DOES MICROWAVE IRRADIATION HAVE OTHER THAN THERMAL EFFECTS ON GLUTARALDEHYDE CROSS-LINKING OF COLLAGEN

The effects of microwave irradiation (MWI) can theoretically be divide d in thermal and nonthermal effects. Because there is still much debat e on the contribution of non-thermal microwave effects, experiments we re carried out in which the effects of isothermal microwave irradiatio n on glutaraldehyde (GA) crosslinking of native collagen membranes (NC M) is studied. A total of 20 strips of collagen membrane of porcine or igin were isothermally irradiated in 300 ml of a 0.1 (w/w) GA solution , 10 strips at 4 degrees C, and 10 strips at 20 degrees C, A temperatu re controlled microwave oven (630W) was adapted to allow for simultane ous cooling of the fixation solution preventing the MWI to induce any measurable thermal effects. Any possible temperature variations were r ecorded employing continuous fiberoptic temperature measurement. Contr ol experiments were carried out under the same (isothermal) fixation c onditions, but without MWI. The crosslinking action of the GA was eval uated by determining the shrinkage temperature (Ts) of the collagen st rips. No significant difference (p > 0.05) could be observed between t he increase in (Ts) of the microwaved and the increase in Ts of the no nmicrowaved strips. The increase in Ts at 4 degrees C (c. 14 degrees C ) was lower than that obtained at 20 degrees C (c. 16 degrees C). It w as concluded that MWI induces no substantial nonthermal effect on enha ncement of GA crosslinking of collagen at these temperatures.