Significance of in situ quantitative membrane property-morphology relation (QmPMR) analysis.

Deformation of the cell membrane is well understood from the viewpoint of protein interactions and free energy balance. However, the various dynamic properties of the membrane, such as lipid packing and hydrophobicity, and their relationship with cell membrane deformation are unknown. Therefore, the deformation of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and oleic acid (OA) giant unilamellar vesicles (GUVs) was induced by heating and cooling cycles, and time-lapse analysis was conducted based on the membrane hydrophobicity and physical parameters of "single-parent" and "daughter" vesicles. Fluorescence ratiometric analysis by simultaneous dual-wavelength detection revealed the variation of different hydrophilic GUVs and enabled inferences of the "daughter" vesicle composition and the "parent" membrane's local composition during deformation; the "daughter" vesicle composition of OA was lower than that of the "parents", and lateral movement of OA was the primary contributor to the formation of the "daughter" vesicles. Thus, our findings and the newly developed methodology, named in situ quantitative membrane property-morphology relation (QmPMR) analysis, would provide new insights into cell deformation and accelerate research on both deformation and its related events, such as budding and birthing.

Exploring the Influence of Morphology on Bipolaron-Polaron Ratios and Conductivity in Polypyrrole in the Presence of Surfactants.

This research aims to deepen the understanding of the relationship between conductivity and morphology in polypyrrole (PPy) via a comparison of the bipolaron to polaron ratios with a focus on the C-H deformation area. PPy samples were synthesized with different surfactants: sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and tween 80 (TW). This study revealed that SDS significantly altered the bipolaron and polaron in the C-H deformation region and showed higher conductivity than other surfactants. Notably, the morphological shifts to a sheet-like structure when using ammonium sulfate (APS) contrasted with the particle-like form observed with ferric chloride (FeCl3). These results showed that if the oxidant changed, the bipolaron and polaron ratios in C-H deformation were unrelated to PPy morphology. However, this work showed a consistent relationship between SDS use, the bipolaron and polaron ratios in the C-H deformation, and the conductivity properties. Moreover, the natural positive charge of PPy and negatively charged SDS molecules may lead to an electrostatic interaction between PPy and SDS. This work assumes that this interaction might cause the transformation of polaron to bipolaron in the C-H deformation region, resulting in improved conductivity of PPy. This work offers more support for the future investigation of PPy characteristics.

Multiplicity of solvent environments in lipid bilayer revealed by DAS deconvolution of twin probes: Comparative method of Laurdan and Prodan.

Laurdan and Prodan were designed for the evaluation of the surrounding hydration state. When inserted into lipid bilayer systems, both probes are located at different positions and their fluorescence properties are drastically varied, depending on their surrounding environment. In this study, a novel method using the above fluorescence probes was proposed on the basis of fluorescence lifetime (τ) and emission peak (λ), called as τ vs. λ plot, determined by global analysis of their multiple fluorescence decays and deconvolution of these decay-associated spectra. According to the evaluation of τ vs. λ plot, the existence of multiple fluorescence components in the membrane was revealed. In addition, their fluorescence distribution properties, described on τ vs. λ plot, of each probe tended to correspond to the phase state and vertical direction of the lipid membrane. To assess the contribution of environmental effect to each distribution, we defined the region in the τ vs. λ plot, which was modeled from a series of solvent mixtures (hexane, acetone, ethanol and water) to emulate the complex environment in the 1,2-dipalmitoyl-sn-glycero-3-phosphocholine bilayer system. The distributions of fluorescence components of Laurdan and Prodan in lipid membranes were classified into each solvent species, and Prodan partition into bulk water was distinguished. The sensitivity of Prodan to the phase pretransition of the 1,2-dipalmitoyl-sn-glycero-3-phosphocholine bilayer system was also observed in increasing the temperature. Noticeably, most of the fluorescence components was assigned to the solvent model, except for a single component that has longer lifetime and shorter emission wavelength. This component was dominant in solid-ordered phase; hence, it is assumed to be a specific component in lipid membranes that cannot be represented by solvents. Although these are still qualitative analytical methods, the unique approach proposed in this study provides novel insights into the multi-focal property of the membrane.

