Chitosan micro/nanobubbles: novel chemical structure and characterization

Abstract Microbubbles (MBs) are gaining increased interest in biomedical applications. MBs size typically range from 0.1 to 10 µm and formed with different shells such as (lipid, polymer, protein, and surfactant). The shell encapsulates a gaseous core containing gases such as oxygen, sulfur hexafluoride SF6, or perfluorocarbons. MBs have a range of medical applications, such as medical imaging, drug delivery, and gas delivery. Freeze-drying of MBs have been used by different groups to help reconstitute them at the point of care. This would become advantageous for better control of the encapsulated drug and gas, MB concentration, and protocols of administration and would also allow off-site production at lower cost. In this study, we developed a protocol to use chitosan and glycerol to produce Chitosan-coated MBs with SF6 as the gas core at high concentration and stability. Moreover, freeze drying has been used to change the gas core to oxygen to enhance the benefits of using these MBs. The idea is to be able to produce oxygen MBs with better stability to enhance the chemotherapy and radiotherapy effect on cancerous cells by relieving hypoxia and increasing the cell sensitivity. We used different characterization techniques for our systems to demonstrate that we have developed a novel CS shell for micro/nanobubbles as shell with SF6 as core at low cost. We obtained not only MBs with mean diameter 3.57 ± 0.71µm but also nanobubbles with 55 ± 37nm diameter with a surface positive charge and high concentration of 1.02x1012 MBs/ml. Moreover, freeze-drying was used to change the gas core to oxygen producing MBs with mean diameter 1 ± 0.7 µm and concentration of 6.5 × 108 MBs/ml.