Femoral Cementation in Knee Arthroplasty-A Comparison of Three Cementing Techniques in a Sawbone Model Using the ATTUNE Knee.

Femoral component loosening is a rare but severe complication in total knee arthroplasty. Former studies have repeatedly demonstrated radiolucent lines behind the ventral and dorsal anchoring shields of the femoral components, which has led us to investigate this matter further. Therefore, three different cementing techniques were tested in a group of nine Sawbone samples each. These differed in the amount of cement applied on the femoral component as well as in the pressure application. Computed tomography was performed to evaluate and classify the cement penetration into the bone adjacent to the prosthesis according to the zones defined by the Knee Society scoring system. The results show significantly deeper cement penetration in all zones when a pressurizer is used. In the other two groups, no significant difference in the dorsal bevel cement penetration was noted. Additionally, no difference in ventral and dorsal cement penetrations (Zones 1 and 4) was delineated. In contrast, there was a significant difference in both the ventral bevel (Zone 2) as well as the distal anchoring surface (Zones 5-7). The use of a pressurizer results in greater cement penetration into all anchoring areas. Completely covering the component back surface results in a significantly higher penetration, which is mainly due to differences in volume. These data show significantly improved cementation results when using a pressurizer. Whether this improves the biomechanical properties and ultimately the revision rate requires further investigation.

Ionic conductivity of solid polyelectrolyte complexes with varying water content: application of the dynamic structure model.

We present a systematic study of the dc conductivity of solid polyelectrolyte complexes (PEC) of type xPSS PSS·(1 - xPSS) PDADMA as a function of temperature, and of PSS and water content, respectively. PSS stands for poly(styrenesulfonate) and PDADMA for poly(diallyldimethylammonium). Apart from these polyions, small ions like Na+ and Cl- can be incorporated into the complexes. The amount of small ions and its type (Na+ or Cl-) depend on the PEC composition. We show that, in contrast to dried polyelectrolyte complexes where the chloride ions are macroscopically immobile, Cl- ions become mobile if water is absorbed into the PEC. In PEC with an excess of PDADMA (xPSS < 0.5), hydrated Cl- ions govern the ionic conductivity. On the other hand, in PEC with an excess of PSS (xPSS > 0.5), the conductivity is determined by the sodium ions. For the first time we show that the dependence of the conductivity on composition can be described by power-laws as derived within the framework of the dynamic structure model originally developed for glassy ion conductors by Bunde, Ingram and Maass (J. Non-Cryst. Solids, 1994, 172-174, 1222). This power-law behavior is found in PEC with an excess of Cl- ions as well as in those with an excess of Na+ ions. Also the model predictions concerning the temperature dependence of the power-law exponents on the one hand and the composition dependence of the activation enthalpy on the other hand, are found to be valid. These findings indicate that in polyelectrolyte complexes ions travel via pathways of ion specific sites through the polyelectrolyte matrix. The results on hydrated PEC are compared to those of dry PEC where the dynamic structure model is only applicable for PEC with an excess of PSS (xPSS > 0.5).

Comparison of the stability of three fixation techniques between porous metal acetabular components and augments.

OBJECTIVES: In order to address acetabular defects, porous metal revision acetabular components and augments have been developed, which require fixation to each other. The fixation technique that results in the smallest relative movement between the components, as well as its influence on the primary stability with the host bone, have not previously been determined. METHODS: A total of 18 composite hemipelvises with a Paprosky IIB defect were implanted using a porous titanium 56 mm multihole acetabular component and 1 cm augment. Each acetabular component and augment was affixed to the bone using two screws, while the method of fixation between the acetabular component and augment varied for the three groups of six hemipelvises: group S, screw fixation only; group SC, screw plus cement fixation; group C, cement fixation only. The implanted hemipelvises were cyclically loaded to three different loading maxima (0.5 kN, 0.9 kN, and 1.8 kN). RESULTS: Screw fixation alone resulted in up to three times more movement (p = 0.006), especially when load was increased to 100% (p < 0.001), than with the other two fixation methods (C and SC). No significant difference was noted when a screw was added to the cement fixation. Increased load resulted in increased relative movement between the interfaces in all fixation methods (p < 0.001). CONCLUSION: Cement fixation between a porous titanium acetabular component and augment is associated with less relative movement than screw fixation alone for all implant interfaces, particularly with increasing loads. Adding a screw to the cement fixation did not offer any significant advantage. These results also show that the stability of the tested acetabular component/augment interface affects the stability of the construct that is affixed to the bone.Cite this article: N. A. Beckmann, R. G. Bitsch, M. Gondan, M. Schonhoff, S. Jaeger. Comparison of the stability of three fixation techniques between porous metal acetabular components and augments. Bone Joint Res 2018;7:282-288. DOI: 10.1302/2046-3758.74.BJR-2017-0198.R1.

