Rod-Shaped Liquid Plasticine as Cuttable Minireactor for Photodynamic Therapy of Tumors.

Photodynamic therapy (PDT) has emerged as a promising non-invasive approach for cancer treatment. Enhancing its efficacy and understanding its absorption-induced attenuation are significant while the solutions are limited, particularly for the latter. In this study, a rod-shaped liquid plasticine (LP), comprised of a tumor cell solution encased by a nanoparticle monolayer, is used to serve as a powerful minireactor for addressing these issues. The channel structure, openness, and cuttability of the LP reactor are exploited for providing benefits to PDT. The resulting PDT efficacy is several times higher than those from droplet reactors with common spherical shapes. The attenuation law, which is fundamental in PDT yet poorly understood due to the lack of experimental approaches, is preliminarily uncovered here from the perspective of in vitro experiments by using the LP's cuttability, affording quantitative understanding on this difficult subject. These findings provide insights into the widely-concerned topics in PDT, and highlight the great potential of an LP reactor in offering innovation power for the biochemical and biomedical arenas.

Multi-Interface Electromagnetic Wave Absorbing Material Based on Liquid Marble Microstructures Anchored to SEBS.

The direct application of liquid marbles in electromagnetic wave (EMW) absorption is challenging due to their poor stability, susceptibility to gravitational collapse, and shaping difficulties. To address this issue, a novel strategy is proposed to incorporate liquid marble microstructures (NaCl/nano-SiO2) encapsulated in organic phases (Octadecane) into the rubber-matrix (SEBS) using the ultrasound-assisted emulsion blending method. The resulting NaCl/SiO2/Octadecane microstructures anchored to SEBS offer a substantial solid-liquid interface consisting of NaCl solution and SiO2. When subjected to an alternating electromagnetic (EM) field, the water molecules and polysorbate within SiO2 exhibit heightened responsiveness to the EM field, and the movement of Na+ and Cl- within these microstructures leads to their accumulation at the solid-liquid interface, creating an asymmetric ion distribution. This phenomenon facilitates enhanced interfacial polarization, thereby contributing to the material's EMW absorption properties. Notably, the latex with 16 wt% SEBS (E-3), exhibiting a surface morphology similar to human cell tissues, achieves complete absorption of X-band (fE = 4.20 GHz, RLmin = -33.87 dB). Moreover, the latex demonstrates light density (0.78 g cm-3) and environmental stability. This study not only highlights the predominant loss mechanism in rubber-based wave-absorbing materials but also provides valuable insights into the design of multifunctional wave-absorbing materials.

Polyhedral Vinyl Polymer Particles Synthesized Via Solvent-Free Radical Polymerization.

Liquid marbles (LMs) with a cubic shape are created by using various vinyl monomers as an inner liquid and polymer plates with mm size as a stabilizer. The relationship between the surface tension of the vinyl monomers and formability of the LMs is investigated. LMs can be fabricated using vinyl monomers with surface tensions of 42.7-40.3 mN m-1. The cubic polymer particles are successively synthesized via free-radical polymerizations by irradiation of the cubic LMs with UV light in a solvent-free manner. In addition, controlling the number of polymer plates per one LM, the shape of the plate or the coalescence of the LMs can lead to production of polymer particles with desired forms (e.g., Platonic and rectangular solids) that correspond to the shapes of the original LMs.

Capillarity in Interfacial Liquids and Marbles: Mechanisms, Properties, and Applications.

The mechanics of capillary force in biological systems have critical roles in the formation of the intra- and inter-cellular structures, which may mediate the organization, morphogenesis, and homeostasis of biomolecular condensates. Current techniques may not allow direct and precise measurements of the capillary forces at the intra- and inter-cellular scales. By preserving liquid droplets at the liquid-liquid interface, we have discovered and studied ideal models, i.e., interfacial liquids and marbles, for understanding general capillary mechanics that existed in liquid-in-liquid systems, e.g., biomolecular condensates. The unexpectedly long coalescence time of the interfacial liquids revealed that the Stokes equation does not hold as the radius of the liquid bridge approaches zero, evidencing the existence of a third inertially limited viscous regime. Moreover, liquid transport from a liquid droplet to a liquid reservoir can be prohibited by coating the droplet surface with hydrophobic or amphiphilic particles, forming interfacial liquid marbles. Unique characteristics, including high stability, transparency, gas permeability, and self-assembly, are observed for the interfacial liquid marbles. Phase transition and separation induced by the formation of nanostructured materials can be directly observed within the interfacial liquid marbles without the need for surfactants and agitation, making them useful tools to research the interfacial mechanics.

