then be skewered onto a platinum coil and or platinum wire along the ling axis of the cylindrical hydrogel sections after skewering the sections are dried at 55 c under vacuum for at least 2 hours the hydrogel sections are then subjected to an acidifying treatment preferably by immersing them in an acidifying solution such as 50 hydrochloric acid 50 water at 37 c for approximately 70 hours the excess acidifying solution is then washed off this may be accomplished by placing the hydrogel sections in a series of baths as follows after completion of the acidifying treatment e g after removal from the acidifying treatment bath 4 the hydrogel segments i e u201c pellets u201d are dried in a vacuum oven at approximately 60 c for about 1 to 2 hours this completes the preparation of the pellets these pellets will expand substantially when they come into contact with a liquid e g blood at physiological ph i e a ph of approximately 7 4 the following examples 2 4 are directed to some of the many biomedical applications of the porous hydrogels having controlled rates of expansion as described herein although these examples are limited to a few biomedical applications wherein the hydrogels are implanted into the body of a human or vetrinary patient it will be appreciated that the hydrogel materials of the present invention may be used for many other medical and non medical applications in addition to the specific examples set forth herebelow for the embolization of aneurysms 1 52 g 0 021 moles acrylamide 0 87 g 0 009 moles sodium acrylate 0.