Publications by authors named "Atsushi Hotta"

22 Publications

  • Page 1 of 1

Fabrication of Gd-DOTA-functionalized carboxylated nanodiamonds for selective MR imaging (MRI) of the lymphatic system.

Nanotechnology 2021 Mar 3. Epub 2021 Mar 3.

Department of Mechanical Engineering, Keio University Faculty of Science and Technology Graduate School of Science and Technology, 3-14-1 Hiyoshi Kohoku-ku, Yokohama, 223-8542, JAPAN.

Magnetic resonance imaging (MRI) contrast agents with the particle diameter of around 3-10 nm hold the potential to be selectively uptaken by lymphatic vessels and be filtered in the kidney for final excretion. However, there are no existing MRI contrast agents based on gadolinium (Gd) complexes within the size of this range, and thus the selective imaging of the lymphatic system has not yet been achieved. In our previous report, we succeeded in fabricating nano-scale MRI contrast agents by complexing ordinary contrast agents (Gd-diethylenetriaminepentaacetic acid (DTPA)) with carboxylated nanodiamond (CND) particles to conquer this problem. However, DTPA has recently been reported to release Gd ions in the course of time, leading to the potential danger of severe side effects in the human body. In this study, we utilized cyclic-chained DOTA as an alternative chelating material for DTPA to fabricate CND-based MRI contrast agents for the selective lymphatic imaging. The newly fabricated contrast agents possessed the diameter ranging from 3 nm to 10 nm in distilled water and serum, indicating that these particles can be selectively uptaken by lymphatic vessels and effectively filtered in the kidney. Furthermore, the DOTA-applied CND contrast agents exhibited stronger MRI visibility in water and serum compared to DTPA-applied CND contrast agents. These results indicate that DOTA-applied CND contrast agents are promising materials for the selective MR imaging of lymphatic systems.
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http://dx.doi.org/10.1088/1361-6528/abeb9cDOI Listing
March 2021

Synthesis of Thermoplastic Poly(2-methoxyethyl acrylate)-Based Polyurethane by RAFT and Condensation Polymerization.

Macromol Rapid Commun 2020 Oct 17;41(19):e2000346. Epub 2020 Aug 17.

Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, 223-8522, Japan.

Thermoplastic solid poly(2-methoxyethyl acrylate) (PMEA)-based polyurethane (PU) is synthesized through the reversible addition-fragmentation chain transfer (RAFT) polymerization and the condensation polymerization, using hydroxyl-terminated RAFT reagents and diisocyanate, respectively. Neat PMEA is a promising antithrombogenic liquid used in the medical fields. The thermoplastic property of the solid PMEA-based PU due to hydrogen bonding is confirmed by the dynamic mechanical analysis (DMA) at temperature below 72 °C. The antithrombogenic property of PMEA-based PU is also analyzed by the platelet adhesion test. The number of platelets on PMEA-based PU is 17 cells per unit area, which is smaller than that on the fluorinated diamond-like carbon (F-DLC), a well-known highly antithrombogenic material. It is concluded that a newly synthesized PMEA-based PU exhibits thermoplastic characteristics with excellent antithrombogenicity.
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http://dx.doi.org/10.1002/marc.202000346DOI Listing
October 2020

Thermophysical Property Measurements of Tetrabutylphosphonium Oxalate (TBPOx) Ionic Semiclathrate Hydrate as a Media for the Thermal Energy Storage System.

Front Chem 2020 16;8:547. Epub 2020 Jul 16.

Department of Mechanical Engineering, Keio University, Tokyo, Japan.