Revealed Properties of Various Self-Assemblies in Two Catanionic Surfactant Systems in Relation to Their Polarity and Molecular Packing State.

A catanionic surfactant system is an aqueous solution or dispersion of cationic and anionic surfactants that spontaneously self-assemble into structures such as micelles, vesicles, and coacervates. Their structural diversity varies depending on the ratios of cationic and anionic surfactants (compositions), the chemical structure of the constituent molecules, etc. Herein, two types of catanionic surfactant systems were systematically characterized: (i) cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS), both typical ionic surfactants; and (ii) dodecylmethylimidazolium ammonium bromide ([C12mim]Br) and SDS, where the former is an ionic liquid. By observing the sample appearance, turbidity, and particle size, the phase state of each system was analyzed according to the total concentration of surfactants and the molar ratio of cationic surfactants to the total concentration. Especially, for specific compositions of catanionic surfactant vesicles (cataniosome), the closed structure of the vesicles was confirmed through calcein entrapment and release detected with a fluorescence assay. The polarities of the interface of the prepared self-assemblies were evaluated using a fluorescence probe, Laurdan. The packing state of the molecules in the formed self-assembly structure was estimated using Raman spectroscopy. The results clearly indicate consistent phase-transition behavior for the CTAB-SDS (i) and [C12mim]Br-SDS (ii) systems, depending on the total surfactant concentration and composition, while the membrane properties of the two systems differed. The cataniosome formed in the CTAB-SDS system was in a tightly packed membrane state and more hydrophobic than that formed in the [C12mim]Br-SDS system owing to the difference in the structure of the constituting molecule: [C12mim]Br has a larger head group and shorter acyl chain than CTAB. The self-assembly properties evaluated in this study were compared with those of typical lipid membranes, liposomes (lipid vesicles), to determine a possible application of the catanionic systems with various self-assembly formulations.

Modulation of the Belousov-Zhabotinsky Reaction with Lipid Bilayers: Effects of Lipid Head Groups and Membrane Properties.

The Belousov-Zhabotinsky (BZ) reaction is an oscillating reaction due to periodic oscillations that happen in the concentration of some intermediates. Such systems can be applied together with hydrophobic membranes to create an autonomous behavior in artificial systems. However, because of a complex set of reactions happening in such systems, the interferences caused by hydrophobic membranes are not easily understood. In this study, we tested lipid membranes composed of trimethylammonium-propane (TAP) and phosphate (PA) lipids in an attempt to break down how the polar region of phosphatidylcholine (PC) lipid membranes affect the BZ reaction. According to our findings, the trimethylammonium group and membrane fluidity are crucial to change the frequency of oscillations in the reaction. In addition, the results also indicate a possible complexation of cerium ions with membranes with a phosphate head group.

Insight into the Exosomal Membrane: From Viewpoints of Membrane Fluidity and Polarity.

Numerous research studies have been done for exosomes, particularly focusing on membrane proteins and included nucleic acids, and the volume of the knowledge about the lipids in the exosomal membrane has been increasing. However, the dynamic property of the exosomal membrane is hardly studied. By employing milk exosome as an example, herein the exosomal membrane was characterized focusing on the membrane fluidity and polarity. The lipid composition and phase state of milk exosome (exosome from bovine milk) were estimated. The milk exosome contained enriched Chol (43.6 mol % in total lipid extracts), which made the membrane in the liquid-ordered (lo) phase by interacting with phospholipids. To suggest a model of exosomal vesicle cargo, the liposome compositions that mimic milk exosome were studied: liposomes were made of cholesterol (Chol), milk sphingomyelin (milk SM), and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). By using fluorescent probes 1,6-diphenyl-1,3,5-hexatriene and 6-dodecanoyl-2-dimethylaminonaphthalene, the microenvironments of submicron-sized membranes of exosome and model liposomes were investigated. The membrane fluidity of milk exosome was slightly higher than those of Chol/milk SM/POPC liposomes with a similar content of Chol, suggesting the presence of enriched unsaturated lipids. The most purposeful membrane property was obtained by the liposome composition of Chol/milk SM/POPC = 40/15/45. From the above, it is concluded that Chol is a fundamental component of the milk exosomal membrane to construct the enriched lo phase, which could increase the membrane rigidity and contribute to the function of exosome.

