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1. Introduction
Ultra high molecular weight polyethylene (PE-UHMW) is a
very frequently used material in artificial joint replacement
systems. It provides easy usability,extreme high mechanical wear resistance,high biocompatibility and is to acertain
extent self-lubricating. However,the number of revision
surgeries is still high,sometimes necessary because of the
rapid shelf life aging process and in vivo degradation due to
few selected protein and carbohydrate species, e.g. albumin
and hyaluronic acid . It is known that the major abundant
components of synovial fluid, e.g. hyaluronic acid,albumin or
immunoglobulin,interact with PE-UHMW and tend to adsorb
on the surface in model fluid systems.However,the interaction of the whole synovial proteome in the presence of lipids
etc. with PE-UHMW has never been investigated.Because the
synovial fluid composition is very similar to blood plasma
(except for the high hyaluronic acid content)it is also highly
affected by the patient’s age,sex,life style and pathological
status . Therefore it is of high interest,which proteins
except albumin and immunoglobulin in fact adsorb on PE-UHMW before a deeper understanding of the pathological
process can be obtained and/or material related selective adsorption effects can be gathered.
Different compositions of PE-UHMW,Vitamin E doped
material, highly cross-linked PE-UHMW and materials under-
going different kinds of sterilization strategies have already
been tested in clinical studies for improving the materials’
properties and reducing protein adsorption.Highly abundant
glycoproteins have been shown to adsorb on PE-UHMW in
simulating models and adsorption has been investigated to
occur unspecific and concentration independent . In the
same study model fluids containing only one glycoprotein
of interest revealed that the formed protein layer enhances
the lubrication and friction behavior of PE-UHMW.However,
besides the selected glycoproteins also other high abundance
and acute phase proteins occurring during inflammation and
oxidative stress, e.g. during rheumatic diseases,are relevant
for adsorption,friction behavior and consequently material
modification.
The presented study focuses on the unbiased identification
and localization of proteins present in synovial fluid adsorbing on different varieties of PE-UHMW material.To answer
both questions,protein identity and spatial distribution,mass
spectrometry imaging(MSI) by means of matrix assisted laser
desorption/ionization time-of-flight(MALDI-TOF)examination was correlated to SDS PAGE analysis of adsorbed proteins.
MSI isawell-established method for the localization and
identification of analytes of interest within an untargeted
approach. To date MSI has been applied to a huge variety
of biological samples and it has to be mentioned that
surface analysis of biomaterials is an exponentially growing
field gaining more importance for the analysis of lubrication
interaction and material modifications.
One limiting fact of MSI is that protein identification in
the high molecular mass range is only possible based on
the tentative assignment of proteins to measured m/z values, respectively the molecular weight of detected molecules. To corroborate protein assignment after MSI analysis,
SDS PAGE analysis was chosen,providing the possibility to
compare synovial protein patterns to patterns of protein compounds adsorbed on PE-UHMW of different compositions
with respect to overall detected proteins.In parallel MS-based protein identification after in-gel digestion is feasible.
Protein identification for adsorbed molecules was furthermore verified by on-tissue (“on polymer”)digestion. The
hydrophobic surface of PE-UHMW supports the preservation
of protein localization during trypsin application in aqueous buffer systems,however,diffusion is acritical point for
mechanical wear,oxidation and material modification.
Synovial fluid(SF),the major lubricating system in the joint
compartment, directly interacts with the material surface,
leading to biomolecule adsorption and diffusion possibly altering the polymer characteristics and stability.The
major components have already been investigated,however
it has not been determined yet,whether modified PE-UHMW
surface areas lead to enhanced biomolecule adsorption and
diffusion or vice versa. Furthermore,protein layer formation
on PE-UHMW has so far not been investigated except for a
both enzyme and matrix application.To obtain reliableresults
homogeneous layers of tryps in and MALDI matrix solution
were applied using a piezo printer(Chemical Inkjet Printer,
ChIP-1000 ) to the protein-carrying PE-UHMW material
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