Environmentally responsive polyelectrolytes and zwitterionic polymers

Switchable and Responsive Surfaces and Materials for Biomedical Applications 

It is well understood that the choice of the underlying monomers used to synlhe-size polyelectrolytes, polyampholytes, and betaine polymers have a significant impact on the final properties of the resulting material. This is especially important when identifying polymers for use in biomedical applications, as the underlying chenfistry may not be tolerated well in the in vivo environment even if it has the most desirable physical characteristics. Because of this, only a subset of charged monomers has been adapted for biomedical applications. 

To create surfaces that are responsive to environmental cues, polyampholytes, polye-lecttolytes, or betaine polymer coatings and/or materials must first be formed through controlled polymerization techniques. There are a number of excellent reviews on polymerization techniques (Barbey et al., 2009 Lowe McCormick, 2002 Matyjaszewski Xia, 2001), so only a brief overview of the most relevant approaches is provided here. 

---

The first section of Part One provides a detailed overview of switchable and responsive materials, exploring thermoresponsive polymers (Chapter 1), environmentally responsive polyelectrolytes and zwitterionic polymers (Chapter 2), peptide/protein-based natural responsive materials (Chapter 3), and photonic sensitive switchable materials (Chapter 4). 

The second most widely investigated environmental stimulus is salt. This stimulus includes the impacts of both salt concentration and composition and their impact on polyelectrolytes and zwitterionic polymers. In fact, many of the recent studies investigating the ability to control the properties of polyelectrolytes and zwitterionic polymers through pH have also included a component based on salt. However, it is much more challenging to take advantage of the responsiveness to salt for many biomedical applications, so most of the work has focused on one primary apphcation. 

The third environmental stimulus that has been used with polyelectrolytes and zwitterionic polymer systems is temperature. As with pH and salt, the primary temperature-induced response is a change in the conformational state of the polymer structure. The conformational state change is caused by one or more of the monomers passing through its lower critical solution temperature (LCST). This has been demonstrated in polyelectrolytes and zwitterionic polymers, where the charged monomers are responsible for the change, and in systems in which an additional temperature-sensitive monomer is included as a copolymer. 

---