The thermal and mechanical properties of a new family of biodegradable hydrogels made of photocrosslinked dextran derivative of allyl isocyanate (dex-AI) and poly (D,L) lactide diacrylate macromer (PDLLAM) were studied. The changes of thermal and mechanical properties of the dex-AI/PDLLAM hydrogels as functions of dex-AI to PDLLAM composition ratio and immersion time in phosphate buffer solution at 37 degrees C were also investigated. Thermal property data showed that the chemical modification, crosslinking, swelling and hydrolytic degradation affected the glass transition and melting temperatures. Based on thermal data, no phase separation was observed in the bicomponent dex-AI/PDLLAM hydrogels. Mechanical property data showed that, by changing the composition ratio, dex-AI/PDLLAM hydrogels having a wide range of dry and swollen compression moduli could be obtained. The moduli of the dex-AI/DPLLAM hydrogels in dry state decreased with an increase in the PDLLAM composition due to the reduction in glass transition temperature of the hydrogels. The loss of mechanical strength in buffer solutions was attributed to the swelling-induced formation of 3D porous network structure in the early stage of immersion and the hydrolytic degradation of the PDLLAM in the late stage via the chain scission of ester linkages located in the PDLLAM backbone. Because swelling and degradation were composition dependent, the magnitude of the loss of mechanical strength was also composition-dependent.