Nanostructured Hydroxyapatite Coatings for Improved Adhesion and Corrosion Resistance for Medical Implants

Abstract

Hydroxyapetite (HA) coating on medical implant has been used in commercial application for several decades. The coating, commercially made by thermal spray method, functions as a intermediate layer between human tissues and the metal implant. The coating can speed up early stage healing after operation but the life span is much limited by low interfacial bond strength, which comes from the dissolution of amorphous HA in human body fluid during its service. This amorphous phase is formed in coating process under high temperature. To overcome these problems, we have developed a novel room temperature electrophoretic deposition process to fabricate nanostructured HA coating. This nanostructured HA coating significantly improved coating's bond strength up to 50-60 MPa, 2-3 times better than the thermal sprayed HA coating. The nanostructured HA coating also has corrosion resistance 50-100 times higher than the conventional HA coating. X-ray diffraction shows that all the HA coating is fully crystalline phase. It is expected that the implants with the nanostructured HA coating will have much longer service life. Other benefits derived from this process include room temperature deposition, the ability to control the coating microstructure and phases, and low cost for production.

TiO2 Nanotubes on Ti Dental Implant. Part 1: Formation and Aging in Hank’s Solution

“…For further aging (216 h) the NT sample exhibits an OCP decrease that, following Zhang [38] is due to a two steps mechanism involving H+ produced at the interface area where corrosion occurs: …”

Corrosion Resistance Evaluation of HVOF Produced Hydroxyapatite and TiO2-hydroxyapatite Coatings in Hanks' Solution

“…The electrolyte may then achieve the substrate across the coating, forming a local cell, according to Lavos-Valereto and co-workers 36 , that induced the latter corrosion. The formation of local cells has been evoked to explain the higher activity of surfaces covered with porous film or coatings whereas proton is formed by a corrosion reaction of the substrate (Ti for instance) with water on the bottom of the pore; the pH decreases locally due to the fact that H + is almost closed at the interface due to the difficulty to go away; and in a second step the proton dissolves the HA near substrate/HA interface, probably beginning by the dissolution of the amorphous phase 42 . The E OCP of the 80-20 sample stabilized at around -0.22 and -0.32 V in the absence and presence of BSA, respectively.…”

Reduced bacterial growth and increased osteoblast proliferation on titanium with a nanophase TiO₂ surface treatment

“…6 One major restriction on the incorporation of antibiotics in coatings is the use of high temperature processes such as plasma spraying that denatures the coating. [7][8][9] Furthermore, the loading capacity and the release kinetics of antibiotics are restricted by their physical adsorption onto substrates and their use could trigger antibiotic resistance, which is a problem yet to be solved. 10,11 Coatings that reduce bacterial attachment are possible by modifying the implant surface to have structures that alter the surface energy and also provide mechanical cues that disrupt the bacterial membrane.…”