Tensile cortical bone

The stress-strain curves for cortical bones at various strain rates are shown in Figure 5.130. The mechanical behavior is as expected from a composite of linear elastic ceramic reinforcement (HA) and a compliant, ductile polymer matrix (collagen). In fact, the tensile modulus values for bone can be modeled to within a factor of two by a rule-of-mixtures calculation on the basis of a 0.5 volume fraction HA-reinforced... 

A follow-up study showed the relation between the composition and the redistribution of stress [47], Cortical bone was loaded with external compression and tension, and the stress stored within the apatite crystals was assessed via the shift in phosphate Vi band in two regions a collagen-rich area and an apatite-rich area. In the collagen-rich areas, stress was released under external tension, but localized stress intensification occurred under external. In apatite-rich areas, both tensile and compressive stresses were observed. 

The mechanical properties of cortical bone (specifically, the femur, tibia, humerus, and radius) of various species (specifically, horse, cattle, pig, and human) in tension, compression, and torsion are listed in Table I. It should be noted, for example, that human femur tensile strength (namely, 124 MPa) (Yamada, 1970) is in the same order of magnitude to that of cast iron (170 MPa) (Beer and Johnston, 1981) but, surprisingly, low in weight (Kaplan et al., 1994 Fung, 1993). These unique properties of bone are a direct consequence of the synergy of its molecular, cellular, and tissue arrangement. 

Sintered HAp particles are remodeled by the host tissue when implanted into bone. Implantation into the cortical bone of the femur of sheep has revealed that stoichio-metrically pure HAp resorbs by several microns after 18 months with dissolution occurring mainly at the grain boundaries (Benhayoune et al. 2000). The tensile strength of bone from the tibia of a rabbit onto a HAp cylinder is 0.85 MPa after 3 months (Edwards et al. 1997). 

Aging also affects the mechanical properties of cortical bone. Tensile ultimate stress decreases at a rate of approximately 2 percent per decade (Fig. 8.7a). Perhaps most important, tensile ultimate strain decreases by about 10 percent of its young value per decade, from a high of almost 5 percent... 

FIGURE 8.6 (a) Dependence of the ultimate tensile stress of human coitical bone on volume fraction (expressed as a percentage). Ages of the specimens were in the range 20 to 100 years. From Ref. 10.) b) Modulus versus calcium content (in mg/gm of dehydrated bone tissue) for cortical bone taken from 18 different species. From Ref 24.)... 

McCalden, R. W., McGeough, J. A., Barker, M. B., and Conrt-Brown, C M. (1993), Age-related changes in the tensile properties of cortical bone The relative importance of changes in porosity, mineralization, and microstructure, J. Bone Joint Surg. 75A(8) 1193-1205. 

Vincentelli, R., and Grigorov, M. (1985) The effect of haversian remodeling on the tensile properties of human cortical bone. J. Biomeck, 18, 201-207. 

The application of force will generate stresses within a bone. These may be either compressive, tensile or shear. Cortical bone will tolerate compressive stresses better than tensile or shear. 

Cyanoacrylates were shown to form a strong durable bond between bones in vitro. Tensile adhesive strength betw een smooth bovine cortical bone specimens bonded together with the isobutyl monomer and tested after one day storage in water was approximately 6.5 mPa (Brauer et al, 1979). The monomer was used, without evidence of histotoxicity, to repair osteochondral fractures (Harper and Ralston, 1983) and recently to improve meniscal repairs (Koukabis et al, 1995). Butylcyanoacrylate was also used in facial bone surgery for frontal bone reconstitution (Avery and Ord, 1982). 

The Young s modulus and the tensile strength of injection-moulded PEEK/HAp composites were reported to be in the range of 3-10 GPa and 40-90 MPa, respectively [106]. These results indicate that the mechanical properties of PEEK/HAp composites are in the region of cortical bone, making them a potential candidate for... 

The first glass-ceramics material for clinical applications was developed by H. Bromer and E. Pfeil in 1973 [108,109] called Ceravital. This name includes a number of compositions. In its origins Ceravital were considered very optimistically, to even replace bones in zones of load and teeth. Nevertheless, like it is possible to be observed, in mentioned Table V, its mechanical properties (flexural, tensile strength) are below of the 160 MPa that presents the cortical hmnan bone. 

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