Deposition of phosphate coatings on titanium within scaffold structure

Purpose. Existing knowledge about the appearance, thickness, and chemical composition of 37 phosphate coatings on titanium inside porous structures is insufficient. Such knowledge is 38 important for the design and fabrication of porous implants. 39 Methods. Metallic scaffolds were fabricated by selective laser melting of 316L stainless steel 40 powder. Phosphate coatings were deposited on Ti sensors placed either outside the scaffolds 41 or in the holes in the scaffolds. The electrochemically-assisted cathodic deposition of 42 phosphate coatings was performed under galvanostatic conditions in an electrolyte containing 43 the calcium and phosphate ions. The phosphate deposits were microscopically investigated; 44 this included the performance of mass weight measurements and chemical analyses of the content of Ca2+ and PO4 2‒ 45 ions after the dissolution of deposits. 46 Results. The thicknesses of the calcium phosphate coatings were about 140 and 200 nm for 47 isolated titanium sensors and 170 and 300 nm for titanium sensors placed inside pores. 48 Deposition of calcium phosphate occurred inside the pores up to 150 mm below the scaffold 49 surface. The deposits were rich in Ca, with a Ca/P ratio ranging between 2 and 2.5. 50 Conclusions. Calcium phosphate coatings can be successfully deposited on a Ti surface 51 inside a model scaffold. An increase in cathodic current results in an increase in coating 52 thickness. Any decrease in the cathodic current inside the porous structure is slight. The 53 calcium phosphate inside the pores has a much higher Ca/P ratio than that of stoichiometric 54 HAp, likely due to a gradual increase in Ca fraction with distance from the surface.