Biodegradable Polymers for Micro Elastofluidics.

Micro elastofluidics is an emerging research field that encompasses characteristics of conventional microfluidics and fluid-structure interactions. Micro elastofluidics is expected to enable practical applications, for instance, where direct contact between biological samples and fluid handling systems is required. Besides design optimization, choosing a proper material is critical to the practical use of micro elastofluidics upon interaction with biological interface and after its functional lifetime. Biodegradable polymers are one of the most studied materials for this purpose. Micro elastofluidic devices made of biodegradable polymers possess exceptional mechanical elasticity, excellent bio compatibility, and structural degradability into non-toxic products. This article provides an insightful and systematic review of the utilization of biodegradable polymers in digital and continuous-flow micro elastofluidics.

Digital Imaging-based Colourimetry for Enzymatic Processes in Transparent Liquid Marbles.

Liquid marbles are a promising microreactor platform that recently attracts significant research interest owing to their ability to accommodate a wide range of micro reactions. However, the use of destructive and ex-situ methods to monitor reactions impairs the potential of liquid-marble-based microreactors. This paper proposes a non-destructive, in situ, and cost-effective digital-imaging-based colourimetric monitoring method for transparent liquid marbles, using the enzymatic hydrolysis of starch as an illustrative example. The colourimetric reaction between starch and iodine produces a complex that exhibits a dark blue colour. We found that the absorbance of red channel of digital images showed a linear relationship with starch concentration with high sensitivity and repeatability. This digital-imaging-based colourimetric method was used to study the hydrolysis of starch by α-amylase. The results show high accuracy and applicability of first-order kinetics for this reaction. The demonstration of digital-imaging-based colourimetry indicates the potential of liquid marble-based microreactors.

Responsive Photonic Liquid Marbles.

Liquid marbles have potential to serve as mini-reactors for fabricating new materials, but this has been exploited little and mostly for conventional chemical reactions. Here, we uncover the unparalleled capability of liquid marbles to act as platforms for controlling the self-assembly of a bio-derived polymer, hydroxypropyl cellulose, into a cholesteric liquid crystalline phase showing structural coloration by Bragg reflection. By adjusting the cholesteric pitch via quantitative water extraction, we achieve liquid marbles that we can tailor for structural color anywhere in the visible range. Liquid marbles respond with color change that can be detected by eye, to changes in temperature, exposure to toxic chemicals and mechanical deformation. Our concept demonstrates the advantages of using liquid marbles as a miniature platform for controlling the liquid crystal self-assembly of bio-derived polymers, and their exploitation to fabricate sustainable, responsive soft photonic objects.

Granular impact cratering by liquid drops: Understanding raindrop imprints through an analogy to asteroid strikes.

When a granular material is impacted by a sphere, its surface deforms like a liquid yet it preserves a circular crater like a solid. Although the mechanism of granular impact cratering by solid spheres is well explored, our knowledge on granular impact cratering by liquid drops is still very limited. Here, by combining high-speed photography with high-precision laser profilometry, we investigate liquid-drop impact dynamics on granular surface and monitor the morphology of resulting impact craters. Surprisingly, we find that despite the enormous energy and length difference, granular impact cratering by liquid drops follows the same energy scaling and reproduces the same crater morphology as that of asteroid impact craters. Inspired by this similarity, we integrate the physical insight from planetary sciences, the liquid marble model from fluid mechanics, and the concept of jamming transition from granular physics into a simple theoretical framework that quantitatively describes all of the main features of liquid-drop imprints in granular media. Our study sheds light on the mechanisms governing raindrop impacts on granular surfaces and reveals a remarkable analogy between familiar phenomena of raining and catastrophic asteroid strikes.

