Investigating the effect of a simplified perfume accord and dilution on the formation of mixed-surfactant microemulsions

The phase analysis of a mixed surfactant system is much more complex than that for a single surfactant system. The addition of fragrance further enhances the complexity of such colloidal systems. The wide variation in structure and log P values of perfume raw materials influence its partitioning into the micellar phase. Herein, we have created a simplified perfume accord consisting of three perfume raw materials (3-PRM) and investigated its loading within a mixed-surfactant system consisting of sodium trideceth-2 sulfate/ST2S and cocamidopropyl betaine/CAPB, along with citric acid and dipropylene glycol. We performed a systematic phase diagram analysis and identified the isotropic phases and compositions of interest. Select compositions from the phase diagram were further investigated to learn how the geometry of the surfactant self-assembly and the localization of the PRMs within the surfactant self-assembly changed when water or perfume is added. A combined small-angle neutron scattering/SANS and NMR methodology was used to identify variation in colloidal domains and positioning of perfume molecules at varying dilutions/rinse off scenarios. The results obtained were utilized to better distinguish distorted micelles from true microemulsions. The systematic investigation here provides a fundamental understanding about the self-assembly, encapsulation and perfume release from a commercially relevant mixed surfactant system.

Structural changes and phase analyses of a three-PRM accord in sodiumtrideceth-2 sulfate and cocamidopropyl betaine, citric acid and diproplylene glycol surfactant system as a function of dilution.     

A gemini surfactant-containing system with abundant self-assembly morphology and rheological behaviors tunable by photoinduction

Photoresponsive micellar systems with adjustable aggregate morphologies and rheological properties may be useful in a number of fields such as in microfluidics, controlled release, and sensors. However, the complexity and great difficulty of synthesising photosensitive molecules hamper their practical applications to a significant degree. In this study, we constructed a novel photoinduced self-assembly system by introducing the photoresponsive derivative trans-2-methoxy-cinnamate (trans-OMCA) into the gemini surfactant N,N′-bis(dodecyldimethyl)-1,2-ethane diammonium dibromide (12-2-12·2Br⁻) solutions. The system displays abundant phase behaviors, and the long worm-like micelles, vesicles, as well as an aqueous two-phase system (ATPS) are observed in the 12-2-12·2Br⁻/trans-OMCA mixed system even at lower surfactant concentrations. The UV-responsive behavior of the formed vesicles and the worm-like micelles is investigated systematically. The results have shown that OMCA undergoes photoisomerization from the trans-form to the cis-form through UV light irradiation that alters the molecular packing at the micellar interface and thus leads to the transformation of micellar morphologies. The long worm-like micelles will turn into much shorter units when the sample is exposed to 365 nm UV light accompanied by a decrease in solution viscosity by more than an order of magnitude. The formed vesicle system, however, can be utilized to generate a multi-state self-assembly structure, including a worm-like micelle and a small spherical micelle, depending on the UV irradiation time. The morphologies of micelles in a 12-2-12·2Br⁻/trans-OMCA mixed system can be tailored by adjusting the system composition and the duration of UV light irradiation. Correspondingly, the rheological behavior of the 12-2-12·2Br⁻/trans-OMCA mixed system can be purposely tuned. The light-induced system with abundant self-assembly behaviors and tunable rheological properties would widen the potential application of gemini surfactants in drug delivery, smart fluids, and materials science.

The photoisomerization of OMCA affects the degree of OMCA participation in the formation of mixed micelles and results in the transformation of micellar morphologies.     

Supramolecular thermogels from branched PCL-containing polyurethanes

Thermogels are temperature-responsive hydrogels which are most commonly formed by supramolecular self-assembly of polymer amphiphiles comprising of both hydrophobic and hydrophilic segments. Although polyurethane thermogels have shown great promise as biomaterials, their synthesis by step-growth polymerisation of diols and diisocyanates can also result in formation of allophanate branches, which arise from the reaction between free isocyanate groups and urethane linkages along the polymer backbone. In this paper, we investigate the effects of different synthetic conditions on the degree of allophanate branching on polyurethane amphiphiles, and explore the influences of these branches on the polymers'' critical micelle concentration (CMC), thermodynamics of micellization and subsequent thermogel properties. Our findings offer new insights into the relationship between polymer structure, micelle and gel properties. These results highlight the importance of taking polymer branching into account for understanding the hierarchical self-assembly of polymer amphiphiles and the resulting thermogel properties and behaviour.

Polymer branching exerts notable influence on the spontaneous temperature-triggered self-assembly of amphiphilic polymers into micelles and thermogels in water.     

