nickel(II) cages.     

Azobenzene Polyesters Used as Gate‐Like Scaffolds in Nanoscopic Hybrid Systems

The synthesis and characterisation of new capped silica mesoporous nanoparticles for on‐command delivery applications is reported. Functional capped hybrid systems consist of MCM‐41 nanoparticles functionalised on the external surface with polyesters bearing azobenzene derivatives and rhodamine B inside the mesopores. Two solid materials, Rh‐PAzo8‐S and Rh‐PAzo6‐S, containing two closely related polymers, PAzo8 and PAzo6, in the pore outlets have been prepared. Materials Rh‐PAzo8‐S and Rh‐PAzo6‐S showed an almost zero release in water due to steric hindrance imposed by the presence of anchored bulky polyesters, whereas a large delivery of the cargo was observed in the presence of an esterase enzyme due to the progressive hydrolysis of polyester chains. Moreover, nanoparticles Rh‐PAzo8‐S and Rh‐PAzo6‐S were used to study the controlled release of the dye in intracellular media. Nanoparticles were not toxic for HeLa cells and endocytosis‐mediated cell internalisation was confirmed by confocal microscopy. Furthermore, the possible use of capped materials as a drug‐delivery system was demonstrated by the preparation of a new mesoporous silica nanoparticle functionalised with PAzo6 and loaded with the cytotoxic drug camptothecin (CPT‐PAzo6‐S). Following cell internalisation and lysosome resident enzyme‐dependent gate opening, CPT‐PAzo6‐S induced CPT‐dependent cell death in HeLa cells.     

Acid‐Labile Acyclic Cucurbit[n]uril Molecular Containers for Controlled Release

Stimuli‐responsive molecular containers are of great importance for controlled drug delivery and other biomedical applications. A new type of acid labile acyclic cucurbit[n ]uril (CB[n ]) molecular containers is presented that can degrade and release the encapsulated cargo at accelerated rates under mildly acidic conditions (pH 5.5–6.5). These containers retain the excellent recognition properties of CB[n ]‐type hosts. A cell culture study demonstrated that the cellular uptake of cargos could be fine‐tuned by complexation with different containers. The release and cell uptake of cargo dye was promoted by acidic pH.     

Thermal actuation of hydrogels from PNIPAm,alginate, and carbon nanofibres

Composite ionic‐covalent entanglement (ICE) hydrogel networks were prepared from poly(N‐isopropylacrylamide), alginate, and carbon nanofibres. An optimised triple network hydrogel with 86% water content exhibited a compressive strength of 3.0 ± 0.1 MPa and 66 ± 13 mS/cm electrical conductivity. Thermal actuation was shown to have a shorter response time for gels containing nanofibres, compared to those which did not and hydrogel samples more than halved in volume within 1 minute when placed in a 60 °C water bath. Controlled dye release was demonstrated as a potential application and used to further quantify thermal actuation over short times. Joule heating techniques were used to electronically actuate the hydrogel samples, removing the traditional requirements for immersion in a temperature controlled liquid. It is expected that devices based on these materials will find potential applications in soft robotics and micro fluidics. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 46–52     

All‐Silica Submicrometer Colloidosomes for Cargo Protection and Tunable Release

Colloidosomes have received considerable attention for the controlled delivery of active ingredients in medicine, agrochemicals, and cosmetics. However, most reported colloidosomes are highly permeable and size is larger than 1 μm. All silica colloidosomes have now been prepared with adjustable size, compact shell and low permeability. Our approach is based on the formation of inverse water‐in‐oil (w/o) emulsions stabilized solely by hydrophobic silica nanoparticles and subsequent locking of the particle at the oil–water interface by a simple sol–gel reaction of silica precursor at room temperature. The colloidosomes obtained display a robust and closed shell, ensuring a long‐term retention of small hydrophilic molecules such as Methylene Blue. Remarkably, unlike all other reported silica colloidosomes, a timely and stepwise release of the encapsulated cargo can be triggered by adding ethanol or surfactant without destroying the capsule shell.     

