Surface coatings with so-called protein-repellent or nonfouling polymers have become indispensable for the development of modern therapeutic and diagnostic medical devices such as biosensors, drug-delivery capsules, and biomedical implants. Nowadays, poly(ethylene glycol) (PEG) is routinely used for these purposes. However, there is increasing evidence that PEG has limited long-term stability, particularly in vivo. Here we investigate poly(2-methyl-2-oxazoline) (PMOXA) as a potential alternative polymer. We designed comb copolymers consisting of a polycationic poly(l-lysine) backbone and PMOXA side chains by analogy to precisely studied and highly protein-repellent PEG-based systems. Using optical waveguide lightmode spectroscopy, we quantitatively compare the in situ self-assembly of the comb copolymers on negatively charged surfaces and the exposure of the formed monolayers to full human serum. We find that the PMOXA-based coatings with an optimal side-chain grafting density eliminate protein adsorption to a level of <2 ng/cm2; that is, they quantitatively equal the protein-repellent properties of the best PEG-based coatings.

Non-fouling surfaces that resist non-specific adsorption of proteins, bacteria, and higher organisms are of particular interest in diverse applications ranging from marine coatings to diagnostic devices and biomedical implants. Poly(ethylene glycol) (PEG) is the most frequently used polymer to impart surfaces with such non-fouling properties. Nevertheless, limitations in PEG stability have stimulated research on alternative polymers that are potentially more stable than PEG. Among them, we previously investigated poly(2-methyl-2-oxazoline) (PMOXA), a peptidomimetic polymer, and found that PMOXA shows excellent anti-fouling properties. Here, we compare the stability of films self-assembled from graft copolymers exposing a dense brush layer of PEG and PMOXA side chains, respectively, in physiological and oxidative media. Before media exposure both film types prevented the adsorption of full serum proteins to below the detection limit of optical waveguide in situ measurements. Before and after media exposure for up to 2 weeks, the total film thickness, chemical composition, and total adsorbed mass of the films were quantified using variable angle spectroscopic ellipsometry (VASE), X-ray photoelectron spectroscopy (XPS), and optical waveguide lightmode spectroscopy (OWLS), respectively. We found (i) that PMOXA graft copolymer films were significantly more stable than PEG graft copolymer films and kept their protein-repellent properties under all investigated conditions and (ii) that film degradation was due to side chain degradation rather than due to copolymer desorption.

No abstract

Biomaterials-associated-infections (BAI) are serious complications in modern medicine. Although non-adhesive coatings, like polymer-brush coatings, have been shown to prevent bacterial adhesion, they do not support cell growth. Bi-functional coatings are supposed to prevent biofilm formation while supporting tissue integration. Here, bacterial and cellular responses to poly(ethylene glycol) (PEG) brush-coatings on titanium oxide presenting the integrin-active peptide RGD (arginine-glycine-aspartic acid) (bioactive "PEG-RGD") were compared to monofunctional PEG brush-coatings (biopassive "PEG") and bare titanium oxide (TiO 2 ) surfaces under flow. Staphylococcus epidermidis ATCC 35983 was deposited on the surfaces under a shear rate of 11 s -1 for 2 h followed by seeding of U2OS osteoblasts. Subsequently, both S. epidermidis and U2OS cells were grown simultaneously on the surfaces for 48 h under low shear (0.14 s -1

Surface fouling, i.e. the non-specific surface adhesion of proteins, bacteria and higher organisms, poses a severe problem in many areas ranging from modern diagnostic and therapeutic medical devices to food processing and food wrapping technology to corrosion prevention and marine technology. One approach to address these problems is to coat surfaces with nonfouling polymers. The properties of a new class of nonfouling polymer coatings made from poly(2-methyl-2-oxazoline) (PMOXA) were investigated here in comparison with the most frequently used polymer in this context, poly(ethylene glycol) (PEG). Both polymers were side-chain grafted onto a polycationic poly-L-lysine (PLL) backbone. The PMOXA graft copolymers spontaneously self-assembled to form monolayers on negatively charged surfaces. PMOXA surface coatings were as efficient as PEG-based coatings in suppressing protein and bacterial adsorption. The minimal number of side chain monomer units per surface area that are needed to obtain fully resistant surfaces was lower though for PMOXA than for PEG graft copolymers as a result of the higher molecular weight of the PMOXA monomer unit.

Poly(ethylene glycol) (PEG) has been the most frequently reported and commercially used polymer for surface coatings to convey nonfouling properties. PEGylated surfaces are known to exhibit limited chemical stability, particularly due to oxidative degradation, which limits long-term applications. In view of excellent anti-adhesive properties in the brush conformation and resistance to oxidative degradation, poly(2-methyl-2-oxazoline) (PMOXA) has been proposed recently as an alternative to PEG. In this study, the authors systematically compare the (bio)chemical stability of PEG- and PMOXA-based polymer brush monolayer thin films when exposed to cultures of human umbilical vein endothelial cells (HUVECs) and human foreskin fibroblasts (HFFs). To this end, the authors used cell-adhesive protein micropatterns in a background of the nonfouling PEG and PMOXA brushes, respectively, and monitored the outgrowth of HUVECs and HFFs for up to 21 days and 1.5 months. Our results demonstrate that cellular micropatterns spaced by PMOXA brushes are significantly more stable under serum containing cell culture conditions in terms of confinement of cells to the adhesive patterns, when compared to corresponding micropatterns generated by PEG brushes. Moreover, homogeneous PEG and PMOXA-based brush monolayers on Nb2O5 surfaces were investigated after immersion in endothelial cell medium using ellipsometry and x-ray photoelectron spectroscopy.

No abstract

In this study, we present the preparation, characterization and application of a novel bioactive copolymer poly(l-lysine)-graft-folic acid-coupled poly(2-methyl-2-oxazoline) (PLL-g-PMOXA-c-FA), which has a specific interaction with folate receptor (FR)-positive cancer cells. Glass surface immobilized with PLL-g-PMOXA-c-FA was demonstrated to be adhesive to FR-positive cancer cells (HeLa, JEG-3) while nonadhesive to FR-negative ones (MCF-7, HepG2) in 3 h. The specific interaction between conjugated FA on the substrate and FRs on the cells could hardly be inhibited unless a high concentration (5 mM) of free FA was used due to the multivalent nature of it. The FA functionality ratio of the copolymer on the substrate had a significant influence on the adhesion of HeLa cells, and our experiments revealed that the affinity of the substrate to the cells declined dramatically with the decrease of functionality ratio. This was believed to be caused by the polydispersity of PMOXA tethers, as supported by GPC and ToF-SIMS data. As a proof of concept in the application of our material, we demonstrated successful recovery of HeLa cells from mixture with MCF-7 (1:100) on the copolymer-coated glass, and our results showed that both high sensitivity (95.6 ± 13.3%) and specificity (24.3 ± 8.6%) were achieved.