Papers - Fujimoto, Keiji

One-pot synthesis of fluorescent hybrid nanoparticles and their assembly into transparent and multi-coloured nanofilms

Yuuka Fukui, Yui Ozawa and Keiji Fujimoto

Journal of Materials Chemistry C (Journal of Materials Chemistry C)  1 ( 6 ) 1231-1237 - 1237 2013

Research paper (scientific journal), Joint Work, Accepted,  ISSN  20507534

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We developed a route for one-pot synthesis of fluorescent hybrid nanoparticles and their assembly into a nanofilm by utilizing a fusion and fission-triggered nanoreactor system based on water-in-oil "mini- emulsion". A fluorescent nanocrystal, ZnS:Mn²⁺, was produced in a confined system via fusion and fission of nanodroplets induced by ultrasonication and the amount of nanocrystals formed in each nanoreactor was easily controlled. Then, in situ polymerisation allowed for encapsulation of nanocrystals inside polymer nanoparticles, leading to an efficient surface capping of nanocrystals with polymers and hence a strong light emission under UV irradiation. Also, hybrid nanoparticles with different colours could be created by tuning of Mn²⁺ doping into ZnS nanocrystals, which can give rise to an energy transfer from carboxylic groups of surface capping polymers to the Mn²⁺. These hybrid nanoparticles were then spin-coated to form hybrid nanofilms where nanocrystals were uniformly distributed. The multicolour tuning of nanofilms was achieved simply by mixing nanoparticles with ZnS-derived blue emission and those with ZnS:Mn²⁺-derived orange emission. We believe that our nanoreactor system would offer a viable way in creating fluorescent nanomaterials. © 2013 The Royal Society of Chemistry.

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Preparation of thermosensitive polymer nanoparticles by protein-mimetic cross-linking.

Kaihara, Sachiko; Narikawa, Masatoshi; Fujimoto, Keiji.

Colloid and Polymer Science (Colloid and Polymer Science)  290 ( 13 ) 1317-1325 - 1325 2012.08

Research paper (scientific journal), Joint Work, Accepted,  ISSN  0303402X

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Thermosensitive nanoparticles were prepared by mimicking protein folding where polymer aggregates were formed by precipitation of thermosensitive polymer chains followed by disulfide formation of their thiol groups. N-Isopropylacrylamide (NIPAM) and methacryloxy succini-mide (SuMA) were co-polymerized and then cysteamine was allowed to react with succinimide moieties of the polymer to render thiol moieties. A polymer aqueous solution precipitated to form nano-sized aggregates by increasing temperature above its lower critical solution temperature (LCST), and their sizes were monodispersed and tunable by the polymer concentration. The aggregates were cross-linked to produce nanoparticles by oxidation of thiol groups in a manner similar to formation of a disulfide bond of protein. As a result, the cross-linked nanoparticles exhibited swelling by decreasing temperature below the LCST of the copolymer. Fluorescein and bovine serum albumin (BSA) were chosen as a small and a large substance, respectively, and were encapsulated into the swollen nanoparticles at 25 °C. Fluorescein was rapidly released from both swollen and shrunken nanoparticles. Although BSA exhibited little release at any temperatures, it was released from nanopar-ticles by adding the reducing agent to dissociate the disul-fide cross-linking and incubating below the LCST. © Springer-Verlag 2012.

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Bio-inspired nanoreactor based on a miniemulsion system to create organic-inorganic hybrid nanoparticles and nanofilms

Fukui Y., Fujimoto K.

