Glycol Silane Research Articles

Anti-Thrombogenicity Study of a Covalently-Attached Monolayer on Stent-Grade Stainless Steel.

Implantable devices fabricated from austenitic type 316L stainless steel have been employed significantly in medicine, principally because the material displays excellent mechanical characteristics and corrosion resistance. It is well known, however, that interaction of exposure of such a material to blood can initiate platelet adhesion and blood coagulation, leading to a harmful medical condition. In order to prevent undesirable surface platelet adhesion on biomaterials employed in procedures such as renal dialysis, we developed an ultrathin anti-thrombogenic covalently attached monolayer based on monoethylene glycol silane chemistry. This functions by forming an interstitial hydration layer which displays restricted mobility in the prevention of surface fouling. In the present work, the promising anti-thrombogenic properties of this film are examined with respect to platelet aggregation on 316L austenitic stainless steel exposed to whole human blood. Prior to exposure with blood, all major surface modification steps were examined by X-ray photoelectron spectroscopic analysis and surface free-angle measurement by contact angle goniometry. End-stage anti-thrombogenicity detection after 20 min of blood exposure at 100 s−1, 300 s−1, 600 s−1, 750 s−1, and 900 s−1 shear rates revealed that a significant reduction (>90%) of platelet adhesion and aggregation was achieved for surface-modified steel, compared with untreated material. This result is confirmed by experiments conducted in real time for 60-minute exposure to blood at 100 s−1, 600 s−1, and 900 s−1 shear rates.

Enhanced Long-term Antithrombogenicity Instigated by Covalently-Attached Surface Modifier on Biomedical Polymers

During a variety of medical procedures such as renal dialysis, bypass surgery, and lung transplantation patient blood is exposed to the surface of a number of polymeric materials such as polycarbonate (PC), poly (vinyl chloride) (PVC) and polysulfone (PS) for a period up to several days. Such exposure may result in undesirable protein-material interactions that can potentially trigger deleterious biological processes including thrombosis, which may be responsible for other complications such as cognitive disability. In order to address this issue, we have further examined the behavior of an ultrathin antifouling and antithrombogenic coating based on monoethylene glycol silane surface chemistry. Samples of polymeric substrates were exposed to blood flow at a shear rate of ~20 s-1 for time periods of 3 and 6 hours, as well as 3 days. No additional anticoagulant chemistry was applied in the experiments. For all time periods, platelet adhesion, aggregation, and thrombus formation on the coated surfaces was inhibited compared to bare substrates (coated PC performing the best, followed by PVC-, and then PS-coated), strongly supporting the results of previous research conducted over far shorter blood contact times.

Multifunctional Polystyrene Core/Silica Shell Microparticles with Antifouling Properties for Bead-Based Multiplexed and Quantitative Analysis.

Commercial bead-based assays are commonly built upon polystyrene particles. The polymeric carrier can be encoded with organic dyes and has ideal material properties for cytometric applications such as low density and high refractive index. However, functional groups are conventionally integrated during polymerization and subsequent modification is limited to the reactivity of those groups. Additionally, polystyrene as the core material leads to many hydrophobic areas still being present on the beads' surfaces even after functionalization, rendering the particles prone to nonspecific adsorption during an application. The latter calls for several washing steps and the use of additives in (bio)analytical assays. In this contribution, we show how these limitations can be overcome by using monodisperse polystyrene (PS) core/silica (SiO2) shell particles (SiO2@PS). Two different hydrophobic BODIPY (boron-dipyrromethene) dyes were encapsulated inside a poly(vinylpyrrolidone) (PVP) -stabilized polystyrene core in different concentrations to create 5-plex arrays in two separate detection channels of a cytometer. A subsequent modification of the silica shell with an equimolar APTES/PEGS (aminopropyltriethoxysilane/polyethylene glycol silane) blend added multifunctional properties to the hybrid core/shell microparticles in a single step: APTES provides amino groups for the attachment of a caffeine derivative (as a hapten) to create antigen-coupled microspheres; the PEG moiety effectively suppresses nonspecific binding of antibodies, endowing the surface with antifouling properties. The particles were applied in a competitive fluorescence immunoassay in suspension, and a highly selective wash-free assay for the detection of caffeine in beverages was developed as a proof of concept.

