Study On Assembly Behavior Of Human Like Collagen

Human like collagen(HLC)is a class of recombinant collagen.It is produced by genetic engineering technology based on the amino acid sequence of the human body with some unique advantages in structure and function.Theoretically,the collagen with higher and more complex structure would have better properties.In this thesis,the active sites of HLC were designed at molecular level.It would lead to that intermolecular recognition and assembly were enhanced or changed.Research was conducted on self-assembly behavior and intermolecular forces of different assembly ways.Furthermore,a series of multi-scale molecular assembly functional systems were constructed.It lays a theoretical and practical foundation for the application of HLC and its aggregates in biological medical application.The main research contents includes:(1)Study on HLC self-assembly.The results showed that HLC had the secondary structure of typical collagen.The HLC chain contained many hydrophobic and hydrophilic amino acids with the ability to assemble.The turbidimetry was used to find the optimum self-assembly conditions:37?,pH 7.0,0.3 mg/mL,and 600 min.It proved that HLC had a coating ability for hydrophobic substances.The morphology showed HLC self-assembled into microspheres at low pH and self-assembled into microtubules at high pH.It had a pH sensibility.Kinetic study was proved that the self-assembly process conformed to the "nucleation-growth" mechanism.Thermodynamic proved that HLC self-assembly was a typical thermally promoted aggregation,which was spontaneous and irreversible.(2)Study on self-assembly of hydrophilic and hydrophobic modified HLC.Hydrophilic monomer Glycidol(GCD)and hydrophobic monomer Y-glycidyl ether oxy-propyl trimethoxy silane(GLH)were used to modify hydrophilic and hydrophobic of HLC,respectively.The measurement results of FT-IR,epoxy acetone method,dynamic contact angle(DCA)and static contact angle(SCA)showed that hydrophilic GCD/HLC and hydrophobic GLH/HLC were prepared successfully.When the molar ratio of the epoxy groups of GCD and GLH to the amino group of HLC was 1:1,the time was 12 h,the reaction pH was 10.0 and the amino conversion rate reaches the maximum.The GCD/HLC and GLH/HLC molar ratios of hydrophilic and hydrophobic functional groups were 0.51:1 and 0.76:1,respectively.And HLC's was 0.63:1.The turbidimetry was found that both met the "nucleation-growth" mechanism and the assembly rate of HLC>GCD/HLC>GLH/HLC.Observations revealed that GCD/HLC was mainly a band-like structure,and GLH/HLC was an unsealed microsphere structure.The GLH/HLC showed better resistance to water degradation.(3)Study on co-assembly of HLC and L2P4.HLC was combined with anticancer small molecule drug L2P4.Energy dispersive X-ray spectrum(EDS)and fluorescence analysis showed that L2P4 was coated inside the HLC hydrophobic cavity successfully,and the coating amount was about 65%.The turbidity was found that the co-assembly process satisfied the"nucleation-growth" mechanism.The self-assembly rate were about 1 order of magnitude higher than HLC.AFM observation was found that the morphology of L2P4@HLC did not change significantly after storage at 4? for 30 d,and it was stable.The drug release behavior research showed that it was favorable for release at pH 5.5(the microenvironment)and was good for encapsulation at pH 7.4(normal physiological environment).It showed that L2P4@HLC can be used as intelligent probe drug delivery system.(4)Study on "surface modification-assembly" of HLC and oxidized hyaluronic acid(oxi-HA).Firstly,the hyaluronic acid(HA)film was oxidized and opened on the surface.Then the reaction between the aldehyde group of oxi-HA film and the amino group of HLC was performed.Finally,HLC molecules assembled on the surface.The FT-IR,SEM,AFM,et al.of structure and morphology analysis showed that the film had a fibrous network crosslinked structure;and the surface of the HLC/oxi-HA film was dense and smooth.The performance results showed the HLC/oxi-HA film was pale yellow,pH was 5.38,ash content was 0.778%,and weight loss on drying was 20.7%,with a tensile strength of 30 MPa,good hydrophilicity,thermal stability and biocompatibility.