Surface modification of a biocompatible polymer based on polyurethane for artificial blood vessels

An OH-functionalized poly(carbonate urethane) (PCU) is used for developing a new antithrombogenic surface. Biomolecules like glycine or the fibronectin fragment Gly-Arg-Gly-Asp-Ser (GRGDS) are covalently bound to the PCU surface by succinyl dichloride coupling. The modification steps are controlled by infrared spectroscopy and amino acid analysis. Successfully modified films are tested under stationary cell culture conditions.This paper was presented at thebiomat 90 Conference.     

Surface modification of poly(dimethylsiloxane) microfluidic devices by ultraviolet polymer grafting

Poly(dimethylsiloxane) (PDMS)-based microfluidic devices are increasing in popularity due to their ease of fabrication and low costs. Despite this, there is a tremendous need for strategies to rapidly and easily tailor the surface properties of these devices. We demonstrate a one-step procedure to covalently link polymers to the surface of PDMS microchannels by ultraviolet graft polymerization. Acrylic acid, acrylamide, dimethylacrylamide, 2-hydroxylethyl acrylate, and poly(ethylene glycol)monomethoxyl acrylate were grafted onto PDMS to yield hydrophilic surfaces. Water droplets possessed contact angles as low as 45 degrees on the grafted surfaces. Microchannels constructed from the grafted PDMS were readily filled with aqueous solutions in contrast to devices composed of native PDMS. The grafted surfaces also displayed a substantially reduced adsorption of two test peptides compared to that of oxidized PDMS. Microchannels with grafted surfaces exhibited electroosmotic mobilities intermediate to those displayed by native and oxidized PDMS. Unlike the electroosmotic mobility of oxidized PDMS, the electroosmotic mobility of the grafted surfaces remained stable upon exposure to air. The electrophoretic resolution of two test peptides in the grafted microchannels was considerably improved compared to that in microchannels composed of oxidized PDMS. By using the appropriate monomer, it should be possible to use UV grafting to impart a variety of surface properties to PDMS microfluidics devices.     

Adjuvant properties of a biocompatible thermo-responsive polymer of N-isopropylacrylamide in autoimmunity and arthritis

To evaluate the thermo-responsive poly(N-isopropylacrylamide) (PNiPAAm) polymer as an adjuvant, we synthesized PNiPAAm through free radical polymerization and characterized it both in vitro and in vivo. The polymer when mixed with collagen type II (CII) induced antigen-specific autoimmunity and arthritis. Mice immunized with PNiPAAm–CII developed significant levels of CII-specific IgG response comprising major IgG subclasses. Antigen-specific cellular recall response was also enhanced in these mice, while negligible level of IFN-γ was detected in splenocyte cultures, in vitro. PNiPAAm–CII-immunized arthritic mouse paws showed massive infiltration of immune cells and extensive damage to cartilage and bone. As determined by immunostaining, most of the CII protein retained its native configuration after injecting it with PNiPAAm in naive mice. Physical adsorption of CII and the high-molecular-weight form of moderately hydrophobic PNiPAAm induced a significant anti-CII antibody response. Similar to CII, mice immunized with PNiPAAm and ovalbumin (PNiPAAm–Ova) induced significant anti-ovalbumin antibody response. Comparable levels of serum IFN-γ, IL-1β and IL-17 were observed in ovalbumin-immunized mice with complete Freund, incomplete Freund (CFA and IFA) or PNiPAAm adjuvants. However, serum IL-4 levels were significantly higher in PNiPAAm–Ova and CFA–Ova groups compared with the IFA–Ova group. Thus, we show for the first time, biocompatible and biodegradable thermo-responsive PNiPAAm can be used as an adjuvant in several immunological applications as well as in better understanding of the autoimmune responses against self-proteins.     

Surface treatment for adhesive-bonded joints by excimer laser

In this work a treatment for surface preparation to improve mechanical resistance in adhesive bonding of plastic composites reinforced with fibres and metallic material, has been performed using an excimer laser. The following couplings have been selected to reproduce joints commonly used in the aerospace and automotive industry: CFC (carbon fibre composite) with CFC, CFC with Al 2024T3, Al 99% with Al 99%, GFC (glass fibre composite) with zinc-coated sheet in low carbon steel FeP01. The surfaces have been prepared using an excimer laser, adopting several values of laser parameters. The obtained surfaces have been examined by optical and scanning electron microscope: comparative measures of wetting and roughness have been performed to obtain an accurate characterisation and to select the proper finishes suitable to improve the mechanical resistance of the joints. The results obtained show that laser treatment always improves the final resistance of the joint; notable increases, and no significant surface damages have been highlighted. Better results have been obtained with the Al 99% with Al 99% joints which, with a low number of pulses treatment, have shown an increase of mechanical resistance up to the 70%.     

