Meditech applications in extracorporeal devices

Textiles in medical applications have vast scope, and in this, extracorporeal devices play a vital role because life-saving products in artificial form can be developed through intense research, affirm M Saravanan and A Thambidurai.

Extracorporeal devices are mechanical organs that are used for blood purification and include artificial kidney (dialyser), artificial liver, and mechanical lung (blood oxygenator). Blood purification is an effective therapy for incurables such as end-stage renal failure. It is used to correct the abnormality of blood quality and quantity in treating sickness. Use of an artificial organ is a life saving treatment which can restore the spring that does not function, and a dynamic balance can be obtained by organ transplantation to recover health again. The function and performance of extracorporeal devices benefit from fibre and textile technology.

Principles of blood purification

Principles of blood purification therapies are dialysis, filtration and adsorption as depicted in figure 1. Separation membranes and adsorbents are used in blood purification devices. The membrane separation depends on membrane pore size. Purification methods are hemodialysis (dialysis, membrane pore size 1-8 nm), hemofiltration (filtration, membrane pore size 3-60 nm), plasma exchange (filtration, porous membrane pore size 0.2-0.6 micrometre) and hemoadsorption. Hemodialysis accounts for more than 90 per cent of the blood purification treatment in the world which corresponds to 30 million treatments per year keeping 3,00,000 patients alive. Hemodialysis includes removal of metabolic substances, adjustment of electrolytes and pH, removal of excess water by ultrafiltration and, dialysis which is usually a membrane separation process.

Textile materials for extracorporeal devices

Extracorporeal fibres are those used in mechanical organs such as hemodialyser (artificial kidney), artificial liver and mechanical lung. Textile materials used in extracorporeal devices for blood purification and the function of each device are shown in Table 1.

Artificial kidney

The kidneys serve as filtering devices of the blood. The nephrons, the working units of the kidney, filter waste materials out of the blood and produce urine to secrete toxins from body. The kidneys also maintain normal concentrations of body fluids, which play a key role in homeostasis. In the natural kidney, ultrafiltration of the blood occurs through the glomerular capillaries leading to the removal of waste products and the purification of blood. In an artificial unit a membrane-dependent-ultrafiltration achieves essentially the same result. Hemodialysis is indispensable for people suffering from kidney disease.

The function of the artificial kidney is achieved by circulating the blood through a membrane, which may be either a flat sheet or a bundle of hollow regenerated cellulose fibres in the form of cellophane that retain the unwanted waste materials. Multilayer fibres composed of numerous layers of needle-punched fabrics with varying densities may also be used and are designed to remove the waste materials rapidly and efficiently. The synthetic polymer substitute being experimented with is a polyethylene glycol-polyethylene terephthalate block copolymer membrane which can selectively filter.

The material used in dialysis membranes are regenerated cellulose, cellulose triacetate, acrylonitrile copolymer, poly (methyl methacrylate), ethylene-vinyl alcohol copolymer, polusulfone and polyamide which can be grouped as cellulose and synthetic polymer systems. Eighty per cent of the dialysers use cellulose materials which have excellent permeability for low molecular substances. Pore sizes of mem