Dissipative particle dynamics simulation of multicompartment micelle nanoreactor with channel for reactants

The structural variation of multicompartment micelles is investigated using a dissipative particle dynamics simulation method for nano-reactor application. It turns out that well-defined multicompartment micelles with channel structures can be generated through the self-assembly of triblock copolymers consisting of a hydrophilic (A), a lipophilic (B), and a fluorophobic (C) block arranged in a B–A–C sequence: The corona and core are formed by the hydrophilic A block and the fluorophilic C block, respectively while the channel between the aqueous phase and core is formed by the lipophilic B block and the core. By performing a set of simulations, it is confirmed that channel size can be controlled as a function of the block length ratios between blocks A and B. Furthermore, it is also confirmed that the reactants pass through such channels to reach the micelle core by analyzing the pair correlation functions. By monitoring the change of the number of reactants in the multicompartment micelle, it is revealed that the diffusion of reactants into the core is slowed down as the concentration gradient is decreased. This work provides mesoscopic insight for the formation of multicompartment micelles and transport of reactants for use in the design of micelles as nanoreactors.

The structural variation of multicompartment micelles is investigated using a dissipative particle dynamics simulation method for nano-reactor application.     

A nano-fibrous platform of copolymer patterned surfaces for controlled cell alignment

The last decade has witnessed great progress in understanding and manipulating self-assembly of block copolymers in solution. A wide variety of micellar structures can be created and many promising applications in bioscience have been reported. In particular, nano-fibrous micelles provide a great platform to mimic the filamentous structure of native extracellular matrix (ECM). However, the evaluation of this kind of filomicellar system with potential use in tissue engineering is virtually unexplored. The question behind it, such as if the block copolymer nano-fibrous micelles can regulate cellular response, has lingered for many years because of the difficulties in preparation and 3D manipulation of these tiny objects. Here, by using a combination approach of self-assembly of block copolymers and soft lithography, we establish a novel and unique nano-fibrous 2D platform of organized micelles and demonstrate that patterned micelles enable control over the cellular alignment behavior. The area density and orientation of fibrous micelles determine the alignment degree and directionality of cells, respectively. Furthermore, when cells were cultured on multi-directionally aligned micelles, a competitive response was observed. Due to the virtually infinite possibilities of functionalization of the micelle corona, our work opens a new route to further mimic the native fibrous networks with artificial micelles containing various functionalities.

A method to transfer-print quenched, ultra-long copolymer cylindrical micelles to a flat surface and the use of these nano-structures to promote spontaneous cell alignment is proposed. Endless possibilities of corona end-group chemical modification provide a new tool to control cell response.     

Biodegradable reduction and pH dual-sensitive polymer micelles based on poly(2-ethyl-2-oxazoline) for efficient delivery of curcumin

A series of disulfide-linked amphiphilic polymers polyoxaline-SS-poly(lactide) (PEtOx-SS-PLA) were prepared and self-assembled into nano-micelles in water. The anticancer drug curcumin (Cur) was selected as a model drug, the entrapment of Cur in PEtOx-SS-PLA micelles was investigated and the intracellular transport and release of Cur-loaded micelles was studied in C6 cells. The preparation of Cur-loaded polymer micelles showed that micelle size decreased after drug loading, favoring cell phagocytosis. MTT experiments showed that PEtOx-SS-PLA 52 micelles have a small IC₅₀ (2.05 μg mL⁻¹). The release behavior of PEtOx-SS-PLA 52 drug-loaded micelles in C6 cells showed that polymer micelle enhanced the intracellular release of Cur, and increased the inhibition effect of cancer cells. In a word, these reduction and pH-dual sensitive, biodegradable, hydrophilic shell-discarding PEtOx-SS-PLA micelles have great potential for future tumour administration.

A series of disulfide-linked amphiphilic polymers polyoxaline-SS-poly(lactide) (PEtOx-SS-PLA) were prepared and self-assembled into nano-micelles in water.     

Surfactant concentration modulates the motion and placement of microparticles in an inhomogeneous electric field

This study examined the effects of surfactants on the motion and positioning of microparticles in an inhomogeneous electric field. The microparticles were suspended in oil with a surfactant and the electric field was generated using sawtooth-patterned electrodes. The microparticles were trapped, oscillating, or attached to the electrodes. The proportion of microparticles in each state was defined by the concentration of surfactant and the voltage applied to the electrodes. Based on the trajectory of the microparticles in the electric field, we developed a new physical model in which the surfactant adsorbed on the microparticles allowed the microparticles to be charged by contact with the electrodes, with either positive or negative charges, while the non-adsorbed surfactant micellizing in the oil contributed to charge relaxation. A simulation based on this model showed that the charging and charge relaxation, as modulated by the surfactant concentration, can explain the trajectories and proportion of the trapped, oscillating, and attached microparticles. These results will be useful for the development of novel self-assembly and transport technologies and colloids sensitive to electricity.

