RESUMEN
Cryopreservation is a critical procedure in autologous hematopoietic stem cell transplantation. Dimethyl sulfoxide (DMSO) is the cryoprotectant of choice. Optimization of the cryopreservation protocol in the past revealed a dramatic loss of cell viability associated with a reduction of the DMSO concentration below 2 vol % in the freezing medium. The cryoprotective mechanism of DMSO is usually ascribed to the ability to suppress ice formation and reduce the adverse effects of the freeze-concentrated solution. This work proposes an alternative hypothesis considering the detrimental impact of NaCl eutectic crystallization on cell viability. Thermoanalytical and microstructural analysis of the DMSO effect on eutectic phase transformation of cryoprotective mixtures revealed a correlation between the loss of cell viability and eutectic NaCl crystallization. DMSO inhibits the eutectic crystallization of NaCl and preserves cell viability. Thermodynamic description of the inhibitory action and possible mechanism of cryoinjury are provided.
Asunto(s)
DimetilsulfóxidoRESUMEN
A microstructural study of bisphenol-A diglycidyl ether (BADGE), prepared via both "classical" and novel photo- and thermally-induced cationic frontal polymerization, can help to understand the relationships between the microstructure of epoxides and their material properties, as well as the propagation of frontal polymerization waves. Microstructural PALS characteristics, such as the ortho-positronium lifetime (τ o-Ps), lifetime distribution, and void fraction, were investigated in relation to the extension of H bonds obtained from ATR/FTIR and the bulk density. The thermal profiles of differently-induced RICFP revealed that photo-triggered propagation is twice as fast as thermally-induced RICFP, with a comparable maximal reaction temperature (â¼283 °C) and heat conductivity. Both RICFP-based samples, induced by UV light and heat, showed a lower τ o-Ps, narrower lifetime distributions, and a reduced void fraction, in comparison to the "classical" cured anhydride-based epoxy sample. These may be the main factors which result in better material properties. In addition, both their radial and angular profiles of free volume fraction confirmed experimentally the rotational movement of the propagating frontal waves and their influence on the microstructural inhomogeneities, and the final material properties.
RESUMEN
This work investigates the free-volume properties of the dimethyl sulfoxide (DMSO)-water mixtures by positron annihilation lifetime spectroscopy over a wide temperature range of 20-320 K. The processes of melting and solidification of the water, DMSO and the DMSO-water mixtures at 1.8, 2.0 and 10% vol. DMSO respectively were studied. It was found that the recrystallization during heating of the water-DMSO cryoprotective mixtures above 160 K at low DMSO concentrations is affected by the amount of DMSO in the mixture. The amount of amorphous phase formed during cooling influences the hysteresis between cooling and heating cycles which could be crucial for cell survival. Experiments also show the time dependence of crystallization which indicates that rapid heating can suppress this secondary crystallization which is undesirable during the cell thawing process. Similar concentrations of DMSO (1.8% and 2% vol. DMSO in water) where a 2% vol. DMSO mixture secures cell survival but 1.8 vol% does not, showed differences in structural and dynamic properties that are key factors in cell survival. These results were supported by differential scanning calorimetry and low frequency dielectric spectroscopy measurements. The obtained data are in strong agreement with the observed cryoprotective efficacy of the DMSO-water mixtures on living cells.