Ultrasound-assisted extraction of collagen from broiler chicken trachea and its biochemical characterization

Broiler chicken tracheas are a co-product from chicken slaughterhouses which are normally turned into low value animal feed despite their high levels of collagen. Typical collagen extraction by acid and/or pepsin usually results in relatively low yield. Ultrasound-assisted extraction (UAE) could be a means to improve collagen yield. The objectives of this study were to investigate the effects of ultrasonic parameters on the yield and biochemical properties of trachea collagen (TC). Conventional extraction using acetic acid and pepsin for 48 h resulted in acid-soluble (AS) and pepsin-soluble (PS) collagen with a yield of 0.65% and 3.10%, respectively. When an ultrasound with an intensity of 17.46 W·cm-2 was applied for 20 min, followed by acid extraction for 42 h (U-AS), the collagen yield increased to 1.58%. A yield of 6.28% was obtained when the ultrasound treatment was followed by pepsin for 36 h (U-PS). PS and U-PS contained collagen of 82.84% and 85.70%, respectively. Scanning electron microscopy images revealed that the ultrasound did not affect the collagen microstructure. All collagen samples showed an obvious triple helix structure as measured by circular dichroism spectroscopy. Fourier transform infrared spectroscopy indicated that the ultrasound did not disturb the secondary structure of the protein in which approximately 30% of the α-helix content was a major structure for all collagen samples. Micro-differential scanning calorimetry demonstrated that the denaturation temperature of collagen in the presence of deionized water was higher than collagen solubilized in 0.5 M acetic acid, regardless of the extraction method. All collagen comprised of α1 and α2-units with molecular weights of approximately 135 and 116 kDa, respectively, corresponding to the type I characteristic. PS and U-PS collagen possessed higher imino acids than their AS and U-AS counterparts. Based on LC-MS/MS peptide mapping, PS and U-PS collagen showed a high similarity to type I collagen. These results suggest that chicken tracheas are an alternative source of type I collagen. UAE is a promising technique that could increase collagen yield without damaging its structure.

Viscoelastic Properties of Human Tracheal Tissues

The physiological performance of trachea is highly dependent on its mechanical behavior, and therefore, the mechanical properties of its components. Mechanical characterization of trachea is key to succeed in new treatments such as tissue engineering, which requires the utilization of scaffolds which are mechanically compatible with the native human trachea. In this study, after isolating human trachea samples from brain-dead cases and proper storage, we assessed the viscoelastic properties of tracheal cartilage, smooth muscle, and connective tissue based on stress relaxation tests (at 5% and 10% strains for cartilage and 20%, 30%, and 40% for smooth muscle and connective tissue). After investigation of viscoelastic linearity, constitutive models including Prony series for linear viscoelasticity and quasi-linear viscoelastic, modified superposition, and Schapery models for nonlinear viscoelasticity were fitted to the experimental data to find the best model for each tissue. We also investigated the effect of age on the viscoelastic behavior of tracheal tissues. Based on the results, all three tissues exhibited a (nonsignificant) decrease in relaxation rate with increasing the strain, indicating viscoelastic nonlinearity which was most evident for cartilage and with the least effect for connective tissue. The three-term Prony model was selected for describing the linear viscoelasticity. Among different models, the modified superposition model was best able to capture the relaxation behavior of the three tracheal components. We observed a general (but not significant) stiffening of tracheal cartilage and connective tissue with aging. No change in the stress relaxation percentage with aging was observed. The results of this study may be useful in the design and fabrication of tracheal tissue engineering scaffolds.

