Nonlinear rheological study of magneto responsive soft gels

Swollen physical magnetorheological (MR) gels were obtained by self-assembly of triblock copolymers containing dispersed magnetic particles. We carry out a detailed investigation of the nonlinear rheological properties of MR gels under large amplitude oscillatory shear flow. A strong Payne effect is observed for strains above 0.05% which is the limit of linear viscoelastic region. The onset strain for the transition from linear to nonlinear viscoelastic behaviour is much smaller than in the absence of a magnetic field. We show that the magnetic Payne effect strongly depends on the magnetic flux density, the particle volume fraction, the sample's initial particle distribution and viscoelastic properties of the matrix.The rheological response of MR gels is strongly related to the ability for rearrangement of the particles in the presence of the magnetic field. Upon sudden application of a magnetic field, the particle network embedded in a soft matrix becomes more anisotropic than is the case in a hard matrix since the resistance of the matrix to particle rearrangement is smaller. The induced anisotropic particle network parallel to the field provides larger absolute rheological response.     

Polymer nanocomposites for bone tissue substitutes

Following the quest for new composite biomaterials for bone tissue engineering, this work presents the processing of new nanocomposite made of polycaprolactone matrix and wollastonite particles. Wollastonite nanopowder was obtained by thermal treatment of polymethyloxosilane resin mixed with silica and calcium hydroxide. Bioactive character of the ceramic nanopowder was verified in simulated body fluid (SBF). The apatite formation on wollastonite grain surface after immersion in SBF was observed. Basic mechanical properties of the samples containing various amount of ceramic nanoparticles have been examined. It was shown that the presence of small amount of wollastonite nanoparticles (0.5–1.0 wt%) improves significantly the Young's modulus, tensile strength, and work-of-fracture of polymer matrix composite. Increased content of ceramic nanoadditive (>2%) in nanocomposites resulted in degradation of their mechanical characteristics.     

Temperature sensitive gels as extraction solvents

Crosslinked poly(N-isopropylacrylamide) gel and crosslinked copolymers of 97% N,N-diethylacrylamide and 3% sodium methacrylate which are swollen with water collapse abruptly at 33°C and near 55°C, respectively. These collapses apparently occur because each gel is near its lower critical solution temperature. The gels can be used to extract water and low molecular weight solutes from macromolecular solutions. After they have extracted the water, the gels can be regenerated by warming to release the absorbed water. The resulting separation process is effective for proteins and other polymers, and may be operated with waste heat which is usually discarded.     

Elasticity,tear strength,and strength of adhesion of soft PVC gels

An experimental study is described of the tensile modulus E of elasticity, tear strength G_c, and strength G_a of adhesion to a Mylar substrate, for PVC gels prepared with a wide range of PVC concentrations and with four different plasticizers. The modulus E, measured under quasiequilibrium conditions, was found to be approximately proportional to c³, where c is the volume concentration of PVC. The tensile behavior suggests that the molecular strands comprising the undiluted elastic network are relatively short, only about 26 C atoms long. G_c under threshold conditions was found to vary with c^2.25 and to be considerably larger than (about 10 X) the value expected for a molecular network of short PVC chains. This difference is attributed to yielding of crystallites before molecular rupture can take place. Adhesion of PVC gels to Mylar was relatively weak. Both the tear strength and strength of adhesion were strongly dependent upon rate of fracture propagation and temperature, in good accord with the WLF rate-temperature equivalence for simple glass-forming substances. Thus, the strength of PVC gels appears to be determined largely by the glass temperature of the composition, and not by the amount or type of plasticizer except insofar as they affect the glass temperature.     

