Bone Cement
Analysis of Bone Cements
Bone cements are used for the mechanical fixation of artificial joints in bone. They enable the transfer of force between the rigid implant and elastic bone. Additionally, other properties such as X-ray absorption, local reduction of infections, etc., can be important. Most bone cements consist of a two-component system of powder (PMMA) and liquid.
Particle Size and Shape
The processing properties of a bone cement are critically dependent on the particle size of the powder. The smaller the particles, the larger the surface area, and the faster the liquid component can react with the surface. This changes the viscosity, pot life, and also the curing time. Knowledge of the particle size distribution is necessary for reproducible product properties.
The measurement is carried out in our laboratory using laser diffraction as part of routine raw material control. We have decades of experience with accredited measurements and successfully passed a corresponding interlaboratory comparison in 2024.
With the help of microscopy, it is also possible to examine the particle shape and visualize the tendency to agglomerate. The latter influences the bulk and mixing behavior.
Average Molecular Weight
The chain length of the molecules influences the solubility of the polymer and the mechanical properties of the cured bone cements. The molecular weight distribution is measured using Gel Permeation Chromatography (GPC). Different chain lengths in polymers correlate with solubility behavior. Additionally, a longer chain length positively affects aging (implant service life). For example, it significantly decreases due to some sterilization steps.
With the help of microscopy, it is also possible to examine the particle shape and visualize the tendency to agglomerate. The latter influences the bulk and mixing behavior.
Monomer Ratio and Additives
Depending on the properties of the bone cements, pure PMMA or mixtures of various polymers (MMA, MA, styrene, etc.) are used in the powder. If the powder consists of different monomer units, this can be checked with NMR, and the monomer ratio can be quantitatively determined. Furthermore, it is possible to confirm purity (residual monomer content or impurities) and detect additives such as dibenzoyl peroxide (DBPO) as an initiator.
The liquid component of the bone cement can also be characterized in more detail. For this purpose, the content of activator, stabilizer, or dye is measured. In addition to NMR, HPLC and UV/Vis spectroscopy are also used here.
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