Preparation of silk sericin beads using LiCl/DMSO solvent and their potential as a drug carrier for oral administration

Silk sericin (SS) was fabricated into beads using LiCl/DMSO solution as a solvent. Up to 30 % (w/v) of SS could be dissolved within 3 hours, and the shape of solidified SS depends on the concentration of SS. Ethanol was the best coagulant among alcohols, making beads with suitable mechanical strength for further application. SS beads swell more at a pH above the isoelectric point (pl) than below the pl. The pH and the presence of an enzyme greatly affect the dissolution rate of SS beads. Whereas only 10 % of SS beads were dissolved at pH 2.2 in the presence of pepsin, more than 45 % of SS beads were dissolved at pH 7.4 in the presence of trypsin. The release of drug was suppressed in a stomach-like environment while promoted in an intestine-like environment.     

Modeling of anisotropic creep behavior of coated textile membranes

The present study aims at characterizing and modeling the anisotropic creep behavior of coated textile membrane, a class of flexible textile composites that are used for moderate span enclosures (roofs and air-halls). The objective is to develop a creep model for predicting the lifetime of coated textile membrane. Uniaxial creep tests were conducted on three off-axis coupon specimens to obtain the directional creep compliance. A potential with three parameters is shown to be adequate for modeling the anisotropic creep behavior of coated textile membrane. Furthermore, a possibility of predicting the creep deformation of coated textile membrane in a multi-axial stress state is discussed using the three-parameter potential.     

Real-time identification of the draft system using neural network

Making a good model is one of the most important aspects in the field of a control system. If one makes a good model, one is now ready to make a good controller for the system. The focus of this thesis lies on system modeling, the draft system in specific. In modeling for a draft system, one of the most common methods is the “least-square method”; however, this method can only be applied to linear systems. For this reason, the draft system, which is non-linear and a time-varying system, needs a new method. This thesis proposes a new method (the MLS method) and demonstrates a possible way of modeling even though a system has input noise and system noise. This thesis proved the adaptability and convergence of the MLS method.     

Preparation of high molecular weight poly(methyl methacrylate) with high yield by room temperature suspension polymerization of methyl methacrylate

To obtain high molecular weight (HMW) poly(methyl methacrylate) (PMMA) with high conversion, methyl methacrylate (MMA) was polymerized in suspension using a room temperature initiator, 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN), and the effects of polymerization conditions on the polymerization behavior of MMA and the molecular parameters of PMMA were investigated. On the whole, the experimental results well corresponded to the theoretically predicted tendencies. These effects could be explained by a kinetic order of ADMVN concentration calculated by an initial rate method and an activation energy difference of polymerization obtained from the Arrhenius plot. Suspension polymerization at 25 °C by adopting ADMVN proved to be successful in obtaining PMMA of HMW (number-average degree of polymerization (P_n): 30,900–36,100) and of high yield (ultimate conversion of MMA into PMMA: 83–93 %) with diminishing heat generated during polymerization. The P_n and lightness were higher and polydispersity index was lower with PMMA polymerized at lower temperatures.     

Crosslinking reaction of phenolic side chains in silk fibroin by tyrosinase

Tyrosinase oxidizes the tyrosyl residues in silk fibroin (SF) with oxygen, resulting in the production ofo-quinone residues. Subsequently, the inter- or intramolecular crosslinks are formed by reaction with amino groups in through nonenzymatic process. The measurement of oxygen consumption proved that the tyrosyl residues in SF were mostly oxidized to quinone residues by tyrosinase. The reaction mechanisms were proposed in this study and the crosslinking reaction ofo-quinone residues and the enzymatic oxidation of tyrosyl residues could be confirmed by the measurements of UV,¹H-NMR and GFC.     

Permeability measurement of a circular braided preform for resin transfer molding

Permeability of the preform is one of key factors in design of RTM (Resin Transfer Molding) mold, determination of processing conditions, and modeling of flow in the mold. According to previous studies, permeability measured in the unsaturated fiber mats are higher than that in the saturated fiber mats by about 20 % because of the capillary pressure. In this study, permeabilities of several fiber preforms are measured for both saturated and unsaturated flows. A saturated experiment of radial flow has been adopted to measure the permeability of anisotropic fiber preforms with high fiber content, i.e., circular braided preforms. In this method, four pressure transducers are used to measure the pressure distribution. Permeabilities in different directions are determined and the experimental results show a good agreement with the theory. Since permeability is affected by the capillary effect, permeability should be measured in the unsaturated condition for the textile composites to be manufactured under lower pressure as in the Vacuum Assisted Resin Transfer Molding (VARTM).     

