Rupert Konradi
ETH Zurich
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Rupert Konradi.
Langmuir | 2008
Rupert Konradi; Bidhari Pidhatika; and Andreas Mühlebach; Marcus Textor
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.
Macromolecular Rapid Communications | 2012
Rupert Konradi; Canet Acikgöz; Marcus Textor
The prevention of surface fouling is becoming increasingly important for the development of anti-infective medical implants, biosensors with improved signal-to-noise ratios, and low-fouling membranes to name a few examples. We review a direct comparison of poly(ethylene glycol), the gold standard polymer to impart surfaces with nonfouling properties, to an alternative polymer, poly(2-methyl-2-oxazoline) (PMOXA), and show that both polymers are equally excellent in rendering surfaces nonfouling while PMOXA coatings are more stable in oxidative environments. We discuss prerequisites for the fabrication of nonfouling surface coatings and implications for the polymer choice according to application requirements.
Biomaterials | 2010
Bidhari Pidhatika; Jens Möller; Edmondo M. Benetti; Rupert Konradi; Ekaterina Rakhmatullina; Andreas Mühlebach; Ralf Zimmermann; Carsten Werner; Viola Vogel; Marcus Textor
Surface platforms were engineered from poly(L-lysine)-graft-poly(2-methyl-2-oxazoline) (PLL-g-PMOXA) copolymers to study the mechanisms involved in the non-specific adhesion of Escherichia coli (E. coli) bacteria. Copolymers with three different grafting densities α (PMOXA chains/Lysine residue of 0.09, 0.33 and 0.56) were synthesized and assembled on niobia (Nb₂O₅) surfaces. PLL-modified and bare niobia surfaces served as controls. To evaluate the impact of fimbriae expression on the bacterial adhesion, the surfaces were exposed to genetically engineered E. coli strains either lacking, or constitutively expressing type 1 fimbriae. The bacterial adhesion was strongly influenced by the presence of bacterial fimbriae. Non-fimbriated bacteria behaved like hard, charged particles whose adhesion was dependent on surface charge and ionic strength of the media. In contrast, bacteria expressing type 1 fimbriae adhered to the substrates independent of surface charge and ionic strength, and adhesion was mediated by non-specific van der Waals and hydrophobic interactions of the proteins at the fimbrial tip. Adsorbed polymer mass, average surface density of the PMOXA chains, and thickness of the copolymer films were quantified by optical waveguide lightmode spectroscopy (OWLS) and variable-angle spectroscopic ellipsometry (VASE), whereas the lateral homogeneity was probed by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Streaming current measurements provided information on the charge formation of the polymer-coated and the bare niobia surfaces. The adhesion of both bacterial strains could be efficiently inhibited by the copolymer film only with a grafting density of 0.33 characterized by the highest PMOXA chain surface density and a surface potential close to zero.
Biosensors | 2012
Rupert Konradi; Marcus Textor; Erik Reimhult
The great wealth of different surface sensitive techniques used in biosensing, most of which claim to measure adsorbed mass, can at first glance look unnecessary. However, with each technique relying on a different transducer principle there is something to be gained from a comparison. In this tutorial review, different optical and acoustic evanescent techniques are used to illustrate how an understanding of the transducer principle of each technique can be exploited for further interpretation of hydrated and extended polymer and biological films. Some of the most commonly used surface sensitive biosensor techniques (quartz crystal microbalance, optical waveguide spectroscopy and surface plasmon resonance) are briefly described and five case studies are presented to illustrate how different biosensing techniques can and often should be combined. The case studies deal with representative examples of adsorption of protein films, polymer brushes and lipid membranes, and describe e.g., how to deal with strongly vs. weakly hydrated films, large conformational changes and ordered layers of biomolecules. The presented systems and methods are compared to other representative examples from the increasing literature on the subject.
Biomaterials | 2011
Thomas von Erlach; Sven Zwicker; Bidhari Pidhatika; Rupert Konradi; Marcus Textor; Heike Hall; Tessa Lühmann
Successful gene delivery systems deliver DNA in a controlled manner combined with minimal toxicity and high transfection efficiency. Here we investigated 15 different copolymers of poly(l-lysine)-graft-poly(2-methyl-2-oxazoline) (PLL-g-PMOXA) of variable grafting densities and PMOXA molecular weights for their potential to complex and deliver plasmid DNA. PLL(20)g(7)PMOXA(4) formed at N/P charge ratio of 3.125 was found to transfect 9 ± 1.6% of COS-7 cells without impairment of cell viability. Furthermore these PLL-g-PMOXA-DNA condensates were internalized 2 h after transfection and localized in the perinuclear region after 6 h. The condensates displayed a hydrodynamic diameter of ∼100 nm and were found to be stable in serum and after 70 °C heat treatment, moreover the condensates protected DNA against DNase-I digestion. The findings suggest that DNA-PMOXA-g-PLL condensate formation for efficient DNA-delivery strongly depends on PMOXA grafting density and molecular weight showing an optimum at low grafting density between 7 and 14% and medium N/P charge ratio (3.125-6.25). Thus, PLL(20)g(7)PMOXA(4) copolymers might be promising as alternative to PLL-g-PEG-DNA condensates for delivery of therapeutic DNA.
