Abstract
Advanced additive manufacturing techniques such as electron beam melting (EBM), can produce highly porous structures that resemble the mechanical properties and structure of native bone. However, for orthopaedic applications, such as joint prostheses or bone substitution, the surface must also be bio-functionalized to promote bone growth. In the current work, EBM porous Ti6Al4V alloy was exposed to an alkali acid heat (AlAcH) treatment to bio-functionalize the surface of the porous structure. Various molar concentrations (3, 5, 10M) and immersion times (6, 24 h) of the alkali treatment were used to determine optimal parameters. The apatite forming ability of the samples was evaluated using simulated body fluid (SBF) immersion testing. The micro-topography and surface chemistry of AlAcH treated samples were evaluated before and after SBF testing using scanning electron microscopy and energy dispersive X-ray spectroscopy. The AlAcH treatment successfully modified the topographical and chemical characteristics of EBM porous titanium surface creating nano-topographical features ranging from 200–300 nm in size with a titania layer ideal for apatite formation. After 1 and 3 week immersion in SBF, there was no Ca or P present on the surface of as manufactured porous titanium while both elements were present on all AlAcH treated samples except those exposed to 3M, 6 h alkali treatment. An increase in molar concentration and/or immersion time of alkali treatment resulted in an increase in the number of nano-topographical features per unit area as well as the amount of titania on the surface.
Highlights
Titanium has long been used for biomedical applications because of its combined superiority in biocompatibility, mechanical properties and corrosion resistance [1,2,3]
Porous titanium fabricated by electron beam melting (EBM) was alkali acid heat (AlAcH) treated to produce nano-topographical features and a crystalline titania layer to stimulate the formation of Ca and P, with a final objective of improving apatite forming ability
The use of artificial nanostructures allows intimate interactions with the first level of bone structural hierarchy allowing repopulation and re-synthesis of a new matrix for bone. Based on this understanding of the significance of nano-features, the current results suggest that an AlAcH treatment with higher molar concentration is ideal as stronger molar concentrations of NaOH
Summary
Titanium has long been used for biomedical applications because of its combined superiority in biocompatibility, mechanical properties and corrosion resistance [1,2,3]. The porous structure will allow for bone ingrowth and incorporation of functional molecules while the mechanical properties are important in avoiding stress shielding effects Various manufacturing methods such as gel casting [6], loose powder sintering [7], powder metallurgy space holder and titanium fibre sintering [8] have been successfully developed. Ideal mechanical properties and structure can be obtained through advanced additive manufacturing techniques, porous titanium structures must be bio-functionalized to aid bone growth and integration Several surface treatments such as plasma spray [26], gelatin [27], anodization [28] and chemical [28,29,30] treatments have been applied to porous titanium to improve its bio-functionality. The micro-topography and surface chemistry of AlAcH treated porous titanium samples were examined before and after immersion in SBF using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS)
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