Alginate:
Alginates are cell-wall constituents of brown algae (Phaeophycota). They are chain-forming heteropolysaccharides made up of blocks of mannuronic acid and guluronic acid. Composition of the blocks depends on the species being used for the extraction and the part of the thallus from which extraction is made.
Alginates are linear unbranched polymers containing ?-(l?4)- linked D-mannuronic acid (M) and ?-(l?4)-linked L-guluronic acid (G) residues. According to the source algae, alginates can consist of blocks of similar and strictly alternating residues (i. e. MMMMMM, GGGGGG and GMGMGMGM), each of which have different conformational preferences and behavior. Alginates may be prepared with a wide range of average molecular weights (50 -100,000 residues) to suit the application.
Because of their abundance in source and low in prices, Alginates have been widely used in the food and pharmaceutical industry as thickeners, emulsifying agents, binder and disintegrating agent for tablet and capsule formulations. Because of their biocompatibility, alginates have been used in medical applications such as wound dressings, scaffolds for tissue engineering and hepatocyte culture and surgical or dental impression materials. Alginates are also known to be broken down to simpler glucose type residues and can be totally absorbed.
When used as biomaterials for implantation or tissue engineering scaffolds, alginates have to be cross-linked. Alginate can be easily cross-linked by calcium ions to form ionic bonding between alginate molecules. The cross-link is a fast process. As an example, cross-linked alginate beads can be obtained instantly by dripping sodium alginate solution into calcium chloride solution.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
|