Jingchuan Liu

Surface modification of poly(styrene-b-(ethylene-co-butylene)-b-styrene) elastomer via UV-induced graft polymerization of N-vinyl pyrrolidone

Poly(N-vinyl pyrrolidone) (PNVP) was covalently grafted onto the surface of biomedical poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) elastomer via a technique of UV-induced graft polymerization combined with plasma pre-treatment. The surface graft polymerization of N-vinyl pyrrolidone (NVP) was confirmed by ATR-FTIR and XPS. Effect of the parameters of graft polymerization, i.e., the initiator concentration, the UV irradiation time and the monomer concentration on the grafting density was investigated. The morphology and the wettability of the PNVP-modified surfaces were characterized by AFM and DSA, respectively. Protein adsorption and platelet adhesion were obviously suppressed after PNVP was grafted onto the SEBS substrates.

Fabrication of a Detection Platform with Boronic-Acid-Containing Zwitterionic Polymer Brush

Development of technologies for biomedical detection platform is critical to meet the global challenges of various disease diagnoses, especially for point-of-use applications. Because of its natural simplicity, effectiveness, and easy repeatability, random covalent-binding technique is widely adopted in antibody immobilization. However, its antigen-binding capacity is relatively low when compared to site-specific immobilization of antibody. Herein, we report that a detection platform modified with boronic acid (BA)-containing sulfobetaine-based polymer brush. Mainly because of the advantage of oriented immobilization of antibody endowed with BA-containing three-dimensional polymer brush architecture, the platform had a high antigen-binding capacity. Notably, nonspecific protein adsorption was also suppressed by the zwitterionic pendants, thus greatly enhanced signal-to-noise (S/N) values for antigen recognition. Furthermore, antibodies captured by BA pendants could be released in dissociation media. This new platform is promising for potential applications in immunoassays.

Intra-day variability observations of S5 0716+714 over 4.5 years at 4.8 GHz

Aims. We aim to search for evidence of annual modulation in the time scales of the BL Lac object S5 0716+714.

Improving hemocompatibility of polypropylene via surface-initiated atom transfer radical polymerization for covalently coupling BSA

Bovine serum albumin (BSA) modified polypropylene (PP) was fabricated via surface-initiated atom transfer radical polymerization (SI-ATRP) of poly(ethylene glycol) methacrylate (PEGMA) and glycidyl methacrylate (GMA). Kinetics study revealed an approximately linear increase in graft density of the functional brushes with polymerization time. Attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy confirmed that comonomers and BSA were successfully immobilized onto PP film. The hydrophilicity of PP was improved by modification with PEGMA and GMA. The balance between the inhibition of BSA adsorption by PEGMA and the covalent immobilization of BSA by GMA through the ring-opening reaction of the epoxy group resulted in the moderate fluorescence intensity of FITC–BSA immobilized PP-g-P (PEGMA-co-GMA). The hemolysis test showed that BSA could decrease the hemolysis rate. Red blood cell membrane maximal stress can be reduced by the inertness of BSA as well as the repulsion caused by its electrostatic interactions. Whole blood cell attachment tests showed that BSA molecules weakened the interaction between blood cells and the PP surface. Therefore, the immobilization of BSA on PP film is an effective approach for improving the hemocompatibility of PP.

Stimuli-Responsive Polypropylene for the Sustained Delivery of TPGS and Interaction with Erythrocytes

Hemocompatibility and oxidative stress are significant for blood-contacting devices. In this study, N-isopropylacrylamide (NIPAAm) and N-(3-aminopropyl)methacrylamide hydrochloride (APMA) were cografted on polypropylene (PP) membrane using ultraviolet grafting to load antioxidative d-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) and control the release of TPGS. The immobilization of NIPAAm and APMA onto PP membrane was confirmed by attenuated total reflectance Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Combined with data from platelet adhesion, red blood cell (RBC) attachment, and hemolysis rate, the hemocompatibility of PP was significantly improved. An in-depth characterization using hemolysis rate test, scanning electron microscopy, atomic force microscopy, and confocal laser scanning microscopy was conducted to confirm that the mechanism of the release of TPGS interacted with RBCs was different at different stages. The release of TPGS from the loading PP membranes affected hemolysis at different stages. At the early stage of release, TPGS maintained the tiny (nanometer-sized) tubers on the membrane surface and enhanced the membrane permeabilization by generating nanosized pores on the cell membranes. Afterward, the incorporated TPGS slowed the lipid peroxidation of erythrocytes and filled in the lipid bilayer of erythrocyte to prevent hemolysis. Thus, the approach implemented to graft NIPAAm and APMA and load TPGS was suitable to develop medical device with excellent hemocompatibility and antioxidative property.

Effect of grafted PEG chain conformation on albumin and lysozyme adsorption: A combined study using QCM-D and DPI

In this study, elucidation of protein adsorption mechanism is performed using dual polarization interferometry (DPI) and quartz crystal microbalance with dissipation (QCM-D) to study adsorption behaviors of bovine serum albumin (BSA) and lysozyme (LYZ) on poly (ethylene glycol) (PEG) layers. From the analysis of DPI, PEG2000 and PEG5000 show tight and loose mushroom conformations, respectively. Small amount of LYZ could displace the interfacial water surrounding the tight mushroomed PEG2000 chains by hydrogen bond attraction, leading to protein adsorption. The loose mushroomed PEG5000 chains exhibit a more flexible conformation and high elastic repulsion energy that could prevent protein adsorption of all BSA and most of LYZ. From the analysis of QCM, PEG2000 and PEG5000 show tight and extended brush conformations. The LYZ adsorbed mass has critical regions of PEG2000 (0.19 chain/nm(2)) and PEG5000 (0.16 chain/nm(2)) graft density. When graft density of PEG is higher than the critical region (brush conformations), the attraction of hydrogen bonds between PEG and LYZ is the dominant factor. When graft density of PEG is lower than the critical region (mushroom conformations), elastic repulsion between PEG and proteins is driven by the high conformation entropy of PEG chains, which is the dominant force of steric repulsion in PEG-protein systems. Therefore, the adsorption of BSA is suppressed by the high elastic repulsion energy of PEG chains, whereas the adsorption of LYZ is balanced by the interactions between the repulsion of entropy elasticity and the attraction of hydrogen bonds.

