【正文】 1，按固定的細(xì)胞類型不同分為三類： （ 1）微生物； （ 2）動物； （ 3）植物。適用于一種酶催化的反應(yīng)。適用于多酶反應(yīng)，特別是需要輔酶的反應(yīng)。下面對這幾種做具體介紹。吸附法可分為物理吸附和離子吸附兩種。 2，載體的材料 采用吸附法固定細(xì)胞，所用的載體主要有：硅藻土、木屑、多孔玻璃、活性炭、 多孔陶瓷、離子交換樹脂和等。用該法制備的固定化細(xì)胞一般為死細(xì)胞。常用的交聯(lián)劑包括：戊二醛、甲苯二異氰酸酯、雙重氮聯(lián)苯胺。 四、包埋法 包埋法是細(xì)胞固定化最常用 的方法。 常用的包埋劑為：聚丙烯酰胺、瓊脂、海藻酸、卡拉膠、二醋酸纖維、三醋酸纖維、明膠等。但操作穩(wěn)定性差。但由于試劑的毒性，易引起細(xì)胞的破壞。 包埋法：細(xì) 胞和載體間沒有束縛，固定化后，細(xì)胞仍保持較高活力。 第三節(jié)固定化細(xì)胞的形狀及性質(zhì) 一、形狀 固定化細(xì)胞由于其用途和制備方法不同，可以是顆粒狀、塊狀、條狀、薄膜狀或不規(guī)則狀等。 二、性質(zhì) 1，最適 pH 細(xì)胞經(jīng)固定化后，其最適 pH 因固定化方法不同而有一些調(diào)整。但用同一方法包埋的大腸桿菌中的青霉素酰胺酶的最適 pH 則沒有變動。 3，穩(wěn)定性 一般而言，細(xì)胞經(jīng)固定化后，其穩(wěn)定性會有所提高。 二、固定化細(xì)胞反應(yīng)器的類型 固定化細(xì)胞反應(yīng)器包括以下幾種類型：細(xì)胞再循環(huán)系統(tǒng)（ Cell recycle systems ）、固定床反應(yīng)器（ Fixed bed reactors ）、流化床反應(yīng)器（ Fluidized bed reactors ）、絮凝細(xì)胞系統(tǒng)（ Flocculated cell systems ）。 thus minimising cell removal from the fermenter Cell recycle system Cell recycle is used in activated sludge systems. A portion of the cells are separated in a settling tank and returned to the activated sludge fermenter. Biomass recycling for product or biomass production is more difficult due to the need for maintaining sterility during cell separation. Centrifugation w hich is a faster process than settling would be used to separate the cells. Biomass recycle systems can be easily modelled. 固定床反應(yīng)器（ Fixed bed reactors ） In fixed bed fermenters, the cells are immobilized by absorption on or entrapment in solid, nonmoving solid surfaces. In one type of fixed bed fermenter, the cells are immobilized on the surfaces of immobile solid particles such as plastic blocks, concrete blocks, wood shavings or fibrous material such as plastic or glass wool. Fixed bed reactors The liquid feed is either pumped through or allowed to trickle over the surface of the solids where the immobilized cells convert the substrates into products. Once steady state has been reached there will be a continuous cell loss from the solid surfaces. These types of fermenters are widely used in waste treatment In other types of fixedbed fermenters, the cells are immobilized in solidified gels such as agar or carrageenin In these fermenters, the cells are physically trapped inside the pores of the gels and thus giving better cell retention and a large effective surface area for cell entrapment. In order to increase the surface area for cell immobilization, some researchers have investigated the use of hollow fibres and pleated membranes as immobilization surfaces. Industrial applications of fixed bed reactors include waste water treatment, production of enzymes and amino acids, and steroid transformations One advantage fixed bed reactors is that nongrowing cells can be used. In such systems, the cells enzymatically act on substrates in the feed. The cells can be either inactivated or not fed nutrients required for growth. 流化床反應(yīng)器（ Fluidized bed reactors） The fluidisation of the particles in the reactor leads to the surface of the particles being continuously turned over. This also increases the mass transfer rate. Fluidised beds are typically categorized as either being a 2 phase system which are not aerated and 3 phase system which is aerated by sparging Fluidized bed reactors Fluidized bed bioreactors are used widely in wastewater treatment. Fluidized bed bioreactors are also used for animal cell culture. Animal cells are trapped in gels or on the surface of special particles known as microcarriers. Fluidized bed reactors are one example of perfusion culture technology used for animal cell culture. Comparing fluidised bed and fixed reactors Fluidised bed reactors are considerably more efficient than fixed bed reactors for the following reasons: (1) A high concentration of cells can be immobilized in the reactor due to the larger surface area for cell immobilization is available (2) Mass transfer rates are higher due to the larger surface area and the higher levels of mixing in the reactor