• Physical
• Biological
• Chemical
• Medical Applications

Physical

CONCENTRICITY - is a measure of the degree to which the circles are forming the inner and outer diameters of the tube are evenly spaced. If evenly spaced around the full 360 degrees, they are said to be concentric. Variations in concentricity are to be minimized as non-concentric diameters correlate to uneven wall sizes which can lead to tube imbalance and weakening.

DIELECTRIC STRENGTH - a measure of the voltage required to puncture a material, expressed in volts per millimeter of thickness. A high dielectric strength correlates to good electrical insulation ability.

FLEXIBILITY - an indication of the bending stiffness of the material. The Flexural Modulus is a coefficient of elasticity, which represents the ratio of stress to strain as a material is deformed under dynamic load.

KINK RESISTANCE - refers to the ability of a tube to withstand bending and coiling without deforming or 'kinking' (a fold in the wall). Kinking weakens the structural strength of the tube and can block or slow the transference of media through the tube as well. Kink resistance is to a large extent a function of wall thickness and shore hardness.

LUBRICITY (co-efficient of friction) - measures the frictional properties or "tackiness" of material. A low coefficient of friction is usually desired in medical applications to minimize bodily trauma and tissue irritation. This is especially true in lengthy insertion techniques such as catheterization.

OVALITY - is a measure of the non-circularity of a tube. Ovality is to be minimized as tubes with a high ovality lose structural strength.

SHORE HARDNESS - the relative resistance of a materials surface to indentation by an indentor of specified dimensions under specified load. Shore hardness refers to the general stiffness of a material. The hardnesses are measured according to the Durometer A & D, and Rockwell R scales, which overlap as follows:

							50R	70R	100R	120R
					40D		55D	70D	85D
	20A	30A	50A	70A	90A	95A
	Softest			Hardest

SPECIFIC GRAVITY - the ratio of a weight of a given volume of a substance to that of an equal volume of water at the same temperature. Specific gravity is related to the density of the molecular grouping of a polymer. The higher the figure for specified gravity, the denser the material.

STERILIZATION ABILITY - ethylene oxide and radiation (gamma) sterilization are the most frequently utilized techniques for the sterilization of medical devices. Interest in gamma sterilization is growing as regulations governing ethylene oxide use continue to tighten due to its adverse environmental effects. In addition, gamma sterilization has proven less expensive than ethylene oxide sterilization. However, not all materials react well to gamma sterilization. Therefore suppliers and OEM customers need to be aware of the sterilization ability of materials utilized in their products.

TENSILE STRENGTH - Tensile properties are a measure of the force required to stretch a plastic and the percent of stretching the plastic can withstand before breaking. Ultimate tensile strength is the maximum stress a material withstands at the point of rupture. A good tensile strength allows for design of thinner wall thicknesses which result in smaller diameters. A high tensile also aids in ease of catheter insertion. Related to this is Ultimate Elongation, which is the total elongation by percentage of a sample at the point of rupture.

TORQUE - a measure of force related to the rotational stability of the tube. If rotated at one end, a tube with a high degree of torque will rotate at nearly the ratio at the other (untouched) end. A high degree of torque can be desirable in invasive applications. Braiding of tubes is a method used to increase torque.

UV RESISTANCE - the ability of a plastic to resist damage from Ultra-violet light waves (from the sun) for a sustained time interval. Some materials witness effects such as discoloration, surface cracking, hardening, and changes in electrical properties when continually exposed to ultra-violet waves.

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Biological

BIOCOMPATIBILITY - These tests are used for screening plastics materials suitable for biomedical applications. Tests include implants in research animals and the injection of resin extracts in various liquids into animals to detect toxic responses. Other tests include tissue cultures on resins and resin extracts using mammalian and human cells, rabbit implants, hemolysis testing, intracutaneous injection of rabbits, systemic toxicity in mice, cell growth inhibition of aqueous extracts, and total and extractable heavy metals and buffering capability.

CYTOTOXICITY - measures of cytotoxicity refer to the deleterious effect upon cells, a cytotoxin being an agent having a specific toxic action on cells of special organs.

THROMBOGENICITY - the tendency of an agent to cause blood clot formation around the invasive area. This is a deleterious phenomenon which can lead to further complications. In plastics applications, a smooth surface is desirable in order to avoid activation of the clotting mechanism. Hydrophilic (water loving) surfaces are known to prevent absorption of protein and cells and therefore prevent the blood clotting immune response. The more hydrophilic the plastic is (the ability to form H-bonds with water molecules), the less foreign the material is to the body. Silicone is one of the hydrophilic compounds, this explaining the common use of silicone for implants.

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Chemical

CHEMICAL RESISTANCE - refers to the general degree of reactivity of an extruded material to a range of chemicals. The chemical resistance of a plastics material is as good as its weakest point. If it is intended that a plastics material is to be used in the presence of a certain chemical, then each ingredient must be unaffected by the chemical. There are a limited number of chemical structures utilized in plastics extrusion today and it is therefore possible to make some generalizations about chemical reactivity.

BOND ABILITY - refers to the degree to which the finished material is able to be attached to their components with solvents or adhesives. Some materials, such as FEP, are very difficult to bond because of their non-reactive/non-stick characteristics.

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Medical Applications

ANGIOGRAPHY - radiological examination of the blood vessels using an opaque contrast medium.

ANGIOPLASTY - plastic surgery of blood vessels. Often, a small balloon is inserted into a vein or artery and blown up to clear blockage and calcified build-up on the lining of the vessel.

DIALYSIS - a process employed to remove waste and toxic products from the blood in cases of renal insufficiency.

DILATOR - an instrument used for enlarging an opening or cavity such as the rectum, the male urethra or the cervix. Dilators are also used to widen a punctured opening for easier insertion of invasive applications such as catheters.

EMBOLECTOMY - surgical removal of an embolus (a substance carried by the bloodstream until it causes obstruction by blocking a blood vessel), frequently arterial emboli that are cutting off the blood supply to the limbs.

ENDOSCOPY - the use of instrumentation for direct visual inspection of a hollow organ or cavity.

ENDOTRACHEAL - within the trachea. An Endotracheal tube is an airway catheter which is inserted into the trachea when a patient requires ventilatory support. It also allows for the removal of secretions by suction.

ENTERAL - within the gastrointestinal tract. Enteral diets or enteral feeding diets taken by mouth or through as nasogastric tube.

EPIDURAL CATHETER - a catheter inserted in the lower back often used for the injection of a local analgesic in order to block the spinal nerves during labor or chronic back pains.

IRRIGATION - the washing out of a cavity or wound with a stream of lotion or water.

NEPHROSTOMY - creation of a permanent opening into the renal pelvis.

ONCOLOGY - the study and treatment of tumors.

PERENTERAL - apart from the alimentary canal. Applied to the introduction into the body of drugs or fluids by routes other than the mouth or rectum, for instance intravenously or subcutaneously.

PLASMAPHERESIS - a method of removing apportion of the plasma from circulation. Venesection is performed, the blood is allowed to settle, the plasma, is removed, and the red blood cells are returned to the circulation. Used in the treatment of those diseases caused by antibodies circulating in the patient's plasma.