Mechanical Testing of Cancellous Bone - Research Paper Example

 Mechanical Testing of Cancerous Bone Abstract This was a practical experiment, in which the cancerous bone considered as rigorous porous materials was tested mechanically with the use of the ASTM standard.This was done with a view to finding out if stiffness and strength depended on the bone density, testing conditions, or animal species, an experiment was set up. Using the ASTM testing standard to determine weights for 24 samples of the bones from the pig and cow it was observed that the general pattern of stress against strain looked similar to that shown in the ASTM standard for testing rigid cellular plastics. Therefore, the plotting of stress curves was done. Basing on the intercept and the slope of the graph obtained in this experiment, compressive strength, the stiffness, the zero strain point, as well as the failure strain were then calculated. It was found that density was in directly proportion with the three mechanical properties (stiffness, strength, and failure strain) for samples from porcine, as well as bovine bone. Following these results, it was concluded therefore, that the mechanical behaviour of cancerous bone in both pig and the cow is almost similar although it was somewhat lower in the cow samples relative to that from porcine. Introduction Trabecular bone or the cancerous bone is the porous material that often represent a type of osseous tissue forming bones (Jee, 1996). Research indicates that trabecular bone has a higher surface area relative to other types of osseous tissues (Foss, 1992). Contrary, it has been found to have less density and stiffness (Currey, 1987). Arguably, the cancerous bone mechanical behaviour is somewhat similar to the other related cellular materials including the polymeric. This is because of its possessing a cellular structure consisting of the connected network of plates and rods (Bursten, & Frankel, 1999). There are contributing factors to the cancerous bone strength with bone density identified as one such factor. According to WHO (1994) there is need to determine the fracture risks using bone mineral density. It is also worth noting that other than the density of the bone, testing conditions, as well as the species of the animal are essential factors affecting the stiffness and strength of cancerous bones (Bell, Olive & Grabb, 1988). From the explored body of literature, it is evident that there are numerous experiments that have been conducted with a view of evaluating the density, and strength of a bone. However, there are limited research conducted on dependent of the strength of the cancerous bone on either testing conditions or animal species. Because of this gap in research, this experiment is set to carry out an investigation on the dependence of cancerous bone density, testing conditions and the testing condition. Aim of the Experiment This experimental was set up with an aim of analyzing the stress-strain curve standard obtained with a view to ascertain whether strength and stiffness of cancerous bone depended upon the bone density, the animal species or testing condition. Experimental protocol Apparatus This being an experimental set up, there were materials and apparatus that were used to perform the experiment. They included a digital balance from 60-2 N, Kern & Sohn, Germany, a core drill, the LVD, the material testing machine, as well as the digitalized Vernier callipers from MW110-15DDL, Moore and Wright, UK. Materials & Methods In order to achieve the set objectives, a certain definite procedure was followed in this experiment. In this case, a thin bone slice was obtained from bovine tibias proximal by utilizing a band saw. It was then that a core drill was used in obtaining samples of cancerous bone. The measurements were such that diameter of the bone was 9mm and the measuring of sample dimensions achieved through the use of the vernier caliper. Moreover, the digital balance was used to measure the sample weights with the samples that were allocated for each species being divided into two groups of about six samples each. After this, the first group was subjected to the unconstrained loading with the second being subjected to constrained loading. In this regard, for the constrained loading, samples were first placed on the flat surface into a machine for testing materials. The samples were