Journal of Materials Chemistry (Journal of Materials Chemistry)  22 ( 8 ) 3493 - 3499 2012.02

Research paper (scientific journal), Accepted,  ISSN  09599428

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We developed a novel route to control both mineralization and polymerization inside a nanoreactor based on a miniemulsion system to create organic-inorganic hybrid nanomaterials with diverse structures and morphologies. Nanodroplets of calcium nitrate (Ca(NO 3) 2)/monomer and nanodroplets of sodium carbonate (Na 2CO 3) were separately prepared and suspended in the oil phase. They were mixed through the fusion and fission process triggered by ultrasonication to precipitate a biomineral only inside the nanodroplets. In the presence of monomer, 2-hydroxyethyl methacrylate (HEMA), we could obtain unique structures of nano-sized CaCO 3 particles, which were crystalline with spherical or rod-like shapes or amorphous. By subsequent polymerization, we could encapsulate nano-CaCO 3 inside the polymeric nanoparticles at a desired stage of crystal growth. The preincubation period for CaCO 3 nucleation and growth and the polymerization rate were important factors to manipulate the structures and polymorphs of nano-CaCO 3 inside the hybrid nanoparticles, owing to inhibition of crystal growth and transformation by polymerization of HEMA. Also, the growth of rod-like CaCO 3 inside the nanoparticles led to formation of spheroidal hybrid nanoparticles. By using hybrid nanoparticles as building blocks, we could produce nanofilms containing nano-CaCO 3 with a variety of sizes and structures. Crystal transformation of amorphous CaCO 3 was induced inside the nanofilm by increasing the temperature to above the T g of PHEMA. © 2012 The Royal Society of Chemistry.

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Bio-inspired nanoreactor based on miniemulsion system to create organic-inorganic hybrid nanoparticles and nanofilms

Yuuka Fukui & Keiji Fujimoto

Journal of Materials Chemistry (RSC)  22 ( 8 ) 3493-3499 2012.01

Research paper (scientific journal), Joint Work, Accepted

Production of nanofibers by atto-incubator-assisted assembly of urea using the particle array

S. Watanabe, M. Yamazaki, S. Kaihara and K. Fujimoto

Colloids and Surfaces A: Physicochemical and Engineering Aspects (Colloids and Surfaces A: Physicochemical and Engineering Aspects)  399   83-91 - 91 2012

Research paper (scientific journal), Joint Work, Accepted,  ISSN  09277757

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We exploited three approaches to fabricate urea nanofibers by using an array of core-shell particles as a template. Core-shell particles were prepared by seeded polymerization and used as an atto-liter scale incubator (atto-incubator) to form nanofibers of urea crystal. Firstly, the mixture of the particle suspension and a urea aqueous solution was spin-coated to promote arrangement of core-shell particles and urea crystallization simultaneously (mix-spin method). Secondly, core-shell particles were arranged by a Langmuir-Blodgett apparatus and then the spin-coating of a urea aqueous solution was performed (LB-spin method). Then, the nano-network of urea crystals was produced by heat treatment at 80 °C. The interparticle distance and the amount of the remaining solution were important to determine the shapes, orientation and amounts of urea crystals. In the LB-natural drying method, one-directionally oriented nanocrystals were obtained over the wide range of the interparticle distance. As preliminary attempts, the obtained nanofibers were used as a template for the production of nanoscale metallic materials. Au nanofibers, nanotubes and nanorods could be obtained by gold sputtering deposition on the urea nanofiber and dissolving urea crystals. Ag-urea hybrid nanofibers were also produced using a mixture of urea and Ag nanoparticles by the modified LB-spin method. © 2012 Elsevier B.V.

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Preparation and Assembly of Poly(arginine)-coated liposomes to Create a Free-standing Bio-scaffold

