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- Engineering Approaches for the Detection and Control of Orthopaedic Biofilm Infections

Infected artificial joints require extensive and expensive surgical and medical interventions, the latter modalities often require months of treatment. These adminstrations are required because chronic bacterial infections are associated with the formation of bacterial biofilms on host tissues and implant surfaces. Biofilm bacteria are highly resistant to both host defenses, including innate and adaptive immune responses, and to pharmaceutical antimicrobial agents. These multi-fold resistances are attributable to fundamental difference in the metabolism of biofilm bacteria compared with their planktonic counterparts (4, 5).

The best strategy to combat orthopedic implant biofilm infections is to prevent their occurrence in the first place. This should be possible as bacterial infections are always intially planktonic in nature, and only after an acute phase do the bacteria attach and elaborate a biofilm matrix. To realize such a preemptive strategy will require a marriage of engineering, surgical, and microbiological strategies. Towards this end a multidisciplinary team of scientists, surgeons, and engineers has been assembled to develop strategies and devices to either: A) continuously treat the impant using the bioelectric effect; or B) utlize and intelligent implant that can, 1) continuously monitor implant sites for the presence of bacteria; 2) release a cocktail of antimicrobial compounds upon the detection of bacteria; 3) monitor the release of the antimicrobial agents; and 4) report all bacterial detections and treatments via telemetry to the patient and physician.

The technical challenges to realizing an “intelligent implant” are nontrivial and will require a concerted effort by a large multidisciplinary team over an extended period of time. Whereas the development of a device to deliver a bioelectric effect is much more straightforward as such devices already exist for other orthopedic applications, notably in the realm of inducing bone growth in the case of nonunion fractures. The most complicated aspect of the intelligent implant project will likely be the construction of a chimeric protein switch that upon binding a bacterial signaling ligand will undergo a conformational change that activates an enzymatic function. However, the most difficult challenge may be the no technical issues associated with finding a manufacturer willing to underwrite the development of such a device and then shepard it through the regulatory process. Finally, assuming such a device was available for implant, it would require a major educational campaign to get the rank and file reconstructive orthopedic surgeon to adopt such an instrument.

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