Cell-Mimic Directional Cargo Transportation in a Visible-Light-Activated Colloidal Motor/Lipid Tube System.

Active tether and transportation of cargoes on cytoskeletal highway enabled by molecular motors is key for accurate delivery of vesicles and organelles in the complex intracellular environment. Here, a hybrid system composed of colloidal motors and self-assembled lipid tubes is designed to mimic the subcellular traffic system in living cells. The colloidal motors, composed of gold-coated hematite, display light-activated self-propulsion tunable by the light intensity and the concentration of hydrogen peroxide fuel. Importantly, the motors show light-switchable binding with lipid cargoes and attachment to the lipid tubes, whereby the latter act as the motor highways. Upon assembly, the colloidal motor/lipid tube system demonstrates directional delivery of lipid vesicles, emulating intracellular transportation. The assembly and function of the hybrid system are rationalized by a cooperative action of light-triggered electrophoretic and hydrodynamic effects, supported by finite element analysis. A synthetic analog of the biological protein motor/cytoskeletal filament system is realized for the manipulation and delivery of different matter at the microscale, which is expected to be a promising platform for various applications in materials science, nanotechnology, microfluidics, and synthetic biology.

Inorganic-Organic Hybrid Copolymeric Colloids as Multicolor Emission, Fuel-Free, UV- and Visible-Light-Actuated Micropumps.

Light-actuated micromachines are of enormous interest due to their ability to harvest light for triggering catalytic reactions to acquire free energy for mechanical work. This work presents an inorganic-organic hybrid copolymeric poly(cyclotriphosphazene-co-barbituric acid) colloid, which displays multiwavelength excited emission and catalytic activities, exploiting the unique structural, chemical, and optical features of inorganic heterocyclic ring hexachlorocyclotriphosphazene and organic co-monomer barbituric acid. Specifically, this work reveals particle-resolved unusual multicolor emission under excitation with the same or different wavelengths of light using fluorescence microscopy. The result is rationalized by density functional theory studies. In this work, the authors find that emission is coincident with fluorometric measurements, and the photocatalytic properties are anticipated from the overall band structure. This work also demonstrates the use of these colloids as micropumps, which can be remotely activated by UV, blue, and green lights under fuel-free conditions, and ascribe the behavior to ionic diffusiophoresis arising from light-triggered generation of H+ and other charged species. This work offers a new class of polymeric colloids with multiple-wavelength excited emission and catalytic activities, which is expected to open new opportunities in the design of fuel-free, photo-actuated micromachines and active systems.

Magnetic Manipulation and Assembly of Nonmagnetic Colloidal Rods in a Ferrofluid.

We investigated experimentally and theoretically the interactions and assembly of rodlike colloids in a ferrofluid confined at solid/liquid interface by the gravity under external magnetic fields. We first derived analytical expressions for the interaction energy of a single rod with the external magnetic field and the interaction between two rods using classical electromagnetism. The theory well captured the experimentally observed alignment of a single rod along the field direction under an in-plane field and switching between the horizontal and the vertical configurations in an out-of-plane field due to the competition between the magnetic energy and the gravitational energy. The theory can also predict the symmetric position fluctuations of a free rod on a fixed one at 90° and the gradual bias toward the end of the fixed rod as the angle was reduced to 0°, favoring the tip-toe arrangement. Finally, we showed that this anisotropic interaction led to the formation of chain-like structures, whose growth kinetics followed a simple scaling behavior with time. This work provides a theoretical framework for understanding the behaviors of rodlike colloids in ferrofluids and highlights the importance of shape anisotropy in manipulating colloids and their self-assembly.

Thermoresponsive Hydrogel Induced by Dual Supramolecular Assemblies and Its Controlled Release Property for Enhanced Anticancer Drug Delivery.

