Haikun Zhu

Star-shaped poly(2-methyl-2-oxazoline)-based films: rapid preparation and effects of polymer architecture on antifouling properties

Development of surfaces with antifouling properties is of great interest in biomedical applications. In this paper, the research was aimed at rapid preparation of poly(2-methyl-2-oxazoline)-based antifouling coating. We designed and synthesized a set of well-defined multiarm star copolymers hyperbranched poly(ethylenimine)-graft-poly(2-methyl-2-oxazoline) (PEI-g-PMOXA) with different PMOXA grafting ratios and chain lengths. The cytotoxicity of the polymer was tested and the PMOXA-based films were successfully deposited rapidly onto substrates via a simple one-step dopamine-assisted codeposition method. The effect of polymer architecture (linear PMOXA with different molecular weights, star PMOXA with different PMOXA grafting ratios and arm lengths) on deposited films with respect to their deposition kinetics, surface composition, wettability, morphology, cytotoxicity, and antifouling properties was investigated systematically. The antifouling properties of PMOXA-based films were found to be dependent on the surface PMOXA chain densities, which were controlled by the PMOXA grafting ratios and chain lengths. Moreover, the star PMOXA structures gave the surfaces with higher PMOXA chain densities and enhanced antifouling properties compared to the linear ones. Among the star copolymers, PEI-g(70)-PMOXA(5K)/polydopamine and PEI-g(70)-PMOXA(7K)/polydopamine deposited films showed the highest resistance to protein adsorption (96-99% relative to the bare gold surface) and cell attachment (97-99% relative to the bare glass surface), as well as complete inhibition against platelet adhesion. At last, the stability test results showed that the PMOXA-based film exhibited superior stability in long-term applications than the poly(ethylene glycol)-based film.

Polydopamine-assisted partial hydrolyzed poly(2-methyl-2-oxazolinze) as coating for determination of melamine in milk by capillary electrophoresis

Nitrogen-rich melamine (66% by mass) had been found to be illegally adulterated to milk products and animal feed in order to increase the apparent protein content, and ingestion of melamine may lead to the formation of kidney stones. Hence, the development of reliable analytical methods for the monitoring of melamine in milk products is necessary. The common methods for melamine analysis in milk products are performed via GC-MS or HPLC, however, these procedures require a large of organic solvent and several pretreatment steps. In this study, a new and facile approach was developed to modify a fused-silica capillary inner surface based on poly(dopamine) (PDA) and partial hydrolyzed poly(2-methyl-2-oxazoline) (PMOXA-EI) mixed coating, which was used to determine the melamine in milk powder quantitatively by capillary electrophoresis with ultraviolet (CE-UV) detection with simple analytes pretreatment. Firstly, the influences of the molecular mass of poly(2-methyl-2-oxazoline) (PMOXA), the hydrolysis degree of PMOXA, and the concentration ratio of DA to PMOXA-EI on the separation properties of a mixture of four basic proteins (cytochrome c, lysozyme, ribonuclease A, and α-chymotrypsinogen A) were studied in detail. As a consequence, fast and efficient separation of four proteins was obtained using PDA/PMOXA1k-EI0.4 coating (once coating). Then, a modified facile coating workflow was carried out to acquire a novel twice coating (i.e. PDA/PMOXA1k-EI0.4+PMOXA1k-EI0.4 coated capillary) for highly sensitive and stable analysis of melamine. Under the optimal conditions, the linear response of melamine concentration ranged from 6.25 to 100 µg/mL with high correlation coefficient of 0.9910, and the limit of detection (LOD) for melamine was 0.097 µg/mL. The minimum amount of melamine determined in milk powder with our proposed method was 4 mg/kg. The recoveries and relative standard deviations (RSDs) were 92.13-102.47%, 92.22-100.30%, 2.07-4.98%, and 2.43-3.77%, respectively for the intraday and interday analysis. After being used continually for 45 days, the PDA/PMOXA1k-EI0.4+PMOXA1k-EI0.4 coated capillary could be still used to detect the melamine from milk powder, with the recovery from 91.85% to 106.14%. The technique developed in this study provides a simple and relatively sensitive method for determination of melamine in milk powder.

Stable antifouling coatings by hydrogen-bonding interaction between poly(2-methyl-2-oxazoline)- block -poly(4-vinyl pyridine) and poly(acrylic acid)

Surface modified with so-called protein-repellent or antifouling polymers has become indispensable for the development of modern therapeutic and diagnostic medical devices. In this work, a series of novel well-defined poly(2-methyl-2-oxazoline)-block-poly(4-vinyl pyridine) (PMOXA-b-P4VP) diblock copolymers were synthesized by using copper-catalyzed azide-alkyne cycloaddition reaction of α-alkynyl-PMOXA and ω-N3-P4VP, in which α-alkynyl-PMOXA and ω-N3-P4VP were prepared by cationic ring opening polymerization and atom transfer radical polymerization, respectively. Stable coatings were formed when dropping PAA solution on the top of PMOXA-b-P4VP pre-coatings, due to hydrogen-bonding interaction between P4VP and poly(acrylic acid) (PAA). The long-term stability of these PMOXA-b-P4VP/PAA coatings showed that increasing PMOXA chain length can improve not only the hydrophilicity but also the stability of the coatings. This simple method can form stable coatings on either inorganic (such as, silicon wafer and coverslip) or organic material [such as, poly(methyl methacrylate) sheet] surface. At the same time, for the high-hydratability of PMOXA chains, these crosslinked coatings showed well protein-resistant and platelet/cell-repellent properties, and the antifouling properties and long-term availability were enhanced increasing PMOXA polymerization degree.