Liquid marbles as bioreactors for the study of three-dimensional cell interactions.

Liquid marble as a bioreactor platform for cell-based studies has received significant attention, especially for developing 3D cell-based assays. This platform is particularly suitable for 3D in-vitro modeling of cell-cell interactions. For the first time, we demonstrated the interaction of olfactory ensheathing cells (OECs) with nerve debris and meningeal fibroblast using liquid marbles. As the transplantation of OECs can be used for repairing nerve injury, degenerating cell debris within the transplantation site can adversely affect the survival of transplanted OECs. In this paper, we used liquid marbles to mimic the hostile 3D environment to analyze the functional behavior of the cells and to form the basis for cell-based therapy. We show that OECs interact with debris and enhanced cellular aggregation to form a larger 3D spheroidal tissue. However, these spheroids indicated limitation in biological functions such as the inability of cells within the spheroids to migrate out and adherence to neighboring tissue by fusion. The coalescence of two liquid marbles allows for analyzing the interaction between two distinct cell types and their respective environment. We created a microenvironment consisting of 3D fibroblast spheroids and nerve debris and let it interact with OECs. We found that OECs initiate adherence with nerve debris in this 3D environment. The results suggest that liquid marbles are ideal for developing bioassays that could substantially contribute to therapeutic applications. Especially, insights for improving the survival and adherence of transplanted cells.

A novel technique for in vitro maturation of sheep oocytes in a liquid marble microbioreactor.

PURPOSE: The aim of this work was to develop a microbioreactor using liquid marble (LM) as a novel system for oocyte in vitro maturation (IVM) in small volumes. METHODS: Cumulus-oocyte complexes (COCs) obtained from slaughterhouse sheep ovaries were in vitro matured in a LM system prepared by placing a drop (30 µl containing 10 COCs) suspended in TCM 199 supplemented with 10 % (v/v) oestrus sheep serum (OSS) and 0.1 IU FSH and LH onto a polytetrafluoroethylene (PTFE) particle bed (LM group). As a control group (CTRL group), COCs were in vitro matured in standard volume and conditions (600 µl of IVM medium in a four-well dish). After 24-h culture at 38.5 °C in 5 % CO2 in air, COCs were released from LM and the following parameters were evaluated: (a) percentage of MII oocytes, (b) oocyte developmental competence following in vitro fertilization (IVF) or parthenogenetic activation (PA) and embryo culture for 8 days in synthetic oviductal fluid (SOF) medium at 38.5 °C in 5 % O2, 5 % CO2, and 90 % N2. RESULTS: The results indicated similar percentage of MII oocytes in LM and CTRL groups (88.0 vs. 92.0 %). No differences were observed in blastocyst rate after IVF (LM 47.5 % vs. CTRL 50.2 %, P=0.637) or PA (LM 44.4 % vs. CTRL 48.3 %, P=0.426). CONCLUSIONS: The results indicate that LM microbioreactor is a viable technique that provides a suitable microenvironment to induce oocyte in vitro maturation.

Graphene liquid marbles as photothermal miniature reactors for reaction kinetics modulation.

We demonstrate the fabrication of graphene liquid marbles as photothermal miniature reactors with precise temperature control for reaction kinetics modulation. Graphene liquid marbles show rapid and highly reproducible photothermal behavior while maintaining their excellent mechanical robustness. By tuning the applied laser power, swift regulation of graphene liquid marble's surface temperature between 21-135 °C and its encapsulated water temperature between 21-74 °C are demonstrated. The temperature regulation modulates the reaction kinetics in our graphene liquid marble, achieving a 12-fold superior reaction rate constant for methylene blue degradation than at room temperature.

Experimental investigation on the bouncing dynamics of a liquid marble during the impact on a hydrophilic surface.

