Quantification of grafted poly(ethylene glycol)-silanes on silicon by time-of-flight secondary ion mass spectrometry

A Versatile Hydrophilic and Antifouling Coating Based on Dopamine Modified Four-Arm Polyethylene Glycol by One-Step Synthesis Method

A versatile hydrophilic and antifouling coating was designed and prepared based on catechol-modified four-arm polyethylene glycol. The dopamine (DA) molecules were grafted onto the end of the four-arm polyethylene glycol carboxyl (4A-PEG-COOH) through the amidation reaction, which was proven by ¹H NMR and FTIR analysis, assisting the strong adhesion of PEG on the surface of various types of materials, including metallic, inorganic, and polymeric materials. The reduction of the water contact angle and the bacteria-repellent and protein-repellent effects indicated that the coating had good hydrophilicity and antifouling performance. Raman spectroscopy analysis demonstrated the affinity between the polymeric surface and water, which further confirmed the hydrophilicity of the coating. Finally, in vitro cytotoxicity assay demonstrated good biocompatibility of the coating layer.

Recovery of Polyphenols from Grape Pomace Using Polyethylene Glycol (PEG)-Grafted Silica Particles and PEG-Assisted Cosolvent Elution

Adsorption on a functionalized surface can be an effective way of purifying polyphenols from complex plant extracts. Polymeric resins that rely on hydrophobic interactions suffer from low selectivity, weak affinity towards polyphenols, and lack tunability therefore making the purification of polyphenols less efficient. In this study, a purification process for the recovery of polyphenols from grape pomace extract was successfully developed using hydrogen bonding affinity ligands grafted on silica particles and PEG-assisted elution solvents. Bare silica (SiO₂) and polyethylene glycol (mPEG)-grafted silica microparticles with molecular weights of 2000 and 5000 were tested to determine their polyphenol binding and release characteristics. Functionalizing the surface of bare silica with mPEG ligands increased the adsorption capacity by 7.1- and 11.4-fold for mPEG-2000 and mPEG-5000 compared to bare silica particles, respectively. This was likely due to the introduction of more polyphenol binding sites with mPEG functionalization. Altering the molecular weight (MW) of mPEG grafted on silica surfaces provided tunability in the adsorption capacity. A complete recovery of polyphenols (~99.9%) from mPEG-grafted silica particles was achieved by utilizing PEG–ethanol or PEG–water cosolvent systems. Recovered polyphenols showed up to ~12-fold antioxidant activity compared to grape pomace extract. This study demonstrates that mPEG-grafted silica particles and elution of polyphenols with PEG cosolvents can potentially be used for large-scale purification of polyphenols from complex plant extracts and simplify the use of polyphenols, as PEG facilitates remarkable solvation and is an ideal medium for the final formulation of polyphenols.

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.

Tuning drug loading and release properties of diatom silica microparticles by surface modifications

Diatomaceous earth (DE), or diatomite silica microparticles originated from fossilized diatoms are a potential substitute for its silica-based synthetic counterparts to address limitations in conventional drug delivery. This study presents the impact of engineered surface chemistry of DE microparticles on their drug loading and release properties. Surface modifications with four silanes, including 3-aminopropyltriethoxy silane (APTES), methoxy-poly-(ethylene-glycol)-silane (mPEG-silane), 7-octadecyltrichlorosilane (OTS), 3-(glycidyloxypropyl)trimethoxysilane (GPTMS) and two phosphonic acids, namely 2-carboxyethyl-phosphonic acid (2 CEPA) and 16-phosphono-hexadecanoic acid (16 PHA) were explored in order to tune drug loading and release characteristics of water insoluble (indomethacin) and water soluble drugs (gentamicin). Successful grafting of these functional groups with different interfacial properties was confirmed using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Thermogravimetric analysis (TGA) was applied to determine the amount of loaded drugs and UV-spectrophotometry to analyse in vitro drug release from modified DE microparticles. Differences in drug release time (13-26 days) and loading capacity (14-24%) were observed depending on functional groups on the surface of DE microparticles. It was found that hydrophilic surfaces, due to the presence of polar carboxyl, amine or hydrolyzed epoxy group, favor extended release of indomethacin, while the hydrophobic DE surface modified by organic hydrocarbons gives a better sustained release profile for gentamicin. This work demonstrates that by changing surface functionalities on DE microparticles, it is possible to tune their drug loading and release characteristics for both hydrophobic and hydrophilic drugs and therefore achieve optimal drug delivery performance.

Surface manipulation of microtubules using self-assembled monolayers and electrophoresis

We integrate microtubule (MT)-resistant self-assembled monolayers (SAMs) with lithographically patterned electrodes to control MTs in a cell-free environment. Formed through a facile, one-step assembly method, the poly(ethylene glycol) trimethoxysilane SAM prevents MT adsorption on both silicon substrates and Au microstructures without casein. We characterize the SAM using ellipsometry, X-ray photoelectron spectroscopy, and atomic force microscopy and compare it with other MT passivation techniques. The SAM retains its passivating ability when used as a substrate for electron beam lithography, a key feature that allows us to pattern microtubules on lithographically defined Au structures. Moreover, by combining the SAM-passivated Au microelectrodes and DC electrophoresis, we demonstrate reversible trapping of MTs as well as capture and alignment of individual MTs.

