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Practical Experiment: Mechanical Testing of Cancerous Bone

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Abstract

It was a practical experiment, where the cancerous bone deemed to be robust porous materials was mechanically tested using the ASTM standard. This was done to determine if stiffness and strength depended on the bone density, testing conditions, or animal species, an experiment was set up. Using the ASTM test standard to assess weights for 24 samples of the pig and cow bones, it was observed that the general stress pattern against strain looked close to the one shown in the ASTM test standard for rigid cellular plastics. The plotting of stress curves was thus completed. 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 directly proportional to the three mechanical properties (stiffness, strength, and failure strain) for samples from porcine and bovine bone. Following these results, it was concluded that the mechanical behavior of cancerous bone in both pig and the cow is almost similar. However, it was somewhat lower in the cow samples relative to that from porcine.

Introduction

Trabecular bone or the cancer bone is the porous material that often represents a type of bone-forming osseous tissue (Jee, 1996). Research indicates that trabecular bone has a higher surface area than other types of skeletal muscles (Foss, 1992). Contrary, it has been found to have less density and stiffness (Currey, 1987). Arguably, the cancerous bone mechanical behavior is somewhat similar to the other related cellular materials, including polymeric. This is because it possesses a cellular structure consisting of plates and rods (Bursten & Frankel, 1999). There are contributing factors with bone density defined as one of those contributors to the cancerous bone strength. According to WHO (1994), there is a need to determine the fracture risks using a bone mineral density. It is also worth noting that other than the thickness of the bone, testing conditions and the animal species 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 numerous experiments have been conducted to evaluate the density and strength of a bone. However, there is limited research conducted on dependent on the power of the cancerous bone on either testing conditions or animal species. Because of this gap in research, this experiment is set to investigate the dependence of cancerous bone density, testing conditions, and the testing condition.

Aim of the Experiment

This experiment was set up to evaluate the norm of stress-strain curve obtained to decide if the strength and rigidity of the cancerous bone depended on the bone density, the animal type, or the condition of the test.

Experimental protocol

Apparatus

This being an innovative setup, there were materials and equipment that were used to experiment. They included a digital balance from 60-2 N, Kern & Sohn, Germany, a core drill, the LVD, the material testing machine, and the digitalized Vernier calipers from MW110-15DDL, Moore and Wright, UK.

Materials & Methods

To achieve the set objectives, a specific, correct 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 the diameter of the bone was 9mm, and the size of the sample dimensions was 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 and the LVDT, the flat-ended displacement surface was measured alongside force applied or the accuracy, the power, and the displacement was 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 bottle 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 cover 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 ethanol was changed every 3 to 4 days. After which they were removed from ethanol and subjected to drying conditions. Finally, the samples were a weight on a digitalized beam balance for purposes of determining their importance.

Results

Microsoft word and excel were used in this experiment to collect and analyze 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 the calculation as Elastic modulus (E) = with MPa as the unit of measurement. In this case, the slope function of 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 used the function “x= -INTERCEPT/SLOPE “to measure this point, which in turn is used to find the failure strain. From this, the Failure strain equals the pressure at a point of compressive failure subtracting it the zero pressure.

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, strength samples from porcine, and bovine bone. In the bovine specimens, the constrained test’s average stiffness was relatively more compared to the case of the unconstrained analysis by a margin of about 3.5%. However, the average strength is sharply increased in loading constrained test by a margin of 25%. Additionally, the failure strain is increased by about 18% in the restricted analysis (table a).

Table a.

Cow specimens

 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.

stress strain curve graph

The Porcine Bone Specimens

Considering the second specimens from porcine, it is clear that the samples’ strength for the constrained test was somewhat higher by a margin of 23.5% compared to the power in other trials. Additionally, the average failure strain and stiffness in the restricted test are 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.

stress-strain graph

Figure 1. Graphs A and B represent the relationship between Stiffness and Density. Graph C and D represent the relationship between Strength and Density for the samples from cow bone of both constrained and unconstrained.

Pigs specimens

Discussion

Generally, the mechanical behavior of cancerous bone specious given is almost similar, though, from the result, it is lower in the samples of cow samples than it is from a porcine source. The experiment indicated that specimens from the bovine (cow) source were much more reliable than those from the pig. This happens following differences in density as noted in which case; density has a substantial impact on the mass upon the mechanical properties as shown in figures 1 and 2). Frequency is directly proportional to the strength and stiffness. The type of test also affected the results. As observed, in the constrained analysis, as earlier mentioned in the result, the average values of the cancerous bone’s mechanical properties were more than the unconstrained test. In this case, the cow samples’ compressive behavior was, to some extent, to Carter and Hayes’s results for cow bones. An experimental finding supports these findings for Dennis et al., (1977) on human bone samples without marrow at a 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 increases by around 74%.

The major shortcoming of this experiment is that the samples were limited. It should have more examples to reduce errors (produce a reasonable level of accuracy) and then have a good representation of the tested cancerous bone’s mechanical behavior. If the sample size is too small, the experiment will lack the precision to provide reliable answers. Therefore, large specimens are needed to give a 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

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