Article pubs.acs.org/Biomac
Temperature-Induced Ultradense PEG Polyelectrolyte Surface Grafting Provides Effective Long-Term Bioresistance against Mammalian Cells, Serum, and Whole Blood Ryosuke Ogaki,*,† Ole Zoffmann Andersen,† Grethe Vestergaard Jensen,†,‡ Kristian Kolind,† David Christian Evar Kraft,§ Jan Skov Pedersen,†,‡ and Morten Foss† †
Interdisciplinary Nanoscience Center (iNANO) and ‡Department of Chemistry, Faculty of Science and Technology, and Department of Orthodontics, School of Dentistry, Aarhus University, Aarhus, Denmark
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S Supporting Information *
ABSTRACT: We report a facile method of generating ultradense poly(L-lysine)-graf t-poly(ethylene glycol) (PLL-gPEG) surface by using high temperature alone, which in turn provides dramatic improvement in resisting nonspecific bioadsorption. X-ray photoelectron spectroscopy (XPS) revealed that the surface graft density increased ∼4 times higher on the surface prepared at 80 °C compared to 20 °C. The studies from small-angle X-ray scattering (SAXS) and the effect of varying ionic strength during/post assemblies at 20 and 80 °C indicated that the “cloud point grafting effect” is not the cause for obtaining high density grafting. Stringent long-term bioresistance tests have been conducted and the temperature-induced PLL-g-PEG surfaces have achieved (1) zero mammalian cell adsorption/migration for up to 36 days and (2) extremely close-tozero protein adsorptions have been observed even after 36 days in 10% serum media and 24 h in whole blood within the ultrasensitive detection limit of time-of-flight secondary ion mass spectrometry (ToF-SIMS).
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INTRODUCTION Material surfaces with nonfouling properties are essential for a wide range of biorelated applications in vitro and in vivo. Among a repertoire of candidate materials,1−4 poly(ethylene glycol) (PEG) has been one of the most studied and widely utilized bioresistant polymers. It is hypothesized that PEG and other “nonfouling” polymers share a common ability of forming physical (steric) and energetic (thermodynamic) barriers against protein adsorption. Several theoretical approaches, including those by de Gennes5−7 and Szleifer,8,9 and, more recently, Hess10 have provided critical understanding of the kinetics and mechanisms of complex polymer−protein interfacial interactions. Together with the experimental approaches, it is hypothesized that polymer grafting density and chain length are the two critical parameters for resisting nonspecific bioadsorption.1,11,12 Significant advances have also been made in the development of nonfouling polymer grafting strategies. The “grafting-from” approaches such as atom transfer radical polymerization (ATRP),3,13−16 reversible addition−fragmentation chain transfer polymerization (RAFT),17 and nitroxide-mediated free radical polymerization18,19 as well as the “grafting-to” approaches via self-assembly of, for example, thiols,20−25 silanes,26,27 polyelectrolytes,28−32 and catechol derivatives,33−37 as well as plasma polymerization,38−41 have all shown to significantly reduce nonspecific adsorption of cells and proteins. Although some of these and other experimental results have shown reduction in cell © 2012 American Chemical Society
adsorption over a long period, the resistance toward protein adsorption is demonstrated only over a short period typically from minutes up to a few hours. Furthermore, most protein characterization studies have been conducted with analytical techniques having above 1 ng/cm2 protein detection sensitivity. The challenge thus remains to be the generation of surface capable of exhibiting robust bioresistant performance under more application-orientated and stringent conditions over a longer period; for example, for blood contacting device applications, none of the currently available surfaces have yet to demonstrate its ability to significantly reduce protein adsorption from whole blood confirmed by using highly sensitive analytical techniques. Herein, we demonstrate that the high grafting temperature alone has a dramatic effect on the final grafted density of nonfouling PLL-g-PEG on TiO2 capable of providing robust and long-term bioresistance against cells, serum, and whole blood. The PLL-g-PEG surfaces have been previously tested against heparinized blood plasma42 and whole blood.43 However, the protein adsorption studies were only carried out using blood plasma for 30 min and found to be below the detection limit of ellipsometry (
