Biodegradable polyphosphazene biomaterials for tissue engineering and delivery of therapeutics

Degradable biomaterials continue to play a major role in tissue engineering and regenerative medicine as well as for delivering therapeutic agents. Although the chemistry of polyphosphazenes has been studied extensively, a systematic review of their applications for a wide range of biomedical applications is lacking. Polyphosphazenes are synthesized through a relatively well-known two-step reaction scheme which involves the substitution of the initial linear precursor with a wide range of nucleophiles. The ease of substitution has led to the development of a broad class of materials that have been studied for numerous biomedical applications including as scaffold materials for tissue engineering and regenerative medicine. The objective of this review is to discuss the suitability of poly(amino acid ester)phosphazene biomaterials in regard to their unique stimuli responsive properties, tunable degradation rates and mechanical properties, as well as in vitro and in vivo biocompatibility. The application of these materials in areas such as tissue engineering and drug delivery is discussed systematically. Lastly, the utility of polyphosphazenes is further extended as they are being employed in blend materials for new applications and as another method of tailoring material properties.