Use of porous biodegradable polymer implants in meniscus reconstruction. 1) Preparation of porous biodegradable polyurethanes for the reconstruction of meniscus lesions

Porous biodegradable poly(urethanes) for reconstructing menisci have been prepared using two different combinations of techniques: freeze-drying/salt-leaching and in-situ polymerization/salt-leaching. Using these methods, homogenous porous materials with a controllable and reproducible morphology can be prepared. The materials were made of three different poly(urethanes): a methylenediphenyldiisocyanate-based polyurethane, a lysine diisocyanate-based poly(urethane), and a poly(-caprolactone)-based poly(urethane). The compressive stress-strain behavior of the Estane foams was determined. Foams made by the freeze-drying/salt-leaching technique implanted in dogs showed healing and good ingrowth of fibrocartilaginous tissue.     

Dielectric relaxation in polymeric solids Part 1. A new model for the interpretation of the shape of the dielectric relaxation function

A model is proposed which explains the shape of the dielectric relaxation function at the glass transition of polymers. The model is based on the idea that the molecular mobility at the glass transition is controlled by intra- and intermolecular interaction. In addition, a specific model for the local chain dynamics in amorphous polymer systems is used. According to the scaling hypothesis of molecular dynamics the model relates the high frequency dependence of the dielectric loss curve to the local chain dynamics and the low frequency dependence to the intermolecular correlation.     

Orientation,recognition, and photoreaction of nucleolipids in model membranes

Amphiphiles with nucleobases and nucleosides as headgroups have been synthesized. Their surface behavior was investigated in monolayers at the air/water interface. The double chain nucleolipids form stable monolayers with nearly identical surface pressure-area diagrams, whereas the spreading behavior of the mono chain amphiphiles is dominated by the various nucleobase-headgroups. When measuring the interactions between nucleolipid monolayers and nucleobases (monomeric and polymeric ones), specific base-base effects could be observed: the complementary nucleobases solubilized in the subphase expand the monolayer more than the non-complementary ones. Photodimerization reactions of thymine-amphiphiles were investigated in mono- and multilayers as well as in spin-coated films.     

Time domain dielectric spectroscopy. A new effective tool for physical chemistry investigation

The general principles of time domain dielectric spectroscopy (TDS) are summarized. The methods of data treatment and presentation, and different TDS methods which enable one to obtain the permanent spectrum of ^* () in the frequency range of 10⁵–10¹⁰ are given. The examples of TDS application for the investigation of dielectric properties in samples of different nature and structure are considered in this review.     

An absolute differential maximum bubble pressure surface tensiometer employing displaced capillaries

A modification of the differential maximum bubble pressure method for determining surface tensions is described. In this method, surface tension is calculated from the difference between maximum bubble pressures reached at capillaries of differing internal radii, vertically displaced by an amount calculated from the theory of Cuny and Wolf (1956) Ann Physik 17:57). The density dependence of the technique is eliminated and surface tension becomes a truly linear function of the differential maximum bubble pressure, which is easily measured. The absolute measuring technique is illustrated for equilibrium and dynamic surface tensions of a series of pure liquids and aqueous solutions.For dynamic measurements on surfactant solutions some important experimental considerations and limitations are described. In particular, a previously unrecognized source of error in estimating bubble surface ages is identified. It was found that the maximum bubble pressure for a large capillary does not immediately precede the detachment of the bubble, but occurs at one-third the overall bubble period. Thus, for large capillaries, subsequent to attaining the maximum bubble pressure, there exists a significant decay time in addition to the dead time. In general, surface ages corresponding to maximum pressure at small and large capillaries bubbling with the same period are not equal. This can lead to a large error in dynamic and equilibrium surface tensions of surfactant solutions. With suitable correction the technique is capable of measuring absolute surface tension, even for quite slowly equilibrating surfactant solutions.     

Effect of thick fixed-charge layers on electrostatic interaction — a theoretical approach

