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The mechanical properties of three wet commercial bone cements, namely Braxel (from Bioland®), Simplex-P (from Howmedica®) and CMW1-G (from DePuy®) are investigated by means of stress relaxation and dynamic mechanical analysis (DMA). The geometry of loading that was used is the three point bending method (ASTM D790); all the tests were performed in a water chamber by means of temperature sweeps between 17 and 57 °C and spanning four frequency decades. The results show that viscoelastic properties are strongly dependent on specimen conditioning (i.e. water uptake and heat treatment). The results also show that all the cements that were analyzed show mechanical properties which are intermediate between the ones of the cancellous bone and of the metals of which prostheses are normally made. As a consequence, the cement is able to reduce the stress concentrations due to the interfacing of materials which have very different stiffnesses. Moreover, the results of the DMA, particularly the ones concerning the damping factor (tan δ), indicate that at body temperature the bone cements tested show an increased capacity of dissipation, the higher is the loading frequency, thus displaying shock absorbing properties.

The development of a completely biodegradable composite artificial tendon prosthesis that mimics the structure and stress-strain response of natural tendon is presented. The artificial tendon is a composite of water-swollen poly(2-hydroxyethylmethacrylate)/poly(caprolactone) blend hydrogel matrix reinforced with poly(lactic acid) fibres.

The polymerization behaviour of bone cements during total hipreplacements is characterized by a fast and highly non-isothermal bulk reaction.In the first part of this paper the reaction kinetics are analysed bycalorimetric analysis in order to determine the rates of polymerization inisothermal and non-isothermal conditions. A phenomenological kinetic model,accounting for the effects of autoacceleration and vitrification, is presented.This model, integrated with an energy balance, is capable of predicting thetemperature across the prosthesis, the cement and the bone and the degree ofreaction in the cement, during in situ polymerization. The temperatureand the degree of reaction profiles are calculated, as a function of the settingtime, taking into account the system geometry, the thermal diffusivity of bone,prosthesis and cement, and the heat rate generated by the reaction according tothe kinetic model. Material properties, boundary and initial cond!itions are the input data of the heat transfer model. Kinetic and heat transfermodels are coupled and a numerical solution method is used. The model is appliedin order to study the effects of different application procedures on temperatureand degree of reaction profiles across the bone–cement–prosthesissystem.

The mechanical characterization of rabbit Achilles' tendon and anterior cruciate ligament is presented. Both static and dynamic mechanical tests have been performed on fresh explanted tissues. Experimental results are presented and discussed in terms of a relationship between structural architecture and mechanical properties. The differences in collagen fibre configuration and composition between tendon and ligament influence the tensile and viscoelastic properties. In particular, tendons and ligaments showed a gradual transition from a rubber-like to a glassy-like behaviour during the loading process due to the traightening of collagen fibres.