Answer: NON- POLAR
Explanation:
The blood brain barrier is the security system of the brain, it selectively allows material,drugs and nutrients into the cerebrospinal fluid and further into the brain and spinal cord respectively.
The blood brain barrier sometimes in it's effective way,prevents certain drugs that are life saving drugs from being able to repair injured or diseased brain cells,a way of being protective.
Non- polar substances cross the blood brain barrier easier than polar molecules.
Non- polar molecules/agents are fat loving (lipophilic),they effortlessly cross the blood brain barrier by just diffusing through the lipid membrane of the endothelial cells of the brain whereas polar drugs/agents cross the blood brain barrier less frequently because their charged structure gives them an aversion to the lipids in the membranes of the endothelial cells if the brain.
So if a lipidoid is able to cross the blood-brain barrier it would be expected that the blood brain barrier to be non-polar.