Supramolecular hydrogels based on inclusion complexation between cyclodextrins (CDs) and polymers have attracted much interest because of their potential for biomedical applications. It is also attractive to incorporate stimuli-responsive properties into the system to create "smart" hydrogels. Herein, a poly(N-isopropylacrylamide) (PNIPAAm) star polymer with a ß-CD core and an adamantyl-terminated poly(ethylene glycol) (Ad-PEG) polymer were synthesized. They self-assembled into a thermoresponsive pseudo-block copolymer through host-guest complexation and formed supramolecular micelles with the change in environment temperature. Subsequently, an injectable polypseudorotaxane-based supramolecular hydrogel was formed between α-CD and the PEG chains of the pseudo-block copolymer. The hydrogel had a unique network structure involving two types of supramolecular self-assemblies between cyclodextrins and polymers, that is, the host-guest complexation between ß-CD units and adamantyl groups and the polypseudorotaxane formation between α-CD and PEG chains. We hypothesize that the dual supramolecular hydrogel formed at room temperature may be enhanced by increasing the temperature over the lower critical solution temperature of PNIPAAm because of the hydrophobic interactions of PNIPAAm segments. Furthermore, if the hydrogel is applied for sustained delivery of hydrophobic drugs, the copolymer dissolved from the hydrogel could micellize and continue to serve as micellar drug carriers with the drug encapsulated in the hydrophobic core. Rheological tests revealed that the hydrophobic interactions of the PNIPAAm segments could significantly enhance the strength of the hydrogel when the temperature increased from 25 to 37 °C. As compared to hydrogels formed by α-CD and PEG alone, the sustained release property of this thermoresponsive hydrogel for an anticancer drug, doxorubicin (DOX), improved at 37 °C. The hydrogel dissolved slowly and released the pseudo-block copolymer in the form of micelles that continued to serve as drug carriers with DOX encapsulated in the hydrophobic core, achieving a better cellular uptake and anticancer effect than free DOX controls, even in multidrug-resistant cancer cells. According to these findings, the dual supramolecular hydrogel developed in this work with remarkable thermoresponsive properties might have potential for sustained anticancer drug delivery with enhanced therapeutic effect in multidrug-resistant cancer cells.

High salinity effects on the depletion attraction in colloid-polymer mixtures.

HYPOTHESIS: Depletion attraction induced by polymers can be employed across multiple disciplines. Previous studies implied that besides screening the electrostatic repulsion between colloids, adding salt may also affect the polymers even in a nonpolar solvent. Here, we study the depletion-induced gelation of a colloid-polymer model system, focusing on the salt effects on the depletion attraction. EXPERIMENTS: Confocal microscopy was used to quantitatively characterize the colloidal gels formed by the polymethylmethacrylate (PMMA)/polystyrene (PS) model system. The attraction experienced by colloids was estimated by correlating the colloidal dynamics with the local structure. Correspondingly, static light scattering was employed to systematically investigate the polymers. The resulting radius of gyration Rg and osmotic pressure were used to evaluate the depletion attraction offered by polymers. FINDINGS: Salt was discovered to lower the strength of inter-particle attraction, which can be attributed to the salt-induced decrease in Rg. The depletion attraction grew sublinearly with c, owing to the considerable decrease in Rg in the good solvent as c increased. We demonstrated how the close form equations in the framework of renormalization group theory can be employed to predict the depletion interaction using the properly determined zero-concentration radius of gyration.

Compositions analysis and insecticidal activity of Aconitum polycarpum Chang ex W.T.Wang petroleum ether fractions and essential oils.

ETHNOPHARMACOLOGICAL RELEVANCE: The Aconitum genus plants as a natural pesticide for insecticide and rodent control has been recorded in Chinese folk. However, the insecticide effect, mechanism, and active composition of Aconitum polycarpum Chang ex W.T.Wang have not been studied further. AIM OF THE STUDY: This study was designed to analyze the chemical composition, evaluate contact toxicity of petroleum ether extracts (PEEs) and essential oils (EOs) of A. polycarpum, and further explore their possible insecticidal mechanism. MATERIALS AND METHODS: The roots of A. polycarpum were extracted with 90% methanol, and then extracted with petroleum ether to obtain PEEs; the EOs was extracted by distillation. The chemical compositions of PEEs and EOs were analyzed by GC-MS. Contact toxicity was evaluated by the immersion method. Exploring insecticidal mechanisms through in vitro enzyme inhibitory activity. RESULTS: 12 compounds were identified from PEEs by GC-MS, mainly including aliphatic (94.8%), the main compositions were Octadecadienol (ODO) (aliphatic, 53.2%) and L-Ascorbyl dipalmitate (LADP) (aliphatic, 36.1%). 24 compounds were identified in EOs. About 44.6% of the identified components were terpenoids and their derivatives, and the rest were mainly aliphatic (34.7%) and phenols (3.0%). The main chemical components were L (-)-Borneol (LB) (terpenoid, 28.3%), LADP (aliphatic, 19.1%), and Isoborneol (terpenoid, 9.1%). The contact toxicity indicated that the PEEs showed great contact toxicity against Spodoptera exigua (LC50 = 126.2 mg/L). Meanwhile, LADP (LC50 = 128.1 mg/L) and ODO (LC50 = 121.3 mg/L) was similar to that of Cyhalothrin (LC50 = 124.2 mg/L) in contact toxicity. In addition, we found that LADP and ODO exhibited excellent inhibitory activity against CarE (IC50 = 58.0, 56.1 mg/L, respectively) by measuring in vitro enzyme inhibitory activity, which was superior than Cyhalothrin (IC50 = 68.1 mg/L). CONCLUSIONS: The chemical compositions and contact toxicity of EOs and PEEs of A. polycarpum were analyzed and evaluated, and their insecticidal mechanisms were preliminarily discussed for the first time. It proved PEEs of A. polycarpum and its main components (LADP and ODO) exhibited excellent contact toxicity against S. exigua, and CarE was identified as a potential target for contact toxicity. This study indicated that the insecticidal activity of petroleum ether extracts from A. polycarpum is quite promising, and provides a practical and scientific basis for the development and application of botanical pesticides.

