Chitosan membranes results

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. 

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+. 

If a greater pH difference and an electric potential difference between both sides could be kept for a long time, that is, the diffusive transport of metal ion from the B side to the A side should be prevented, the uphill transport of Br" ion might be promoted. This expectation has been revealed by the result in Figure 34.19, in which the uphill transport of the Cl" ion through the chitosan membrane was promoted by trapping the metal ions with crown ether in the basic side in order to prevent the diffusion of metal ion from the basic side to the acidic side. 

The results of the platelet adhesion to the urokinase complex modified albumin blended chitosan membranes is shown in Table 3. The number of adhering platelets seen on the urokinase derivative immobilized surface has been dramatically reduced when compared with the albumin blended membrane. The permeability of various molecules through the albumin blended chitosan and the urokinase derivative immobilized mem-branes, as a function of time, is demonstrated in Figures 1 and 2, respectively. It is evident from these studies that the urokinase complex modified membranes had similar permeability properties to those of the... 

The ionic conductivity in the wet state of phosphorylated chitosan membranes prepared from the reaction of orthophosphoric acid and urea on the surface of chitosan membranes in AA -dimethylformamide was investigated by Wan et alP The authors observed that similarly to unmodified chitosan membranes phosphorylated chitosan membranes are hardly conductive in their dry states with conductivities between 10" and 10 S/cm. The entire conduction process occurs after the water incorporation increases the ionic conductivity values up to 10 and 10 S/cm depending on the phosphorus content in the sample. The best result of 1.2 x 10" S/cm was obtained with the sample containing 87.31 mg/m of phosphorus content. They also observed that the increase in the phosphorus content promotes a decrease in the crystallinity of phosphorylated chitosan membranes, an increase in the swelling index and not a significant loss of their tensile strength and thermal stability in comparison with the unmodified chitosan membranes. 

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