Synthesis And Properties Of Peptide/Nano Calcium Phosphate Composite Hydrogel

In the field of tissue engineering,materials with biocompatibility and sufficient mechanical strength to mimic bone tissue are always the research focuses.These biomimetic materials are usually organic/inorganic composite materials.The organic components are biocompatible hydrogels,which simulate extracellular matrix and provide three-dimensional growth environment for the cell growth,migration and differentiation.Whilst the inorganic components are usually calcium phosphate?CaP?particles,which not only enhance the mechanical strength of the hydrogel,but also provide the hydrogels with osteogenic induction ability.The hydrogel materials formed through peptide self-assembly can mimic the structure and biocompatibility of extracellular matrix.Therefore,they have broad application prospects in the field of regenerative medicine and tissue engineering.In this thesis,peptide self-assembled nanofibers were used to form the hydrogel skeleton,and CaP particles were in situ synthesized on the surface of peptide nanofibers to form peptide-CaP hybrid hydrogels.The composite materials were used as scaffolds for mouse osteoblasts?MC-3T3?cell culturing and its performance in cell division and differentiation has been investigated.The research works of the thesis mainly include the preparation of ionic complementary peptides EIK11 and EVK11 as well as two surfactant-like peptides,Ac-I₄D₂-NH₂ and Ac-I₄E₂-NH₂ which are rich in aspartic acid?D?and glutamate?E?.The effects of the pH,salt ions introduced in the synthesis of composite materials and the situ precipitation of CaP in hydrogels on the secondary structure,assembly morphology and gel strength of the peptide assembly,and cell-culture performance of the hybrid hydrogels.The results shows that pH has great influence on the ability of the assembly and gelling properties of ion complementary peptides EIK11 and EVK11,as well as the two surfactant-like peptides,Ac-I₄D₂-NH₂and Ac-I₄E₂-NH₂.Under lower pH value,the gel was difficult to form because of the less deprotonation,stronger hydrophobicity and poor solubility.The charge number of peptides increased,and thus their hydrophilic properties increaseed.They could be solubilized easily and self-assemble into better gelatin materials.Whereas,if the pH was too high,it would make the above four peptide molecules highly hydrophilic,weaken the influence of hydrophobic interaction and hydrogen bonding during self-assembly process.The Na⁺,Cl^-and HPO₄^2-of 8 mM have no obvious influence on the secondary structures and morphology of the assemblies of the above four peptides.However,Ca²⁺and CaP have a strong cross-linking effects.Theh increased the degree of cross-linking between the assemblies and promoted the growth of the assemblies in width.The reasons for the cross-linking effects may originate from two points:?1?the electrostatic interaction of the negatively charged peptide assemblies and positively charged Ca²⁺,?2?the selective cross-linking of Ca²⁺on carboxyl groups on aspartic acid?D?and glutamic acid?E?.The peptides-CaP hybrid hydrogel materials were used as culture scaffolds for the mouse osteoblast?MC-3T3?cells.The results showed that the hybrid hydrogels had good biocompatibility.Compared with the growth and splitting rate of cells in the TCPS wells,the I₄D₂-CaP and I₄E₂-CaP composite hydrogel materials had a certain promoting effect on the growth of MC-3T3 cells.The survival rate of the cells on the composite hydrogel of EIK11-CaP and EVK11-CaP was about 70%.