医用软组织黏合剂的研究进展

按医用软组织黏合剂材料分类,介绍了合成类黏合剂、天然类黏合剂和仿生类黏合剂的发展现状及展望,并分别对其部分黏合剂的粘接机理、特点进行了详细论述。     

Injectable polyMIPE scaffolds for soft tissue regeneration

Injury caused by trauma, burns, surgery, or disease often results in soft tissue loss leading to impaired function and permanent disfiguration. Tissue engineering aims to overcome the lack of viable donor tissue by fabricating synthetic scaffolds with the requisite properties and bioactive cues to regenerate these tissues. Biomaterial scaffolds designed to match soft tissue modulus and strength should also retain the elastomeric and fatigue-resistant properties of the tissue. Of particular design importance is the interconnected porous structure of the scaffold needed to support tissue growth by facilitating mass transport. Adequate mass transport is especially true for newly implanted scaffolds that lack vasculature to provide nutrient flux. Common scaffold fabrication strategies often utilize toxic solvents and high temperatures or pressures to achieve the desired porosity. In this study, a polymerized medium internal phase emulsion (polyMIPE) is used to generate an injectable graft that cures to a porous foam at body temperature without toxic solvents. These poly(ester urethane urea) scaffolds possess elastomeric properties with tunable compressive moduli (20–200 kPa) and strengths (4–60 kPa) as well as high recovery after the first conditioning cycle (97–99%). The resultant pore architecture was highly interconnected with large voids (0.5–2 mm) from carbon dioxide generation surrounded by water-templated pores (50–300 μm). The ability to modulate both scaffold pore architecture and mechanical properties by altering emulsion chemistry was demonstrated. Permeability and form factor were experimentally measured to determine the effects of polyMIPE composition on pore interconnectivity. Finally, initial human mesenchymal stem cell (hMSC) cytocompatibility testing supported the use of these candidate scaffolds in regenerative applications. Overall, these injectable polyMIPE foams show strong promise as a biomaterial scaffold for soft tissue repair.     

Design of artificial extracellular matrices for tissue engineering

The design of artificial extracellular matrix (ECM) is important in tissue engineering because artificial ECM regulates cellular behaviors, including proliferation, survival, migration, and differentiation. Artificial ECMs have several functions in tissue engineering, including provision of cell-adhesive substrate, control of three-dimensional tissue structure, and presentation of growth factors, cell-adhesion signals, and mechanical signals. Design criteria for artificial ECMs vary considerably depending on the type of the engineered tissue. This article reviews the materials and methods that have been used in fabrication of artificial ECMs for engineering of specific tissues, including liver, cartilage, bone, and skin. This article also reviews artificial ECMs used for modulation of stem cell behaviors for tissue engineering applications.     

Lignin gels as a medium in gel permeation chromatography

The preparation of spherical lignin gel beads, based on the crosslinking reaction between epichlorohydrin and kraft lignin (Indulin AT), is described. The lignin gels prepared were found to be an efficient resin in gel permeation chromatography. The separation of polystyrenes in dimethylformamide is described. The resin was found to separate polystyrenes with molecular weights up to 110,000. An inverse linear relationship between log M and elution volume or the partitioning coefficient was established.     

Boron-containing bioactive glasses in bone and soft tissue engineering

Boron is considered to influence the performance of several metabolic enzymes and boron deficiency is associated with impaired growth and abnormal bone development. As such, boron is a beneficial bioactive element for animals and humans. It is also well known that boron stimulates wound healing and improves bone health. The addition of boron in different proportions to bioactive glasses has significant effects on glass structure, glass processing parameters, biodegradability, biocompatibility, bioactivity and cytotoxicity. Different compositions of bioactive glasses (BGs) containing boron, including boron-doped, borosilicate and borate glasses, are being investigated for bone and soft tissue engineering under the premise that these BGs are suitable carriers of boron, indicating controlled release of B species in the biological environment. This paper reviews up to date research and applications of borate, borosilicate, and boron doped silicate and phosphate BGs focussing on their physical, structural, degradation and biological properties for hard and soft tissue regeneration.     

