Cross-links, covalent, introduction

Some cross-linking takes place in the form of side reactions such as biuret and allophanate bonds. Deliberate introduction of covalent cross-linking can be carried out by the introduction of multifunctional agents (mainly triols) into either the prepolymer or chain extension system. 

Oxidases are enzymes that catalyze oxidation-reduction processes that do not involve insertion of oxygen atoms. Modification of proteins by oxidases allows the introduction of covalent cross-links between polypeptide chains. 

Other surface modification techniques include the use of free radical-, photochemical-, radiation- redox- and plasma-induced grafting. These are used to covalently attach some useful monomers onto the membrane surface [20]. Gas plasma treatment is also used to induce surface modification water permeabihty is improved by oxygen plasma treatment due to the introduction of hydrophihc carboxylate groups, whereas argon plasma treatment can enhance chlorine resistance by increasing the extent of cross-linking at the nitrogen sites. 

A and B, and to produce a fibrin monomer. The new N-termini of the a and 3 chains now bind to the terminal domain of a different fibrin monomer causing the spontaneous polymerization to form insoluble fibrin polymers. This fibrin network is further strengthened by the introduction of covalent cross-links by factor Xllla. 

A major problem of lipid vesicles in pharmaceutical applications has always been their minor stability. Stabilization of vesicles can be achieved by introduction of covalent cross-links or the attachment of stabilizing polymers (87,166-168). The most common methods involve the... 

The preparation (Fig. 4.1) and structure (Fig. 4.3) of an HsPOa-doped ionically cross-linked acid-base blend membrane (membranes 1927A and 1940 in Table 4.7) was already depicted schematically in the introduction. Figure 4.11 presents the preparation and the structure of a covalently cross-linked blend membrane (membranes 1921C, 1925C, and 1938), and Fig. 4.12 the preparation and structure of a covalent-ionically cross-linked blend membrane (membrane 1943). 

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