Composites PMMA - carbon fibre as an alternative to connection of endoprosthesis with bone
Arkadiusz Szarek, Przemysław Postawa
Quarterly No. 1, 2010 pages 46-51
DOI:
keywords: composite, carbon filament, modified PMMA, mechanical properties
abstract Surgical cements, being polymer composites, constitute the substances which fix prostheses to bones. Due to the load which they are expected to bear and responsibility for maintenance of a stable connection of the bone and prosthesis, cements should be characterized by enhanced mechanical strength and biocompatibility. Basic mechanical parameters indicated by PMMA under variable load might affect durability of biomechanical systems, such as artificial femoral joint. For these reasons, analysis of functional properties of bone cements under empirical conditions is of essential importance since it allows for determination of cement’s behaviour in human body. Analysis of clinical results demonstrated that bone cements used for hip joint replacement, despite a number of modifications, still do not meet sufficient requirements of biofunctionality, mainly due to high toxicity of liquid monomer. Bone cements are still characterized by insufficient biocompatibility and poor mechanical properties. Furthermore, they show tendency to cracking, chipping and, in consequence, to loosening of prosthesis in bone. This paper aims at determination of the factors which cause destruction of cement layer in human body. Examination of the parts of artificial joint removed from human body because of the destruction of PMMA revealed that cement mass does not adhere to the prosthesis on the whole contact surface but only in some random areas. It was also observed that connection of the cement with bone occurs based on sticking whereas dendrite surfaces of cement show tendency to generate microcracks, which, in the course of time, are progressing and cause destruction of PMMA. The attempts were also made to develop, on the basis of commercial cements, a new composite reinforced with carbon fibre. The investigations aimed at obtaining a cement with limited percentage of toxic monomer, enhanced mechanical strength and porous surface which will allow for osseointegration of composite mass with the bone. It was determined on the basis of the investigations that optimal fraction of carbon fibre fillers in commercial bone cements accounts for 30%. This modification allows for obtaining a composite characterized by higher compressive strength [MPa] as compared to pure cements, from 20 to 26%. The developed PMMA composite with carbon fibre also showed higher impact strength (by approx. 20÷26%), which, in the case of the nature of load it is expected to bear, can considerably extend the time of use inside human body. Another essential advantage of the developed composite is that a porous surface was obtained, which will allow for osseointegration of the modified PMMA with bone and will increase mechanical strength in bone-cement arrangement. It is also remarkable that implementation of the filler limits the percentage of monomer in cement mass, which results in a higher biocompatibility in the obtained composite as compared to pure cement.