Hydrogels, primarily due to their relatively high water content, have been used in tissue engineering and drug delivery, and can allow for nearly free diffusion of drugs and/or nutrients.  Regarding their water content, hydrogels can contain up to 60-70% by weight of water.  Hydrogels can be modified readily with a range of chemical functionalities, which may impart at least one of bioactivity, controlled degradability, and a variety of pore sizes. 
Hydrogels also can be advantageous due to their ability to be injected in a fluid state, conform to the shape of a tissue, and/or be solidified in situ using a variety of chemical and physical crosslinking methodologies.  The crosslinking methods often can be extended to create hydrogels that are cohesive and capable of adhering to a surrounding tissue, thereby possibly enhancing tissue-biomaterial integration. 
Hydrogels, however, generally have weak mechanical properties, e.g., modulus, toughness, and/or strength, compared to many biological tissues.  Most hydrogels are quite brittle and weak.  As a result, hydrogels frequently are applied only to softer tissues.  Also, some injected hydrogels flow too readily prior to gelation, thereby complicating their implantation in wet conditions and/or in difficult geometries. 
There exists a need for hydrogels that have mechanical properties that permit their use with a number of different tissues in a variety of locations.