Achieving Light-induced Sterilization In Small Animals By Using Highly Biocompatible Magnetic Nanoparticles

In recent years,the synthesis and usage of multifunctional magnetic nanoparticles have attracted extensive attention in biomedical field.Magnetic nanoparticles with different structures and their functional derivatives have been widely used in targeted drug therapy,tissue engineering,nuclear magnetic imaging,and tumor therapy.As a metal oxide approved by the US Food and Drug Administration(FDA)for biomedical use,Fe₃O₄ nanoparticles can be used in clinical MRI and diagnosis of solid liver tumors.Because of their stable physical and chemical properties,low toxicity,high biosafety,as well as easy preparation and modification,these nano-size biomaterials have a broad medical prospect.As a new strategy with simple operation,low toxicity,and strong controllability,photothermal therapy(PTT)has been widely used in anti-tumor and anti-bacteria treatments.With the assistance of near-infrared(NIR)light,PTT makes the use of photothermal conversion characteristics of photothermal materials to increase the local temperature and thus induce cell death to achieve the purpose of removing lesions.Ferroptosis is an iron-dependent mode of cell death characterized by the abnormal ferrous concentration and excessive accumulation of lipid peroxides.The occurrence of local Fenton reaction usually induces the generation of various reactive oxygen species,resulting in excessive deposition of lipid peroxides,intracellular ion disorder and damage to various membrane structures,as well as ultimately cell death.Our current design pioneered the use of magnetic nanoparticles,photothermal treatment,and ferroptosis in the field of small animal sterilization.The photothermal properties and biosafety of magnetic nanoparticles were well investigated,and iron oxide-based photothermal sterilizing materials were proved to have high biosafety and biomedical application prospect.These magnetic nanoclusters were firstly in situ injected into the testis of mice,and the testis were irradiated with an 808 nm near infrared light to achieve local temperature rising.Above treatments leaded to the destroy of testicular tissue and achievement of male animal sterilization.Moreover,we discussed the potential light induced mechanisms of photoinduced sterilization by using our well-prepared magnetic nanoparticles.Our experimental conclusion were attached as follows.(1)Four types of Fe₃O₄ nanoparticles were synthesized via solvothermal method.Different reaction period and raw materials during above synthesis could result in different topological structure and surface charge were different by adjusting the reaction materials and reaction time.These four types of Fe₃O₄nanoparticles were further characterized via transmission electron microscopy(TEM),scanning electron microscopy(SEM),X-ray crystal diffraction(XRD)and other detection methods of physical and chemical properties.Our results indicated that these four types of Fe₃O₄ nanoparticles exhibited different structures,such as solid,cluster and hollow structures.In addition,above four types of Fe₃O₄ held different surface electrical properties.(2)Photothermal properties of these four types of Fe₃O₄ nanoparticles were well explored.Our results demonstrated that the photothermal effects of all these Fe₃O₄ nanoparticles exhibited concentration-,light intensity-,and illumination period-dependent manners.Moreover,these Fe₃O₄ nanoparticles had similar photothermal conversion efficacies.It was noteworthy that Fe₃O₄nanoparticles with cluster structure revealed stronger absorption capacity under the near infrared light illumination and better dispersion in various physiological solutions.(3)Hemolysis analysis of above four types of Fe₃O₄ nanoparticles demonstrated that Fe₃O₄ nanoparticles with cluster structure and negative charges,named as magnetic nanoclusters(MCNs),showed lowest hemolysis ratio even upon a high co-incubation concentration of 0.8 mg/m L,as compared with other three types of Fe₃O₄ nanoparticles.These exciting results therefore promoted us to investigate the long-term toxicity of MNCs.Typical in vivo toxicity explorations usually included weight monitoring,urine analysis,blood analysis,and histopathological sections.As expected,our well-prepared MNCs exhibited extremely low long-term toxicity and high biocompatibility based on animal experiments.According to our above experimental results,MNCs were selected and used in further light-induced small animal sterilization.(4)Owing to their excellent photothermal effect and negative charges,our well-designed MNCs were then used to sterilize small animals,and the potential mechanism was further discussed in detail.As compared with the groups of control,NIR,and MNCs,MNCs+NIR group exhibited great light-induced sterilization effect.The levels of serum testosterone of mice in the group of MNCs+NIR decreased sharply after treatments.Moreover,it could be easily found that testis atrophied and the volumes of the testis were decreased in the group of MNCs+NIR as compared with other three groups.During the whole experiment period,no abnormalities in diet and behavior were detected between the experimental mice and the mice without any treatments,indicating the overall safety and practicability of current light-induced sterilization technique for small animals designed in this study.Histological analysis and pathological analysis further demonstrated that our small animal sterilization process was a synergistic effect of light-induced cell apoptosis and ferroptosis in testis.Our experimental results would provide experimental basis and theoretical guidance for the following biomedical mechanism of iron-based materials.