Systematic Characterization of Nanostructured Lipid Carriers from Cetyl Palmitate/Caprylic Triglyceride/Tween 80 Mixtures in an Aqueous Environment.

Nanostructured lipid carriers (NLCs) are gaining attention as the new generation of lipid vehicles. These carriers consist of saturated lipids with small drops of liquid oil dispersed into the inner lipid matrix and are stabilized by a surfactant. Conventionally, NLC-based drug delivery systems have been widely studied, and many researchers are looking into the composition of NLC properties to improve the performance of NLCs. The membrane fluidity and polarity of self-assembling lipids are also essential properties that must be affected by membrane compositions; however, such fundamental characteristics have not been studied yet. In this study, NLCs were prepared from cetyl palmitate (CP), caprylic triglyceride (CaTG), and Tween 80 (T80). Structural properties, such as particle size and ζ-potential of the CP/CaTG/T80 ternary mixtures, were investigated. Then, the systematic characterization of self-assembly properties using fluorescence-based analysis was applied for the first time to the NLC system. As a final step, the ternary diagram was developed based on the self-assembly properties to summarize the possible structures formed at different compositions. The results showed four states: micelle-like, oil-in-water (O/W) emulsion-like, solid lipid nanoparticle-like, and intermediate (solid-liquid coexistence). For the purpose of making the lipid matrix more liquified, the heterogeneous state and the disordered state of the O/W emulsion-like structure might fulfill the criteria of NLCs. Finally, the ternary diagram provides new information about the assembly state of NLC constituents that could become an important reference for developing high-performance NLCs.

Evaluation of Molecular Ordering in Bicelle Bilayer Membranes Based on Induced Circular Dichroism Spectra.

Bicelles are submicrometer-sized disc-shaped molecular self-assemblies that can be obtained in aqueous solution by dispersing mixtures of certain amphiphiles. Although phospholipid bicelle and phospholipid vesicle assemblies adopt similar lipid bilayer structures, the differences in bilayer characteristics, especially physicochemical properties such as bilayer fluidity, are not clearly understood. Herein, we report the lipid ordering properties of bicelle bilayer membranes based on induced circular dichroism (ICD) and fluorescence polarization analyses using 1,6-diphenyl-1,3,5-hexatriene (DPH) as a probe. Bicelles were prepared by using 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC), while pure DMPC vesicles and pure DHPC micelles were used as references. At temperatures below the phase transition temperature of DMPC, the bicelles showed lower membrane fluidities, whereas DHPC micelles showed higher membrane fluidity, suggesting no significant differences in bilayer fluidity between the bicelle and vesicle assemblies. The ICD signals of DPH were induced only when the membrane was in ordered (solid-ordered or ripple-gel) phases. In the bicelle systems, the ICD of DPH was more significant than that of the DMPC vesicle. The induced chirality of DPH was dependent on the chirality of the bilayer lipid. Compared to that of the DMPC/DHPC bicelle, the ICD of the 1,2-dipalmitoyl-sn-glycero-3-phosphocholine/DHPC bicelle was higher, while that of the bovine sphingomyelin/DHPC bicelle was lower. Because the lipids are tightly packed in the ordered phase, the ICD intensity reflects the molecular ordering state of the lipids in the bicelle bilayer.

Gel-Phase-like Ordered Membrane Properties Observed in Dispersed Oleic Acid/1-Oleoylglycerol Self-Assemblies: Systematic Characterization Using Raman Spectroscopy and a Laurdan Fluorescent Probe.