Yamamoto, Saika; Fukui, Yuuka; Kaihara, Sachiko; Fujimoto, Keiji

Langmuir (ACS)  27 ( 15 ) 9576-82 - 9582 2011.08

Research paper (scientific journal), Joint Work, Accepted,  ISSN  07437463

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We created a free-standing membrane as a novel bioscaffold through the assembly of polymer-coated liposomes. Polyarginine (PArg) possessing a cell-penetrating activity was used to form the polymer layer onto a negatively charged liposome (lipo-PArg). The capsule wall of PArg over liposomes made it possible to improve the mechanical property of capsules and to display deoxyribonucleic acid (DNA) over the vesicle surface through the electrostatic attraction (lipo-PArg-DNA). The release rates of a fluorescent probe encapsulated in lipo-PArg and lipo-P Arg-DNA were tunable by the number of polymeric layers of the capsule walls. To investigate the cell-membrane permeability of lipo-P Arg-DNA, polymer-coated liposomes were incubated with human umbilical vein endothelial cells (HUVECs) at 4 °C. It was found that lipo-P Arg underwent a significant cellular uptake, whereas bare liposomes and liposomes modified with chitosan were incapable of overcoming the plasma membrane barrier. To prepare a free-standing membrane composed of polymer-coated liposomes, a suspension of lipo-PArg-DNA was cast over a mesh hole and dried up. SEM observation revealed that a free-standing membrane was obtained through drying-mediated assembly process without rupturing polymer-coated liposomes inside the membrane. On the other hand, it was not possible to obtain a complete membrane from a mixture of lipo-PArg and DNA. In summary, lipo-PArg-DNA capsules possess versatile functions as a drug carrier, and their assembly enables us to create a free-standing membrane applicable as a bioscaffold. © 2011 American Chemical Society.

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In situ synthesis of polysaccharide nanoparticles via polyion complex of carboxymethyl cellulose and chitosan

Kaihara,S, Suzuki,Y and Fujimoto,K.

Colloids & Surfaces B: Biointerfaces (Colloids and Surfaces B: Biointerfaces)  85 ( 2 ) 343-348 - 348 2011.03

Research paper (scientific journal), Joint Work, Accepted,  ISSN  09277765

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Biocompatible polymer-magnetite hybrid nanoparticles were prepared by means of in situ synthesis of magnetite within polysaccharide hydrogel nanoparticles. Hydrogel nanoparticles were first fabricated by blending high-molecular-weight carboxymethyl cellulose as an anionic polymer, and low-molecular-weight chitosan as a cationic polymer to form polyion complexes (CC particles). These polyion complexes were then chemically crosslinked using genipin, a bio-based cross-linker, to form stable nanoparticles having a semi-IPN structure (CCG particles). Magnetite was lastly synthesized within CCG particles by the coprecipitation method to obtain polymer-magnetite hybrid nanoparticles (CCGM particles). The formations of CC, CCG and CCGM particles were mainly observed by transmittance, absorbance of genipin and TEM, respectively, and their hydrodynamic diameters and zeta-potentials were analyzed. It was confirmed that the hydrodynamic diameters and the zeta-potentials of these particles were significantly influenced by pH of the suspension, which was attributed to the charges of polymers. The diameters of CCGM particles were smaller than 200. nm at any pH conditions, suggesting the possibility to apply them as drug delivery carriers. CCGM particles exhibited the responsiveness to a magnetic field in addition to their high dispersion stability, indicating their potential to be utilized as a biomaterial for hyperthermia. © 2011 Elsevier B.V.

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Control in Mineralization by the Polysaccharide-Coated Liposome via the Counter-Diffusion of ions

Yuuka Fukui and Keiji Fujimoto

Chemistry of Materials (ACS)  23 ( 21 ) 4701-4708 - 4708 2011

Research paper (scientific journal), Joint Work, Accepted,  ISSN  08974756

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We created an organic-inorganic hybrid nanocapsule by utilizing polysaccharide-coated liposomes as a reaction site for the deposition of calcium phosphate (CaP). Phosphate ions were encapsulated in a liposome, followed by the layer-by-layer deposition of chitosan (CHI), dextran sulfate (DXS), or DNA onto the liposome surface. Calcium ions were added to an aqueous suspension of the phosphate ion-incorporated nanocapsules to prepare the nanocapsules that provide a variety of walls for the counter-diffusion of ions and the surface for CaP deposition. As a result, control in biomineralization, such as thickness and crystal properties, over the nanocapsules was achieved by tuning the counter-diffusion of the calcium ions and the phosphate ions through the capsule wall and the surface chemical composition of nanocapsules. Furthermore, we carried out DNA adsorption onto CaP-coated liposomes. DNA was releasable from the nanocapsules because of the dissolution of CaP under acidic conditions. © 2011 American Chemical Society.