Polymer blends as high explosive binders

An approach to high-density, high-modulus binders for explosives is to blend low-density, high-modulus polymers with high-density, low-modulus polymers. Improved properties, which these pairs theoretically should have, are discussed. Two attempts to achieve miscibility between a high-density fluoropolymer (Kel-F 800) and high-modulus thermoplastics (Lucite 130 and Phenoxy PKHJ) were unsuccessful. These blends are immiscible and their physical properties are additive or only slightly enhanced. Anelastic properties of the blends indicate phase separation by the presence of two glass transitions, one associated with each phase.     

Polymer opals as novel photonic materials

Synthetic opals, based on self‐assembled arrays of core–shell (bead–matrix) polymer microparticles, are a promising platform for next‐generation bulk‐scale photonic structures, coatings, fibres and sensors. This perspective article highlights recent work in this area, ranging from characterization and application, to advances in more fundamental understanding of structural colour effects. These advances include viscoelastically tuned symmetry breaking, the observation of anisotropic optical scattering and the study of polymer opals as an analogue to the intrinsically disordered, low‐refractive‐index contrast systems associated with opals seen in nature. © 2013 Society of Chemical Industry     

Polymer LEDs as a physics tool

We present a systematic experimental and theoretical study of physical mechanisms governing the operation of polymer light-emitting diodes. We show that through self-consistent modeling we can address both charge transport and exciton generation. Electron and hole mobility in several polymers has been characterized experimentally. Characterization of excitons and especially of triplet-excitons is achieved through use of a triplet-emitting molecule.     

l-ascorbic acid modified poly(ester urethane)s as a suitable candidates for soft tissue engineering applications

In this paper we created novel poly(ester urethane)s (PESUs) designed specifically for tissue engineering. The PESUs were derived from oligomeric α,ω-dihydroxy(ethylene-butylene adipate) (dHEBA), 1,4-butanediol (BDO) and aliphatic 1,6-hexamethylene diisocyanate (HDI) and modified with l-ascorbic acid to improve their biocompatibility. In addition, we determined their mechanical properties (such as tensile strength, elongation at break and hardness). To determine how these materials may potentially behave after implementation in tissue, we estimated the degradation behavior of obtained PESUs in various chemical environments, which were exemplified by canola oil, saline solution, distilled water and phosphate buffered saline (PBS). Finally, the PESU biocompatibility and hemocompatibility tests were carried out. Biocompatibility was determined with a MTT assay and it was performed with 3T3 cell line. The results showed satisfactory mechanical properties, good hemocompatibility and improved biocompatibility, which let us to conclude that PESUs modified with ascorbic acid might find an application in biomedical field of soft tissues engineering.     

Super soft elastomers as ionic conductors

Melts of linear brush polymers with PEO side chains attached at each repeat unit of the backbones have been doped with CF₃SO₃⁻Li⁺. Mechanical properties and ionic conductivity of such systems have been analyzed using mechanical and dielectric spectroscopies. Mechanical spectra indicated a presence of super soft states for samples with long backbones or for systems which have been slightly cross-linked (G′<10⁴ Pa). In the case of the polymer with longer crystallizing PEO side chains (MW_av=1100 g/mol), the ionic conductivity reaching the 10⁻³ S/cm level at the optimum CF₃SO₃⁻Li⁺ concentration (EO/Li⁺=10:1) have been detected at temperatures not far above the room temperature. The presence of lithium ions suppresses completely the crystallization of PEO side chains.     

Fibrous materials as artificial soil substrates

Artificial soil compositions have been used as substrates for growing plants on the basis of modified polyacrylonitrile (PAN) fibers and films of sodium alginate. The agrophysical characteristics of these artificial substrates based on modified PAN fibers indicate that such composites have low volume mass, high water capacity, and a good level of capillary water rise. These artificial substrates provide for normal plant development. At the end of the experiments, the root systems of grasses had penetrated the substrates, which provided for firm plant embedding. Most of the parameters for grass on artificial substrates correspond to those for grass grown on natural soil, and in some cases even exceed those results. The best results are obtained with fibers modified by urea (PAN-KA), because urea acts as a nutrient during growth. Artificial soils containing alginate films bearing mineral nutrients have also given good results. In that case it is possible to mount the seeds directly on the film, which provides for convenient transportation and facilitates planting. Translated from Khimicheskie Volokna, No. 4, pp. 18–22, July–August, 2008.     