This study revealed that surfactant micelles played two roles for microparticle motions in an inhomogeneous electric field (trapping, oscillating, or attachment to electrodes): particle charging and charge relaxation, depending on its concentration.     

Effect of solvophobicity on the phase behavior of linear ABC triblock copolymers in selective solvents: a Monte Carlo study

The microphase separation behavior of linear ABC triblock copolymers in A-selective solvents are studied using Monte Carlo simulation. The ABC triblock copolymer used in this study has a short solvophilic block A and two long solvophobic blocks B and C. The effects of the solvophobicity difference and the incompatibility between solvophobic blocks B and C on the micelle morphologies formed by linear ABC triblock copolymers are investigated, and phase diagrams as a function of the solvophobicity of blocks B and C are given at different repulsions between blocks B and C, respectively. A series of multicompartment micelles with distinct solvophobic parts is obtained, such as pupa-like multi-layered micelles, hamburger-like micelles and bumpy disks. Remarkably, when the solvophobicity of blocks B is much stronger than that of blocks C, a novel reverse core–shell–corona micelle with solvophilic blocks A located in the center of the micelle is obtained. Moreover, the results indicate that the competition between the effects of the incompatibility and solvophobicity difference between blocks B and C determines the microphase separation structures in the multicompartment micelles. These simulation results elucidate the mechanism of the formation of ABC triblock copolymer nanostructures and provide theoretical guidance for experimental studies.

The solvophobicity difference and incompatibility between different solvophobic blocks determine the overall shapes and micro-structures of micelles formed by linear ABC terpolymers.     

Formation of disk-like micelles of triblock copolymers in frustrating solvents

Coil–coil block copolymers rarely self-assemble into flat low-curvature micelles due to the lack of proper interchain association. Here, we report a facile route to prepare disk-like micelles through the self-assembly of amphiphilic polystyrene-b-polybutadiene-b-poly(2-vinylpyridine) triblock copolymers in a mixture of acetone and cyclohexane, which shows distinct selectivity towards the PS, PB and P2VP blocks. Subtle solvation/aggregation of these blocks in this frustrating solvent system provides access to low-curvature micellar structures, and thus favors the formation of uniform disk-like micelles. Further variation of the volume ratio of the mixed solvents also leads to the emergence of other interesting morphologies, including disk arrays, disk clusters and perforated disk-like micelles. This work provides a complementary insight into the solution self-assembly of block copolymers in a view of selective solvents and demonstrates a distinctive pathway to unconventional micellar nanostructures through the use of complex solvent systems.

Self-assembly of amphiphilic triblock copolymers in a frustrating solvent system leads to the formation of various low-curvature micellar structures.     

Amphiphilic poly(caprolactone-b-N-hydroxyethyl acrylamide) micelles for controlled drug delivery

To increase the bioavailability and water solubility of hydrophobic medicine, an amphiphilic block copolymer, polycaprolactone-block-polyhydroxyethyl acrylamide (PCL-b-PHEAA), was synthesized. The copolymer can self-assemble into micelles by dialysis. The micelles were characterized by the Tyndall effect, static drop method, fluorescence spectrometry, dynamic light scattering, scanning electron microscopy and transmission electron microscopy. Ibuprofen was encapsulated inside the micelles by dialysis as a model medicine. The results show that the amphiphilic copolymer forms a uniform micelle system, with spherical micelles dispersed well in solution which have a low critical micelle concentration. In addition, the system shows good amphipathic behavior. Average particle size of a micelle is 104 nm, which increases a lot after drug loading and standing for half a month. In the first few hours, the cumulative release of the drug increases gradually; the rate of increase in the first ten hours is faster, then reaching a plateau which tends to be flat finally. It is similar under two different pH conditions. This biocompatible, biodegradable amphiphilic block copolymer has potential applications in the biomedical field.

To increase the bioavailability and water solubility of hydrophobic medicine, an amphiphilic block copolymer, polycaprolactone-block-polyhydroxyethyl acrylamide (PCL-b-PHEAA), was synthesized.     

White-emitting film of diblock copolymer micelles with perovskite nanocrystals

Perovskite nanocrystals are synthesized in diblock copolymer micelles to improve their processability and stability. The copolymer micelle approach allows fluorescence from a stretchable or flexible substrate by coating processes, and stable emission in water by protecting the nanocrystals in the micelles. Fluorescent films in three primary colors of blue, green, and red are also produced with the assistance of anion exchange reactions for perovskite nanocrystals in the micelles. Then, by stacking films in three primary colors, we are able to produce a white-emitting film of copolymer micelles containing only perovskite nanocrystals without the support of other kinds of emissive materials.

A white-emitting film is produced by stacking films in three primary colors of diblock copolymer micelles containing perovskite nanocrystals without the support of other kinds of emissive materials.     

