An aqueous-based surface modification of poly(dimethylsiloxane) with poly(ethylene glycol) to prevent biofouling

We report a simple modification of poly(dimethylsiloxane) (PDMS) surfaces with poly(ethylene glycol) (PEG) through the adsorption of a graft copolymer, poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) from aqueous solution. In this approach, the PDMS surface was treated with oxygen plasma, followed by immersion into aqueous solution containing PLL-g-PEG copolymers. Due to the hydroxyl/carboxylic groups generated on the PDMS surface after oxygen plasma, the polycationic PLL backbone is attracted to the negatively charged surface and PEG side chains exhibit an extended structure. The PEG/aqueous interface generated in this way revealed a near-perfect resistance to nonspecific protein adsorption as monitored by means of optical waveguide lightmode spectroscopy (OWLS) and fluorescence microscopy.     

Novel tricomponent membranes containing poly(ethylene glycol)/poly(pentamethylcyclopentasiloxane)/poly(dimethylsiloxane) domains

The synthesis and characterization of novel tricomponent networks consisting of well‐defined poly(ethylene glycol) (PEG) and poly(dimethylsiloxane) (PDMS) strands crosslinked and reinforced by poly(pentamethylcyclopentasiloxane) (PD₅) domains are described. Network synthesis occurred by dissolving α,ω‐diallyl PEG and α,ω‐divinyl PDMS prepolymers in a common solvent (toluene), introducing a stoichiometric excess of pentamethylcyclopentasiloxane (D₅H) to the charge, inducing the cohydrosilation of the prepolymers by Karstedt's catalyst and completing network formation by the addition of water. Water in the presence of the Pt‐based catalyst oxidizes the SiH groups of D₅H to SiOH functions that immediately polycondense and bring about crosslinking. The progress of cohydrosilation and polycondensation was followed by monitoring the disappearance of the SiH and SiOH functions by Fourier transform infrared spectroscopy. Because cohydrosilation and polycondensation are essentially quantitative, overall network composition can be controlled by calculating the stoichiometry of the three network constituents. The very low quantities of extractable (sol) fractions corroborate efficient crosslinking. The networks swell in both water and hexanes. Differential scanning calorimetry showed three thermal transitions assigned, respectively, to PEG (melting temperature: 46–60 °C depending on composition), PDMS [glass‐transition temperature (T_g) = ～?121 °C], and PD₅ (T_g = ～?159 °C) and indicated a phase‐separated tricomponent nanoarchitecture. The low T_g of the PD₅ phase is unprecedented. The strength and elongation of PEG/PD₅/PDMS networks can be controlled by overall network composition. The synthesis of networks exhibiting sufficient mechanical properties (tensile stress: 2–5 MPa, elongation: 100–800%) for various possible applications has been demonstrated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3093–3102, 2002     

Surface modification of nanoporous alumina surfaces with poly(ethylene glycol)

Nanoporous alumina surfaces have a variety of applications in biosensors, biofiltration, and targeted drug delivery. However, the fabrication route to create these nanopores in alumina results in surface defects in the crystal lattice. This results in inherent charge on the porous surface causing biofouling, that is, nonspecific adsorption of biomolecules. Poly(ethylene glycol) (PEG) is known to form biocompatible nonfouling films on silicon surfaces. However, its application to alumina surfaces is very limited and has not been well investigated. In this study, we have covalently attached PEG to nanoporous alumina surfaces to improve their nonfouling properties. A PEG-silane coupling technique was used to modify the surface. Different concentrations of PEG for different immobilization times were used to form PEG films of various grafting densities. X-ray photoelectron spectroscopy (XPS) was used to verify the presence of PEG moieties on the alumina surface. High-resolution C1s spectra show that with an increase in concentration and immobilization time, the grafting density of PEG also increases. Further, a standard overlayer model was used to calculate the thickness of PEG films formed using the XPS intensities of the Al2p peaks. The films formed by this technique are less than 2.5 nm thick, suggesting that such films will not clog the pores which are in the range of 70-80 nm.     

