Stimulus-Responsive Gold Nanoparticles For CT Imaging Tracking Of Transplanted Stem Cells In The Treatment Of Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis(IPF)is a severely damaging lung disease with high mortality and a short survival period.There is no effective treatment to reverse this state at present.In recent years,stem cells have made important progress in the treatment of IPF,but still a long way goes for the clinical transformation.One of the important reasons is that there is a lack of effective means for real-time and precise tracking of transplanted stem cells and monitoring the process of therapeutic effects in vivo.In the application of stem cell therapy for IPF,gold nanoparticles as a nanotracer for CT imaging tracing of stem cells have high values and prospects for practical application and clinical transformation.The safety and effectiveness of CT imaging tracking for stem cells depend on the structure and physicochemical properties of nanotracers.Therefore,the development of suitable nanotracers is the key to achieving CT imaging tracking of the transplanted stem cells in vivo.This PhD thesis aims to develop innovative strategies for enhanced and long-term CT imaging tracking of transplanted stem cells.To reach this goal,functional modification is used to regulate the hydrophobicity,size,surface charge,and aggregation state of gold nanoparticles,thereby improving their interaction with cells,and achieving enhanced CT imaging and long-term tracking of transplanted stem cells.The following two parts of research work were carried out:In the first part of this thesis,the temperature-responsive polymer pNIPAAm-b-pAAm and polyethylene glycol are used to co-modify gold nanoparticles to obtain TRAuNPs with good colloidal stability and temperature-sensitive properties.The physicochemical properties of TRAuNPs at different temperatures are employed to achieve enhancing the stem cell labeling efficiency and prolonging the labeling time.By thermally stimulating the incubation process of TRAuNPs and mesenchymal stem cells(MSCs)(39?)to change the hydrophobicity and size of the particles,the labeling efficiency of the tracer on the cells is significantly improved.After intracellular loading of nanotracers,the physiological temperature makes the phase transition of TRAuNPs to a hydrophilic state,which slows down the exocytosis rate of MSCs to the tracers and thus prolongs the labeling time to MSCs.In addition,TRAuNPs and their labeling strategy showed good biocompatibility to MSCs.TRAuNP labeling imposes a negligible adverse effect on the function of MSCs,including viability,proliferation,apoptosis,cell cycle,and differentiation.In in vivo experiments,CT technology could track the transplanted stem cells for 10 days,monitoring the location,distribution,and migration of transplanted stem cells.However,the labeling strategy has no obvious advantage in the amount of nanotracer loading,which limits further application for CT imaging tracking of stem cells.As an integral effort to develop a series of stimuli-responsive CT nanotracers,the second part of the PhD thesis described a sequential modification of pH-responsive polymers(PSD)and cell-penetrating peptides(CPP)the surface of gold nanoparticles to construct a pH-responsive gold nanoparticle(CPP-PSD@Au)for optimal stem cell imaging tracking.The experimental results show that CPP-PSD@Au can efficiently label MSCs due to the modification of CPP,and the Au content can reach up to 480 pg per cell,which exceeds most of the gold nanotracers reported in the current literature.Because nanoparticles would pass through acidic environments such as lysosomes or endosomes during the intracellular transport,CPP-PSD@Au would exhibit pH-responsive behavior in the cell,triggered nanoparticle aggregation,which can constrain the exocytosis of cells,to achieve long-term labeling and CT imaging tracing.At the same time,CPP-PSD@Au labeling did not cause significant side effects on the viability,proliferation,apoptosis,and differentiation of MSCs.In in vivo experiments,the stem cells transplanted in IPF model mice can be traced for 35 days through CT imaging,monitoring the distribution and migration of transplanted stem cells in the lungs.Besides,MSCs transplantation can significantly delay the progress of IPF and may exert the therapeutic effect by participation in inflammation,which is evidenced by analysis of pathological sections and immunohistochemical staining.In short,CPP-PSD@Au has a good application prospect in CT imaging tracing of transplanted MSCs in IPF treatment.