In {HEAD ~ one aspect} of {TAIL ~ the present invention}, the polymer hydrogel is characterized by a repeating unit having the formula 
of
In { HEAD ~ one aspect } of { TAIL ~ the present invention } , the polymer hydrogel is characterized by a repeating unit having the formula
OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH