Design Of Functional Hybrid Nanogels For Tumor Magnetic Resonance Diagnosis

Magnetic resonance?MR?imaging is one of the common used molecular imaging techniques,which has many advantages,for example,noninvasive nature,non-toxicity,nonionizing radiation source,high spatial resolution and tomographic capability.However,the currently common used contrast agents in MR imaging are Gd-chelates with low molecular weight,which could be cleared away from the body rapidly due to their short blood circulation time.Moreover,they may lead to the nephrogenic systemic fibrosis in the patients with renal malfunctions.With the development of nanotechnology,many nanosized imaging contrast agents are synthesized for the diagnosis of dif-ferent diseases by means of the incorporation of various nanocarriers and contrast agents,in order to improve the imaging performance.However,the nanosized imaging contrast agents widely de-veloped in these years still have some problems and challenges,for example,the relatively low relaxivity and the low accumulation in tumor sites.It is very necessary to seek a safe and efficient nanocarrier to improve the above situations.Among many various nanocarriers,nanogels?NGs?,which possess many excellent properties,such as good stability,biocompatibility,high loading capability,controlled size and high endocyto-sis by tumor cells,have been widely applied in drug delivery and tissue engineering fields.The NGs could be used as the carriers of imaging elements to develop novel nanosized imaging contrast agents,in order to improve the relaxation performance and enhance the cellular uptake of tumor cells due to the high loading capability and high endocytosis by tumor cells.In this thesis,the algi-nate nanogels?AG?and poly?N-vinylcaprolactam?nanogels?PVCL NGs?with good biocompati-bility were used as platforms to combine different MR imaging elements to synthsize a series of functional hybrid NGs for MR diagnosis of tumor.The main research contents of this thesis are as follows:?1?Immobilization of iron oxide nanoparticles within hybrid alginate nanogels for enhanced MR imaging applications.Polyethyleneimine coated iron oxide nanoparticles?PEI-Fe₃O₄ NPs?were first synthesized using the facile hydrothermal method.Then the hybrid AG NGs containing Fe₃O₄NPs?AG/PEI-Fe₃O₄ NGs?were formed through emulsification crosslinking approach.PEI-Fe₃O₄NPs were used as crosslinkers.Many different techniques were employed to characterize the phys-icochemical properties of the AG/PEI-Fe₃O₄ NGs.The formed AG/PEI-Fe₃O₄ NGs with a narrow size distribution were colloidally stable,cytocompatible and hemocompatible in the given concen-tration range.The transverse relaxivity?r₂?of the AG/PEI-Fe₃O₄ NGs was calculated to be 170.87mM^-1s^-1,which was larger than that of PEI-Fe₃O₄ NPs(137.1 mM^-1s^-1).The results of ICP-OES?inductively coupled plasma optical emission spectrometer?analysis and Prussian blue staining in-dicate that the AG/PEI-Fe₃O₄ NGs could be more significantly taken up by cancer cells compared with the carboxylated Fe₃O₄-PEI·SAH NPs,which is helpful to significantly enhance the accumu-lation of contrast agents in tumor sites.The formed AG/PEI-Fe₃O₄ NGs are able to be used as an effective contrast agent for the MR imaging of liver and the xenografted tumor model in vivo after intravenous injection.Additionally,the AG/PEI-Fe₃O₄ NGs can be metabolized and cleared away from the body of mice.?2?Construction of hybrid alginate nanogels loaded with manganese oxide nanoparticles for enhanced tumor MR imaging.Hybrid AG NGs loaded with manganese oxide?Mn₃O₄?NPs?AG/PEI-Mn₃O₄ NGs?were prepared through the emulsification crosslinking approach between the AG with activated carboxyl groups and PEI coated Mn₃O₄ NPs?PEI-Mn₃O₄ NPs?.The morphology,size,composition,structure,colloidal stability and cytocompatibility were characterized through different techniques.The AG/PEI-Mn₃O₄ NGs displayed a typical spherical shape with a mean size of 141.6 nm and a narrow size distribution.They have colloidal stability and cytocompatibility in a given concentration range.The AG/PEI-Mn₃O₄ NGs have a high r₁ relaxivity of 26.12 mM^-1s^-1,which is about 19.5 times higher than that of PEI-Mn₃O₄ NPs.They displayed enhanced MR imag-ing performance of cancer cells in vitro as well as a subcutaneous tumor model in vivo.The results of pharmacokinetics,in vivo biodistribution and Hematoxylin and eosin?H&E?staining demon-strated the AG/PEI-Mn₃O₄ NGs possess prolonged blood circulation time,can be cleared away from the body of mice,and have no obvious bio-toxicity to mice.?3?Facile loading of gold nanoparticles and gadolinium within alginate nanogels for enhanced dual mode tumor MR/CT?computed tomography?imaging.It is difficult to present whole diagnosis information of diseases using single mode imaging technique.Based on previous work,hybrid AG NGs loading of gold nanoparticles and gadolinium?AG/PEI-Au-Gd NGs?were formed through emulsification crosslinking method for enhanced tumor dual-modal MR/CT imaging applications.The AG/PEI-Au-Gd NGs with a size of 83.3 nm exhibit excellent colloidal stability,good cytocom-patibility in the studied concentration range,and enhanced celluar uptake ability.In particular,the hybrid NGs exhibit a high r₁ and a great X-ray attenuation properties.Furthermore,the AG/PEI-Au-Gd NGs enable better MR and CT imaging performance of cancer cells in vitro as well as a subcutaneous tumor model in vivo than clinical MR or CT agents?Magnevist?R or Omnipaque?.In vivo biodistribution analysis and organ compatibility study indicated the developed AG/PEI-Au-Gd NGs could be metabolized through the normal pathway,and have a good biosafety confirmed.The AG/PEI-Au-Gd NGs may be potentially employed as an efficient contrast agent for enhanced dual-modal MR/CT imaging applications.?4?Gadolinium-loaded poly?N-vinylcaprolactam?nanogels for enhanced tumor MR imaging application.The NGs were synthesized by emulsification crosslinking method in the above work.The operation process is a little complex,and it is not eco-friendly enough due to the use of organic solvent during the synthesis process.In chapter 5,poly?N-vinylcaprolactam?nanogels?PVCL NGs?were synthesized through precipitation polymerization in aqueous solution based on the biocompat-ible polymer of PVCL,followed by covalently binding with varying amounts of Gd chelates to obtain hybrid PVCL NGs with different Gd loading?PVCL-Gd NGs?for T₁ MR imaging study of tumor.PVCL-Gd NGs having a mean size of 180 nm are water dispersible,colloidally stable,and uniform in size distribution.The r₁ of PVCL-Gd NGs with different Gd loading was measured to be6.38-7.10 mM^-1s^-1,which is higher than the clinically used Gd chelates under the same measurement conditions.Taking into account of the results of r₁ relaxivity,and cell viability assay data,the PVCL-Gd NGs-0.1%were chosen for further MR imaging applications.The results of tumor MR imaging studies indicated that PVCL-Gd NGs-0.1%could significantly enhance the tumor MR signal inten-sity when compared with the clinical used Magnevist?R.In vivo biodistribution and H&E staining of major organs showed the developed PVCL-Gd NGs-0.1%with good bio-safety could be cleared away from mice.In summary,AG NGs and PVCL NGs were used as platforms to combine different MR imag-ing elements to synthsize a series of functional hybrid NGs for MR diagnosis of tumor by means of the high loading capability and high endocytosis by tumor cells of NGs.This thesis will provide new direction to develop new MR imaging contrast agents.