then compressed using a surface that was flat ended. With the help of the load cell, as well as the LVDT, the flat-ended displacement surface was measured alongside force applied or accuracy, the force and the displacement were sampled digitally at a 5Hz frequency and stored on a Pc. The test was done continuously up to when a yield point was reached or a 0.65mm deformation. For the constrained loading, on the other hand, the sample was first placed inside an aluminum cylinder whose internal diameter was 9mm with a height of 5mm. The cylinder containing a sample was placed on a flat surface inside a material testing machine. At a rate of 0.5 mm per min, the sample was compressed with a flat ended surface whose diameter was approximately 8.9mm. It was then that the sample weighing was initiated. First, each sample was placed inside a vial and for purposes of dissolving the bone marrow, samples were stored inside ethanol. This was done ensuring that that ethanol was changed after every 3 to 4 days. After which they were removed from ethanol and subjected to drying conditions. Finally, the samples were weight on a digitalized beam balance for purposes of determining their weight. Results. Microsoft word and excel were used in this experimental to collect and analyse data. Considering that the stiffness or the elastic modulus is the slope or gradient of the stress strain curve in linear area, Hook’s law can be applied in calculation as Elastic modulus (E) = with MPa as the unit of measurement. In this case, the slope function of the Excel can be used this can be used to implement this calculation. This way, the maximum strength (MPa) is obtained from the “Max” function. From the gradient formula, it is clear that the stress-strain linear part does cross the horizontal axis at a point (y=0), referred to as zero strain point for the (ASTM standard). In this experiment we made use of the function “x= -INTERCEPT/SLOPE “ for purposes of measuring this point which in turn is used to find the failure strain. From this, the Failure strain equals the strain at a point of compressive failure subtracting it the zero strain. The results were recorded on the tables below "CanBon" samples Sample thickness(mm) Diameter(mm) Weight (gr) Species Constrained 1 5.15 8.84 0.2559 Cow No 2 5.17 8.69 0.2806 Cow No 3 4.9 8.61 0.2059 Cow No 4 5.05 8.75 0.2132 Cow No 5 4.95 8.78 0.2144 Cow No 6 5.02 8.63 0.2062 Cow No 7 5.16 8.62 0.2423 Cow Yes 8 5.15 8.77 0.243 Cow Yes 9 5.13 8.81 0.2662 Cow Yes 10 5.03 8.67 0.1915 Cow Yes 11 5.04 8.84 0.1981 Cow Yes 12 5.13 8.8 0.212 Cow Yes "Bonesample" samples 1 5.18 8.7 0.2374 Pig No 2 4.88 8.4 0.3304 Pig No 3 5.04 8.56 0.2956 Pig No 4 5.19 8.71 0.1972 Pig No 5 5.03 8.55 0.2241 Pig No 6 5.03 8.55 0.2627 Pig No 7 5.1 8.62 0.2606 Pig Yes 8 4.96 8.48 0.227 Pig Yes 9 5.14 8.66 0.2056 Pig Yes 10 4.96 8.48 0.2723 Pig Yes 11 4.96 8.48 0.245 Pig Yes 12 4.98 8.5 0.2918 Pig Yes The bovine bone Spacemen From the experiment, it was clear that density is directly proportional to; stiffness, failure strain and strength samples from porcine, as well as bovine bone. In the bovine specimens, the average stiffness for the constrained test was relatively more compared to the case of unconstrained test by a margin of about 3.5%. However, for the average strength, it is strongly increased in loading constrained test by a margin of 25%. Additionally, the failure strain is increased by about 18% in the constrained test (table a). Table a. Cow specimens 1st group unconstrained test Average Stiffness (MPa) Strength(MPa) Failure strain Density Stiffness (MPa) 181.0278MPa Canbon01 210.2249 9.709871 0.076966 0.2025018 Strength(MPa) 7.828 Canbon02 299.58672 12.31607 0.061437 0.2288906 Failure strain 0.05568 Canbon03 59.2866 7.925117 0.049267 0.1805196 Canbon04 182.3787 7.429938 0.047827 0.1756103 Canbon05 100.1258 5.730006 0.062675 0.1789373 Canbon06 134.5629 4.019341 0.036197 0.1756442 2nd group constrained test Average Canbon07 130.4679 9.70981 0.077488 0.201261 Stiffness (MPa) 174.6773MPa Canbon08 189.6835 11.16284 0.073419 0.1953756 Strength(MPa) 10.488. Canbon09 178.5347 11.97884 0.072284 0.2129165 Failure strain 0.058467 Canbon10 134.808 9.676711 0.076504 0.1612995 Canbon11 178.353 9.061484 0.065433 0.1601842 Canbon12 238.2374 11.13101 0.054752 0.1699509 Values for the mechanical property of 12 samples obtained from the bovine cancerous bone