Polyimides as precursors for artificial carbon

The pyrolysis behavior of different commercially available polyimides has been studied by means of thermoanalysis, dilatometry and analysis of the gaseous pyrolysis products. Based on the results of these measurements the chemistry of the thermal degradation is discussed. The carboneous residues have been investigated by X-ray, nitrogen adsorption and elemental analysis. The polyimides were successfully applied as binder precursor for C/C-composites.     

Cell removal with supercritical carbon dioxide for acellular artificial tissue

BACKGROUND: The objective of this work was to decellularize artificial tissue without using surfactant solutions. For this purpose, supercritical carbon dioxide was used as the extraction medium. RESULTS: Supercritical carbon dioxide containing a small amount of entrainer was a suitable medium to extract both cell nuclei and cell membranes from artificial tissue. Under gentle extraction conditions (15 MPa, 37 °C), cell nuclei were satisfactorily extracted from tissue within 1 h. In contrast, the efficiency of phospholipid removal depended strongly on the transfer rate of carbon dioxide in the interior of the tissue. Mechanical strength of tissue was not decreased even with prolonged treatment. CONCLUSION: Acellular artificial tissues could be prepared quickly by treatment with a carbon dioxide/entrainer system. The prepared acellular tissue could be obtained in absolutely dry condition. This is advantageous from the viewpoint of long‐term preservation without putrefaction and contamination. Copyright © 2008 Society of Chemical Industry     

新型导电高分子抗静电剂进展

本征型导电高分子抗静电剂是目前发现的使用效果最好的抗静电剂之一．本文简要综述了本征型导电高分子抗静电剂的工作原理、特点、国内外发展现状及发展趋势，其中重点介绍了聚(3，4-二氧乙基噻吩)／聚对苯乙烯磺酸，以及它在感光材料中作为抗静电剂显示的重要作用．     

Polymer supported nitrite esters as diazotising reagent

Summary Glycidyl methacrylate based terpolymer resin was prepared in spherical beads form by suspension polymerization of glycidyl methacrylate (0.4mol)-methyl methylacrylate (0.5mol)-divinyl benzene (0.1mol) mixture. Acid catalysed reaction of the resin beads (110–220 μm ) with excess of glycerol gives corresponding modified resin with hydroxyl functions ( 6.86 mmol g⁻¹). Upon standing in 2 M HNO₂ solution, hydroxyl groups of the later esterified with nitrous acid (3.55 mmol g⁻¹). The nitrite ester functions of the resin have been demonstrated to be efficient nitrous acid precurser in diazotisation of aromatic amines. Diazotisation of aniline in 2 M HCl solutions at 0°C takes place in less than 15 minutes. Applicability and pratical yields of the method presented have been investigated by diazo coupling reaction of β- naphthol. Received: 8 June 2000/Revised version: 6 February 2001/Accepted: 28 February 2001     

Synthesis of copper bearing borosilicate glass for soft tissue wound healing

To date, various wound dressings have been developed to increase the ability of healing and to recover the functions of wounded tissues. A complicated series of signaling pathways participate during the main phases of wound healing, i.e. hemostasis, inflammation, proliferation, and remodeling. The ions at the injury site could induce pathways either directly or indirectly; however, they must be presented slowly otherwise they would saturate the microenvironment and cause toxicity. Boron and copper ions upregulate cell recruitment, proliferation, and angiogenesis at the injury site. In this study, the synthesis of a biodegradable and slow-releasing copper-borosilicate glass via conventional melt casting and sol-gel was compared. In contrast to the melt casting-derived sample, the sol-gel glass exhibited a more regulated ion release. Thus it was selected as the optimized sample and was loaded into a gelatin-based wound dressing. In an in vivo study, after 15 days of dressing and compared to untreated models, a remarkable epidermal layer was regenerated on the wound area in the test group.