The results of a study conducted by researchers at the Polytechnic University of Madrid reveal that the addition of reduced graphene oxide improves the mechanical and thermal properties of bone cements used to fix prostheses.
Bone cements are materials used as adhesives to fix bone prostheses (hip, knee, shoulder…) when the quality of the patient’s bone is insufficient. However, since their manufacturing process reaches high temperatures, they can cause necrosis in the patient’s surrounding tissues. Adding highly reduced graphene oxide helps to avoid this problem and also improves the mechanical and thermal properties of the materials, according to a study carried out by researchers at the Polytechnic University of Madrid (UPM). Given that this type of surgery (insertion of prostheses fixed with bone cements) is mostly performed on the elderly, improvements in its implementation have a growing social and health impact on our society.
The implantation of prostheses is an increasingly common practice throughout the world, due to causes such as the increase and aging of the population, and to a higher incidence of pathologies such as obesity or osteoarthritis. Bone cements are used to adhere and fix prostheses to the damaged bone when the bone does not have sufficient mechanical resistance and is unable to grow over the prosthesis and stabilize it. In addition, these bone cements distribute the loads on the bone and help to cushion the stresses at the prosthesis-bone junction.
However, this material has some limitations. Let us imagine that the maximum life of this bone cement is 20 years, and that statistically it is too risky to operate on people over 85 years of age. Thus, after that age, it would no longer be appropriate to repair a prosthesis whose materials have deteriorated. Therefore, a 65-year-old patient who is implanted with a hip prosthesis fixed to the bone with a bone cement will be exposed to the risk of the bone cement degrading or breaking, due to cracks that grow slowly over time, which would cause discomfort for the rest of his or her life because a new surgery is not feasible.
“Improving the durability of these bone cements is essential to improve the quality of life of our elders. In other words, to prevent them from having to endure an existence with chronic pain due to the broken prosthesis,” says José Ygnacio Pastor, a researcher at the UPM who participated in the study.
In the research conducted by members of the Center for Research in Structural Materials (CIME) of the UPM, several materials have been developed with potentially interesting results, such as reducing the maximum curing temperature that damages adjacent tissues.
“So far we have mainly talked about the mechanical strength and durability of bone cement. However, there are more problems associated with the use of these cements in the human body,” says Jaime Orellana, a member of the research team that carried out the work. The usual cements are made up of two components, which, once they come together, begin to react and harden. During this reaction the material solidifies rapidly, and there are only a few minutes to place it between the bone and the prosthesis. In addition, a lot of energy is released during this reaction that reaches the surrounding tissues. Since at 42⁰C and above the proteins denature, if the bone gets too hot the cells die and necrosis of the tissue surrounding the prosthesis occurs. Thus, “it is essential to prevent the bone from heating up, a result we have achieved by slowing down the reaction thanks to the addition of highly reduced graphene,” continues Orellana.
Regarding the mechanical properties mentioned above, the researchers have found that adding an excess of graphene is detrimental and worsens them, but small amounts (between 0.01 % and 0.1 % by weight) could also produce improvements in mechanical properties while maintaining the thermal benefit.
Expectations for these new materials are very promising, as there are also indications that graphene has antibacterial properties, which is ideal for reducing infection problems after surgery. “However, much work remains to be done, since not only must the amount of graphene to be introduced be optimized, but also the chemical treatments that allow the graphene to adhere and disperse better in the bone cement must be studied,” the researchers conclude.
Jaime Orellana, Ynés Yohana Pastor, Fernando Calle and José Ygnacio Pastor. Influence of HRGO Nanoplatelets on Behaviour and Processing of PMMA Bone Cement for Surgery. Polymers (Basel). 2021 Jun; 13(12); DOI: 10.3390/polym13122027.
Ynés Yohana Pastor, Jaime Orellana, Miguel Sánchez-Lozano, Fernando Calle and José Ygnacio Pastor. Physical-Mechanical Behaviour and Processing Evolution of PMMA Bone Cement due to Graphene Addition. Biomedical Journal of Scientific & Technical Research. April, 2021, Volume 35, 1, pp 273