Improvement of hemocompatibility of polycaprolactone film surfaces with zwitterionic polymer brushes

Polycaprolactone (PCL) has been widely adopted as a scaffold biomaterial, but further improvement of the hemocompatibility of a PCL film surface is still needed for wide biomedical applications. In this work, the PCL film surface was functionalized with zwitterionic poly(3-dimethyl(methacryloyloxyethyl) ammonium propane sulfonate) (P(DMAPS)) brushes via surface-initiated atom transfer radical polymerization (ATRP) for enhancing hemocompatibility. Kinetics study revealed an approximately linear increase in graft yield of the functional P(DMAPS) brushes with polymerization time. The blood compatibilities of the modified PCL film surfaces were studied by platelet adhesion tests of platelet-rich plasma and human whole blood, hemolysis assay, and plasma recalcification time (PRT) assay. The improvement of hemocompatibility is dependent on the coverage of the grafted P(DMAPS) brushes on the PCL film. Lower or no platelet and blood cell adhesion was observed on the P(DMAPS)-grafted film surfaces. The P(DMAPS) grafting can further decrease hemolysis and enhance the PRT of the PCL surface. With the versatility of surface-initiated ATRP and the excellent hemocompatibility of zwitterionic polymer brushes, PCL films with desirable blood properties can be readily tailored to cater to various biomedical applications.     

Synthesis and characterization of poly(2‐methacryloyloxyethyl phosphorylcholine) onto graphene oxide

The polyzwitterionic brushes comprised of poly(2‐methacryloyloxyethyl phosphorylcholine) (pMPC) segments, which are used for surface modification of polymers and biocompatible coatings, were investigated. In this work, reverse surface‐initiated atom transfer radical polymerization (RATRP) of zwitterionic 2‐methacryloyloxyethyl phosphorylcholine (MPC) is employed to tailor the functionality of graphene oxide (GeneO) in a well‐controlled manner and produce a series of well‐defined hemocompatible hybrids (termed as GeneO‐g‐pMPC). The complexes were characterized by FT‐IR, XRD, and Raman. Results show that MPC has been coordinated on the graphene oxide sheet. Thermal stability of the nanocomposites in comparison with the neat copolymer is revealed by thermogravimetric analysis and differential thermal analysis. Scanning electron microscopy and transmission electron microscope images of the nanoconposite displays pMPC chains were capable of existing on GeneO sheet by RATRP. The biocompatibility properties were measured by plasma recalcification profile tests, hemolysis test, and MTT assays, respectively. The results confirm that the pMPC grafting can substantially enhance the hemocompatibility of the GeneO particles, and the GeneO‐g‐pMPC hybrids can be used as biomaterials without causing any hemolysis. With the versatility of RATRP and the excellent hemocompatibility of zwitterionic polymer chains, the GeneO‐g‐pMPC nanoparticles with desirable blood properties can be readily tailored to cater to various biomedical applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Fibrous membranes electrospinning from acrylonitrile-based polymers: specific absorption behaviors and states of water

Fibrous membranes with a fiber diameter ranging from 80 to 800 nm are prepared from polyacrylonitrile and poly[acrylonitrile-co-(N-vinyl-2-pyrrolidone)] by the electrospinning process. The parameters can be controlled to fabricate fibrous membranes with similar fiber diameters (between 600 and 800 nm) for further studies on the swelling behaviors and water states. Water swelling experiments indicate that the fibrous membrane has a great capacity for water sorption, which reaches a maximum in a few minutes because of its extremely high porosity. Furthermore, a remarkable overshoot occurs as a result of polymer chain relaxation and the non-compact structure of the fibrous membranes. Contrary to the dense membrane, the equilibrium water content in the fibrous membrane decreases with the content of hydrophilic NVP though the maximum is almost the same. Results from DSC experiments demonstrate that only non-freezable bound water and free water can be distinguished in the fibrous membrane. On the basis of the results of water swelling and DSC experiments, it is concluded that the specific behaviors of the fibrous membranes are induced by the non-compact and pore-fiber discontinuous structure, which is different from either dense membranes or hydrogels. [GRAPHS: SEE TEXT] DSC curves of fully swollen electrospun fibrous membranes and of fully swollen dense membranes with different NVP contents.     

