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PubMedDate not supplied

Linear poly(ethylene oxide)-based polyurethane hydrogels: polyurethane-ureas and polyurethane-amides.

Over the last 30 years, water-swellable and water-insoluble hydrogels have been extensively investigated and developed, leading to a large family of materials which have found uses in a wide range of biomedical applications. While hydrogels usually present a crosslinked structure, linear polyurethane-ureas (PUUs) based on poly(ethylene oxide) have been shown to be able to absorb and swell with aqueous media without dissolving. This behavior is due to the phase separated domain morphology, where hydrogen bonded urethane/urea hard segment domains are dispersed in a PEO soft segment domain. This work investigates the possibility of obtaining linear poly(ethylene oxide)-based polyurethane-amide (PUA) hydrogels using two amide diols as chain extenders, a mono amide diol (AD) and a diamide diol (DD), and a dicarboxylic acid (maleic acid, MA). Poly(ethylene oxide) based PUAs were obtained using a "one-shot" bulk polymerization technique. The chemicophysical characterization and water-solubility tests showed that these materials, while having molecular weights similar to the PUUs, do not possess sufficient phase separation, hydrogen bonding and hydrophobicity of the hard segment domains to exhibit hydrogel behavior. Crosslinked PUAs using maleic acid as chain extender show interesting hydrogel properties.

Journal Article↗

PubMed2000

Hydrophilic sponges based on 2-hydroxyethyl methacrylate: part VII: modulation of sponge characteristics by changes in reactivity and hydrophilicity of crosslinking agents.

Despite previous unsuccessful attempts to use hydrated poly(2-hydroxyethyl methacrylate) sponges as implantable biomaterials, recently these materials became important as peripheral components in an artificial cornea of the core-and-skirt design. The low mechanical strength of sponges prompted this study on possible improvement of tensile properties by the use of a variety of crosslinking agents. Three vinylic (dimethacrylates) and two allylic compounds were used at different concentrations (0.1 to 2% (mol)) as crosslinking agents in the production of sponges. Their influence on the mechanical properties, porous morphology and swelling behavior of resulting sponges was evaluated. The onset of phase separation during polymerization was also measured by visible spectrophotometry. The results suggested an inherent heterogeneity of sponges, i.e. pores of non-uniform size and structural inhomogeneities. While the effects of changes in the nature and concentration of crosslinking agents on the equilibrium water content of sponges were ambiguous, some of the mechanical properties, such as toughness and elasticity, were improved by crosslinking with allylic agents. Scanning electron microscopic examination suggested that the mechanical effect is related to the variation of size of the polymer particles constituting the sponge structure, which was proved to be dependent upon the onset of phase separation during polymerization.

Journal Article↗

PubMed1992

Photoinduced destabilization of liposomes.

The stability of two-component liposomes composed of the polymerizable 1,2-bis-[10-(2',4'-hexadienoyloxy)decanoyl]-sn-glycero-3-phosphati dylcholine (SorbPC) and either a phosphatidylethanolamine (PE) or a phosphatidylcholine (PC) were examined via fluorescence leakage assays. Ultraviolet light exposure of SorbPC-containing liposomes forms poly-SorbPC, which phase separates from the remaining monomeric lipids. If the nonpolymerizable lipids are PE's, then the photoinduced polymerization destabilizes the liposome with loss of aqueous contents. The permeability of the control dioleoylPC/SorbPC membranes was not affected by photopolymerization of SorbPC. The photodestabilization of dioleoylPE/SorbPC (3:1) liposomes required the presence of oligolamellar liposomes. NMR spectroscopy of extended bilayers of dioleoylPE/SorbPC (3:1) showed that the photopolymerization lowers the temperature for the appearance of 31P NMR signals due to the formation of isotropically symmetric lipid structures. These observations suggest the following model for the photoinduced destabilization of liposomes composed of PE/SorbPC; photopolymerization induced phase separation with the formation of enriched domains of PE, which allows the close approach of apposed regions of enriched PE lamellae and permits the formation of an isotropically symmetric structure between the lamellae. The formation of such an interlamellar attachment (ILA) between the lamellae of an oligolamellar liposome provides a permeability pathway for the light-stimulated leakage of entrapped water-soluble reagents.