Modulating Guest Uptake in Core–Shell MOFs with Visible Light

A two‐component core–shell UiO‐68 type metal–organic framework (MOF) with a nonfunctionalized interior for efficient guest uptake and storage and a thin light‐responsive outer shell was prepared by initial solvothermal MOF synthesis followed by solvent‐assisted linker exchange. The bulky shell linker features two tetra‐ortho‐fluorinated azobenzene moieties to exploit their advantageous photoisomerization properties. The obtained perfect octahedral MOF single crystals can be switched repeatedly and with an unprecedented efficiency between E‐ and Z‐rich states using visible light only. Due to the high photoswitch density per pore of the shell layer, its steric demand and thus molecular uptake (and release) can be conveniently modulated upon green and blue light irradiation. Therefore, the “smart” shell acts as a light‐controlled kinetic barrier or “gate” for the diffusion of cargo molecules in and out of the MOF crystals.     

Morphology Regulation in Redox Destructible Amphiphilic Block Copolymers and Impact on Intracellular Drug Delivery

In two ABA type amphiphilic block copolymers (P1, P2), the hydrophobic B block consists of a bioreducible segmented poly(disulfide) (PDS), while poly‐N‐isopropylacrylamide (PNIPAM) or poly(triethyleneglycol)methylether‐methacrylate (PTEGMA) serve as the hydrophilic A blocks in P1 and P2, respectively, leading to the formation of polymersome and micelle, owing to the difference in the packing parameters. Both exhibit comparable doxorubicin (Dox) encapsulation efficiency, but glutathione (GSH) triggered release appears much faster from the polymersome than micelle owing to the complete degradation of the PDS segment in polymersome morphology unlike in micelle. Dox‐loaded polymers (P1‐Dox and P2‐Dox) exhibit minimum toxicity to normal cells like C2C12. By contrast, P1‐Dox shows excellent killing efficiency to the HeLa cells (cancer cell) (in which the GSH concentration is significantly higher). However, P2‐Dox reveals a rather poor activity even to HeLa cells. Fluorescence microscopy studies show comparable cellular uptake of P1‐Dox and P2‐Dox. But the polymersome entrapped dye escapes fast from the cargo and reach the nucleus, while the drug‐loaded micelle remains trapped in the perinuclear zone explaining the significant difference in the drug delivery performance of polymersome and micelle.     

A New Multiresponsive Drug Delivery System using Smart Nanogels

This paper addresses the synthesis and characterization of a novel temperature‐ and pH‐responsive nanogel system based on poly(vinylcaprolactam‐co‐2‐dimethylaminoethyl methacrylate) [P(VCL‐co‐DMAEMA)] by using a surfactant‐free emulsion polymerization procedure for the multiresponsive drug delivery of hydrophobic drugs. The effects of solvent, monomer, pH, and temperature were studied to tailor the average particle hydrodynamic diameters and the polydispersity index of the final particles. According to dynamic light‐scattering measurements, the obtained nanogels show a narrow particle‐size distribution and their hydrodynamic diameters can be varied from 81 to 368 nm. The nanogels display a re‐entrant phase‐transition state, and the equilibrium volume swelling ratio of the nanogels decreases drastically down to 47 °C and then increases up to 65 °C. In addition, the nanogels show pH‐dependent behavior. They exhibit a maximum size at pH 5.0. Rhodamine B (RhB) was chosen as a model compound for drug loading and release studies from P(VCL‐co‐DMAEMA) on the basis of particles in different phosphate buffer solutions at different temperatures. The temperature/pH‐dependent cumulative release and ultrasound‐enhanced pulsatile release properties were investigated for RhB‐loaded nanogels for long‐term and one‐shot delivery. The nanogels display efficient delivery for both long‐term and one‐shot delivery systems. We provide here a proof of concept for the novel use of multiresponsive nanogels having an overall size below 200 nm as a cargo system for hydrophobic drugs and for controlled release mediated by temperature/pH and ultrasound.     