Depth profiling of latex blends of fluorinated and fluorine‐free acrylates with laser‐induced secondary mass spectrometry

We explored phase separation and self‐assembly of perfluoroalkyl segments at the surface of polymer films obtained from latices of semifluorinated acrylate copolymers and the corresponding latex blends of nonfluorinated and semifluorinated polyacrylates. With laser‐induced secondary mass spectrometry the fluorine distribution was measured after annealing above the minimum film‐forming temperature of the polymers up to a depth of several micrometers. Depth profiles of a semifluorinated acrylate homopolymer and latex blends thereof with fluorine‐free alkylacrylates with 25, 50, and 75 mol % semifluorinated acrylate as well as a copolymer comprised of alkyl acrylate and semifluorinated acrylate (50/50 mol %) were investigated. In the case of latex blends containing both semifluorinated polyacrylates and fluorine‐free or low‐fluorine polymers, self‐assembly accounted for enrichment of the perfluoroalkyl segments at the surface. Coatings exhibiting low surface energy and having a substantially reduced total fluorine content were obtained. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 360–367, 2003     

光引发N-乙烯基吡咯烷酮在嵌段聚醚聚氨酯膜上接枝聚合的研究

本文研究了在碱性介质中,氮气氛下 N-乙烯基吡咯烷酮(N-VP)在嵌段聚醚聚氨酯(SPEU)膜上的接枝聚合。测定了接枝率与接枝液中 N-VP单体浓度、光照时间、催化剂浓度等条件的关系。测定了接枝后 SPEU 膜的吸水性,并用扫描电镜对膜表面进行了观察。对碱性介质中的接枝机理进行了初步探讨。     

Preparation and characterization of nonfouling polymer brushes on poly(ethylene terephthalate) film surfaces

In this study, a surface grafting of nonfouling poly(ethylene glycol) methyl ether acrylate (PEGMA) on poly(ethylene terephthalate) (PET) was carried out via surface-initiated atom-transfer radical polymerization (SI-ATRP) to improve hemocompatibility of polymer based biomaterials. To do this, the coupling agent with hydroxyl groups for the ATRP initiator was first anchored on the surface of PET films using photochemical method, and then these hydroxyl groups were esterified by bromoisobutyryl bromide, from which PET with various main chain lengths of PEGMA was prepared. The structures and properties of modified PET surfaces were investigated using water contact angle (WAC), ATR-FTIR, X-ray photoelectron spectroscopy (XPS) and Atomic force microscopy (AFM). The molecular weights of the free polymer from solution were determined by gel permeation chromatography (GPC). These results indicated that grafting of PEGMA on PET film is a simple way to change its surface properties. The protein adsorption resistance on the surfaces of PET was primarily evaluated by an enzyme-linked immunosorbent assay (ELISA). The result demonstrated that the protein adsorption could be well suppressed by poly(PEGMA) brush structure on the surface of PET. This work provides a new approach for polymers to enhance their biocompatibility.     

Sorption and swelling in ultra-thin polymer films

Different polymers were investigated with respect to the sorption of solvents and gases. Depending on the chemical nature of the polymers this sorption leads to polymer swelling. The degree of swelling D/D₀ was measured utilizing Small angle X-ray scattering (SAXS) as well as Surface plasmon resonance (SPR). From the change in film thickness after swelling in different solvents Hildebrand parameters of the polymers were determined. By crosslinking of the polymer films the degree of swelling can be controlled. In the case of ultra-thin polyimide films a higher degree of crosslinking led to a decreased selectivity of the transport of gases through the membrane. Reptation of macromolecules was also investigated and the influence of polymer swelling in different solvents has a great influence on the selectivity and diffusion coefficient.     

A novel quartz crystal microbalance gas sensor based on porous film coatings. A high sensitivity porous poly(methylmethacrylate) water vapor sensor

We describe a novel and generally applicable approach for creating voids in films deposited on the surface of solid substrates. Such films are advantageous when a quartz crystal microbalance (QCM) is the basis of a sensor. We show that films with large void volumes produce more sensitive sensors than with the original film. Poly(methylmethacrylate) (PMMA) was used as the polymer layer deposited on a quartz crystal microbalance (QCM) to demonstrate our technique for the model system of water vapor analysis in flowing nitrogen gas. A film of pure PMMA on a QCM is a sensor for water vapor in a gas phase. A more sensitive sensor was created by dip coating QCM crystals into solutions containing mixtures of PMMA and poly(d,l-lactide) (PDLL) and then evaporating the solution films on the QCM crystals to form mixed polymer films of varying PDLL content. The PDLL was then removed from the mixed polymer films by exposure to a NaOH solution to form pure PMMA films having various void volumes. A leached PMMA film that originally contained 50% by weight PDLL had a 3.7 times larger QCM sensitivity for water vapor than a pure PMMA film.     