Drug Stability↗

PubMed2005

[Spectral study on intermolecular coupling interaction and relation to microstructure in polyester/inorganic hybrid materials].

The coupling form of the polymeric-inorganic component and the relation between intermolecular special hydrogen bonding interaction and the microstructure of crystallizable polymer, as well as micro-phase separation scale in non-covalently coupled poly (epsilon-caprolactone) (PCL)/silica (SiO2) hybrid materials were investigated by means of Fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The results show that the coupling form between PCL and SiO2 mainly depend on a strong intermolecular hydrogen bonding interaction in the hybrid system. The hydrogen bonding strength increases with increasing TEOS content, while the crystallization of PCL decreases, and the optical transparency of hybrid materials increases. In addition, it affects the scale of micro-phase separation in hybrid materials.

Calorimetry, Differential Scanning↗

PubMed1988

Biochemical properties of a 24 kilodalton membrane glycoprotein antigen complex from Schistosoma mansoni.

Antibodies were affinity purified from crude antiserum by elution from the 24 kDa region of preparative one-dimensional Western blots containing immobilized adult Schistosoma mansoni inner bilayer membrane proteins. They were shown to be specific for a single acidic polypeptide complex, Smgp24, following immunoblotting from two-dimensional polyacrylamide gels. These antibodies were then used to detect the presence of the Smgp24 complex in fractions prepared from lectin affinity chromatography, phase separation in Triton X-114 and chemical and enzymatic carbohydrate modification treatments. The 24 kDa antigen was bound and specifically eluted from both concanavalin A and lentil lectin affinity matrices. In addition, the electrophoretic mobility of the antigen was shifted to approximately 20 kDa after treatment with endoglycosidase F and N-glycanase, but was not appreciably altered following treatment with endoglycosidase H, neuraminidase, or sodium meta-periodate. The 20 kDa species produced by endoglycosidase F or N-glycanase treatment no longer bound to the lectin affinity resins. The Smgp24 complex also partitioned almost quantitatively into the detergent-enriched phase after phase separation in Triton X-114 solutions. These results indicate that the Smgp24 complex is an antigenic integral membrane glycoprotein and may consist of a single polypeptide backbone which is extensively post- or co-translationally modified.

Animals↗

PubMedDate not supplied

Complex coacervation of whey proteins and gum arabic.

Mixtures of gum arabic and whey protein (whey protein isolate, WP) form an electrostatic complex in a specific pH range. Three phase boundaries (pH(c), pHphi(1), pHphi(2)) have been determined using an original titration method, newly applied to complex coacervation. It consists of monitoring the turbidity and light scattering intensity under slow acidification in situ with glucono-delta-lactone. Furthermore, the particle size could also be measured in parallel by dynamic light scattering. When the pH is lowered, whey proteins and gum arabic first form soluble complexes. This boundary is designated as pH(c). When the interaction is stronger (at lower pH), phase separation takes place (at pHphi(1)). Finally, at pHphi(2) complexation was suppressed by the charge reduction of the gum arabic. The major constituent of the whey protein preparation used was beta-lactoglobulin (beta-lg), and it was shown that beta-lg was indeed the main complex-forming protein. Moreover, an increase of the ionic strength shifted the pH boundaries to lower pH values, which was summarized in a state diagram. The experimental pH(c) values were compared to a newly developed theory for polyelectrolyte adsorption on heterogeneous surfaces. Finally, the influence of the total biopolymer concentration (0-20% w/w) was represented in a phase diagram. For concentrations below 12%, the results are consistent with the theory on complex coacervation developed by Overbeek and Voorn. However, for concentrations above 12%, phase diagrams surprisingly revealed a "metastable" region delimited by a percolation line. Overall, a strong similarity is seen between the behavior of this system and a colloidal gas-liquid phase separation.

Electrochemistry↗

PubMed2006

Aging of oil-in-water emulsions: the role of the oil.

