Two-Chambered Chitosan Nerve Guides With Increased Bendability Support Recovery of Skilled Forelimb Reaching Similar to Autologous Nerve Grafts in the Rat 10 mm Median Nerve Injury and Repair Model

Tension-free surgical reconstruction of transected digital nerves in humans is regularly performed using autologous nerve grafts (ANGs) or bioartificial nerve grafts. Nerve grafts with increased bendability are needed to protect regenerating nerves in highly mobile extremity parts. We have recently demonstrated increased bendability and regeneration supporting properties of chitosan nerve guides with a corrugated outer wall (corrCNGs) in the common rat sciatic nerve model (model of low mobility). Here, we further modified the hollow corrCNGs into two-chambered nerve guides by inserting a perforated longitudinal chitosan-film (corrCNG[F]s) and comprehensively monitored functional recovery in the advanced rat median nerve model. In 16 adult female Lewis rats, we bilaterally reconstructed 10 mm median nerve gaps with either ANGs, standard chitosan nerve guides (CNGs), CNGs (CNG[F]s), or corrCNG[F]s (n = 8, per group). Over 16 weeks, functional recovery of each forelimb was separately surveyed using the grasping test (reflex-based motor task), the staircase test (skilled forelimb reaching task), and non-invasive electrophysiological recordings from the thenar muscles. Finally, regenerated tissue harvested from the distal part of the nerve grafts was paraffin-embedded and cross-sections were analyzed regarding the number of Neurofilament 200-immunopositive axons and the area of newly formed blood vessels. Nerve tissue harvested distal to the grafts was epon-embedded and semi-thin cross-sections underwent morphometrical analyses (e.g., number of myelinated axons, axon and fiber diameters, and myelin thicknesses). Functional recovery was fastest and most complete in the ANG group (100% recovery rate regarding all parameters), but corrCNG[F]s accelerated the recovery of all functions evaluated in comparison to the other nerve guides investigated. Furthermore, corrCNG[F]s supported recovery of reflex-based grasping (87.5%) and skilled forelimb reaching (100%) to eventually significantly higher rates than the other nerve guides (grasping test: CNGs: 75%, CNG[F]s: 62.5%; staircase test: CNGs: 66.7%, CNG[F]s: 83.3%). Histological and nerve morphometrical evaluations, in accordance to the functional results, demonstrated best outcome in the ANG group and highest myelin thicknesses in the corrCNG[F] group compared to the CNG and CNG[F] groups. We thus clearly demonstrate that corrCNG[F]s represent promising innovative nerve grafts for nerve repair in mobile body parts such as digits

PVDF and P(VDF-TrFE) Electrospun Scaffolds for Nerve Graft Engineering: A Comparative Study on Piezoelectric and Structural Properties, and In Vitro Biocompatibility

Polyvinylidene fluoride (PVDF) and its copolymer with trifluoroethylene (P(VDF-TrFE)) are considered as promising biomaterials for supporting nerve regeneration because of their proven biocompatibility and piezoelectric properties that could stimulate cell ingrowth due to their electrical activity upon mechanical deformation. For the first time, this study reports on the comparative analysis of PVDF and P(VDF-TrFE) electrospun scaffolds in terms of structural and piezoelectric properties as well as their in vitro performance. A dynamic impact test machine was developed, validated, and utilised, to evaluate the generation of an electrical voltage upon the application of an impact load (varying load magnitude and frequency) onto the electrospun PVDF (15–20 wt%) and P(VDF-TrFE) (10–20 wt%) scaffolds. The cytotoxicity and in vitro performance of the scaffolds was evaluated with neonatal rat (nrSCs) and adult human Schwann cells (ahSCs). The neurite outgrowth behaviour from sensory rat dorsal root ganglion neurons cultured on the scaffolds was analysed qualitatively. The results showed (i) a significant increase of the β-phase content in the PVDF after electrospinning as well as a zeta potential similar to P(VDF-TrFE), (ii) a non-constant behaviour of the longitudinal piezoelectric strain constant d33, depending on the load and the load frequency, and (iii) biocompatibility with cultured Schwann cells and guiding properties for sensory neurite outgrowth. In summary, the electrospun PVDF-based scaffolds, representing piezoelectric activity, can be considered as promising materials for the development of artificial nerve conduits for the peripheral nerve injury repair

Einfluß schneller Neutronen auf das Transportverhalten fester Spaltprodukte in pyrokohlenstoffbeschichteten Kernbrennstoffteilchen

The transport behaviour of metallic fission products in pyrocarbon-coated fuel particles is investigated by means of postirradiation annealing at 1400°C as a function of the fast neutron fluence. The release of barium and strontium are both increased by fast neutrons, and that even, if the kernels contain alumina additives, which improve the fission product retention by forming aluminates (e.g. BaAl $_{2}$O$_{4}$). The release of these two fission products is controlled by the effective diffusion coefficient in the kernel, which is in the case of Sr 90 in the range of 5,7·10$^{-15}$cm$^{2}$s$^{-1}$ (nonirradiated) and 5,3·10$^{-13}$ cm$^{2}$s$^{-1}$ (fluence 2· 10$^{22}$ cm$^{-2}$ at E> 0,1 MeV). The most significant increase is observed in the low fluence region. Ruthenium and ceriüm are released from the kernels by recoil only, not by diffusion. The caesium release is controlled by diffusion in the outer coating layer and depends on the microstructure of the pyrocarbon: The diffusion coefficient is decreasedby fast neutrons, if the amount of fiber component in the pyrocarbon is high. At low amounts of fiber component the diffusion coefficient is increased by fast neutrons

