Convection enhanced delivery is an attractive option for the treatment of several neurodegenerative diseases such as Parkinson, Alzheimer, and brain tumors. However, the occurrence of a backflow is a major problem impeding the widespread use of this technique. In this paper, we analyze experimentally the force impact of high flow microinfusion on the deformable gel matrix. To investigate these fluid structure interactions, two optical methods are reported. First, gel stresses during microinfusion were visualized through a linear polariscope. Second, the displacement field was tracked using 400 nm nanobeads as space markers. The corresponding strain and porosity fields were calculated from the experimental observations. Finally, experimental data were used to validate a computational model for fluid flow and deformation in soft porous media. Our studies demonstrate experimentally, the distribution and magnitude of stress and displacement fields near the catheter tip. The effect of fluid traction on porosity and hydraulic conductivity is analyzed. The increase in fluid content in the catheter vicinity enhances the gel hydraulic conductivity. Our computational model takes into account the changes in porosity and hydraulic conductivity. The simulations agree with experimental findings. The experiments quantified solid matrix deformation, due to fluid infusion. Maximum deformations occur in areas of relatively large fluid velocities leading to volumetric strain of the matrix, causing changes in hydraulic conductivity and porosity close to the catheter tip. The gradual expansion of this region with increased porosity leads to decreased hydraulic resistance that may also create an alternative pathway for fluid flow.
Convection-enhanced delivery (CED) is a promising technique to deliver large molecular weight drugs to the human brain for treatment of Parkinson's, Alzheimer's, or brain tumors. Researchers have used agarose gels to study mechanisms of agent transport in soft tissues like brain due to its similar mechanical and transport properties. However, inexpensive quantitative techniques to precisely measure achieved agent distribution in agarose gel phantoms during CED are missing. Such precise measurements of concentration distribution are needed to optimize drug delivery. An optical experimental method to accurately quantify agent concentration in agarose is presented. A novel geometry correction algorithm is used to determine real concentrations from observable light intensities captured by a digital camera. We demonstrate the technique in dye infusion experiments that provide cylindrical and spherical distributions when infusing with porous membrane and conventional single-port catheters, respectively. This optical method incorporates important parameters, such as optimum camera exposure, captured camera intensity calibration, and use of collimated light source for maximum precision. We compare experimental results with numerical solutions to the convection diffusion equation. The solutions of convection-diffusion equations in the cylindrical and spherical domains were found to match the experimental data obtained by geometry correction algorithm.
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In this paper, development of a three-simultaneous-velocity component, miniature, traversable fibre-optic laser Doppler velocimetry probe head is described. The cylindrical probe head has a diameter of D = 12 mm and a length of about L = 75 mm. While the two velocity components perpendicular to the probe axis are measured using conventional laser- Doppler velocimetry concepts, the third component along the probe axis is measured using a heterodyne technique. The miniature probe was designed small enough to be inserted into wind-tunnel models and to fit into most common spark-plug ports to make measurements in working car engines. The probe was initially tested in a round free-jet flow to demonstrate its capabilities.
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