Corrigendum: Self Organization of Binary Colloidal Mixtures via Diffusiohporesis.

[This corrects the article DOI: 10.3389/fchem.2022.803906.].

Self-Organization of Binary Colloidal Mixtures via Diffusiophoresis.

Catalytic activity of the colloids and chemotactic response to gradients of the chemicals in the solution leads to effective interaction between catalytic colloids. In this paper, we simulate mixtures of active and passive colloids via a Brownian dynamics algorithm. These particles interact via phoretic interactions, which are determined by two independent parameters, surface activity and surface mobility. We find rich dynamic structures by tuning passive colloids' surface mobility, size, and area fractions, which include schools of active colloids with exclusion zone, yolk/shell cluster, and stable active-passive alloys to motile clusters. Dynamical cluster can also be formed due to the nonreciprocity of the phoretic interaction. Increasing the size ratio of passive colloids to active colloids favors the phase separation of active and passive colloids, resulting in yolk/shell structure. Increasing the area fraction of active colloids tends to transfer from dynamical clusters into stable alloys. The simulated binary active colloid systems exhibit intriguing nonequilibrium phenomena that mimic the dynamic organizations of active/passive systems.

Binary Phases and Crystals Assembled from Active and Passive Colloids.

Classic binary materials, ranging from polymer blends to table salts, contain equilibrium phases or crystals of two interacting components. Here, we report on the construction of binary colloidal materials out of equilibrium by employing active particles and passive particles that dynamically interact and organize. Key to our scheme is the introduction of photoactive microspheres whose activity can be precisely tuned. This allows us to leverage the complex nonequilibrium interplay between the constituent components for dynamic coassembly. A wide variety of binary structures have thus been realized, including the liquid-crystal phases and crystal-crystal phases via phase separation and, counterintuitively, the binary crystalline compounds. The obtained structures are validated by computer simulations, which reveal unexpected kinetic pathways that are unique for active systems. With these findings, our strategy could facilitate the design and fabrication of multicomponent materials beyond equilibrium.

Estimating the velocity of chemically-driven Janus colloids considering the anisotropic concentration field.

The application of the active colloids is strongly related to their self-propulsion velocity, which is controlled by the generated anisotropic concentration field. We investigated the effect of this anisotropy on velocity induced by numerical treatments and size of Janus colloids. The far-field approximation is effective in estimating the velocity, even though it neglects the shape effect on the anisotropy of the concentration field. If the surface mobility contrast between the active and the inert part is moderate, the spherical approximation is feasible for sphere-like Janus colloids. Legendre expansion of the concentration field causes artificial anisotropy. Raising the order of the expansion can suppress this effect, but also distorts the concentration field at the top of active part. Thus, the order of the expansion should be chosen carefully depending on the goal of the study. Based on the verified Legendre expansion method and ionic-diffusiophoresis model, we show that due to the size-effect on both the concentration field and the surface mobility, increasing size of colloids can lower the self-propulsion velocity. Our finding is consistent with previous experimental observations without fitting parameter, shedding new light on the self-propulsion mechanism of chemically-driven active colloids. We further show a velocity reversal at high overall ζ potential induced by increasing size, providing a new way for controlling the dynamics of acitve colloids.