Synaptic Vessels are a very important special material in Mortal Shell 2. Using them increases the healing amount of health flasks. To obtain all Synaptic Vessels, you can search for them one by one. The first Synaptic Vessel is located at Fallgrim Tower, where you can purchase it from the merchant.
How to Obtain Synaptic Vessels in Mortal Shell 2
1. Fallgrim Tower -- Synaptic Vessel