Microfluidic One-step Preparation Of Calcium Alginate Microspheres Encapsulated With In Situ-formed Gold Nanostars And Their Photothermal Effect

Transcatheter arterial chemoembolization therapy takes the advantage of transcatheter arterial embolization and the local chemotherapy,which has been regarded as a preferred choice for the advanced liver cancer patients.However,the therapy effect is yet limited.Near infrared?NIR?light-mediated photothermal therapy can kill tumor cells directly with high temperature raised up from some photothermal reagents absorbing NIR light and converting it into heat and without damaging the normal cells.Due toits unique targeting,minimal invasiveness,high efficacy and low side effect,photothermal therapy has been paid much attention by the researchers.In addition,thermal therapycan alsosensitize the radiotherapy and chemotherapy.Therefore,the combination of photothermal therapy and chemoembolization therapy is expected to have a better synergistic therapeutic effect.However,this kind of multi-functional materials has rarely been reported.In this paper,mono-dispersed spherical calcium alginate microspheres encapsulated with in situ-formed gold nanostars?named Au@CA microspheres?have been prepared by one-stepusing adroplet-based microfluidic technique and then loaded with anti-cancer drug.Therefore the obtained microspheres were multi-functional combined withphotothermal therapy,controlled chemotherapy and embolization.Another kind of calcium alginate microspheres encapsulated with drug-loaded nanogels?named drug-loaded nanogel@CA microspheres?has also been prepared using the same microfluidic device.The main works and results in detail are as follows:?1?A serial ofAu@CA microspheres have been prepared using a flow-focusing microfluidic device?FFD?based on polydimethylsiloxane.Herein,a mixed aqueous solution of sodium alginate and chloroauric acid?HAuCl₄?with different concentration was used as the dispersed phase,the liquid paraffin containingCaCl₂nanoparticles was used as the continuous phase,and the CaCl₂solution containing vitamin C was used as the collection solution.The morphologies and sizes of the prepared various microspheres were characterized by an optical microscopy and a scanning electron microscopy?SEM?.The absorption spectra of the dispersed phases and the degraded dispersion of the microspheres wererecorded by a UV-Vis-NIRspectrophotometer.The morphologies of gold nanoparticles in above solution were further characterized by transmission electron microscopy?TEM?.The crystal form of gold nanostars and the thermal stability of the microspheres were characterized by X-ray diffraction?XRD?and thermogravimetric analyzer?TGA?,respectively.The contents of Au in the microspheres weredetermined by the atomic absorption spectrometry?AAS?.The photothermal effect of the various microspheres wasmeasured under the irradiation of 808 nm NIR laser.The anti-cancer drug doxorubicin hydrochloride?DOX·HCl?was loaded into the microspheres by an adsorption method.The drug release experiments were carried out at 37?and the irradiation of NIR laser respectively.The cytotoxicity of the microspheres was also studied.The results indicate that the prepared microspheres have uniform size and shape with a diameter of about 200?m for the wet microspheres,which would benefit to being used as embolic materials.The polycrystalline gold nanostars?Au NSs?was situ-formed and loaded in the microspheres,and the contents of gold could be adjusted by changing the amount of HAuCl₄ in thedispersed phase.The highest content of Au in the prepared microspheres was 13.50%in the dry microspheres.The microspheres had the ability to absorb theNIR light and the temperature of the microspheres'suspension could be increase more than 60?under the irradiation of the NIR light.These microspheres could be applied in thephotothermal therapy.In addition,the results from the drug release experiment in vitro showed that the drug release ratefrom the microspheres could be accelerated by the irradiation of NIR laser.The results from the cytotoxicity testindicated thatthe combination of photothermal therapy and chemotherapy could significantly improve the effeciency of killing the tumor cellscompared with a single chemotherapy or photothermal therapy.?2?The calcium alginate microspheres encapsulated with drug-loaded thermosensitive nanogels?DOX@nanogel@CA?have been prepared by using the same microfluidic device mentioned above.Herein,the mixed solution of the drug-loaded temperature-sensitive nanogels and sodium alginate solution was used as the dispersed phase and CaCl₂aqueous solution was used as the collection bath.The morphology and size of the nanogel were characterized by TEM.The morphology and size of the prepared microspheres were characterized by optical microscopy and SEM.The drug release behavior of the microsphereswas studied in vitro.These results show thatthe preparedmicrospheres haduniform morphology and the diameter was about 200?m in wet.Compared with free DOXloaded CA microspheres?DOX-CA'?and free DOX and nanogels loaded CA microspheres?DOX-nanogel@CA?,DOX@nanogel@CA microspheres had significant sustained release ability with 19%of the cumulative release rate ever after 7 days.In contrast,there were obvious burst release behavior in the beginning for the two control groups mentioned above,which were 41%and 43%of the cumulative release rate after 7days,respectively.In conclusion,the uniform spherical calcium alginate microspheres encapsulated with in situ-formed gold nanostars have been prepared by onestepusing adroplet-based microfluidic device.The obtained microspheres integated multifunction including photothermal therapy,controlled chemotherapy and embolization,which wouldbe expected to improve the antitumor effect.In addition,the calcium alginate microspheresencapsulated with drug-loadednanogelshad a sustainable drug releaseprofile.