Photopolymerization of poly(ethylene glycol) diacrylate on eosin-functionalized surfaces

We describe a new method that allows photopolymerization of hydrogels to occur on surfaces functionalized with eosin. In this work, glass and silicon surfaces were derivatized with eosin and photopolymerization was carried out using visible light (514 nm). This mild condition may have advantages over methods that use ultraviolet (UV) light (e.g., for encapsulation of cells and proteins, in drug screening, or in biosensing applications). The hydrogel formed on the modified surface is remarkably stable for an extended period of time. The resultant hydrogel was hydrated for more than 18 months without suffering delamination from the substrate surface. This strongly suggests covalent attachment of the hydrogel to the surface. Contact angle titration measurements and X-ray photoelectron spectroscopy analysis of eosin surfaces before and after irradiation in the presence of triethanolamine suggest that the eosin radical is responsible for the covalent attachment of the gel onto the substrate surface. This method allows for 2-D patterning of hydrogels, which is demonstrated here using the microcontact printing technique. However, noncontact photolithography could be used to form similar patterns by directing light through a mask. This method can be easily implemented to form arrays of fluorophores and proteins in situ.     

Zeta potentials of PDMS surfaces modified with poly(ethylene glycol) by physisorption

Controlling zeta potential of PDMS surface coated with a layer of PEG is important for electroosmosis and electrophoresis in PDMS made microfluidic chips. Here, zeta potentials of PDMS surfaces modified by simple physisorption of PEG of different concentrations in phosphate buffer solutions, pure water, and PEG solution were reported. Coating PEG on PDMS surfaces was achieved by immersing a PDMS layer into the PEG solution for 10 min and then taking it out and placing it in an oven at 80℃ for 10 h. To avoid damaging the PEG layer on the PDMS surface, an induction current method was employed for zeta potential measurement. Zeta potentials of PEG modified PDMS in electrolyte solutions were measured. The results show that 2.5% PEG can effectively modify PDMS surface with positive zeta potential value in phosphate buffer solutions, pure water and 10% PEG solution. Further increase in PEG solution beyond 5% for surface modification has no obvious effect on zeta potential change.     

Effect of magnetic field on the rheological properties of poly(ethylene glycol) and poly(dimethylsiloxane) mixtures with aerosil and iron nanoparticles

The effect of a magnetic field on the viscosity of magnetorheological poly(ethylene glycol)-aerosil-iron nanoparticle and poly(dimethylsiloxane)-aerosil-iron nanoparticle suspensions is studied. The magnetic field leads to an increase in the viscosity of the suspensions by a factor of 20–300. The concentration dependence of the effect of magnetic field on the viscosity of the systems is described by a curve with a maximum. The dependences of viscosity on shear rate upon loading and unloading do not coincide, thus indicating the relaxation character of the flow process.     

Segmented block copolymers of poly(ethylene glycol) and poly(ethylene terephthalate)

A new series of segmented copolymers were synthesized from poly(ethylene terephthalate) (PET) oligomers and poly(ethylene glycol) (PEG) by a two‐step solution polymerization reaction. PET oligomers were obtained by glycolysis depolymerization. Structural features were defined by infrared and nuclear magnetic resonance (NMR) spectroscopy. The copolymer composition was calculated via ¹H NMR spectroscopy. The content of soft PEG segments was higher than that of hard PET segments. A single glass‐transition temperature was detected for all the synthesized segmented copolymers. This observation was found to be independent of the initial PET‐to‐PEG molar ratio. The molar masses of the copolymers were determined by gel permeation chromatography (GPC). © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4448–4457, 2004     

Dendritic structures of poly(ethylene glycol) on silicon nitride and gold surfaces

