Synthesis,Gelation And Biomedical Application Of Multifunctional Poly(Ethylene Glycol)Derivatives

Poly(ethylene glycol)(PEG)has been widely used in biomedical applications due to its excellent water-solubility and biocompatibility.Linear PEG is usually synthesized by the anionic ring-opening polymerization(AROP)of ethylene oxide.Unfortunately,the modification and multifunctionalization of PEG are limited by the only two terminal hydroxyl groups.The copolymerization of ethylene oxide with other functional epoxides has been used to overcome these limits,whichis a main strategy for the synthesis of multifunctional PEG derivatives in the last years.However,the applications of these multifunctional PEG derivatives are still limited due to the critical conditions of AROP,inadequate resources of functional epoxides,undegradability of the products.In this thesis,we developed a new strategy to synthesize multifunctional PEG derivatives with degradability by "one-pot" polycondensation of oligo(ethylene glycol)(OEG)with functional diacids directly.Gelations of these PEG derivatives under physiological conditions and their biomedical applications were further investigated.OEG diols were used as a macromonomers to copolymerize with mercaptosuccinic acid(MSA)or maleic anhydride(MAH)directly using scandium trifluoromethanesulfonate[Sc(OTf)3]as a highly efficient and chemoselective catalyst under mild temperature and vacuum,resulting in poly[oligo(ethylene glycol)mercaptosuccinate](POEGMS)and poly[oligo(ethylene glycol)maleate](POEGM),which are degradable PEG derivatives with multiple reactive thiols or maleates.Sc(OTf)3 has been reported to be efficient catalyst for ROP of lactones.Such PEG derivatives with two terminal hydroxyl groups were first synthesized by adjusting the feed molar ratio of OEG to functional diacid,which can initiate the ROP of sequentially added?-caprolactone(CL).Amphiphilic triblock PEG derivatives,poly(?-caprolactone)-b-poly[oligo(ethylene glycol)maleate]-b-poly(?-caprolactone)[PCL-b-P(OEGM)-b-PCL]and poly(?-caprolactone)-b-poly[oligo(ethylene glycol)mercaptosuccinate]-b-poly(?-caprolactone)[PCL-b-POEGMS-b-PCL],were thus synthesize faciley by this "one-pot,two-steps" method without any protection and deprotection procedures.Recently,thiol-ene "click" reaction has played an important role in the preparation of biomedical materials due to the fact that it can proceed efficiently under physiological conditions.In this study,the gelation of POEGMS and POEGM under physiological conditions was investigated in details.Hydrogels were formed within tens to hundreds of seconds depending on the solid contents of the hydrogels.In vitro cell viability tests demonstrated their good biocompatibility.These in situ formed PEG hydrogel can be used as a physical barrier to lower the extent and the severity of postoperative adhesions.The abrasion of cecum and abdominal wall were made with a surgical blade in rat model,a blend of POEGMS and POEGM PBS solutions were distributed on the abrasion areas to form a hydrogel barrier rapidly.The adhesion was obviously lower in the test group compared with the control group.Histological examination revealed that these PEG-based injectable hydrogels remarkably reduced inflammation and improved healing of the serosa.Hydrogels can be used as local drug delivery carrier due to the high drug concentration,sustained drug release and low side effects.Injectable hydrogels containing doxorubicin hydrochloride(DOX-HCI),a water-soluble anticancer drug,were rapidly formed by using POEGMS and POEGM as precursors via in situ thiol-ene "click" reaction under physiological conditions.The moduli of hydrogels were up to 69 KPa tested by a rheometer.The degradation time of hydrogels had great dependence on solid content,which is up to 25 days.DOX-HCl could be sustained released from the hydrogels,which is obviously influenced by the pH value of the release medium.and faster release rate was observed in the pH=6.8 medium than that of pH=7.4 medium.In vitro antitumor efficiency tests