Surface activity and flocculation behavior of polyethylene glycol-functionalized silica nanoparticles

Colloidal silica nanoparticles have been functionalized with methyl polyethylene glycol silane (mPEG silane) and the PEGylated particles have been characterized with focus on exploring their surface chemical properties. The degree of surface functionalization was quantified using NMR diffusometry, and the measurements showed that the silane binds covalently to the silica surface. Samples with surface coverages ranging from 0.068 to 0.315μmolsilane/m2 have been analyzed. The functionalized particles proved to be surface active and showed a significant reduction in surface charge and zeta potential with increasing degree of PEG functionalization. All samples showed colloidal stability at neutral pH and above within the range studied. At lower pH, the samples with low surface coverage displayed a reversible flocculation behavior, while samples with a high surface coverage and samples without functionalization remained stable. This suggests that steric stabilization is effective at low pH when the surface coverage is high enough; electrostatic stabilization is effective for samples without functionalization; and that inter-particle PEG–silica interactions cause flocculation of particles with too low degrees of PEG functionalization.

Prevention of Thrombogenesis from Whole Human Blood on Plastic Polymer by Ultrathin Monoethylene Glycol Silane Adlayer

In contemporary society, a large percentage of medical equipment coming in contact with blood is manufactured from plastic polymers. Unfortunately, exposure may result in undesirable protein-material interactions that can potentially trigger deleterious biological processes such as thrombosis. To address this problem, we have developed an ultrathin antithrombogenic coating based on monoethylene glycol silane surface chemistry. The strategy is exemplified with polycarbonate--a plastic polymer increasingly employed in the biomedical industry. The various straightforward steps of surface modification were characterized with X-ray photoelectron spectroscopy supplemented by contact angle goniometry. Antithrombogenicity was assessed after 5 min exposure to whole human blood dispensed at a shear rate of 1000 s(-1). Remarkably, platelet adhesion, aggregation, and thrombus formation on the coated surface was greatly inhibited (>97% decrease in surface coverage) compared to the bare substrate and, most importantly, nearly nonexistent.

Probing the Hydration of Ultrathin Antifouling Organosilane Adlayers using Neutron Reflectometry

Neutron reflectometry data and modeling support the existence of a relatively thick, continuous phase of water stemming from within an antifouling monoethylene glycol silane adlayer prepared on oxidized silicon wafers. In contrast, this physically distinct (from bulk) interphase is much thinner and only interfacial in nature for the less effective adlayer lacking internal ether oxygen atoms. These results provide further insight into the link between antifouling and surface hydration.

Tamoxifen loaded folic acid armed PEGylated magnetic nanoparticles for targeted imaging and therapy of cancer

Magnetic nanoparticles (MNPs) have been widely used as drug delivery nanosystems and contrast agent for imaging and detection. To engineer multifunctional nanomedicines for simultaneous imaging and therapy of cancer cells, in the current study, we synthesized tamoxifen (TMX) loaded folic acid (FA) armed MNPs to target the folate receptor (FR) positive cancer cells. To this end, Fe3O4 nanoparticles (NPs) were synthesized through thermal decomposition of Fe(acac)3. Polyethylene glycol (PEG) was treated with excess bromoacetyl chloride (BrAc) and then with 3-aminopropyltriethoxysilane (APS) to synthesize bromoacetyl-terminal polyethylene glycol silane (APS-PEG-BrAc). The latter complex was treated with protected ethylene diamine to form a bifunctional PEG compound containing triethoxysilane at one end and amino group at the other end (APS-PEG-NH2). The Fe3O4-APS-PEG-NH2 NPs were prepared through self-assembly of APS-PEG-NH2 on MNPs, while the amino groups at the end of Fe3O4-APS-PEG-NH2 were conjugated with folic acid (FA), then loaded with TMX (Fe3O4-APS-PEG-FA-TMX). The average size of “Fe3O4-APS-PEG-FA-TMX” NPs was approximately 40nm. The engineered MNPs were further characterized and examined in the human breast cancer MCF-7 cells that express FR. The TMX loaded MNPs (with loading efficiency of 49.1%) showed sustained liberation of TMX molecules (with 90% release in 72h). Fluorescence microcopy and flow cytometry analyses revealed substantial interaction of Fe3O4-APS-PEG-FA-TMX NPs with the FR-positive MCF-7 cells. Cytotoxicity analysis resulted in significant growth inhibition in MCF-7 cells treated with Fe3O4-APS-PEG-FA-TMX NPs. Based on these findings, the TMX-loaded FA-armed PEGylated MNPs as a novel multifunctional nanomedicine/theranostic for concurrent targeting, imaging and therapy of the FR-positive cancer cells.

