Osteogenic and antibacterial surfaces on additively manufactured porous Ti-6Al-4V implants: Combining silver nanoparticles with hydrothermally synthesized HA nanocrystals

Abstract

The recently developed additively manufacturing techniques have enabled the fabrication of porous biomaterials that mimic the characteristics of the native bone, thereby avoiding stress shielding and facilitating bony ingrowth. However, aseptic loosening and bacterial infection, as the leading causes of implant failure, need to be further addressed through surface biofunctionalization. Here, we used a combination of (1) plasma electrolytic oxidation (PEO) using Ca-, P-, and silver nanoparticle-rich electrolytes and (2) post-PEO hydrothermal treatments (HT) to furnish additively manufactured Ti-6Al-4V porous implants with a multi-functional surface. The applied HT led to the formation of hydroxyapatite (HA) nanocrystals throughout the oxide layer. This process was controlled by the supersaturation of Ca 2+ and PO 4 3− during the hydrothermal process. Initially, the high local supersaturation resulted in homogenous nucleation of spindle-like nanocrystals throughout the surface. As the process continued, the depletion of reactant ions in the outermost surface layer led to a remarkable decrease in the supersaturation degrees. High aspect-ratio nanorods and hexagonal nanopillars were, therefore, created. The unique hierarchical structure of the microporous PEO layer (pore size < 3 μm) and spindle-like HA nanocrystals (<150 nm) on the surface of macro-porous additively manufactured Ti-6Al-4V implants provided a favorable substrate for the anchorage of cytoplasmic extensions assisting cell attachment and migration on the surface. The results of our in vitro assays clearly showed the important benefits of the HT and the spindle-like HA nanocrystals including a significantly stronger and much more sustained antibacterial activity, significantly higher levels of pre-osteoblasts metabolic activity, and significantly higher levels of alkaline phosphatase activity as compared to similar PEO-treated implants lacking the HT.

Wear Resistance of Plasma Electrolytic Oxidation Coatings on Ti-6Al-4V Eli Alloy Processed by Additive Manufacturing

“…Figure 3A illustrates the grazing incidence X-ray diffraction patterns of the u Ti-6Al-4V ELI alloy and the PEO coatings produced at different electrical param The three samples had formed coatings that were extremely well attached to the AM substrate composed of two different layers, one dense inner layer, and a porous outer layer, as seen in Figure 1. This result agrees with those found by Fazel et al [29] in their work on PEO coatings obtained on Ti-6Al-4V alloy processed by the L-PBF technique. The inner layer, which grows direct into the metal under high pressures and temperatures, is dense, crystalline, and firmly attached to the substrate.…”

“…Yu and Choe [28] demonstrate that PEO coatings composed of Ca/P and TiO 2 , formed on Ti-6Al-4V substrate, were capable to induce the formation of hydroxyapatite (HA) by immersion in SBF, which exhibits superior bioactivity when compared with the naked substrate [21]. The biological response of PEO coatings, combined with a hydrothermal layer of HA, obtained on Ti-6Al-4V substrate produced by additive manufacture techniques, was evaluated by Fazel et al [29]. According to the authors, the coatings showed a biological response facilitating the proliferation and osteogenic differentiation of cells.…”

Antibacterial Designs for Implantable Medical Devices: Evolutions and Challenges

“…Silver and hydroxyapatite are two typical materials with antibacterial and osteogenic properties, respectively. Recently, Fazel et al developed a duplex process that sequentially employed micro-arc oxidation and hydrothermal treatment to decorate Ag NPs and hydroxyapatite nanocrystals on the surface of a porous Ti6Al4V substrate (fabricated by using selective laser melting), creating surfaces of both osteogenic and antibacterial properties [ 206 ]. Bacterial infection in burn wounds is common and fatal [ 207 ].…”

Biocomposites Containing Silver Nanoparticles for Biomedical Applications

“…The AgNP-based composites have been combined with natural and synthetic polymeric substances for tissue engineering applications [27,[49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67]. Biocomposites containing AgNPs and HA have been produced using ecofriendly techniques [68].…”