Negative effective Li transference numbers in Li salt/ionic liquid mixtures: does Li drift in the "Wrong" direction?

The electrophoretic mobilities µ of all ion species in the lithium salt/ionic liquid mixtures LiTFSA/EmimTFSA and LiBF4/EmimBF4 are determined by 1H, 19F and 7Li electrophoretic NMR. The average drift direction of Li is identical to that of the anions TFSA- or BF4-. This proves a correlated ion motion of Li with the anions in negatively charged Li-containing clusters in both systems. The effective charge of these clusters is determined as -1, or -2 in the system with TFSA or BF4, respectively, pointing at the existence of [Li(TFSA)2]- or [Li(BF4)3]2-. This behavior is described by a negative effective transference number of Li, resulting in a negative contribution of Li ions to the overall conductivity. Li effective transference numbers are in the range of -0.04 to -0.02, depending on Li salt concentration and anion type. Transference numbers thus clearly deviate from apparent transference numbers estimated from diffusion coefficients, as an effect of a vehicular transport mechanism. This has important implications for the mechanism of Li mass transport in Li ion batteries as the drift of charged clusters has to be overcompensated by diffusive mass transport of neutral, Li-containing aggregates.

Spin relaxation studies of Li+ ion dynamics in polymer gel electrolytes.

Two ternary polymer gel electrolyte systems are compared, containing either polyethylene oxide (PEO) or the poly-ionic liquid poly(diallyldimethylammonium) bis(trifluoromethyl sulfonyl)imide (PDADMA-TFSI). Both gel types are based on the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethyl sulfonyl)imide (P14TFSI) and LiTFSI. We study the influence of the polymers on the local lithium ion dynamics at different polymer concentrations using 7Li spin-lattice relaxation data in dependence on frequency and temperature. In all cases the relaxation rates are well described by the Cole-Davidson motional model with Arrhenius dependence of the correlation time and a temperature dependent quadrupole coupling constant. For both polymers the correlation times are found to increase with polymer concentration. The activation energy of local motions slightly increases with increasing PEO concentration, and slightly decreases with increasing PDADMA-TFSI concentration. Thus the local Li+ motion is reduced by the presence of either polymer; however, the reduction is less effective in the PDADMA+ samples. We thus conclude that mechanical stabilization of a liquid electrolyte by a polymer can be achieved at a lower decrease of Li+ motion when a cationic polymer is used instead of PEO.

Quantifying and controlling the cation uptake upon hydrated ionic liquid-induced swelling of polyelectrolyte multilayers.

Controlling the uptake of specific ions in polyelectrolyte multilayers is of interest for various fields of application. Here, we quantify the amount of cation of an ionic liquid, namely 1,3-bis(cyanomethyl)imidazolium chloride, incorporated into polyelectrolyte multilayers upon contact with an ionic liquid solution. The ion partition equilibrium is determined depending on concentration in solution, employing attenuated total reflection infrared spectroscopy. Generating an excess charge in multilayers by post-preparative manipulation of their charge balance, one can control the incorporated amount. Three multilayer systems are assembled for this purpose, i.e., PSS/PDADMAC, PSS/PAH and PAA/PDADMAC, employing poly(styrene sulfonate) (PSS), poly(diallyldimethylammonium chloride) (PDADMAC), poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA). The charge balance of the latter two films is manipulated by an external pH stimulus generating an excess positive or negative internal charge, respectively. The concentration of cations in PEM amounts to 30% to 100% of the bulk concentration and scales as PAA/PDADMAC > PSS/PDADMAC > PSS/PAH. Thus, post-preparative pH treatment may be a future tool to create ion-conductive polymer gel films with a desired concentration of small cations.

Scaling properties of the shear modulus of polyelectrolyte complex coacervates: a time-pH superposition principle.

We analyze the scaling properties of pH-dependent shear modulus spectra of complex coacervates made of weak polyanions and strong polycations. For the first time, we report on a "time-pH superposition principle". This principle implies that the charge density in complex coacervates made of not fully charged polyions only influences the time scale of the relaxation dynamics, but not the mechanisms of the underlying dynamics.

Time-humidity-superposition principle in electrical conductivity spectra of ion-conducting polymers.