Molecular dynamics simulation of four typical surfactants in aqueous solution

The thermodynamic values of the four surfactants, anionic surfactants, nonionic surfactants, zwitterion surfactants and gemini surfactants, were calculated by molecular dynamics simulation. The calculated results of thermodynamic parameters showed that the four surfactant can form micelles spontaneously. The mainly force for micellization process is entropy-driven, and as the temperature increases, the entropy-driven contribution is gradually reduced. There are linear enthalpy–entropy compensation phenomena for the four surfactants. Among the studied four surfactants, the gemini surfactant is the easiest to form micelles and has good stability, the zwitterion surfactant is the second, and the anionic surfactant is the least stable.

The thermodynamic values of the four surfactants, anionic surfactants, nonionic surfactants, zwitterion surfactants and gemini surfactants, were calculated by molecular dynamics simulation.     

Electrolyte and pH-sensitive amphiphilic alginate: synthesis,self-assembly and controlled release of acetamiprid

In this study, a pH-responsive amphiphilic alginate (Ugi-Alg) was synthesized via Ugi reaction without using a catalyst. The structure of Ugi-Alg was confirmed by FT-IR and ¹H NMR spectroscopy. Amphiphilic alginate can form micelles in an aqueous medium due to it''s amphiphilic nature.. The impacts of Na⁺ concentration and pH on the micelle size were characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The dynamic light scattering observations showed that micelle size increases with the decrease in Na⁺ concentration in aqueous solution. However, the micelle size decreases first and then increases as the pH value decreases from 5.3 to 2.0. Transmission electron microscopy confirmed that the mean size of micelles is 30–200 nm. In addition, a model hydrophobic pesticide (acetamiprid) was loaded in the micelles. The encapsulation efficiency and release behavior of micelles were studied, which could be controlled by Na⁺ concentration and pH. The results indicated that encapsulation efficiency of acetamiprid increases from 55% to 96% due to the increase in Na⁺ concentration from 0.01 M to 0.3 M. Moreover, with the decrease in pH from 5.3 to 2.0, encapsulation efficiency increases from 55% to 80%. Furthermore, the data of acetamiprid release kinetics could be well-fitted by the Weibull model.

Schematic of Ugi-Alg aggregation in aqueous solution of different NaCl concentrations and pH values.     

Synthesis,characterization, physical and thermodynamic properties of a novel anionic surfactant derived from Sapindus laurifolius

The present study deals with the synthesis, characterization, physical and thermodynamic properties of a novel anionic surfactant derived from Sapindus laurifolius for its potential application against conventional non-biodegradable surfactants. The synthesized surfactant was characterized by FTIR, GC-MS, EDX and FE-SEM analyses. The surfactant showed good thermal stability at different temperatures as obtained from TGA studies. Critical micelle concentration (CMC) values were obtained by surface tensiometry measurements. DLS studies revealed the micelle structures of the CMC aggregates at higher concentrations. Low interfacial tension values were obtained at the oil–aqueous interfaces for surfactant solutions. The effect of temperature on the interfacial behaviour was also investigated. Thermodynamic studies showed that adsorption was more favoured in comparison to micellization for all systems. Foam stability studies were performed as a function of time and concentration by the Bartsch method. The surfactant also formed stable emulsions at concentrations near the CMC value. A comprehensive assessment of the thermal, interfacial, foaming and emulsifying properties of the soap-nut-based surfactant provides grounds for potential application in a wide range of industries.

The present study deals with the synthesis, characterization, physical and thermodynamic properties of a novel anionic surfactant derived from Sapindus laurifolius for its potential application against conventional non-biodegradable surfactants.     

Commutability assessment of potential reference materials using a multicenter split-patient-sample between-field-methods (twin-study) design: study within the framework of the Dutch project "Calibration 2000"

BACKGROUND: The Dutch project "Calibration 2000" aims at harmonization of laboratory results via calibration by development of commutable, matrix-based, secondary reference materials. An alternative approach to the NCCLS EP14 protocol for studying commutability of reference materials is presented, the "twin-study design", which in essence is a multicenter, split-patient-sample, between-field-methods protocol. METHODS: The study consisted of the simultaneous analysis of fresh patient sera and potential reference materials (PRMs) for HDL-cholesterol (HDL-C) by 86 laboratories forming 43 laboratory couples. Six subgroups of method combinations were formed. The patient sera were selected and interchanged by each laboratory couple. The PRMs consisted of three types: C37, prepared according to the NCCLS C37 protocol; Fro, frozen selectively pooled human serum; and Lyo, which was the same serum pool as Fro but lyophilized in the presence of sucrose. All PRMs were provided in three HDL-C concentrations. The regression line residuals for the PRMs were normalized by expressing them as multiples of the state-of-the-art within laboratory SD (SD(SA)). In addition, the extra contribution of each PRM to the total measurement uncertainty, CV(Netto), was calculated. RESULTS: Averaged over the three PRM concentrations, 1.6% of the C37 residuals were outside the 3 SD(SA) limit. For the Fro and Lyo PRMs, these values were 2.4% and 11.1%. CV(Netto) values for C37, Fro, and Lyo were 2.9%, 4.3%, and 5.3%, respectively. CONCLUSIONS: The present twin-study design, as a practical alternative to the NCCLS EP14 protocol, is a viable way of studying commutability characteristics of PRMs. The study suggests that the C37 PRMs are the best candidates for a future reference material.     