With increasing global power demand, thermal energy storage technology could play a role ensuring a sustainable energy supply in power generation from renewable energy sources and power demand concentration. Hydrates have high potential as phase change materials (PCMs) for the use as a thermal energy storage medium. To develop thermal energy storage technology using a hydrate-based material, further investigation of thermophysical properties and the selection of a suitable hydrate are required. Tetrabutylphosphonium oxalate (TBPOx) ionic semiclathrate hydrate contains oxalic acid in salt form, as a guest compound, which is classified as carboxylic acid group with low environmental impact. In the present study, the phase equilibrium temperature and the dissociation heat of TBPOx hydrate were measured. The highest equilibrium temperature of the solid hydrate formed was 9.4°C at the mass fraction 0.35 of TBPOx in aqueous solution. The largest dissociation heat was 186.0 ± 0.5 kJ·kg at the mass fraction of 0.35. Comparing with other PCMs with close phase equilibrium temperatures, TBPOx hydrate is superior in safety and sustainability. These results indicate that TBPOx hydrate would be suitable as the thermal storage medium for the general air conditioning systems.
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http://dx.doi.org/10.3389/fchem.2020.00547DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7378790PMC
July 2020

SANS study on the nano-crystalline network structure of elastic physical gels made of syndiotactic polypropylene.

Soft Matter 2019 Jul;15(27):5521-5528

Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan.

The structure-property relationship of an elastic physical gel, obtained by simply quenching syndiotactic polypropylene (sPP)/decahydronaphthalene solution with liquid nitrogen, was investigated based on small-angle neutron scattering (SANS) analysis. The SANS analysis revealed that sPP nanocrystals with a constant radius of 4-5 nm existed in the sPP gels regardless of the sPP concentration, whereas the correlation length of the nanocrystals drastically decreased from ∼130 to ∼20 nm upon increasing the sPP concentration from 2 to 12 wt%. The volume fraction and the number density of the sPP nanocrystals increased monotonously with the increase in the sPP concentration. The rheological properties and the melting behavior of the quenched sPP gels were highly consistent with the number density of the nanocrystals calculated from the SANS analysis, strongly suggesting that the sPP nanocrystals actually worked as crosslinking points by inducing elasticity in the quenched sPP gels.
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http://dx.doi.org/10.1039/c9sm00582jDOI Listing
July 2019

Thermo-Responsive Nanocomposite Hydrogels Based on PEG--PLGA Diblock Copolymer and Laponite.

Polymers (Basel) 2019 Feb 2;11(2). Epub 2019 Feb 2.

Frontier Research Center for Applied Atomic Sciences, Ibaraki University, 162-1 Shirakata, Tokai, Ibaraki 319-1106, Japan.

Poly(ethylene glycol)--poly(d,l-lactide--glycolide) (PEG--PLGA) diblock copolymers are widely known as polymeric surfactants for biomedical applications, and exhibit high solubility in water compared to PLGA--PEG--PLGA triblock copolymers known as gelation agents. In order to overcome the difficulties in the preparation of thermo-responsive hydrogels based on PLGA--PEG--PLGA due to the low solubility in water, the fabrication of thermo-responsive hydrogels based on PEG--PLGA with high solubility in water was attempted by adding laponite to the PEG--PLGA solution. In detail, PEG--PLGA with high solubility in water (i.e., high PEG/PLGA ratio) were synthesized. Then, the nanocomposite solution based on PEG--PLGA and laponite (laponite/PEG--PLGA nanocomposite) was fabricated by mixing the PEG--PLGA solutions and the laponite suspensions. By using the test tube inversion method and dynamic mechanical analysis (DMA), it was found that thermo-responsive hydrogels could be obtained by using PEG--PLGA, generally known as polymeric surfactants, and that the gelation temperature was around the physiological temperature and could be regulated by changing the solution composition. Furthermore, from the structural analysis by small angle neutron scattering (SANS), PEG--PLGA was confirmed to be on the surface of the laponite platelets, and the thermosensitive PEG--PLGA on the laponite surface could trigger the thermo-responsive connection of the preformed laponite network.
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http://dx.doi.org/10.3390/polym11020250DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6419014PMC
February 2019

Micropatterning of a 2-methacryloyloxyethyl phosphorylcholine polymer surface by hydrogenated amorphous carbon thin films for endothelialization and antithrombogenicity.

Acta Biomater 2019 03 31;87:187-196. Epub 2019 Jan 31.

Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan. Electronic address:

The existing first-generation drug-eluting stent (DES) has caused late and very late stent thrombosis related to incomplete stent endothelialization. Hence, biomaterials that possess sufficient anti-thrombogenicity and endothelialization with the controlled drug release system have been highly required. In this work, we have developed a newly designed drug-release platform composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer, a non-thrombogenic polymer, and micropatterned hydrogenated amorphous carbon (a-C:H), a cell-compatible thin film. The platelet adhesion and the endothelial cell adhesion behavior on the micropatterned substrates were investigated in vitro. The results indicated that the micropatterned a-C:H/MPC polymer substrates effectively supported the human umbilical vein endothelial cell (HUVEC) proliferation, while suppressing the platelet adhesion. Interestingly, the HUVEC exhibited different shape and behavior by changing the island size of the micropatterned a-C:H. By introducing both a non-thrombogenic polymer and cell-compatible thin films through a simple patterning method, we demonstrated that the platform had the potential to be utilized as a base material for DES with cell controllability. STATEMENT OF SIGNIFICANCE: The current first-generation drug-eluting stents (DES) would cause late and very late stent thrombosis due to the incomplete endothelialization of the metal stent material. In this work, we have developed a new DES platform composed of a 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer micropatterned by hydrogenated amorphous carbon (a-C:H). Two types of differently micropatterned a-C:H stent surface were made. Our studies revealed that the micropatterned a-C:H/MPC polymer substrates could effectively enhance the endothelial cell (EC) proliferation, simultaneously suppressing the platelet adhesion, becoming a highly biocompatible material especially for indwelling devices including a drug-release device. The new drug-release platform could be utilized as a base material for cell-controllable coating on DES.
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http://dx.doi.org/10.1016/j.actbio.2019.01.059DOI Listing
March 2019

Nanocomposite injectable gels capable of self-replenishing regenerative extracellular microenvironments for in vivo tissue engineering.

Biomater Sci 2018 Feb;6(3):550-561

Department of Nanobiochemistry, Frontiers of Innovative Research in Science and Technology (FIRST), Konan University, 7-1-20 Minatojima-Minamimachi, Kobe 650-0047, Japan.

Injectable hydrogels are biomaterials that have the potential to provide scaffolds to cells for in situ tissue regeneration with a minimally invasive implantation procedure. The success of in vivo tissue engineering utilizing injectable gels depends on providing cells with appropriate scaffolds that present an instructive extracellular microenvironment, which strongly influences the survival, proliferation, organization, and function of cells encapsulated within gels. One of the most important abilities of injectable gels to achieve this function is to adsorb and retain a wide variety of requisite bioactive molecules including nutrients, extracellular matrices, and growth/differentiation factors within gels. Previously, we developed nanocomposite injectable gels fabricated by simple combination of common biodegradable copolymers, poly(lactide-co-glycolide)-b-poly(ethylene glycol)-b-poly(lactide-co-glycolide) (PLGA-PEG-PLGA), and synthetic clay nanoparticles (LAPONITE®). We revealed that the nanocomposite injectable gels strongly adsorb ECM molecules including collagen and heparin within gels and retain them due to the ability of LAPONITE® in synchronization with the degradation of PLGA-PEG-PLGA and subsequent release of the degradation products. Human dermal fibroblast cells cultured on the nanocomposite gels showed enough high cell viability and proliferation for at least a week. Moreover, various kinds of human cells encapsulated within the nanocomposite gels exhibited significantly higher survival, proliferation, and three-dimensional organization in comparison with the PLGA-PEG-PLGA gel, LAPONITE® gel, and Matrigel. Furthermore, transplantation of mouse myoblast cells with the nanocomposite gels in model mice of skeletal muscle injury dramatically enhanced tissue regeneration and functional recovery, whereas cell transplantation with the PLGA-PEG-PLGA gel did not. Thus, the nanocomposite injectable gels possess unique abilities to self-replenish the regenerative extracellular microenvironment within the gels in the body, demonstrating the potential utility of the nanocomposite injectable gels for in vivo tissue engineering.
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http://dx.doi.org/10.1039/c7bm01167aDOI Listing
February 2018

In vitro basic fibroblast growth factor (bFGF) delivery using an antithrombogenic 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer coated with a micropatterned diamond-like carbon (DLC) film.

J Biomed Mater Res A 2017 Dec 23;105(12):3384-3391. Epub 2017 Sep 23.

Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, 223-8522, Japan.

