Inhibition of Protein Adsorption onto Stainless Steel by a PEG Layer
Adsorption of proteins onto a solid surface is believed to be the initial and controlling step in biofouling. A better knowledge of the fouling process can be obtained by controlling the formation of the first protein layer at a solid surface. Understanding how this protein layer is affected by changes in the experimental conditions and how it can be reduced, is a necessary step forward to significantly reduce fouling in biotechnology, pharmaceutical and dairy processing equipment. It has been demonstrated that coating surfaces with poly(ethylene glycol) (PEG) chains can reduce or even prevent protein adsorption. For optimal surface protection, it appears that the surface coverage (number of chains per unit area) should be high (forming a “molecular brush”), and the length of chain should be high enough with flexibility to sweep across the whole surface.
In this study, three different proteins, beta casein, alpha lactalbumin and lysozyme were adsorbed onto a stainless steel surface. PEG chains were grafted onto a stainless steel surface pre-functionalized with either amine or silanol reactive groups. The proteins were adsorbed first onto a bare stainless steel surface then onto the functionalized surfaces. The effect of temperature, bulk protein concentration and PEG molecular weight and concentration towards protein adsorption were investigated. The kinetics of protein adsorption was followed using a quartz crystal microbalance (QCM), interpreted by resonant frequency and dissipation. Generally, the results obtained showed that PEG grafted stainless steel gives better resistance to protein adsorption to lysozyme and beta casein but not for alpha lactalbumin.