Poly (2-methyl-2-oxazoline) coating by thermally induced immobilization for determination of bovine lactoferrin in infant formula with capillary electrophoresis

In this work, a one-step coating procedure by a simple annealing protocol of poly (2-methyl-2-oxazoline)-random-glycidyl methacrylate (PMOXA-r-GMA) copolymer was used to yield covalent and cross-linked PMOXA-based antifouling coating on a fused-silica capillary inner surface, which was used to determine the bovine lactoferrin (Lf) in infant formula by capillary electrophoresis with ultraviolet (CE-UV) detection. The X-ray photoelectron spectroscopy (XPS) confirmed that PMOXA-r-GMA could be bonded onto fused-silica capillary inner wall and stable electroosmotic flow (EOF) was obtained in the PMOXA-r-GMA coated capillary at pH 2.2-9.0. The separation of a mixture of four basic proteins indicated that the PMOXA-r-GMA coated capillary exhibited excellent separation efficiency for the basic proteins. Therefore, the PMOXA-r-GMA coated capillary was used to determine the quantity of Lf in infant formula. Under the optimal conditions, the peak area (A) and the concentration of Lf showed a good linear relationship within the range of 10-500μg/mL with a linear correlation coefficient of 0.9995. The limit of detection (LOD) and limit of quantitation (LOQ) for Lf were 5.0μg/mL and 16.7μg/mL, respectively. The recoveries at spiked concentrations of 0.20 and 0.40mg/mL Lf in infant formula were 97.1±5.5% - 97.8±5.1%. The determined values of Lf in infant formula samples with Lf were consistent with the nominal values, indicating that our CE method could be successfully applied to the quantitative analysis of Lf in commercial infant formula.

Pseudopeptide polymer coating for improving biocompatibility and corrosion resistance of 316L stainless steel

This article described for the first time using a pseudopeptide polymer, poly(2-methyl-2-oxazoline) (PMOXA), to form a bionic non-brush coating on a 316L stainless steel surface by electrochemical assembly for improving biocompatibility and corrosion resistance. In order to produce a stable coating, dopamine (DA) and partially hydrolysed PMOXA (H-PMOXA) were used to assemble on the surfaces of the 316L stainless steel via electrochemical oxidation and a Michael addition between the multi-imino groups of H-PMOXA and poly(dopamine). The effect of the molecular weights and hydrolysis degree of PMOXA on the formed coatings with respect to the biocompatibility and corrosion resistance of the modified stent materials were studied in detail. The results showed that the coating formed by PMOXA with moderate molecular weights and hydrolysis degree possessed excellent anti-fouling properties and biocompatibility. Moreover, the migration and proliferation of Human Umbilical Vein Endothelial Cells (HUVECs) on this kind of coating were also greatly enhanced.

Reversible Protein Adsorption on PMOXA/PAA Based Coatings: Role of PAA

In this study we report design of stimuli-responsive coating based on poly(2-methyl-2-oxazoline-random-glycidyl methacrylate) (PMOXA-r-GMA) comb copolymer and poly(acrylic acid)-block-poly(glycidyl methacrylate) (PAA-b-PGMA) block copolymers and scrutinize its ability to control protein adsorption. Firstly, PMOXA/PAA based coatings were prepared by simply spin coating the mixture of PMOXA-r-GMA and PAA-b-PGMA copolymer solutions onto silicon substrates followed by annealing at 110 °C. Then coatings were rigorously characterized by X-ray photoelectron spectroscopy (XPS), the static water contact angle (WCA) test, ellipsometry and atomic force microscopy (AFM). After that, the relationship of switchable behavior of PMOXA/PAA based coatings with PAA content and chain length was investigated through the change of thickness and WCA upon pH and ionic strength (I) trigger, which indicated that the change in thickness and WCA was triggered when PAA contents were increased as well as by increasing chain length of PAA in PMOXA/PAA based coatings. Finally, real-time adsorption/desorption of lysozyme (Lyso) on PMOXA/PAA based coatings was monitored using quartz crystal microbalance with dissipation monitoring (QCM-D). The results showed that the Lyso adsorption amount was increased upon increasing chain length and contents of PAA in PMOXA/PAA based coatings. The adsorbed Lyso was then efficiently desorbed by changing pH and I of medium with the maximum desorption (> 90% desorption percentage) observed for the suitable ratio of PMOXA and PAA while chain length of PAA was kept longer than that of PMOXA. Furthermore, the prepared coatings were found to repeatedly adsorb and desorb Lyso for four successive cycles of adsorption/desorption, which confirmed the stability of prepared coatings.