In this study, a newly designed drug-release platform composed of an antithrombogenic 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer was introduced, which was impregnated with basic fibroblast growth factor (bFGF) (bFGF/MPC polymer) to enhance the endothelial cell activation. The platform was also coated with an ultrathin micropatterned diamond-like carbon (DLC) film (DLC/bFGF/MPC polymer) to precisely control the drug release rate and the cell compatibility. The resulting DLC/bFGF/MPC polymer could effectively prolong the bFGF release rate by depositing the micropatterned DLC. The number of adherent platelets on the DLC/bFGF/MPC polymer was significantly lower (about 1/14) than that on a currently used stent made of stainless steel (SUS316L), indicating the enhanced antithrombogenicity in the DLC/bFGF/MPC polymer. The proliferation of endothelial cells on the DLC/bFGF/MPC polymer and the DLC/MPC polymer (without bFGF) were also examined. It was found that the optical density of HUVEC on the DLC/bFGF/MPC polymer determined by WST-8 assay was higher by 25%than that on the DLC/MPC polymer (without bFGF) measured after 72 h of incubation. Our results suggest that the released bFGF that contributes to the expression of other growth factors results in the early proliferation of the HUVEC on the DLC/bFGF/MPC polymer. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3384-3391, 2017.
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http://dx.doi.org/10.1002/jbm.a.36201DOI Listing
December 2017

Effects of salt concentrations of the aqueous peptide-amphiphile solutions on the sol-gel transitions, the gelation speed, and the gel characteristics.

J Phys Chem B 2014 Oct 23;118(39):11537-45. Epub 2014 Sep 23.

Department of Mechanical Engineering, Keio University , 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan.

Hydrogels made of peptide amphiphiles (PA) have attracted a lot of interest in biomedical fields. Considering the applications of PA hydrogels, the control of the gelation speed and the gel characteristics is essential to predominantly determine the usefulness and practicability of the hydrogels. In this work, the effects of the salt concentrations using sodium dihydrogenorthophosphate (NaH2PO4) on the sol-gel transition behaviors, especially the gelation speed and the gel characteristics of the designed PA (C16-W3K) hydrogels in aqueous solution were discussed. It was found that the original solution state before rheological testing was independent of the salt concentration, which was confirmed by observing the self-assembly structures and the peptide secondary structures of PA through transmission electron microscopy (TEM) and circular dichroism spectroscopy (CD). The PA solutions with different salt concentrations, however, presented a profound difference in the gelation speed and the gel characteristics: the solution exhibited higher gelation speeds and higher mechanical properties at higher salt concentrations. Concurrently, the density, the length of wormlike micelles, and the conformational ratio of β-sheets to α-helices in the equilibrium PA solutions all increased with the increase in the salt concentrations.
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http://dx.doi.org/10.1021/jp5031569DOI Listing
October 2014

A nanocomposite approach to develop biodegradable thermogels exhibiting excellent cell-compatibility for injectable cell delivery.

Biomater Sci 2014 Aug 23;2(8):1057-1062. Epub 2014 Jun 23.

Department of Nanobiochemistry, Frontiers of Innovative Research in Science and Technology, Konan University, 7-1-20 Minatojima-minamimachi, Kobe 650-0047, Japan.

A new class of injectable nanocomposite thermogels having excellent cell-compatibility were developed through cooperative self-assembly of biodegradable poly(lactide-co-glycolide)-b-poly(ethylene glycol)-b-poly(lactide-co-glycolide) copolymer micelles and clay nanosheets for effective cell delivery. This study will be valuable for the establishment of injectable cell delivery technology.
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http://dx.doi.org/10.1039/c4bm00074aDOI Listing
August 2014

Transcranial extracellular impedance control (tEIC) modulates behavioral performances.

PLoS One 2014 21;9(7):e102834. Epub 2014 Jul 21.

Graduate School of Information Science and Technology, The University of Tokyo, Tokyo, Japan.