In-vivo fluorescence imaging technique using colloid solution of multiple quantum dots/silica/poly(ethylene glycol) nanoparticles

This paper describes a method for producing silica particles containing multiple quantum dots (QD/SiO2), a method for surface-modifying the particles with poly(ethylene glycol) (QD/SiO2/PEG), and an in vivo fluorescence imaging technique using colloid solution of the QD/SiO2/PEG particles. The QDs used were ZnS-coated CdSexTe1−x nanoparticles surface-modified with carboxyl groups, and had an average size of 10.3 ± 2.1 nm. The QD/SiO2 particles were fabricated by performing sol–gel reaction of tetraethyl orthosilicate using NaOH as a catalyst in the presence of the QDs. The produced particles formed core–shell structure composed of multiple QDs and silica shell, and had an average size of 50.2 ± 17.9 nm. Surface-modification of the QD/SiO2 particles with PEG, or PEGylation of the particle surface, was performed by using methoxy polyethylene glycol silane. Fluorescence of QD colloid solution was not quenched even through the silica-coating and the PEGylation. Tissues of a mouse could be imaged by injecting the concentrated colloid solution into it and measuring fluorescence intensity emitted from the tissues.

Selective filling of nanowells in nanowell arrays fabricated using polystyrene nanosphere lithography with cytochrome P450 enzymes

This work describes an original and simple technique for protein immobilization into nanowells, fabricated using nanopatterned array fabrication methods, while ensuring the protein retains normal biological activity. Nanosphere lithography was used to fabricate a nanowell array with nanowells 100 nm in diameter with a periodicity of 500 nm. The base of the nanowells was gold and the surrounding material was silicon dioxide. The different surface chemistries of these materials were used to attach two different self-assembled monolayers (SAM) with different affinities for the protein used here, cytochrome P450 (P450). The nanowell SAM, a methyl terminated thiol, had high affinity for the P450. The surrounding SAM, a polyethylene glycol silane, displayed very little affinity toward the P450 isozyme CYP2C9, as demonstrated by x-ray photoelectron spectroscopy and surface plasmon resonance. The regularity of the nanopatterned array was examined by scanning electron microscopy and atomic force microscopy. P450-mediated metabolism experiments of known substrates demonstrated that the nanowell bound P450 enzyme exceeded its normal activity, as compared to P450 solutions, when bound to the methyl terminated self-assembled monolayer. The nanopatterned array chips bearing P450 display long term stability and give reproducible results making them potentially useful for high-throughput screening assays or as nanoelectrode arrays.

Versatile ferrofluids based on polyethylene glycol coated iron oxide nanoparticles

Versatile ferrofluids based on polyethylene glycol coated iron oxide nanoparticles were obtained by a facile protocol and thoroughly characterized. Superparamagnetic iron oxide nanoparticles synthesized using a modified forced hydrolysis method were functionalized with polyethylene glycol silane (PEG silane), precipitated and dried. These functionalized particles are dispersable in a range of solvents and concentrations depending on the desired properties. Examples of tunable properties are magnetic behavior, optical and magneto-optical response, thermal features and rheological behavior. As such, PEG silane functionalized particles represent a platform for the development of new materials that have broad applicability in e.g. biomedical, industrial or photonic environments. Magnetic, optical, magneto-optical, thermal and rheological properties of several ferrofluids based on PEG coated particles with different concentrations of particles dispersed in low molecular mass polyethylene glycol were investigated, establishing the applicability of such materials.

