Injectable thermoresponsive magnetic hydrogel composite incorporating iron oxide and hydroxyapatite nanoparticles for bone tissue engineering

Introduction: Injectable bone cements (IBC) are liquid at normal conditions, but when injected into bone defect, they will stabilize and mold to the defect shape and aids in bone regeneration. Commercially available IBC are... [ view full abstract ]

Introduction: Injectable bone cements (IBC) are liquid at normal conditions, but when injected into bone defect, they will stabilize and mold to the defect shape and aids in bone regeneration. Commercially available IBC are based on polymethylmethacrylate, calcium phosphate or calcium sulfate. These IBC have several drawbacks such as low radiopacity, lack of bioactivity, heat induced necrosis of surrounding tissue, poor mechanical strength etc. The objective of this study is to fabricate a novel thermosensitive injectable bone cement with incorporation of super paramagnetic iron oxide nanoparticles and nanohydroxyapatite (nHA) and test their suitability of bone healing.
Methods: Composite hydrogel was prepared by homogenization of Poly (N-isopropyl acrylamide)-co-acrylic acid (pNIPAM-co-AA) polymer solution with citrate modified magnetic iron oxide nanoparticles (MNP, 15-20 nm), nHA (200 nm) and strontium ranelate (SR). The obtained hydrogel was characterized for its structural, thermal and mechanical properties. Human mesenchymal stem cells (hMSC) were grown on the composite hydrogels in vitro and the structure, proliferation, osteogenic differentiation and mineralization ability of the cells on the hydrogel was analysed using MTS, alkaline phosphatase (ALP) assays, alizarin red staining and immunocytochemistry.
Results: The hydrogel composite comprised of a microporous structure with uniform distribution of the nanoparticles. LCST of the composite was observed as 35oC with 80.25% water content. FT-IR analysis showed characteristic peaks for amide, acid, cyanide, phosphate and carbonate groups. The onset of thermal degradation was observed at 144oC with residual weight of 16% at 900oC. The cells grown on hydrogel composite showed significantly higher proliferation and ALP activity (p<0.01). Further, the quantification of ARS staining revealed significantly higher mineralization (p<0.01) in the composite hydrogel. Immunohistochemistry studies showed that the cells expressed both CD90 and osteocalcin, indicating that the cells are differentiating towards osteogenic lineage.
Discussion: The results suggest that the fabricated composite hydrogel could serve as injectable bone cements for non-invasive or minimally invasive defect filling in bone tissue engineering. The hydrogel is also capable of inducing mesenchymal stem cell differentiation towards osteogenic lineage.
Acknowledgement: This work was supported by MOE AcRF Tier 1 research grant (1T1-01/15) awarded to Asst. Prof. Dinesh Kumar Srinivasan, LKCMedicine, NTU.