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