Liquid marbles are droplets coated by hydrophobic particles. At low Weber numbers (We), when impacting a hydrophilic surface, the marble may bounce on the substrate repeatedly without any rupturing until the quiescence condition is achieved. The marble bouncing has gained far less attention, although its rich underlying physics is due to the interaction between liquid core, hydrophobic grain, and surrounding air. Accordingly, this research experimentally scrutinizes the marble impact and subsequent bouncing on a hydrophilic surface for the first time. Additionally, the conversion of kinetic, gravitational potential, inertial, and surface energies occurring regularly during the impact is exhaustively surveyed. Moreover, the effect of Weber and gravitational Bond numbers (Bo) on the bouncing time, maximum spreading time, maximum spreading ratio, maximum elongation ratio, and maximum restitution are investigated, which characterize the marble impact and bouncing dynamics. This study is one of the limited investigations exploring the effects of the gravitational Bond number on the results. Dimensionless correlations are proposed for the mentioned parameters based on the experimental data. Furthermore, utilizing the simplifying theoretical presumptions, correlations are suggested based on the scale analysis for the spreading time and maximum spreading ratio. The results imply that the mentioned parameters behave differently at low and moderate Weber numbers, though the distinction is more pronounced in the case of the bouncing time, maximum spreading time and maximum spreading ratio. Although increasing with the Weber number when WeWecr. In addition, the maximum elongation ratio linearly grows with the Weber number.

Effect of surface roughness on the solar evaporation of liquid marbles.

HYPOTHESIS: Nanostructured materials are widely used for solar energy harvesting and conversion due to their excellent photothermal properties. It is generally accepted that the better the light absorption ability, the better the photothermal conversion efficiency. EXPERIMENT: A series of experiments in solar evaporation of liquid marbles (LMs) by coating the droplets with Fe3O4, Ni nanoparticles (NPs) and carbon nanotubes (CNTs) are conducted. FINDINGS: Conversely, we found that the surface roughness of solar absorber plays a significant role in solar evaporation rather than the light absorption. The results disclose that the Fe3O4 NPs with the lowest absorptivity has the largest roughness on drop surface, while that of CNTs show the opposite properties. The evaporation dynamics of LMs are featured with dome or constant spherical collapse with different roughness. Such dynamic difference arises from the mechanical competition between the capillary force and interparticle interaction. Besides, the strong light-harvesting and near-field radiation enabled by the rough surfaces enhance the solar evaporation. The Fe3O4-LM shows the highest evaporation rate of 6.55 µg/s, which is 1.09 and 1.30 times larger than that of Ni-LM and CNT-LM, respectively. Numerical analysis reveals that the rough surface with stacking arrangement of NPs greatly enhances the light-induced electromagnetic field and heat concentration over the interface, leading to a plasmon-coupling boundary with high temperature for the fast evaporation. Uncovering these properties could be of much help for developments of heatable miniature evaporators or reactors and their counterparts, permitting a broad range of processes with precise temperature and kinetic control.

Suppression of droplet pinch-off by early onset of interfacial instability.

HYPOTHESIS: Interfacial instabilities cause undesirable droplet breakage during impact. Such breakage affects many applications, such as printing, spraying, etc. Particle coating over a droplet can significantly change the impact process and stabilize it against breakage. This work investigates the impact dynamics of particle-coated droplets, which mostly remains unexplored. EXPERIMENTS: Particle-coated droplets of different mass loading were formed using volume addition. The prepared droplets were impacted on superhydrophobic surfaces, and their dynamics were recorded using a high-speed camera. FINDINGS: We report an intriguing phenomenon where an interfacial fingering instability helps suppress pinch-off in particle-coated droplets. This island of breakage suppression, where the droplet maintains its intactness upon impact, appears in a regime of Weber numbers where bare droplet breakage is inevitable. The onset of fingering instability in particle-coated droplets is observed at much lower impact energy, around two times less than the bare droplet. The instability is characterized and explained using the rim Bond number. The instability suppresses pinch-off because of the higher losses associated with the formation of stable fingers. Such instability can also be seen in dust/pollen-covered surfaces, making it useful in many applications related to cooling, self-cleaning, anti-icing etc.