Application of electrospun silk fibroin nanofibers as an immobilization support of enzyme

Silk fibroin (SF) nanofibers were prepared by electrospinning and their application as an enzyme immobilization support was attempted. By varying the concentration of SF dope solution the diameter of SF nanofiber was controlled. The SF nanofiber web had high capacity of enzyme loading, which reached to 5.6 wt%. The activity of immobilizedα-chymotrypsin (CT) on SF nanofiber was 8 times higher than that on silk fiber and it increased as the fiber diameter decreased. Sample SF8 (ca. 205 nm fiber diameter) has excellent stability at 25°C by retaining more than 90 % of initial activity after 24 hours, while sample SF11 (ca. 320 nm fiber diameter) shows higher stability in ethanol, retaining more than 45% of initial activity. The formation of multipoint attachment between enzyme and support might increase the stability of enzyme. From these results, it is expected that the electrospun SF nanofibers can be used as an excellent support for enzyme immobilization.     

Egg yolk fatty acid profile of avian species – influence on human nutrition

Lipids are an important nutritional component of the avian egg. A review of the literature was completed to determine the fatty acid compositions in egg yolk from some avian species. Additionally, the nutritional influence of lipid and lipoprotein content on the plasma of male participants during 30‐day feeding was discussed. The ostrich eggs had the highest unsaturated fatty acid and the lowest cholesterol content in relation to other avian species. Ostrich had a higher proportion of 18:3n‐3 (p < 0.01) compared with other species. Chicken yolk numerically contained much higher levels of 22:6n‐3 than those found in turkeys, quails and geese, but the amount of 22:6n‐3 in ostrich egg was lower by comparison with other species (p < 0.01). After the storage of eggs at the room temperature, there was a notable loss of vitamin E (vitE) in the yolks of all species and this decrease was marginal (p < 0.01) in ostrich compared with other species. There were significant (p < 0.05) increases in plasma low‐density lipoprotein (LDL) level in all male subjects. Plasma high‐density lipoprotein (HDL) level decreased (p < 0.05) only in men who were fed chicken or ostrich eggs daily. Consumption of different species’ eggs had no influence on the total male plasma cholesterol and triglyceride levels. LDL‐C:HDL‐C ratio increased (p < 0.05) after goose and turkey egg consumption. Consumption of one egg/month by healthy human subjects had no effect on serum total cholesterol and triglyceride. The LDL‐C:HDL‐C ratio (which is a strong predictor of coronary heart disease risk) increased, although non‐significantly, by consuming chicken, quail and ostrich eggs.     

Mechanical properties of denim fabric reinforced poly(lactic acid)

Denim, a twilled cotton fabric, was used to enhance the mechanical and thermal properties of poly(lactic acid) (PLA). The denim fabric reinforced composites with different numbers of denim layers were fabricated by using a hand layup method. The impact, tensile, and dynamic mechanical properties of the composites were observed with increasing denim layers to examine the reinforcing effect of denim fabrics. Numerical analysis was carried out to model the elastic modulus of the composite by using a commercial software. Three-dimensional geometry of the denim fabric reinforced PLA composite was generated through a CAD program, and the elastic modulus was calculated by applying uniform deformation on one surface. The impact strength, tensile strength, and thermal properties of the composites were improved by piling denim fabrics. The denim fabric reinforced composites exhibited outstanding impact strength due to the retarded crack propagation as well as large energy dissipation. The 3 layer denim reinforced composite showed best results among all specimens, and its impact strength, tensile strength, and tensile modulus were measured to be 82 J/m, 75.76 MPa, and 4.65 GPa, respectively. The PLA/denim composites have good mechanical properties and can substitute traditional composites such as glass fiber or carbon fiber reinforced composites.     

Determination of the transition temperature of shape memory polyurethanes using constrained recovery test

Shape memory polymers (SMPs) are smart materials whose original (permanent) shape can be restored from a temporarily fixed one by applying an external stimulus such as heat, acidity, light, etc. In particular, thermo-responsive shape memory polyurethanes (SMPUs) show shape memory behavior when heated. Here, it is important to characterize the transition temperature at which the materials memorize their permanent shape from the temporary shape. Differential scanning calorimetry (DSC) or dynamic mechanical thermal analysis (DMTA) are employed to determine the transition temperature of SMPUs depending on their molecular conformation. A new method is proposed that can determine the transition temperature by making use of the thermo-mechanical behavior of SMPUs using a general tensile tester with an environmental chamber. This method focuses on the constrained recovery behavior of the SMPUs upon heating, i.e., they are prevented from contracting or deforming during the test, thereby causing them to develop a certain stress. The rate of the developed stress according to the temperature depends on the micro-structures of the SMPUs, which determine their transition temperature.