Computer simulation study on the self-assembly of tethered nanoparticles with tunable shapes

We built a tethered nanoparticle (TNP) model that is composed of a nanoparticle with a hydrophobic tethered polymer chain. The shape of the nanoparticle can be tuned from a pure rigid cube to a soft sphere, mimicking the increase of grafting density on the nanocube surfaces. With this model, we study the self-assembly of TNPs in dilute solution using a dissipative particle dynamics simulation technique, and especially focus on the influence of particle shape, tethered chain length, and grafting density on the self-assembly structures. Some intriguing aggregates such as spherical micelles, pearl-necklace-like structures, cubic columnar structures, handshake structures, core–shell–corona micelles, and four-patch micelles have been observed when varying the interactions between cubes and solvents and the lengths of tethered chain. Modifying the nanocube surface with some hydrophilic grafted chains helps the TNPs form small micelles. Increased steric repulsion due to chain overlapping at larger grafting densities results in shape transformation of the nanoparticle from a rigid cube to a soft sphere. In these cases, the self-assembled structures are characterized by the packing of nanoparticles on the micelle surface, and the typical packing mode turns from rectangular (typical for cubes) to hexagonal (typical for spheres).

The self-assembled structures are characterized by the packing of nanoparticles on the micelle surface, and the typical packing mode turns from rectangular (typical for cubes) to hexagonal (typical for spheres).     

Selection,preparation, and characterization of commutable frozen human serum pools as potential secondary reference materials for lipid and apolipoprotein measurements: study within the framework of the Dutch project "Calibration 2000"

BACKGROUND: The Dutch project "Calibration 2000" aims at harmonization of laboratory results via calibration by development of matrix-based secondary reference materials. We considered the selection, preparation, and characterization of 34 potential reference materials (PRMs). METHODS: Sixteen PRMs were prepared either strictly according to the NCCLS C37-A protocol or in a less stringent and more convenient way. In addition, 18 commercial, so-called human serum-based calibrators or controls were purchased and tested. Lipoprotein integrity was evaluated by examining the physicochemical characteristics of the materials. Commutability of the PRMs was assessed in 86 Dutch clinical laboratories, using a multicenter split-patient-sample between-field-method (twin-study) design. Normalized residuals of the PRMs with respect to the patient regression lines were calculated; in addition, the extra contribution of each PRM to the total measurement uncertainty (CV(Netto)) was calculated. On the basis of these results, the most native PRM was selected to investigate its potential to reduce interlaboratory variation and to improve lipid and apolipoprotein standardization. RESULTS: In general, only the NCCLS C37-A-type materials displayed normalized residuals below the decision limit for commutability and had small CV(Netto) values ranging between 0 and 3.8%. This contrasts with the findings in regularly pooled frozen sera and lyophilized cryoprotected PRMs. In two subsequent external quality assessment surveys, the NCCLS type C37-A materials contributed to reducing the intermethod lipid and (apo)lipoprotein variation to approximately 2-4%. CONCLUSIONS: NCCLS C37-A materials have a strong potential as secondary reference materials, not only for cholesterol but also for HDL-cholesterol, LDL-cholesterol, triglyceride, and apolipoprotein measurements.     

Mitochondria-targeted curcumin loaded CTPP–PEG–PCL self-assembled micelles for improving liver fibrosis therapy

Liver fibrosis, originating from activated hepatic stellate cells (HSCs), is receiving much attention in the treatment of clinical liver disease. In this study, mitochondria-targeted curcumin (Cur) loaded 3-carboxypropyl-triphenylphosphonium bromide–poly(ethylene glycol)–poly(ε-caprolactone) (CTPP–PEG–PCL) micelles were constructed to prolong the systemic circulation of Cur, improve the bioavailability of Cur and play a precise role in anti-fibrosis. The prepared Cur–CTPP–PEG–PCL micelles with a spherical shape had satisfactory dispersion, low critical micelle concentration (CMC) and high encapsulation efficiency (92.88%). The CTPP modification endowed good endosomal escape ability to the CTPP–PEG–PCL micelles, and micelles could be selectively accumulated in mitochondria, thereby inducing the enhanced cell proliferation inhibition of HSC-T6 cells. Mitochondrial Membrane Potential (MMP) was greatly reduced due to the mitochondrial-targeting of Cur. Moreover, the system circulation of Cur was extended and bioavailability was significantly enhanced in vivo. As expected, Cur loaded CTPP–PEG–PCL micelles were more effective in improving liver fibrosis compared with Cur and Cur–mPEG–PCL micelles. In conclusion, the Cur–CTPP–PEG–PCL based micelles can be a potential candidate for liver fibrosis treatment in future clinical applications.