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The Preparation of Sugar Polymer-Coated Nanocapsules by the Layer-by-Layer Deposition on the Liposome

Fukui,Y. and Fujimoto,K.

Langmuir (Langmuir)  25 ( 17 ) 10020-10025 - 10025 2009.03

Research paper (scientific journal), Joint Work, Accepted,  ISSN  07437463

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We intended to combine the liposomal preparation and the layer-by-layer deposition to prepare a nanosized capsule. Chitosan (CHI) was deposited to form the cationic polymeric layer onto a negatively charged liposomal surface and further deposition was carried out using anionic polymers dextran sulfate (DXS) or deoxyribonucleic acid (DNA). ζ-Potentials of nanocapsules changed between positive and negative charges at each deposition. FE-TEM revealed that the liposome remained a spherical shape even after the layer-by-layer (LbL) deposition. The capsule wall showed a dramatic increase in stability against the surfactant Triton X-100 compared to a bare liposome, and the stability was controllable by the adsorption amount of the polymer. These suggest that the polymer multilayer was generated on the liposome surface by the layer-by-layer depositions of polysaccharides. The three kinds of chemical substances with different charges, 1-hydroxy pyrene-3,6,8-trisulfonic acid (HPTS), alendronate, and glucose, were encapsulated into nanocapsules and the release was suppressed by the polymeric capsule wall irrespective of charges. The release from DNA-deposited nanocapsules (liponano-CHI-DNA) was clearly increased by raising temperature from 25 to 60 °C. This indicates that the temperature-dependent release was achieved by applying DNA denaturation as a temperaturedependent "switch", which influenced the permeability of the capsule wall. © 2009 American Chemical Society.

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Effect of nano-scale roughness on detachment of a cell sheet from a particle monolayer

Miura M., Fujimoto K.

8th World Biomaterials Congress 2008 (8th World Biomaterials Congress 2008)  1 2008.12

Research paper (scientific journal), Accepted,  ISSN  9781615670802

Formation and recovery of a cell sheet by a particle monolayer with the surface roughness

Manabu MIURA and Keiji FUJIMOTO

Colloids and Surfaces B: Biointerfaces (Elsevir)  66 ( 1 ) 125-133 - 133 2008

Research paper (scientific journal), Joint Work, Accepted,  ISSN  09277765

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We studied the topographical effect of roughness displayed by a closely packed particle monolayer on formation of a cell monolayer (cell sheet). Particle monolayers were prepared by Langmuir-Blodgett deposition using particles, which were 527 nm (SA053) and 1270 nm (SA127) in diameter. Human umbilical vein endothelial cells (HUVECs) were seeded at a high density (2.0 × 105 cells/cm2) onto particle monolayers. It was found that cells gradually became into contact with adjacent cells on the SA053 monolayer and the formed cell sheet could be readily detached from the particle monolayer by gentle pipetting. On the other hand, cells adhering onto the tissue culture polystyrene (TCPS) and the SA127 particle monolayer were difficult to peel off. At a low cell seeding density (5.0 × 104 cells/cm2), pre-coating with bovine plasma fibronectin (FN) allowed cell growth on an SA053 particle monolayer, and a confluent monolayer was able to be peeled as a cell sheet from the particle monolayer just by pipetting. By immunostaining of human fibronectin, we found that fibronectin was secreted and concentrated onto the substrate side of a cell sheet. The obtained cell sheet adhered and grew on the TCPS again within 20 min. © 2008 Elsevier B.V. All rights reserved.