A hydrophilic silicon nitride surface was grafted with poly(ethylene glycol) monomethyl ether (average formula weight of 5000 Da) in a one-step protocol. The domains of stable dendritic structures of self-assembled monolayer islands on a silicon nitride surface were observed with atomic force microscopy. The moduli of elasticity of these dendritic structures in air and in KCl aqueous solution were compared. The value of the Young's modulus of these structures is reduced by more than 3 orders of magnitude, from approximately 12 GPa measured in air to approximately 5 MPa in KCl solution. This dramatic reduction in elasticity was attributed to the swelling of the dendritic structures in aqueous solution, which was verified by the increased film thickness. These dendritic structures were not stable in the aqueous environment and could be removed by soaking in water for 22 h because of the hydrolysis of the silicate bonds. This fact was confirmed by the reduction of the C1s signal in the X-ray photoelectron spectroscopy experiments. These morphologies are not unique to silicon nitride substrate; similar features were also observed for thiolated poly(ethylene glycol) monomethyl ether molecules absorbed on a gold surface.     

Platelet and bacterial repellence on sulfonated poly(ethylene glycol)-acrylate copolymer surfaces

Novel poly(ethylene glycol) (PEG) and sulfonated PEG (PEG-SO₃) acrylate copolymers have been prepared and characterized to apply as coating and blending materials for biomedical applications. The modified surfaces using acrylate copolymers demonstrated increased hydrophilicity, possibly due to the hypothesized reorientation of PEG/PEG-SO₃ chains into water phase. All copolymer surfaces demonstrated less platelet adhesion than control. In addition, platelet adhesion on copolymer surfaces decreased as the chain length of PEG and sulfonated PEG in copolymers increases. All copolymer surfaces reduced bacterial adhesion significantly and the adhesion level differs depending on surfaces as well as media. The obtained results attest to the usefulness of these copolymers as a coating or additive material to improve the blood compatibility of blood contacting devices.     

Micropallet arrays with poly(ethylene glycol) walls

Arrays of releasable micropallets with surrounding walls of poly(ethylene glycol) (PEG) were fabricated for the patterning and sorting of adherent cells. PEG walls were fabricated between the SU-8 pallets using a simple, mask-free strategy. By utilizing the difference in UV-transmittance of glass and SU-8, PEG monomer was selectively photopolymerized in the space surrounding the pallets. Since the PEG walls are composed of a cross-linked structure, the stability of the walls is independent of the pallet array geometry and the properties of the overlying solution. Even though surrounded with PEG walls, the individual pallets were detached from the array by the mechanical force generated by a focused laser pulse, with a release threshold of 6 microJ. Since the PEG hydrogels are repellent to protein adsorption and cell attachment, the walls localized cell growth to the pallet top surface. Cells grown in the microwells formed by the PEG walls were released by detaching the underlying pallet. The released cells/pallets were collected, cultured and clonally expanded. The micropallet arrays with PEG walls provide a platform for performing single cell analysis and sorting on chip.     

Strategies toward biocompatible artificial implants: Grafting of functionalized poly(ethylene glycol)s to poly(ethylene terephthalate) surfaces

Epoxide and aldehyde end‐functionalized poly(ethylene glycol)s (PEGs) (M_w = 400, 1000, 3400, 5000, and 20,000) were grafted to poly(ethylene terephthalate) (PET) film substrates that contained amine or alcohol groups. PET‐PAH and PET‐PEI were prepared by reacting poly(allylamine) (PAH) and polyethylenimine (PEI) with PET substrates, respectively; PET‐PVOH was prepared by the adsorption of poly(vinyl alcohol) (PVOH) to PET substrates. Grafting was characterized and quantified by the increase of the intensity of the PEG carbon peak in the X‐ray photoelectron spectra. Grafting yield was optimized by controlling reaction parameters and was found to be substrate‐independent in general. Graft density consistently decreased as PEG chain length was increased. This is likely due to the higher steric requirement of higher molecular weight PEG molecules. Water contact angles of surfaces containing long PEG chains (3400, 5000, and 20,000) are much lower than those containing shorter PEG chains (400 and 1000). This indicates that longer PEG chains are more effective in rendering surfaces hydrophilic. Protein adsorption experiments were carried out on PET‐ and PEG‐modified derivatives using collagen, lysozyme, and albumin. After PEG grafting, the amount of protein adsorbed was reduced in all cases. Trends in surface requirements for protein resistance are: surfaces with longer PEG chains and higher chain density, especially the former, are more protein resistant; PEG grafted to surfaces containing branched or network polymers is not effective at covering the underlying substrate, and thus does not protect the entire surface from protein adsorption; and substrates containing surface charge are less protein‐resistant. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5389–5400, 2004     

