Smart hydrogels have been applied widely as sensors and actuators in many fields

such as artificial muscles

drug control release

fluid control and so on However

their further applications have been hindered by the slow respond rate and the critical surrounding medium．A macroporous nonionie poly(vinyl formal) hydrogel (PVFM) sensitive to water content

was synthesized by adding pore-forming agent．It showed a satisfied swelling/deswelling rate with the change in water content due to the presence of interconnecting pores．The swelling pressure of this hydrogel in water may reach its maximum within 80s．and the deswelling pressure of the swollen hydrogel may decrease to 5％ of its initial value within 4 h in the process of air-drying．Comparing with the conventional dense hydrogel

the maeroporous PVFM showed many different behaviors

the volume did not decrease with the loss of water

but a phenomenon of volume recovery occurred during the air-drying process．On the other hand

the compressive modulus of the macropomus hydrogel did not increase monotonously with the decrease of water content as that of conventional hydrogels did

but decreased about 47％ at the initial stage of drying process This abnormal behavior is mainly related to the load-bearing modes of macroporous gels is with different water contents．The rapid response of macropomus gels is attributed to the weaker interaction between polymer and water

the higber porosity and the elasticity recovery of network．Since the maemporous PVFM hydmgels show the rapid swelling/deswelling rate and the satisfied sensitivity of mechanical properties to water content

they have the large potentialities to be used as sensors and actuators in flow eontrol．humidity control and so on．