The molecular origin of birefringence in skeletal muscle. Contribution of myosin subfragment S-1

Study on anisotropy orientation due to well-ordered fibrous biological microstructures

Significance

Most biological fibrous tissues have anisotropic optical characteristics, which originate from scattering by their fibrous microstructures and birefringence of biological macromolecules. The orientation-related anisotropic interpretation is of great value in biological tissue characterization and pathological diagnosis.

Aim

We focus on intrinsic birefringence and form birefringence in biological tissue samples. By observing and comparing the forward Mueller matrix of typical samples, we can understand the interpretation ability of orientation-related polarization parameters and further distinguish the sources and trends of anisotropy in tissues.

Approach

For glass fiber, silk fiber, skeletal muscle, and tendon, we construct a forward measuring device to obtain the Mueller matrix image and calculate the anisotropic parameters related to orientation. The statistical analysis method based on polar coordinates can effectively analyze the difference in anisotropic parameters.

Results

For those birefringent fibers, the statistical distribution of fast-axis values derived from Mueller matrix polar decomposition was found to exhibit bimodal characteristics, which is a key point in distinguishing the single-layer birefringent fiber sample from a layered, multioriented fibrous sample. The application conditions and interference factors of anisotropic orientation parameters are analyzed. Based on the parameters extracted from the orientation bimodal distribution, we can evaluate the relative change trend of intrinsic birefringence and form birefringence in anisotropic samples.

Conclusions

The cross-vertical bimodal distribution of the fast axis of anisotropic fibers is beneficial to accurately analyze the anisotropic changes in biological tissues. The results imply the potential of anisotropic orientation analysis for applications in pathological diagnosis.

Single-shot Mueller-matrix imaging of zebrafish tissues: In vivo analysis of developmental and pathological features

Zebrafish is a well-established animal model for developmental and disease studies. Its optical transparency at early developmental stages allows in vivo tissues visualization. Interaction of polarized light with these tissues provides information on their structure and properties. This approach is effective for muscle tissue analysis due to its birefringence. To enable real-time Mueller-matrix characterization of unanesthetized fish, we assembled a microscope for single-shot Mueller-matrix imaging. First, we performed a continuous observation of 48 species within the period of 2 to 96 hpf and measured temporal dependencies of the polarization features in different tissues. These measurements show that hatching was accompanied by a sharp change in the angle and degree of linearly polarized light after interaction with muscles. Second, we analyzed nine species with skeletal disorders and demonstrated that the spatial distribution of light depolarization features clearly indicated them. Obtained results demonstrated that real-time Mueller-matrix imaging is a powerful tool for label-free monitoring zebrafish embryos.

Light backscatter fiber optic sensor: a new tool for predicting the stability of pork emulsions containing antioxidative potato protein hydrolysate

The objective of this study was to determine whether light backscatter response from fresh pork meat emulsions is correlated to final product stability indices. A specially designed fiber optic measurement system was used in combination with a miniature fiber optic spectrometer to determine the intensity of light backscatter within the wavelength range 300-1100 nm (UV/VIS/NIR) at different radial distances (2, 2.5 and 3mm) with respect to the light source in pork meat emulsions with two fat levels (15%, 30%) and two levels (0, 2.5%) of the natural antioxidant hydrolyzed potato protein (HPP). Textural parameters (hardness, deformability, cohesiveness and breaking force), cooking loss, TBARS (1, 2, 3, and 7 days of storage at 4 °C) and CIELAB color coordinates of cooked emulsions were measured. The light backscatter was directly correlated with cooking losses, color, breaking force and TBARS. The optical configuration proposed would compensate for the emulsion heterogeneity, maximizing the existing correlation between the optical signal and the emulsion quality metrics.

Rigorous analysis of light diffraction ellipsometry by striated muscle fibers

A rigorous analysis of both the transverse electric and the transverse magnetic modes of light diffracted from a muscle fiber is performed. From the expressions of electromagnetic field components, ellipsometry parameters, differential field ratio, r, and birefringence, delta n, have been obtained. A theoretical formulation that introduces myofibril skew planes and a randomization factor about the average skew plane yields a relationship that shows good fit to experimental data of Chen et al. (Biophys. J. 56:595, 1989) and Burton et al. (J. Muscle Res. Cell Motil. 11:258, 1990). Using indices of refraction within each of the regions of the sarcomeric unit that are consistent with our knowledge of the molecular structure of the sarcomere in the analysis, it is shown that the transition from the rigor state to the resting state leads to as much as a approximately 13% decrease in the r-value and an equally significant change in delta n.