Antimicrobial Bone Cement

Author: Lisa-Marie Rauschendorfer
Published On: September 19, 2018
Copyright: Wiley-VCH Verlag GmbH & Co. KGaA

Poly(methyl methacrylate) (PMMA, also known as acrylic) is used in orthopedic surgeries as an interface between metallic implants and the patient’s skeleton to secure implant fixation. To minimize the risk of infection, PMMA is commonly preloaded with antibiotics.

Unfortunately, this approach has some drawbacks. Firstly, only thermo-stable antibiotics can be used, as the free-radical polymerization reaction during the preparation of PMMA is highly exothermic. Secondly, high concentrations of the antibiotics impair the physical properties of PMMA. Thirdly, the release kinetics of the antibiotics from PMMA are usually poor: After an initial boost, there are only low concentrations detectable, which can promote microbial resistances.

Horst A. von Recum, Case Western Reserve University, Cleveland, OH, USA, and colleagues have used cyclodextrins (CDs) to overcome these drawbacks. CDs are cyclic oligosaccharides with 6–8 glucose units in a ring structure with a non-polar interior and a polar exterior. The team synthesized insoluble polymerized CD microparticles and filled them with antibiotics (either gentamicin, tobramycin, or rifampicin). The microparticles were then added during PMMA preparation and embedded in the polymer.

The physical properties of PMMA are maintained upon the addition of up to 10 wt % CDs. The modified PMMA shows a prolonged release of antibiotics (pictured left), which the team proved by the detection of antimicrobial activity. Furthermore, it was possible to “refill” the CDs with antibiotics after implantation (pictured right). This was demonstrated by injecting a drug solution into tissue-mimicking agarose models. The developed material allows a larger therapeutical window of up to 100 days and broadens the range of usable antibiotics, as the drugs are protected from the high temperatures used during PMMA polymerization.