Quaternized and Unmodified Chitosans: Hydrodynamic Properties

Molecular properties of N-[(2-hydroxy-3-trimethylammonium)propyl]chitosan (modified chitosan) series with the averaged quaternization degree 90% have been studied in comparison with the unmodified chitosan series by the method of translation isothermal diffusion, viscometry and static light scattering in dilute solutions in 0.33M CH3COOH+0.2M.CH3COONa at pH 3.54. Molecular mass, translation diffusion coefficient, and hydrodynamic size of the homologues samples in the modified/unnmodified series have been determined as well as their chain rigidity and Mark-Kuhn-Houwink equations at acidic pH. It was established that the size of modified chitosan molecules might be smaller than the initial polysaccharide of an equal polymerization degree in the same solvent, which was explained by the change of thermodynamic conditions and the change of the ratio of thermodynamic/electrostatic contributions to the total chain rigidity. Quaternized chitosan molecules displayed the different hydrodynamic behavior in 0.33M CH3COOH+0.2M.CH3COONa and in 0.2M NaCl (neutral pH). Solution properties of quaternized chitosan at neutral pH had been identified as the concentration dependent. The threshold influence of the secondary amino group protonation on the hydrodynamic properties of modified chitosan molecules was detected in 0.2M NaCl at the solute concentration range 0.001-0.004 g/cm3

A novel comprehensive approach for human vascular allografts cryopreservation and radiation sterilization for the tissue engineering industry

Aim: to verify new techniques for human cadaveric vascular allografts cryopreservation, thawing and sterilization for the tissue engineering purposes. We use polydimethylsiloxane (PDMS) as a well-known, promising coolant. This allowed us to completely omit any cryoprotective or vitrifying solutions. Using of PDMS also makes possible an applying these allografts directly after freezing and decellularization and also it will also provide an opportunity to develop secure protocols of tissue— engineered vascular conduits cryopreservation. Matherial and methods. After mathematical modeling of cooling process and its validation the experiment for sealed (isolated) freezing at low temperature conditions of 30 femoral arterial segments has been conducted. The segments were at least 10 cm in length and taken from 15 cadaveric donors in the age of 65-85 years. The freezing process was carried out using the abovementioned coolant— PDMS, and then physico-mechanical properties of these allografts were evaluated with the special Instron machine. According to the results obtained, a modeling of their sterilization conditions was conducted (the grafts were freezed). Results. By physico-mechanical properties validation and restricted histological analysis it was shown that there was an accordance between freezed/thawed allografts properties and native vessels. Conclusion. The abovementioned approach for allografts cryopreservation and thawing was efficient enough for further work in this direction