Controlling stability and aging of emulsions is important from commercial and scientific perspectives. Achieving such control comes through gaining an understanding of the relationship between emulsion constituents and microstructure and how these influence the kinetics and mechanism of destabilisation. We present here an investigation determining the rate of destabilisation as a function of time for a series of water/n-alkane/Triton X-100 oil-in-water emulsions. The time dependence of the emulsions was investigated using static light scattering, PFG-NMR and measurement of gross phase separation. By changing the chain length of the oil from hexane to tetradecane, an almost five orders of magnitude variation in emulsion lifetime could be achieved, while maintaining most of the other chemical and physical characteristics of the emulsions. Further, we show that while Ostwald ripening is the dominant destabilisation mechanism, two distinct regimes are evident. Initially, we observed an enhanced Ostwald ripening regime due to the presence of oil-swollen micelles in the aqueous continuum, that is a depletion flocculation mechanism is followed. The presence of oil-swollen micelles was confirmed using PFG-NMR. The micelles aid the gross oil transport between the discrete oil domains. Upon phase separation the oil-swollen micelles are predominantly removed from the emulsion along with the excess water resulting in a concomitant reduction in the ripening rate, producing the more general Ostwald ripening cubic dependence of droplet radius as a function of time for the lower molecular weight oils. The oils with higher molecular weight (decane and above), however, were observed to switch over to destabilisation via creaming. PFG-NMR was shown to be a powerful technique to fully probe emulsion microstructure as a function of time with droplet size and spacing being directly obtained from the data.

Journal Article↗

PubMed2001

Phospholipase A(2) activity towards vesicles of DPPC and DMPC-DSPC containing small amounts of SMPC.

Phospholipase A(2) (PLA(2)) is an interfacially active enzyme whose hydrolytic activity is known to be enhanced in one-component phospholipid bilayer substrates exhibiting dynamic micro-heterogeneity. In this study the activity of PLA(2) towards large unilamellar vesicles composed of DPPC:SMPC and DMPC:DSPC:SMPC is investigated using fluorescence and HPLC techniques. Phase diagrams of the mixtures are established by differential scanning calorimetry and the PLA(2) activity, monitored by the lag time, is correlated with the phase behavior of the mixtures. In addition, the degree of lipid hydrolysis in the DMPC:DSPC:SMPC lipid mixtures is detected by HPLC. The PLA(2) activity is found to be significantly increased in the temperature range of the coexistence region where the lipid mixtures exhibit lateral gel-fluid phase separation. Furthermore, in the entire temperature range it is demonstrated that PLA(2) preferentially hydrolyzes the short chain DMPC lipid. This discriminative effect becomes less pronounced when the asymmetric lipid SMPC is present in the lipid substrate. Inclusion of SMPC into either DPPC or DMPC:DSPC vesicles prolongs the lag time. The results clearly show that the PLA(2) activity is significantly enhanced by lipid bilayer micro-heterogeneity in both one-component and multi-component lipid bilayer substrates. The PLA(2) activity measurements are discussed in terms of dynamic gel-fluid lipid domain formation due to density fluctuations and static lipid domain formation due to gel-fluid phase separation.

1,2-Dipalmitoylphosphatidylcholine↗

PubMedDate not supplied

Surface composition and morphology of starch, amylose, and amylopectin films.

The surfaces of solution-cast films of starch, amylose, and amylopectin were examined with scanning electron microscopy (SEM), atomic force microscopy (AFM), electron spectroscopy for chemical analysis (ESCA), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The surface topography visualized by SEM showed that amylopectin films were very smooth whereas amylose and starch films were rougher. It appears that crystallinity or phase separation in the bulk of the film affects the surface topography. AFM showed that the outmost surfaces of all films were covered with small protrusions, 15-35 nm wide and 1-4 nm high. Studies with ESCA revealed the presence of 3-8% nitrogen on the surfaces. ToF-SIMS indicated that the nitrogen originates from protein because ionic fragments from amino acids and the peptide backbone were found. Extracts from the top surface layer of the starch film showed protein bands in gel electrophoresis (SDS-PAGE) around 60 kDa, which is in the same molecular weight range as the biosynthesizing enzyme GBSS I present in starch granules. The proteins apparently phase separated during film formation and migrated to the surface, resulting in an extensive enrichment of proteins in the film surface, where about 8% of the protein is present in the top 0.01% of the film. We believe that the protrusions observed with AFM could be one or a few proteins aggregated side by side.