The electrostatic interaction pressure of charged surface layers is considered qualitatively and quantitatively. In the case of mutual penetration of the surface layers in addition to Maxwell stress and osmotic resp. hydrostatic pressure an isotropic stress on the fixed charges carrying molecules of the surface layers has to be taken into account. The derivation of the pressure-distance equations is given starting from both thermodynamic/electrostatic and hydrostatic/electrostatic principles. A possible biological significance of the additional stress is discussed emphasizing its role in modifying the structure of surface layer molecules.List of symbols e ₀ elementary charge - k Boltzmann constant - n _i concentration of theith ionic species in the bulk solution - P hydrostatic pressure - P hydrostatic pressure in the bulk volume (× ) - P ^h integration constant, independent on ×:P ^h =P(h) - T absolute temperature - Z _i electrovalence of theith ionic species - thickness of the surface layer - , ₀ relative and absolute permittivities - II(×) osmotic pressure at position × - II osmotic pressure in the bulk solution (× ) - osmotic pressure in the symmetry plane of interacting identical surface layers (electric field strength equals zero) - integration constant, independent on ×: - _e ^h electrostatic component of the disjoining pressure _e ^h = _e (h) - (×) mobile charge density profile (cations and anions of the electrolyte) - (×) fixed charge density profile - ^t(x) total charge density profile ( ^t = +) - ¹(x) fixed charge density profile of one of the two surface layers ( ¹(×) 0 for 0×) - (×) electric potential profile     

Micellization and surface activity ofn-alkyldimethylaminopropanesulfonates in aqueous solutions

Surface tension experiments were performed on severaln-alkyldimethylaminopropanesulfonate aqueous solutions at 15°, 25°, and 35°C. The critical micellar concentrations have been obtained and the surface properties calculated. The enthalpic and entropic contributions to either micellization and adsorption processes have been discussed. The observed properties have been related to the zwitterionic character of these surfactants.     

Thermotropic rigid chain copolymers I. crystallization kinetics and thermodynamic properties

The kinetics of structure formation and the thermal properties of the ordered phase were analyzed calorimetrically for a rigid polymer, characterized by an irregular chemical structure. The transition from the nematic melt to a partially ordered state was found to involve two different processes, a fast and a slow one. The fast one corresponds apparently to a thermally activated nucleation and growth mechanism, whereas the slow one is strongly self delaying. Its transition rate is only weakly dependent on the temperature. The thermal properties of the ordered phase, resulting from this process, vary strongly with the annealing temperature and annealing time. The enthalpy and entropy of fusion, characteristic for the pure ordered phase, are lower by a factor of about 10 in comparison to the corresponding values of flexible chain molecules.     

Interaction between an ion-penetrable particle and a solid particle. 1. Electrical double-layer interaction

Expressions are derived for the force and potential energy of the electrical double layer interaction between two parallel plates of different nature, i. e., an ion-penetrable plate and an ion-impenetrable plate. The latter may have either constant surface potential or constant surface charge density. It is shown that when the ion-impenetrable plate has a constant surface potential, the interaction force may, under certain conditions, become attractive even if the surface potentials of the two plates at infinite separation are of the same sign. In contrast, when the ion-impenetrable plate has a constant surface charge density, the interaction force may, under certain conditions, become repulsive even if the two plates at infinite separation are of opposite sign. This means that an ion-penetrable plate shows a dual behavior. That is, under certain conditions, it behaves like a solid plate with constant surface potential or surface charge density, depending on whether it interacts with a solid plate having a constant surface potential or a constant surface charge density.     

Functionalization of colloidal silica and silica surfaces via silylation reactions

A series of trialkoxysilane compounds tipped with primary amine groups were used to functionalize the surfaces of glass and colloidal silica. Streaming potential and microelectrophoretic mobility measurements were used to monitor the stability of the functionalized surfaces.Hydrolytic breakdown of the surface-to-silane coupling was induced by either successively increasing and decreasing the pH of the solution in contact with the surface, or by aging the derivatised surfaces in aqueous solution over prolonged periods of time. The chemistry of the spacer units between the trialkoxysilane group and the primary amine tip had a major influence on the subsequent hydrolytic stability. Large hydrophobic spacer groups showed small changes in the electrokinetic properties on storage, but large changes when successively titrated with acid and base through the pH range. The behavior observed with small hydrophobic spacer groups was that large changes in electrokinetic properties were obtained on storage and with pH titration.     

Microscopic observation of ordered colloids in sedimentation equilibrium and the important role of Debye screening length. 3. Heavy and monodisperse polystyrene type spheres in aqueous solution of neutral polymers

The ordered structures are observed directly by the metallurgical microscope for the heavy (specific gravity=1.50) and monodisperse polystyrene type spheres in sedimentation equilibrium and in the presence of neutral polymers, polyvinylalcohol (PVA), polyethyleneglycol (PEG), polyvinyl-pyrrolidone (PVP), hydroxypropylcellulose (HPC), and polyacrylamide (PAA_m). The intersphere distances in the ordered lattices decrease by the addition of neutral polymer in the order, PVA < PEG < PVP < HPC < PAA_m. These effects of neutral polymers are reasonably well-explained by the intersphere repulsion from the electrical double layer interaction, which is influenced by the polymer adsorption on the latex surface by the hydrophobic and/or dipole-dipole interactions.     