Bestrahlungsverhalten von beschichteten Brennstoffteilchen mit spaltproduktbindenden Kernadditiven

The four irradiation experiments FRJ2-P17, FRJ2-P18, FRJ2-P19, and FRJ2-P20 for testing the efficiency of fission product-retaining kernel additives in coated fuel particles are described. The evaluation of the obtained experimental data led to the following results:- zirconia and alumina kernel additives are not suitable for an effective fission product retention in oxide fuel kernels,- alumina-silica kernel additives reduce the in-pile release of Sr 90 and Ba 140 from BISO-coated particles at temperatures of about 1200°C by two orders of magnitude, and the Cs release from kernels by one order of magnitude,- effective transport coefficients including all parameters which contribute to kernel release are given for (Th,U)O$_{2}$ mixed oxide kernels and low enriched UO$_{2}$ kernels containing 5 wt. % alumina-silica additives: log D$_{K}$/cm$^{2}$s$^{-1}$ = - $\frac{36028}{T}$ + 6,261 (Sr 90), log D$_{K}$/cm$^{2}$s$^{-1}$ = - $\frac{29646}{T}$ + 5,826(Cs134/137), -alumina-silica kernel additives are ineffective for retaining Ag 110 m in coated particles. However, also an intact SiC-interlayer was found not to be effective at temperatures above 1200 C.- the penetration of the buffer layer by fission product containing eutectic additive melt during irradiation can be avoided by using additives which consist of alumina and mullite without an excess of silica,- annealing of LASER-failed irradiated particles and the irradiation test FRJ2-P20 indicate that the efficiency of alumina-silica kernel additives is not altered if the coating becomes defect

Bestrahlungsverhalten von beschichteten Brennstoffteilchen für das Abbrand/Brut Partikelsystem

The cross evaluation of 30 irradiation experiments which were carried out in the last ten years in order to test fuel particles for the separate use of high enriched uranium in fissile particles and thorium in fertile particles, led to the following results: - An oxide-based fissile/fertile particle system (UO$_{2}$ fissile kernel/ThO$_{2}$ fertile kernel) can be used as well as the American carbide/oxide particle system (UC$_{2}$ fissile kernel/ThO$_{2}$ fertile kernel) under the operation conditions of a high temperature reactor with spherical fuel elements. - The swelling of fissile kernels as a consequence of fission gas pores is much more pronounced in UO$_{2}$ than in UC$_{2}$ fissile kernels but the buffer layer topes with the swelling without any problems. - Ceramic kernel additives (e. g. Al$_{2}$O$_{3}$) as well as carbon additives proved not to be suitable because they deteriorate the mechanical properties of the fissile kernels. - Kernel migration in a temperature gradient ("amoeba effect") is observed during irradiation of UO$_{2}$ fissile particles but this does not cause any coating failure. The amoeba effect is suppressed completely by 10 % UC$_{2}$ additives to the UO$_{2}$ kernel. - The silicon carbide interlayer is absolutely necessary for an efficient retention of the solid fission products and has also proved sucessfully for fertile particles. Inner corrosion of the SIC layer by traces of chlorine can be avoided by a suitable coating process. The SIC corrosion caused by metallic fission products (especially Pd) starts at high temperatures which, however, decrease wich increasinq fast neutron fluentes. - A measurable fraction of-defective particle coatings was not observed before exceeding the target values of burnup and fast neutron fluence. The failure fraction is described quantitatively and correctly by a model which takes account of the increasing internal pressure due to burnup and the decreasing ultimate tensile strength and the SiC layer due to the influence of fast neutrons. - The irradiation-induced dimensional changes of the graphite matrix are Independent of the fuel volume loading and have no influence on the irradiation behaviour of the embedded fissile and fertile particles

NACA Technical Memorandums

This report was made to study the velocity distribution in an open, in a partially open, and in a partially expanding jet. The open-jet observations reveal minor systematic discrepancies from Tollmien's theoretical velocity distribution. The shearing-stress distribution for the partially open jet was determined. The value derived for the ratio of mixing distance to jet width was found to be in close agreement with the corresponding value for the open-jet boundary

Die chemischen Grundlagen des Hydrolyseverfahrens zur Herstellung spärischer Kernbrennstoffteilchen

The preparation of UO$_{2}$ microspheres by the Hydrolysis Process is based on the solidification of droplets of a concentrated uranyl " nitrate solution in hot oil. The uranyl nitrate is complexed by urea and partly hydrolized by adding solid hexamethylentetramine. The temperature depending solidification reaction of the metastable solution is a continuous polymerisation of [(U0$_{2}$ (OH)$_{2}$)$_{n}$ UO$_{2}$]$^{2+}$ ions forming kolloidal UO$_{2}$(OH)$_{2}$. The crystallite size of the spherical gel particles is increased by washing with hot water. Heat treatment of the washed and dried particles in reducing atmosphere leds to UO$_{2}$ with excellent sintering behaviour. The process was also successfully applied to the preparation of ThO$_{2}$ and (U,Th)O$_{2}$ microspheres