EFFECT OF (MONOMER TO POLYMER RATIO) ON MECHANICAL AND THERMAL CHARACTERISTICS OF ACRYLIC BONE CEMENT

Abstract

Introduction: Acrylic bone cement (ABC) manufacturers vary their products by using different proportions of the principle ingredients to optimize handling time or mechanical properties.

There is limited research showing the effect that varying the monomer to polymer ratio (independent from other constituents) has on thermal and mechanical properties of ABC.

Materials and Methods: The formula for CMW1 (DePuy) was reproduced using original ingredients obtained separately from different suppliers. The commercially available CMW1 monomer/polymer ratio is approximately (0.6 ml/gm). Six variants of CMW1 bone cement were prepared with varying monomer/polymer ratio (0.4–1 ml/gm). The specimens were cured and aged in an incubator for 7 days at 37°C.

Thermal characteristics of the polymerization reaction such as maximum polymerization reaction temperature (Tmax) and setting time (ts) were recorded using a Picolog digital data recorder.

Compressive mechanical properties (Young’s modulus and yield stress) were measured using a TestexpertII Universal Testing System from Zwick Roell implementing ISO5833 test criteria.

SPSS 14 for Windows software was used for calculating statistics and data analysis.

Results: An increase in monomer/polymer ratio was associated with a significant (p= 0.00) increase in setting time (5.3–11.3 minutes) with a strong correlation (r2=0.988). However, there seemed to be no effect on Tmax (p=0.792).

Compression tests showed a significant (p=0.022) decrease in E-modulus (2.63 to 2.22 GPa) with a strong Pearson correlation negative coefficient (r2= −0.827).

Similarly, yield compressive stress showed a significant (p=0.002) decrease (121.83–101.19 MPa) with a strong negative correlation (r2= −0.93)

Conclusion: This experimental study shows that varying the ratio of monomer to polymer independently from other constituents in acrylic bone cement significantly affects setting time and compressive mechanical properties. Setting time can be prolonged to increase handling time; however this will occur at the expense of a reduction in compressive stiffness and strength.