Characterization and photothermal effect of indocyanine green encapsulated poly lactic acid-co-glycolic acid microspheres
Fan Yaru1, 2, Li Ruixin2, Li Fengji2, Luo Rui2, Liu Hao2, Yan Yingbin2
1School of Stomatology, Tianjin Medical University, Tianjin 300070, China; 2Affiliated Stomatological Hospital of Nankai University, Tianjin Stomatological Hospital, Tianjin Key Laboratory of Oral and Maxillofacial Function Reconstruction, Tianjin 300041, China
Abstract: BACKGROUND: Indocyanine green, an efficient photothermal conversion agent, can be used for photothermal therapy of oral squamous cell carcinoma, but it has some shortcomings such as water instability and photodegradation. Using a carrier to encapsulate indocyanine green to improve its stability was of great significance for exploring photothermal therapy of oral squamous cell carcinoma.
OBJECTIVE: Indocyanine green encapsulated poly lactic acid-co-glycolic acid microspheres were fabricated to delay the photodegradation of indocyanine green and improve its photothermal stability.
METHODS: (1) The indocyanine green encapsulated poly lactic acid-co-glycolic acid microspheres were prepared by emulsion-solvent evaporation method. The morphology, particle size distribution, surface charge, drug loading and encapsulation efficiency were characterized. (2) The free indocyanine green solution and the indocyanine green microsphere suspension were irradiated with near-infrared light at different mass concentrations (0.6, 0.8, 1.0, 1.2 g/L) for 5 minutes to investigate the temperature changes of the solutions. The free indocyanine green solution and the indocyanine green microsphere suspension were exposed to natural light for 0, 3, 6, and 9 days at a mass concentration of 1.0 g/L to observe the temperature changes within 5 minutes of near-infrared light irradiation. The free indocyanine green solution and the indocyanine green microsphere suspension were subjected to four on-off laser irradiation cycles at a mass concentration of 1.0 g/L to investigate the temperature changes of the solutions. (3) The tongue squamous cell carcinoma cell line SCC-25 was inoculated in a 48-well plate and cultured in eight groups: control group, blank microsphere group, 1.0 g/L free indocyanine green group, 1.0 g/L indocyanine green microsphere group, near-infrared light group, blank microsphere+near-infrared light group, 1.0 g/L free indocyanine green+near-infrared light group, and 1.0 g/L indocyanine green microsphere+near-infrared light group. After 12 hours of treatment, cell viability was detected by CCK-8 assay.
RESULTS AND CONCLUSION: (1) The indocyanine green microspheres had smooth surfaces with particle sizes of (2.54±0.29) μm and zeta potential of −(20.2±1.58) mV. Encapsulation efficiency and loading efficiency were (69.24±1.29)% and (4.87±0.15)%, respectively. (2) Free indocyanine green and indocyanine green microspheres had similar photothermal conversion ability, but after increasing the number of laser irradiation or storage without light, the photothermal conversion ability of free indocyanine green obviously decreased compared with indocyanine green microspheres. (3) The SCC-25 cells in the 1.0 g/L free indocyanine green+near-infrared light group and the 1.0 g/L indocyanine green microsphere+near-infrared light group shrank to a spherical shape, and the cell viability of the two groups was lower than that of the control group (P < 0.001). (4) Indocyanine green microspheres possess efficient photothermal conversion ability and can obviously delay photobleaching and photodegradation of indocyanine green.
Key words: poly lactic acid-co-glycolic acid, indocyanine green, microsphere, oral squamous cell carcinoma, photothermal therapy, SSC-25 cell, near-infrared, emulsion-solvent evaporation method