Patterned layers of a semiconducting polymer via imprinting and microwave-assisted grafting

Enhancements in both the rate and extent of grafting of poly(9,9'-n-dihexyl fluorene) (PDHF) onto flat and nanopatterned crosslinked photopolymer films are described. Reactivity of the surfaces toward grafting via the Yamamoto-type Ni(0)-mediated coupling reaction is increased by synthesizing and incorporating 2,7-dibromo-9-fluorenyl methacrylate (DBFM, 2) as a new grafting agent. Varying the concentration of surface-embedded DBFM is shown to control both overall graft formation and fluorescence with a maximum thickness of up to 30 nm and peak emission at 407 nm for 40 wt% loading. In addition, microwave irradiation is introduced as an effective means to drive graft formation and thus allows fabrication of PDHF-functionalized surfaces in as little as 30 min. Both forms of improvement are extended to DBFM-embedded, nanocontact-molded features ranging in size from 100 microm to 100 nm in width and 60 nm in height. Microwave-assisted grafting from these patterned surfaces produces fluorescent features as imaged by optical microscopy and a corresponding increase in feature height as measured by atomic force microscopy.     

Surface modification and functionalization of electroactive polymer films via grafting of polyelectrolyte,polyampholyte and polymeric acids

Films of electroactive polymers, such as polyaniline (PAN) in its emeraldine base form, and poly(3-alkylthiophene), poly(3-hexylthiophene) (P6TH), poly(3-octylthiophene) (P8TH), and poly(3-dodecylthiophene) (P12TH) can be readily functionalized via thermal or near ultraviolet-light-induced surface graft copolymerization with monomers of polyelectrolyte, polyampholyte and polymeric acids. The monomers used in the present work include dimethyl sulphate quaternized dimethylamino-ethylmethacrylate (DMAEM·C₂H₆SO₄), 3-dimethyl(methacryloyloxyethyl)ammonium propane sulphonate (DMAPS), acrylic acid (AAc) and a sodium salt of styrene sulphonic acid (NaSS). The surface structures and compositions of the electroactive polymer films after functionalization via graft copolymerization were characterized by angle-resolved X-ray photoelectron spectroscopy. Graft copolymerization of poly(3-alkylthiophene) films, but not PAN films, with the hydrophilic monomers readily results in a stratified surface microstructure arising from the migration of the hydrophilic graft chains beneath a thin surface layer which is much richer in the substrate chains. On the other hand, graft copolymerization of PAN films with AAc and NaSS readily gives rise to a self-protonated (and thus conductive) surface structure.     

Surface modification of nano-TiO2 with trimellitylimido-amino acid-based diacids for preventing aggregation of nanoparticles

Nanoparticles (NPs) are an essential material for science and technology, for instance in materials, medicals, and cosmetics. Controlling the dispersion of NPs is necessary to manage the properties of the final products. For this reason the surface modification of NPs is done by many techniques. In this work Nano-TiO₂ were modified using methanol as solvent and diacids based on natural amino acids as modifier at room temperature and using ultrasonic irradiation. Diacids were grafted onto the surface of TiO₂ NPs to improve the dispersion of the particles. The obtained modified TiO₂ were characterized by Fourier transform IR spectroscopy (FT-IR), X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) techniques. These analyses proved this modification process at room temperature was possible. TEM and FE-SEM showed that fairly good dispersed TiO₂ NPs were obtained after surface modification. Since TiO₂ and diacids which were used in this work are biologically active, the modified powder would be environmentally friendly.     

Patterned immobilization of biomolecules on a polymer surface functionalized by radiation grafting

Patterned graft polymerization of a functional monomer on a hydrophobic polymer surface was proposed for biomolecule patterning. A poly(vinylidene fluoride) (PVDF) film surface was selectively activated by ion implantation through a pattern mask and acrylic acid (AA) was then graft polymerized onto the activated regions of the PVDF surfaces. The peroxide concentration on the implanted surface depended on the fluence, which had a considerable effect on the grafting degree of AA. Afterwards, amine-functionalized biotin and probe DNA were immobilized on the poly(acrylic acid)-grafted regions of the PVDF surfaces. Specific binding of biotin with streptavidin and hybridization of probe DNA with complimentary DNA proved successful protein and DNA patterning and well-defined 50 microm dot-type patterns of the streptavidin and DNA were obtained. These results confirmed the potential of this strategy for patterning of various biomolecules.     

