Materials for Biomedical Engineering. Mohamed N. Rahaman

material.

       The physical properties of a material, such as strength, elastic modulus, electrical conductivity, magnetic susceptibility, thermal conductivity, and refractive index are controlled by its atomic structure and they can be modified by the microstructure of the material

       An understanding of the mechanisms by which materials respond to an applied physical stimulus and how the properties of materials depend on their atomic bonding and microstructure is critical in designing and creating biomaterials with a desirable combination of properties for the intended application

       Mechanical properties are among the most important physical properties for biomaterials that are subjected to mechanical stresses at some point or during their entire application. Consequently, designing biomaterials for mechanical reliability must take into account the inherent response of different types of materials to stresses.

       As the applications of biomaterials normally involve a combination of physical properties, an understanding of other physical properties in addition to, or instead of mechanical properties, is desirable.

Problems

      1 4.1 The figure below shows general stress–strain curves for different types of materials at room temperature:Which curve best represents the mechanical response of (i) alumina, (ii) high density polyethylene, (iii) polystyrene, (iv) stainless steel, and (v) titanium.Which curve represents the toughest material?Which curve represents the material with the lowest Young’s modulus?Explain your answers.

      2 4.2 A cylindrical specimen of length 100 mm and diameter 10 mm is loaded in tension in a mechanical testing machine. Upon application of a force of 1000 N, the length increased to 100.5 mm. Determine the engineering (nominal) stress and strain in the specimen. If all the deformation occurred within the elastic region of its mechanical response, determine the Young’s modulus of the material.

      3 4.3 Determine the stress on the femoral bone of average diameter 2.5 cm in a human when it is subjected to a compressive force equal to the weight of a human of mass 90 kg (~200 pounds). How does this stress compare with the tensile strength of human cortical bone?

      4 4.4 The following data were obtained in tensile testing of an aluminum alloy specimen of gage length 50.8 mm and diameter 12.8 mm:Force (kN)Length (mm)050.808.950.8517.850.9035.651.0044.551.0553.451.1657.851.3162.352.0771.253.369.4 (fracture)54.2Plot the engineering stress–strain curveDetermine the Young’s modulus, yield strength (at an offset strain 0.2%), and the ultimate tensile strengthDetermine the engineering fracture strength and the true fracture strength, given that the diameter of the fractured specimen was 10.16 mm.

      5 4.5 Define toughness and resilience. Draw a stress–strain curve for a ductile material and indicate how the toughness and resilience can be determined from it.

      6 4.6 Explain why and how grain size influences the strength of metals. Give a relationship (name and equation) between strength and grain size, and define the terms in the equation.

      7 4.7 Explain why a metal that has undergone mechanical fatigue often fails at stresses far smaller than those for a similar metal that has not. Is the fracture of a fatigued metal expected to be ductile or brittle in character?

      8 4.8 Explain why a ceramic material such as Al2O3 commonly shows a compressive strength that is far higher than its flexural strength.

      9 4.9 Discuss the most important properties that should be considered in designing metals, ceramics, and polymers for use as biomaterials in load‐bearing applications in vivo.

      10 4.10 Explain the differences between diamagnetism, paramagnetism, ferromagnetism, and ferrimagnetism, and how these differences influence the applications of biomaterials.

      11 4.11 Distinguish between phonons and photons. Explain how phonons influence the thermal conductivity of materials.

      12 4.12 Metals typically have high electrical and thermal conductivities. On the other hand, diamond has a high thermal conductivity but is an electrical insulator. Explain.

      13 4.13 Determine the number of unpaired electrons in the following atoms or ions: Cr, Al3+, Zn, Ni, O2−, Co2+.

      14 4.14 Assuming that the magnetization of nickel results from its unpaired electrons only, calculate the saturation magnetization per kilogram of nickel which has a density of 8.9 g/cm3 and an FCC structure of unit cell length 0.352 nm.

References

      1 Balint, R., Cassidy, N.J., and Cartmell, S.H. (2014). Conductive polymers: toward a smart biomaterial for tissue engineering. Acta Biomaterialia 10: 2341–2353.

      2 Callister, W.D. (2007). Materials Science and Engineering: An Introduction, 7e. New York: Wiley.

      3 Le Guéhennec, L., Soueidan, A., Layrolle, P., and Amouriq, Y. (2007). Surface treatments of titanium dental implants for rapid osseointegration. Dental Materials 23: 844–854.

      4 Guimard, N.K., Gomez, N., and Schmidt, C.E. (2007). Conducting polymers in biomedical engineering. Progress in Polymer Science 32: 876–921.

      5 Liu, X., Rahaman, M.N., Hilmas, G.E., and Bal, B.S. (2013). Mechanical properties of bioactive glass (13‐93) scaffolds fabricated by robotic deposition for structural bone repair. Acta Biomaterialia 9: 7025–7034.

      6 McCrum, N.G., Buckley, C.P., and Bucknall, C.B. (1997). Principles of Polymer Engineering, 2e. New York: Oxford University Press Chapter 4.

      7 Pankhurst, Q.A., Connolly, J., Jones, S.K., and Dobson, J. (2003). Applications of magnetic nanoparticles in biomedicine. Journal of Physics D: Applied Physics 36: R167–R181.

      8 Peddi, L., Brow, R.K., and Brown, R.F. (2008). Bioactive borate glass coatings for titanium alloys. Journal of Materials Science. Materials in Medicine 19: 3145–3152.

      9 Wachtman, J.B., Cannon, W.R., and Matthewson, M.J. (2009). Mechanical Properties of Ceramics, 2e. New York: Wiley Chapter 6.

Further Reading

      1 Chiang, Y.M., Birnie, D.P., and Kingery, W.D. (1997). Physical Ceramics. New York: Wiley Chapter 1.

      2 DRH, J. and Ashby, M.F. (2018). Engineering Materials I: An Introduction to Properties, Applications and Design, 5e. Oxford: Butterworth‐Heinemann.

      3 Ratner, B.D., Hofmann, A.S., Schoen, F.J., and Lemons, J.E. (eds.) (2013). Biomaterials Science: An Introduction to Materials in Medicine, 3e. New York: Elsevier Chapter 1.

5 Surface Properties of Materials

      5.1 Introduction

      Surface properties are important because, together with bulk properties (Chapter 4), they determine the performance of biomaterials in vivo. Upon implantation, it is the surface of the biomaterial that is first encountered by the physiological environment. The interaction between the surface and components of the physiological fluid, such as water molecules, inorganic ions, amino acids and proteins, strongly influences the response of cells and, thus, the biocompatibility of the implant. In the healing of bone defects using nondegradable implants, for example, if the surface properties and characteristics of the implant are not selected properly, cells can form fibrous tissue around the implant instead of new bone. Consequently, the ability of the implant to integrate with host bone is limited, jeopardizing a successful outcome of the procedure (Chapter 23).

The surface of a material consists of a thin layer with properties and characteristics that are different from those of its interior due to a variety of physical and chemical factors (Figure