Polymer

The Polymer in the story of Breathe Deeply is an advanced plastic that could be used to create functioning organs such as a heart.

Background
Sei Inaba developed the substance in response to the death of Yuko Kazama and had a functioning heart prepared fifteen years after her passing away.

Function
A polymer gel was developed to create a functioning artificial heart that can beat on its own. It uses the metabolic process of the mitochondrial matrix as well as a TCA circuit to expand and contract itself.

A development was to affix the polymer gel to a patients weakened heart at the molecular level to assist the heart in its functions.

Story
A central research project by university professor Sei Inaba, the heart brought along with it various ethical concerns on whether it was right to place it in humans, they are not robots being a point of contention.

With Yuko revealed as alive, Sei returned to university to claim his polymer gel he developed.