Biologically inspired rosette nanotubes and nanocrystalline hydroxyapatite hydrogelnanocomposites as improved bone substitutes

Abstract

Today, bone diseases such as bone fractures, osteoporosis and bone cancer represent acommon and significant public health problem. The design of biomimetic bonetissue engineering materials that could restore and improve damaged bone tissuesprovides exciting opportunities to solve the numerous problems associated withtraditional orthopedic implants. Therefore, the objective of this in vitro study was tocreate a biomimetic orthopedic hydrogel nanocomposite based on the self-assemblyproperties of helical rosette nanotubes (HRNs), the osteoconductive properties ofnanocrystalline hydroxyapatite (HA), and the biocompatible properties of hydrogels(specifically, poly(2-hydroxyethyl methacrylate), pHEMA). HRNs are self-assemblednanomaterials that are formed from synthetic DNA base analogs in water to mimic thehelical nanostructure of collagen in bone. In this study, different geometries ofnanocrystalline HA were controlled by either hydrothermal or sintering methods. 2 and10 wt% nanocrystalline HA particles were well dispersed into HRN hydrogels usingultrasonication. The nanocrystalline HA and nanocrystalline HA/HRN hydrogels werecharacterized by x-ray diffraction, transmission electron microscopy, and scanningelectron microscopy. Mechanical testing studies revealed that the well dispersednanocrystalline HA in HRN hydrogels possessed improved mechanical propertiescompared to hydrogel controls. In addition, the results of this study provided thefirst evidence that the combination of either 2 or 10 wt% nanocrystalline HA and0.01 mg ml−1 HRNs in hydrogels greatly increased osteoblast (bone-forming cell) adhesion up to 236%compared to hydrogel controls. Moreover, this study showed that HRNs stimulated HAnucleation and mineralization along their main axis in a way that is very reminiscent of theHA/collagen assembly pattern in natural bone. In summary, the presently observedexcellent properties of the biomimetic nanocrystalline HA/HRN hydrogel compositesmake them promising candidates for further study for bone tissue engineeringapplications.