Vat photopolymerization and phosphatization of biopolymer-calcium nitrate composite scaffolds for bone substitution

In recent years, additive manufacturing, including VAT photopolymerization (VP), is becoming increasingly popular due to its simplicity in use and high printing resolution, allowing the fabrication of objects with complex shapes, and permitting customization which is an aspect of particular importance in the biomedical field. In this work, a biobased polymer, consisting of a matrix of soybean oil acrylate, was mixed with calcium nitrate tetrahydrate for the preparation of composite scaffolds printed through VP. As the porous structure of bone substitutes plays a pivotal role in bone ingrowth, the scaffolds were printed with a porosity of 90%. In addition, calcium nitrate was successfully converted into hydroxyapatite (HAp), by simple immersion of scaffolds in a phosphatizing bath (aqueous solution of 1 mol/L sodium phosphate, at 80 °C for 14 days), developing biobased polymer-hydroxyapatite composite scaffolds. The phosphatization of Ca-nitrate and assessing the amount of hydroxyapatite were observed throughout the two weeks. Mechanical compression tests were performed on the various scaffolds before and after phosphatization, in order to compare their mechanical properties to those of natural bone, as well as cell adhesion tests to verify biological properties, such as biocompatibility.