Ognen Pop-Georgievski

Controlled Cell Adhesion on Poly(dopamine) Interfaces Photopatterned with Non‐Fouling Brushes

Bioinspired poly(dopamine) (PDA) films are merged with antifouling poly(MeOEGMA) brushes utilizing a nitrile imine-mediated tetrazole-ene cycloaddition (NITEC)-based phototriggered surface encoding protocol. The antifouling brushes were photopatterned on PDA surfaces, leading cells to form confluent layers in the non-irradiated sections, while no adhesion occurred on the brushes resulting in a remarkably precise cell pattern. The presented strategy paves the way for the design of tailor-made patterned cell interfaces.

Poly(ethylene oxide) Layers Grafted to Dopamine-melanin Anchoring Layer: Stability and Resistance to Protein Adsorption

In this study, we propose substrate-independent modification for creating a protein-repellent surface based on dopamine-melanin anchoring layer used for subsequent binding of poly(ethylene oxide) (PEO) from melt. We verified that the dopamine-melanin layer can be formed on literally any substrate and could serve as the anchoring layer for subsequent grafting of PEO chains. Grafting of PEO from melt in a temperature range 70-110 °C produces densely packed PEO layers showing exceptionally low protein adsorption when exposed to the whole blood serum or plasma. The PEO layers prepared from melt at 110 °C retained the protein repellent properties for as long as 10 days after their exposure to physiological-like conditions. The PEO-dopamine-melanin modification represents a simple and universal surface modification method for the preparation of protein repellent surfaces that could serve as a nonfouling background in various applications, such as optical biosensors and tissue engineering.

Nonfouling poly(ethylene oxide) layers end-tethered to polydopamine

Nonfouling surfaces capable of reducing protein adsorption are highly desirable in a wide range of applications. Coating of surfaces with poly(ethylene oxide) (PEO), a water-soluble, nontoxic, and nonimmunogenic polymer, is most frequently used to reduce nonspecific protein adsorption. Here we show how to prepare dense PEO brushes on virtually any substrate by tethering PEO to polydopamine (PDA)-modified surfaces. The chain lengths of hetero-bifunctional PEOs were varied in the range of 45-500 oxyethylene units (M(n) = 2000-20,000). End-tethering of PEO chains was performed through amine and thiol headgroups from reactive polymer melts to minimize excluded volume effects. Surface plasmon resonance (SPR) was applied to investigate the adsorption of model protein solutions and complex biologic medium (human blood plasma) to the densely packed PEO brushes. The level of protein adsorption of human serum albumin and fibrinogen solutions was below the detection limit of the SPR measurements for all PEO chains end-tethered to PDA, thus exceeding the protein resistance of PEO layers tethered directly on gold. It was found that the surface resistance to adsorption of lysozyme and human blood plasma increased with increasing length and brush character of the PEO chains end-tethered to PDA with a similar or better resistance in comparison to PEO layers on gold. Furthermore, the chain density, thickness, swelling, and conformation of PEO layers were determined using spectroscopic ellipsometry (SE), dynamic water contact angle (DCA) measurements, infrared reflection-absorption spectroscopy (IRRAS), and vibrational sum-frequency-generation (VSFG) spectroscopy, the latter in air and water.

Biomimetic non-fouling surfaces: extending the concepts

In this study, we propose a substrate-independent biomimetic modification route for the creation of antifouling polymer brushes. This modification route consists of the formation/deposition of a biomimetic polydopamine anchor layer followed by a well-controlled surface-initiated atom transfer radical polymerization of antifouling polymer brushes initiated by 2-bromo-2-methylpropanoyl groups covalently attached to the hydroxyl and amine groups present in the anchor layer. In this way, we synthesized polymer brushes of methoxy- and hydroxy-capped oligoethylene glycol methacrylate, 2-hydroxyethyl methacrylate and carboxybetaine acrylamide. Spectroscopic ellipsometry (SE) indicated well-controlled polymerization kinetics of the brushes, thus the thickness of the ultra-thin films could be precisely tuned at a nanometer scale. The covalent structure and organization of the brushes grown from the polydopamine anchor layer were accessed by infrared reflection-adsorption spectroscopy (IRRAS) while the change in hydrophilicity caused by the presence of the brush was determined by dynamic water contact angle measurements. Surface plasmon resonance as well as ex situ IRRAS and SE measurements were applied to investigate the adsorption of model protein solutions and undiluted human blood plasma to the brushes. The biomimetic brushes completely suppressed the fouling from single protein solutions and reduced the fouling from plasma to less than 3% from the fouling measured on bare gold surfaces. The proposed modification procedure is non-destructive and does not require any chemical pre-activation or the presence of reactive groups on the substrate surface. Contrary to other antifouling modifications the coating can be performed on various classes of substrates and preserves its properties even in undiluted blood plasma. This work offers a promising technology for the facile fabrication of different surface-based biotechnological and biomedical devices able to perform tailor-made functions while resisting the fouling from the complex biological media where they operate.

