Electrolytic Deposition of Hydroxyapatite Coating on CoNiCrMo Substrates

Abstract

Cobalt-based alloys have long been used as prosthetic implant in orthopedic surgery. [1,2] However, the lack of bioactivity and the consequent slow osteointegration (typically taking 3-6 months) limits their application in clinics. Hydroxyapatite (HA, Ca 10 (PO 4 ) 6 (OH) 2 ) is the mineral component of natural bone, and shows excellent osteointegration when used as implant material in orthopedic fields. In order to achieve bioactivity for load-bearing metallic implants, HA coatings have been introduced recently due to their degradable property.To date, various techniques, such as plasma spraying, [3] laser ablation, [4] biomimetic, [5] and electrolytic deposition (ELD), [6,7] have been employed in the preparation of HA coatings. Among them, ELD possesses various advantages in the following aspects: (1) being conducted in mild aqueous solution;(2) being suitable to complex or porous surface structures; (3) with high efficiency and low cost; (4) the obtained coating being porous and thus degradable in vivo. [8] Hence, ELD of HA coating has attracted considerable attention in recent years. [9][10][11] However, the previous researches have all focused on the deposition on pure Ti and its alloys. It is generally believed that the reduction of H 2 O causes rise of local pH of the electrolyte in the vicinity of the cathode titanium surface and, consequently, results in Ti-OH layer formation. Calcium ions are incorporated in the hydrated Ti-OH layer. The positively charged Ca 2þ may act as nucleation sites by attaching to negatively charged (PO 4 ) 3 to form Ca-P crystals. During this process, the Ti-OH layer (including physisorbed hydroxyls and chemisorbed OH hydroxyl groups) is considered to play a role in the nucleation of apatite by a number of researchers. [7,12,13] In the present work, we explored the possibility of depositing HA coating on a CoCrMoNi alloy substrate by the ELD technique. We also constructed a unique experiment to reveal the importance of the local pH to the crystallization and investigate whether the substrate surface property is vital to the nucleation of apatite during ELD process. ExperimentalA sheet (10 mm  10 mm  1 mm) made of wrought 35Co-35Ni-20Cr-10Mo alloy (ASTM F562) was used as cathode. Prior to ELD, the cathode was mechanically ground on SiC papers from P120 to P800 grit before polishing, cleaned ultrasonically in acetone, rinsed with DI water, and dried.ELD was carried out in a three-electrode macrocell. During the process of ELD, an accompanying uncharged specimen (including CoNiCrMo alloy, Ti plate, and nonconducting polyethylene plate and glass) was placed parallel to the cathodic CoCrMoNi specimen with a spacing of 1 mm. The bath contained 0.6 mM Ca(NO 3 ) 2 Á 4H 2 O and 0.36 mM NH 4 H 2 PO 4 with Ca/P ratio being 1.67 in DI water. The pH was adjusted to 6.0 at room temperature by ammonia additions. A Pt foil and an Ag/AgCl electrode were used as counterelectrode (anode) and reference electrode, respectively. The ELD was conducted with a CHI1140 (USA) potentionstat/galvanostat ...

Interlayer TiO2–HAP composite layer for biomedical applications

“…This can be overcome by using a crucial coating material like Hydroxyapatite [Ca 10 (PO 4 ) 6 (OH) 2 , HAP] which possesses anti-corrosion [6] and biocompatibility [7] properties. Hence, bioactive HAP coatings on titanium can be achieved by methods such as sol-gel processing, pulsed laser deposition, electrodeposition, plasma spraying, electrolytic deposition, and electrophoretic deposition (EPD) [8][9][10][11][12][13]. However, among these techniques EPD has numerous advantages like simple equipment with ease of control over coating parameters, ability to coat intricate shapes of implants, low cost and completion of the coating process in a few minutes with uniform distribution [14].…”

“…Hence, bioactive HAP coatings on titanium can be achieved by methods such as sol-gel processing, pulsed laser deposition, electrodeposition, plasma spraying, electrolytic deposition, and electrophoretic deposition (EPD). [8][9][10][11][12][13] However, among these techniques EPD has numerous advantages like simple equipment with ease of control over coating parameters, ability to coat intricate shapes of implants, low cost and completion of the coating process in a few minutes with uniform distribution. 14 Since HAP coating is microporous in nature, there is a direct pathway for body uids in to the metal which leads to corrosion process.…”