Single nanocrystal arrays on patterned poly(ethylene glycol) copolymer microstructures using selective wetting and drying

Single nanocrystal arrays were fabricated on sub-microwells of poly(ethylene glycol) (PEG) copolymer using selective wetting on the hydrophilic regions of the exposed substrate surface and subsequent drying. Templates were produced by molding a thin film of a PEG-based random copolymer on hydrophilic substrates such as glass or silicon dioxide. The polymeric microstructures provide a topographical barrier around the well, which makes it possible to create nanocrystal arrays with controlled geometrical features. The size of the nanocrystal was found to decrease with decreasing well size and also decrease with decreasing topological height. A simple empirical equation was derived to predict the size of the crystal as a function of the pattern size and height, which is in good agreement with the experimental data.     

Complex formation of daunomycin with poly(vinylpyrrolidone) and poly(ethylene glycol)

Russian Journal of General Chemistry - Complexes of the anthracycline antitumor antibiotic daunomycin with biocompatible polymer carriers, poly(vinylpyrrolidone) and poly(ethylene glycol), have...     

Glass surfaces grafted with high-density poly(ethylene glycol) as substrates for DNA oligonucleotide microarrays

Surfaces carrying a dense layer of poly(ethylene glycol) (PEG) were prepared, characterized, and tested as substrates for DNA oligonucleotide microarrays. PEG bis(amine) with a molecular weight of 2000 was grafted onto silanized glass slides bearing aldehyde groups. After grafting, the terminal amino groups of the PEG layer were derivatized with the heterobifunctional cross-linker succinimidyl 4-[p-maleimidophenyl]butyrate to permit the immobilization of thiol-modified DNA oligonucleotides. The stepwise chemical modification was validated with X-ray photoelectron spectroscopy. Goniometry indicated that the PEG grafting procedure reduced surface inhomogeneities present after the silanization step, while atomic force microscopy and ellipsometry confirmed that the PEG layer was dense and monomolecular. Hybridization assays using DNA oligonucleotides and fluorescence imaging showed that PEG grafting improved the yield in hybridization 4-fold compared to non-PEGylated maleimide-derivatized surfaces. In addition, the PEG layer reduced the nonspecific adsorption of DNA by a factor of up to 13, demonstrating that surfaces with a dense PEG layer represent suitable substrates for DNA oligonucleotide microarrays.     

叶酸和聚乙二醇接枝作基因载体用壳聚糖的合成与表征

本研究将叶酸和聚乙二醇接枝到四种不同分子量的壳聚糖氨基侧链上,以改善壳聚糖的靶向性和水溶性作基因载体。用FTIE、1HNMR、UV-Vis、DSC和TEM对产物进行了表征,结果表明,叶酸和聚乙二醇被成功地接枝到壳聚糖上,所制得的载体有望作为潜在的肿瘤细胞靶向基因载体。     

Synthesis and characterization of poly(ethylene glycol) methyl ether endcapped poly(ethylene terephthalate)