Donator acceptor behavior of aerosil in several organic liquids

Aerosil is studied with regards to its acceptor behavior by means of electrokinetic measurements and UV measurements in various organic liquids. Whereas the values of the general negativ zeta-potential only approximately correspond with the donor number of the liquids determined according to Gutmann, Marie and Gal, and Kravtzov et al., an excellent agreement between zeta-potential and the UV maximum of a dicyano-bis(1,10-phenanthrolin)-ferric [Fe(phen)₂(CN)₂] complex adsorbed at the solid-liquid interface was found. The fact that traces of water decrease the negative zeta-potential of aearosil in organic liquids is attributed to hydration of the aerosil surface.Dedicated to Professor Dr. Josef Schurz on the occasion of his 65th birthday.     

Dielectric relaxation in polymer solids Part 2: Application of the new model to polyurethane systems

Measurements of the complex permittivity of crosslinked polyurethanes at different temperatures in the frequency range 1–10⁵ Hz are discussed with respect to shape of relaxation curves. Using a new model (published in preceding paper) the shape parameters are related to small and large scale interaction.     

Synthesis and physical behavior of polyamide 6,10-poly(butadiene-co-acrylonitrile) segmented block copolymers

Segmented copolymers, characterized by polyamide 6,10 and poly(butadieneco-acrylonitrile) random blocks, were studied. Samples of such copolymers, having different relative content of the two components, were synthesized. Films were prepared by pressure molding and studied using differential scanning calorimetry and dynamicmechanical analysis. Results indicate that a phase segregation occurs and the system can be described by a matrix model. The matrix can be polyamidic or polybutadienic, depending on sample composition, while, in the matrix, the other component is organized in segregated domains.     

Melittin and ionic surfactant interactions in monomolecular films

The interaction between the anionic and cationic surfactants with Melittin spread monolayers at the air-water interface was investigated. The addition of anionic Cl^–, under the films of Melittin gives rise to a change in both surface pressure and surface potential. These interactions are different when surfactants are present, due to specific interactions between Melittin and the ionic-surfactants.     

Influence of sodium sulfate or sodium sulfite on the solubilization of benzylalcohol in cationic micellar solutions

The enthalpy of benzylalcohol (BzOH) solution has been determined as a function of alcohol concentration in aqueous trimethyltetradecylammonium bromide (TTAB) solutions in the presence of sodium sulfite or sodium sulfate up to high salt concentration. The electrolytes studied do not seem to induce TTAB sphere-torod transition at least up to 0.6 mol/kg of salt. Comparison with the enthalpic behavior of BzOH in sodium dodecylsulfate solutions and with that of 1-pentanol in both cationic and anionic micellar solutions suggests that the solubilization of BzOH in TTAB solutions is specifically favored by intramolecular interactions between alcohol molecules within the cationic micelles. The replacement of the bromide counterions by the sulfite or sulfate ions has been studied using potentiometry with an ionselective electrode in the case of trimethylhexadecylammonium bromide (CTAB). No difference could be detected between the effects of either divalent anions on the rate of change of the bromide ion-condensation with the salt/surfactant concentration ratioR. The degree of counter-ion condensation on micellar surface depends not only on theR values, but also on the total surfactant concentration.     

Potential theory in the problems of interfraction at small gap widths. A solid sphere and a droplet

A solid sphere approaches a spherical droplet at small gap widths. The radii of the particles are identical. Potential theory is applied and the problem of interaction brought to the solution of an integrodifferential equation for radial velocity at the droplet/ thin layer interface. Asymptotic formulae are reported for interface velocity and drag force for small and large viscosity ratios. The results are compared with the solutions for a solid sphere and flat tangentially mobile interface. Thus, two major effects may be distinguished: opening of the gap and curving of the streamlines inside the droplets. The latter is shown to cause a relative increase in the drag force.     

Structural and property correlations of ethylen-α-olefin copolymers

Ethylene-olefin copolymers differ from other polyethylenes in that:

Modified precipitated silicas as polyurethane fillers

Results have been presented from studies on physico-chemical properties of precipitated silicas, their modification with silanes and the suitability of such precipitated silicas as polyurethane fillers. Effect of unmodified and modified fillers on the course of synthesis and chosen physico-mechanical properties of urethan elastomers have been described.