Effects of particle size on the electrocoalescence dynamics and arrested morphology of liquid marbles.

HYPOTHESIS: The coalescence of bare droplets when surface tension dominates always results in one larger spherical droplet. In contrast, droplets coated with particles may be stabilized into non-spherical structures after arrested coalescence, which can be achieved by different approaches, such as changing the particle surface coverage. The size of particles coating the initial liquid marbles can be used to control the coalescence dynamics and the resulting morphology of arrested droplets. EXPERIMENT: We characterized the electrocoalescence of liquid marbles coated with particles ranging from hundred nanometers to hundred micrometers. The electrocoalescence was recorded using high-speed imaging. FINDINGS: When the electrocoalescence initiates, particles jam and halt the relaxation of the marbles at different stages, resulting in four possible final morphologies that are characterized using the Gaussian curvature at the neck region. The four regimes are total coalescence, arrested puddle coalescence, arrested saddle coalescence, and non-coalescence. The coalescence is initiated at the center of the contact zone, independent of the particle size. Small particles show little resistance to the coalescence, while marbles coated by large particles demonstrate a viscous-like behavior, indicated by the growth of the liquid bridge and the damping. The present study provides guidelines for applications that involve the formulation of liquid marbles with complex morphologies.

Magnetically Driven Manipulation of Nonmagnetic Liquid Marbles: Billiards with Liquid Marbles.

Liquid marbles are droplets encapsulated by a layer of hydrophobic nanoparticles and have been extensively employed in digital microfluidics and lab-on-a-chip systems in recent years. In this study, magnetic liquid marbles were used to manipulate nonmagnetic liquid marbles. To achieve this purpose, a ferrofluid liquid marble (FLM) was employed and attracted toward an electromagnet, resulting in an impulse to a water liquid marble (WLM) on its way to the electromagnet. It was observed that the manipulation of the WLM by the FLM was similar to the collision of billiard balls except that the liquid marbles exhibited an inelastic collision. Taking the FLM as the projectile ball and the WLM as the other target balls, one can adjust the displacement and direction of the WLM precisely, similar to an expert billiard player. Firstly, the WLM displacement can be adjusted by altering the liquid marble volumes, the initial distances from the electromagnet, and the coil current. Secondly, the WLM direction can be adjusted by changing the position of the WLM relative to the connecting line between the FLM center and the electromagnet. Results show that when the FLM or WLM volume increases by five times, the WLM shooting distance approximately increases by 200% and decreases by 75%, respectively.

Hydrophobically Modified Gelatin Particles for Production of Liquid Marbles.

The unique properties and morphology of liquid marbles (LMs) make them potentially useful for various applications. Non-edible hydrophobic organic polymer particles are widely used to prepare LMs. It is necessary to increase the variety of LM particles to extend their use into food and pharmaceuticals. Herein, we focus on hydrophobically modified gelatin (HMG) as a base material for the particles. The surface tension of HMG decreased as the length of alkyl chains incorporated into the gelatin and the degree of substitution (DS) of the alkyl chains increased. HMG with a surface tension of less than 37.5 mN/m (determined using equations based on the Young-Dupré equation and Kaelble-Uy theory) successfully formed LMs of water. The minimum surface tension of a liquid in which it was possible to form LMs using HMG particles was approximately 53 mN/m. We also showed that the liquid-over-solid spreading coefficient SL/S is a potential new factor for predicting if particles can form LMs. The HMG particles and the new system for predicting LM formation could expand the use of LMs in food and pharmaceuticals.

Fabrication of robust superhydrophobic magnetic multifunctional coatings and liquid marbles.

