Acoustic emission monitoring and 3D visualization of polymerization-induced damage of acrylic polymer materials

To improve the longevity of total hip replacements, techniques such as vacuum mixing have been developed to reduce the amount of porosity within the cement. However, data from the Swedish hip registry has demonstrated an increased risk of revision for vacuum-mixed cemented devices in the first 5 years postoperatively. Theoretical and experimental evidence suggests that stresses induced by cement shrinkage during polymerization alone are sufficient to induce cracking. However, very little evidence of preload cracking is available due to the limitations of current inspection methods. The present work combines two forms of nondestructive evaluation technique to assess the state of an acrylic-based polymer mantle both in real time during polymerization using the acoustic emission (AE) technique and immediately post polymerization using micro-computed tomography (CT). AE data enabled the location, type, and chronology of events to be obtained. The use of micro-CT in combination with a radiopaque dye-penetrant was shown to be an effective method for highlighting preload polymerization cracking and verified the findings of the AE data. The AE data indicated that the first signs of damage occurred approximately 3-6 min after the peak temperature obtained during exotherm, confirming that thermal contraction rather than pure volumetric shrinkage is the dominant factor in preload damage initiation. The methodology developed in this study enables detailed information on the condition of a cement mantle to be obtained without the need for serial sectioning.