Today, we are going to talk about a kind of naturally occuring polymeric
bimaterials,
今天，我们要谈论一种存在于自然界的的聚合生物材料，
也就是我们常说的天然聚合物材料，名字叫做Celluose，纤维素。
Maybe you are not familier with Celluose, actually, Cellulose is by far the
most abundant organic substance in nature.
可能你对纤维素并不熟悉，实际上，纤维素是迄今为止自然界中最丰富的有机物质。 有缘学习更多驾卫星ｙｇｄ３０７６
It can be found in all plant matter and is the main constituent of the cell
wall in green plant.
所有植物中都包含它，并且它是绿色植物细胞壁的主要成分。
其实纤维素存在于我们自然界广泛的绿植当中。
As a polymer,do you know the basic structure of cellulose? And what is
the repeating unit of cellulose?
作为一种聚合物，你知道纤维素的基本结构吗？ 什么是纤维素的重复单元？
Celluose is made up of several hundreds to thousands of D-glucose units.
纤维素由数百至数千个D-葡萄糖单元组成。
This rings are linked togethor between the C-1 of one glucose unit and the C-4 of another glucose unit by single oxygen atoms called the beta-1,4 glycosidic bonds linkages.
这些环通过单个氧原子连接将一个葡萄糖单元的C-1键和另一个葡萄糖单元的C-4键相连，相连的键称为β-1,4糖苷键。
我们将糖环之间相连的键称为糖苷键。
It is very interesting that cellulose is water insoluble. 一个有趣的现象是纤维素是不溶于水的。
这里我们要提到纤维素很有趣的一个特征，纤维素不溶于水。
The water-insolubility of cellulose is due to the presence of intramolecular and intrastrand bonding within the crystalline structure that provides polymer with high fiber strength.
纤维素的水不溶性是由于在晶体结构内存在分子内和链内键，从而为聚合物提供高纤维强度。
纤维素不溶于水的特性是由于分子内及分子链间作用力形成的不用的结晶度导
致的。
In regions of the cellulose fibers that are less ordered or less crystalline, the cellulose chains are farther apart and are more readily available for bonding with other molecules.
在纤维素纤维的有序性较低或结晶较少的区域，纤维素链分开较远并且更易于与其他分子键合。
As such, when immersed in water, the presence of these less crystalline regions permits cellulose to swell as result of absorbing large quantities of water and thus making cellulose structures hygroscopic.
这样，当浸入水中时，由于低结晶区域可以吸收大量的水分从而使得纤维素具有吸湿性。
也就是说明纤维素局域的结晶度不同，使得纤维素可以不溶于水，但是部分又具备吸水的特性。
Other cellulose properties such as viscosity are governed by its molecular weight. Variation in molecular weight is controlled by the degree of polymerization of the cellulose backbone, which in turn is dependent on the cellulose source and isolation process.
其他纤维素性质如粘度受其分子量控制。 分子量的变化受纤维素主链聚合度的
控制，而纤维素主链又取决于纤维素来源和分离过程。
那么我们提到的纤维素的粘度特性是取决于它的分子链长短。
Cellulose can be converted to many derivatives and makes it an attractive raw material.
纤维素可以转化为许多衍生物，使其成为一种有吸引力的原料。
Purification and isolation of cellulose involves a variety of steps including a pulping process (碎浆过程), partial hydrolysis (水解过程), dissolution (溶解过程), repeated precipitation (沉淀过程), and extraction with organic solvents (萃取过程).
纤维素的纯化和分离包括碎浆过程，水解过程，溶解过程，沉淀过程和萃取过程等各种步骤。
These purification and isolation processes almost always degrade the cellulose as well as allow the cellulose to undergo oxidation by reacting with both acids and bases.
这些纯化和分离过程几乎总是降解纤维素，并使纤维素通过与酸和碱反应而发生氧化。
也就是说在整个的纤维素制备过程中通常会存在纤维素的降解，但是同时也为纤
维素的修饰提供了条件。
The biocompatibility of cellulose and its derivatives has been well established.
纤维素及其衍生物的生物相容性已得得到了广泛的研究。
我们在前面的课程已经学过，作为生物材料，biocompatibility也就是生物相容性是非常重要的。
Cellulose ethers, being the largest groups of cellulose derivatives, have been well documented for medical and pharmaceutical applications.。 作为纤维素衍生物的最大分类的纤维素醚已经在医学和药物应用方面得到很好的应用。
Cellulose ethers can be divided into nonionic, cationic and anionic subgroups.
纤维素醚可分为非离子型，阳离子型和阴离子型。
在这里我们重点介绍几种纤维素的衍生物，分别是非离子型，阳离子型和阴离子型纤维素醚。
Hydroxypropyl cellulose (HPC) as a kind of nonionic cellulose has been
材料导论(51)