Poly(ethylene glycol) monolayer formation and stability on gold and silicon nitride substrates

Poly(ethylene glycol) (PEG) self-assembled monolayers (SAMs) are extensively used to modify substrates to prevent nonspecific protein adsorption and to increase hydrophilicity. X-ray photoelectron spectroscopy analysis, complemented by water contact angle measurements, is employed to investigate the formation and stability upon aging and heating of PEG monolayers formed on gold and silicon nitride substrates. In particular, thiolated PEG monolayers on gold, with and without the addition of an undecylic spacer chain, and PEG monolayers formed with oxysilane precursors on silicon nitride have been probed. It is found that PEG-thiol SAMs are degraded after less than two weeks of exposure to air and when heated at temperatures as low as 120 degrees C. On the contrary, PEG-silane SAMs are stable for more than two weeks, and fewer molecules are desorbed even after two months of aging, compared to those desorbed in two weeks from the PEG-thiol SAMs. A strongly bound hydration layer is found on PEG-silane SAMs aged for two months. Heating PEG-silane SAMs to temperatures as high as 160 degrees C improves the quality of the monolayer, desorbing weakly bound contaminants. The differences in stability between PEG-thiol SAMs and PEG-silane SAMs are ascribed to the different types of bonding to the surface and to the fact that the thiol-Au bond can be easily oxidized, thus causing desorption of PEG molecules from the surface.

Poly(ethylene glycol)-Assisted Two-Dimensional Self-Assembly of Zinc Sulfide Microspheres

A simple fabrication of two-dimensional zinc sulfide colloidal arrays with the assistance of a multihydroxy polymer is described, which can potentially be utilized in different technological fields, such as biosensor and electrooptical devices as well as a platform for studies of energy transfer between colloidal particles.

INTEGRATION OF NANOPARTICLES WITH PROTEIN MICROARRAYS

A variety of DNA, protein or cell microarray devices and systems have been developed and commercialized. In addition to the biomolecule related analysis, they are also being used for pharmacogenomic research, infectious and genetic disease and cancer diagnostics, and proteomic and cellular analysis.1 Currently, microarray is fabricated on a planar surface; this limits the amount of biomolecules that can be bounded on the surface. In this work, a planar protein microarray chip with nonplanar spot surface was fabricated to enhance the chip performance. A nonplanar spot surface was created by first coating the silica nanoparticles with albumin and depositing them into the patterned microwells. The curve surfaces of the nanoparticles increase the surface area for immobilization of proteins, which helps to enhance the detection sensitivity of the chip. Using this technique, proteins are immobilized onto the nanoparticles before they are deposited onto the chip, and therefore the method of protein immobilization can be customized at each spot. Furthermore, a nonplanar surface promotes the retention of native protein structure better than planar surface.2 The technique developed can be used to produce different types of microarrays, such as DNA, protein and antibody microarrays.

Micropatterning of proteins on nanospheres

Currently micropatterning of proteins is mainly carried out on a planar substrate, which involves multi-step surface modifications directly on the substrate. Efficiency of chemical reactions is usually low, resulting in low signal-to-noise (S/N) ratio and poor repeatability of results. Here we presented a micropatterning method using polystyrene nanospheres with non-planar surface as a solid support for attaching proteins, which introduces many advantages. The patterning of proteins was carried out in two approaches: one was to dispense polystyrene nanospheres into an array of microwells and then attach proteins onto the nanospheres, and another was to coat polystyrene nanospheres with proteins first and then deposit the spheres into the microwells. For both approaches, a uniform pattern of proteins was generated. The amount of proteins attached via nanospheres was much higher than that on planar surface.

Characterization of Poly(l-lysine)-graft-Poly(ethylene glycol) Assembled Monolayers on Niobium Pentoxide Substrates Using Time-of-Flight Secondary Ion Mass Spectrometry and Multivariate Analysis

Control of protein adsorption onto solid surfaces is a critical area of biomaterials and biosensors research. Application of high performance surface analysis techniques to these problems can improve the rational design and understanding of coatings that control protein adsorption. We have used static time-of-flight secondary ion mass spectrometry (TOF-SIMS) to investigate several poly(L-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) adlayers adsorbed electrostatically onto negatively charged niobium pentoxide (Nb(2)O(5)) substrates. By varying the PEG graft ratio (i.e., the number of lysine monomers per grafted PEG chain) and the molecular weights of the PLL and PEG polymers, the amount of protein adsorption can be tailored between 1 and 300 ng/cm(2). Detailed multivariate analysis using principal component analysis (PCA) of the positive and negative ion TOF-SIMS spectra showed changes in the outermost surface of the polymer films that were related to the density and molecular weight of the PEG chains on the surface. However, no significant differences were noted due to PLL molecular weight, despite observed differences in the serum adsorption characteristics for adlayers of PLL-g-PEG polymers with different PLL molecular weights. From the PCA results, multivariate peak intensity ratios were developed that correlated with the thickness of the adlayer and the enrichment of the PEG chains and the methoxy terminus of the PEG chains at the outermost surface of the adlayer. Furthermore, partial least squares regression was used to correlate the TOF-SIMS spectra with the amount of protein adsorption, resulting in a predictive model for determining the amount of protein adsorption on the basis of the TOF-SIMS spectra. The accuracy of the prediction of the amount of serum adsorption depended on the molecular weight of the PLL and PEG polymers and the PEG graft ratio. The combination of multivariate analysis and static TOF-SIMS provides detailed information on the surface chemistry and insight into the mechanism for protein resistance of the coatings.