A mitochondria-targeting micelle system based on CTPP–PEG–PCL polymer was designed to deliver curcumin to active HSC-T6 cells and prolong the systemic circulation and bioavailability of curcumin in vivo for effective treatment of liver fibrosis.     

Enzymatic dephosphorylation-triggered self-assembly of DNA amphiphiles

In this work, phosphorylated lipid-conjugated oligonucleotide (DNA-lipid-P) has been synthesized to develop an enzyme-responsive self-assembly of DNA amphiphiles based on dephosphorylation-induced increase of hydrophobicity. Since elevated ALP level is a critical index in some diseases, ALP-triggered self-assembly of DNA amphiphiles shows promise in disease diagnosis and cancer treatment.

Enzymatic dephosphorylation-triggered self-assembly of DNA amphiphiles is developed by integrating enzymatic dephosphorylation-induced increase of hydrophobicity and intermolecular aggregation of lipid-conjugated oligonucleotides.

Lipid-conjugated oligonucleotides are DNA amphiphiles that can self-assemble into lipid-based DNA micelles. As such, lipid tails act as a hydrophobic core and DNA act as a hydrophilic corona.^1–3 Because of their advantages of facile preparation, programmable design, small size (<100 nm) and biocompatibility, lipid-based DNA micelles show potential in the imaging of intracellular targets (mRNA and small molecules) and drug delivery.^4–6To further improve their potential for better drug delivery and disease diagnosis, stimuli-responsive control of the change of morphology or assembly/disassembly of DNA micelles has attracted enormous attention in practical applications. It was reported that photo-irradiation and nucleic acid hybridization have been used to trigger assembly/disassembly or the change of morphology of DNA micelles.^7–10 For example, Jin et al. developed stability-tunable DNA micelles by using photo-controllable dissociation of an intermolecular G-quadruplex.⁷ The intermolecular parallel G-quadruplexes were introduced into lipid-based DNA micelles to lock the whole structure, resulting in enhanced structural stability against disruption by serum albumin. However, photo-controlled release of complementary DNA blocks the formation of G-quadruplexes and thus leads to the dissociation of micelles by the existence of serum albumin. In addition, Chien et al. reported stimuli-responsive programmable shape-shifting DNA micelles by controlling geometric structure and electrostatics.⁸ DNA hybridization and dissociation change the geometric structure and electrostatics of hydrophilic moiety, leads to the conversion of DNA assemblies between spherical and cylindrical structures.In spite of these advances, enzyme-responsive regulation of self-assembly of DNA amphiphiles has scarcely reported. Since the hydrophobicity of lipid tail plays a critical role in the aggregation of DNA micelles, we speculated that the self-assembly of lipid-conjugated oligonucleotides can be regulated by controlling the hydrophobicity of lipid tails. Carry this idea forward, we noted that ALP is a hydrolase that removes phosphate groups from nucleic acids or proteins.^11,12 Remarkably, ALP has been widely employed to convert hydrophilic phosphorylated small molecules to hydrophobic dephosphorylated products for molecular imaging, disease diagnosis and cancer therapy.^13–16 Herein, therefore, enzymatic dephosphorylation-triggered self-assembly of DNA amphiphile is reported. As shown in Fig. 1, DNA-lipid-P is composed of four segments: DNA, linker, lipid and phosphate groups. Four negatively charged phosphate groups at lipid terminus decrease their hydrophobicity. Therefore, DNA-lipid-P exhibits weak self-assembly. However, ALP converts DNA-lipid-P to DNA-lipid by removing phosphate groups. The newly generated DNA-lipid shows greater hydrophobicity compared to DNA-lipid-P thus enables self-aggregation in aqueous solution.Open in a separate windowFig. 