Published papers

© 2020 Wiley-VCH GmbH 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.

© Copyright © 2020 Miyamoto, Koyama, Kurokawa, Hotta, Alavi and Ohmura. 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−1 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.

Mechanical and thermal properties of the newly synthesized solid poly(2-methoxyethyl acrylate) (PMEA)-based polyurethane (PU) were studied. The obtained PMEA-based PUs with various molecular weights were thermoplastic, synthesized by reversible addition-fragmentation chain transfer (RAFT) and polyaddition. Dynamic mechanical analysis (DMA) revealed that the storage modulus and the melting temperature of PMEA-based PU significantly increased from 1.5 × 104 Pa to 2.3 × 105 Pa and from 25 °C to 73 °C, respectively, as the molecular weight of PMEA-based PU increased. This enhancement in the properties could be due to the formation of an ordered structure in PMEA-based PU, studied using small-angle and wide angle X-ray scattering (SAXS, WAXS). Glass transition temperature, 5% weight-reduction temperature, and the amount of intermediate water of PMEA-based PU were also analyzed using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). This journal is

Mechanically tough poly(L-lactide) (PLLA)/N,N-dimethylacetamide (DMAc) gels by rapid quenching using liquid nitrogen (LN) were synthesized. PLLA/DMAc solution at 110 °C was cooled at room temperature (PLLA-RT), or quenched by LN before keeping at RT (PLLA-LN). PLLA-RT with the PLLA concentrations of 5, 8, and 11 wt% did not form gel, while PLLA-RT with 14 and 17 wt% could form brittle gel exhibiting coarse structures. In contrast, PLLA-LN could form stable gel regardless of the PLLA concentration. The storage modulus of the gel with the PLLA concentration of 17 wt% increased from 78.7 kPa (PLLA-RT) to 563.7 kPa (PLLA-LN) at the strain of 0.1%. From the structural analysis, PLLA-RT formed spherulites (100–200 μm in diameter), whereas PLLA-LN formed relatively uniform network structures with continuous microporous skeletons without spherulites. The structural changes significantly contributed to the formation of stable, re-moldable, biodegradable, and biocompatible physical gels with ecofriendly and enhanced mechanical properties.

Movement towards the gradual replacement of gasoline combustion vehicles to electrical vehicles is occurring on a global scale. Heat management of lithium-ion batteries (LIB) is necessary for long-term operation and safety of the power sources of electrical vehicles. This research suggests pinacol hydrate as a phase change material (PCM) for use as an alternative cooling media for LIB. The pinacol hydrate crystallizes under atmospheric pressure and temperatures around 45 °C, which are compatible with LIB operating conditions. Its dissociation enthalpy can control the excessive heating of the battery. The equilibrium phase transition temperature of pinacol hydrate was reported about a decade ago, but its thermal storage capacity has not been reported yet and updated quantitative measurements are required. Hence, in this study the equilibrium temperatures and dissociation enthalpies are experimentally measured for pinacol aqueous solutions prepared with mass fractions between 0.40 and 0.85. The maximum thermal storage capacity is measured by differential scanning calorimetry to be 301.9 kJ/kg for mass fraction of 0.50 which is compatible with operating conditions of up to 45.6 °C. A minimization of reservoir tank mass by 35% of that needed for conventional technologies may be possible by using pinacol hydrate.

© 2018 Elsevier Ltd To enhance the mechanical properties of regenerated cellulose nanofibers (RC-NF), the annealing and the saponification of electrospun cellulose-acetate nanofibers (CA-NF) have been investigated. It was found that, by increasing the annealing time of CA-NF at 50 °C from 0 to 12 h, the crystallinity of RC-NF increased from 37% to 41%, which became constant after 12 h. By applying the theory proposed by Tsai, the Young's modulus of RC-NF was found to increase from 9.0 to 28.0 GPa by increasing the annealing time from 0 to 12 h, which also became constant after 12 h. The optimized annealing time for the maximum crystallinity and Young's modulus became shorter by increasing the annealing temperature, indicating that the crystallinity and the Young's modulus of RC-NF were strongly correlated. Eventually, the Young's modulus of RC-NF/PVA increased from 2.1 to 3.0 GPa at the maximum, while that of pure PVA was 1.5 GPa.

