BioMEMS for biosensors and closed-loop drug delivery.

The efficacy of pharmaceutical treatments can be greatly enhanced by physiological feedback from the patient using biosensors, though this is often invasive or infeasible. By adapting microelectromechanical systems (MEMS) technology to miniaturize such biosensors, previously inaccessible signals can be obtained, often from inside the patient. This is enabled by the device's extremely small footprint which minimizes both power consumption and implantation trauma, as well as the transport time for chemical analytes, in turn decreasing the sensor's response time. MEMS fabrication also allows mass production which can be easily scaled without sacrificing its high reproducibility and reliability, and allows seamless integration with control circuitry and telemetry which is already produced using the same materials and fabrication steps. By integrating these systems with drug delivery devices, many of which are also MEMS-based, closed loop drug delivery can be achieved. This paper surveys the types of signal transduction devices available for biosensing-primarily electrochemical, optical, and mechanical-looking at their implementation via MEMS technology. The impact of MEMS technology on the challenges of biosensor development, particularly safety, power consumption, degradation, fouling, and foreign body response, are also discussed.

Magnetic nanoparticle/polymer composites for medical implant infection control.

New potential medical applications for magnetic nanoparticle/polymer composite coatings, including deactivation of bacterial biofilms, require much higher power densities than can be supplied by previously developed polymer composites. These coatings in turn require much higher nanoparticle concentrations, where particle-particle and particle-polymer interactions play a significant role in the material's performance. This paper investigates the effect of several key design parameters on the resulting specific absorption rate of magnetite nanoparticle composites. Hydrophobic (poly(styrene), (PS)) and hydrophilic (poly(vinyl alcohol), (PVA)) polymer composite coatings were compared in both aqueous and non-aqueous solvents at multiple nanoparticle loadings and film thicknesses. Heating rates up to 717 W g-1 Fe were observed in a typical (2.32 kA m-1, 302 kHz) alternating magnetic field (AMF), achieving heating power densities up to 7.5 W cm-2. To estimate in vivo power requirements, electrical resistance heating beneath a tissue mimic heat sink indicated a peak power requirement of only 4.5 W cm-2 to achieve an 80 °C surface temperature in 15 s, demonstrating that these composites can exceed the power densities needed for applications such as treating bacterial infections on medical implants in situ. Polymer identity, solvent identity, and especially orientation within the magnetic field were shown to strongly affect the power density with effects that are interrelated.