Methods for determining agent concentration profiles in agarose gel during convection-enhanced delivery

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.     

Effect of plasticizer on production of bioactive synthetic calcium phosphates/glass composites and their properties

Bioactive synthetic calcium phosphates/glass composites have been produced using PVA as a plasticizer (0, 10, 15, 20 mass%). Changes in the linear, volumetric and weight parameters of samples upon sintering at 800 °C as well as in the density, porosity and compression strength have been investigated. It was established that all of the ceramics studied (both produced with and without PVA) exhibit a linear (0.7–1.9%) and volumetric (2.3–4.9%) shrinkage, which increases with using PVA and raising its content. The microstructure examination of samples obtained with a plasticizer revealed a complex porous morphology and the presence of complex-shaped 10–50 µm pores. An increase in PVA amount led to transformation of a flake-like structure and formation of particles of regular rounded shape. The pycnometric density did not depend on using PVA and equaled 2.58–2.61 g/cm³. PVA promoted an increase in the total porosity from 24.7 to 35.8% and a decrease in the density by 1.66 to 1.89%. Porosity increased proportionally to the amount of introduced PVA and was the highest for composites produced with 20 mass% addition of PVA. Open porosity dominated in all of the composites with PVA addition. The ultimate compression strength was in the range 42–93 MPa and reduced with increasing PVA amount.     

Diffusion models for evaporation losses during electron-beam melting of alpha/beta-titanium alloys

An analysis of the evaporation of aluminum during electron-beam melting (EBM) of alpha/beta-titanium alloys was performed. The analysis was based on the solution of the one-dimensional diffusion equation for the solute-concentration gradient in the melt pool subject to the flux boundary condition for the evaporation rate at the melt surface quantified using the Langmuir equation. The effect of process parameters and material coefficients (e.g., the diffusivity and solute activity in the melt) on predicted concentration gradients and melt losses under steady-state melting conditions was established for both the finite-domain and the semi-infinite-domain diffusion problems. The accuracy of the modeling approach was validated by comparison to previous measurements for the EBM of alloys with a nominal Ti-6Al-4V composition.     

Multichannel System for the Investigation of Isothermal and Cyclic Thermal Creep

A 16-channel system aimed at testing specimens for isothermal and cyclic thermal creep is developed and constructed on the contemporary element base. The system makes it possible to perform continuous long-term measurement of strains, forces, and temperature, accumulate and store the data of measurements. In the course of the tests, the specimens can be heated to a temperature of 1700°C. Due to the possibility of isothermal and cyclic thermal testing of specimens with simultaneous application of tensile loads, one can simulate the operation of structural elements under the conditions of complex changes in the force and thermal loads. __________ Translated from Problemy Prochnosti, No. 6, pp. 124 – 131, November – December, 2005.