Aqueous dispersions of oleic acid (OA) and those modified with 1-oleoylglycerol (monoolein, MO) form various kinds of self-assembled structures: micelles, vesicles, oil-in-water (O/W) emulsions, hexagonal phases, and dispersed cubic phases. Conventionally, these self-assembled structures have been characterized using cryogenic transmission electron microscopy or X-ray diffraction spectroscopy. However, these methodologies require specialized treatment before they can be used, which may lead to the self-assemblies not adopting their true equilibrium state. Herein, we systematically characterized the self-assemblies composed of OA and MO in aqueous solution using Raman spectroscopy and fluorescent probe 6-dodecanoyl-2-dimethylaminonaphthalene (Laurdan). The OA/MO dispersions at pH 5.0 showed increased chain packing in comparison to the OA micelle at pH 11 or OA vesicle at pH 9.0, which were characterized by the intensity ratio of the Raman peaks at 2850 and 2890 cm-1, R = I2890/I2850. In the Laurdan fluorescence measurements, the obtained spectra were deconvoluted to two peak fractions (A1: λem= 490 nm; A2: λem = 440 nm), and the peak area ratio, A1/(A1 + A2), was defined as the membrane hydrophilicity Øm. The Øm value of the OA/MO dispersion at pH 5.0 was similar to that of the OA O/W emulsion, indicating that the membrane surfaces of these self-assemblies were relatively dehydrated compared to the OA micelle or OA vesicle. To categorize the type of self-assembly dispersion, a Cartesian diagram plot was systematically drawn: R on the x axis and Øm on the y axis, with the cross point at x = 1, y = 0.5. By comparing the membrane properties of the OA-based micelles, O/W emulsions, and dispersed cubic phases, we determined that the OA/MO dispersion at pH 5.0 possessed higher chain packing (R > 1) and a dehydrated membrane surface (Øm < 0.5), which is similar to that of the ordered membranes in gel phases. This characterization method can be useful in evaluating the ordered membrane properties in dispersed self-assemblies in aqueous media.

Characterization of DDAB/Cholesterol Vesicles and Its Comparison with Lipid/Cholesterol Vesicles.

Vesicles prepared by synthetic surfactant, DDAB (dilauryldimethylammonium bromide), were modified with cholesterol and their membrane surface properties of the vesicle were characterized through the analyses of fluorescent probes, such as Laurdan (6-lauroyl-2-dimethylaminonaphthalene) and DPH (1,6-diphenyl-1,3,5-hexatriene). The self-assembly of DDAB with cholesterol showed stable vesicle structure with a mean diameter of 127 nm through the dynamic light scattering analysis. While the DDAB vesicle showed high polarity and high fluidity, the modification of the DDAB vesicle with cholesterol lead to the formation of "heterogeneous phase" on the vesicle membrane. DDAB:cholesterol = 70:30 vesicle showed unique characteristics that represents polar environment but lower fluidity. A novel platform for the chemical process in aqueous media can be expected by using the artificial surfactant vesicles modified with cholesterol.

Preferential Adsorption of l-Histidine onto DOPC/Sphingomyelin/3ß-[N-(N',N'-dimethylaminoethane)carbamoyl]cholesterol Liposomes in the Presence of Chiral Organic Acids.

We investigated the effect of organic acids such as mandelic acid (MA) and tartaric acid (TA) on the adsorption behavior of both histidine (His) and propranolol (PPL) onto liposomes. A cationic and heterogeneous liposome prepared using 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/sphingomyelin (SM)/3ß-[N-(N',N'-dimethylaminoethane)carbamoyl]cholesterol (DC-Ch) in a ratio of (4/3/3) showed the highest adsorption efficiency of MA and TA independent of chirality, while neutral liposome DOPC/SM/cholesterol = (4/3/3) showed low efficiency. As expected, electrostatic interactions were dominant in MA or TA adsorption onto DOPC/SM/DC-Ch = (4/3/3) liposomes, suggesting that organic acids had adsorbed onto SM/DC-Ch-enriched domains. The adsorption behaviors of organic acids onto DOPC/SM/DC-Ch = (4/3/3) were governed by Langmuir adsorption isotherms. For adsorption, the membrane polarities slightly decreased (i.e., membrane surface was hydrophilic), but no alterations in membrane fluidity were observed. In the presence of organic acids that had been preincubated with DOPC/SM/DC-Ch = (4/3/3), the adsorption of l- and d-His onto those liposomes was examined. Preferential l-His adsorption was dramatically prevented only in the presence of l-MA, suggesting that the adsorption sites for l-His and l-MA on DOPC/SM/DC-Ch = (4/3/3) liposomes are competitive, while those for l-His and d-MA, l-TA, and d-TA are isolated.

Induction of Chiral Recognition with Lipid Nanodomains Produced by Polymerization.

We report the induction and control of chiral recognition in liposomal membranes by the photopolymerization of diacetylenic lipids (DiynePC). The specific properties of polymerized DiynePC liposomes were characterized, and then the chiral separation performance was estimated. As the polymerization proceeds, chiral recognition to ibuprofen was induced, and its efficiency increased due to the formation of rigid nanodomains and boundary edges. Furthermore, the chiral recognition and adsorbed amount could be controlled by the ratio of rigid nanodomains, varying the composition ratio of DiynePC. Finally, the optimum condition and dominant interactions for enantioselective adsorption were clarified. Thus, our findings and results will be helpful to understand the induction of chiral recognition by polymerizable liposomes, and also become a guideline for the construction of liposomal chiral stationary phases.

Electrophoretic separation method for membrane pore-forming proteins in multilayer lipid membranes.

In this paper, we report on a novel electrophoretic separation and analysis method for membrane pore-forming proteins in multilayer lipid membranes (MLMs) in order to overcome the problems related to current separation and analysis methods of membrane proteins, and to obtain a high-performance separation method on the basis of specific properties of the lipid membranes. We constructed MLMs, and subsequently characterized membrane pore-forming protein behavior in MLMs. Through the use of these MLMs, we were able to successfully separate and analyze membrane pore-forming proteins in MLMs. To the best of our knowledge, this research is the first example of membrane pore-forming protein separation in lipid membranes. Our method can be expected to be applied for the separation and analysis of other membrane proteins including intrinsic membrane proteins and to result in high-performance by utilizing the specific properties of lipid membranes.

Characterization of Aqueous Oleic Acid/Oleate Dispersions by Fluorescent Probes and Raman Spectroscopy.

Oleic acid (OA) and oleates form self-assembled structures dispersible in aqueous media. Herein, the physicochemical properties of OA/oleate assemblies were characterized using fluorescent probes and Raman spectroscopy, under relatively high dilution (<100 mM of total amphiphile) at 25 °C. Anisotropy analysis using 1,6-diphenyl-1,3,5-hexatriene showed that the microviscosity of the OA/oleate assembly was highest at pH 7.5 (the pH range of 6.9-10.6 was investigated). The fluorescence spectra of 6-lauroyl-2-dimethylaminonaphthalene revealed the dehydrated environments on membrane surfaces at pH < 7.7. The pH-dependent Raman peak intensity ratios, chain torsion (S = I1124/I1096) and chain packing (R = I2850/I2930), showed local maxima, indicating the occurrence of metastable phases, such as dispersed cubic phase (pH = 7.5), vesicle (pH = 8.5), and dispersed cylindrical micelle (pH = 9.7). These results suggest that large-scale OA/oleate assemblies could possess particular membrane properties in a narrow pH region, e.g., at pH 7.5, and 9.7.

Membrane surface-enhanced Raman spectroscopy for sensitive detection of molecular behavior of lipid assemblies.

