Synthesis And Biological Effects Of Cylindrical Polymer Brushes

Over the past two decades,there has been a consensus that the size of nano materials(NMs)plays a key role in determining their cellular internalization,biodistribution,tumor accumulation and penetration,blood and tissue clearance in vivo.At present,the size effect studies of nano drug carriers are mainly focused on spherical systems.Because it is very difficult to synthesize the nanomaterials with different shapes according to requirements,there are relatively few studies on the in vitro and in vivo behaviors of anisotropic nanomaterials.Cylindrical polymer molecular brushes(CPBs)have typical one-dimensional worm-like nanostructures,adjustable flexibility,precisely controlled length and diameter,ideal chemical stability and high functionality.To obtain the optimum performance of CPBs,it is important for us to clearly understand the effects of their physicochemical properties such as length,backbone and side chain structure on their biological properties both in vitro and in vivo.In this paper,CPBs with different lengths and shapes were designed and synthesized.The biological differences of the polymer brushes caused by different sizes and shapes were systematically studied,and the transfection efficiency using CPBs as gene delivery vehicles was preliminarily explored.The details are as follows:1.Polyglycidyl methacrylate(PGMA)with different polymerization degrees was prepared by reversible addition-fragmentation chain transfer(RAFT)method,and azide-modified polyglycidyl methacrylate was subsequently synthesized through the reaction of epoxy side groups in the polymer and sodium azide.After the conjugation of PEG chains to the azide-modified polyglycidyl methacrylate by Cu(I)-catalyzed alkyne-azide 1,3-dipolar cycloaddition(CuAAC)reaction,cylindrical polymer brushes(CPBs)were obtained.By tuning the molecular weight of the backbones,we synthesized three sets of CPBs with different lengths of about 34 nm(CPBs 1),61 nm(CPBs 2),and 117(CPBs 3)nm,respectively.Atomic force microscope(AFM)studies showed that the CPBs had a uniform worm-like structure,which encouraged us to study the length effects on their biological properties.In addition,by using precise testing techniques such as laser confocal,flow cytometry,and positron emission tomography,we found that compared to the longer CPBs,the shorter counterparts had lower cell uptake,higher tissue permeability,longer blood circulation time and higher tumor enrichment.2.By taking advantages of atom transfer free radical polymerization(ATRP)and CuAAC,we synthesized unimolecular spherical polymer nanoparticles(SPNPs)and CPBs with the same volume and surface chemistry.Both the two materials had the high water solubility and desirable biocompatibility.Further,we used laser confocal,flow cytometry,and positron emission tomography to study the biological properties of the two types of unimolecular polymer nano materials.The results showed that the worm-like polymer brushes had higher cell uptake,higher tissue permeability and faster body clearance than the spherical counterparts,and it was also easier to be enrolled by the phagocytes.In addition,we also found that the SPNPs had longer blood circulation time and rapider tumor vascular extravasation than the CPBs.3.Using RAFT(synthesis method of the main chain),ATRP(synthesis method of the side chain)and CuAAC(conjugation method of the side chain to the main chain),we synthesized two worm-like cationic CPBs with different potentials.Using DNA gel electrophoresis,fluorescence imaging and flow cytometry,we explored and analyzed their DNA complexing ability and gene transfection efficiency.The results showed that the cationic polymer brush PB-1 with higher potential had stronger gene complexing ability and higher gene transfection efficiency than the PB-2 with lower potential.The transfection efficiency of PB-1 was also significantly higher than that of commercial PEI transfection reagents and the PB-1 also showed lower cytotoxicity.This suggests that PB-1 has higher application potentials as a gene delivery vehicle.4.Four-arm polyglycidyl methacrylate was synthesized by using an ATRP initiator with four initiating sites,and then the star-shaped polymer brush with four arms was synthesized by using CuAAC grafting method.The chemical structure and morphology was characterized by nuclear magnetic resonance,gel permeation chromatography and atomic force microscopy,and the cell uptake behavior was studied.