ABSTRACT
Silk fibroin is an important biomaterial for photonic devices in wearable systems. The functionality of such devices is inherently influenced by the stimulation from elastic deformations, which are mutually coupled through photo-elasticity. Here, we investigate the photo-elasticity of silk fibroin employing optical whispering gallery mode resonation of light at the wavelength of 1550 nm. The fabricated amorphous (Silk I) and thermally-annealed semi-crystalline structure (Silk II) silk fibroin thin film cavities display typical Q-factors of about 1.6 × 104. Photo-elastic experiments are performed tracing the TE and TM shifts of the whispering gallery mode resonances upon application of an axial strain. The strain optical coefficient K' for Silk I fibroin is found to be 0.059 ± 0.004, with the corresponding value for Silk II being 0.129 ± 0.004. Remarkably, the elastic Young's modulus, measured by Brillouin light spectroscopy, is only about 4% higher in the Silk II phase. However, differences between the two structures are pronounced regarding the photo-elastic properties due to the onset of ß-sheets that dominates the Silk II structure.
Subject(s)
Fibroins , Fibroins/chemistry , Silk/chemistry , Elastic Modulus , Biocompatible Materials , Optics and PhotonicsABSTRACT
A ferrofluid immersed, D-shape optical fiber exhibits differential loss up to 12 dB with respect to an azimuthally rotating magnetic field placed around its longitudinal axis, manifested in its measured transmission power. Investigating the magneto induced refractive index and loss changes by using ferrofluid overlaid diffractive elements a differential loss mechanism is revealed, associated with the relative light polarization direction and the magnetic field application direction. The results were used for performing modal profile simulations of ferrofluid immersed D-shape optical fiber. It is demonstrated that such an optical system can act as a magnetic field sensor with field angle and intensity sensing capabilities.
ABSTRACT
Of the more than two million people worldwide with multiple sclerosis, 40% to 65% experience cognitive impairment, many of them early in the course of the disease. Cognitive impairment has been found in patients with all subtypes of multiple sclerosis. Because both pharmacologic and nonpharmacologic interventions may improve patients' brain function, cognitive assessment should be a routine part of the clinical evaluation. Traditional paper-and-pencil neuropsychological tests and batteries can help detect and monitor patients' cognitive problems. Computerized cognitive batteries also show promise. Controversy continues over which test is most reliable at assessing cognitive impairment in both everyday clinical practice and research. Each battery has possible disadvantages, such as practice effects, poor sensitivity and specificity, and questionable applicability to multiple sclerosis. Based on our review of the literature, we describe the tests that are currently being used or that might be used in assessing cognitive deficits in patients with multiple sclerosis, and we summarize the strengths and limitations of each.
