Osmolar devices and methods for preventing tissue swelling

A device for treating brain swelling, comprising:

• a solid comprising a shell occupying a device volume, and defining a chamber;
• a solution in said chamber, said solution having an osmolarity greater than or equal to 300 mOsm/L;
• and
• a gas in said chamber;
• wherein said device is configured to absorb at least a portion of a fluid from a brain of a patient and is capable of removable insertion into a skull of said patient.

A device for treating brain swelling, said device occupying a device volume, said device comprising:

• a solid comprising:
• a semipermeable membrane;
• and
• solute particles enclosed in said semipermeable membrane;
• wherein said device is configured such that upon at least partial submersion of said solid in a brain fluid, said solute particles cause an osmotic gradient such that a portion of said brain fluid flows into said solid through said semipermeable membrane.