Interpenetrating polymer network hydrogel scaffolds for artificial cornea periphery

Three-dimensional scaffolds based on inverted colloidal crystals (ICCs) were fabricated from sequentially polymerized interpenetrating polymer network (IPN) hydrogels of poly(ethyleneglycol) and poly(acrylic acid). This high-strength, high-water-content IPN hydrogel may be suitable for use in an artificial cornea application. Development of a highly porous, biointegrable region at the periphery of the artificial cornea device is critical to long-term retention of the implant. The ICC fabrication technique produced scaffolds with well-controlled, tunable pore and channel dimensions. When surface functionalized with extracellular matrix proteins, corneal fibroblasts were successfully cultured on IPN hydrogel scaffolds, demonstrating the feasibility of these gels as materials for the artificial cornea porous periphery. Porous hydrogels with and without cells were visualized non-invasively in the hydrated state using variable-pressure scanning electron microscopy.     

Bioinspired phospholipid polymer biomaterials for making high performance artificial organs

Novel polymer biomaterials, which can be used in contact with blood, are prepared with strong inspiration from the surface structure of biomembrane. That is, the polymers with a phospholipid polar group in the side chain, 2-methacrylooyloxyethyl phosphorylcholine (MPC) polymers were synthesized. The MPC polymers can inhibit surface-induced clot formation effectively, when they are in contact with blood even in the absence of an anticoagulant. This phenomenon was due to the reduction of plasma protein and suppression of denaturation of adsorbed proteins, that is the MPC polymers interact with blood components very mildly. As the molecular structure of the MPC polymer was easily designed by changing the monomer units and their composition, it could be applied to surface modification of artificial organs and biomedical devices for improving blood and tissue compatibility. Thus, the MPC polymers are useful polymer biomaterials for manufacturing high performance artificial organs and biomedical devices to provide safe medical treatments.     

聚偏氟乙烯基聚合物电解质接枝改性研究进展

聚偏氟乙烯基聚合物是锂离子电池用聚合物电解质较理想的基质材料,但也存在结晶度高、亲液性差等问题。主要综述了采用γ射线、电子束、紫外等辐射,原子转移自由基聚合及溶液接枝聚合等方法接枝苯乙烯、甲基丙烯酸缩水甘油酯、新戊二醇二丙烯酸酯、聚甲基丙烯酸甲酯、三丙烯乙二醇醚醋酸酯、聚乙二醇甲基丙烯酸酯、2-丙烯酰胺基-2-甲基丙磺酸、聚乙二醇等对聚偏氟乙烯基聚合物电解质的改性研究进展。接枝改性后的聚偏氟乙烯聚合物电解质对电解液的亲和性、离子电导率、电化学稳定性和循环性能都有一定程度的提高。     

Surface hardening of biocompatible ultrafine-grained niobium zirconium alloy by two-stage oxidation treatment

The present study reports on an optimized surface hardening process for biocompatible ultrafine-grained (UFG) niobium 2.3 wt% zirconium (NbZr) alloy, a promising candidate implant material. The as-received material of conventional grain size (CG) was processed using multipass equal channel angular processing at room temperature to obtain an UFG microstructure featuring high strength and ductility. Subsequent surface hardening was performed by a heat treatment leading to internal oxidation. Using a thermogravimetric system, the influence of temperatures, time, and partial pressure of oxygen ( $ p_{{\text{O}}_2} $ ) on the oxidation kinetics were investigated. Metallographic and microscopic analyses and hardness measurements were employed to evaluate maximum hardness, penetration-depth and scale formation under various conditions. Heat treatment at 620 °C for 6 h at a $ p_{{\text{O}}_2} $ of 0.2 hPa led to sufficiently rapid oxidation kinetics yielding a relatively high depth of penetration without formation of loose Nb₂O₅ on the surface, which was observed at higher $ p_{{\text{O}}_2} $ . As compared to CG material, improved hardness profiles were reached using the same heat treatment parameters, since the UFG structure significantly changes diffusion conditions and therefore oxidation kinetics. After a second heat treatment in high vacuum the high maximum hardness of 820 HV0.01 in the UFG material was reduced effectively and a less steep hardness gradient was achieved, both contributing to a less brittle behavior under mechanical loading. High-cycle fatigue tests performed on surface-hardened UFG NbZr samples showed a substantial improvement of fatigue life in tests conducted near the endurance limit. Especially when high fatigue and wear resistance are key issues for a given application, the internal oxidation process offers an effective way to further improve the properties of UFG NbZr.     

空心玻璃微球表面接枝聚苯乙烯及其性能研究

空心玻璃微球表面改性有利于改善其与基体间的相容性,提高复合泡沫性能.通过接枝聚苯乙烯对空心玻璃微球进行表面处理,采用SEM、IR、热失重等方法分析了反应条件对接枝的影响.结果表明,接枝反应过程中提高反应温度、延长反应时间有利于接枝率的提高,但温度过高会加速单体自聚,降低接枝率.接枝处理后,随着聚合物层的增厚,空心玻璃微球表面缺陷减小,破损率降低,抗压强度得到一定程度提高.