© 2019 Elsevier Ltd The size of spherulites observed in the poly(butylene succinate-co-adipate) (PBSA) gel was found to be effectively controlled by the careful selection of the types of solvent and the gel preparation temperature. Additionally, the degradation behavior of the PBSA dried-gels with different sizes of spherulites was studied. By using different solvents, such as toluene (TOL), o-dichlorobenzene (o-DCB), and cyclohexanone (CHN), the diameter of the spherulites could be changed from 16.7 μm to 186.2 μm, while the gel preparation temperature was kept constant at 28 °C. The gel preparation temperature was then changed from −50 °C to 28 °C using CHN, and it was found that the diameter of the spherulites changed from 25.2 μm to 186.2 μm. Regarding the degradation behavior, the PBSA dried-gel with relatively smaller spherulites (∼20 μm in diameter) exhibited higher weight loss of over 80% at the immersion time of 6 days, while the PBSA dried-gels with relatively larger spherulites (∼186 μm in diameter) presented lower weight loss of below 30% at the immersion time of 6 days. It was therefore concluded that the degradation rate became lower with the increase in the size of spherulites.

Copyright © Materials Research Society 2019. Poly(ϵ-caprolactone) (PCL) is one of the leading biocompatible and biodegradable polymers. However, the mechanical property of PCL is relatively poor as compared with that of polyolefins, which has limited the active applications of PCL as an industrial material. In this study, to enhance the mechanical property of PCL, cellulose nanofibers (C-NF) with high mechanical property, were employed as reinforcement materials for PCL. The C-NF were fabricated via the electrospinning of cellulose acetate (CA) followed by the subsequent saponification of the CA nanofibers. For the enhancement of the mechanical property of the PCL composite, the compatibility of C-NF and PCL was investigated: the surface modification of the C-NF was introduced by the ring-opening polymerization of the ϵ-caprolactone on the C-NF surface (C-NF-g-PCL). The polymerization was confirmed by the Fourier transform infrared (FTIR) spectroscopy. Tensile testing was performed to examine the mechanical properties of the C-NF/PCL and the C-NF-g-PCL/PCL. At the fiber concentration of 10 wt%, the Young's modulus of PCL compounded with neat C-NF increased by 85% as compared with that of pure PCL, while, compounded with C-NF-g-PCL, the increase was 114%. The fracture surface of the composites was analyzed by scanning electron microscopy (SEM). From the SEM images, it was confirmed that the interfacial compatibility between PCL and C-NF was improved by the surface modification. The results demonstrated that the effective surface modification of C-NF contributed to the enhancement of the mechanical property of PCL.

© 2020 The hydrate-based thermal energy storage system is one of the most effective supplemental technologies to stabilize the energy supply for renewable energies. The system is expected to solve the global energy-management issues related to energy-demand increase and energy supply chain. In fact, this eco-friendly technology requires prospective hydrate candidates for the thermal energy storage media, followed by the extensive investigation of the thermophysical properties of the selected hydrates. In this study, to satisfy these requirements, the equilibrium temperature and the dissociation heat of tetrabutylphosphonium acrylate (TBPAc) ionic semi-clathrate hydrate were studied. It was found that the highest equilibrium temperature was 14.4 °C at the mass fractions from 0.37 to 0.40. It was also found that the largest dissociation heat was (210.4 ± 5.3) kJ kg−1 at the mass fraction 0.39. These values indicate that TBPAc hydrate could be a new promising thermal-storage medium for the general or data-centre air-conditioning systems. The experimental results of this study also revealed an underlying tendency between the thermophysical properties of the tetrabutylphosphonium (TBP) + carboxylate salt hydrates and the molar mass of the guest anion in salt.

Copyright © 2020 American Chemical Society. Stereocomplex poly(lactic acid) (sc-PLA) crystallites exhibit higher mechanical strength and thermal stability than PLA homocrystallites. In sc-PLA, a hydrogen bond that governs the physical properties is formed between two enantiomeric PLA chains during crystallization. Therefore, the investigation of this hydrogen bond is essential for a better understanding of the properties of sc-PLA. Here, we report on the terahertz spectroscopy of sc-PLA films with low crystallinities. The dielectric function in the terahertz regime allows us to estimate the crystallinity of sc-PLA because various intra- and intermolecular vibration modes lie in the terahertz frequency range. By comparison with X-ray diffraction measurements, the validity of the crystallinity evaluation based on terahertz spectroscopy is verified. Furthermore, a remarkable red-shift of the peak in the imaginary part of the dielectric function occurs as the crystallinity increases. By comparison with Fourier transform infrared spectroscopy, it is considered that this red-shift is caused by the anharmonic nature of the vibrational potential corresponding to the intermolecular libration mode of the sc-PLA crystallites. The hydrogen bond formation associated with the sc-PLA crystallization increases the anharmonicity of the vibrational potential of sc-PLA, and then the red-shift of the peak occurs. Our findings suggest that structural changes due to the stereocomplexation can be sensitively probed by terahertz spectroscopy.