Synthesis of non-fouling poly[N-(2-hydroxypropyl)methacrylamide] brushes by photoinduced SET-LRP

Surface-initiated photoinduced single-electron transfer living radical polymerization (SET-LRP) was employed to assemble brushes of poly[N-(2-hydroxypropyl) methacrylamide] (poly(HPMA)) from silicon surfaces. The linear increase in thickness of the poly(HPMA) brushes with time and the ability to prepare block copolymers indicate the living nature of this grafting-from process. Copper concentrations as low as 80 ppb were sufficient for this surface-initiated SET-LRP. Micropatterns of poly(HPMA) brushes on the silicon surface were constructed for the first time by this method. Negligible fouling was observed after contact with undiluted blood plasma. This report provides the first example of non-fouling polymer brushes prepared by SET-LRP of HPMA.

Click & seed approach to the biomimetic modification of material surfaces.

A simple, versatile, protein-repulsive, substrate-independent biomimetic surface modification is presented that is based on the creation of a PEO brush on a polydopamine anchoring layer and its capacity for selective follow-up modifications with various ligands using a copper-catalyzed alkyne-azide cycloaddition reaction. The desired surface concentration of peptide biomimetic ligands can be controlled by adjusting the peptide concentration in the reaction mixture, then measuring the activity of (125)I-radiolabeled peptides that are immobilized on the substrates. The performance of the prepared substrates is tested in cell cultures with MEF cells and a human ECC line.

Exploiting end group functionalization for the design of antifouling bioactive brushes

Biologically active surfaces are essential in many applications in the fields of biosensing, bioimplants, and tissue engineering. However, the introduction of bioactive motifs without impairment of their ability to resist non-specific interactions with biological media remains a challenge. Herein, we present a straightforward, facile strategy for the creation of bioactive surfaces based on the end-group biofunctionalization of state-of-the-art polymer brushes via an ultra-fast Diels–Alder “click” reaction. Surface-initiated atom transfer radical polymerization is employed to grow antifouling polymers preserving the end groups. These groups are then further converted to a reactive cyclopentadienyl moiety and exploited for the immobilization of biomolecules on the topmost layer of the brush. The minimal chemical modification of the antifouling polymer brush accounts for the full preservation of the fouling resistance of the surface even after biofunctionalization, which is critical for the aforementioned applications.

Antifouling Polymer Brushes Displaying Antithrombogenic Surface Properties

The contact of blood with artificial materials generally leads to immediate protein adsorption (fouling), which mediates subsequent biological processes such as platelet adhesion and activation leading to thrombosis. Recent progress in the preparation of surfaces able to prevent protein fouling offers a potential avenue to mitigate this undesirable effect. In the present contribution, we have prepared several types of state-of-the-art antifouling polymer brushes on polycarbonate plastic substrate, and investigated their ability to prevent platelet adhesion and thrombus formation under dynamic flow conditions using human blood. Moreover, we compared the ability of such brushes--grafted on quartz via an adlayer analogous to that used on polycarbonate--to prevent protein adsorption from human blood plasma, assessed for the first time by means of an ultrahigh frequency acoustic wave sensor. Results show that the prevention of such a phenomenon constitutes one promising route toward enhanced resistance to thrombus formation, and suggest that antifouling polymer brushes could be of service in biomedical applications requiring extensive blood-material surface contact.

Surface Grafting via Photo‐Induced Copper‐Mediated Radical Polymerization at Extremely Low Catalyst Concentrations

Surface-initiated photo-induced copper-mediated radical polymerization is employed to graft a wide range of polyacrylate brushes from silicon substrates at extremely low catalyst concentrations. This is the first time that the controlled nature of the reported process is demonstrated via block copolymer formation and re-initiation experiments. In addition to unmatched copper catalyst concentrations in the range of few ppb, film thicknesses up to almost 1 μm are achieved within only 1 h.

Hepatitis B plasmonic biosensor for the analysis of clinical serum samples

A plasmonic biosensor for rapid detection of protein biomarkers in complex media is reported. Clinical serum samples were analyzed by using a novel biointerface architecture based on poly[(N-(2-hydroxypropyl) methacrylamide)-co-(carboxybetaine methacrylamide)] brushes functionalized with bioreceptors. This biointerface provided an excellent resistance to fouling even after the functionalization and allowed for the first time the direct detection of antibodies against hepatitis B surface antigen (anti-HBs) in clinical serum samples using surface plasmon resonance (SPR). The fabricated SPR biosensor allowed discrimination of anti-HBs positive and negative clinical samples in 10min. Results are validated by enzyme-linked immunoassays of the sera in a certified laboratory. The sensor could be regenerated by simple treatment with glycine buffer.