We analyze the scaling properties of the ac conductivity spectra of ion-conducting polyelectrolyte complexes of different compositions. Spectra were taken at ambient temperature but at different relative humidities. For the first time, we report on a scaling principle for conductivity spectra termed "time-humidity-superposition principle" in analogy with the well-known time-temperature-superposition principle. This model-free scaling holds for different materials over several decades in frequency. It implies that the hydration is activating ion motion over short and long distances in a similar general way, a concept so far only established for thermal energy.

Foreign-ion and self-ion diffusion in a crosslinked salt-in-polyether electrolyte.

We present an extensive study of ionic transport in PolyG(30)LiPF(6), which is a crosslinked poly(ethylene oxide)-poly(propylene oxide(PEO-PPO) random copolymer complexed with LiPF(6) to an oxygen-to-cation ratio of 30 : 1. Self-diffusion coefficients of the constituent ions were measured by pulsed field gradient nuclear magnetic resonance (PFG-NMR) as a function of temperature using the signals of (7)Li and (19)F. These data were compared with the charge diffusivity as derived with the Nernst-Einstein equation from the ion conductivity obtained by impedance spectroscopy. In addition, the diffusion behaviour of a foreign cation (sodium) and that of a foreign anion (iodine) in PolyG(30)LiPF(6) were investigated by means of the radiotracers (22)Na and (125)I. All different types of diffusivities were evaluated in a comprehensive ion transport model which allows for the occurrence of charged single ions and neutral ion pairs. Simultaneous fitting of all data within this model yields best values of the model parameters which include Vogel-Tammann-Fulcher parameters and enthalpies/entropies of pair formation. Two distinct variants of the same general model reproduce the experimental data equally well, i.e., with closely similar results for the pair contribution to the migration of each ionic species. In the first variant, this pair contribution is due to a small fraction of ion pairs with a high mobility. By contrast, the second variant results in a very large fraction of pairs characterized by a relatively low mobility. The assumptions and implications connected with both model variants are discussed in detail.

Unconventional scaling of electrical conductivity spectra for PSS-PDADMAC polyelectrolyte complexes.

For the first time, we analyze ac conductivity spectra of various dried ionically cross-linked polyelectrolyte complexes in terms of the time-temperature superposition principle. The temperature-dependent spectra of some complexes show scaling properties that are distinctly different from the behavior of all other ion-conducting materials reported so far, but in agreement with model predictions by Roling [B. Roling, Phys. Chem. Chem. Phys. 3, 5093 (2001).10.1039/b105094j]. We conclude that the dc conductivity of the investigated PEC is always governed by the Na+ ions, even in complexes with excess of polycations and chloride anions.

Melting and freezing of water in cylindrical silica nanopores.

Freezing and melting of H(2)O and D(2)O in the cylindrical pores of well-characterized MCM-41 silica materials (pore diameters from 2.5 to 4.4 nm) was studied by differential scanning calorimetry (DSC) and (1)H NMR cryoporometry. Well-resolved DSC melting and freezing peaks were obtained for pore diameters down to 3.0 nm, but not in 2.5 nm pores. The pore size dependence of the melting point depression DeltaT(m) can be represented by the Gibbs-Thomson equation when the existence of a layer of nonfreezing water at the pore walls is taken into account. The DSC measurements also show that the hysteresis connected with the phase transition, and the melting enthalpy of water in the pores, both vanish near a pore diameter D* approximately equal to 2.8 nm. It is concluded that D* represents a lower limit for first-order melting/freezing in the pores. The NMR spin echo measurements show that a transition from low to high mobility of water molecules takes place in all MCM-41 materials, including the one with 2.5 nm pores, but the transition revealed by NMR occurs at a higher temperature than indicated by the DSC melting peaks. The disagreement between the NMR and DSC transition temperatures becomes more pronounced as the pore size decreases. This is attributed to the fact that with decreasing pore size an increasing fraction of the water molecules is situated in the first and second molecular layers next to the pore wall, and these molecules have slower dynamics than the molecules in the core of the pore.

Enhanced lithium transference numbers in ionic liquid electrolytes.

Ion transport processes in mixtures of N-butyl- N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (BMP-TFSI) and lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) were characterized by ac impedance spectroscopy and pulsed field gradient NMR. Molar ratios x = n Li-TFSI/( n Li-TFSI + n BMP-TFSI) up to 0.377 could be achieved without crystallization. From the bulk ionic conductivity and the individual diffusion coefficients of cations and anions we calculate the Haven ratio and the apparent lithium transference number. Although the Haven ratio exhibits typical values for ionic liquid electrolytes, the maximal apparent lithium transference number is higher than found in other recent studies on ionic liquid electrolytes containing lithium ions. On the basis of these results we discuss strategies for further improving the lithium transference number of such electrolytes.

