The more critical the role of the device and the more important the properties of its materials are to device performance, the more detailed the characterization program should be. These tests may be carried out directly on material samples or on material extracts prepared under specified conditions. In this test, IR energy is passed through a thin film of material and the amount of energy absorbed at various wavelengths is measured. By matching the IR spectrum of an unknown material with that of a known material, proof of identity can be established within the limits of the method. Infrared analysis provides a rapid, effective means of identifying a polymeric material and of comparing samples to ensure consistency.
Thermal analyses are also useful for fingerprinting materials.
Testing also can be conducted to determine the unique melting point, degree of crystallinity, and glass transition temperature of a polymer. The significant physical properties of a material can be identified with various test instruments. Material hardness is determined by means of a durometer that measures the extent to which the material can be compressed. Some potential extractables from medical device materials are water soluble, while others are soluble only in nonpolar environments. For materials that will contact body tissues, extraction activity in both polar and nonpolar environments is relevant.