Swelling Kinetics of Interpenetrating Polymer Hydrogels Composed of Poly(Vinyl Alcohol)/Chitosan

Interpenetrating polymer network (IPN) hydrogels based on poly(vinyl alcohol)/chitosan were prepared by UV irradiation. The swelling behavior of the IPN hydrogels was studied by immersion of the films in deionized water at various temperatures and in buffer solutions at various pHs. IPN3 exhibited a relatively high swelling ratio. The swelling ratio increased with an increase in the content of chitosan and were higher in acidic rather than in alkaline pHs. The overall swelling process was anomalous diffusion due to polymer relaxation. The diffusion coefficient values increased with an increase in temperature and the content of chitosan.     

Spontaneous film formation from a polymer solution

An unusual continuous film formation process of lateral pentyloxy substituted poly(p-phenylene terephthalate)s (s-PPPT) and poly(carbonate) (PC) is observed. A liquid film of polymer solution creeps over the surface of water dropped into the polymer solution. By vaporization of the solvent a solid polymer film is formed on the water surface and can be removed. The driving force for the film formation mechanism is assumed by the reduction of the surface tension of water. Experiments verify this mechanism by increasing the film formation speed using a gas stream, by reducing the formation speed through lowering the surface tension by rinsing agents, and by lowering the solubility of the polymer. As expected, no effects are found by variation of the pH-value of water. Necessary conditions for the film formation process are: good solubility of the polar polymers in organic solvents having a high vapor pressure, complete phase separation, solution density higher than water density, and a surrounding gas phase unsaturated with solvent vapor.The thickness of the mechanically stable films is less than 0.5 m. The films are amorphous by microscopical, FT-IR, x-ray, and DTA investigations.     

Swelling and biocompatibility of sodium alginate/poly(γ‐glutamic acid) hydrogels

Sodium alginate (Alg) hydrogel films were crosslinked with either calcium poly(γ‐glutamate) (Ca‐PGA) or CaCl₂. The hydrophilicity of the resulting hydrogel films was evaluated through swelling tests, water retention capacity tests, and water vapor permeation tests. The swelling ratio, water retention capacity, and the water vapor transmission rate (WVTR) of Alg/Ca‐PGA were higher than those of Ca‐Alg. The swelling ratio of Alg/Ca‐PGA was 651 and 190% at pH 7.4 and pH 1.2, respectively. The tensile strength of Alg/Ca‐PGA hydrogel was lower than that of Ca‐Alg. The results of hemocompatibility test showed that Alg/Ca‐PGA caused shorter activated partial thromboplastin time (APTT) than Ca‐Alg. Both Ca‐Alg and Alg/Ca‐PGA exhibited almost no adsorption of human serum albumin (HSA), whereas the adsorption of human plasma fibrinogen (HPF) of Ca‐Alg was 10 times of that of Alg/Ca‐PGA. In addition, Alg/Ca‐PGA exhibited platelet adhesion higher than Ca‐Alg. Furthermore, both Alg/Ca‐PGA and Ca‐Alg exhibited no cytotoxicity. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of physical aging of poly(1‐trimethylsilyl‐1‐propyne) films synthesized with TaCl5 and NbCl5 on gas permeability,fractional free volume,and positron annihilation lifetime spectroscopy parameters

The effect of physical aging on the gas permeability, fractional free volume (FFV), and positron annihilation lifetime spectroscopy (PALS) parameters of dense, isotropic poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) films synthesized with TaCl₅ and NbCl₅ was characterized. As‐cast films were soaked in methanol until an equilibrium amount of methanol was absorbed by the polymer. When the films were removed from methanol, film thickness initially decreased rapidly and was almost constant after 70 h in air for both catalysts. This timescale was much longer than the timescale for complete methanol desorption (ca. 5 h). From the film‐thickness data, the reduction in FFV with time was estimated. For samples prepared with either catalyst, the kinetics of FFV reduction were well‐described by a simple model based on the notion either that free‐volume elements diffuse to the surface of the polymer film and are subsequently eliminated from the sample or that lattice contraction controls polymer densification. Methane permeability decreased rapidly during the first 70 h, which was the same timescale for the thickness change. The decrease in methane permeability was smaller in films prepared with NbCl₅ than with TaCl₅. The logarithm of methane permeability decreased linearly as reciprocal FFV increased, in accordance with free‐volume theory. The PALS results indicate that the concentration of larger free‐volume elements (as indicated by the intensity I₄) decreased with aging time and that the other PALS parameters were not strongly influenced by aging. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1222–1239, 2000     

