Preparation Of Polyelectrolyte Nanogels Based On Electrostatic Assembly Directed Polymerization And Their Applications

Polyelectrolyte nanogel,nanosized hydrogel particle with crosslinked charged polymer networks,integrates the advanced features of nanogel and polyelectrolyte.These features make polyelectrolyte nanogels as soft template and nano-carrier for loading and transporting functional bio-molecules(such as enzymes,DNA,RNA,peptides,ect.)without disturbing these molecules'(secondary)structure and biological function,which is widely used in drug delivery,tissue engineering,biosensing,and catalysis field.However,preparing polyelectrolyte nanogel in high efficiency and large scale is still very difficult.In this thesis,a generic strategy for fabricating polyelectrolyte nanogel has been developed.The method is based on polymerizing an ionic monomer in the presence of an oppositely charged polyion-neutral diblock copolymer,while adding a cross-linker.This robust and generic approach for synthesis of functional nanogel may therefore be expected to hold great potential for many different applications in a variety of fields.The main contents of this thesis are provided as follows:1.The new strategy,Electrostatic Assembly Directed Polymerization(EADP),for preparing PDMAEMA nanogel in the presence of oppositely charged polyion-neutral diblock copolymer PAA-b-PEO and crosslinker MBA was investigated.The effects of pH,salt concentration,cross-linker fractions,as well as monomer concentration on the synthesis of PDMAEMA nanogel were fully studied.The results indicate that sufficient charge interaction between the charged building blocks is beneficial for nanogel preparation,which can obtain uniformly spherical structure,as well as get enhanced nanogel yield.PDMAEMA nanogel can be prepared at high monomer concentration(10wt%)with EADP method,which paves the way for preparing polyelectrolyte nanogel in large-scale.The free template polymers could be recycled and reused for continuous synthesis.These results optimize the reaction condition for preparing a large diversity of polyelectrolyte nanogel.2.The versatility in preparing polyelectrolyte nanogel using EADP method was investigated.The electrical and responsive property of polyelectrolyte nanogel were tuned by altering monomer type.The functionality and swelling property of polyelectrolyte nanogels were regulated by changing the crosslinker type and fractions.By changing salt concentration,the size of polyelectrolyte nanogel can be controlled.These results indicate that Electrostatic Assembly Directed Polymerization is generic for preparing poly electrolyte nanogel and the structure and properties of poly electrolyte nanogel can be tuned and controlled.3.The charge-driven loading function of poly electrolyte nanogel was studied.First,the loading and releasing property for different charged dyes were investigated using PDMAEMA nanogel as carrier.It is found that only anionic dye can be adsorbed in the positively charged PDMAEMA nanogel through charge interaction.The obtained PDMAEMA nanogel exhibits dual-responses to pH and salt,which allow to manipulate the positive charges of the nanogels for selective loading and controlled release of anionic dye.Then the AuCl4-ions can be embedded in the positively charged PDMAEMA nanogel,followed with in-situ reduction by NaBH4.The results show that Au nanoparticles can be loaded in the PDMAEMA nanogel without disturbing their size and size distribution,which can be used as catalyst for the reduction of p-nitrophenol to p-aminophenol by NaBH4.These results indicate that polyelectrolyte nanogel possesses charge characteristics which can be used as carrier for loading charged substances.4.The enzyme immobilization and enzymatic catalysis was studied using poly electrolyte nanogel as nano-carrier.It is found that lipase incorporation was driven by charge interaction,which can be influenced by salt concentration and pH.The enzymatic activity of lipase loaded in polyelectrolyte nanogel displays a more than twice higher activity in the hydrolysis of 4-nitrophenyl butyrate as compared to the free enzyme.These results indicate that poly electrolyte nanogel can be used as carrier with good biocompatibility for loading biomolecule.