Influence of the Degree of Deacetylation of Chitosan and BMP-2 Concentration on Biocompatibility and Osteogenic Properties of BMP-2/PLA Granule-Loaded Chitosan/β-Glycerophosphate Hydrogels

Compositions based on chitosan/β-glycerophosphate hydrogels with highly porous polylactide granules can be used to obtain moldable bone graft materials that have osteoinductive and osteoconductive properties. To eliminate the influence of such characteristics as chain length, degree of purification, and molecular weight on a designed material, the one-stock chitosan sample was reacetylated to degrees of deacetylation (DD%) of 19.5, 39, 49, 55, and 56. A study of the chitosan/β-glycerophosphate hydrogel with chitosan of a reduced DD% showed that a low degree of deacetylation increased the MSCs (multipotent stromal cells) viability rate in vitro and reduced the leukocyte infiltration in subcutaneous implantation to Wistar rats in vivo. The addition of 12 wt% polylactide granules resulted in optimal composite mechanical and moldable properties, and increased the modulus of elasticity of the hydrogel-based material by approximately 100 times. Excessive filling of the material with PLA (polylactide) granules (more than 20%) led to material destruction at a ~10% strain. Osteoinductive and osteoconductive properties of the chitosan hydrogel-based material with reacetylated chitosan (39 DD%) and highly porous polylactide granules impregnated with BMP-2 (bone morphogenetic protein-2) have been demonstrated in models of orthotopic and ectopic bone formation. When implanted into a critical-size calvarial defect in rats, the optimal concentration of BMP-2 was 10 μg/mL: bone tissue areas filled the entire material’s thickness. Implantation of the material with 50 μg/mL BMP-2 was accompanied with excessive growth of bone tissue and material displacement beyond the defect. Significant osteoinductive and osteoconductive properties of the material with 10 μg/mL of BMP-2 were also shown in subcutaneous implantation.     

Structure of a poly(2,5‐benzimidazole)/phosphoric acid complex

As‐cast films of poly(2,5‐benzimidazole) exhibit uniplanar orientation in which the planes of the aromatic rings lie parallel to the film surface. Upon doping with phosphoric acid, the original crystalline order is lost, but the doped film can be stretched to produce films with uniaxial orientation. After thermal annealing at 540 °C, nine Bragg reflections are resolved in the fiber diagram, and these are indexed by an orthorhombic unit cell with the dimensions a = 18.1 Å, b = 3.5 Å, and c = 11.4 Å, containing four monomer units of two chains. The absence of odd‐order 00l reflections points to a 2₁ chain conformation, which is probably planar so that the aromatic units can be stacked along the b axis. The water and phosphoric acid contents of the crystalline structure cannot be determined exactly because of the presence of extensive amorphous regions that probably have different solvation. The best agreement between the observed and calculated intensities is for an idealized structure containing two phosphoric acids and two water molecules per unit cell. However, the phosphoric acid is probably present mainly in the form of pyrophosphoric acid and its higher oligomers. In addition, the X‐ray data are consistent with a more disordered structure containing chains with random (up and down) polarity and a lack of c‐axis registry. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2576–2585, 2004     

Electrophysical properties of nanocomposites based on poly(p-xylylene) and copper nanoparticles

Poly(p-xylylene)-based nanocomposites containing various amounts of copper have been prepared by vacuum codeposition on a cooled substrate. On the basis of the relationship between the electrical conductivity of composites and the volume content of copper, the percolation threshold has been estimated as 10%. This value coincides with the corresponding parameter derived from the concentration dependence of the electrical resistance temperature coefficient. It has been shown that the conductivity of the nanocomposites increases with the moisture content and their moisture sensitivity decreases with an increase in the content of copper from a concentration of 4%. An analysis of the kinetics of the sensor response measured for various moisture contents has shown that the capacity structure of the samples rearranges during adsorption of water. According to the advanced model, the value of the sensor response is determined by a reduction in the height of the potential barrier between nanoparticles and a change in the fractal characteristics of nanocomposites that results from the adsorption of water molecules.     

Synthesis of monodisperse polymer suspensions with a narrow particle size distribution in the presence of water-insoluble triple block copolymers of polypropylene oxide and polyethylene oxide (pluronics)

The colloidal chemical properties of triple block copolymers of polypropylene oxide and polyethylene oxide (pluronics of various structures) were studied in comparison. All of them are shown to be surfactants but differ in interfacial tension, surface activity, surface area occupied in the adsorption layer, and adsorption layer thickness. The kinetic regularities of polymerization of styrene and methyl methacrylate were studied. The particle diameters and their size distribution were determined. Distinctions in the kinetic regularities of polymerization are shown: the shape of the conversion—time curves (for the duration of the initial and stationary stages of polymerization) and the dependences of the diameter on the surfactant concentration and monomer to water volume ratio. In the presence of the water-insoluble pluronics, the mechanism of formation of polymer—monomer particles and interfacial layer on the surface differs from that when using water-soluble surfactants, which makes it possible to distinguish these processes into an independent type of heterophase polymerization.

