Chemically Modified Graphene For Surface Modification Of Three-Dimensional Porous Chitosan Scaffolds

Tissue engineering and regeneration is one of the most important fields of scientific research which must be based on the fundamental principles and approaches from life science,engineering,chemical to material science in efforts to improve biological replacements with high potential to reinstate or cure tissue/organ functions.Among three factors in the development of tissue engineering,scaffold materials have been paid more attentions and investigated for years by scientific researchers.In the past few decades,numerous classes of biomaterials have been found,created and explored for potential applications in the field of tissue engineering.As a natural biopolymer,chitosan(CS)is a high-molecular-weight linear cationic polysaccharide derived from the extensive deacetylation of chitin.Chitosan not only has a wide range of raw materials,but also has many special properties.Therefore,chitosan is considered as an appropriate functional material for biomedical applications.Firstly,chitosan can be formed interconnected-porous structure by freezing and lyophilizing of chitosan solution,which has beneficial effects on tissue regeneration.Secondly,its chemical structure allows for pH-dependent electrostatic interactions which are good for cell proliferation.Moreover,chitosan has excellent biodegradability depending on deacetylated degree,high biocompatibility,low antigenicity of human immunity,considerable antibacterial activity against a broad spectrum of bacteria.Even if chitosan and its derivatives had been researched and developed as biomedical materials in tissue engineering,the poor mechanical properties and stability of three dimensional porous chitosan make it difficult to take on high load bearing structure,which limits its applications in the field of cartilage and bone integration.21 Century has been called "carbon century".As a highlight members of carbon material family,graphene-based materials have burst onto the world stage,and are heralded as a star performer in materials science.Due to its unique physicochemical and biological properties,graphene not only has been widely researched and applied in fields of energy,electronic and composite materials,but more and more researchers pay attention to its application of tissue engineering scaffolds in biomedical fields.As coatings for two-dimensional substrates,graphene and its derivatives exhibit good biocompatibility,supporting adhesion,proliferation,and differentiation of mammalian cells.However,the study of graphene as modified coating of three-dimensional structure has just started.Compare to the two-dimensional structure,three-dimensional porous network is a more ideal circumstance for cell growth.Graphene has the characteristics of easily interacting with other materials by covalent or non-covalent interaction,thus forming composite materials with novel structures,morphology and properties,and achieving the function of regulating a variety of biological processes.For this reason,we assumed to coat chemically modified graphene on the hole-wall of porous chitosan.The structure of this thesis is arranged as follows:The main contents of the second chapter of this thesis is to prepare graphene modified chitosan scaffolds through impregnation method and heat treatment,and the physical and chemical properties of these materials are characterized.The experimental results showed that graphene has successfully coated on the wall of substrates,without changing the chitosan matrix composition mechanism,and substantially increase the mechanical properties of substrate,alter the surface morphology of the pore-wall.On the basis of the second chapter,we selected scaffold materials to evaluate their biocompatibility and biodegradability.The experimental results suggest that all scaffolds have good biocompatibility.Graphene coatings can induce cell growth and the growth of cell is related to the GO concentration and annealing temperature of graphene coatings.In physiological saline,all the scaffolds can maintain a stable state for a long time,and the modified chitosan scaffolds are more stable.The molecular weight of chitosan can affect its biological properties,so,the fourth chapter of this thesis has preliminarily studied the effect of molecular weight and concentration of chitosan solution on physicochemical properties of 3D scaffolds.The results indicated that increasing of molecular weight and concentration of chitosan solution and stirring leads to the decreased order of chitosan molecules and crystallinity.In the same molecular weight,porosity and water absorptions of scaffolds decreased with the increased concentration of chitosan solution.In brief,based on the unique structure,morphology,physical chemistry and biological properties of grapheme-based materials,three-dimensional porous chitosan scaffolds with surface modified film were prepared by the low-temperature thermal reduction technique.Research findings show that the chemically modified graphene film can effectively improve the compressive strength of chitosan scaffolds.Compared with the scaffold,the cultured cells have higher activity.