A series of thermo-sensitive hydrogels has been prepared from reactions of acylated poly(ethylene glycol) bis(carboxymethyl) ether (PEGBCOCl) (M-n = 600 dalton) with lactitol-based polyether polyols (LPEPs). These LPEP hydrogels swelled extensively in water at neutral pH and their swelling behaviors depended strongly on the PEGBCOCl:LPEP molar ratios or extent of PEGBCOCl crosslinking. A maximum swelling of 81 fold was observed on hydrogels formed with LPEP (M-n = 4055 dalton) at a PEGBCOCl:LPEP molar ratio of 4.25. At temperatures above 25 degrees C, the hydrogels exhibited a phase transition and collapsed, expelling water. These super-absorbent hydrogels were stable under acidic conditions, but were sensitive to base hydrolysis. Enzyme proteins, i.e. lipase, were incorporated in the hydrogels (0.4-1.2 mg/g) by immersing the collapsed hydrogels in the protein solutions at 25 degrees C. Protein desorption at 40 degrees C occurred rapidly with over 90% of protein released during the first hour. The extent of protein desorption was similar among hydrogels with varying levels of absorbed proteins. The release of the lipase protein molecules is due to the structural collapse of the hydrogels and is not diffusion controlled.