Chitosans membranes

The intrinsic ionic conductivities of hydrated chitosan membranes investigated using impedance spectroscopy were as high as 10 S cm [232]. 

Superficially phosphorylated chitosan membranes prepared from the reaction of orthophosphoric acid and urea in DMF, showed ionic conductivity about one order of magnitude larger compared to the unmodified chitosan membranes. The crystallinity of the phosphorylated chitosan membranes and the corresponding swelling indices changed pronouncedly, but these membranes did not lose either tensile strength or thermal stability [234]. 

Chitosan membranes can also be superficially modified, for instance with 3-isocyanatopropyl triethoxysilane. Silanol groups and calcium salt acted as nucleation sites and accelerator, respectively, for the formation of apatite crystals therefore, this chitosan membrane is a bioactive guided bone-regeneration material thanks to its apatite-forming ability [341]. 

The majority of the aforementioned capsules were either not sufficiently mechanically stable or suffered from other surface or matrix related deficiencies. These deficiencies include poor morphology, such as capsule sphericity and surface smoothness, which result from an osmolar imbalance. Membranes are also often leaky (an internal polymer slowly diffuses out through the capsule wall) or shrink in either PBS or in culture media over a period of a few hours. Exceptionally, some capsules are observed to swell excessively and burst. Furthermore, some complex membranes, although stable in water, dissolve over several days upon a contact with culture media. This is true for pectin based capsules (pectin/calcium salt) and for alginate-chitosan membranes and maybe a consequence of the polycation substitution by electrolytes present in the media [10]. In order to improve the existing binary capsules several approaches, both traditional and novel, have been considered and tested herein. These are discussed in the following sections. 

Ghen, X., Yang, H., Gu, Z., and Shao, Z. (2001) Preparation and characterization of HY zeolite-filled chitosan membranes for pervaporation separation. /. Appl. 

Takahashi, T., Imaia, M., Suzukia, I., and Sawai, J. (2008). Growth inhibitory effect on bacteria of chitosan membranes regulated by the deacetylation degree. Biochem. Eng.. 40, 485-491. 

Ogawa, S., Decker, E.A., McClements, D.J. (2003). Influence of environmental conditions on the stability of oil-in-water emulsions containing droplets stabilized by lecithin-chitosan membranes. Journal of Agricultural and Food Chemistry, 51, 5522-5527. 

Fig. 17 Optical images of the DNA-chitosan membrane bound onto rabbit peritoneum. The DNA-chitosan complex membrane showed an adhesive property to rabbit peritoneum tissue...

Zhang LH, Bai CH, Wang YS et al (2009) Improvement of chloroperoxidase stability by covalent immobilization on chitosan membranes. Biotechnol Lett 31 1269-1272... 

Ogawa, S., Decker, E. A., and McClements, D. J. (2002), Production and characterization of o/w emulsions containing cationic droplets stabilized by lecithin-chitosan membranes, J. Agric. Food Chem., 51, 2606-2812. 

The stracture of the multilayered emulsions may be preserved during spraydrying, enabling the delivery of emulsions with multilayered interfaces in a powder format. Spray-dried tuna oil powders made from emulsions containing oil droplets with lecithin-chitosan membranes, with added com symp showed good oil retention and water dispersibility (Klinkesom et al. 2006). 

V-acetylated chitosan membrane Sulzer Pervap-2255 membrane Cuprophane membranes... 

Huang RYM, Moon GY, and Pal R. N-acetylated chitosan membranes for the pervaporation separation of alcohol/toluene mixtures. J. Memb. Sci. 2000 176(2) 223-231. 

Nakatsuka S, Andrady LA. Permeability of vitamin-B-12 in chitosan membranes effect of crosslinking and blending with poly(vinyl alcohol) on permeability. ] Appl Polym Sci 1992 44 7-28. 

Kubota N, Ohga K, Moriguchi M. Permeability properties of glycol chitosan membrane modified with thiol groups. ] Appl Polym Sci 1991 42 495-501. 

Feng, X.S. Huang, R.Y.M. Pervaporation with chitosan membranes I. Separation of water from ethylene glycol by a chitosan/polysulfone composite membrane. J. Membr. Sci. 1996, 116, 67-76. 

Figure 6.38 Typical characteristics of a chitosan membrane in the dehydration of alcohol-water mixtures by pervaporation. (A) Separation factor (a) (O) permeability coefficients of water (X) permeability coefficients of alcohols. Pervaporation of 28 mol% alcohol-water mixed solution was carried out at 60 °C.

T. Uragami, F. Yoshida and M. Sugihara, Studies on syntheses and permeabilities of special polymer membranes. 59. Active transport of organic ions through cross-linked chitosan membrane, Separation Sci. Technol., 1988, 23, 1067-1082. 

Saxena et al. produced a permselective membrane from a combination of these oppositely functionalized chitosan chains. Both modifications were found to have good hydrophilic interaction with water and the mixed solution resulted in charge neutralization. The resultant membrane was shown to discriminate between different ionic radii, specifically perturbing the diffusive properties of molecules with a larger ionic radius such as Mg and Ca, while facilitating the diffusion of Na, which has a smaller ionic radius. This implies the suitability of the bimodal functionalized chitosan membrane for separation of Na from Ca + and Mg +, allowing for specific detection of Na+. 

While Nafion , a perfluorinated polymer developed by DuPont, is the most commonly used proton conductive polymer electrolyte membrane it is an insufficient solution in a number of areas. It has high cationic transport (approximately 9.56 5/cm) [8] but also has high levels of methanol fuel crossover, slow anode kinetics and very high cost [12]. Fuel cell membrane performance can be estimated from the ratio of proton conductivity (a) to methanol permeability (P). The higher the value of a/P, the better the membrane performance would be [13]. Chitosan has been shown to have a much lower methanol permeability than Nafion [14], and as such, a great deal of attention focused on developing chitosan membranes with high levels of ionic conduction and low methanol permeability as delineated in Table 3.1. 

Overall, a great deal of attention has been paid to inducing ionic conductivity in chitosan membranes for application in fuel cell membranes. In both cationic and anionic membranes, the fuel cell performance values are approaching that of the industry standard Nation membranes. 

Mi EL, Shyu SS, Wu YB et al (2001) Fabrication and characterization of a sponge-like asymmetric chitosan membrane as a wound dressing. Biomaterials 22 165-173... 

Hu and coworkers [126, 127] firstly developed an in situ precipitation approach to fabrication of 3D ordered chitosan rods with a structure of concentric circles through the formation process illustrated in Fig. 11. Briefly, the chitosan/acetic acid solution is filled into a bag made of chitosan membrane, and then immersed into 5% NaOH aqueous solution. When OH ions from the outside solution permeate into... 

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