demonstrated that the hydrogels loaded with DOX·HCl could efficiently kill HeLa cells.Water soluble drugs could be easily loaded into hydrogel network homogeneously.However,hydrophobic drugs can't be well dispersed in hydrogels because of the hydrophilic framework of PEG hydrogels.In order to imporve the loading homogeneity of hydrophobic drugs in PEG hydrogels,amphiphilic triblock PEG derivatives,PCL-b-POEGM-b-PCL,were synthesized to solubilize ibuprofen,which was used as a hydrophobic model drug PBS solution of PCL-b-POEGM-b-PCL with dispersed ibuprofen was mixed with the PBS solution of POEGMS,and a ibuprofen loaded hydrogel was in situ formed rapidlythrough thiol-ene "click" reaction under physiological conditions.Differential scanning calorimeter(DSC)and X-ray diffraction(XRD)analyses of the lyophilized ibuprofen loaded hydrogels confirmed that ibuprofen had been loaded homogeneously into hydrogels in a molecular scale.The storage modulus of hydrogels is up to 51 kPa tested by a rheometer.The sustained release time of ibuprofen from hydrogels is more than 60 hours in vitro.The resultant hydrogels without ibuprofen,as well as their precursors,showed low cytotoxicity to HeLa cells,indicating they could be a kind of biocompatible carrier for localized drug delivery.Camptothecin(CPT)has shown significant antitumor activity in a broad spectrum of human malignancies.However,it cannot be dispersed homogeneously in the above mentioned PEG hydrogels due to its high hydrophobicity.Herein,POEGM with two terminal hydroxyl groups was first synthesized by the polycondensation of OEG with MA by adjusting the molar ratio of the monomers.Then CPT was conjugated to the chain end of POEGM via carbonate ester bond via a phosgene strategy.The resultant water-soluble CPT-POEGM conjugate could be in-situ crosslinked by POEGMS rapidly through thiol-ene "click" reaction under physiological conditions,which can be used as injectable CPT-hydrogels.Bright blue fluorescence emitted from CPT-hydrogels under UV lamp excited at 365 nm demonstrated the homogeneity of CPT loading.The CPT release by the breakage of carbonate ester bond and the degradation of hydrogels by the breakage of ester bonds were observed simultaneously within one week to 36 days,depending on the solid content of hydrogels and pH value.The CPT-hydrogels exhibited significant cytotoxicity to HepG2 cells based on in vitro cell viability assays.This kind of CPT-hydrogels could be a potential candidate for intratumoral anticancer drug delivery.Thiol-epoxy "click" reaction was investigated for the first time to prepare injectable hydrogels.Radical copolymerization of N,N-dimethylacrylamide(DMA)and glycidyl methacrylate(GMA)was carried out to synthesize water-soluble P(DMA-co-GMA)with multiple epoxy groups,which was used to prepare injectable hydrogels with POEGMS through thiol-epoxy "click" reaction under physiological conditions.The mechanical properties of these thiol-epoxy "click" hydrogels were investigated by a rheometer,which can be precisely tuned by the precursor concentration.In vitro cell viability assays demonstrate that this kind of thiol-epoxy "click" hydrogels has good biocompatibility and could be regarded as a promising candidate for biomedical applications.The chain state of PEG segments in hydrogels is extended due to their high hydrophilicity,which leads to the fact that the external force on the PEG hydrogels cannot be dispersed without macromolecular conformation changes,resulting in brittle PEG hydrogels.In order to improve the ductilty of PEG hydrogels,PEG20-PPG70-PEG20(P123),an amphiphilic triblock copolymer with a hydrophobic PPG segment,was incorporated into PEG network by thiol-ene "click"reaction.Because of the collapsed PPG segments in the framework of hydrogels,the external force on the hydrogels could be well dispersed via the sliding of PPG segments,to give a ductile hydrogel with a strain up to 400%and a maximum stress of 250 KPa.Cyclic tensile tests demonstrated that these hydrogels showed reversible behaviors under repeated stretch.