Calcification of synthetic polymers functionalized with negatively ionizable groups: A critical review

The functionalization of polymers with ionizable carboxyl and oxyphosphorus (phosphate, phosphonate, etc.) groups has been frequently advocated as a method of enhancing their calcification capacity as a prerequisite in certain biomedical applications. However, the existing literature regarding in vitro and in vivo experimental calcification of functionalized polymers is rather a collection of contradictory reports. Some investigators found that carboxyl or oxyphosphorus substituents increased the calcification capacity of polymers, while others could not notice any effect, and in some instances an inhibitory effect was unambiguously demonstrated. Although this problem is of immediate relevance to the field of orthopaedic and dental biomaterials, no study of the results published to date is available. This work presents a thorough overview of the subject and analyzes critically the extant reports.