Diffusion exchange NMR spectroscopic study of dextran exchange through polyelectrolyte multilayer capsules.

Diffusion exchange of dextran with molecular weights 4.4 and 77 kDa through polyelectrolyte multilayer (PEM) hollow capsules consisting of four bilayers of polystyrene sulfonate/polydiallyldimethylammonium chloride has been investigated using two-dimensional nuclear-magnetic-resonance methods: diffusion-diffusion exchange spectroscopy (DEXSY) and diffusion-relaxation correlation spectroscopy (DRCOSY). Results obtained in DRCOSY experiments show that the diffusion process of dextran 77 kDa exhibits an observation time dependence suggesting a diffusion behavior restricted by confinement. We find evidence for both single capsule and capsule aggregate states, with a partitioning of the 77-kDa dextran between the free and capsule states much larger than that suggested by volume fraction alone. Results from DEXSY experiments show that dextran 77 kDa is in diffusive exchange through the capsules with an exchange time of around 1 s. In contrast, the capsules have no detectable influence on the diffusion process of the dextran 4.4 kDa. This quantitative information may be used in designing PEM capsules as drug carriers.

Fluorescence correlation spectroscopy as a tool to investigate single molecule probe dynamics in thin polymer films.

Fluorescence correlation experiments were performed on rhodamine 6G in PDMS spin-coated films on glass surfaces. With polarised excitation, ensemble bleaching of the dye and single molecule intensity fluctuations were observed. From the statistics of single molecule intensity data taken at different positions in the film, correlation functions were calculated. Two modes of motion with exponential decay shapes and correlation times of tau(c) = 0.15 s and tau(c) = 0.7 s could be detected. Potential origins of intensity fluctuations are lateral diffusion, rotational diffusion or intramolecular fluctuations of dyes involving spectral diffusion or photoinduced processes. From the experimental results, lateral diffusion can be ruled out as a motional mode. Single molecule fluctuations are assigned to changes of the molecular configuration of the dyes, which are rigidly bound to the glass. To assess the environmental influence on such molecular motions, the bulk viscosity of the PDMS was varied over two orders of magnitude, leading to changes of tau(c) of the slow mode by a factor of four. This result proves the sensitivity of the single molecule fluctuations to the molecular scale dynamics of the surrounding polymer matrix and makes the correlation time a measure of the local environment of dye probes.

Exchange dynamics of surfactants in adsorption layers investigated by PFG NMR diffusion.

Surfactant adsorption layers on polystyrene latex particles are investigated concerning their equilibrium exchange dynamics with surfactant molecules in solution. Pulsed field gradient (PFG) nuclear magnetic resonance (NMR) self-diffusion measurements of the nonionic surfactant C12(EO)5 are performed, making use of the difference of the diffusion coefficients of adsorbed and free surfactant in solution. On variation of the gradient pulse spacing the echo decay data show a transition from fast to slow exchange, giving the possibility of a quantitative evaluation. A two-site model is applied to fit the data and obtain average residence times of the surfactant in both sites. The results are consistent with diffusion-controlled adsorption of surfactant monomers and additional micellar contributions to the exchange, whereas no evidence for kinetic barriers is found for these nonionic surfactants on the relevant timescale (10 ms).

The Fundamental Vibrations of NC-CC-CN (Dicyanoacetylene)

In the infrared spectrum of dicyanoacetylene the rotation vibration bands nu1 - nu9/2nu5 - nu9, nu1 + nu9/2nu5 + nu9 (Fermi resonance), nu2 - nu9, nu2 + nu8, nu4, nu6 - nu9, nu6 + nu8 - nu6, nu4 - nu7, nu4 + nu7, nu4 + nu7 - nu7, nu7 + nu8 - nu7, and 2nu7 + nu8 - nu7 (I and II) have been recorded with high resolution. From these bands the vibrational levels v1 = 1, v2 = 1, v4 = 1, v6 = 1, and v7 = 1 including the corresponding effective rotational constants have been calculated. Different methods for calculating the unperturbed position of the v1 = 1 level have been compared and the unperturbed B1 has been calculated. Additional information on the rotational constants of v8 = 1 and v9 = 1 is also given. Copyright 1997 Academic Press. Copyright 1997Academic Press