Notes on what Artificial lungs would need to be

The number one thing that the designer would have to consider when building artificial lungs is gas exchange, the ability to put oxygen into blood and remove carbon dioxide. Let's keep this in mind.

How gas exchange happens in lungs (factors that affect it)

• A gas soluble membrane: Solubility allows O2 and CO2 to freely diffuse across the cells lining the alveoli.
• Surface area: Lots and lots of thin gas-soluble membranes with lots of capillaries surrounding them getting O2 and CO leaving
• Partial pressure difference: O2 in air sacs (pressure = ~100mmHg) in blood (40mmHg) so O2 flows to where it is least ie. into blood. CO2 in air sacs (pressure =40mmHg ) in blood(45mmHg). so CO2 flows into air sacs where it is lower. later breathed out.
• thickness of the blood vessels & membranes it needs to diffuse across: the smaller the better.

Primer to gas exchange in alveoli: https://youtu.be/uah-1eXBjmQ?si=1ETuWq6T-Kd3tsOo

Artificial lungs would:

1. Posses the apparatus to mimic functionality of the above mentioned. i.e:
   1. synthetic thin gas soluble membranes and vessels
   2. pumps(ideally connected to the patients neuro-musculature) to "breathe in/out".
2. Be implantable i.e.
   1. fit in a chest cavity
   2. be entirely powered by a power source that operates & is in rechargeable in vivo
3. Potentially surpass function of biological ones i.e:
   1. Active Oxygen-Carbon dioxide transport- One could embed a carrier molecule in the membrane that reversibly and reactively binds one specific gas, shuttling it across, then releasing it on the other side. Carrier-mediated transport is essentially how our own blood already solves this problem, just not at the membrane(Hemoglobin is a carrier molecule that reversibly binds oxygen with high specificity for later transport)
   2. Modified selective diffusion: One can pick or design a polymer whose chemistry makes one gas dissolve and diffuse through it much more readily than another. Different polymers have wildly different permeabilities for different gases based on their chemical structure, polarity, and free volume. This is the basis of most commercial gas separation membranes, used for things like separating CO2 from natural gas or nitrogen from air.
   3. Modified gas uptake: They could have a series of micro pumps that better enforce a required pressure gradient in the synthetic air sacs.
   4. etc.