Functional Properties of Low-Modulus PMMA Bone Cements Containing Linoleic Acid

Abstract

Acrylic bone cements modified with linoleic acid are a promising low-modulus alternative to traditional high-modulus bone cements. However, several key properties remain unexplored, including the effect of autoclave sterilization and the potential use of low-modulus cements in other applications than vertebral augmentation. In this work, we evaluate the effect of sterilization on the structure and stability of linoleic acid, as well as in the handling properties, glass transition temperature, mechanical properties, and screw augmentation potential of low-modulus cement containing the fatty acid. Neither ¹H NMR nor SFC-MS/MS analysis showed any detectable differences in autoclaved linoleic acid compared to fresh one. The peak polymerization temperature of the low-modulus cement was much lower (28-30 °C) than that of the high-modulus cement (67 °C), whereas the setting time remained comparable (20-25 min). The T_g of the low-modulus cement was lower (75-78 °C) than that of the high-stiffness cement (103 °C). It was shown that sterilization of linoleic acid by autoclaving did not significantly affect the functional properties of low-modulus PMMA bone cement, making the component suitable for sterile production. Ultimately, the low-modulus cement exhibited handling and mechanical properties that more closely match those of osteoporotic vertebral bone with a screw holding capacity of under 2000 N, making it a promising alternative for use in combination with orthopedic hardware in applications where high-stiffness augmentation materials can result in undesired effects.

Keywords: PMMA bone cement; bending; kyphoplasty; low-modulus; mechanical properties; screw pull-out; sterilization; vertebroplasty.

Figure 1

¹H NMR spectra of non-sterilized LA (LA-NS) and sterilized (LA-S). Only one spectrum per group is plotted in the figure.

Figure 2

Example chromatogram of alpha linoleic acid (C18:2) from Standard (A) and Autoclaved standard (B).

Figure 3

Injectability curves of the control (VS) and LA-modified cements (sterilized and non-sterilized LA) when injected at a crosshead speed of (A) 1.5 mm·min⁻¹ and (B) 5 mm·min⁻¹; n = 3 for each group but only one (typical) specimen per group and speed of injection is shown in the figure.

Figure 4

Flexural mechanical properties: (A) Bending modulus and (B) Bending strength of the control (VS) and non-sterilized LA-modified cements (VSLA-NS); n = 5 for each group and time point. The “*” indicates the samples that did not break.

Figure 5

Pullout force of vs. and VSLA-NS augmented screws from cement only (pilot hole of 3.8 mm; n = 5) and from Sawbone^® (pilot hole of 3.2 mm; n = 8). The pull-out force from Sawbone^® only is 36.3 ± 8.4 N [57].