1Schematic illustration of enzymatic dephosphorylation-triggered self-assembly of DNA amphiphile.Lipid-conjugated oligonucleotides are amphiphiles which compose of two segments: hydrophobic lipid tails and hydrophilic oligonucleotides. Generally, lipid-conjugated oligonucleotides can self-assemble into aggregated DNA nanostructures, for example, DNA micelles, in aqueous solution by intermolecular hydrophobic interaction. To investigate whether the hydrophobicity affects the self-assembly of lipid-conjugated oligonucleotides, a series of lipid phosphoramidites with different length of alkyl chains (six, nine, twelve and fifteen) at the lipid tail were conjugated with oligonucleotide on a DNA synthesizer. The obtained lipid-conjugated oligonucleotides named as C6-DNA, C9-DNA, C12-DNA and C15-DNA, respectively (Fig. 2a). High-performance liquid chromatography (HPLC) is a universal tool to assess the hydrophobicity of DNA by comparing their retention times. Greater retention time indicates the stronger hydrophobicity. As shown in Table S2,^† the retention time of DNA, C6-DNA, C9-DNA, C12-DNA and C15-DNA is 10.0, 19.1, 23.8, 27.3 and 30.8 minutes, respectively, suggesting that DNA with longer alkyl chains has stronger hydrophobicity. The result is consistent with the previous report.¹⁷ Next, the self-assembly of these lipid-conjugated oligonucleotides was investigated by agarose gel electrophoresis and dynamic light scattering (DLS) assays. As shown in Fig. 2b, only C15-DNA shows a tailed nucleic acids band which is belongs to the self-assembled nanostructure. In addition, results of DLS assays exhibit that the particle size of 10 μM C6-DNA, C9-DNA, C12-DNA and C15-DNA in buffer solution is 2.7 nm, 4.2 nm, 6.5 nm and 28.2 nm, respectively (Fig. 2c). Besides, the morphology of self-assembled C15-DNA micelles was visualized with atomic force microscopy (AFM) and the result shows the spherical nanostructure with diameter of 36.8 ± 6.1 nm (Fig. S7^†). Both evidences support the self-assembly of C15-DNA in buffer solution. In another word, the self-assembly of lipid-conjugated oligonucleotides into DNA micelles is hydrophobicity-dependent. A greater hydrophobicity indicates a stronger tendency of aggregation.Open in a separate windowFig. 2Hydrophobicity-dependent self-assembly of lipid-conjugated oligonucleotides. (a) Chemical structures of lipid-conjugated oligonucleotides with different length of alkyl chains at the terminus of lipid tail. (b) 1% agarose gel electrophoresis analysis of 1 μM TAMRA-labeled C6-DNA, C9-DNA, C12-DNA and C15-DNA. C15-DNA shows a tailed band in agarose gel which can be attributed to the formation of aggregated micellar nanostructure. (c) DLS size analysis of C6-DNA, C9-DNA, C12-DNA and C15-DNA in buffer solution. The average size of C6-DNA, C9-DNA, C12-DNA and C15-DNA in buffer solution is 2.7 nm, 4.2 nm, 6.5 nm and 28.2 nm, respectively.Next, we further synthesize DNA-lipid-P by solid-phase synthesis and phosphoramidite chemistry. In a previous literature, we developed a novel lipid phosphoramidite in which two DMT-protected hydroxyl groups was modified at the terminus of lipid tails thus enables further chemical phosphorylation during DNA synthesis.¹⁷ As shown in Fig. 3, linker and lipid phosphoramidites were successively conjugated at the 5′-terminus of DNA, followed by coupling with chemical phosphorylation reagent. After deprotection and purification, DNA-lipid-P was obtained and characterized by mass spectrum. As shown in Fig. S8,^† the calculated molecular weight of DNA-lipid-P is 7789.8 Da, and the observed molecular weight is 7792.4 Da. The mass error is 2.6 Da (0.03%) which is within the mass error tolerance (0.03%), suggesting the successful synthesis of DNA-lipid-P. As such, DNA-lipid was also successfully synthesized with high purity (>98%) (Fig. S9^†).Open in a separate windowFig. 3Solid-phase synthesis route of DNA-lipid-P.Having confirmed the successful synthesis of DNA-lipid-P, we further investigate the self-assembly of DNA-lipid and DNA-lipid-P in buffer solution. Nile red, a fluorescent dye that exhibits significant fluorescence in hydrophobic media, but negligible emission in aqueous solution, was used to determine the encapsulation of guest molecules to further assess the formation of the micellar structure.^7,18 Nile red (1 μM) were incubated with various concentrations of DNA, DNA-lipid or DNA-lipid-P and the corresponding fluorescence spectroscopies were recorded. As shown in Fig. 4, both DNA (Fig. 4b) and DNA-lipid-P (Fig. 4c) show weaker fluorescence emission at 630 nm, even the concentration was upper to 10 μM. However, DNA-lipid (Fig. 4d) exhibits a bright fluorescence emission at 630 nm, suggesting the formation of hydrophobic core. After calculation, the critical micelle concentration (CMC) of DNA-lipid is 0.36 μM (Fig. 4e). The remarkable difference of CMC between DNA-lipid and DNA-lipid-P indicates that enzymatic conversion of DNA-lipid-P to DNA-lipid could trigger the spontaneous intermolecular aggregation.Open in a separate windowFig. 