Photo-crosslinked alginate nano-hydroxyapatite paste for bone tissue engineering.

In this study, methacrylation of alginate was carried out by reacting sodium alginate with methacrylic anhydride in the presence of sodium hydroxide (NaOH). Separately synthesized nano-hydroxyapatite (n-HA) powder was surface functionalized using mercaptopropionic acid (MPA) and EGMP (Ethylene Glycol Methacrylate Phosphate) in the presence of Azobisisobutyronitrile benzene (AIBN) as a free radical initiator in a nitrogen atmosphere. Methacrylated alginate solution was mixed with the required amount of surface functionalized HAp nanoparticles in the presence of 0.05% irgacure as photoinitiator and was placed at the centre ofa 8 KW of UV light source of 265 nm to prepare photocrosslinked bone paste.XRD analysis indicated that surface functionalization did not alter phase purity of hydroxyapatite nanopowder in the prepared paste. The graft polymerization of EGMP on the surface of HAp was confirmed by the presence of 1732 cm-1 band which belongs to C=O stretching of EGMP, in addition to the characteristic peaks of nano HAp and alginate in the composite paste. Storage modulus and loss modulus of all the prepared pastes increased non-linearly with time upto 100s exhibiting its pseudo plastic behaviour. The rate of release of BMP2 was significantly faster in the first few days, and the release curve gradually levelled off prior to slowing down upto 22 days. Mesenchymal stem cell adhesion studies revealed that cells could attach to the paste material and stretch over the surface of the material after 14days of incubation. MTT assay showed that prepared paste materials were conducive to mesenchymal stem cells attachment and proliferation. Immunocytochemistry analysis revealed that addition of surface functionalized nano HAp and BMP2 to alginate hydrogel enhanced osteogenic potential of the prepared paste. The result indicated that the newly developed photocrosslinked paste may be physically and biologically suitable for application as bone filler.