In the past, human bone has been the go-to material for experiments analyzing bone mechanics, although issues ranging from ethical questions to quality variability have created a need for lower-cost, more accessible alternatives. As it turns out, the answer was in our own back yard.
A recent study conducted by a student at Newcastle University revealed that polyurethane foam — donated by General Plastics for the student’s experiment — acted as the most preferable substitute in lab testing of artificial joints over any other polymer material. Bone had previously been the most accurate in tests outside of the human body that closely simulated how bones would react inside of the body. However, many issues arose, including “limited availability, storage issues and storage requirements, the possibility of infection and the inconsistency of the mechanical properties of the bone samples” (Iwejua 1). The challenge posed was finding a material that could provide reliable simulation, while being easily affordable and accessible, all of which was satisfied by polyurethane foam.
The student, Iwejua Chamberlain, compared bone with six other materials, including high density polyethylene, polytetrafluoroethylene, polyethylene with recycled material, and three grades of rigid cellular polyurethane foams, through tensile and compressive strength tests. Bone has elastic properties, and “in response to a decrease or increase in function, unlike inorganic materials, bone has adaptive mechanisms which give the tissue to ability to alter or repair itself thereby varying its mechanical properties and morphology” (Iwejua 5). Chamberlain was seeking a substitute with similar elastic values.
Chamberlain compared the compressive strength values and densities of our polyurethane foam, and found that several samples “fell within the range of density and compressive strength of cancellous bone,” as seen in Figure 1 (Iwejua 13). Both the 6720 and the 7120 had densities and compressive strength that were most similar to human bone.
Chamberlain then conducted tests to find which substance would operate as closely to bone in different situations. Tensile tests are “used to determine the static property of a material” and are “useful for determining the load carrying capacity of a material” (Iwejua 15). Compression tests, on the other hand, put material under pressure to determine how it reacts (Iwejua 20). In both tests, polyurethane foam was the most similar to cancellous bone, as indicated in Figure 2. These results show that the “Polyurethane materials are similar in tensile and compressive strength to cancellous bone” (flyer).
These results indicate that polyurethane foam can be used in place of bone, offering new options for laboratory testing of artificial joints that is cheaper, accessible, and more consistent across products. It also shows the versatility of polyurethane foam, and how the variety of applications is not only useful for creating high-temperature tooling boards or molded parts, but in assisting with scientific innovation as well.
Works Cited Iwejua, Chamberlain Chinedu. Alternative to Bone for Laboratory Testing of Artificial Joints. Sept. 2014. PDF file.