system
Given the following post, respond as if you're commenting on Reddit:
human
Why are hydrogels used in tissue engineering, what is the main advantage over just sterile water?
gpt
Some context would be helpful, as this is a vast field. Some important aspects:

- Hydrogels have a shear modulus and don't drip away, in contrast to water.

- Hydrogels can have a stiffness and viscoelasticity that's tunable in situ, unlike water.

- Hydrogels may contain electrolytes to maintain isotonicity with physiological fluids; pure water isn't isotonic.

- Hydrogels can hold useful cells (e.g., stem cells) in position in the manner of a scaffold; water can't.

- Hydrogels can be fabricated to present tissue-like mechanical properties that drive cells toward certain behavior; water doesn't provide this.