Research On Biomimetic Collagen And RGD Peptide Bioactive Coatings On Carbon/Carbon Composites

Carbon/carbon composite(C/C)is a kind of biomaterials with good biocompatibility in orthopedic medicine.Its surface is hydrophobic and belongs to biological inert materials.In order to make C/C composites bioactive as well as reduce carbon debris production,bioactive coatings should be prepared on its surface.In order to improve surface biological activity of C/C composite,soft and hard bioactive coatings with different implant area and application were prepared on C/C composite.For the soft coating preparation,a collagen(COL)coating with good bonding strength was prepared on C/C composite firstly,then a collagen/nano-hydroxyapatite(COL/nHA)scaffold coating with three-dimensional biomimetic structure was prepared.For the hard coating preparation,a graphite-like carbon(GLC)film was prepared on C/C composite,and then Arg-Gly-Asp(RGD)peptides were crosslinked.The main research contents and conclusions are listed as follows:Mixed acid oxidation and hydrogen peroxide oxidation methods were used to modify the surface of C/C composites.The results showed that the surface wettability of C/C composites was greatly improved by the mixed acid oxidation modification.Surface contact angle of C/C composites was decreased to 26.3±4.5° and a large number of oxygen-containing functional groups were formed.However,pyrolytic carbon matrix exfoliation and S element residues were detected after the mixed acid oxidation modification.Further applications of this method are limited.Hydrogen peroxide oxidation methods also improved the surface wettability of C/C composites,and its surface contact angle was decreased to 65.3±8.4°.Although the surface wettability improvement of C/C composites using hydrogen peroxide oxidation method was less than that of the mixed acid oxidation method,oxygen-containing functional groups,such as hydroxyl(C-OH),carboxyl(COOH)and carbonyl(C=O),were formed on the surface of C/C composites.Hydrogen peroxide oxidation could be a mild oxidation and did not damage C/C composites.In addition,cell adhesion and proliferation of mouse osteoblasts(MC3T3-E1)on the hydrogen peroxide modified C/C(H-C/C)composites were enhanced when compared with C/C composites.Cell morphologies of MC3T3-E1 osteoblasts on C/C and H-C/C matrix of were carefully compared and analyzed.It was found that residual air in the surface pores of C/C compositescould inhibit the cell adhesion of MC3T3-E1 osteoblasts.MC3T3-E1 osteoblasts could growth into the large surface pores of H-C/C substrates caused by the surface wettability improvement.Air-dried method was used to prepare soft COL transition coatings with different initial pH values on the surface of H-C/C substrates.Carbodiimide(EDC)crosslinking and dehydrothermal treatment(DHT)were used to improve the bonding strength between COL coating and H-C/C substrate.The results showed that all COL coatings with different initial pH value had strong bonding strength with H-C/C substrates.MC3T3-E1 osteoblasts had excellent cell adhesions and proliferations on all COL coatings.DHT treatment could improve the bonding strength between all COL coatings with different initial pH values and H-C/C substrates.However,EDC crosslinking made none positive effect between COL coating and H-C/C substrate.The bonding strength between COL coating and H-C/C substrate can reach to 8 MPa when the initial pH value of COL coating was 2.5.After a DHT treatment,crosslinking temperature at 105°C for 2 days,the bonding strength between COL coating and H-C/C substrate could have a 50% increasing,over 12 MPa.Freeze-drying method was used to prepare a COL/nHA scaffold coating with three-dimensional biomimetic structure on the surface of COL transition coating.MC3T3-E1 osteoblasts were cultured in the scaffold coatings to detect their bioactivity and mineralization induction ability.Compression strength of the scaffold coating could reach to 52.2 KPa at50% strain,when the mass ratio of collagen and nano-hydroxyapatite was 1:3.During a 3weeks culture,MC3T3-E1 osteoblasts had well adhesions and proliferations in the COL/nHA scaffold coatings.A dynamic balance of living cells number in the COL/nHA scaffold coatings was found during the 2nd to 3rd week with mineralization induction.This phenomenon was caused by the different cell states,including proliferation,differentiation and apoptosis,in the COL/nHA scaffold coating.At the same time,extracellular matrix remodeling phenomenon was also observed in the COL/nHA coating.In addition,interlaced nano-particles and nanofibers structures,which are similar to the bone tissue morphology,were formed in the COL/nHA scaffold coating.Unbalanced magnetron sputtering method was used to prepare a GLC coating on the surface of C/C composites.The GLC coating was modified by hydrogen peroxide,and then grafted with RGD peptides.The results showed that there was a good match between the GLCcoating and C/C substrate.A transition layer was not needed to improve the bonding between GLC coating and C/C substrate.A large number of oxygen-containing functional groups were formed on the GLC coating when the oxidation temperature of hydrogen peroxide was at40°C.Surface wettability was greatly improved and the surface contact angle was 27.2±2.8°.RGD peptides were grafted on the modified GLC coating,and the bioactivity of GLC coating was improved.Cell adhesion of MC3T3-E1 osteoblasts on RGD peptides grafted GLC coating had a significant enhancement when compared with GLC coating.