(30n) Polymer-Cerium Oxide Nanocomposites Synthesized By Hydrothermal Method for Bone Tissue Regeneration Applications

One common detrimental effect on biological system caused by orthopedic pathogenesis is bone tissue degeneration. Relevant orthopedic pathogeneses include bone cancer and age-related illnesses, such as osteoporosis and osteopenia. One major cause of bone tissue degeneration is the high generation of reactive oxygen species (ROS) associated with many related pathologies. The accumulation of ROS stimulates the activities of osteoclasts, while inhibiting the activities of osteoblasts. Thus, overall there is a significant loss in bone tissue. Additionally, the accumulation of ROS also hinders the activities of naturally-occurring enzymes such as superoxide dismutase (SOD) and catalase (CAT) that normally function to catalyze the removal of ROS from biological tissue. Bisphosphonates are currently used in medical practice to slow bone tissue degeneration and facilitate healing. However, bisphosphonate therapeutic efficacy is compromised due to short circulation times, limited bioavailability to target tissues, and uncontrolled release by current methods. To overcome these limitations, we have synthesized polymer-cerium oxide nanocomposites (pCNP) using sacrificial template materials. Sacrificial template materials allowed us to control the size of the porous cerium oxide nanoparticles. Recent studies show pCNPs formulations have high ROS scavenging abilities to mitigate bone degeneration. This property can be attributed to the redox potential of the Ce³⁺ state and surface SOD-mimetic and CAT-mimetic properties of polymer cerium oxide nanocomposites. Synthesizing pCNPs increases nanocomposite surface area and drug encapsulation relative to conventional cerium oxide nanoparticles. To optimize particle specific surface area and surface defect morphology for optimally efficient drug loading, we have experimented with the following different templates: silica, agarose, glucose, polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and cetrimonium bromide (CTAB). Each templated synthesis had its own variability in size and offered unique characteristics to the polymer cerium oxide nanocomposites. pCNPs were synthesized via a hydrothermal method, to promote cation hydrolysis and oxide crystallization. These chemical processes yielded higher surface area through maximization of surface defects. Successful synthesis of the polymer-cerium oxide nanocomposites was confirmed through characterization studies such as thermogravimetric analysis, FTIR, UV-Vis, DLS size analysis, and TEM imaging. Surface area (BET pore size analysis) measurements were performed to investigate pCNP specific surface areas for formulations produced from different templates to determine optimal synthesis procedures. Superoxide dismutase and catalase enzyme-mimetic activity assays confirmed pCNP formulations abilities to interact with ROS and enhance their clearance: facilitating bone tissue regeneration. MTT cell viability assays showed pCNP’s biocompatibility with human mesenchymal stem cells. These cell viability assays showed that 10 ug/mL concentration was the ideal biocompatible concentration. Furthermore glucose-cerium oxide nanocomposites and agarose-cerium oxide nanocomposites yielded the best cell viability over a 7 day period. CTAB-cerium oxide nanocomposite did not show to have the optimal biocompatibility with human mesenchymal stem cells. However, overall for all synthesized polymer-cerium oxide nanocomposites, cell viability over 7 days exceeded 80%, indicating that our formulations had no cytotoxicity on human mesenchymal stem cells. Studies were also performed to determine if pCNPs can induce human mesenchymal stem cell differentiation into osteoblasts bone stem cell. This was assessed through the Alkaline Phosphatase (ALP) and Alizarin Red (ARS) assays. ALP assays, quantification, and staining showed that the synthesized polymer-cerium oxide nanocomposites have promising potential to induce human mesenchymal stem cell differentiation into osteoblasts. The ALP assays showed that glucose-cerium oxide, agarose-cerium oxide, and PVP-cerium oxide nanocomposites had the best ability to facilitate mesenchymal stem cell differentiation. Currently, further tests through the ARS assay are being conducted to determine the polymer-cerium oxide nanocomposite formulations ability to stimulate calcium deposition and bone formation. Overall, comprehensive studies show pCNP’s capability to facilitate bone tissue regeneration in orthopedic diseases. Thus, polymer cerium oxide nanocomposites show great potential to provide a synergistic effect with conventional clinical bisphosphonate to amplify therapeutic efficacy.