Sample Literature Review On Material Comparison

Metallic and non-metallic materials has been successfully used to manufacture implants. While some metallic implants can be cemented with bioactive bone cements, other metallic implants are manufactured without cement (cementless). However, some implants are cemented with normal PMMA bone materials. These materials exhibit different physical and mechanical properties.
Metals are not bioactive by nature and to obtain bioactive materials from metals, the surface of a metal material used to manufacture the implant is coated with a bioactive ceramic (Nasab and Hassan, 2010). One of the most widely used ceramic is hydroxyapatite (HA) (Navarro et al, 2008). Various techniques has been proposed for coating metallic surfaces which include radio frequency, laser ablation (Pradhaban et al, 2014), electrophoretic deposition, plasma spraying, and hot isostatic pressure. However, all these techniques have been found to be not cost-effective. Furthermore, none of them produce covalent linkages with the substrate. Nonetheless, the most preferred method for HA for clinical applications is plasma spray deposition (Das et al, 2013). The method involve projecting HA at a temperature of 1000 degrees Celsius onto a colder metallic surface at a temperature of 100 to 150 degrees Celsius followed by rapid cooling resulting in the formation of a mechanical link between the substrate and the ceramic. The method, however, has some weaknesses. For example, the composition of the final ceramic has been found to be difficult to control while there is a great likelihood that the resulting coating will be crystalline. Other weakness are attributed to the unstable thermal stability of the HA structure, heterogenic conditions (air bubbles) existing between the coating and the substrate, and also the resulting residual stresses in the coating formed. All these weaknesses conspire to increase the chances of failure during the service life of the coating.
Polymethylmethacrylate (PMMA) is one of the first generation materials used to manufacture implants. A self-polymerizing PMMA cement has been applied in the manufacture of some implants. The technique involves the mixing of two components (one of them being a monomer) that hardens upon setting. Although PMMA bone cement has been found to offer excellent primary fixing of the prosthesis, it lacked the ability to promote a biological secondary fixation (Lye et al, 2013). PMMA has also been found to exhibit other weaknesses. For example, the residual monomer may find its way into the circulatory system and causing fat embolism. A thermal necrosis may be produced in the surrounding bone owing to the large exotherm in setting. During the process of polymerization, there is a likelihood of shrinkage which causes the formation of gaps between the bone and the cement as well as gaps between prosthesis and the cement. These gaps leads to loss of contacts between the interfaces of prosthesis/cement and bone/cement. The bone and metallic prosthesis exhibit differences in their stiffness. This differences might induce too much stress or too much strain that might lead to fractures in the cement thus releasing cementious particles. An inflammatory reaction has been found to occur when cementious particles interacts with the surrounding tissues. Particles of the ceramic radiopacifier causes discontinuities in the ceramic matrix leading to a reduction of mechanical properties by up to 10%. Despite the disadvantages associated with PMMA bone cements, they are still being used with high rates of success due to an improvement in both mechanical properties (especially cement microstructure) and surgical procedures (Rickers, 2008). The very good knowledge of the advantages and disadvantages of these materials include the availability of alternative materials for implant anchorage has made them to be applied only in clinical procedures where they exhibit superior performance (Navarro et al, 2008).

References

Das, S., Chanda, A., & Banerjee, G. (2013). Plasma Spray: A Proposed Augmentation to Achieve Better Orthopedic Coating For Industrial Application. Structure, 2(5).
Lye, K. W., Tideman, H., Wolke, J. C., Merkx, M. A., Chin, F. K., & Jansen, J. A. (2013). Biocompatibility and bone formation with porous modified PMMA in normal and irradiated mandibular tissue. Clinical oral implants research, 24(A100), 100-109.
Nasab, M. B., & Hassan, M. R. (2010). Metallic biomaterials of knee and hip-A review. Trends in Biomaterials and Artificial Organs, 24(1), 69-82.
Navarro, M., Michiardi, A., Castano, O., & Planell, J. A. (2008). Biomaterials in orthopaedics. Journal of the Royal Society Interface, 5(27), 1137-1158.
Pradhaban, G., Kaliaraj, G. S., & Vishwakarma, V. (2014). Antibacterial effects of silver–zirconia composite coatings using pulsed laser deposition onto 316L SS for bio implants. Progress in Biomaterials, 3(2-4), 123-130.
Ricker, A. (2008). The influence of nano MgO and BaSO. International journal of nanomedicine, 3(1), 125-132.