Medical Application Terms
BIOCOMPATIBILITY refers to the tests used for screening plastics materials to determine if they are suitable for biomedical applications. Tests include:
CYTOTOXICITY refers to the deleterious effect upon cells, a cytotoxin being an agent having a specific toxic action on cells of special organs.
THROMBOGENICITY is 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.
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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 plastic extrusions and it is therefore possible to make some generalizations about chemical reactivity.
BONDABILITY refers to the degree to which the finished material can be attached to their components with solvents or adhesives. Some materials, such as FEP (Fluorinated Ethylene Propylene), are very difficult to bond because of their non-reactive/non-stick characteristics.
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ANGIOGRAPHY is radiological examination of the blood vessels using an opaque contrast medium.
ANGIOPLASTY is 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 is a process employed to remove waste and toxic products from the blood in cases of renal insufficiency.
DILATOR is an instrument used for enlarging an opening or cavity such as the rectum, the male urethra, or the cervix. Dilators also are used to widen a punctured opening for easier insertion of invasive applications such as catheters.
EMBOLECTOMY is 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 is the use of instrumentation for direct visual inspection of a hollow organ or cavity.
ENDOTRACHEAL refers to 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 refer to within the gastrointestinal tract. Enteral diets or enteral feeding diets taken by mouth or through as nasogastric tube.
EPIDURAL CATHETER is 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.
PERENTERAL refers to 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 is a method of removing a portion 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.
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CONCENTRICITY is a measure of the degree to which the circles forming the inner and outer diameters of the tube are evenly spaced. Variations in concentricity are to be minimized as non-concentric diameters correlate to uneven wall sizes which can lead to tube imbalance and weakening.
CO-POLYMER is a material composed by combining two different monomers joined in the same polymer chain.
DENIER is a unit of measure for the linear mass density of fibers, specifically the number of unit weights of 0.05 grams per 450-meter length. Lower numbers indicate finer sizes while higher numbers indicate coarser sizes.
DIELECTRIC STRENGTH is 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.
FIBER is a thread or filament of a suture material. A fiber is defined by having a length at least 100 times its width or diameter.
FLEXIBILITY is 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.
INHERENT VISCOSITY OR INTRINSIC VISCOSTIY (IV) is a viscometric method for measuring molecular size involving the ratio of the specific viscosity of a solution of a known concentration compared to the concentration of a solute at zero concentration.
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. Kink resistance is 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.
RESIN is a solid or semi-solid pellet of raw material soluble in ether or alcohol but not in water.
SHORE HARDNESS is the relative resistance of a material’s surface to indentation by an indentor of specified dimensions under specified load. Shore hardness refers to the general stiffness of a material. Hardness is measured according to the Durometer A and D, and Rockwell R scales.
SPIN LUBRICANT (or spin finish) is a lubricated finish applied to fibers during processing to make them more pliable.
TENSILE STRENGTH is the maximum stress a material withstands at the point of rupture. Tensile properties are a measure of the force required to stretch a plastic and the percent of stretching the plastic can withstand before breaking. 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 is the 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 of the other (untouched) end. A high degree of torque can be desirable in invasive applications.
UV RESISTANCE is 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.
YARN is a continuous cord or strand of fibers suitable for weaving or forming a textile fabric.
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