Even at rest, the human body is in constant motion. The heart beats to keep blood flowing. The lungs inflate with every breath taken. The gut contracts in a wave-like rhythm to nudge food along.
So how do you repair organs that keep moving? A biomaterial would need to be both tough and flexible to withstand the stresses it will experience once it’s in place.
Mechanical engineers Luc Mongeau and Jianyu Li from McGill University led the development of an injectable biomaterial with both of these properties. Their study was published in Advanced Science.
The material is an injectable hydrogel, forming a three-dimensional network of polymer chains that can hold a large amount of water, thereby lending a structured environment where cells can grow. The idea is that one day we might be able to place it in the body using a needle, making it less invasive than the alternatives.
But for cells to survive, a hydrogel also needs to feature large pores to allow blood to circulate. Pre-formed pores often collapse during injection, so the team used a multi-step process to form pores after injection.
In the syringe, the polymer chains are loose strands that are easy to push through a fine needle at room temperature. After injection, the body warms up the mixture, which quickly triggers it to form a gel. Next, the hydrogel reacts to the body’s pH and undergoes a process called phase separation, creating a network of areas that are polymer-rich that surround pores that are water-rich. Lastly, a crosslinker chemically links the polymer strands together to form a stable mesh.
Many porous hydrogels are weakened by their pores, but this one has two different kinds of polymers in it (glycol–chitosan and glyoxal), creating a double network that makes it more resilient. Instead of being prone to fracture, the hydrogel is stretchy. Even under millions of cycles of deformation, simulating the conditions of vocal cords in motion, the network doesn’t crack.
The team hopes that one day their approach may be a launch point for restoring the voices of patients with laryngeal cancer, repairing damaged hearts, or delivering drugs to various moving organs. It could also be used to make stretchy organ models or inside microfluidic devices to test drugs in the lab.
The body is a dynamic place, and biomaterials for regeneration need to be flexible to stay in place long enough for the body to heal before they ultimately biodegrade. This stretchy, pore-forming network could be an important tool to help realize that goal.