© 2020 Elsevier Ltd New radiopaque/biodegradable drug-eluting beads (DEBs) for transarterial chemoembolization (TACE) were fabricated using Lipiodol and polycaprolactone (PCL) (Lipiodol/PCL beads) through a microfluidic device. TACE is the most extensively-applied therapy for unresectable hepatocellular carcinoma (HCC). DEBs are embolic microspheres with sustained and tumor-selective drug-delivery characteristics for tumor-feeding arteries. As the conventional DEBs are not radiopaque by themselves and not biodegradable, it is difficult to monitor bead localization and attenuation through CT images after DEB-TACE procedures, and the complication after non-target embolization becomes potentially more serious. In this work, we found that our new biodegradable Lipiodol/PCL lost 63.5% of their weight 11 days after immersion, simultaneously releasing 0.94 μg of miriplatin (a lipophilic platinum-based anticancer drug) from the Lipiodol/PCL beads in 11 days. We also found that the degradation speed could be controlled from 18.2% to 63.5% of the weight loss in 11 days by changing the molecular weight of PCL and the ratio of Lipiodol/PCL. The mean diameter of the bead could be well controlled by changing the flow-rate ratio of the microfluidic device. Regarding the radiopacity in vitro, the Lipiodol/PCL beads were clearly visualized through CT imaging, with a mean attenuation of over 5600 HU. Furthermore, it was found from the radiopacity experiments in vivo, that the embolization by the Lipiodol/PCL beads in the rabbit vessel was clearly recognized through CT images, indicating high potential of the newly synthesized biodegradable beads to improve the current TACE procedures by providing refined locational information on drug and embolic particles.

The thermoresponsive gelation behavior and the degradation behavior of the nanocomposites consisting of poly(ethylene glycol)-b-poly(lactic acid-co-glycolic acid) (PEG-b-PLGA) diblock copolymers and clay nanoparticles (laponite) (laponite/PEG-b-PLGA nanocomposites) were studied by changing the blend ratio of the PEG-b-PLGA diblock copolymers using different PLGA molecular weights of 800 g/mol and 1600 g/mol: PEG-b-PLGA (1000-800, Diblock0.8k) and PEG-b-PLGA (1000-1600, Diblock1.6k). It was found that each gelation temperature was in the temperature range between 25°C and 37°C, when the PEG-b-PLGA concentration and the laponite concentration were kept at 3–4 wt% and 1 wt%, respectively. The degradation rate at 37°C was found to be effectively regulated by the Diblock1.6k/Diblock0.8k blend ratio (DR). In detail, after 15 days of the degradation experiments, the weight loss was decreased by ∼14% when DR changed from DR=0/100 to DR=100/0. It was, therefore, confirmed that DR was the key parameter to control the degradation behavior of the laponite/blended PEG-b-PLGA nanocomposites.

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 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.

MRI contrast agents with a size of 3-10 nm are considered to be an effective pathway for selective MR lymphatic imaging. In our previous study, we fabricated nanosized MRI contrast agents (Gd-DTPA-ND) with the condensation of nanodiamond (ND) particles and gadolinium chelates (Gd-DTPA). However, these Gd-DTPA-ND particles formed microscale aggregates in distilled water, exceeding the size required for selective lymphatic MR imaging. In this study, carboxylated nanodiamond (CND) particles were utilized as alternative platforms for condensation with gadolinium complexes. The carboxyl groups introduced by oxidation were expected to induce hydrophilicity with a negative charge on the ND surface, resulting in the high dispersity of gadolinium-complexed CND particles. The fabricated Gd-DTPA-CND particles possessed a hydrodynamic diameter of around 4-5 nm without any signs of aggregation in distilled water and human serum. Furthermore, the T1-weighted image of Gd-DTPA-CND particles in distilled water and human serum presented strong contrast, indicating the excellent MRI visibility of the particles. Therefore, the Gd-DTPA-CND particles can become practical MRI contrast agents for the achievement of selective MR imaging of the lymphatic system.

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.