     

Dielectric Properties of Halloysite Nanotube Suspensions in Polydimethylsiloxane

Russian Journal of Physical Chemistry A - The frequency dependences of electrical conductivity with both real and imaginary components of a dielectric permittivity of polydimethylsiloxane oil...     

Kinetics of D,L–Lactide Polymerization Initiated with Zirconium Acetylacetonate

The kinetic of D,L-lactide polymerization in presence of biocompatible zirconium acetylacetonate initiator was studied by differential scanning calorimetry in isothermal mode at various temperatures and initiator concentrations. The enthalpy of D,L-lactide polymerization measured directly in DSC cell was found to be ΔH=−17.8±1.4 kJ mol⁻¹. Kinetic curves of D,L-lactide polymerization and propagation rate constants were determined for polymerization with zirconium acetylacetonate at concentrations of 250–1000 ppm and temperature of 160–220 °C. Using model or reversible polymerization the following kinetic and thermodynamic parameters were calculated: activation energy E_a=44.51±5.35 kJ mol⁻¹, preexponential constant lnA=15.47±1.38, entropy of polymerization ΔS=−25.14 J mol⁻¹ K⁻¹. The effect of reaction conditions on the molecular weight of poly(D,L-lactide) was shown.     

Effect of the chemical grafting of epoxy resin onto organomodified montmorillonite on the structure and heat resistance of an epoxy nanocomposite

It is shown that the noncatalyzed chemical grafting of an epoxy oligomer onto the surface of montmorillonite platelets may proceed via the reaction between the epoxy groups and the hydroxyl groups of the organic modifying agent of the layered aluminosilicate. The effect of grafting on the structure and heat resistance of the cured epoxy nanocomposite is studied. Complete exfoliation of montmorillonite particles into individual platelets is shown to be a necessary but insufficient condition for increasing the glass-transition temperature of the nanocomposite relative to that of the initial matrix. A much higher contribution to the increase in the glass-transition temperature is ensured by grafting of epoxy molecular chains onto the surface of aluminosilicate platelets; i.e., strong covalent matrix-aluminosilicate bonds form in addition to physical bonds, a process that entails development of a thicker three-dimensional network.     

Effect of Temperature on the Electrorheological Behavior of Porous Chitosan Particles in Polydimethylsiloxane

Doklady Physical Chemistry - The rheological behavior of a 1 wt % suspension of highly porous chitosan particles in polydimethylsiloxane in a high electric field has been studied as a function of...     

Effect of stereoregularity on the structure and thermophysical characteristics of isotactic polypropylene

The structure, thermophysical, and thermomechanical characteristics of metallocene-synthesized isotactic PPs of different molecular masses containing different amounts of stereodefects have been studied. The degree of crystallinity and the content of a and g modifications in slowly cooled and melt quenched films are estimated by three independent methods, i.e., X-ray analysis, DSC, macroscopic density measurements, and changes in their phase structure upon annealing and orientation are analyzed. As the content of stereodefects increases, the fraction of g crystallites in the films increases, while the degree of crystallinity decreases (down to 5%). The formation of the g phase is assumed to be related to the epitaxial crystallization; this process is assisted by stresses induced on chains upon slow melt crystallization and after annealing of the oriented samples. This evidence allows the analysis of structural and thermodynamic characteristics of thermoplastic and elastic samples of the isotactic PP.     

A comparative analysis of self-assembly in poly(methacrylates) with bulky side substituents of different molecular masses in the solid state and in solutions

A comparative investigation of self-assembly in poly(methacrylates) with bulky substituents based on gallic acid both in the condensed state and in hexane solutions has been performed by using the methods of SAXS and DSC. The size and shape of the formed supramolecular aggregates have been analyzed for the polymers of two different degrees of polymerization (150 and 21). In fresh solutions of a low-molecular-mass polymer, extended piles composed of several molecules are formed. Each molecule from a disk with a diameter of ～4.4 nm, which is similar to the diameter of columnar phase cylinders in the solid state. In solutions of a highmolecular-mass polymer, several molecules form a wormlike particle. The observed supramolecular aggregates are unstable: within several months, their order breaks down and particles are dissolved.