Electric brain stimulations such as transcranial direct current stimulation (tDCS), transcranial random noise stimulation (tRNS), and transcranial alternating current stimulation (tACS) electrophysiologically modulate brain activity and as a result sometimes modulate behavioral performances. These stimulations can be viewed from an engineering standpoint as involving an artificial electric source (DC, noise, or AC) attached to an impedance branch of a distributed parameter circuit. The distributed parameter circuit is an approximation of the brain and includes electric sources (neurons) and impedances (volume conductors). Such a brain model is linear, as is often the case with the electroencephalogram (EEG) forward model. Thus, the above-mentioned current stimulations change the current distribution in the brain depending on the locations of the electric sources in the brain. Now, if the attached artificial electric source were to be replaced with a resistor, or even a negative resistor, the resistor would also change the current distribution in the brain. In light of the superposition theorem, which holds for any linear electric circuit, attaching an electric source is different from attaching a resistor; the resistor affects each active electric source in the brain so as to increase (or decrease in some cases of a negative resistor) the current flowing out from each source. From an electrophysiological standpoint, the attached resistor can only control the extracellular impedance and never causes forced stimulation; we call this technique transcranial extracellular impedance control (tEIC). We conducted a behavioral experiment to evaluate tEIC and found evidence that it had real-time enhancement and depression effects on EEGs and a real-time facilitation effect on reaction times. Thus, tEIC could be another technique to modulate behavioral performance.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0102834PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4105436PMC
November 2015

Basic fibroblast growth factor as a potential stent coating material inducing endothelial cell proliferation.

J Atheroscler Thromb 2014 21;21(5):477-85. Epub 2013 Dec 21.

Department of Radiology, Toho University Sakura Medical Center.

Aim: The use of drug-eluting stents has reduced the incidence of in-stent restenosis following percutaneous coronary intervention; however, almost all drugs eluting from polymers on stents induce antiproliferative effects on vascular endothelial and vascular smooth muscle cells. Due to injury of the endothelium and delayed reendothelialization, the risk of thrombosis increases over time. Enhancing rapid reendothelialization after stent placement is important for solving these problems. Basic fibroblast growth factor (bFGF) is one of the most important growth factors involved in vascular lesion formation. In this study, we evaluated the potential of bFGF as a stent coating promoting endothelial cell proliferation.

Methods: Human umbilical vein endothelial cells (HUVECs) and human aortic smooth muscle cells (HASMCs) were cultured with various doses of bFGF in vitro, and the effects of bFGF on the degree of cell proliferation and migration were monitored. We also investigated the effects of bFGF on the protein expression of endothelial nitric oxide synthase (eNOS) in HUVECs using Western blotting.

Results: Cell proliferation and migration were promoted in HUVECs by bFGF in a dose- and time-dependent manner. On the other hand, bFGF stimulation had little effect on the HASMCs. Basic FGF increased the eNOS protein levels in the HUVECs, with a maximum at 10 ng/mL followed by a decline at 100 ng/mL.

Conclusions: Basic FGF is a possible candidate stent coating and/or eluting drug material stimulating endothelial cell proliferation and early reendothelialization without excessive vascular smooth muscle cell proliferation.
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http://dx.doi.org/10.5551/jat.20404DOI Listing
January 2015

Micropatterning of silica nanoparticles by electrospray deposition through a stencil mask.

J Lab Autom 2014 Feb 2;19(1):75-81. Epub 2013 Jul 2.

1Department of Mechanical Engineering, Keio University, Kanagawa, Japan.

This article describes the local deposition, or micropatterning, of silica nanoparticles (NPs) using an electrospray method with a stencil mask. The proposed technique can be carried out in a single step at room temperature and atmospheric pressure under dry conditions, allowing it to be used with water- or vacuum-sensitive materials, and leading to cost reductions and high throughput. An evaluation of the patterning accuracy using a 20 µm thick mask showed that for patterns with line widths greater than 50 µm, the pattern was reproduced with an accuracy greater than 95%. When silver NPs were preferably deposited on the silica NPs using a modified silver mirror reaction, they were found to exhibit strong surface-enhanced Raman scattering effects. The proposed process is readily applicable to the development of high-performance micro total analysis systems.
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http://dx.doi.org/10.1177/2211068213495205DOI Listing
February 2014

Ultrastructural characterization of surface-induced platelet activation on artificial materials by transmission electron microscopy.

