Four-dimensional (4D) printing of naturally-derived hydroxyapatite nanocomposite-based scaffolds for biomedical applications: A review

Due to advancements in 4D printing (4DP) technology, bioprinted materials can have many functions and dynamic features. Occluders, stents, microneedles, wound closures, smart cell microenvironments, implants, and drug delivery systems, are some examples of biomedical objects that have been manufactured using 4DP peocess. Due to similarity to bioapatite, hydroxyapatite nanocomposites (HAp NCs) are promising biomaterials in tissue engineering. Conventionally, bone/tissue engineering has extensively used HAp NCs due to their osteogenic and biocompatible qualities. However, traditional HAp production procedures restrict their extensive application in fabrication of biomedical materials, including bones, teeth, cartilage, etc. Novel techniques like 4DP have been used to create customized HAp NC–based scaffolds for the patients. In this review, we provide an overview of different 4DP methods that are utilized in the HAp NC-based scaffolds fabrication. Various natural sources of HAp and different synthesis methods have been investigated. Several 4DP HAp NC-based scaffolds, their properties, biomedical applications, advantages, disadvantages, and future prospects are discussed.