Engineering approaches for the detection and control of orthopaedic biofilm infections

Abstract

Artificial joints are subject to chronic infections associated with bacterial biofilms, which only can be eradicated by the traumatic removal of the implant followed by sustained intravenous antibiotic therapy. We have adopted an engineering approach to develop electrical-current-based approaches to bacterial eradication and microelectromechanical systems that could be embedded within the implanted joint to detect the presence of bacteria and to provide in situ treatment of the infection before a biofilm can form. In the former case we will examine the combined bactericidal effects of direct and indirect electrical fields in combination with antibiotic therapy. In the latter case, bacterial detection will occur by developing a microelectromechanical-systems-based biosensor that can "eavesdrop" on bacterial quorum-sensing-based communication systems. Treatment will be effected by the release of a cocktail of pharmaceutical reagents contained within integral reservoirs associated with the implant, including a molecular jamming signal that competitively binds to the bacteria's quorum sensing receptors (which will "blind" the bacteria, preventing the production of toxins) and multiple high dose antibiotics to eradicate the planktonic bacteria. This approach is designed to take advantage of the relatively high susceptibility to antibiotics that planktonic bacteria display compared with biofilm envirovars. Here we report the development of a generic microelectromechanical systems biosensor that measures changes in internal viscosity in a base fluid triggered by a change in the external environment.

Fig 1

An intraoperative photograph taken during excisional surgery to remove an infected prosthetic joint shows a bacterial biofilm on an infected arthroplasty. The white material that the arrow is pointing to is pus that contains huge numbers of micro-organisms and host-derived leukocytes.

Fig 2

A–D. The basic concept of the MEMS biosensing device is illustrated showing how the binding of staphylococci-derived quorum sensing peptides on the outside will trigger an internal change in viscosity. (A) A cantilever viscometer is positioned within a microchamber filled with a high-viscosity glucose polysaccharide, and a dextran gel cross-linked with Con-A. (B) The bacterial quorum sensing molecule (RAP, blue ovals) binds to an engineered chimeric receptor protein, (TRAP, orange parabolas) embedded in an artificial membrane. The binding of TRAP induces a conformational change in the transmembrane portion of the chimeric protein(orange rectangles changing to green rectangles) which activates a galactosidase function which cleaves glucose monomers from a polysaccharide substrate. The glucose displaces dextran on the Con-A resulting in a drop in viscosity which is registered by increased deflection of the cantilever. (C) shows the entire unit which would be flush mounted into the artificial joint. (D) photograph of a functional cantilever-based viscometer with scale bar.

Fig 3

The viscosity (measured as amplitude) of the dextran-Con-A hydrogel as a function of glucose concentration is measured by the microviscometer.

Fig 4

A schematic diagram shows the main components for in vitro testing of the bioelectric effect. The biofilm is grown or positioned in the exposure chamber. Antibiotics can be pumped into the chamber with nutrients and a DC current can be applied through an anode and cathode. +ve = positive electrode, −ve = negative electode