Thermally Reversible Gel-Sol Transition of Hydrogels via Dissociation and Association of an Artificial Protein Nanocage

Oligomeric protein nanocages often disassemble into their subunits and reassemble by external stimuli. Thus, using these nanocages as cross-linkers for hydrogel network structures is a promising approach to allow hydrogels to undergo stimuli-responsive gel-sol transitions or self-healing. Here, we report hydrogels that show a reversible gel-sol transition resulting from the heat-induced dissociation and reassociation of protein nanocages. The hydrogel contained the 60-mer artificial protein nanocage, TIP60, as a supramolecular cross-linker for polyethylene glycol network structures. The hydrogel showed a gel-to-sol transition upon heating at a temperature above the melting point of TIP60 and immediately returned to a gel state upon cooling to room temperature. During the heating and cooling treatment of the hydrogel, small-angle X-ray scattering analysis suggested the dissociation and reassociation of TIP60. Furthermore, we demonstrated redox-responsive cargo release from TIP60 in the hydrogel. These results showed the potential of TIP60 as a component of multi-stimuli-responsive hydrogels.

Contact-Killing Antibacterial Polystyrene Polymerized Using a Quaternized Cationic Initiator

Contact-killing antibacterial materials are attracting attention owing to their ability for sustained antibacterial activity. However, contact-killing antibacterial polystyrene (PS) has not been extensively studied because its chemically stable structure impedes chemical modification. In this study, we developed an antibacterial PS sheet with a contact-killing surface using PS synthesized from 2,2'-azobis-[2-(1,3-dimethyl-4,5-dihydro-1H-imidazol-3-ium-2-yl)]propane triflate (ADIP) as a radical initiator with cationic moieties. The PS sheet synthesized with ADIP (ADIP-PS) exhibited antibacterial activity in contrast to PS synthesized with other azo radical initiators. Surface ζ-potential measurements revealed that only ADIP-PS had a cationic surface, which contributed to its contact-killing antibacterial activity. The ADIP-PS sheets also exhibited antibacterial activity after washing. In contrast, PS sheets containing silver, a typical leachable antibacterial agent, lost all antibacterial activity after the same washing treatment. The antibacterial ADIP-PS sheet demonstrated strong broad-spectrum activity against both Gram-positive and Gram-negative bacteria, including drug-resistant bacteria. Cytotoxicity tests using L929 cells showed that the ADIP-PS sheets were noncytotoxic. This contact-killing antibacterial PS synthesized with ADIP thus demonstrated good prospects as an easily producible antimicrobial material.

Multifunctionality of Iodinated Halogen-Bonded Polymer: Biodegradability, Radiopacity, Elasticity, Ductility, and Self-Healing Ability

A polymer with high contents of ester bonds and iodine atoms was synthesized, exhibiting sufficient biodegradability and radioactivity for biomedical applications. The iodine moieties of the synthesized polyester can generate halogen bonding between molecules, which may develop additional functional properties through the bonding. In this study, poly(glycerol adipate) (PGA) was selected and synthesized as a polyester, which was then adequately conjugated with three different types of iodine compounds via the hydroxy groups of PGA. It was found that the iodine compounds could effectively work as donors of halogen bonding. The thermal analysis by differential scanning calorimetry (DSC) revealed that the glass transition temperature increased with the increase in the strength of interactions caused by π-π stacking and halogen bonding, eventually reaching 49.6 °C for PGA with triiodobenzoic groups. An elastomeric PGA with monoiodobenzoic groups was also obtained, exhibiting a high self-healing ability at room temperature because of the reconstruction of halogen bonding. Such multifaceted performance of the synthesized polyester with controllable thermal/mechanical properties was realized by halogen bonding, leading to a promising biomaterial with multifunctionality.

Compensation for Orientation Birefringence of PMMA by Blending Bottlebrush Polymers Composed of Well-Controlled Graft Chains

The birefringence of optical polymers is a great issue in optical devices, inhibiting major applications of polymers to optical lenses and films. In this study, we have synthesized effective bottlebrush polymers with which we could attain almost zero birefringence when mixed with optical poly(methyl methacrylate) (PMMA). In detail, the PMMA bottlebrush polymers (PMMA-BBP) were synthesized by the ring-opening metathesis polymerization (ROMP) of norbornene-terminated PMMA macromonomers prepared via atom transfer radical polymerization (ATRP). Linear PMMA and PMMA-BBP were mixed to fabricate blend-film samples (PMMA/PMMA-BBP), which were uniaxially drawn to introduce molecular orientations. Linear PMMA possessed a negative value for its orientation birefringence, while the value of PMMA/PMMA-BBP increased as the PMMA-BBP content increased, whose orientation birefringence could reach almost zero when the ratio of the linear PMMA to PMMA-BBP became 73:27, regardless of the magnitude of the strain. The results reveal that the orientation birefringence of PMMA can be effectively controlled and removed by blending the appropriate content of PMMA-BBP.

[Can Echocardiography Adjust Corrected Contrast Injection Condition in Coronary CT Angiography?]

PURPOSE

The purposes were to search which factor of cardiac function in echocardiography correlates with the CT value, to correct contrast injection conditions with cardiac function in addition to suppress error in the contrast effect between patients, and to achieve the target CT value (350 HU) in coronary computed tomography angiography (CCTA).