Biointerphases | 2014
Yin Chen; Bidhari Pidhatika; Thomas von Erlach; Rupert Konradi; Marcus Textor; Heike Hall; Tessa Lühmann
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.
Langmuir | 2009
Qiong Ye; Rupert Konradi; Marcus Textor; Erik Reimhult
Self-assembly of planar supported lipid bilayers on top of hydrophilic polymer brushes is a desirable alternative to solid supported lipid bilayers and covalently tethered lipid bilayers for applications like sensing on transmembrane proteins which require a large aqueous volume between membrane and substrate. We present a simple dip-and-rinse method to produce poly(ethylene glycol) (PEG) brushes with sparse positively charged hydrophobic tethers, using poly(l-lysine)-graft-poly(ethylene glycol)-quaternary ammonium compound copolymers. The interaction of such polymer coatings with liposomes of different compositions and the conditions for formation of planar lipid bilayers of extraordinarily high fluidity on top of the >10 nm thick reservoir by liposome self-assembly and sequentially triggered rupture are investigated.
Biomaterials | 2011
Xiao Xie; Jens Möller; Rupert Konradi; Malgorzata Kisielow; Alfredo Franco-Obregón; Erich Nyfeler; Andreas Mühlebach; Mamta Chabria; Marcus Textor; Zuhong Lu; Erik Reimhult
Surface biofouling poses an increasing problem in industrial and health care applications, driving research for surface coatings to prevent anti-microbial colonization and characterization of the efficacy of the same. The diversity and increasing sophistication of such coatings, which postulate different types of anti-microbial action on planktonic and surface adhering bacteria, challenge the suitability of current approaches to evaluate and compare the different approaches as well as the speed and accuracy at which screening can be made. We describe and provide proof of principle for a method to use microparticles functionalized with molecular coatings through self-assembly together with flow cytometry readout to evaluate Escherichia coli bacteria surface adhesion and killing efficiency. Advantages of the method are the automation of the method that allows recording an immense number of interactions and the possibility to simultaneously record effects on both surface adhering and planktonic bacteria. We demonstrate and discuss design criteria to obtain this information on two coatings, poly(L-lysine)-graft-C(3)H(6)N(+)(CH(3))(2)C(12)H(25) (PLL-g-QAC) and poly(L-lysine)-graft-poly(ethylene glycol)-C(3)H(6)N(+)(CH(3))(2)C(12)H(25) (PLL-g-PEG-QAC), which exemplify two different approaches to creating anti-microbial interfaces. Despite an apparent higher killing efficiency of the PLL-g-QAC during brief exposures, the rapid fouling of that surface quickly reduces its efficiency, whereas the PLL-g-PEG-QAC coating showed greater promise in reducing the growth and interfacial colonization of bacteria over longer time scales.
Biointerphases | 2013
Ima Avalos Vizcarra; Philippe Emge; Philipp Miermeister; Mamta Chabria; Rupert Konradi; Viola Vogel; Jens Möller
Bacterial adhesion and biofilm growth can cause severe biomaterial-related infections and failure of medical implants. To assess the antifouling properties of engineered coatings, advanced approaches are needed for in situ monitoring of bacterial viability and growth kinetics as the bacteria colonize a surface. Here, we present an optimized protocol for optical real-time quantification of bacterial viability. To stain living bacteria, we replaced the commonly used fluorescent dye SYTO® 9 with endogenously expressed eGFP, as SYTO® 9 inhibited bacterial growth. With the addition of nontoxic concentrations of propidium iodide (PI) to the culture medium, the fraction of live and dead bacteria could be continuously monitored by fluorescence microscopy as demonstrated here using GFP expressing Escherichia coli as model organism. The viability of bacteria was thereby monitored on untreated and bioactive dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (DMOAC)-coated glass substrates over several hours. Pre-adsorption of the antimicrobial surfaces with serum proteins, which mimics typical protein adsorption to biomaterial surfaces upon contact with host body fluids, completely blocked the antimicrobial activity of the DMOAC surfaces as we observed the recovery of bacterial growth. Hence, this optimized eGFP/PI viability assay provides a protocol for unperturbed in situ monitoring of bacterial viability and colonization on engineered biomaterial surfaces with single-bacteria sensitivity under physiologically relevant conditions.
Journal of the American Chemical Society | 2011
Torben Gillich; Edmondo M. Benetti; Ekaterina Rakhmatullina; Rupert Konradi; Wen Li; Afang Zhang; A. Dieter Schlüter; Marcus Textor