7 Use of Human and Animal Specimens in Biomechanical Testing
In order to investigate the effect of aging, disease, treatments, and injury on the mechanical properties of tissues, it is required to perform mechanical testing on biological tissues. While the primary aim of this research will be to obtain knowledge about the effects of these properties on human tissue, it is not always possible to obtain a supply of the required tissue at the desired quality and in sufficient quantity to allow testing to be performed if only human tissue is to be used. Therefore, it is required that alternative materials are used for testing. Although manmade biomaterials have been produced, they do not mimic closely enough the wide range of material properties that are present in true biological tissues. Therefore, in lieu of using human tissue, animal tissue is widely used as a substitute. While it is recognized that there are differences between species, in both the geometry and material properties, these still provide a suitable surrogate for biomechanical testing. In addition to the greater availability of animal sources of tissue for biomechanical testing, there are less legal and ethical restrictions to their use for this purpose. However, the guidelines relating to the ethical treatment of animals for research purposes must be strictly adhered to.
7.1 Use of Animals for Biological Research
It can often be easier to obtain animal material of sufficient quantity and of a reliable quality than to use human bone. Additionally, in the earlier stages of research into a treatment method or drug, it is prohibited to test on humans until the required testing has first been carried out in an animal model. If animals are to be used for research, it is imperative that they are treated humanely. This applies to animals that are used purely as a source of material for testing in vitro or whether a treatment method or drug is to be investigated and the effect studied in vivo. In the United Kingdom, relevant governance is provided by “The Animals (Scientific Procedures) Act 1986.” 1 It should be noted that the European governance provided by “Directive 86/609/EEC” 2 must also be complied with (when the research is carried out in the European Union where this law is applicable, along with any individual requirements of the member state).
7.1.1 Biological Variability
Bone is known to be an heterogeneous and anisotropic material (see Chapter 9); therefore, the properties derived from mechanical testing, even from the same animal, depend on the type (e.g., rib, femur, tibia), the location (e.g., anterior, medial, distal, etc.), and the orientation of testing with respect to the bone (e.g., longitudinal, transverse, radial).
Jargon Simplified: Loading Direction
The terms longitudinal, transverse, and radial should refer to the normal loading axis of the bone. In most cases, the long axis of the bone can be considered the longitudinal axis, the transverse axis runs at 90 degrees to this, and the radial axis runs from the endosteal to periosteal surfaces, as shown in Fig. 7.1.
As well as variations from anatomical location and between different animals of the same species, there can be considerable interspecies differences in mechanical properties. Table 7.1 shows the range of mineral volume fraction (MVf), the volume of mineral in parts per thousand, Young modulus (E), ultimate tensile strength (σult), ultimate tensile strain (εult), and work to failure (W) for a selection of animal species. 3 This shows the wide range of values for these properties that can be encountered.
It is important to bear in mind these differences in material constitution and mechanical properties when examining the results from mechanical testing, especially if comparisons are being made between specimens from different species.
Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
