Results 1 - 10 of 1015
Results 1 - 10 of 1015. Search took: 0.023 seconds
|Sort by: date | relevance|
[en] The next step beyond conventional scaffold-based tissue engineering is cell-based direct biofabrication techniques. In industrial processes, various three-dimensional (3D) prototype models have been fabricated using several different rapid prototyping methods, such as stereo-lithography, 3D printing and laser sintering, as well as others, in which a variety of chemical materials are utilized. However, with direct cell-based biofabrication, only biocompatible materials can be used, and the manufacturing process must be performed under biocompatible and physiological conditions. We have developed a direct 3D cell printing system using inkjet and gelation techniques with inkjet droplets, and found that it had good potential to construct 3D structures with multiple types of cells. With this system, we have used alginate and fibrin hydrogel materials, each of which has advantages and disadvantages. Herein, we discuss the roles of hydrogel for biofabrication and show that further developments in biofabrication technology with biomatrices will play a major part, as will developments in manufacturing technology. It is important to explore suitable biomatrices as the next key step in biofabrication techniques.
[en] In our previous work, linear polyelectrolyte cross-linker-bridged hydrogel showed fast gelation within hours, which constrained in-depth deployment of such gels. In the present report, precipitation polymerization of bifunctional VBCTHt monomers in ethanol and acetonitrile generated the nano-gel cross-linkers bearing cyclic sulfonium moieties. The addition of nano-gels cross-linkers to partially hydrolyzed poly(acrylamide) formed covalently cross-linked in situ gels at the temperatures greater than 25 °C. As the morphology of the cross-linker changed from linear form to nano-gel in the state of sphere, the gelation time was controlled from 3 to 40 h. Nano-gel–HPAM system showed three orders of magnitude of delayed gelation while maintaining comparable mechanical integrity in comparison with conventional metallic cross-linked in situ gel, where sulfonium-functionalized nano-gel cross-linkers acting as covalent gelator were utilized for in situ gel formation. The change in cross-linker morphology and bonding nature of the gels dramatically extended gelation time. The mechanics of nano-gel cross-linker-derived covalently cross-linked HPAM in situ gels could be tuned by nano-gel cross-linkers concentration. The viscosity of HPAM and ionic cross-linker gelant had lower viscosity compared to conventional Cr3+–HPAM gel system as confirmed by rheological measurements. The gelant showed excellent salt and pH resistance, rendering it applicable to reservoir conditions. We believe this pioneer work in examination of cross-linker morphology to dictate hydrogel gelation offered the possibility to deploy mechanically tunable gels with delayed gelation for in-depth treatment of reservoir formation to improve fossil energy recovery.
[en] The mechanisms of the cryotropic gelation of poly(vinyl alcohol) solutions as well as the influence of the characteristics of the polymer and the conditions of the cryogenic treatment on the structure and physicochemical properties of the cryogels obtained are examined. Data on the characteristics of the freezing of concentrated poly(vinyl alcohol) solutions are presented. The influence of soluble additives, possessing different lyotropic properties, on the course of gelation in frozen systems is discussed. The possibility of the cryocracking of poly(vinyl alcohol) chains is considered. The bibliography includes 349 references.
[en] True downhole rheological properties affect equivalent circulating density, hole cleaning, barite sag, surge/swab pressures during tripping, pump pressure, and bit hydraulics. Gelation and excessive viscosity are major concerns at high temperatures. When using oil-based drilling fluids lightened by an injection of de-oxygenated air (containing small amounts of oxygen, usually around five per cent) in underbalanced drilling (UBD) operations, there is a need to be able to predict the effect of oxidation on the viscosity of the oil-based muds as a function of temperature and pressure. This paper presents the results of an experimental investigation that was aimed at establishing the effect of oxidation on the viscosity of an oil-based drilling fluid. The drilling fluid was aged for 2.5 days and for 7 days in the presence of air at temperatures ranging from 100 to 150oC and at pressures ranging from 14 to 44 MPa. The viscosity of the drilling fluid samples after aging is compared with the corresponding fresh samples (before aging). The results show that oxidation causes an increase in viscosity. The amount of the increase depends on the amount of oxygen reacted, which is a function of temperature, pressure, and time. The higher temperatures of the reactors lead to the higher increases in viscosity. Furthermore, at higher temperatures, solid (mostly coke) formation was observed. (author)
[en] Highlights: • Successful incorporation of surfactant exfoliated graphene as an intrinsic component of an alpha-cyclodextrin based gel. • Exploration of gelation properties of the hybrid gels and the relationship with PEO composition. • Demonstration of photothermally induced drug release through near-infrared irradiation of embedded graphene. • Extensive characterization of the gels produced with a focus on the drug release properties.
[en] In the present paper preparation conditions for the formation of various types of uranyl gel, using the internal gelation route, are described. Various types of the gel can be prepared differing in their physico-mechanical properties. The research parameters were selected with respect to practical preparation conditions. The results of the paper represent an attempt to investigate systematically some of the basic chemistry problems of the gel process. (Auth.)
[en] An internal gelation process was adopted for the fabrication of carbon-dispersed UO3 microspheres which will be fed to the fabrication for uranium nitride microsphere fuels by the carbothermic reduction. For investigating the proper process conditions, a composition range of feed solution for preparing good UO3 gel spheres was firstly defined by observing the gelation behavior. Within the defined solution compositions, carbon-dispersed microspheres were prepared and carbon distribution in microspheres were observed by SEM. The results showed that production of good carbon-dispersed microspheres was possible, and the most of carbon were evenly distributed in the microspheres although large carbon-rich aggregates were sparsely existent
[en] The end linking of difunctional poly(dimethylsiloxane) with trifunctional cross linkers in the bulk has been simulated with a computer. A random array of primary chains with a Gaussian end-to-end distribution is generated in an image container on the computer. By joining chain ends at nearby junctions, inter- and intramolecular reactions occur in all species, allowing formation of cyclic structures of any size. At high extents of reaction, the sol components extracted from the spanning forest thus constructed consist of a substantial amount of cycles such as cyclic dimers. The effect of intramolecular reaction increases the extent of reaction by several percent for molecular weights in the range of thousands. Structural statistics of various types of network imperfections and the cycle ranks of the networks are reported. The gels obtained at complete conversions contain loop defects, their populations increasing with lower molecular weights of the prepolymers. The elastic activities of nonstoichiometric systems are compared and discussed
[en] The shear-influenced gelation of three aqueous suspensions consisting of silica particles of nominal diameter 7, 12 and 24 nm, respectively, is reported. It is shown that the viscosity/stress of a gelling system increases with time after gel initiation, reaches a maximum, then falls to a plateau value. A very simple relation between this maximum stress and the precursor volume fraction is verified experimentally