An increasing number of applications, including non- or minimally invasive diagnostics and treatment as well as various cosmetic procedures, has resulted in a need to determine the optical properties of hair and its structures. We report on the measurement of the total attenuation coefficient of the cortex and the medulla of blond, gray, and Asian black human scalp hair at a 633-nm wavelength. Our results show that for blond and gray hair the total attenuation coefficient of the medulla is more than 200 times higher compared to that of the cortex. This difference is only 1.5 times for Asian black hair. Furthermore, we present the total attenuation coefficient of the cortex of blond, gray, light brown, and Asian black hair measured at wavelengths of 409, 532, 633, 800, and 1064 nm. The total attenuation coefficient consistently decreases with an increase in wavelength, as well as with a decrease in hair pigmentation. Additionally, we demonstrate the dependence of the total attenuation coefficient of the cortex and the medulla of Asian black hair on the polarization of incident light. A similar dependence is observed for the cortex of blond and gray hair but not for the medulla of these hair types.
Although venipuncture is one of the most common clinical procedures and is performed by trained medical staff, difficulties arise in 5% of insertion procedures. An instrument that guarantees the insertion of a needle into a vein in a single approach is expected to be beneficial to both medical staff and patients. The next step towards automatic venipuncture is to determine if insertion force feedback can be used, irrespective of insertion speed, insertion angle, or vein depth and diameter. Needle insertion experiments are performed on phantom and porcine tissues to study the interaction between the needle and tissue. A prototype instrument is developed to perform automatic venipuncture on the phantom. From the experiments, we conclude that an increased insertion speed of the needle leads to an increase in insertion force and tissue deformation. Furthermore, distinct force peaks are observed at the penetration of phantom skin and vein, thus enabling automatic detection of phantom vein puncture.
Some lab‐on‐a‐chip applications require to establish a controlled spatial concentration gradient of (chemical) species, for example for iso‐electrical focusing or to study chemotactic properties of cells. We show that covering a microchannel floor with special grooves or ridges, well‐controlled concentration gradients can be created, depending on the geometrical design of the grooves or ridges. In our case, the pattern consists of ridges that are slanted with respect to the main channel direction. Similar patterns have been applied in the past to achieve mixing by introducing chaotic advection. We present experimental and numerical results that prove the mixing effectiveness of the ridges. In addition, making use of the local mixing capabilities of the ridge patterns, we show, using numerical simulations, how to achieve a concentration gradient across a microfluidic channel. magnified image
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