Abstract
Surface modification of biomaterials with polymer chains has attracted great attention because of their ability to control biointerfacial interactions such as protein adsorption, cell attachment and bacterial biofilm formation. The aim of this study was to control the immobilisation of biomolecules on silicon wafers using poly(ethylene glycol)(PEG) chains by a “grafting to” technique. In particular, to control the polymer chain graft density in order to capture proteins and preserve their activity in cell culture as well as find the optimal density that would totally prevent bacterial attachment. The PEG graft density was varied by changing the polymer solubility using an increasing salt concentration. The silicon substrates were initially modified with aminopropyl-triethoxysilane (APTES), where the surface density of amine groups was optimised using different concentrations. The results showed under specific conditions, the PEG density was highest with grafting under “cloud point” conditions. The modified surfaces were characterised with X-ray photoelectron spectroscopy (XPS), ellipsometry, atomic force microscopy (AFM) and water contact angle measurements. In addition, all modified surfaces were tested with protein solutions and in cell (mesenchymal stem cells and MG63 osteoblast-like cells) and bacterial (Pseudomonas aeruginosa) attachment assays. Overall, the lowest protein adsorption was observed on the highest polymer graft density, bacterial adhesion was very low on all modified surfaces, and it can be seen that the attachment of mammalian cells gradually increased as the PEG grafting density decreased, reaching the maximum attachment at medium PEG densities. The results demonstrate that, at certain PEG surface coverages, mammalian cell attachment can be tuned with the potential to optimise their behaviour with controlled serum protein adsorption.
Highlights
Polymer surfaces have attracted great attention because of their enormous range of applications [1,2]
Of particular interest is the N 1s spectra for the wafers after APTES grafting (Figure 2a), which predominantly shows nitrogen in the form of primary amine groups with the peak at 399 eV; there is a weaker peak at 400.5 eV assigned to a protonated amine and a lower binding energy peak that we assign to contamination [33]
We modified silicon wafer surfaces with an amino functionalised silane (APTES) that was used to covalently attach poly(ethylene glycol) (PEG) chains of different densities aimed at enhancing protein adsorption in order to promote human cell attachment and at the same time resist bacterial adhesion with the potential to eliminate infection on implants
Summary
Polymer surfaces have attracted great attention because of their enormous range of applications [1,2]. Polymer brushes can be created on surfaces by either “grafting to” or “grafting from” approaches. With the “grafting to” technique, the surface is usually exposed to the desired polymer in solution or as a melt. In this case, the polymer chain gets attached to the substrate by strong interactions between one end of each chain and the substrate [3]. The polymer chain gets attached to the substrate by strong interactions between one end of each chain and the substrate [3] These interactions include charged groups [4], highly polar groups [5] and chemically reactive groups [6]. With the “grafting from” approach, the Polymers 2017, 9, 343; doi:10.3390/polym9080343 www.mdpi.com/journal/polymers
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