Preparation of HA/Gelatin coatings on C/C composites via modified electrocrystallization/posthydrothermal treatments

Electrocrystallized calcium phosphate (CP) coatings generally show a porous structure on carbon/carbon composites (C/Cs) and poor adhesive strength that limit their application in orthopedics. To overcome this disadvantage, ultrasonic and ice bath were employed in the electrocrystallization process of preparing CP/gelatin coating with a thickness of 50 μm on C/Cs. The CP/gelatin coating was hydrothermally treated in aqueous ammonia and sodium silicate solutions, respectively, to obtain an ion-doped hydroxyapatite(HA)/gelatin coating on C/Cs. Results showed that the modified electrocrystallized process could achieve a compactly stacked flaky structure coating of brushite and gelatin on C/Cs, whose adhesive strength could reach a critical load of 6.3 N. HA/gelatin coating that contains nanoneedle crystals could be achieved after performing the ammonia hydrothermal treatment, but its adhesive strength decreased to 4.1 N. Further hydrothermal treatment of the HA/gelatin coating in the sodium silicate solution obtained a Na, Si-doped HA coating on C/Cs, which could reach a critical load as high as 7.72 N. This value is equivalent to shear strength of 47 MPa. The ion-doping and hydrothermal self-repair processes enhanced the adhesion strength of the Si,Na-HA coating on C/Cs. In vitro experiments showed that the Si, Na-HA/gelatin coating exhibited better cell compatibility than C/Cs and HA/gelatin coating.