To obtain durable and multi-function superhydrophobic surfaces, we reported a facial method to prepare a multifunctional suspension (γ-Fe2O3@SiO2@PDMS suspension) named as FSP suspension, in which γ-Fe2O3 was coated by the silica shell and PDMS was used as the outer layer. Superhydrophobic magnetic polyurethane (SMPU) sponge was prepared by immersing the polyurethane (PU) sponge into the FSP suspension, exhibiting the superior ability to absorb oil. In addition, it could also move directionally by the attraction of magnets and absorb the oil along the fixed path. The heated superhydrophobic magnetic stainless steel (H-SMSS) mesh was acquired by spraying FSP suspension onto the stainless steel mesh and then heating at 400 °C, which demonstrated superior superhydrophobicity and resistance to abrasion and chemical corrosion. Besides, the H-SMSS mesh displayed excellent flux and efficiency to separate the oil/water mixture. Rolling droplets on FSP particles, the superhydrophobic magnetic liquid marbles (SMLMs) were fabricated, in which liquids with different volumes were encapsulated and transported directionally. Further, it was convenient to inject liquid into the SMLM and withdraw liquid from it. Thus, the prepared FSP suspension has promising applications in constructing large-area, robust, and multifunctional surfaces and microreactors.

The gelatin-based liquid marbles for cell cryopreservation.

As an alternative and a straightforward cryopreservation biotechnological tool, liquid marble provides a promising cryopreservation approach. Currently, effective cell preservation mainly based on the addition of dimethyl sulfoxide (DMSO) and fetal bovine serum (FBS). As state-of-the-art cryoprotectant (CPA), DMSO, has intrinsic toxicity, which is the bottleneck of its widespread application. The complex compositions of FBS have the potential risks of pathogenic microorganism contamination. However, efficient cell cryopreservation using liquid marbles, a platform independent of DMSO and FBS, has not been well investigated yet. Herein, we explore the cryoprotection role of liquid marbles based on gelatin solution. Gelatin has a superior biocompatibility, which DMSO is incomparable. During a freeze-thaw cycle, gelatin produces negligible osmotic pressure, and has high ice recrystallization inhibition (IRI) activity to induce the formation of smaller and smooth ice crystals. Moreover, the specific structure of liquid marble also provides favorable supports for cell survival. The cryopreservation efficiency of mouse fibroblasts cells L929 via the gelatin-based liquid marble was as high as 90%, and the recovered cells could maintain their normal functionalities. This work opens a new window of opportunity for non-toxic and efficient cryopreservation of liquid marbles without the need of DMSO and FBS addition.

Microtubular Assessment of C6 Rat Glioma Cell Spheroids Developed in Transparent Liquid Marbles or Hanging Drops.

Glioblastoma is a brain tumour frequently used as an experimental model to exploit innovative therapeutic approaches due to its high lethality and refractoriness to therapies. Part of these innovative anticancer therapies address cytoskeletal microtubules (MTs) since specific tubulin post-translational modifications (PTMs) are considered markers of tumour plasticity. In vitro studies, which traditionally employ two-dimensional (2D) culture systems, are now being replaced by three-dimensional (3D) systems that more closely mimic in vivo physiological conditions and allow a better understanding of the signalling between cells. In this work, we compared 2 liquid base 3D methods for the generation of spheroids from C6 rat glioma cells (RGCs) using 30 µL of liquid marble (LM) or the hanging drops (HDs), which contained 2 different cell numbers (5000 or 15,000). After 24 or 48 h of in vitro culture (IVC), the morphology of the spheroids was observed and the behaviour of the two main tubulin PTMs, tyrosinated α-tubulin (Tyr-T) and acetylated α-tubulin (Ac-T), was evaluated by fluorescence and Western blot (WB). RGCs spontaneously formed spherical agglomerates more rapidly in the LM than in the HD system. Cell density influenced the size of the spheroids, which reached a larger size (> of 300 µm Ø), with 15,000 cells compared to 5000 cells (150 µm Ø). Moreover, an increase in Tyr-T and Ac-T was observed in both the HD and LM system from 24 to 48 h, with the highest values shown in the 48 h/LM spheroids of 5000 cells (p < 0.05). In conclusion, by comparing the morphology and microtubular architecture of spheroids from C6 rat glioma cells developed by LM or HD methodology, our findings demonstrate that the use of a fumed silica microbioreactor boosts the induction and maintenance of a high plasticity state in glioma cells. RGCs cultured in LM express levels of tubulin PTMs that can be used to evaluate the efficacy of new anticancer therapies.