Active And Passive Temperature Control During Thermal Therapy Based On The Photothermal Properties Of Nanoparticles

The micro/nanoscale photothermal conversion and transmission plays an important role in a lot of fields including biomedicine.Published data in 2018 of the world health organization show that the morbidity and death rate of cancer are increasing rapidly all over the world.The specific highly efficient photothermal conversion efficiency of nanomaterials could induce tunable and high output heat flux in nanoscale,which could provide a new solution for the new generation of precision medicine diagnosis and treatment technology and other possible applications.As a very promising and precise alternative tumor treatment,nanoparticle assisted laser induced thermal therapy has been developed rapidly in recent years.Various techniques have been proposed to monitor the temperature in certain points or distribution in the region of interest,such as thermocouples,near-infrared thermal imaging,ultrasound thermal mapping,photoacoustic temperature measurement,magnetic resonance temperature imaging.Most of the available temperature control technologies are based on the results of the above mentioned t emperature measurement techniques.Afterwards,the temperature can be controlled by simply adjusting thermal dosage applied,such as laser power density,ultrasonic intensity,and magnetic field intensity.However,due to the measurement error of temperature and the time lagging of thermal dosage control,the precise and real time control of the temperature in tumorous area are very difficult.In addition,during tumor photothermal therapy,the high temperature zone is always around the interface between tumor and normal tissue,due to the strong attenuation effect of nanoparticle to light.Therefore,the overheating of surrounding healthy tis sue is inevitable owing to the heat diffusion.Based on the above mentioned problems,the localized surface plasmon resonance of isolated nanoparticle and their aggregates induced by external light source triggered unique light absorption and scattering phenomenon is studied in the present work.The corresponding local micro/nanoscale heat source induced phase change process of surrounding matrix is also investigated.On this basis,the active and passive control methods of the temperature field during tumo r thermal therapy based on the photothermal properties of nanoparticles are proposed.The main content of the present work is as follows:At present,the theoretical research on the photothermal conversion characteristics of nanoparticles is mainly focused on the simple shape of nanoparticles,while the research on the complex shape of nanoparticles is mainly focused on the experimental field.To reduce cytotoxicity and achieve other purposes in thermal therapy,the surfaces of nanoparticles are always coated with other materials,like polyethylene glycol(PEG).The dependence of absorption efficiency and absorption quantum yield on the structural parameters of gold nanocage were discussed.It was found that the phenomenon of multipolar plasmon resonances exists on truncated Au nanocage.By adjusting the structural paremeters,the nanocage can be applied in biomedical imaging and laser induced thermal therapy.The impact of polyethylene glycol(PEG)coating thickness on the optical and thermal properties of n anoparticles was then further investigated.The absorption and scattering properties of nanosphere and nanorod with different PEG coating thicknesses and refractive index were investigated.It was found that impact of PEG coating thickness on optical and thermal properties of nanoparticles highly depends on the morphology of nanoparticle.Whether the refractive index of PEG is larger than that of the ambient has an important effect on the photothermal properties of nanoparticles.The precise prediction and spatially control of temperature distribution and phase transition induced by LSPR of nanoparticles assemblies is of great significance for the application of micro-nano scale heating(melting)in biomedical field.On this basis,the photothermal response and phase transition of specific nanoparticle dimer under the illumination of electromagnetic field was investigated.The effective heat capacity method was utilized to investigate phase transition of matrix media around isolated nanoparticles with different morphologies and sizes.The temperature distribution and phase transition of different configurations of nanodimer and its surrounding matrix media were further studied.It shows the tem perature distribution and phase transition of matrix media can be manipulated and precisely controlled in nanoscale by tuning the light polarization angles.This present a way to manipulate and precisely control of temperature distribution and phase transi tion in nanoscale by tuning the light polarization angles.Higher laser intensity will,at the same time,heat other parts of the whole system in thermal therapy.In addition,increasing the size of nanoparticles is not conducive to the diffusion to the tumor region.The interaction between nanoparticles can effectively enhance the photothermal conversion capacity,increase heating power,and greatly enhance the electromagnetic field intensity between nanoparticles.Then,we studied the amplification effect of a nanosphere dimer on the local electromagnetic field on the hot spot.The contribution of thermal superposition effect and plasmonic coupling effect on the temperature rise of the hot spot was also investigated.The optical characteristics of nanoparticle aggregates as a potential theranostic nanoplatform was studied.On this basis,a simple hybrid theranostic nanoagent consisting of isolated nanosphere and nanosphere dimer for tumor diagnosis and treatment was proposed.Additionally,the influence of impurities in the nanohybrids was investigated.To avoid overheating for a long time in the normal tissues during the tumor hyperthermia,the temperature of the tumor region needs to be precisely regulated in a real time.We proposed a way that can optimize the photothermal transfer of tumor hyperthermia by adjusting the anisotropic scattering characteristics of nanoparticles.This method can be applied to increase the uniformity of specific absorption rate(SAR)distribution in tumor during laser induced thermal therapy,and therefore to improve the tumor hyperthermia targeting and then reduce the thermal damage of healthy tissue.The discrete dipole approximation(DDA)was applied to investigate the anisotropic scattering characteristics of nanparticles with different shapes and sizes.On this basis,photothermal transmission characteristics under forward and back scattering conditions and active control of temperature distribution in tissue were obtained.Finally,a passive control method based on optical phase change nanomaterials(solid-solid phase change)was proposed to improve the uniformity of temperature distribution inside tumorous tissue during laser induced thermal therapy.Optical phase change materials refer to one type of materials that exhibit obvious optical properties change when undergo a solid-state phase transition induced by temperature change.After the phase transition,the absorption cross section of the nanoparticle will significantly decrease,and therefore to minimize the heating ra te in the high temperature region and increase the temperature uniformity in tumor,and then reduce overheating and thermal damage of normal tissue.The optical properties of VO 2 and Ge-Sb-Te nanospheres and nanoshells with different sizes,two widely used optical phase change materials were investigated.The influence of the coated Si O 2 shell thickness on the performance of the phase transition nanomaterials was also investigated.