Polyzwitterions: From Surface Properties and Bioactivity Profiles to Biomedical Applications

Long-term biocompatible materials (i.e., nontoxic materials that sustain the healthy functions of surrounding tissue, cause no inflammatory response, and are tissue-integrated without encapsulation) remain elusive. Added to this, poly(ethylene glycol), the “gold standard” for polymeric biomaterials, has been recently reported to be immunogenic. In this setting, protein-repellent, nonthrombogenic, and cell-compatible polyzwitterions are attracting increased scientific interest, particularly in the context of biomedical applications. Due to their high density of charged groups with opposite sign, polyzwitterions are strongly hydrated under physiological conditions yet do not disturb the hydrogen bonding of adjacent bulk water. For this reason, in combination with other enthalpic and entropic contributions, adhesion of biological matter to polyzwitterions is strongly reduced. Their protein repellency and cell compatibility designates them as promising coatings for medical devices such as catheters, wound dressings, and implants. Nowadays, a rich variety of polyzwitterionic structures is accessible, but their potential for various applications still needs to be evaluated. In this context, this work reviews the field of polyzwitterionic surfaces used for biomedical applications. In particular, the interaction of polyzwitterions with biological media and with living organisms such as mammalian cells and bacteria are highlighted. So far, the beneficial properties of polyzwitterions have been deemed to result from their inertness. Yet, very recent research shows that formally polyzwitterionic molecules can be in fact bioactive due to stimulus responsiveness.