Does microwave irradiation have other than thermal effects on glutaraldehyde crosslinking of collagen?

The effects of microwave irradiation (MWI) can theoretically be divided in thermal and non-thermal effects. Because there is still much debate on the contribution of non-thermal microwave effects, experiments were carried out in which the effects of isothermal microwave irradiation on glutaraldehyde (GA) crosslinking of native collagen membranes (NCM) is studied. A total of 20 strips of collagen membrane of porcine origin 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 temperature controlled microwave oven (630W) was adapted to allow for simultaneous cooling of the fixation solution preventing the MWI to induce any measurable thermal effects. Any possible temperature variations were recorded employing continuous fiberoptic temperature measurement. Control experiments were carried out under the same (isothermal) fixation conditions, but without MWI. The crosslinking action of the GA was evaluated by determining the shrinkage temperature (Ts) of the collagen strips. No significant difference (p > 0.05) could be observed between the increase in (Ts) of the microwaved and the increase in Ts of the nonmicrowaved 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 was concluded that MWI induces no substantial nonthermal effect on enhancement of GA crosslinking of collagen at these temperatures.