Amylopectin↗

PubMed2026

Selective Extraction of Genomic DNA From Animal Tissues Using a Hydrophobic Magnetic Ionic Liquid.

The development of green and efficient methods for genomic DNA extraction from animal tissues is crucial for molecular diagnostics, food traceability, and genetic research. Conventional methods often involve toxic reagents, multiple centrifugation steps, and are time-consuming. In this study, a hydrophobic magnetic ionic liquid (MIL), N-octyl-4-dimethylaminopyridinium hexafluorophosphate MIL ([C8DMAP][PF6]‑Ni MIL), was synthesized and applied for the selective extraction of genomic DNA from various animal tissues. The material exhibited strong paramagnetic behavior, high thermal stability, and excellent hydrophobicity, enabling rapid phase separation under an external magnetic field. A mechanical shaking-assisted extraction method was developed, and key parameters including temperature, time, shaking speed, and [C8DMAP][PF6]-Ni MIL dosage were systematically optimized. The method demonstrated high selectivity for DNA over proteins, RNA, and amino acids, with a maximum recovery rate of 78.06 ± 1.91%. Compared to a commercial DNA extraction kit, the [C8DMAP][PF6]-Ni MIL-based approach provided higher yields from several tissues, including mouse liver, brain, and rabbit lung. Furthermore, the [C8DMAP][PF6]-Ni MIL could be reused for at least six cycles while maintaining extraction efficiency. This work not only provides a high-performance material for DNA extraction, but also demonstrates a sustainable and easily retrievable liquid-phase separation strategy, offering a generalizable platform for complex sample pretreatment.

Animals↗

PubMed2026

HP1α binding creates a local barrier against transcription activation and persists during chromatin decondensation.

Mouse pericentric heterochromatin forms compacted, transcriptionally silent domains, termed chromocenters, that are enriched in heterochromatin protein 1 (HP1). Whether HP1α represses chromocenters by binding locally or by maintaining a phase-separated compartment is unresolved. We investigated this question by recruiting transcriptional activators to mouse fibroblast chromocenters and quantifying repression at a transcription reporter. HP1α established a promoter-proximal barrier that suppressed weaker activators (VP16) but was overcome by stronger ones (VP64-p65-Rta [VPR] and p65). Activator-induced decondensation and transcription occurred without displacing HP1α or H3K9 trimethylation, and HP1α retained its granular distribution and stoichiometric binding dynamics. Multi-color super-resolution imaging revealed spatial segregation of transcribed and HP1α-bound regions at the nanodomain scale. A nanodomain model captured how repeat clusters independently transition between silenced and activated states. These data establish that HP1α and H3K9me3 act through independently switchable nanodomains, accounting for chromocenter regulation without invoking phase separation.

Animals↗

PubMedDate not supplied

Development of a gravity-independent wastewater bioprocessor for advanced life support in space.

Operation of aerobic biological reactors in space is controlled by a number of challenging constraints, mainly stemming from mass transfer limitations and phase separation. Immobilized-cell packed-bed bioreactors, specially designed to function in the absence of gravity, offer a viable solution for the treatment of gray water generated in space stations and spacecrafts. A novel gravity-independent wastewater biological processor, capable of carbon oxidation and nitrification of high-strength aqueous waste streams, is presented. The system, consisting of a fully saturated pressurized packed bed and a membrane oxygenation module attached to an external recirculation loop, operated continuously for over one year. The system attained high carbon oxidation efficiencies often exceeding 90% and ammonia oxidation reaching approximately 60%. The oxygen supply module relies on hydrophobic, nonporous, oxygen selective membranes, in a shell and tube configuration, for transferring oxygen to the packed bed, while keeping the gaseous and liquid phases separated. This reactor configuration and operating mode render the system gravity-independent and suitable for space applications.

Bacteria, Aerobic↗

PubMed2005

Micro-convection, dissipative structure and pattern formation in polymer blend solutions under temperature gradients.

