MALDI-TOF Mass Spectrometry Imaging Reveals Molecular
Level Changes in Ultrahigh Molecular Weight Polyethylene Joint Implants
in Correlation with Lipid Adsorption
posted on 2014-10-07, 00:00authored bySophie
M. Fröhlich, Vasiliki-Maria Archodoulaki, Günter Allmaier, Martina Marchetti-Deschmann
Ultrahigh molecular weight polyethylene
(PE-UHMW), a material with
high biocompatibility and excellent mechanical properties, is among
the most commonly used materials for acetabular cup replacement in
artificial joint systems. It is assumed that the interaction with
synovial fluid in the biocompartment leads to significant changes
relevant to material failure. In addition to hyaluronic acid, lipids
are particularly relevant for lubrication in an articulating process.
This study investigates synovial lipid adsorption on two different
PE-UHMW materials (GUR-1050 and vitamin E-doped) in an in vitro model
system by matrix-assisted laser desorption/ionization time-of-flight
(MALDI-TOF) mass spectrometry imaging (MSI). Lipids were identified
by high performance thin layer chromatography (HP-TLC) and tandem
mass spectrometry (MS/MS) analysis, with an analytical focus on phospholipids
and cholesterol, both being species of high importance for lubrication.
Scanning electron microscopy (SEM) analysis was applied in the study
to correlate molecular information with PE-UHMW material qualities.
It is demonstrated that lipid adsorption preferentially occurs in
rough or oxidized polymer regions. Polymer modifications were colocalized
with adsorbed lipids and found with high density in regions identified
by SEM. Explanted, the in vivo polymer material showed comparable
and even more obvious polymer damage and lipid adsorption when compared
with the static in vitro model. A three-dimensional reconstruction
of MSI data from consecutive PE-UHMW slices reveals detailed information
about the diffusion process of lipids in the acetabular cup and provides,
for the first time, a promising starting point for future studies
correlating molecular information with commonly used techniques for
material analysis (e.g., Fourier-transform infrared spectroscopy,
nanoindentation).