No abstract

Magnetotactic bacteria (MTB), a class of non-pathogenic bacteria that grow magnetic nanoparticles (MNPs) internally, have the potential to be used for targeted drug delivery. The MNPs inside MTB cause them to orient and move in response to magnetic field lines, a phenomenon called magnetotaxis. The self-propulsion capabilities of MTB can allow them to penetrate through tissue, and a magnetic field can be used to direct the MTB to the target tissue or organ. However, when MTB are used in the body, they may encounter fluids of different viscoelasticities, depending on the target location. Thus, an understanding of the capability of directing MTB using a magnetic field through viscoelastic fluids will be essential to their use for targeted drug delivery. In this work, we develop a microfluidic-focused experimental setup to evaluate the motility of MTB in viscoelastic fluids under the influence of different magnetic field strengths. We used polyacrylamide (PAM) dissolved in water as a model viscoelastic fluid. A microfluidic channel is filled with PAM solution for MTB studies. A Brookfield viscometer is used to determine the viscosity average molecular weight of three PAM samples and to obtain the shear rate vs. viscosity plots for various PAM concentrations. Custom 3D-printed Helmholtz coils are used to generate the magnetic field for MTB experiments. The coils are mounted on an Olympus BX51 microscope, and the magnetic field at the center of the coils was characterized through finite element analysis simulations and experimentally. Our microfluidic approach offers the advantage of generating precise magnetic fields along microchannels containing a viscoelastic fluid that can be used on the investigation of bacterial motility on-chip.

Magnetotactic bacteria (MTB) Magnetospirilium magneticum strain AMB-1 have shown a great potential as carriers for therapeutic agents within the human body. MTB are a polyphyletic group of bacteria that orientate themselves along the Earth's magnetic field lines due to magnetosomes, specialized magnetic organelles aligned along cytoskeletal filaments which function as intracellular compass needles. Current research has found that MTB are able to survive in many environments and demonstrated their ability to travel through micro-vessels while under both flow and viscous stress. Some studies show the ability of MTB to bond with therapeutic agents, so they can act as natural nanocarriers, but their specific survivability in the human body still needs to be determined. To investigate MTB survival in the human body, microfluidic platforms are used to model the environmental stressors the bacteria will encounter if introduced to the blood stream. These platforms are developed using computer-aided design (CAD) tools and the designs are virtually simulated prior to microfabrication. These microfluidic platforms consist of two injection points, one for MTB and one for fluidic stressors. The MTB and fluidic stressor are combined through diffusive mixing in a long channel ending in an observation chamber. The MTB observed in the chamber, with 40x magnification, and the bacteria health is examined under varying environmental stressors found in the human body including a pH range between 4 and 8 and a temperature range of 22-40 o C. MTB's viability under these conditions is determined through observation of their mobility onchip. After parameters have been set for individual stressors, a different platform is used to examine MTB behavior under multiple stressors. This platform has two injection sites from which the fluidic stressors flow through a concentration gradient generator before separating into channels where the varied concentrations of stressors diffusively mix with MTB before reaching the observation chambers where their mobility is again examined to determine viability. The concentration gradient allows for multiple stressors to be applied to a single chamber, allowing for a more accurate environmental resemblance to the circulatory system. The experiments are designed to interrogate MTB survival under the applied stressors, neglecting the effect of viscous stress.