4.1 Miniature specimen testing techniques are used to characterize the mechanical behavior of polymer stock materials and surgical implants after manufacture, sterilization, shelf aging, radiation crosslinking, thermal treatment, filler incorporation, and implantation (1-3). Furthermore, experimental materials can be evaluated after accelerated aging, fatigue testing, and hip, knee, or spine wear simulation. Consequently, the small punch test makes it possible to examine relationships between wear performance and mechanical behavior. This test method can also be used to rank the mechanical behavior relative to a reference control material.

4.2 Small punch testing results may vary with specimen preparation and with the speed and environment of testing. Consequently, where precise comparative results are desired, these factors must be carefully controlled.

1.1 This test method covers the determination of mechanical behavior of polymeric biomaterials by small punch testing of miniature disk specimens (0.5 mm in thickness and 6.4 mm in diameter). The test method has been established for characterizing surgical materials after ram extrusion or compression molding (1-3)²; for evaluating as-manufactured implants and sterilization method effects (4, 5); as well as for testing of implants that have been retrieved (explanted) from the human body (6, 7).

1.2 The results of the small punch test, namely the peak load, ultimate displacement, ultimate load, and work to failure, provide metrics of the yielding, ultimate strength, ductility, and toughness under multiaxial loading conditions. Because the mechanical behavior can be different when loaded under uniaxial and multiaxial loading conditions (8), the small punch test provides a complementary mechanical testing technique to the uniaxial tensile test. However, it should be noted that the small punch test results may not correlate with uniaxial tensile test results.

1.3 In addition to its use as a research tool in implant retrieval analysis, the small punch test can be used as a laboratory screening test to evaluate new materials with minimal material waste (1).

1.4 The small punch test has been applied to other polymers, including polymethyl methacrylate (PMMA) bone cement, polyacetal, and high density polyethylene (HDPE), ultra high molecular weight polyethylene (UHMWPE), and polyetheretherketone (PEEK) (2, 3, 5, 10, 11). This standard outlines general guidelines for the small punch testing of implantable polymers.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.