["Elastic osteosynthesis" with autocompression plates of carbon fiber reinforced thermoplastic material].
The problem of atrophic bone that occurs in osteosynthesis employing rigid plates is first depicted. Attempts at fabricating "simirigid" plates, which, however, have so far failed to gain any practical importance are then discussed. The reason for this seems to be that made of duroplastics cannot be molded during the operation and the thermoplastics do not have sufficient strength. The production of semirigid plates made of thermoplastic Polyethersulfon (PES), reinforced with 20% short carbon fibres, results in plates which are made moldable by heating in a small oven, white retaining sufficient static strength, although only limited fatigue strength. Biomechanical examinations revealed that with appropriate dimensioning of the plates, "elastic osteosynthesis" results in less loss of mechanical function of the stabilized bones, so that less atrophy of the bone may be expected. During more pronounced exercise loading, a reversible "springiness" of the fracture results, which might stimulate callus formation and improved stability.
Verträglichkeit implantatgeeigneter alloplastischer Werkstoffe im Organismus
Die Bedeutung von Implantaten zur Wiederherstellung von Korperfunktionen, die durch Krankheit, naturliche Abnutzung oder Unfall verlorengegangen sind, nimmt stetig zu und last sich am einfachsten anhand des grosen Bedarfs ermessen. Jahrlich werden mehr als 1 500 000 Personen mit Gefasprothesen versorgt, in 100 000 Fallen werden kunstliche Herzklappen eingesetzt, etwa 220 000 Patienten erhalten einen implantierbaren Herzschrittmacher. Fur die extrakorporale Zirkulation bei Operationen am Herzen werden jahrlich etwa 600 000 Oxygenatoren benotigt. Der Jahresbedarf an kunstlichen Nieren nahert sich der Zahl 1 000 000. Beim Gelenkersatz steht die Huftprothese mit ca. 350 000 Implantationen an erster Stelle vor dem Ersatz des Finger-, Knie-, Schulter- und Ellenbogengelenks. Implantierbare Materialien fur die rekonstruktive Chirurgie haben den Umfang vieler Tonnen erreicht. Einen Eindruck von den vielfaltigen Einsatzgebieten moderner Kunststoffe vermittelt Tabelle 1.
Design of reinforced concrete lining in pressure tunnels, considering thermal effects and jointed rockmass
Abstract Jaeger's theory (Jaeger, Rock Mechanics and Rock Engineering , Cambridge University Press, 1972) of the design of the lining for a pressure tunnel applies to a tunnel located in an isotropic, homogeneous and elastic medium. The theory is derived from the elasticity equations for the plane stress condition. In this paper, Jaeger's theory is extended to a plane strain situation. Also included is a discussion of the effects of a uniform increase (or decrease) in the lining temperature, jointed rockmass, cracking of the tunnel lining, and cracking of the rockmass around the opening. Tables are presented for the modulus of subgrade reaction for various rockmass conditions and for rock sharing pressures for various lining conditions. The reduction factor to include the effect of joints in rockmass is derived by the analysis of a numerical model of the lined tunnel by the finite-infinite-interface element method.