Variation of the mechanical properties of PMMA to suit osteoporotic cancellous bone

Abstract

Poly(methyl methacrylate) (PMMA) is by far the most frequently used bone substitute material for vertebroplasty. However, there are serious complications, such as cement leakage and an increased fracture rate of the adjacent vertebral bodies. The latter may be related to the mechanical properties of the augmented segment within the osteoporotic spine. A possible counter-measure is prophylactic augmentation at additional levels, but this aggravates the risk for the patient. Introduction of pores is a possible method to reduce the inherent high stiffness of PMMA. This study investigates the effect of porosity on the mechanical properties of PMMA bone cement. Different fractions of a highly viscous liquid were mixed into the PMMA during preparation. An open-porous material with adjustable mechanical properties resulted after removal of the aqueous phase. Different radiopacifiers were admixed to investigate their suitability for vertebroplasty. The final material was characterized mechanically by compressive testing, microscopically and radiologically. In addition, the monomer release subsequent to hardening was measured by means of gas chromatography. The Young's modulus in compression could be varied between 2800 +/- 70 MPa and 120 +/- 150 MPa, and the compression ultimate strength between 170 +/- 5 MPa and 8 +/- 9 MPa for aqueous fractions ranging between 0 and 50% of volume. Only a slight decrease of the Young's modulus and small changes of ultimate strength were found when the mixing time was increased. An organic hydrophilic and lipophilic radiopacifier led to a higher Young's modulus of the porous material; however, the ultimate strength was not significantly affected by adding different radiopacifiers to the porous cement. The radiopacity was lost after washing the aqueous phase out of the pores. No separation occurred between the aqueous and the PMMA phase during injection into an open porous ceramic material. The monomer released was found to increase for increasing aqueous fractions, but remained comparable in magnitude to standard PMMA. This study demonstrates that a conventional PMMA can be modified to obtain a range of mechanical properties, including those of osteoporotic bone.

Compressive mechanical properties and cytocompatibility of bone-compliant, linoleic acid-modified bone cement in a bovine model

“…Additional studies, required even more drastic modifications such as up to 12 wt% castor oil to reduce E and σ y by 70% and 83%, respectively 35 ; up to 50% monomer replacement with hyaluronic acid−based hydrogel to reduce E and σ u by 96-97% and 95-99%, respectively 31,32 ;…”

“…Boger et al 31,32 modified the macrostructure of acrylic bone cements by inducing macroporosity through the incorporation of a hydrogel phase into the cement; however, increased levels of particle release 33 seem to have prevented this formulation from further advance. Another approach consisted of physically modifying the cements by partially substituting the monomer with a lactam structure organic plasticizer 34 to reduce the elastic modulus of the cements.…”

The effect of unsaturated fatty acid and triglyceride oil addition on the mechanical and antibacterial properties of acrylic bone cements

“…Several experimental studies have therefore focused on developing novel PMMA-based cements with a lower elastic modulus by using additives such as hydrogels 27,28 or lactam plasticizers. 29 Even though these attempts have proved successful in terms of tailoring the mechanical properties of the cements, none of these cements are commercially available.…”

The effect of sacrificial templates on the pore characteristics of sintered diatomite membranes

“…This can be explained by the difference in the degree of rigidity between the solid polymer spheres and the wheat starch. A solid polymer sphere, which consists PMMA, has an elastic modulus of approximately 3 GPa, 28), 29) whereas the elastic moduli of various starches range from 0 to 500 MPa. 30) Therefore, slit-like pores may be induced when the mixture of diatomite particles and wheat starch is exposed to external pressure during dry pressing at 25 MPa.…”