用光干涉法研究聚对苯二甲酸乙二酯非晶态薄膜的吸水性

<正> 高分子材料的吸水性已有很多研究,这是因为在它们的制造加工过程中,以及在用作防护涂层、薄膜和纤维时,尤其对强吸水性材料,吸水率是表征其性能的重要参数之一,具有很大的实际重要性。吸水率通常是用重量法、容量法和浮力法等基于吸水前后的重量变化的直接方法和通过红外吸收光谱、介电性质、NMR和DSC等间接方法测定的,最近有人提出了一种弯曲-悬臂法研究高分子材料的吸湿溶胀特性的新方法。     

Evaluation of methoxy polyethylene glycol‐polylactide diblock copolymers as additive in hypromellose film coating

This paper deals with a new application of diblock methoxy polyethylene glycol‐polylactide block copolymers, a class of synthetic biomaterials largely studied in the pharmaceutical and biomedical fields owing to their favorable properties such as biocompatibility, biodegradability, low immunogenicity, and good mechanical properties. In this work, these materials were evaluated as additives for gastro‐soluble pharmaceutical coating aimed to reduce film stiffness and water permeability. Two copolymers with different polylactide chain lengths were synthesized and characterized in term of molecular weight and solid‐state properties. A series of free films with different hypromellose/copolymers ratio were prepared and characterized in terms of appearance, components miscibility, plasticity, and water vapor permeability. The obtained results demonstrate that copolymers effectively influence hypromellose film properties according to their concentration and molecular weight. Specifically, the addition of the copolymer with a molecular weight of 6.5 kDa in a ratio hypromellose:polymer 5:1, allowed to obtain films with good appearance, improved plasticization, and water permeability properties. For higher molecular weight, copolymer or different ratios was not possible to observe the improvement of all the properties at the same time. The results also make possible to define the critical features to improve in order to use block copolymers as additive in hypromellose film coating. The availability of new water‐soluble additives able to work as plasticizer and moisture sealer in polymeric films represents an important progress not only in the field of pharmaceutical coating but also in that of food coatings, as for example in the formulation of edible films. Copyright © 2013 John Wiley & Sons, Ltd.     

Chitosan based surfactant polymers designed to improve blood compatibility on biomaterials

We developed chitosan based surfactant polymers that could be used to modify the surface of existing biomaterials in order to improve their blood compatibility. These polymers consist of a chitosan backbone, PEG side chains to repel non-specific protein adsorption, and hexanal side chains to facilitate adsorption and proper orientation onto a hydrophobic substrate via hydrophobic interactions. Since chitosan is a polycationic polymer, and it is thrombogenic, the surface charge was altered to determine the role of this charge in the hemocompatibility of chitosan. Charge had a notable effect on platelet adhesion. The platelet adhesion was greatest on the positively charged surface, and decreased by almost 50% with the neutralization of this charge. A chitosan surface containing the negatively charged SO(3)(-) exhibited the fewest number of adherent platelets of all surfaces tested. Coagulation activation was not altered by the neutralization of the positive charge, but a marked increase of approximately 5-6 min in the plasma recalcification time (PRT) was displayed with the addition of the negatively charged species. Polyethylene (PE) surfaces were modified with the chitosan surfactant resulting in a significant improvement in blood compatibility, which correlated to the increasing PEG content within the polymer. Adsorption of the chitosan surfactants onto PE resulted in approximately an 85-96% decrease in the number of adherent platelets. The surfactant polymers also reduced surface induced coagulation activation, which was indicated by the PEG density dependent increase in PRTs. These results indicate that surface modification with our chitosan based surfactant polymers successfully improves blood compatibility. Moreover, the inclusion of either negatively charged SO(3)(-) groups or a high density of large water-soluble PEG side chains produces a surface that may be suitable for cardiovascular applications.     

Enhanced dehumidification performance of PVA membranes by tuning the water state through incorporating organophosphorus acid

A novel thin film composite membrane with superior propylene dehumidification performance was prepared by coating a high hydrophilic organophosphorus acid ethylene diamine tetra(methylene phosphonic acid) (EDTMPA) doped poly(vinyl alcohol) (PVA) on polysulfone (PS) hollow fiber membranes. Experimental studies and molecular dynamics simulations were combined to probe the existing states and the transport mechanism of water in the membranes. Water vapor sorption experiments revealed that the enhanced dehumidification performance was governed by the diffusion process. Water states and water distribution were investigated by molecular dynamics simulation. At low EDTMPA content (<10 wt.%), states of the water were not obviously changed and the increase of water diffusion coefficient was mainly attributed to enlarged free volume of the membrane. At high EDTMPA content (10–30 wt.%), the increase in the water diffusion coefficient mainly arose from the variations in the water states. Strong interaction between PVA and EDTMPA reduced the amount of water that bounded to the PVA and increased the proportion of free water. The diffusion coefficients of water increased with increasing proportion of free water, since the mobility of free water was higher than that of bound water. The permeance of water reached 997.7 GPU for the PVA–EDTMPA/PS membrane with a 20 wt.% EDTMPA content when the proportion of free water was the highest, and the separation factor increased to infinity.     