METHODS

In 112 patients (conventional group), the contrast material was administered at a fractional dose (FD) of 21 mgI/kg/s. We measured the aortic CT value in the coronary origin part. In 112 patients (correction group), the contrast material was administered at corrected injection conditions with the most correlated functional factor and CT value.

RESULTS

The CT value of the conventional group was an average of 400.8±51.5 HU. The most correlated factor with the CT value was stroke volume [SV (r=-0.555)]. The CT value of the conventional group was an average of 360±46 HU. The case of the aim CT level was improved from 46% to 74%. In the correction group, the average value of FD was 18.5 mgI/kg/s. This enabled the reduction of the contrast material in 95% of patients.

CONCLUSION

The best correlation was obtained between the CT value of coronary arteries and SV. The contrast medium injection conditions were corrected for cardiac function in addition to body weight. As a result, we were able to control the CCTA target CT value of 300 to 400 HU at our hospital.

Investigation of the thermodynamic properties of hydrates as cooling phase change materials for their implementation in electric vehicles

Electric vehicles (EVs) play key roles in realizing a sustainable society.

Finite element analysis of blood clots based on the nonlinear visco-hyperelastic model

Mechanical thrombectomy has become the standard treatment for patients with an acute ischemic stroke. In this approach, to remove blood clots, mechanical force is applied using thrombectomy devices, in which the interaction between the clot and the device could significantly affect the clot retrieval performance. It is expected that the finite element method (FEM) could visualize the mechanical interaction by the visualization of the stress transmission from the device to the clot. This research was aimed at verifying the constitutive theory by implementing FEM based on the visco-hyperelastic theory, using a three-dimensional clot model. We used the visco-hyperelastic FEM to reproduce the mechanical behavior of blood clots, as observed in experiments. This study is focused on the mechanical responses of clots under tensile loading and unloading because in mechanical thrombectomy, elongation is assumed to occur locally on the clots during the retrieval process. Several types of cylindrical clots were created by changing the fibrinogen dose. Tensile testing revealed that the stiffness (E_0.45-value) of clots with fibrinogen could be more than three times higher than that of clots without fibrinogen. It was also found that the stiffness was not proportional to the fibrinogen dose. By fitting to the theoretical curve, it was revealed that the Mooney-Rivlin model could reproduce the hyperelastic characteristics of clots well. From the stress-relaxation data, the three-chain Maxwell model could accurately fit the experimental viscoelastic data. FEM, taking the theoretical models into account, was then carried out, and the results matched well with the experimental visco-hyperelastic characteristics of clots under tensile load, reproducing the mechanical hysteresis during unloading, the stress dependence on the strain rate, and the time-dependent stress decrease in the stress-relaxation test.

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

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.

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

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.

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

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.

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

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.

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

Poly(ethylene glycol)-b-poly(d,l-lactide-co-glycolide) (PEG-b-PLGA) diblock copolymers are widely known as polymeric surfactants for biomedical applications, and exhibit high solubility in water compared to PLGA-b-PEG-b-PLGA triblock copolymers known as gelation agents. In order to overcome the difficulties in the preparation of thermo-responsive hydrogels based on PLGA-b-PEG-b-PLGA due to the low solubility in water, the fabrication of thermo-responsive hydrogels based on PEG-b-PLGA with high solubility in water was attempted by adding laponite to the PEG-b-PLGA solution. In detail, PEG-b-PLGA with high solubility in water (i.e., high PEG/PLGA ratio) were synthesized. Then, the nanocomposite solution based on PEG-b-PLGA and laponite (laponite/PEG-b-PLGA nanocomposite) was fabricated by mixing the PEG-b-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-b-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-b-PLGA was confirmed to be on the surface of the laponite platelets, and the thermosensitive PEG-b-PLGA on the laponite surface could trigger the thermo-responsive connection of the preformed laponite network.

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

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.

Self-assembly of peptide amphiphiles by vapor pressure osmometry and dissipative particle dynamics

Peptide amphiphiles are one of the most promising materials in the biomedical field, so much effort has been devoted to characterizing the mechanism of their self-assembly and thermosensitive gelation. In this work, vapor pressure osmometry measurements were carried out to parameterize the thermosensitivity of interactions between peptide amphiphiles in an aqueous solution. The osmometry measurement verified that the peptides became more hydrophobic as temperature increased, which was quantitatively described with the Flory-Huggins χ parameter. Thereafter, a coarse-grained molecular model was used to simulate peptide amphiphiles dissolved in an aqueous solution. The temperature sensitive coarse-grained parameter a HW, which is the repulsive force between the hydrophilic head of the peptide amphiphile and water was estimated from the aforementioned experimentally obtained χ. Furthermore, the effects of concentration and temperature on the self-assembly behavior of peptide amphiphiles were quantitatively studied by dissipative particle dynamics. The simulation results revealed that a HW plays an important role in self-assembly characteristics and in the resulting microstructure of the peptide amphiphiles, which coincides with previous experimental and computational findings. The methodology in quantitatively linking the coarse-grained parameter from experiment and theory provides a sensible foundation for bridging future simulation studies with experimental work on macromolecules.

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

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.

Solution parameters for the fabrication of thinner silicone fibers by electrospinning

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.