Mechanical Characterization and Constitutive Modeling of Human Trachea: Age and Gender Dependency

Tracheal disorders can usually reduce the free lumen diameter or wall stiffness, and hence limit airflow. Trachea tissue engineering seems a promising treatment for such disorders. The required mechanical compatibility of the prepared scaffold with native trachea necessitates investigation of the mechanical behavior of the human trachea. This study aimed at mechanical characterization of human tracheas and comparing the results based on age and gender. After isolating 30 human tracheas, samples of tracheal cartilage, smooth muscle, and connective tissue were subjected to uniaxial tension to obtain force-displacement curves and calculate stress-stretch data. Among several models, the Yeoh and Mooney-Rivlin hyperelastic functions were best able to describe hyperelastic behavior of all three tracheal components. The mean value of the elastic modulus of human tracheal cartilage was calculated to be 16.92 ± 8.76 MPa. An overall tracheal stiffening with age was observed, with the most considerable difference in the case of cartilage. Consistently, we noticed some histological alterations in cartilage and connective tissue with aging, which may play a role in age-related tracheal stiffening. No considerable effect of gender on the mechanical behavior of tracheal components was observed. The results of this study can be applied in the design and fabrication of trachea tissue engineering scaffolds.

Leatherback sea turtle shell: A tough and flexible biological design

The leatherback sea turtle is unique among chelonians for having a soft skin which covers its osteoderms. The osteoderm is composed of bony plates that are interconnected with collagen fibers in a structure called suture. The soft dermis and suture geometry enable a significant amount of flexing of the junction between adjacent osteoderms. This design allows the body to contract better than a hard-shelled sea turtle as it dives to depths of over 1,000 m. The leatherback turtle has ridges along the carapace to enhance the hydrodynamic flow and provide a tailored stiffness. The osteoderms are of two types: flat and ridged. The structure of the two types of osteoderms is characterized and their mechanical properties are investigated with particular attention to the failure mechanisms. They both are bony structures with a porous core sandwiched between compact layers that form the outside and inside surfaces. The compressive strength is highly anisotropic by virtue of the interaction between loading orientation and arrangement of porous and compact components of osteoderms. The angle of interpenetration at the suture of osteoderms is analyzed and compared with analytical predictions. The sutures have a triangular shape with an angle of ∼30° which provides a balance between the tensile strength of the osteoderms and shear strength of the collagen fiber layer and is verified by Li-Ortiz-Boyce in a previous study. This is confirmed by an FEM analysis. A calculation is developed to quantify the flexibility of the carapace and plastron as a function of the angular displacement at the sutures, predicting the interdependence between geometrical parameters and flexibility.

STATEMENT OF SIGNIFICANCE

The leatherback turtle is a magnificent chelonian whose decreasing numbers have brought it to the brink of extinction in the Pacific Ocean. This first study of the structure of its shell provides important new insights that explain its amazing capacity for diving: depths of over 1,000 m have been recorded. This is enabled by the flexibility between the bony plates comprising its shell, which is covered by a skin and not by hard keratin as all other turtles. We use the arsenal of Materials Science characterization techniques to probe the structure of the shell and explain its amazing structure and capacity for flexing, while retaining its protection capability.

Structure, material characteristics and function of the upper respiratory tract of the pygmy sperm whale

Cetaceans are neckless, so the trachea is very short. The upper respiratory tract is separate from the mouth and pharynx. The dorsal blowhole connects, via the vestibular and nasopalatine cavities, directly to the larynx. Toothed cetaceans (Odontoceti) are capable of producing sounds at depth, either for locating prey, or for communication. It has been suggested that during dives, air from the lungs and upper respiratory tract can be moved to the vestibular and nasal cavities to permit sound generation to continue when air volume within these cavities decreases as ambient pressure rises. The pygmy sperm whale Kogia breviceps is a deep diver (500-1000 m), known to produce hunting clicks. Our study of an immature female shows that the upper respiratory tract is highly asymmetrical, that the trachea and bronchi are extremely compressible, whereas the larynx is much more rigid. Laryngeal and tracheal volumes were established. Calculations based on Boyle’s Law imply that all air from lungs and bronchi would be transferred to larynx and trachea by a depth of 270 m and that the larynx itself could not accommodate all respiratory air mass at a depth of 1000 m. This suggests that no respiratory air would be available for vocalisation. However, the bronchi, trachea and part of the larynx have a thick vascular lining featuring large, thin-walled vessels. We propose that these vessels may become dilated during dives to reduce the volume of the upper respiratory tract, permitting forward transfer of air through the larynx.