Preparation And Characterization Of Injectable Zwitterionic Thermosensitive Nanogels

Injectable hydrogels can be used in targeting drug release,embolization therapy and tissue scaffolds,which are flowable and loaded with drugs easily in vitro while fill the defect of the damaged tissue and become into hydrogel in situ after injected into the body.However,the reported injectable hydrogels usually tended to form protein crown on the surface due to the foreign-body reaction and protein absorption.Especially,a dense collagenous capsule would also form which might block the mass or/and signal transport between the implant and the body.As a result,the applications of the injectable hydrogels in the biomedicine were limited.In this paper,based on the excellent anti-protein absorption and anti-fouling properties of zwitterionic polymers,zwitterionic thermosensitive nanogels have been prepared and the obtained injectable hydrogel have the potential to resist the forgein-body reaction and protein absorption on the surface of the hydrogels,resulting in a better therapeutic effect.Here,a series of zwitterionic thermosensitive poly(N-isopropylacrylamide-comethacryloxyethylsulfobetaine)(poly(NIPAM-co-SBMA))nanogels with various monomer ratios were prepared by the precipitation polymerization.The morphology and size of the nanogels were determined by transmission electron microscopy(TEM)and dynamic light scattering(DLS)instrument.The chemical structure of the nanogels were characterized by FT-IR and 1H NMR.The thermosensitive property and the volume transition temperature(VPTT)of the nanogels were characterized by measuring the changes of the particle size and transmittance with the temperature by DLS and UV-Vis spectrophotometer,respectively.And the sol-gel phase transition behaviors of the dispersions of various nanogels at higher concentration were studied by visual method and dynamic rheology.According to these results,the preferred recipe of nanogels and concentration were confirmed.The protein concentration adsorbed on nanogels particles and on the responding forming hydrogel of the nanogels dispersion were quantified using BCA protein assay kit at 37 ℃,comparing with that of the non-ionic poly(NIPAM-co-AM)(AM,acrylamide)nanogels.The in vitro drug release behaviors of the in situ-formed hydrogels of nanogels dispersions were studied by using doxorubicin hydrochloride(DOX·HCl)and 5-fluorouracil as model drugs,respectively.Then,nanogels dispersions with high nanogels concentration loaded with DOX·HCl were injected into the tumor,which was formed based on H22 hepatoma cells.The anti-tumor effects of the in situ-formed drug-loaded hydrogels were studied by recording the weight of mouse,the size of tumors at intervals and observing tumor sections by the Tunel staining method.The hydrogel states of the above two kinds of nanogel dispersions after subcutaneous injection into mouse were also studied.The results showed that the prepared poly(NIPAM-co-SBMA)nanogels were mono-dispersed with an average hydration diameter of about 100 nm and their VP TT could be regulated by the composition of the comonomer.The dispersion of poly(NIPAM-co-SBMA)nanogel(n NIPAM: n SBMA = 87.5: 12.5)at a concentration of 20% could undergo a sol-gel transition at 37 ℃.Compared with poly(NIPAM-co-AM)nanogels,poly(NIPAM-co-SBMA)nanogel particles and the formed bulk hydrogel of the nanogels dispersion at high concentration had a relative lower protein adsorption amount,along with a faster drug release behavior and a more completely release.Animal experiments results showed that free DOX·HCl and DOX·HCl released from the hydrogel in situ-formed by poly(NIPAM-co-AM)nanogel dispersion were aggregated obviously in tumor tissue,whereas that of poly(NIPAM-co-SBMA)nanogel dispersion was more evenly distributed in tumor tissue and resulting in a better anti-tumor effect.The color of the hydrogel formed by poly(NIPAM-co-SBMA)nanogel dispersion was lighter than that of poly(NIPAM-co-AM)nanogel dispersion in the body.Especially,a dense layer was formed on the later surface,which would prevent the release of drugs from the in situ-formed hydrogel.It might be attributed to the anti-protein adsorption property of poly(SBMA)fragments.In summary,the dispersion of the prepared zwitterionic thermosensitive poly(NIPAMco-SBMA)nanogels at high concentration had good thermosensitive sol-gel phase transition behavior and anti-protein adsorption property.When used as an implanted material,it was expected to having anti-fouling property and controlling release of the loaded drugs and therefore improving the therapeutic effect.