Microsc Res Tech 2013 Apr 30;76(4):342-9. Epub 2013 Jan 30.

Center for Science of Environment, Resources and Energy, Graduate School of Science and Technology, Keio University, Yokohama, Kanagawa 223-8522, Japan.

Platelet adhesion is one of the most pivotal events of blood clotting for artificial surfaces. However, the mechanisms of surface-induced platelet activation have not been fully been elucidated or visualized so far. In this study, we attempted to observe the internal structures and adhesion interfaces of human platelets attached to artificial surfaces by transmission electron microscopy (TEM) during the platelet activation process. We prepared observation samples by a conventional embedding method using EPON 812 resin. The sectioning was sliced perpendicular to the a-platelet/material interface. Observation by TEM indicates that internal granules coalesce in the center of the platelet accompanied by pseudopodial growth in the early stage of platelet activation. Pseudopodia from a platelet attach to the material interface not along a plane but at a point. In addition, along with the process of platelet activation, the gap between the platelet membrane and the material surface at the interface disappeared and a-platelet/material adhesion became much tighter. In the fully activated platelet stage, the platelet becomes thinner and tightly adheres to the substrate. As a result of comparative observation of an adherent platelet on polycarbonate (PC) and on amorphous carbon (a-C:H), it was found that internal granules release was inhibited more remarkably on a-C:H coating rather than on PC. Despite numerous technical difficulties in preparing sectional samples, such a study might prove the essential mechanism of biomaterial-related thrombosis, and it might become possible to modify the surfaces of materials to minimize material-related thrombosis.
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http://dx.doi.org/10.1002/jemt.22172DOI Listing
April 2013

Solution parameters for the fabrication of thinner silicone fibers by electrospinning.

Phys Rev E Stat Nonlin Soft Matter Phys 2012 Jul 17;86(1 Pt 1):011801. Epub 2012 Jul 17.

Graduate School of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan.

Silicone fibers were synthesized by electrospinning, where 17 solvents with different chemical properties (boiling point, conductivity, viscosity, dielectric constant, and solubility parameter) were used to dissolve the silicone polymer for the formation of fibers through electrospinning. Previous reports on the miniaturization of fibers of polymers dissolved in a solvent suggested that the low viscosity and the high conductivity of the polymer solution were the key parameters to form thinner fibers when using a single solvent. Here we have found a powerful way to search for good solvents to reduce the fiber diameters as well as to dissolve the polymers. By considering different types of solvents, it was found that the solubility parameters conclusively determined the smallest fiber diameters of the silicone polymers. The solubility parameter of the silicone polymer should be lower than those of the solvents to make thinner fibers. The results have revealed the strong relationship between the diameters of the fibers and the solubility parameters of the solvents, and they indicate that the solubility parameter could be a good indicative parameter in selecting solvents during the fabrication of thinner fibers by electrospinning, especially for siloxane polymers.
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http://dx.doi.org/10.1103/PhysRevE.86.011801DOI Listing
July 2012

Laminin active peptide/agarose matrices as multifunctional biomaterials for tissue engineering.

Biomaterials 2012 Jun 10;33(16):4118-25. Epub 2012 Mar 10.

Laboratory of Clinical Biochemistry, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan.

Cell adhesive peptides derived from extracellular matrix components are potential candidates to afford bio-adhesiveness to cell culture scaffolds for tissue engineering. Previously, we covalently conjugated bioactive laminin peptides to polysaccharides, such as chitosan and alginate, and demonstrated their advantages as biomaterials. Here, we prepared functional polysaccharide matrices by mixing laminin active peptides and agarose gel. Several laminin peptide/agarose matrices showed cell attachment activity. In particular, peptide AG73 (RKRLQVQLSIRT)/agarose matrices promoted strong cell attachment and the cell behavior depended on the stiffness of agarose matrices. Fibroblasts formed spheroid structures on the soft AG73/agarose matrices while the cells formed a monolayer with elongated morphologies on the stiff matrices. On the stiff AG73/agarose matrices, neuronal cells extended neuritic processes and endothelial cells formed capillary-like networks. In addition, salivary gland cells formed acini-like structures on the soft matrices. These results suggest that the peptide/agarose matrices are useful for both two- and three-dimensional cell culture systems as a multifunctional biomaterial for tissue engineering.
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http://dx.doi.org/10.1016/j.biomaterials.2012.02.044DOI Listing
June 2012

Construction of a xylose-metabolizing yeast by genome integration of xylose isomerase gene and investigation of the effect of xylitol on fermentation.