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Preparation of Bionanocapsules by the Layer-by-Layer Deposition of Polypeptides onto a Liposome

FUJIMOTO KEIJI,TOYODA TOMONORI,FUKUI YUUKA

Macromolecules (Macromolecules)  40 ( 14 ) 5122-5128 - 5128 2007.07

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00249297

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Hollow nanoparticles (bionanocapsules) were prepared using liposomes as a template for the layerby-layer deposition of biopolymers. We carried out the alternative deposition of poly-L-lysine (PLys) and poly-L-aspartic acid (PAsP) onto a negatively charged liposome, which was prepared from dilauroyl phosphatidic acid (DLPA) and dimyristoylphosphatidylcholine (DMPC). Efficient separation of nanocapsules from unbound polymers was achieved by ultrafiltration. ζ-Potentials of nanocapsules changed between positive and negative charges at each deposition. FE-TEM revealed that the liposome was covered with a thin polymeric layer. A fluorescent probe, l-hydroxypyrene-3,6,8- trisulfonic acid (HPTS), was encapsulated into nanocapsules. The release of HPTS was suppressed by the polymer deposition, and the release rate was tunable by coverage of the first PLys layer and the ratio of DLPA. © 2007 American Chemical Society.

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Producing and patterning of nanocrystals using "atto-incubators" composed of the core-shell particles

Fujimoto K., Katsuta I., Adachi T.

Colloids and Surfaces A: Physicochemical and Engineering Aspects (Colloids and Surfaces A: Physicochemical and Engineering Aspects)  290 ( 1-3 ) 118 - 124 2006.11

Research paper (scientific journal), Accepted,  ISSN  09277757

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We developed a small incubator of an atto-liter scale (atto-incubator) for producing and arraying nanosized materials. The core-shell particles with a hydrogel shell were used as an incubator to isolate individual droplets of the solution and to specify the nucleation sites for crystallizing NaCl and urea solutes. Their array was deposited on a polystyrene dish by the spin-coating of a particulate dispersion, and then dried to remove any residual solvent. When the array was exposed to a solution, the hydrogel shell absorbed the solution and swelled. Nucleation of the nanocrystals at the particles occurred as the arrays were dried again. We obtained single crystals as a rectangular solid with a uniform shape at 8 wt.% NaCl. By the use of atto-incubators for urea crystallization, we obtained nanosized fibers of a single crystal, which were aligned in the direction of the flow. The atto-incubator could allow us to control the nucleation region and the size and shape of the crystals. © 2006 Elsevier B.V. All rights reserved.

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Subcellular topological effect of particle monolayers on cell shapes and functions

Miura, M and Fujimoto, K

Colloids and Surfaces B: Biointerfaces (Colloids and Surfaces B: Biointerfaces)  53 ( 2 ) 245-253 - 253 2006

Research paper (scientific journal), Joint Work, Accepted,  ISSN  09277765

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We studied topological effects of subcellular roughness displayed by a closely packed particle monolayer on adhesion and growth of endothelial cells. Poly(styrene-co-acrylamide) (SA) particles were prepared by soap-free emulsion copolymerization. Particle monolayers were prepared by Langmuir-Blodgett deposition using particles, which were 527 (SA053) and 1270 nm (SA127) in diameter. After 24-h incubation, cells tightly adhered on a tissue culture polystyrene dish and randomly spread. On the other hand, cells attached on particle monolayers were stretched into a narrow stalk-like shape. Lamellipodia spread from the leading edge of cells attached on SA053 monolayer to the top of the particles and gradually gathered to form clusters. This shows that cell-cell adhesion became stronger than cell-substrate interaction. Cells attached to SA127 monolayer extended to the reverse side of a particle monolayer and engulfed particles. They remained immobile without migration 24 h after incubation. This shows that the inhibition of extensions on SA127 monolayer could inhibit cell migration and cell proliferation. Cell growth on the particle monolayers was suppressed compared with a flat TCPS dish. The number of cells on SA053 gradually increased, whereas that on SA127 decreased with time. When the cell seeding density was increased to 200,000 cells cm-2, some adherent cells gradually became into contact with adjacent cells. F-actin condensations were formed at the frame of adherent cells and the thin filaments grew from the edges to connect each other with time. For the cell culture on SA053 monolayer, elongated cells showed a little alignment. Cells showed not arrangement of actin stress fibers but F-actin condensation at the contact regions with neighboring cells. Interestingly, the formed cell monolayer could be readily peeled from the particle monolayer. These results indicate that endothelial cells could recognize the surface roughness displayed by particle monolayers and the response was dependent on the pitch of particle monolayers. © 2006 Elsevier B.V. All rights reserved.