Polycationic graft copolymers of poly(N-vinylpyrrolidone) as non-viral vectors for gene transfection

Novel graft copolymers of 2-(dimethylamino)ethyl methacrylate (DMAEMA) with N-vinylpyrrolidone (NVP) were designed and synthesized by the free radical copolymerization of DMAEMA with precursor polymers of vinyl-functionalized poly(N-vinylpyrrolidone) (PVP). The ability of the PVP- grafted copolymers to bind and condense DNA was confirmed by ethidium bromide displacement assay, agarose gel electrophoresis and transmission electron microscopy. The presence of PVP in the copolymers had a favorable effect on the biophysical properties of polymer/DNA complexes. Colloidal stable complexes obtained from the copolymer systems, were shown to be separate, uniformly spherical nanoparticles by transmission electron microscopy. The approximate diameter of the complexes was 150–200 nm, as determined by dynamic light scattering studies. These results confirm an important role played by the PVP grafts in producing compact stable DNA complexes. The ζ-potential measurements revealed that the incorporation of the PVP grafts reduced the positive surface charge of polymer/DNA complexes. The cytotoxicity of the copolymers decreased with an increasing fraction of PVP. Furthermore, in vitro transfection experiments with these copolymers showed improved ability of transfection in cell culture, demonstrating an important role for PVP grafts in enhancement of the transfection efficiency.      

Film protection of polymers

Polymer membranes, slabs, etc. can be effectively protected in time against permeation by an environmental polluting agent by self-regenerating, thin surface films of suitable film-forming materials initially dispersed in small amounts (less than 5 weight percent) in the polymer. These thin surface films (about 0.5 micrometers) can be either chemically passive to the polluting agent or be designed to react or catalyze a reaction with the agent in the presence of atmospheric oxygen or water vapor. We have studied the effectiveness of a number of passive film formers and a reactive film former in protecting a polyurethane elastomer, polyvinyl chloride and polyethylene towards a model polluting agent, tributyl phosphate. The presence on the polymer surface of the film former and its regeneration (within minutes) on scratching was followed by advancing contact angles of water, optical microscopy and scanning electron microscopy. Permeation weight loss of the polluting agent in a modified cup apparatus yielded both steady state permeation fluxes and the Barrer—Daynes time lags. In all cases the film-protected polymers exhibited smaller steady state fluxes and longer time lags than control polymers without the surface film. The decrease due to the presence of the surface film of the effective permeability and diffusion coefficient was sufficiently large to make this a promising method of protection.     

Solubility enhancement for poly(amic acid)s by rapid hydrolysis of the polymer main chain during alkaline development

In an alkaline developer carboxyl containing polymer films possess a higher critical carboxyl group concentration (CGC₀) below which dissolution does not occur, compared with novolac resins; therefore, it is difficult to obtain the polymer film with a lower dissolution rate and less swelling. We describe herein a new approach for reducing CGC₀ of carboxyl containing polymers by introducing an ester group which is labile in the alkaline developer within the time‐scale of development to obtain the polymers with moderate dissolution rates and less swelling. The rapid hydrolysis that leads to polymer degradation is clearly verified by gel permeation chromatography (GPC).     

Control of moisture at buried polymer/alumina interfaces through substrate surface modification

Moisture absorption in poly(4-tert-butoxycarbonyloxystyrene) (PBOCSt) films supported on Al(2)O(3) sputter coated silicon wafers is measured using neutron and X-ray reflectivity. Accumulation of water at the interface during moisture exposure results in an apparent film-thickness-dependent swelling for ultrathin PBOCSt films. The swelling of a film on Al(2)O(3) is less than the swelling of a film of the same thickness on SiO(x) for films thinner than 20 nm. This is due to comparatively less moisture accumulation at the Al(2)O(3)/PBOCSt interface. A simple, zero adjustable parameter model consisting of a fixed water-rich layer at the interface and bulk swelling through the remainder of the film describes the thickness-dependent swelling quantitatively. The influence of four different Al(2)O(3) surface treatments on the moisture distribution within PBOCSt films was examined: bare Al(2)O(3), tert-butylphosphonic acid, phenylphosphonic acid, and n-octyltrichlorosilane. Both the phenyl and the octyl surface treatments reduce the accumulation of water at the polymer/substrate interface. The tert-butyl treatment does not reduce the interfacial water concentration, presumably due to insufficient surface coverage.