Electrodeposited Hydroxyapatite-Based Biocoatings: Recent Progress and Future Challenges

Abstract

Hydroxyapatite has become an important coating material for bioimplants, following the introduction of synthetic HAp in the 1950s. The HAp coatings require controlled surface roughness/porosity, adequate corrosion resistance and need to show favorable tribological behavior. The deposition rate must be sufficiently fast and the coating technique needs to be applied at different scales on substrates having a diverse structure, composition, size, and shape. A detailed overview of dry and wet coating methods is given. The benefits of electrodeposition include controlled thickness and morphology, ability to coat a wide range of component size/shape and ease of industrial processing. Pulsed current and potential techniques have provided denser and more uniform coatings on different metallic materials/implants. The mechanism of HAp electrodeposition is considered and the effect of operational variables on deposit properties is highlighted. The most recent progress in the field is critically reviewed. Developments in mineral substituted and included particle, composite HAp coatings, including those reinforced by metallic, ceramic and polymeric particles; carbon nanotubes, modified graphenes, chitosan, and heparin, are considered in detail. Technical challenges which deserve further research are identified and a forward look in the field of the electrodeposited HAp coatings is taken.

Effect of formula milk on the roughness and hardness of tooth enamel

“…In addition, milk fat that is adsorbed onto the enamel surface may act as a protection, and enzymes in the milk can reduce the acidogenic stage of plaque bacteria. 12 Milk contains proteins that bind calcium and phosphate ions. The remineralisation process starts with the attachment of milk proteins to the enamel surface.…”

“…11 Calcium and phosphate ions form HA crystals in enamel and the number of HA crystals formed affects the thickness of the enamel. 12 The purpose of this study was to compare the different effects of immersion in cow milk formula and soy formula on the roughness and hardness of the enamel surface.…”

Nanohydroxyapatite Electrodeposition onto Electrospun Nanofibers: Technique Overview and Tissue Engineering Applications

“…Electrodeposition refers to an efficient technique to synthesize solid coating (film) on the surface of a conductive material from electrochemical reactions. This technique can be employed to precisely control the chemical composition, thickness, and structure of electrodeposited material, generating more uniform, crystalline, homogeneous, adherent, and thin coatings via a fast, adjustable process at a relatively low temperature [ 17 , 49 , 50 , 51 ].…”

“…Regarding the composition of the electrolyte, in addition to the wide variety of precursors of phosphate (NH 4 H 2 PO 4 [ 56 ], (NH 4 ) 2 HPO 4 [ 57 ], and KH 2 PO 4 [ 58 ]) and calcium (CaCl 2 [ 58 ], Ca(NO 3 ) 2 [ 59 ], and Ca(NO 4 ) 2 [ 60 ]) in their different concentrations, some additives are commonly incorporated into the electrolyte during the electrodeposition of HAp, each with a specific purpose—for example, the addition of NaCl to increase electrolytic conductivity [ 61 ], the incorporation of NaNO 3 to improve ionic strength [ 62 ], and the inclusion of H 2 O 2 that contributes to the formation of hydroxyl ions favoring the formation of HAp [ 58 ]. A detailed discussion of the influence of each of these variables on the electrodeposition process of HAp can be found in a recently published review about this topic [ 49 ].…”

“…The optimal coating thickness should also be further investigated in future works. The literature reports the ideal thickness of HAp coating for osteogenesis (~10 µm) [ 49 ]; nevertheless, this parameter has not been explored in studies that conducted nHAp electrodeposition on polymeric nanofibers.…”