Medical devices hollow fibers

Hollow fiber refers to a membrane tube of very small diameter (e.g., 200 pm). Such small diameters enable a large membrane area per unit volume of device, as well as operation at somewhat elevated pressures. Hollow-fiber modules are widely used in medical devices such as blood oxygenators and hemodialyzers. The general geometry of the most commonly used hollow-fiber module is similar to that of the tubular membrane, but hollow fibers are used instead of tubular membranes. Both ends of the hollow fibers are supported by header plates and are connected to the header rooms, one of which serves as the feed entrance and the other as the retentate exit. Another type of hollow-fiber module uses a bundle of hollow fibers wound spirally around a core. 

DNA has been used to modify the PSf membrane by blending and immobilizing DNA onto its surface [123,124]. PSf is one of the most important polymeric materials and is widely used in artificial and medical devices. However, when used as a hemodialysis hollow fiber, the blood compatibility of the PSf membrane is not adequate. The hydrophilicity of the DNA-modified surface increased, but the amount of adsorbed protein did not decrease significantly, which indicates that the DNA-modified membrane might have a better blood compatibility. 

An early example of a patent on membrane contactor for gas transfer is in Ref. [12]. Harvesting of oxygen dissolved in water and discharging of CO2 to the water is presented in Ref. [13]. A membrane device to separate gas bubbles from infusion fluids such as human-body fluids is claimed in Ref. [14]. A hollow fiber membrane device for removal of gas bubbles that dissolve gasses from fluids delivered into a patient during medical procedures is disclosed in Ref. [15]. Membrane contactors have also found application in dissolved gas control in bioreactors discussed in Refs. [16-17]. 

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... 

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 terms of membrane area used and dollar value of the membrane produced, artificial kidneys are the single largest application of membranes. Similar hollow-fiber devices are being explored for other medical uses, including an artificial pancreas, in which islets of Langerhans supply insulin to diabetic patients, or an artificial liver, in which adsorbent materials remove bilirubin and other toxins. 

Careful consideration should be given to each test article to determine an appropriate approach to the testing. For example, a medical device may be a thin, sealed titanium can containing electronics. Extracting this device with the electronics contained within would not be appropriate, because there is little to no likelihood that a patient will be exposed to the electronics, and it would add mass to the test article and therefore increase the amount of extraction vehicle the can is exposed to. The result is a dilution of extractants leaching from the can, which can potentially mask toxic responses. In the case of hemodialyzers, the hollow fibers and housing are often tested separately, because of the different amount of extraction vehicle required. 

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