Sterilization, membrane devices

Laboratory membrane applications usually involve small samples. Consistency and resolution of the separation is as important as productivity of the membrane. As is typical in analytical work, membranes or membrane devices are usually used once and discarded. Strict compliance to sterility and validation requirements is expected. 

Sterilization. Sterility Is a necessary requirement for all membrane devices used clinically, and the sterilization procedure must not change the functional or blocompatlble character of the device. Sterility, the condition of absolute absence of viable life forms, can be achieved by physical (heat. Irradiation) or chemical means. Chemicals used to sterilize membrane devices may be either gaseous (ethylene oxide) or liquid (formaldehyde, peroxides, hypochlorite) In nature. The generally accepted... 

Ethylene oxide (ETO) Is the predominantly used sterilant In the United States for membrane devices destined for medical use. Conditions for Its use have been well established to assure sterility (51), although some problems arise from the slow diffusion of the gas from thick sections of thermoplastics, such as the headers In hollow fiber devices. The majority of hemodlalyzers are prepared with cellulosic membranes, which are partially... 

Buffer filtration device (either a glass filtration unit, fitted with a 0.45-itm membrane, connected to a side-arm flask or a tissue culture sterilization filter unit). 

Glass-filtration device, or a 500-mL filter-sterilization flask with a 0.45-pm membrane. 

Tub cleaning or sterilization device Automatic CIP cleaning system Coverleaf station with magazine Sealing membrane station with magazine Other functions... 

Steam sterilization of medical devices Is used In Japan. It has the advantage of facilitating removal of water soluble residues left after membrane manufacturing, but requires that the device be shipped filled with water. Steam sterilization appears to alter the pore structure of hydrophobic membranes, despite the fact that their glass transition temperatures may be quite high, for example, the permeability of polysulfone membranes Is altered above 70°C. Literature Cited... 

The excellent sorption capacity of the hypercrosslinked mesoporous poly-DVB with respect to selective removal of P2M from its mixtures with albumin and other semm proteins, combined with superior hemocompat-ibility of the beads surface modified with poly(N-vinyl)pyrrolidone, justified the manufacturing of an experimental batch of the material for initial clinical studies. The polymer was named BetaSorb (RenalTech International, USA) and was used in 300 mL cylindrical polysrdfone devices that were steam-sterilized and filled with normal saline containing 1000 lU heparin. The device was placed in line with the dialysis circuit, upstream of the dialyzer, in order to not affect the pressure drop across the dialyzer membrane. The blood flow was maintained at the customary value of 400 mL/ min, again the optimal flow rate for the dialyzer. The complete setup of the combined hemoperfusion-hemodialysis treatment [361] is displayed in Fig. 15.2. 

The associated disadvantages include (1) requirements for large quantities of nutrients (growth medium) relative to batch and fed batch modes of operation (2) high material costs associated with purchase and preparation/sterilization of the growth medium (3) elevated waste treatment costs and (4) fouling of the surfaces of permselective membranes or conventional or membrane microfiltration devices, which can lead to marked decreases in the flux of... 

Recovery of cells can be accomplished using one of several alternative unit operations, such as centrifugation, membrane filtration, or settling. Subscripts are employed in the figure to identify the usual process variables at particular points in the diagram. We employ the recycle ratio (R) to represent the ratio of the volumetric flow rate of the suspension of cells leaving the separation device to the volumetric flow rate of the net product stream. The symbol t / represents the ratio of the concentration of biomass in the recycle stream to that in the effluent from the CSTBR. You may assume that the system is operating at steady state and that the feed is sterile. 

A very common commercial device for hemodialysis is the C-DAK 4000 artificial kidney of Althin CD Medical, Inc. (acquired by Baxter International, Inc. in March, 2000). This disposable, sterilized membrane module, shown in Figure 19.5, resembles a shell-and-tube heat exchanger. The tubes, which number 10,000, are hollow fibers, 200 microns i.d. by 10 microns wall thickness by 22 cm long, made of hydrophilic microporous cellulose acetate of 15 to 100 A pore diameter. Alternatively, fibers of polycarbonate, polysulfone, and other poly-... 

In the membrane filter process, larger quantities of water can be pressed or sucked through a sterile membrane filter inserted in the sterile filtering device. The filter is then stretched free of bubbles on the surface of the soldified nutrient medium in a Petri culture dish and the culture thus... 

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