Creep behavior of hand-mixed Simplex P bone cement under cyclic tensile loading

Area of Science:

• Biomaterials Science
• Orthopedic Engineering
• Mechanical Engineering

Background:

• Acrylic cement is crucial for orthopedic implant fixation, particularly in total hip replacements.
• Understanding its long-term mechanical behavior is vital due to concerns about prosthetic loosening.
• Dynamic, long-term mechanical failure mechanisms remain poorly understood.

Purpose of the Study:

• To investigate the dynamic creep deformation of hand-mixed acrylic cement under laboratory conditions.
• To characterize the relationship between loading cycles, stress levels, and creep strain.
• To assess the influence of porosity on creep behavior and identify failure modes.

Main Methods:

• Laboratory testing of hand-mixed acrylic cement specimens.
• Dynamic loading applied to assess creep deformation over numerous cycles.
• Measurement of strain patterns and identification of creep phases (primary, secondary, tertiary).

Main Results:

• Acrylic cement demonstrated primary, secondary, and tertiary creep phases under dynamic loading.
• Creep reached approximately 50% of elastic strain after 250,000 cycles at 3 MPa.
• A linear relationship was observed between logarithmic creep-strain and loading cycles.
• Higher loads resulted in significantly greater creep strains.
• Specimens failed at maximal stresses of 7 MPa or 11 MPa, with failure cycles comparable to existing fatigue data.

Conclusions:

• Dynamic creep is a significant factor in the long-term mechanical behavior of acrylic cement.
• The observed creep behavior and failure modes provide critical data for predicting implant lifespan.
• Further research is needed to fully elucidate the complex failure mechanisms in cemented orthopedic implants.