Shape-Memory Polymer Scaffolds

Researchers at Harvard University have recently come up with a method to create polymer scaffolding that can transport drugs and stem cells but doesn't have to be surgically implanted. Instead, it can be injected through a syringe and emerge in the body in the original shape it had because of shape-memory properties. They tested it using scaffolds in circle, heart, and star shapes, and found that it worked each time.

The actual chemistry behind the process of creating these scaffolds relates quite a bit to what was learned in class. The polymers undergo what is known as cryogelation, depicted in the figure below. First the polymer solution is prepared in the liquid phase. Since it is a solution, as we learned in class, the freezing point is going to undergo a depression so the mixture has to be frozen at a subzero temperature. Once frozen, polymerization occurs and ice crystallizes. Then the cryogel is left at room temperature, where it thaws and leaves behind a system with interconnected pores.

Note, however, that this polymerization only occurs in the first place due to the presence of intermolecular forces. The polymer being used is alginate, whose structure is shown below. Because of the hydroxyl groups, there are many polar oyxgen-hydrogen bonds, and the presence of ionized carboxyl groups means that hydrogen bonding will occur. This is what allows the polymers to cross-link so well and form the pores in the first place.

Without the fundamental concepts of intermolecular forces and solution composition as covered in class, these polymer scaffoldings would not even have been possible to make.