Novel Core-shell Nanogels Prepared By Self-assembly Of Globular Proteins And Dextran And Its Applications As Drug Carriers

With the development of science and technology,the knowledge on different subjects is intercrossing and integrating.Nanomedicine that emerges from nanotechnology and medicine shows great potential in diagnosis and therapy. Multifunctional nanocarriers are a particularly hot topic in nanomedicine.The concept of self-assembly in life science was introduced into chemistry,and molecular based self-assembly offers one of the most general strategies for fabricating nanostructure materials.Self-assembled core-shell nanoparticles of amphiphilic polymers with PEG segment show its unique "stealth" properties when they are used as drug carriers.The polymeric nanoparticles based on synthetic polymers have been widely studied; however,they are limited by their high cost,non-green process and health safety.On the other hand,biopolymers such as proteins and polysaccharides with good biocompatibility and biodegradability are extensively used in pharmaceutics fields, because of its natural source and binding abilities with drugs.However,up to now, there are few reports of self-assembled core-shell nanoparticles based on proteins and polysaccharides as well as their biomedical application.Maillard reaction and protein gelation were introduced into our work to prepare nanogels from globular proteins and polysaccharides(dextran).Upon heating globular proteins tend to be denatured and form aggregates,but dextran that conjugated into the protein prevents the macroscopic aggregates leading to nanogels formation.The shell of the nanogels is composed of dextran and their core is protein gels.The nanogels display good stabilities in physiological conditions.The preparation process is carried out in aqueous solution,avoiding of organic solvent,surfactants and other toxic agents.In addition,non-covalent interactions between proteins and drugs were also introduced into our work to obtain high drug loading capacity and sustained release.This thesis contains the following four parts:Firstly,lysozyme and dextran,two natural biopolymers,were used to prepare lysozyme-dextran nanogels.A novel method has been developed for preparing nanogels with globular protein core and dextran shell.The method involves Maillard dry-heat process and heat-gelation process.The effects of different factors on the formation of nanogels were studied,and monodispersed nanogels with 200 nm diameter were obtained under optimum conditions.The nanogels have a spherical shape having a lysozyme core and dextran shell structure and swelling ratio of about 30.The nanogel solutions are very stable against long term storage at 4℃,even with pH and ionic strength changes.Besides,the nanogels can be stored as lyophilized powder.As a drug model,ibuprofen can be loaded into the nanogels by virtue of their electrostatic and hydrophobic interactions.The largest loading amount(8.8%) and the best efficiency(43%) of ibuprofen loading were achieved in its protonated form.The knowledge gained from these studies on the mechanism of formation of lysozyme-dextran nanogels is significant and the strategies developed thereby can be effectively applied to prepare other globular protein-dextran nanogels.Secondly,bovine serum albumin(BSA) and dextran were used to fabricate BSA-dextran nanogels.In general,dextran was first covalent conjugated to albumin by Maillard reaction,and then the conjugate solution was heated to produce BSA-dextran nanogels.Effects of variable parameters of formulation and process on nanogel formation were studied,and monodispersed nanogels with 200 nm diameter were obtained under optimum conditions.TEM and t-potential confirmed a core-shell structure and a spherical shape.The nanogel can be stored for months at 4℃and re-dispersible after lyophilization.In addition,the nanogels are stable in a broad pH range,while unmodified BSA nanoparticles flocculate around the isoelectric point of BSA.A pyrene probe fluorescence measurement shows a relative hydrophobic environment in the nanogels.As a drug model,doxorubicin can be loaded into the nanogels by virtue of their electrostatic and hydrophobic interactions.The largest loading amount(30%) and the best efficiency(75%) of doxorubicin loading were achieved at neutral pH.Thirdly,ibuprofen,bovine serum albumin(BSA) and dextran were used to fabricate ibuprofen-BSA-dextran nanogels.BSA-dextran conjugates were first synthesized,then ibuprofen and the conjugates were mixed together to produce ibuprofen-BSA-dextran nanocomplexes,finally the nanocomplexes were heated to obtain ibuprofen-BSA-dextran nanogels.Effects of variable parameters of formulation and process on ibuprofen-BSA-dextran nanogel formation were studied, and monodispersed nanogels with 60 - 70 nm diameter were obtained under optimum conditions.Besides,the nanogels can be stored as lyophilized powder.The nanogels have a spherical shape having a BSA and ibuprofen core and dextran shell structure. The technique used can produce a high loading capacity for ibuprofen,the largest loading amount and efficiency of ibuprofen in the nanogels is above 50%and 90%, respectively.In vitro release study showed a sustained release of ibuprofen from the nanogels in a low ionic strength solution,and a rapid release of ibuprofen from the nanogels in a high ionic strength solution.Finally,doxorubicin,bovine serum albumin(BSA) and dextran were used to fabricate doxorubicin-BSA-dextran nanogels.BSA-dextran conjugates were first synthesized,then doxorubicin and the conjugates were mixed to produce doxorubicin-BSA-dextran soluble complexes,finally the complexes were further heated to obtain doxorubicin-BSA-dextran nanogels.Effects of variable parameters of formulation and process on doxorubicin-BSA-dextran nanogel formation were studied, and monodispersed nanogels with 120 nm diameter were obtained under optimum conditions.The nanogels have a spherical shape having a BSA and doxorubicin core and dextran shell structure.The technique used can produce a high loading capacity for doxorubicin,the largest loading amount and efficiency of doxorubicin in the nanogels is 45%and 95%,respectively.In vitro release study shows a sustained release of doxorubicin from the nanogels,and a relatively rapider release of doxorubicin at pH 5.0 than that of at pH 7.4.