Synthesis and characterization of porous κ-carrageenan/calcium phosphate nanocomposite scaffolds

The polysaccharide kappa-carrageenan was used in the production of macroporous composites containing nanosized hydroxyapatite, with potential application in bone tissue engineering. Biodegradable composite scaffolds were prepared combining in situ co-precipitation of calcium phosphates with a freeze-drying technique. The effect of the Ca/P molar ratio and total ceramic content on the chemical composition, microstructure and mechanical performance of the scaffolds were investigated by thermal analysis, X-ray diffraction, FTIR, transmission electron microscopy, scanning electron microscopy, He porosimetry and compressive tests. A mixture of amorphous calcium phosphates and/or nanosized calcium-deficient hydroxyapatite was obtained in most of the composites. The formation of hydroxyapatite was induced by higher Ca/P ratios, probably due to competing reticulation of the biopolymer with calcium cations. The composite scaffolds presented interconnected pores (50-400 mu m) and porosity around 97% and calcium phosphates were uniformly dispersed in the kappa-carrageenan matrix. Both microstructure and compressive mechanical properties of the scaffolds were affected by the ceramic content and, for a Ca/P molar ratio of 1.67, maximum compressive strength was achieved for a ceramic content of ca. 25 wt%. Above this value the structural integrity of the composite was damaged and a dramatic decrease in mechanical strength was verified. Compressive mechanical properties of the composites were improved by increasing Ca/P atom ratio.