from stress strain curve graph for samples under unconstrained and constrained tests. A B C D The porcine bone specimens Considering the second specimens from porcine, it is clear that the strength of the specimens for the constrained test was somewhat greater by a margin of 23.5% compared to the strength in other tests. Additionally, the average failure strain and stiffness in the constrained test is slightly higher than those of unconstrained by 6.8% and 5.3% respectively as shown in (Table c). Table b. The mechanical properties of 12 samples for the pig cancerouss bone obtained from the stress-strain graph for each sample in constrained and unconstrained tests. A B C D Figure 1. Graphs A and B represent the relationship between Stiffness and Density, and graph C and D represent the relationship between Strength and Density for the samples from cow bone of both constrained and unconstrained. Pigs specimens 1st group Pig specimens unconstrained test Average Stiffness (MPa) Strength(MPa) Failure strain Density Stiffness (MPa) 130.8649 bonesample01 154.2224 5.96904 0.04906 0.1928336 Strength(MPa) 5.241119 bonesample02 125.739 5.383477 0.04144 0.305585 Failure strain 0.054929 bonesample03 152.0498 6.93191 -9.5937 0.2549158 bonesample04 2.786737 2.278183 0.039002 0.1595047 bonesample05 235.409 6.531443 0.035322 0.194094 bonesample06 84.31322 4.694474 0.077319 0.2275256 2nd group constrained test bonesample07 191.6615 10.22438 0.06926 0.219008 Average bonesample08 101.0481 4.443771 0.05421 0.2026856 Stiffness (MPa) 139.8182 bonesample09 91.5973 2.801957 0.041303 0.1698614 Strength(MPa) 6.823934 bonesample10 160.8015 8.403394 0.068111 0.2431334 Failure strain 0.057887 bonesample11 97.31591 4.824172 0.05755 0.2187576 bonesample12 178.6869 10.46347 0.07119 0.2582786 Discussion. Generally, the mechanical behaviour of cancerous bone specious given is almost similar though from the result, it is lower in the samples of a cow samples than it is from porcine source. The experiment indicated that specimens from the bovine (Cow) source were much stronger compared to those from the pig. This happens following differences in density as indicated in which case, density has a strong impact of the density upon the mechanical properties as shown in figure 1 and 2). Clearly, density is directly proportional to the strength and stiffness. The type of test also affected the results. As observed, in the constrained test, as earlier mentioned in the result, the average values of the mechanical properties of the cancerous bone were more than the unconstrained test. In this case, the compressive behaviour of the cow samples were to some extent to Carter and Hayes results for cow bones. An experimental finding supports these findings for Dennis et al., (1977) on human bone samples without marrow at fixed strain rate 10 per second. In this study, it was indicated that when the density increases by a 20% margin, the compressive strength increases by 77% and the stiffness as well increases by around 74%. The major shortcoming of this experiment is that the samples were limited. It should have more enough samples to reduce errors (produce a reasonable level of accuracy) and then have a good representation of the mechanical behaviour of the tested cancerous bone. If sample size is too low, the experiment will lack the precision to provide reliable answers. Therefore, large specimens are needed to give definite conclusion about the relationship of the above discussed factors on cancerous bone. References Dennis RC, Wilson CH. 1977. The compressive behaviour of bone as a two-phase porous structure. P 957 Jee., R. 1996. The relationship of Bone quantity and Bone Strength in Health Disease, and aging. J. Gerontol., 21: 517-521. Bell, H., Olive, J., & Grabb, A., 1988. Variation in strength of the Vertebrae with age and their relations to Calcif. Tissue res, 1:75-88. Bursten, A., & Frankel, V. 1999. The Viscolastic Properties of the Biological Material. Ann New York acad. Sciences. 146:159-167. Currey, J., 1987. The effect of Strain Rate, Mineral Content and Reconstruction Content on the mechanical properties of Bovine Bone.J. Biomech., 9:81-86. Foss, M., 1992. Bone density, Osteoarthrosis of the Hip, and fracture of the upper End of the Femur. Ann.Rheumt. Dis., 31:298-298. WHO, (1994) ‘World Health Organisation, Technical Report Series, No. 843, WHO, Geneva Read More