RESUMEN
Poly(N-isopropylacrylamide) (PNIPAM) is expected to find utility in tissue engineering and drug delivery, among other biomedical applications. These applications capitalize on the intrinsic lower critical solution temperature (LCST) of the polymer: below the LCST, enthalpic gain from intermolecular hydrogen bonding between PNIPAM and water molecules dominates the solvation; above the LCST, entropic effects resulting from the intramolecular hydrogen bonding between the carboxyl and amide groups of PNIPAM lead to water expulsion. The dependence of the LCST upon the molecular weight, solvent, and solution activity (i.e., solute concentration) has been studied extensively. However, what has not been previously explored is the effect of humidity on the characteristic properties of the polymer. Herein, we show that the relative humidity affects the water adsorption dynamics of PNIPAM as well as the magnitude of the transition that occurs at the LCST of the polymer. In short, the magnitude of the LCST transition decreases with an increasing relative humidity, and the time period over which adsorption occurs decreases with the temperature.
RESUMEN
BACKGROUND: Hypothermia is commonly observed in victims of trauma, and it is generally combined with shock caused by either hemorrhagic or nonhemorrhagic mechanisms. This study deals with phenomena related to nonhemorrhagic mechanisms. The objective is to document through experimental evidence the existence of a natural mechanism in rats that compensates for the inadequate tissue perfusion in the presence of shock by reducing body temperature (hypothermia). METHODS: Different types of trauma are analyzed (i.e., abdominal cavity and bowel exposure) and compared with other groups that suffered, additionally, femur fracture and partial hepatectomy. Further thermal alterations are also studied as consequences of vascular phenomena involving the elevation of intra-abdominal pressure and clamping of arteries and veins, such as the aorta and inferior vena cava. The loss of energy and temperature response of the animals is documented in time through charts with experimental uncertainties. RESULTS: It is concluded that exposure of the bowels is the main factor involved in the genesis of hypothermia, regardless of the associated trauma. Plastic film is shown to be the most effective way to avoid heat loss in bowel exposure. An optimal intra-abdominal pressure, Popt congruent with 12 mm Hg, is found such that heat flux loss is minimum in pneumoperitoneal procedures. CONCLUSION: Aortic and inferior vena cava clamping induces hypothermia at levels comparable to bowel exposure.