And of these people, 137,000 die. An ischemic stroke, the most common kind of stroke, occurs when a blood clot blocks or narrows an artery leading to the brain. This blood clot limits the flow of oxygen and nutrients from flowing through, which starves neurons and results in their death. Our neurons stop dividing after we are eighteen months old, so stroke survivors often suffer permanent brain damage and limited language and mobility. For the International Genetically Engineered Machine competition, our team sought to devise a novel therapy, NeuroTrojan, for stroke survivors. This Trojan horse delivery mechanism delivers proteins that support neuron function after a stroke, which we believe is the next fronteir of stroke research. Given the prevalence of strokes worldwide, our team hopes that research in the NeuroTrojan strategy will continue long after the 2022 iGEM season.

  One of the most well-known therapies for stroke victims is thrombolysis, which involves "clot-busting" medicine. Alteplase, the synthetic form of human tissue plasminogen activator (TPA), can be injected to dissolve blood clots and restore normal blood flow in the brain. However, this medicine is most effective within a couple hours of a stroke. It is not recommended 4.5 hours after a stroke, as the effectiveness of the medicine at this point is unclear. Thromboectomy is another medical procedure that can remove blood clots. This involves inserting a catheter into an artery up into the brain. The device can then remove the blood clot and restore normal blood flow. Just like TPA however, this procedure is only effective a couple of hours after a stroke occurs. People who have suffered a stroke can also take an anticoagulant to reduce their risk of a future stroke. An anticoagulant prevents blood clots from forming by changing the chemical composition of blood cells. Aspirin, an antiplatelet, can also help to reduce the risk of another blood clot forming. Many of the existing therapies remove the cause of the stroke. However, none of them specifically target the neurons that are most affected when a stroke occurs.

  Neurons sustain themselves using an array of signal proteins, the most notable being neurotrophins. The neurons can produce enough of these proteins in normal conditions. However, in an ischemic stroke, neurons are thrust into an abnormal environment with a lack of oxygen and glucose. Near a clogged artery, many neurons die, and the ones that survive are often stressed. The surviving, stressed neurons could be ameliorated with more proteins that sustain neuronal health. However, neurons by themselves do not have mechanisms to increase expression of these proteins after a stroke. On paper, it would be a good idea to deliver these proteins into the brain through a procedure known as transvascular injection. However, just delivering these proteins to arteries in the brain is not enough. The Blood-Brain Barrier is a single-cell lining of endothelial cells that line the arteries in the brain. These cells serve as a permeable barrier between the artery and the neurons in the brain, protecting them from any toxins in the arteries and maintaining a thoroughly controlled flow of substances between the blood and the brain. This flow is so controlled that 100% of large molecules and 98% of small molecules are unable to pass through the blood-brain barrier. Only lipid soluble molecules with a molecular weight under 400-600 Da can cross the BBB.