Characterization of
Poly(l-lysine)-graft-Poly(ethylene glycol)
Assembled Monolayers on Niobium Pentoxide
Substrates Using Time-of-Flight Secondary Ion
Mass Spectrometry and Multivariate Analysis
posted on 2004-03-01, 00:00authored byM. S. Wagner, S. Pasche, D. G. Castner, M. Textor
Control of protein adsorption onto solid surfaces is a
critical area of biomaterials and biosensors research.
Application of high performance surface analysis techniques to these problems can improve the rational design
and understanding of coatings that control protein adsorption. We have used static time-of-flight secondary ion
mass spectrometry (TOF-SIMS) to investigate several poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) adlayers adsorbed electrostatically onto negatively charged
niobium pentoxide (Nb2O5) substrates. By varying the
PEG graft ratio (i.e., the number of lysine monomers per
grafted PEG chain) and the molecular weights of the PLL
and PEG polymers, the amount of protein adsorption can
be tailored between 1 and 300 ng/cm2. Detailed multivariate analysis using principal component analysis (PCA)
of the positive and negative ion TOF-SIMS spectra showed
changes in the outermost surface of the polymer films that
were related to the density and molecular weight of the
PEG chains on the surface. However, no significant
differences were noted due to PLL molecular weight,
despite observed differences in the serum adsorption
characteristics for adlayers of PLL-g-PEG polymers with
different PLL molecular weights. From the PCA results,
multivariate peak intensity ratios were developed that
correlated with the thickness of the adlayer and the
enrichment of the PEG chains and the methoxy terminus
of the PEG chains at the outermost surface of the adlayer.
Furthermore, partial least squares regression was used
to correlate the TOF-SIMS spectra with the amount of
protein adsorption, resulting in a predictive model for
determining the amount of protein adsorption on the basis
of the TOF-SIMS spectra. The accuracy of the prediction
of the amount of serum adsorption depended on the
molecular weight of the PLL and PEG polymers and the
PEG graft ratio. The combination of multivariate analysis
and static TOF-SIMS provides detailed information on the
surface chemistry and insight into the mechanism for
protein resistance of the coatings.