Detection of label-free cancer biomarkers using nickel nanoislands and quartz crystal microbalance

We present a technique for the label-free detection and recognition of cancer biomarkers using metal nanoislands intended to be integrated in a novel type of nanobiosensor. His-tagged (scFv)-F7N1N2 is the antibody fragment which is directly immobilized, by coordinative bonds, onto ~5 nm nickel islands, then deposited on the surface of a quartz crystal of a quartz crystal microbalance (QCM) to validate the technique. Biomarker GTPase RhoA was investigated because it has been found to be overexpressed in various tumors and because we have recently isolated and characterized a new conformational scFv which selectively recognizes the active form of RhoA. We implemented a surface chemistry involving an antibiofouling coating of polyethylene glycol silane (PEG-silane) (<2 nm thick) and Ni nanoislands to reach a label-free detection of the active antigen conformation of RhoA, at various concentrations. The methodology proposed here proves the viability of the concept by using Ni nanoislands as an anchoring surface layer enabling the detection of a specific conformation of a protein, identified as a potential cancer biomarker. Hence, this novel methodology can be transferred to a nanobiosensor to detect, at lower time consumption and with high sensitivity, specific biomolecules.

Photopatterned Surfaces for Site-Specific and Functional Immobilization of Proteins

Photosensitive silanes containing nitroveratryl (Nvoc)-caged amine groups and protein repellent tetraethylene glycol units were synthesized and used for modification of silica surfaces. Functional surface layers containing different densities of caged amine groups were prepared and activated by UV-irradiation of the surface. The performance of these layers for functional and site-selective immobilization of proteins was tested. For this purpose, biotin and tris-nitrilotriacetic acid (tris-NTA) were fist coupled to the activated surface, and the interaction of streptavidin and His-tagged proteins with the functionalized surfaces was monitored by real-time label-free detection. After optimizing the coupling protocols, highly selective functionalization of the deprotected amine groups was possible. Furthermore, the degree of functionalization (and therefore the amount of immobilized protein) was controlled by diluting the surface concentration of the amine-functionalized silane with a nonreactive (OMe-terminated) tetraethylene glycol silane. Immobilized proteins were highly functional on these surfaces, as demonstrated by protein-protein interaction assays with the type I interferon receptor. Protein micropatterns were successfully generated after masked irradiation and functionalization of the caged surface following the optimized coupling protocols.

Poly(dimethylsiloxane) thin films as biocompatible coatings for microfluidic devices: Cell culture and flow studies with glial cells

Oxygen plasma treatment of poly(dimethylsiloxane) (PDMS) thin films produced a hydrophilic surface that was biocompatible and resistant to biofouling in microfluidic studies. Thin film coatings of PDMS were previously developed to provide protection for semiconductor-based microoptical devices from rapid degradation by biofluids. However, the hydrophobic surface of native PDMS induced rapid clogging of microfluidic channels with glial cells. To evaluate the various issues of surface hydrophobicity and chemistry on material biocompatibility, we tested both native and oxidized PDMS (ox-PDMS) coatings as well as bare silicon and hydrophobic alkane and hydrophilic oligoethylene glycol silane monolayer coated under both cell culture and microfluidic studies. For the culture studies, the observed trend was that the hydrophilic surfaces supported cell adhesion and growth, whereas the hydrophobic ones were inhibitive. However, for the fluidic studies, a glass-silicon microfluidic device coated with the hydrophilic ox-PDMS had an unperturbed flow rate over 14 min of operation, whereas the uncoated device suffered a loss in rate of 12%, and the native PDMS coating showed a loss of nearly 40%. Possible protein modification of the surfaces from the culture medium also were examined with adsorbed films of albumin, collagen, and fibrinogen to evaluate their effect on cell adhesion.