Fibrin is the polymerized protein responsible for the stabilizing mesh in blood coagulation. Its superior mechanical properties of being stiff or elastic if needed result from a hierarchical structure, including semiflexible single fibers as well as constituent protein restructuring. Here, we stretch and shear fibrin hydrogels to a regime where unfolding transitions of α-helical structures to β-sheet are induced and observe protein structural changes with spatially-resolved coherent Raman microscopy. We confirm the theoretically predicted orthogonal orientation of helices and sheets in strained networks. Spatially resolved structure protein maps reveal that the extent of structural transition changes with gel composition and becomes highly heterogeneous at large strain, indicative of substantial load-bearing inhomogeneity .
Imaging the optical phase retardation per unit depth (OPR/UD) in the retinal nerve fiber layer (RNFL) may aid in glaucoma diagnosis. Polarization Sensitive Optical Coherence Tomography (PSOCT) was used to record in vivo high-resolution images of the RNFL in two cynomologous monkeys. The depth variation in the Stokes vector of reflected light was used to calculate the OPR/UD as a function of RNFL position. OPR/UD decreased from 35 degree(s)/100 micrometers near the optic nerve to 5 degree(s)/100 micrometers at a location 600 micrometers superior to the optic nerve. Variation of OPR/UD in the RNFL with retinal position demonstrates a change in birefringence for different densities of ganglion cell axons. PSOCT may be useful for noninvasive determination of RNFL thickness and fiber density.
We report results of a study using polarization sensitive optical coherence tomography (PSOCT) to measure physical properties of the retina and to create images of retinal microstructure. Our instrument incorporates a mode-locked Ti:Al2O3 laser and achromatic polarization optics to record high resolution images. High-resolution B scans (two-dimensional images) of the in-vivo rhesus monkey retina have been recorded in the optic disk, peripapillary area and macula. Images of the peripapillary area allow measurement of the retinal nerve fiber layer (RNFL) thickness and calculation of the Stokes parameters of light back-scattered from the retina. Results of our study indicate: 1) PSOCT may be utilized to measure RNFL thickness; 2) PSOCT may be used to measure areas of birefringent tissue in the retina; and 3) selection of a scan pattern surrounding the optic nerve should account for the relatively large radial RNFL thickness gradient. Moreover, since glaucoma manifests in a destruction of the RNFL, PSOCT may be useful as a screening and diagnostic modality.
Conference Committee Involvement (3)
Advanced Chemical Microscopy for Life Science and Translational Medicine 2022
22 January 2022 | San Francisco, California, United States
Advanced Chemical Microscopy for Life Science and Translational Medicine 2021
6 March 2021 | Online Only, California, United States
Advanced Chemical Microscopy for Life Science and Translational Medicine
1 February 2020 | San Francisco, California, United States