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A reduction-triggered delivery by a liposomal carrier possessing membrane-permeable ligands and a detachable coating

Maeda, T. and Fujimoto, K.

Colloids and Surfaces B: Biointerfaces (Colloids and Surfaces B: Biointerfaces)  49 ( 1 ) 15-21 - 21 2006

Research paper (scientific journal), Joint Work, Accepted,  ISSN  09277765

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To control the cellular uptake of drugs and genes, we synthesized a liposomal carrier possessing membrane-permeable ligands and a detachable poly(ethylene glycol) (PEG) coating. For the detachable coating, a lipid having a thiolytic cleavable spacer (PEG-S-S-DOPE) was synthesized by the reaction of dioleoylphosphatidylethanolamine (DOPE) with a PEG chain via a disulfide linkage. The liposomes were prepared from a mixture of dipalmitoylphosphatidylcholine (DPPC), DOPE, PEG-S-S-DOPE, and cholesteryl hemisuccinate (CHEMS). The octamer (R8 peptide) of arginine was chosen as the membrane-permeable ligand and covalently immobilized onto the CHEMS portion of the liposome surface (PEG-S-S-R8-liposome). The disulfide bond of the PEG chain was cleaved to display the R8 peptides on the liposome surface by adding a reducing agent such as l-cysteine, and thereby internalization of the liposomes was significantly facilitated. When l-cysteine was added to the mixture of cells and the liposome that incorporated plasmids encoding the enhanced green fluorescence protein (pEGFP), the expression of EGFP was low but could be observed in almost 100% of the cells. © 2006 Elsevier B.V. All rights reserved.

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Producing and patterning of nanocrystals using “atto-incubators” composed of the core-shell particles

Keiji FUJIMOTO*, Izumi KATSUTA and Tomoko ADACHI

Colloids and Surfaces A: Physicochemical and Engineering Aspects 290   118-124 2006

Research paper (scientific journal), Joint Work, Accepted

Preparation and functionalization of hollow nanoparticles fabricated by the layer-by-layer deposition

Toyoda T., Fujimoto K.

Polymer Preprints, Japan (Polymer Preprints, Japan)  54 ( 2 ) 5163 - 5164 2005.12

Research paper (scientific journal), Accepted

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To prepare hollow particles in a nano size, we used a layer-by-layer deposition. Liposomes were used as a template for this deposition. At first, negatively charged liposomes composed of dilauroyl phosphatidic acid (DLPA) and dimyristoyl phosphatidylcholine (DMPC) were prepared with the extrusion method. Then, polyelectrolytes were adsorbed on the liposomal template. Poly-L-lysine (PLys) and poly-L-aspartic acid (PAsp) were chosen as adsorbates to make a capsule of the biopolymers. When the alternative adsorption of PLys and PAsp on the liposomes was repeated for thickening the capsule layer, their ζ-potentials changed between positive and negative charges at each deposition. To investigate the release behavior from the liposomes and the liposome-polypeptide complexes, we prepared liposomes incorporating 1-hydroxypyrene-3,6,8-trisulfonic acid (HPTS). It was found that the release experiment to the buffered solutions was related to the adsorption of polymers. When the liposomes were completely covered with PLys, the release was suppressed.

Detection of a K-ras point mutation employing peptide nucleic acid at the surface of a SPR biosensor

Sato Y., Fujimoto K., Kawaguchi H.

