Hollow fibers chemical activation

HOLLOW-FIBER MEMBRANES. A hollow-fiher membrane is a capillary having an inside diameter of - inn and an outside diameter < I mm and whose wall functions as a semipermeahlc membrane. The fibers can he employed singly or grouped into a bundle which may contain tens of thousands of fibers and up to several million libers as in reverse osmosis (Fig. 11. In most eases, hollow fibers are used as cylindrical membranes that permit selective exchange of materials across (heir walls. However, they can also he used as containers to effect the controlled release of a specific material, or as reactors to chemically modify a permeate as il diffuses through a chemically activated hollow-liher wall. e g., loaded with immobilized enzyme. 

Hollow membrane fibers are required for many medical application, e.g. for disposable dialysis. Such fibers are made by usmg an appropriate fiber spinning technique with a special inlet in the center of the spinneret through which the fiber core forming medium (liquid or gas) is injected. The membrane material may be made by melt-spinning, chemical activated spinning or phase separation. The thin wall (15-500 xm thickness) acts as a semi-permeable membrane. Commonly, such fibers are made of cellulose-based membrane materials such as cellulose nitrate, or polyacrylonitrile, polymethylmethacrylate, polyamide and polypropylene (van Stone, 1985). 

A capillary lung produced by Dow Chemical Co. (38) can pass 1.4 liters/min/m2 of blood. It has siloxane-polycarbonate copolymer hollow fibers of 150 p inside diameter, 25 /x wall thickness, and is 8.5 cm in active length. Prime volume is 100 ml/m2. One square meter transfers 51 ml/min of oxygen and 66 ml/min of carbon dioxide at 1.4 liters/min/m2... 

Inorganic membranes, usually appUed when high temperatures or chemically active mixtures are involved, are made of ceramics [171,172], zirconia-coated graphite [173],silica-zirconia [174],zeolites [168], or porous glass [175] among others [176]. Ceramic membranes are steam sterilizable and offer a higher mechanical stability [134], thus they may be preferably used in aseptic fermentations, since some hollow fibers are only chemically sterilizable and not very suitable for reuse. Composite materials, in which glass fiber filters are used as support for the polymerization of acrylamide monomers, were developed for the hydrolysis of penicillin G in an electrically immobilized enzyme reactor. By careful adjustment of the isoelectric point of amphoteric membranes, the product of interest (6-aminopenicillanic acid) was retained in an adequate chamber, adjacent to the reaction chamber, while the main contaminant (phenyl acetic acid), was collected in a third chamber [120]. 

Nevertheless to avoid the risk of serious damaging the chemical modification on hollow fibers hemodialyzers has to be performed in the absence of organic solvents and consequently the choice of the activation procedures is very limited. 

To overcome this problem,we developed a simple technique,which involves two steps 1. chemical activation of hollow fibers and their characterization 2. assessment of the functionalized hollow fibers in conventional hemodialyzers and their use for coupling several nucleophiles,such as aminoacids,peptides and enzymes. 

The chemical activation of the cellulose hollow fibers and the coupling of nucleophiles(RNH2) were performed according to the following scheme ... 

In conclusion, the proposed method based on the chemical activation of the hollow fibers followed by their assessment in the bioreactor form,may be a solution to the problems normally encountered during the activation of commercial hemodialyzers. 

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