Appl Microbiol Biotechnol 2010 Nov 19;88(5):1215-21. Epub 2010 Sep 19.

Department of Chemical and Environmental Engineering, Gunma University, Kiryu, Japan.

A yeast with the xylose isomerase (XI) pathway was constructed by the multicopy integration of XI overexpression cassettes into the genome of the Saccharomyces cerevisiae MT8-1 strain. The resulting yeast strain successfully produced ethanol from both xylose as the sole carbon source and a mixed sugar, consisting of xylose and glucose, without any adaptation procedure. Ethanol yields in the fermentation from xylose and mixed sugar were 61.9% and 62.2% of the theoretical carbon recovery, respectively. Knockout of GRE3, a gene encoding nonspecific aldose reductase, of the host yeast strain improved the fermentation profile. Not only specific ethanol production rates but also xylose consumption rates was improved more than twice that of xylose-metabolizing yeast with the XI pathway using GRE3 active yeast as the host strain. In addition, it was demonstrated that xylitol in the medium exhibits a concentration-dependent inhibition effect on the ethanol production from xylose with the yeast harboring the XI-based xylose metabolic pathway. From our findings, the combination of XI-pathway integration and GRE3 knockout could be result in a consolidated xylose assimilation pathway and increased ethanol productivity.
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http://dx.doi.org/10.1007/s00253-010-2870-2DOI Listing
November 2010

Wormlike micelle formation in peptide-lipid conjugates driven by secondary structure transformation of the headgroups.

J Phys Chem B 2009 Oct;113(42):13711-4

Department of Chemical Engineering, University of California Santa Barbara, Santa Barbara, California 93106, USA.

Wormlike micelles are assemblies of amphiphilic molecules of intermediate mean curvature between spherical micelles and flat bilayer membranes, which often form in solutions of peptide amphiphiles (hydrophilic peptide modules conjugated to hydrophobic subunits). In an effort to better understand the factors controlling peptide amphiphile (PA) micellar shape, we synthetically linked a short peptide with an alpha-helix-forming tendency to a hexadecyl tail. These molecules initially dissolve as spherical micelles, which can persist for hours or days, followed by transformation to wormlike micelles, which occurs simultaneously with a transition in the secondary structure of the headgroup peptides to beta-sheet. This observation provides evidence that the extended micelle is the thermodynamically favored state sought by PA micelles in the process of forming beta-sheet structures among the head-groups, though they are not the structures formed during the initial kinetics of assembly.
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http://dx.doi.org/10.1021/jp901727qDOI Listing
October 2009

Pseudo-tetrablock copolymers with ethylene and a functionalized comonomer.

Chem Commun (Camb) 2007 Sep(34):3550-2

Mitsubishi Chemical Center for Advanced Materials, Department of Chemistry, Institute for Polymers and Organic Solids, University of California Santa Barbara, Santa Barbara, California, USA.

Pseudo-tetrablock copolymers comprised of ethylene and 5-norbomen-2-yl acetate (1), were synthesized using the initiator system (L(i)Pr2)Ni(eta1-CH2Ph)(PMe3)(2)[(L(i)Pr2) = N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamide] and 2.5 equivalents of Ni(COD)2 [bis(1,5-cyclooctadiene) nickel.
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http://dx.doi.org/10.1039/b705808jDOI Listing
September 2007

Fluorine doping into diamond-like carbon coatings inhibits protein adsorption and platelet activation.

J Biomed Mater Res A 2007 Dec;83(4):1192-9

Center for Science of Environment, Resources, and Energy, Keio University Faculty of Science and Technology, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan.

