Characterization of PEEK biomaterials using the small punch test

The small punch test is widely used to characterize the ductility and fracture resistance in metals and ceramics, when only a small volume of material is available. This study was conducted to investigate the suitability of the small punch test for characterizing polyetheretherketone (PEEK) polymeric biomaterials for changes in material grade, crystallinity, and molding process. The small punch test reproducibly characterized the mechanical behavior of PEEK and was able to distinguish differences induced by molding process alterations and annealing. Peak load was most sensitive to changes in crystallinity, grade, molding process, and increased with increasing crystallinity, but decreased with the addition of image contrast materials. The ultimate displacement was negatively correlated with crystallinity. Molding process conditions had the greatest influence on metrics of the small punch test, when compared with the effects of annealing and the addition of a radiopacifier. The results of this study validate the small punch test as a repeatable method for measuring the mechanical behavior of PEEK biomaterials.

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► The small punch test was adapted for use with PEEK materials.
► Unfilled and image contrast grades of PEEK were evaluated at three crystallinity levels.
► The most sensitive parameter measured was peak load.
► The test distinguished differences due to crystallinity, processing, or grade.
► Higher crystallinity conferred less ductility, but higher strength to the material.