Screening Of Micro - Level Thermotherapy Medium And Establishment Of In Vitro Heating Model

ObjectiveThis paper aims to study the possibility of magnetic microsphere as medium for magnetic hyperthermia and to select the suitable microspheres for magnetic hyperthermia. The microsphere could show the excellent heating performance in an alternating magnetic field, and have good bio-security. A standard method for in vitro heat generating studies was established to test the efficiency of magnetic microspheres.MethodsAgar gel with concentrations of 0%,0.5%,1%,2%, and 3% were prepared. Three different kinds of microspheres were separately dispersed in these dispersant. Then, the samples were placed in an alternating magnetic field. The temperature increase was measured at three separate sites. The concentration of agar gel was chosen by comparing the setting time and the difference of temperature increase at each site. The heating efficiency of the microspheres in 1% agar gel was investigated under the magnetic field at different magnetic field frequencies and intensities. The value of the specific absorption rate (SAR) was also calculated.Microspheres with three kinds of structures (hollow structure, solid structure, mutilporous structure) were collected. The heat generating properties of all the microspheres under the magnetic field were tested and compared. The morphology of different microspheres were observed using optical microscopy and scanning electron microscopy to selected the optimal microspheres.To characterize the properties of microsphere Z, scanning electron microscope, laser particle size analyzer, vibrating sample magnetometer, and differential scanning calorimeter were used. The EDS and XRF methods were employed to study the composition of microspheres Z. The heat generating properties of microspheres Z at different concentrations in the magnetic field with different frequency and strength were also be investigated. The in vitro haemolysis rate and cytotoxicity of microspheres Z were studied using rabbit blood and c L-929 cells, respectively. The magnetic induction hyperthermia of microspheres Z for liver cancer cells was tested.ResultsAll three kinds of agar gel could be mixed well with these microspheres. The concentration of 1% and 2% agar gel were satisfied.Microspheres with hollow structure showed better heat generating properties than microspheres with solid structure and mutilporous structure. The microspheres Z showed good heating performance under the alternating magnetic field, which had appropriate morphology.The microspheres Z, with good heating performance under the alternating magnetic field, had suitable particle size (181.073 μm) and smooth surface. Magnetic induction hyperthermia for liver cancer cells in Bel-7402 and HepG2 by the microspheres Z showed satisfied result.ConclusionThe microspheres Z could be used for tumor hyperthermia. The method to test the in vitro heating efficiency was successfully established.