We report experimental results on time evolution of phase separation in a polymer blend solution under a temperature gradient. This study is aimed at making a self-organized structure by utilizing convection in a polymer blend solution comprising polystyrene (PS) and polybutadiene (PB) as solute with dioctylphthalate (DOP) as solvent. The polymer blend solution (PS/PB/DOP) with various compositions (PS/PB = 20/80, 50/50 or 80/20) was prepared with a total polymer concentration (PS + PB) at 3.0 wt.%. The solution was confined in a layer (0.1 mm thick), which was further subjected to a temperature gradient by controlling top and bottom temperatures (Ttop and Tbot) independently with a 10 or 20 degrees C temperature difference (Ttop < Tbot). For all compositions, micro-convection was generated due to the Soret effect, which is relevant to the fact that the temperature gradient induces a concentration gradient. An unusual phase separating process was observed as a result of dynamic coupling with convective flows. Especially, an interesting hierarchical structure was formed for a PS/PB = 50/50 solution. This structure is characterized by a doubly surrounding "sea-island". Namely, the "sea" contains large "islands" which involve tiny "islands". The large "islands" are spatially arranged and embedded in polygonal convection cells.

Journal Article↗

PubMed1992

Effect of electrostatic forces on the dynamic rheological properties of injectable collagen biomaterials.

Injectable collagen is a concentrated dispersion of phase-separated collagen fibres in aqueous solution used to correct dermal contour defects through intradermal injection. The effect of electrostatic forces on the rheology of injectable collagen was studied by observation of the birefringence of collagen fibres through a polarizing microscope as well as by oscillatory rheological measurements on dispersions of varying ionic strengths (0.06-0.30). The birefringence of fibres progressively increased as ionic strength was reduced from 0.30 to 0.06. The linear viscoelastic measurements displayed a logarithmic relationship between storage (and loss) moduli and frequency over oscillation frequencies of 0.1-100 rad/s. The associated relaxation time spectra, interpreted using the theory of Kamphuis et al. for concentrated dispersions, show that collagen fibres become more flexible as ionic strength increases. This result was analysed at the molecular level from the perspective that collagen fibres are a liquid-crystalline phase of rigid rod collagen molecules which have phase-separated from solution. Electrostatic forces affect the volume fraction of water present in the collagen fibres which in turn alters the rigidity of the fibres. Flexible collagen fibre dispersions displayed emulsion-like flow properties whereas more rigid collagen fibre dispersions displayed suspension-like flow properties. Changes in fibre rigidity significantly alter the injectability of collagen dispersions which is critical in clinical performance.

Animals↗

PubMed1998

Drug microencapsulation by PLA/PLGA coacervation in the light of thermodynamics. 1. Overview and theoretical considerations.

Phase separation of poly(lactide) (PLA) and poly(lactide-co-glycolide) (PLGA), often called "coacervation" in the pharmaceutical field, is one of the classical methods for peptide drug microencapsulation in biodegradable polyesters. Although numerous studies have used this technique, the underlying physicochemical mechanisms of polyester coacervation under conditions of microsphere production have not been well-described yet. Moreover, the quality of microencapsulation in terms of drug loading efficiency and residual organic solvents is often not entirely satisfactory and depends greatly on the specific drug and polymer used. The first part of this contribution reviews briefly the scientific and patent literature on PLA/PLGA coacervation. Then, the underlying physicochemical principles of polyester coacervation are discussed and relevant thermodynamic models presented. More specifically, attempts were made to clarify the necessary characteristics of polymers, solvents, and coacervating and hardening agents for successful phase separation and microsphere formation. These basic considerations may contribute to a better understanding of the boundary conditions crucial for efficient drug microencapsulation by polyester coacervation.

Drug Compounding↗

PubMed2004

Porous-conductive chitosan scaffolds for tissue engineering, 1. Preparation and characterization.

Novel porous-conductive chitosan scaffolds were fabricated by incorporating conductive polypyrrole (PPy) particles into a chitosan matrix and employing a phase separation technique to build pores inside the scaffolds. Conductive polypyrrole particles were prepared with a microemulsion method using FeCl3 as a dopant. The preparation conditions were optimized to obtain scaffolds with controlled pore size and porosity. The conductivity of the scaffolds was investigated using a standard four-point probe technique. It was found that several kinds of scaffolds showed a conductivity close to 10(-3) S.cm(-1) with a low polypyrrole loading of around 2 wt.-%. The main mechanical properties, such as tensile strength, breaking elongation and Young's modulus of the scaffolds, were examined both in the dry and in the hydrated states. The results indicated that a few different kinds of scaffolds exhibited the desired mechanical strength for some tissue engineering applications. The miscibility of polypyrrole and chitosan was also evaluated using a dynamic mechanical method. The presence of significant phase separation was detected in non-porous PPy/chitosan scaffolds but enhanced miscibility in porous PPy/chitosan scaffolds was observed.

