Each rapid prototyping (RP) process has its special and unique advantages and disadvantages. The paper presems a state-ofthe-art study of RP technologies and classifies broadly all the different types of rapid prototyping methods. Subsequently, the fundamental principles and technological limitations of different methods of RP are closely examined. A comparison of the present and ultimate performance of the rapid prototyping processes is made so as to highlight the possibiIi~, of future improvements for a new generation of RP systems.
The basic mechanism of reinforcement in tendons addresses the transfer of stress, generated by the deforming proteoglycan (PG)-rich matrix, to the collagen fibrils. Regulating this mechanism involves the interactions of PGs on the fibril with those in the surrounding matrix and between PGs on adjacent fibrils. This understanding is key to establishing new insights on the biomechanics of tendon in various research domains. However, the experimental designs in many studies often involved long sample preparation time. To minimise biological degradation the tendons are usually stored by freezing. Here, we have investigated the effects of commonly used frozen storage temperatures on the mechanical properties of tendons from the tail of a murine model (C57BL6 mouse). Fresh (unfrozen) and thawed samples, frozen at temperatures of 2208C and 2808C, respectively, were stretched to rupture. Freezing at 2208C revealed no effect on the maximum stress (s), stiffness ( E), the corresponding strain (e) at s and strain energy densities up to e (u) and from e until complete rupture (u p ). On the other hand, freezing at 2808C led to higher s, E and u; e and u p were unaffected. The results implicate changes in the long-range order of radially packed collagen molecules in fibrils, resulting in fibril rupture at higher stresses, and changes to the composition of extrafibrillar matrix, resulting in an increase in the interaction energy between fibrils via collagen-bound PGs.Keywords: frozen storage temperature, strength, stiffness, strain energy, collagen Implications Ultra-low storage temperature alters (i) the long-range order of collagen packing in fibrils, resulting in fibril rupture at higher stresses, and (ii) the composition of extra-fibrillar matrix, resulting in an increase in the interaction energy between fibrils via collagen-bound proteoglycans. Consequently, the tissue strength, stiffness and fracture toughness increase.
The objective of this study is to evaluate the influence of saline solution (0.9 per cent NaCl) on the tensile properties of freeze-stored tendons. Firstly, 170 pieces of chicken flexor digitorum profundus tendons were retrieved and wrapped in saline-soaked gauze before they were stored at -40degreesC. Then specimens were tensile tested at various time points over 360 days, scanning electron microscopy (SEM) was performed on fresh specimens, and specimens were freeze-stored for 233 days to investigate microstructure change after freeze storage. The mean values of strain ultimate tensile strength (UTS) did not deviate significantly (analysis of variance; p = 0.249) following freeze storage while the UTS and elastic modulus increased gradually with the duration of freeze storage and the growth became significant (p < 0.01) for durations longer than 70 and 40 days respectively. The SEM study showed that the collagen fibre density of specimens stored for 233 days decreased because of porosity growth. These findings suggested that the saline increased the tensile strength and modulus of the collagen.
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