Colloids and Surfaces B: Biointerfaces (Colloids and Surfaces B: Biointerfaces)  27 ( 1 ) 23 - 31 2003.01

Research paper (scientific journal), Accepted,  ISSN  09277765

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A fundamental study of the usage of peptide nucleic acid (PNA) and DNA at the surface of a surface plasmon resonance (SPR) biosensor for detecting a specific point mutation in the K-ras gene for early detection of cancers is reported. The extents of hybridization using DNA analytes of different length which are targets were studied at 25 and 40°C. The 15mer PNA ligand immobilized to the surface of the sensor had a high ability to detect a 11mer DNA analyte point mutation at 25 and 40°C. On the contrary, when DNA was used as a ligand, detection was only confirmed at 40°C which indicates that the difference of melting temperature (Tm) between the complementary and mismatched analyte was a key factor for point mutation detection. This also implied the decrease of Tm by immobilizing a probe to a surface since it was below the one in solution. Therefore, effects from the surface are seen in this system and the surrounding environment makes a difference to the discrimination process. To understand the process in detail, kinetic analysis was performed and association constants were found to be larger for DNA ligands implying the effect coming from the sensor surface. In this case negative charges of the carboxyl groups of the matrix had a tendency to repel negatively charged DNA ligands. Affinity constants (KA) were calculated and as expected, the ratio of KA between the complementary and mismatched analyte was of the order of 102 for PNA interacting with 11mer analytes, making it a promising probe for genetic diagnosis. These results indicate the importance of the effect of analyte length, temperature and the environment surrounding the ligand for accomplishing an all or none single base mismatched detection system. © 2002 Elsevier Science B.V. All rights reserved.

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Thermosensitive two-dimensional arrays of hydrogel particles

Nakahama K., Fujimoto K.

Langmuir (Langmuir)  18 ( 26 ) 10095 - 10099 2002.12

Research paper (scientific journal), Accepted,  ISSN  07437463

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We prepared two-dimensional (2D) arrays composed of nanoscale hydrogel particles as a model of suprastructured assemblages. Poly(N-isopropylacrylamide) (PNIPAM) hydrogel particles and the core-shell particles, which possess a rigid polystyrene core encased in a PNIPAM hydrogel shell, were selected as components for arrays. Below and above 32°C, these two kinds of particles swelled and shrank, respectively, due to temperature-dependent solubility of a PNIPAM chain. The particle dispersion was spread and then compressed to produce particle monolayers closely packed at the air-water interface. To study thermal behavior of 2D arrays, surface pressure and surface area for obtained 2D arrays were measured at 40 and 25°C with leaving the monolayer on the water surface. Both of them varied in response to temperature, indicating that each particle of 2D arrays swelled and shrank at the water surface. Although the pressure and the area for the 2D array of PNIPAM hydrogel particles exhibited great responses at the beginning, they gradually decreased and eventually disappeared with repeating the temperature cycle, due to particle coalescence. On the other hand, the 2D array of core-shell particles maintained the thermosensitive response without relaxation though its variation between 40 and 25°C was still small. By assembling the mixture of PNIPAM and core-shell particles into the monolayer, the 2D array with large and steady responses could be obtained.

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Changes in cell membrane and cellular lipids in apoptotic cells induced by dolichyl phosphate differ from findings in cells induced by etoposide

Horiuchi,A., Yasugi,E., Iwasaki,C., Fujimoto,K., and Oshima,M.

J. Oleo Sci. (Journal of Oleo Science)  51 ( 1 ) 35-42 - 42 2002

Research paper (scientific journal), Joint Work, Accepted,  ISSN  13458957

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Cell membrane fluidity and changes of cellular lipids of U937 cells during apoptosis are compared between the cells treated with dolichyl phosphate (dol-P) and etoposide. Dol-P induced lateral cell membrane perturbation immediately after addition and continued for at least 40 min. However, etoposide induced apoptosis without increase in cell membrane fluidity. Phosphatidylethanolamine was translocated together with phosphatidylserine after 4 hr of treatment in both dol-P and etoposide treated cells. The concentration of lipid levels changed in dol-P-induced cells and the cholesterol/phospholipid ratio almost doubled. Conversely, none of the phospholipid and cholesterol levels changed in etoposide treated cells. Although both dol-P and etoposide induce apoptosis, dol-P, but not etoposide, appeared to function as a modulator of membrane fluidity and to change membrane constituents and membrane physiology during the course of apoptosis.© 2002, Japan Oil Chemists’ Society. All rights reserved.

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