Magneto-electrochemical method for chiral recognition of amino acid enantiomers.

Chiral recognition of enantiomers with identical mirror-symmetric molecular structures is important for the analysis of biomolecules, and it conventionally relies on stereoselective interactions in chiral chemical environments. Here, we develop a magneto-electrochemical method for the enhanced detection of chiral amino acids (AAs), that combines the advantages of the high sensitivity of electrochemiluminescent (ECL) biosensors and chirality-induced effects under a magnetic field. The ECL difference between L- and D-enantiomers can be amplified over 35-fold under a field of 3.5 kG, and the chiral discrimination can be achieved in dilute AA solutions down to the nM level. The field-dependent ECL and chronocoulometry measurements suggest that chiral AAs can lock the spins on their radicals and thus enlarge the ECL change under applied magnetic fields (magneto-ECL, MECL), which explains the field-enhanced chiral discrimination of AA enantiomers. Finally, a detailed protocol is demonstrated for the identification of unknown AA solutions, in which the species, chirality and concentration of AAs can be determined simultaneously from the 2D plots of the ECL and MECL results. This work benefits the development of field-assisted detection methods and represents a promising and universal strategy for the comprehensive analysis of chiral biomolecules.

Experimental Study of Anisotropic Stress/Strain Relationships of Aortic and Pulmonary Artery Homografts and Synthetic Vascular Grafts.

Homografts and synthetic grafts are used in surgery for congenital heart disease (CHD). Determining these materials' mechanical properties will aid in understanding tissue behavior when subjected to abnormal CHD hemodynamics. Homograft tissue samples from anterior/posterior aspects, of ascending/descending aorta (AA, DA), innominate artery (IA), left subclavian artery (LScA), left common carotid artery (LCCA), main/left/right pulmonary artery (MPA, LPA, RPA), and synthetic vascular grafts, were obtained in three orientations: circumferential, diagonal (45 deg relative to circumferential direction), and longitudinal. Samples were subjected to uniaxial tensile testing (UTT). True strain-Cauchy stress curves were individually fitted for each orientation to calibrate Fung model. Then, they were used to calibrate anisotropic Holzapfel-Gasser model (R2 > 0.95). Most samples demonstrated a nonlinear hyperelastic strain-stress response to UTT. Stiffness (measured by tangent modulus at different strains) in all orientations were compared and shown as contour plots. For each vessel segment at all strain levels, stiffness was not significantly different among aspects and orientations. For synthetic grafts, stiffness was significantly different among orientations (p < 0.042). Aorta is significantly stiffer than pulmonary artery at 10% strain, comparing all orientations, aspects, and regions (p = 0.0001). Synthetic grafts are significantly stiffer than aortic and pulmonary homografts at all strain levels (p < 0.046). Aortic, pulmonary artery, and synthetic grafts exhibit hyperelastic biomechanical behavior with anisotropic effect. Differences in mechanical properties among vascular grafts may affect native tissue behavior and ventricular/arterial mechanical coupling, and increase the risk of deformation due to abnormal CHD hemodynamics.

Experimental study of anisotropic stress/strain relationships of the piglet great vessels and relevance to pediatric congenital heart disease.

BACKGROUND: Determining material mechanical properties of neonatal aorta and pulmonary artery will aid understanding tissue behavior when subjected to abnormal hemodynamics of congenital heart disease. METHODS: Aorta and pulmonary arteries were harvested from 6 neonatal piglets (mean weight 3.5 kg). Tissue samples from ventral and dorsal aspects of ascending aorta (AA) and descending aorta (DA), innominate artery (IA), left subclavian artery (LScA), main pulmonary artery (MPA), and left pulmonary artery (LPA) and right pulmonary artery (RPA) were obtained in three orientations: circumferential, diagonal, and longitudinal. Samples were subjected to uniaxial tensile testing. True strain-Cauchy stress curves were individually fitted for each orientation to calibrate the Fung model, and to measure tissue stiffness (10% strain). RESULTS: All samples, for all orientations, demonstrated nonlinear hyperelastic strain-stress response to uniaxial tensile testing (Holzapfel-Gasser and fitted-Fung models R(2) > 0.95). For each vessel segment, stiffness was not significantly different among orientations. Stiffness values in all orientations, including ventral/dorsal samples, were compared between AA > MPA (p = 0.08), DA > MPA (p < 0.01), and DA > AA (p = 0.35). Comparison of circumferential orientation samples showed AA and DA are significantly stiffer than MPA (p < 0.05), and MPA stiffness was similar to that of the RPA but slightly greater than LPA. Also, dorsal circumferential samples of all segments were slightly stiffer than ventral (p = 0.21). Dorsal aspect of AA was slightly stiffer in all orientations (p = 0.248). CONCLUSIONS: The neonatal aorta and pulmonary artery exhibit hyperelastic biomechanical behavior with an anisotropic effect. Differences between aorta and pulmonary artery may play a role in native tissue behavior, ventricular and arterial mechanical coupling, and risk of deformation due to abnormal hemodynamics of congenital heard disease.