The first major event when a medical device comes in contact with blood is the adsorption of plasma proteins. Protein adsorption on the material surface leads to the activation of the blood coagulation cascade and the inflammatory process, which impair the lifetime of the material. Various efforts have been made to minimize protein adsorption and platelet adhesion. Recently, diamond-like carbon (DLC) has received much attention because of their antithrombogenicity. We recently reported that coating silicon substrates with fluorine-doped diamond-like carbon (F-DLC) drastically suppresses platelet adhesion and activation. Here, we evaluated the protein adsorption on the material surfaces and clarified the relationship between protein adsorption and platelet behaviors, using polycarbonate and DLC- or F-DLC-coated polycarbonate. The adsorption of albumin and fibrinogen were assessed using a colorimetric protein assay, and platelet adhesion and activation were examined using a differential interference contrast microscope. A higher ratio of albumin to fibrinogen adsorption was observed on F-DLC than on DLC and polycarbonate films, indicating that the F-DLC film should prevent thrombus formation. Platelet adhesion and activation on the F-DLC films were more strongly suppressed as the amount of fluorine doping was increased. These results show that the F-DLC coating may be useful for blood-contacting devices.
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http://dx.doi.org/10.1002/jbm.a.31340DOI Listing
December 2007

Semicrystalline thermoplastic elastomeric polyolefins: Advances through catalyst development and macromolecular design.

Proc Natl Acad Sci U S A 2006 Oct 10;103(42):15327-32. Epub 2006 Oct 10.

Mitsubishi Chemical Center for Advanced Materials and Department of Materials and Chemical Engineering, University of California, Santa Barbara, CA 93106, USA.

We report the design, synthesis, morphology, phase behavior, and mechanical properties of semicrystalline, polyolefin-based block copolymers. By using living, stereoselective insertion polymerization catalysts, syndiotactic polypropylene-block-poly(ethylene-co-propylene)-block-syndiotactic polypropylene and isotactic polypropylene-block-regioirregular polypropylene-block-isotactic polypropylene triblock copolymers were synthesized. The volume fraction and composition of the blocks, as well as the overall size of the macromolecules, were controlled by sequential synthesis of each block of the polymers. These triblock copolymers, with semicrystalline end-blocks and mid-segments with low glass-transition temperatures, show significant potential as thermoplastic elastomers. They have low Young's moduli, large strains at break, and better than 90% elastic recovery at strains of 100% or less. An isotactic polypropylene-block-regioirregular polypropylene-block-isotactic polypropylene-block-regioirregular polypropylene-block-isotactic polypropylene pentablock copolymer was synthesized that also shows exceptional elastomeric properties. Notably, microphase separation is not necessary in the semicrystalline isotactic polypropylenes to achieve good mechanical performance, unlike commercial styrenic thermoplastic elastomers.
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http://dx.doi.org/10.1073/pnas.0602894103DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1834831PMC
October 2006

Synthesis of block copolymer segments containing different ratios of ethylene and 5-norbornen-2-yl acetate.

J Am Chem Soc 2004 Sep;126(34):10528-9

Institute for Polymers and Organic Solids and Mitsubishi Chemical Center for Advanced Materials, Department of Materials, University of California, Santa Barbara, California 93106, USA.

Block copolymerization of ethylene with 5-norbornen-2-yl acetate (1) by the nickel catalyst system [N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamide]Ni(eta1-CH2Ph)(PMe3) (2) and Ni(COD)2 (bis(1,4-cyclooctadiene)nickel) (3) produces a variety of block copolymer structures that demonstrate microphase separation. Typical block copolymerizations were carried out in an autoclave charged with a solution of the catalyst mixture and 1 (0.15 M) in toluene. The autoclave was sealed and exposed to PC2H4 = 50 psi for a period of time (T1). A pressure jump to PC2H4 = 1100 psi was then applied and the reaction allowed to proceed for another predetermined interval (T2). Independent experiments were performed to isolate and examine the molecular weight and comonomer composition of the first block. Narrow molecular weight distributions and the increase of polymer molecular weight with increases in T1 or T2 are consistent with a product in which an initial block is formed at low ethylene pressures and quantitatively converted to a block copolymer by the jump to high pressure. Transmission electron microscopy confirms that the materials are microphase separated.
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http://dx.doi.org/10.1021/ja047231gDOI Listing
September 2004