Linear and branched poly(ethylene terephthalate) (PET) copolymers with polyethylene glycol) (PEG) methyl ether (700 or 2000 g/mol) end groups were synthesized using conventional melt polymerization. DSC analysis demonstrated that low levels of PEG end groups accelerated PET crystallization. The incorporated PEG end groups also decreased the crystallization temperature of PET dramatically, and copolymers with a high content of PEG (>17.6 wt%) were able to crystallize at room temperature. Rheological analysis demonstrated that the presence of PEG end groups effectively decreased the melt viscosities and facilitated melt processing. XPS and ATR-FTIR revealed that the PEG end groups tended to aggregate on the surface, and the surface of compression molded films containing 34.0 wt% PEG were PEG rich (85 wt% PEG). PEG end-capped PET (34.0 wt% PEG) and PET films were immersed into a fibrinogen solution (0.7 mg/mL BSA) for 72 h to investigate the propensity for protein adhesion. XPS demonstrated that the concentration of nitrogen (1.05%) on the surface of PEG endcapped PET film was statistically lower than PET (7.67%). SEM analysis was consistent with XPS results, and revealed the presence of adsorbed protein on the surface of PET films.     

Synthesis and characterization of poly(ethylene glycol) grafted poly(L-lactide)

Poly(ethylene glycol) grafted poly(L -lactide) was prepared by ring opening polymerization of L -lactide and epoxy-terminated poly(ethylene glycol) methyl ether (PEGME). Stannous octoate and Al(Et)₃·0.5 H₂O were tested as polymerization catalysts, and Al(Et)₃·0.5 H₂O was found to be more effective for the ring-opening of the epoxy group of the modified PEGME monomer. The synthesized polymers were characterized by NMR and the efficiency of the incorporation of epoxy-terminated PEGME in the copolymer was determined.     

Phase separation in mixtures of poly(ethylene glycol monomethylether) and poly(propylene glycol) oligomers

Time-resolved light scattering was employed to investigate kinetics of phase separation in mixtures of poly (ethylene glycol monomethylether) (PEGE)/poly (propylene glycol) (PPG) oligomers. Phase diagrams for PEGE/PPG of varying molecular weights were established by means of cold point measurements. The oligomer mixtures reveal an upper critical solution temperature (UCST). Several temperature quench experiments were carried out with a 60/40 PEGE/PPG blend by rapidly quenching from a single phase (69°C) to two-phase temperatures (66–61°C) at 1°C intervals. As is typical for oligomer mixtures, the early stage of spinodal decomposition (SD) was not detected. The kinetics of phase decomposition was found to be dominated by the late stage of SD. Time-evolution of scattering intensity was analyzed in accordance with nonlinear and dynamical scaling theories. The time dependence of the peak intensity I_m and the corresponding peak wavenumber q_m was found to follow the power-law {I_m(t)? t^α, q_m(t)? t^-β} with the values of α = 3 ± 0.3 and β = 1 ± 0.2, which are very close to the values predicted by Siggia. This process has been attributed to a coarsening mechanism driven by surface tension. In the temporal scaling analysis, the structure function reveals university with time, suggesting self-similarity. Phase separation dynamics in 60/40 PEGE/PPG resembles the behavior predicted for off-critical mixtures.     

Ion conductivity studies of blends of poly(methyl methacrylate)-g-poly(ethylene glycol) and poly(ethylene glycol) complexed with LiCF3 SO3

Polymer electrolytes which are adhesive, transparent, and stable to atmospheric moisture have been prepared by blending poly(methyl methacrylate)-g-poly(ethylene glycol) with poly(ethylene glycol)/LiCF₃ SO₃ complexes. The maximum ionic conductivities at room temperature were measured to be in the range of 10⁻⁴ to 10⁻⁵ s cm⁻¹. The clarity of the sample was improved as the graft degree increased for all the samples studied. The graft degree of poly(methyl methacrylate)-g-poly(ethylene glycol) was found to be important for the compatibility between the poly(methyl methacrylate) segments in poly(methyl methacrylate)-g-poly(ethylene glycol) and the added poly(ethylene glycol), and consequently, for the ion conductivity of the polymer electrolyte. These properties make them promising candidates for polymer electrolytes in electrochromic devices. © 1996 John Wiley & Sons, Inc.