The dynamic properties of phospholipid (PL) membranes (phase state and phase transition) play crucial roles in biological systems. However, highly sensitive, direct analytical methods that shed light on the nature of lipids and their assemblies have not been developed to date. Here, we describe the analysis of PL-modified Au nanoparticles (Au@PL) using membrane surface-enhanced Raman spectroscopy (MSERS) and report the properties of the self-assembled PL membranes on the Au nanoparticle. The Raman intensity per PL concentration increased by 50-170 times with Au@PL, as compared to large unilamellar vesicles (LUVs) at the same PL concentration. The phase state and phase transition temperature of the PL membrane of Au@PL were investigated by analyzing the Raman peak ratio (R = I2882/I2930). The enhancement at 714 cm(-1) (EF(714)) varied with the hydrocarbon chain length of the PLs and the assembled degree of Au@PLs. In calculation, the EF(714),assembled was estimated to be 111-142 when the distance between AuNPs was 7.0-7.5 nm, which was correlated to the speculative enhancement factor, suggesting that the assembly of the Au@PLs contributed to the MSERS.

Systematical characterization of phase behaviors and membrane properties of fatty acid/didecyldimethylammonium bromide vesicles.

Fatty acids (FAs) are known to form vesicle structures, depending on the surrounding pH conditions. In this study, we prepared vesicles by mixing FAs and a cationic surfactant, and then investigated their physicochemical properties using fluorescence spectroscopy and dielectric dispersion analysis (DDA). The assemblies formed from oleic acid (OA) and linoleic acid (LA) were modified by adding didecyldimethylammonium bromide (DDAB). The phase state of FA/DDAB mixtures was investigated with pH titration curves and turbidity measurements. The trigonal diagram of FA/ionized FA/DDAB was successfully drawn to understand the phase behaviors of FA/DDAB systems. The analysis of fluidities in the interior of the membrane with use of 1,6-diphenyl-1,3,5-hexatriene (DPH) indicated that the membrane fluidities of OA/DDAB and LA/DDAB at pH 8.5 slightly decreased in proportion to the molar ratio of DDAB in FA/DDAB systems. The fluorescent probe 6-lauroyl-2-dimethylamino naphthalene (Laurdan) indicated that the LA vesicle possessed a dehydrated surface, while the OA vesicle surface was hydrated. Modification of LA vesicles with DDAB induced the hydration of membrane surfaces, whereas modification of OA vesicles by DDAB had the opposite effect. DDA analysis indicated that the membrane surfaces were hydrated in the presence of DDAB, suggesting that the surface properties of FA vesicles are tunable by DDAB modification.

Preparation and Characterization of Biodegradable Sponge-like Cryogel Particles of Chitosan via the Inverse Leidenfrost (iLF) Effect.

Chitosan-based cryogel particles were synthesized using the inverse Leidenfrost (iLF) effect, with glutaraldehyde employed as the cross-linker. The resulting cryogels exhibited a sponge-like morphology with micrometer-sized interconnected pores and demonstrated resilience, withstanding up to three compression-release cycles. These characteristics highlight the potential of chitosan cryogels for diverse applications, including adsorption and biomedical uses. We further investigated the influence of varying acetic acid concentrations on the properties of the chitosan cryogels. Our findings revealed that the particle size distribution of the cryogels ranged from 1300 to 2900 µm. As the concentration of acetic acid increased, the swelling degree of the chitosan cryogels decreased, stabilizing at an approximate value of around 6 at 0.03 mol of acetic acid. Additionally, the shift in the absorption peak of the OH and free amino groups from 3261 to 3404 cm-1 confirmed the cross-linking reaction between chitosan and glutaraldehyde.

Accelerated cell death 2 suppresses mitochondrial oxidative bursts and modulates cell death in Arabidopsis.

