Shape memory polymer foams with tunable interconnectivity using off-the-shelf foaming components.

The ability to easily and safety tune pore structures of gas-blown polyurethane shape memory polymer (SMP) foams could improve their outcomes as hemostatic dressings or tissue engineering scaffolds and enable overall commercialization efforts. Incorporating physical blowing agents into the polymer mix can be used to tune pore size and interconnectivity without altering foam chemistry. Enovate (HFC-254fa) is a commonly used physical blowing agent in gas-blown foams, but the Environmental Protection Agency (EPA) considers its use unacceptable because it is a hydrofluorocarbon that contributes to global warming. Here, off-the-shelf solvents accepted for use by the EPA, acetone, dimethyoxymethane (methylal), and methyl formate, were used as physical blowing agents by adding small volumes during foam fabrication. Increasing the physical blowing agent volume resulted in greater pore interconnectivity while maintaining SMP foam chemical and thermal properties. Pore size and interconnectivity also impacted cell and blood interactions with the foams. This work provides a safe and easy method for tuning SMP foam interconnectivity to aid in future commercialization efforts in a range of potential biomedical applications.