Development and Scale-up of the Low Density Core Process for Ti-64

A Review of Different Manufacturing Methods of Metallic Foams

Metallic foam is a popular topic due to its diverse industrial applications and unique combination of properties. Metallic foam is significantly lighter than nonfoam metal materials due to its porous structure, which incorporates a substantial amount of air or voids. This lower density makes metallic foam advantageous in applications in which weight reduction is critical. This makes it ideal for the aerospace, automotive, and construction industries; also, its versatile nature continues to make it an attractive material for various industrial applications such as impact absorbers, heat exchangers, and biomedical and marine engineering. However, the choice between metallic foam and nonfoam metal also depends on other factors like mechanical properties, cost, and specific application requirements. This review describes various fabrication methods of metallic foam that include the liquid metallurgy route which uses liquid or semiliquid metal, the powder metallurgy route uses metal in powder form, metal ion, and the metal vapor route which uses electrolytic deposition method to produce metallic foam. These methods include direct gas injection, adding blowing agents in solid or liquid metals, investment casting, the addition of a space holder in the precursor, metallic ion, vapor deposition on a polymer sponge, and many more. The morphology of metallic foam depends upon the method that is chosen for fabrication, and up to 98% porosity can be achieved by these methods. Additive manufacturing for metallic foam fabrication is an emerging field based on selective laser melting and electron beam melting principles. It has exceptional possibilities for generating complicated 3D shapes and customizing the material characteristics. The main purpose of this review article is to give significant insights into the various production procedures for metallic foams to researchers, engineers, and industry experts, assisting in the selection of acceptable methods depending on individual application needs. This review investigates the manufacturing conditions for metallic foams and finally discusses their advantages, drawbacks, and obstacles in mass production. The findings add to current efforts to expand metallic foam technology and encourage its wider application across diverse sectors, opening the path for future research and development.

Hybrid bone implants: self-assembly of peptide amphiphile nanofibers within porous titanium

Over the past few decades there has been great interest in the use of orthopedic and dental implants that integrate into tissue by promoting bone ingrowth or bone adhesion, thereby eliminating the need for cement fixation. However, strategies to create bioactive implant surfaces to direct cellular activity and mineralization leading to osteointegration are lacking. We report here on a method to prepare a hybrid bone implant material consisting of a Ti-6Al-4V foam, whose 52% porosity is filled with a peptide amphiphile (PA) nanofiber matrix. These PA nanofibers can be highly bioactive by molecular design, and are used here as a strategy to transform an inert titanium foam into a potentially bioactive implant. Using scanning electron microscopy (SEM) and confocal microscopy, we show that PA molecules self-assemble into a nanofiber matrix within the pores of the metallic foam, fully occupying the foam's interconnected porosity. Furthermore, the method allows the encapsulation of cells within the bioactive matrix, and under appropriate conditions the nanofibers can nucleate mineralization of calcium phosphate phases with a Ca:P ratio that corresponds to that of hydroxyapatite. Cell encapsulation was quantified using a DNA measuring assay and qualitatively verified by SEM and confocal microscopy. An in vivo experiment was performed using a bone plug model in the diaphysis of the hind femurs of a Sprague Dawley rat and examined by histology to evaluate the performance of these hybrid systems after 4 weeks of implantation. Preliminary results demonstrate de novo bone formation around and inside the implant, vascularization around the implant, as well as the absence of a cytotoxic response. The PA-Ti hybrid strategy could be potentially tailored to initiate mineralization and direct a cellular response from the host tissue into porous implants to form new bone and thereby improve fixation, osteointegration, and long term stability of implants.

Phospholipids as implant coatings

Bio-interfaces such as bio-membranes are of outmost importance for a variety of live processes. Among them are cell-interactions which take place in, on or through cell membranes. Therefore we propose to cover metallic surfaces with phospholipids to facilitate cell-material interaction. Four lipids, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), 1-palmitoyl-2- oleoyl-sn-glycero-3-[phospho-L-serine] (POPS) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-rac-(1-glycerol) (POPG), were applied to four metallic growth substrates with different surface structure, roughness and porosity. The interaction of the osteosarcoma cell line MG-63 was investigated in terms of cell adhesion and viability (MTT (methylthiazolyldiphenyl-tetrazolium bromide) assay). While POPS in general had a negative influence, the most suitable combination in terms of viability per adherent MG-63 is the coating of porous Ti6Al4V material with the phospholipids POPE or POPC. The analysis of viability of mouse macrophages RAW 264.7 and their tumor necrosis factor alpha (TNF-alpha) release showed that the adhesion and viability is worst on POPS while the TNF-alpha release was highest. To elucidate the potential of phospholipids to prevent or support bacterial growth, the bacterial number of Gram positive and Gram negative bacteria was investigated. For lipid concentrations higher than 1 mM in solution a growth stimulating effect independent of the lipid type was detected. On a lipid coated surface the number of bacteria was reduced by 81%, 74% and 51% for POPC, POPG and POPE.