The Arabidopsis ACCELERATED CELL DEATH 2 (ACD2) protein protects cells from programmed cell death (PCD) caused by endogenous porphyrin-related molecules like red chlorophyll catabolite or exogenous protoporphyrin IX. We previously found that during bacterial infection, ACD2, a chlorophyll breakdown enzyme, localizes to both chloroplasts and mitochondria in leaves. Additionally, acd2 cells show mitochondrial dysfunction. In plants with acd2 and ACD2 (+) sectors, ACD2 functions cell autonomously, implicating a pro-death ACD2 substrate as being cell non-autonomous in promoting the spread of PCD. ACD2 targeted solely to mitochondria can reduce the accumulation of an ACD2 substrate that originates in chloroplasts, indicating that ACD2 substrate molecules are likely to be mobile within cells. Two different light-dependent reactive oxygen bursts in mitochondria play prominent and causal roles in the acd2 PCD phenotype. Finally, ACD2 can complement acd2 when targeted to mitochondria or chloroplasts, respectively, as long as it is catalytically active: the ability to bind substrate is not sufficient for ACD2 to function in vitro or in vivo. Together, the data suggest that ACD2 localizes dynamically during infection to protect cells from pro-death mobile substrate molecules, some of which may originate in chloroplasts, but have major effects on mitochondria.

Versatility of the Preparation Method for Macroporous Cryogel Particles Utilizing the Inverse Leidenfrost Effect.

We have investigated the versatility of a two-step preparation method, without a detergent, that combines both the inverse Leidenfrost effect and the cryogelation technique by using the macroporous particles of different kinds of monomers (four vinyl monomers) or a natural polymer (agarose). First, the precursor of polymers was dropped into liquid nitrogen to prepare the spherical frozen droplet by the inverse Leidenfrost effect. Second, the frozen droplets were cryo-polymerized at the frozen temperature; then, cryogel particles were prepared after thawing. Subsequently, the basic characteristics of the macroporous polymer particles obtained above were compared, focusing on the appearances, porous morphologies, and mechanical properties. It was found that the similar polymer particles could be obtained by the two-step preparation method, while there was a slight difference in their characteristics, depending on the type of monomers. Especially for the mechanical properties, the cryogel particles of the hydrophilic polymer exhibited a shape memory function with sponge-like elasticity, whereas the hydrophobic polymer particles were observed to be cracked after compression (i.e., no shape memory function). This work provides a versatile method of adopting various kinds of monomers and natural polymers for the preparation of macroporous particles. Hence, the method possibly has a potential to prepare and design "tailor-made" macroporous polymer particles for the application purpose.

Study of Chemical Polymerization of Polypyrrole with SDS Soft Template: Physical, Chemical, and Electrical Properties.

Polypyrrole (PPy) is a conductive polymer known for its biocompatibility and ease of synthesis. Chemically polymerized PPy was synthesized in the presence of sodium dodecyl sulfate (SDS), showing correlations among chemical properties, physical morphology, and electrical properties. Focused synthesis parameters included the pyrrole (Py) concentration, SDS concentration, and ammonium persulfate (APS)/Py ratio. The addition of SDS during chemical polymerization influenced the physical morphology of PPy by altering the self-assembling process via micelle formation, yielding sheet-like morphologies. However, the phenomenon also relied heavily on other synthesis parameters. Varying SDS concentrations within the 0.01 to 0.30 M window produced PPy sheets with no significant difference in optical band gap or physical size. While using 0.10 M SDS, an increase in Py concentration from 0.10 to 0.30 M yielded a larger size of PPy as the morphology changed from sheet-like to irregular shape. The band gap dropped from 2.35 to 1.10 eV, and the conductivity rose from 6.80 × 10-1 to 9.40 × 10-1 S/m. With an increase in the APS/Py ratio, the PPy product changed from a random to a sheet-like form. The product provided a larger average size, a decreased band gap, and increased electrical conductivity. Py polymerization in the absence of SDS revealed no significant change in shape or size as the Py concentration increased from 0.10 to 0.30 M; only a sphere-like form was observed, with a large band gap and small conductivity. Results from Raman spectral analysis indicated a correlation between optical band gap, physical morphology, and bipolaron/polaron ratio, mainly at the wavelengths associated with C-C stretching and C-H deformation. The increase in average size was associated with a decrease in band gap and resistance as well as an increase in the bipolaron/polaron ratio. This work indicates a strong correlation between size, morphology, electrical properties, and the bipolaron/polaron ratio of PPy in the presence of SDS.