4Characterizations of self-assembly of DNA-lipid-P and DNA-lipid. (a) The chemical structures of DNA-lipid and DNA-lipid-P. Fluorescence spectroscopies of Nile red-encapsulated DNA (b), DNA-lipid-P (c) and DNA-lipid (d) in buffer solution. The concentration of Nile red is 1 μM. (e) Fluorescence intensity of Nile red-encapsulated DNA, DNA-lipid-P and DNA-lipid at 630 nm. The CMC of DNA-lipid is 0.36 μM, and the CMC of DNA-lipid-P is larger than 10 μM.Next, ALP was used to convert DNA-lipid-P to DNA-lipid (Fig. 5a). As shown in Fig. 5b (black and red lines), the retention time of DNA-lipid and DNA-lipid-P is 26.5 and 20.9 minutes, respectively, indicates that the phosphorylation of lipid tail indeed decreases the hydrophobicity of lipid-conjugated oligonucleotides. Then, ALP was incubated with DNA-lipid-P (10 μM) at 37 °C for ten minutes and then 75 °C for five minutes to deactivate ALP, followed by subjected to fluorescence measurements. As shown in Fig. 5b (pink line), after the treatment of ALP (2 U), the DNA peak of DNA-lipid-P at 20.9 minutes disappeared; instead, a new DNA peak at 26.5 minutes was observed. Mass spectrum analysis indicates that the molecular weight of newly generated DNA peak is 7474.2 Da, which is consistent with the calculated molecular weight of DNA-lipid (7470.9 Da) (Fig. S10^†). In a word, ALP enables enzymatic dephosphorylation of DNA-lipid-P; and the generated DNA-lipid has greater hydrophobicity than DNA-lipid-P thus facilitates the controllable self-assembly into DNA micelles.Open in a separate windowFig. 5Enzymatic dephosphorylation of DNA-lipid-P. (a) Schematic of ALP-induced conversion of DNA-lipid-P to DNA-lipid. (b) HPLC chromatograms of DNA-lipid-P (black line), DNA-lipid (red line), and DNA-lipid-P treated with ALP (0.1 U (blue line), 1 U (green line) and 2 U (pink line)) in buffer solution.Encouraged by the ALP-induced dephosphorylation of DNA-lipid-P to DNA-lipid, we further assess whether ALP enables activatable self-assembly of DNA-lipid-P. As shown in Fig. 6a, DNA-lipid-P (1 μM) shows weak self-assembly in buffer solution. However, DNA-lipid (1 μM) exhibits obvious aggregation band in gel electrophoresis assay. After incubation with ALP (1 U), DNA-lipid-P + ALP group also shows tailed band which suggests the formation of aggregated nanostructures. In addition, results of Nile red-encapsulated fluorescence experiments also support the conclusion of ALP-activate self-assembly of DNA-lipid-P (Fig. 6b). Therefore, ALP-induced enzymatic dephosphorylation triggers the self-assembly of DNA-lipid-P.Open in a separate windowFig. 6Enzymatic dephosphorylation-triggered self-assembly of DNA-lipid-P. (a) 1% agarose gel electrophoresis analysis of DNA-lipid-P (lane 1), DNA-lipid (lane 2) and DNA-lipid-P treated with ALP (1 U) (lane 3). (b) Fluorescence spectroscopies of Nile red-encapsulated DNA-lipid, DNA-lipid (ALP), DNA-lipid-P or DNA-lipid-P (ALP).In summary, enzymatic dephosphorylation-triggered self-assembly of DNA amphiphile is developed by integrating enzymatic dephosphorylation-induced increase of hydrophobicity and intermolecular aggregation of lipid-conjugated oligonucleotides. The strategy may also suitable for many other amphiphiles. Since elevated ALP level is a critical index in some diseases and even cancers, we believe that ALP-triggered self-assembly of DNA-lipid-P shows potential in disease diagnosis and cancer therapy.     

Directional effect on the fusion of ellipsoidal morphologies into nanorods and nanotubes

Particle fusion is well-recognized as an important spontaneous process to produce higher-order nanostructures during morphology transition in polymerization-induced self-assembly (PISA). However, to our knowledge, the directional contact, adhesion, and fusion of adjacent nanoparticles have been rarely elucidated in PISA. Herein, a directional fusion of ellipsoidal morphologies was demonstrated during PISA of semi-fluorinated liquid-crystalline (SFLC) block copolymers. The ellipsoidal nanostructures, including micelles and vesicles, preferred to undergo a directional fusion in a head-to-head model, leading to the formation of nanorods and nanotubes, respectively. We believe the directional fusion will offer insightful guidance in PISA to the preparation of complicated functional nanostructures.

Herein, a directional fusion of ellipsoidal morphologies into nanorods and nanotubes was demonstrated through the study of polymerization-induced self-assembly behaviors of semi-fluorinated liquid-crystalline block copolymers.