Multistimuli responsive amphiphilic graft poly(ether amine): Synthesis,characterization, and self‐assembly in aqueous solution

We reported that multiresponsive amphiphilic graft poly(ether amine)s (agPEAs) comprised of hydrophilic poly(ethylene oxide) (PEO) and hydrophobic octadecyl alkyl chain as side‐chain were prepared through one‐pot synthesis. In aqueous solution, these obtained agPEAs can self‐assemble into stable nanomicelles, whose aggregation can be controlled by temperature, pH, and ionic strength with tunable cloud point (CP). In the presence of these obtained agPEAs, hydrophobic dye Nile red can be dispersed into aqueous solution and hydrophilic dye methyl orange can be dispersed into nonpolar toluene. The agPEAs are expected to be potential in application such as encapsulation and controlled release of drugs, due to their simple synthesis, amphiphilicity, and multistimuli response. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 327–335, 2010     

Cathepsin‐B Induced Controlled Release from Peptide‐Capped Mesoporous Silica Nanoparticles

New capped silica mesoporous nanoparticles for intracellular controlled cargo release within cathepsin B expressing cells are described. Nanometric mesoporous MCM‐41 supports loaded with safranin O ( S1‐P ) or doxorubicin ( S2‐P ) containing a molecular gate based on a cathepsin B target peptidic sequence were synthesized. Solids were designed to show “zero delivery” and to display cargo release in the presence of cathepsin B enzyme, which selectively hydrolyzed in vitro the capping peptide sequence. Controlled delivery in HeLa, MEFs WT, and MEFs lacking cathepsin B cell lines were also tested. Release of safranin O and doxorubicin in these cells took place when cathepsin B was active or present. Cells treated with S2‐P showed a fall in cell viability due to nanoparticles internalization, cathepsin B hydrolysis of the capping peptide, and cytotoxic agent delivery, proving the possible use of these nanodevices as new therapeutic tools for cancer treatment.     

Fighting Aggregation‐Caused Quenching and Leakage of Dyes in Fluorescent Polymer Nanoparticles: Universal Role of Counterion

Dye‐loaded polymer nanoparticles (NPs) emerge as a powerful tool for bioimaging applications, owing to their exceptional brightness and controlled small size. However, aggregation‐caused quenching (ACQ) and leakage of dyes at high loading remain important challenges of these nanomaterials. The use of bulky hydrophobic counterions has been recently proposed as an effective approach to minimize ACQ and dye leakage, but the role of counterion structure is still poorly understood. Here, a systematic study based on ten counterions, ranging from small hydrophilic perchlorate up to large hydrophobic tetraphenylborate derivatives, reveals how counterion nature can control encapsulation and emission of a cationic dye (rhodamine B octadecyl ester) in NPs prepared by nanoprecipitation of a biodegradable polymer, poly‐lactide‐co‐glycolide (PLGA). We found that increase in counterion hydrophobicity enhances dye encapsulation efficiency and prevents dye adsorption at the particle surface. Cellular imaging studies revealed that ≥95 % encapsulation efficiency, achieved with most hydrophobic counterions (fluorinated tetraphenylborates), is absolutely required because non‐encapsulated dye species at the surface of NPs are the origin of dye leakage and strong fluorescence background in cells. The size of counterions is found to be essential to prevent ACQ, where the largest species, serving as effective spacer between dyes, provide the highest fluorescence quantum yield. Moreover, we found that the most hydrophobic counterions favor dye–dye coupling inside NPs, leading to ON/OFF fluorescence switching of single particles. By contrast, less hydrophobic counterions tend to disperse dyes in the polymer matrix favoring stable emission of NPs. The obtained structure‐property relationships validate the counterion‐based approach as a mature concept to fight ACQ and dye leakage in the development of advanced polymeric nanomaterials with controlled optical properties.     

Controlled and Tunable Loading and Release of Vesicles by Using Gigahertz Acoustics

Controllable exchange of molecules between the interior and the external environment of vesicles is critical in drug delivery and micro/nano‐reactors. While many approaches exist to trigger release from vesicles, controlled loading remains a challenge. Herein, we show that gigahertz acoustic streaming generated by a nanoelectromechanical resonator can control the loading and release of cargo into and from vesicles. Polymer‐shelled vesicles showed loading and release of molecules both in solution and on a solid substrate. We observed deformation of individual giant unilamellar vesicles and propose that the shear stress generated by gigahertz acoustic streaming induces the formation of transient nanopores, with diameters on the order of 100 nm, in the vesicle membranes. This provides a non‐invasive method to control material exchange across membranes of different types of vesicles, which could allow site‐specific release of therapeutics and controlled loading into cells, as well as tunable microreactors.