Biocompatible Materials↗

PubMed2004

Domain formation induced by the adsorption of charged proteins on mixed lipid membranes.

Peripheral proteins can trigger the formation of domains in mixed fluid-like lipid membranes. We analyze the mechanism underlying this process for proteins that bind electrostatically onto a flat two-component membrane, composed of charged and neutral lipid species. Of particular interest are membranes in which the hydrocarbon lipid tails tend to segregate owing to nonideal chain mixing, but the (protein-free) lipid membrane is nevertheless stable due to the electrostatic repulsion between the charged lipid headgroups. The adsorption of charged, say basic, proteins onto a membrane containing anionic lipids induces local lipid demixing, whereby charged lipids migrate toward (or away from) the adsorption site, so as to minimize the electrostatic binding free energy. Apart from reducing lipid headgroup repulsion, this process creates a gradient in lipid composition around the adsorption zone, and hence a line energy whose magnitude depends on the protein's size and charge and the extent of lipid chain nonideality. Above a certain critical lipid nonideality, the line energy is large enough to induce domain formation, i.e., protein aggregation and, concomitantly, macroscopic lipid phase separation. We quantitatively analyze the thermodynamic stability of the dressed membrane based on nonlinear Poisson-Boltzmann theory, accounting for both the microscopic characteristics of the proteins and lipid composition modulations at and around the adsorption zone. Spinodal surfaces and critical points of the dressed membranes are calculated for several different model proteins of spherical and disk-like shapes. Among the models studied we find the most substantial protein-induced membrane destabilization for disk-like proteins whose charges are concentrated in the membrane-facing surface. If additional charges reside on the side faces of the proteins, direct protein-protein repulsion diminishes considerably the propensity for domain formation. Generally, a highly charged flat face of a macroion appears most efficient in inducing large compositional gradients, hence a large and unfavorable line energy and consequently lateral macroion aggregation and, concomitantly, macroscopic lipid phase separation.

Adsorption↗

PubMed2003

Effects of poly(ethylene glycol) (PEG) chain length of PEG-lipid on the permeability of liposomal bilayer membranes.

The effects of poly(ethylene glycol) (PEG) chain length of PEG-lipid on the membrane characteristics of liposomes were investigated by differential scanning calorimetry (DSC), freeze-fracture electron microscopy (FFEM), fluorescence polarization measurement and permeability measurement using carboxyfluorescein (CF). PEG-liposomes were prepared from mixtures of dipalmitoyl phosphatidylcholine (DPPC) and distearoyl phosphatidylethanolamines with covalently attached PEG molecular weights of 1000, 2000, 3000 and 5000 (DSPE-PEG). DSC and FFEM results showed that the addition of DSPE-PEG to DPPC in the preparation of liposomes caused the lateral phase separation both in the gel and liquid-crystalline states. The fluidity in the hydrocarbon region of liposomal bilayer membranes was not significantly changed by the addition of DSPE-PEG, while that in the interfacial region was markedly increased. From these results, it was anticipated that the CF leakage from PEG-liposomes is accelerated compared with DPPC liposomes. However, CF leakage from liposomes containing DSPE-PEG with a 0.060 mol fraction was depressed compared with regular liposomes, and the leakage decreased with increasing PEG chain length. Furthermore, the CF leakage from liposomes containing DSPE-PEG with a 0.145 mol fraction was slightly increased compared with that of liposomes containing DSPE-PEG with a 0.060 mol fraction. It is suggested that the solute permeability from the PEG-liposomes was affected by not only properties of the liposomal bilayer membranes such as phase transition temperature, phase separation and membrane fluidity, but also the PEG chain of the liposomal surface.

Lipid Bilayers↗