Fracture characteristics of acrylic bone cements. II. Fatigue

Abstract

The vital first phase of the overall materials study to protract the life of total joint replacements is the identification of the fracture toughness and fatigue properties of bone cements. Information gained from fatigue testing, performed in a manner which simulates in vivo conditions, and fracture toughness, which is a measure of the propensity of a crack to propagate, is the first step towards the prediction of the life of the total joint replacement. Part I of this study identified the fracture toughness characteristics of two acrylic bone cements, while the present work has been concerned with determining the fatigue behavior by means of tests conducted in a rotating bending fatigue apparatus. Fatigue specimens were fabricated under conditions which approximated clinical procedures and then tested while immersed in bovine serum at 37°C in order to simulate in vivo conditions. In addition, a similar study was completed on specimens tested in air at ambient temperature for purposes of comparison. Testing was conducted in both of these environments on specimens containing zero and 10.0 wt % BaSO4. Cyclic loading frequency was maintained between 1200 and 1400 cycles/min in order to insure that crack propagation was the sole mechanism of failure, i.e., failure via cyclic thermal softening was obviated. Results of this phase of the study, when analyzed by a Student t‐test at the 90% confidence level with four degrees of freedom, indicate that the fatigue life of specimens tested in bovine serum at 37°C is superior to that of specimens tested in air at ambient temperature. The addition of BaSO4 to Simplex‐P cement, while not significant at the 90% confidence level, was significant in increasing the fatigue life in air at the 80% confidence level; however, this effect was not noticeable when testing in bovine serum at 37°C. Examination of the fracture surfaces enabled calculation of the critical stress intensity factor which when compared with values from an earlier work showed good agreement.

Fatigue of polymers

“…Some additional fatigue tests have been made on rotating beam type specimens of acrylic cements [94]. One interesting result is that the average fatigue lifetime was increased 5 times when tests were run in bovine serum at 37°C, rather than in ambient air, in order to simulate in vivo conditions.…”

Vertebroplasty by Use of a Strontium-Containing Bioactive Bone Cement

“…Alterations in the ratio of barium to PMMA can significantly affect its mechanical properties. 14,15 Our group has previously shown in a porcine model that, when injected into the fractured vertebral body, Sr-HA is effective in fully restoring the stiffness and failure strength to prefracture levels. 34 Other bioactive materials for vertebroplasty have been described.…”

“…12,13 Third, there is a large mechanical mismatch between PMMA bone cements, which has a compressive strength of 80 MPa (based on ISO 5833) and osteoporotic bone, which has a compressive strength of less than 10 MPa. 14,15 This could result in fractures at the adjacent levels after vertebroplasty.…”

Effect of surface modification of polymer beads on the mechanical properties of acrylic bone cement

“…The E value was essentially reduced for the TV-MA cement after the storage in water. A decrease in the E value of acrylic cements after testing under wet conditions has been described in literature [25] and can be explained by the plastification of PMMA in water. However, the E values for the TV-AS cement sample are almost unchanged after the wet storage.…”