Hemocompatible, antioxidative and antibacterial polypropylene prepared by attaching silver nanoparticles capped with TPGS

Infections associated with medical devices cause significant costs, morbidity, and mortality. Medical devices with hemocompatibility, antioxidative stress, and antibacterial properties are difficult to fabricate. In this study, silver nanoparticles (Ag NPs) were synthesized for the first time in the presence of carboxylic d-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) as antibacterial agents. The Ag NPs were characterized by UV-visible spectroscopy, transmission electron microscopy, and zeta potential measurements. The results showed that Ag NPs had a good dispersion stability and uniform size distribution. The introduction of TPGS dispersed the Ag NPs in solution and provided active protection against Ag NP-induced free radical damage. N-Isopropylacrylamide (NIPAAm) and N-(3-aminopropyl) methacrylamide hydrochloride (APMA) were then co-grafted onto polypropylene (PP) membranes by ultraviolet grafting, which can provide antifouling properties. The modified PP surface can be used as a platform to load the Ag NPs capped with TPGS. The loading efficiency of Ag NPs was mediated by electrostatic interactions between the positively charged APMA and the negatively charged Ag NPs. The loaded TPGS can slow the lipid peroxidation of erythrocytes and fill the lipid bilayer of erythrocytes to prevent antioxidative stress and hemolysis. The bacteria adhesion, bacterial activity, and biofilm formation proved that the modified PP surfaces loaded with Ag NPs had excellent antibacterial and bactericidal properties. Therefore, our approach can serve as a basis for developing medical devices with excellent hemocompatibility, as well as simultaneous antioxidative and antibacterial properties, thereby providing a potential prevention measure of medical-device-associated infections.

Immobilization of nattokinase-loaded red blood cells on the surface of superhydrophobic polypropylene targeting fibrinolytic performance

A platform for capture and release of drug-loaded red blood cells (RBCs) is demonstrated by utilizing polymer grafted superhydrophobic polypropylene (PP). Combined with micro/nanobinary structures, thermoresponsive polymers, and lectin-saccharides recognition, this platform enables highly efficient capture and release of RBCs loaded with nattokinase, which endows PP with potent fibrinolytic ability.

Intra-day variability observations and the VLBI structure analysis of quasar S4 0917+624

The IDV observations of S4 0917+624 were carried out monthly, from August 2005 to January 2010, with the Urumqi 25m radio telescope at 4.8 GHz. The quasar S4 0917+624 exhibits only very weak or no IDV during our 4.5 year observing interval. Prior to the year 2000, the source S4 0917+624 was one of the most prominent IDV sources. Our new data indicate that the previous strong IDV has ceased. We analyzed the long-term VLBI structural variability using Gaussian model-fitting. From this we obtained the flux densities and the deconvolved sizes of core and inner-jet components of the source. We studied the properties such as core fraction, angular size, spectral index, and brightness temperature of VLBI core for S4 0917+624, as well as the time delay between 5 and 15 GHz variations, and compared them with the IDV properties of S4 0917+624. The source shows ejection of several jet components that are suspected to have partially reduced the IDV amplitude of S4 0917+624. However, during 2005-2006, the VLBI core size was comparable to the size before the year 2000, but no strong IDV was detected in the period, suggesting that the quenching effect due to source size changes may not be responsible for the lack of strong IDV after the year 2000. The refractive scattering properties for the strong IDV phase of S4 0917+624 before the year 2000 are discussed. The disappearance of strong IDV in S4 0917+624 after the year 2000 is a mystery and cannot be explained via the quenching effect by changes in the observable VLBI structure. However, it may be caused by changes in the interstellar medium, i.e. by interstellar weather, which induces changes in the scintillation pattern on timescales of several years. Further coordinated multi-frequency observations will be required to distinguish between the effect of source-intrinsic variability and changing properties of the interstellar medium.

Facile Fabrication of Hierarchically Thermoresponsive Binary Polymer Pattern for Controlled Cell Adhesion

A versatile platform allowing capture and detection of normal and dysfunctional cells on the same patterned surface is important for accessing the cellular mechanism, developing diagnostic assays, and implementing therapy. Here, an original and effective method for fabricating binary polymer brushes pattern is developed for controlled cell adhesion. The binary polymer brushes pattern, composed of poly(N-isopropylacrylamide) (PNIPAAm) and poly[poly(ethylene glycol) methyl ether methacrylate] (POEGMA) chains, is simply obtained via a combination of surface-initiated photopolymerization and surface-activated free radical polymerization. This method is unique in that it does not utilize any protecting groups or procedures of backfilling with immobilized initiator. It is demonstrated that the precise and well-defined binary polymer patterns with high resolution are fabricated using this facile method. PNIPAAm chains capture and release cells by thermoresponsiveness, while POEGMA chains possess high capability to capture dysfunctional cells specifically, inducing a switch of normal red blood cells (RBCs) arrays to hemolytic RBCs arrays on the pattern with temperature. This novel platform composed of binary polymer brush pattern is smart and versatile, which opens up pathways to potential applications as microsensors, biochips, and bioassays.