Institute of Fundamental Technological Research

In recent decades, several novel Ti alloys have been developed in order to produce improved alternatives to the conventional alloys used in the biomedical industry such as commercially pure titanium or dual phase (alpha and beta) Ti alloys. Gum Metal with the non-toxic composition Ti–36Nb–2Ta–3Zr–0.3O (wt. %) is a relatively new alloy which belongs to the group of metastable beta Ti alloys. In this work, Gum Metal has been assessed in terms of its mechanical properties, corrosion resistance and cell culture response. The performance of Gum Metal was contrasted with that of Ti–6Al–4V ELI (extra-low interstitial) which is commonly used as a material for implants. The advantageous mechanical characteristics of Gum Metal, e.g. a relatively low Young's modulus (below 70 GPa), high strength (over 1000 MPa) and a large range of reversible deformation, that are important in the context of potential implant applications, were confirmed. Moreover, the results of short- and long-term electrochemical characterization of Gum Metal showed high corrosion resistance in Ringer's solution with varied pH. The corrosion resistance of Gum Metal was best in a weak acid environment. Potentiodynamic polarization studies revealed that Gum Metal is significantly less susceptible to pitting corrosion compared to Ti–6Al–4V ELI. The oxide layer on the Gum Metal surface was stable up to 8.5 V. Prior to cell culture, the surface conditions of the samples, such as nanohardness, roughness and chemical composition, were analyzed. Evaluation of the in vitro biocompatibility of the alloys was performed by cell attachment and spreading analysis after incubation for 48 h. Increased in vitro MC3T3-E1 osteoblast viability and proliferation on the Gum Metal samples was observed. Gum Metal presented excellent properties making it a suitable candidate for biomedical applications.

Gum Metal, mechanical behavior, in vitro corrosion resistance, in vitro biocompatibility, implant applications

Mg-based materials are good candidates for biodegradable bone regeneration implants due to their favorable mechanical properties and an excellent compatibility with human bone. However, too high corrosion/degradation rate in body fluids still limits their applicability. Coatings based on chitosan (CS) and bioactive glass (BG) particles fabricated by electrophoretic deposition (EPD) on Dulbecco's Modified Eagle Medium (DMEM) pre- treated magnesium alloys have promising potential to suppress the substrate corrosion and additionally to incorporate bioactivity. However, the impact of processing parameters or type of coating components on the long-term substrate corrosion behavior and cell response have not been investigated previously. In this study, two types of composite coatings based on a high molecular weight CS (Mw 340–360 kDa, DDA ≥95%) and embedded particles: solid BG (2 μm) and a mixture of BG and mesoporous bioactive glass nanoparticles (MBGN, 100–300 nm with mesopores 2.3–5.6 nm) were fabricated by EPD on DMEM pre-treated WE43 magnesium alloy. It was found that partial replacement of BG particles with MBGN (ratio 3:1) in the composite coating increases the water contact angle, surface roughness and induces a positive cell response. Although the acidic CS-based solutions and applied EPD conditions may decrease the stability of the temporary barrier formed during the DMEM pre-treatment on WE43 substrate therewith slightly increasing its corrosion sensitivity, the composite coating with a mixture of different sizes of particles (BG, MBGN) is a promising candidate for bone regeneration applications.

WE43, magnesium alloy, chitosan, bioactive glass, mesoporous nano bioactive glass, electrophoretic deposition

Biodegradable polymeric nanofibrous coatings were obtained by electrospinning different polymers onto sintered 45S5 Bioglass®-based glass-ceramic pellets. The investigated polymers were poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) and a composite of poly(caprolactone) (PCL) and poly(ethylene oxide) (PEO) (PCL–PEO). The fibrous coatings morphology was evaluated by optical microscopy and scanning electron microscopy. The electrospinning process parameters were optimised to obtain reproducible coatings formed by a thin web of polymer nanofibres. In-vitro studies in simulated body fluid (SBF) were performed to investigate the bioactivity and mineralisation of the substrates by inducing the formation of hydroxyapatite (HA) on the nanofiber-coated pellets. HA crystals were detected on all samples after 7 days of immersion in SBF, however the morphology of the HA layer depended on the characteristic fibre diameter, which in turn was a function of the specific polymer-solvent system used. The bioactive and resorbable nanofibrous coatings can be used to tailor the surface topography of bioactive glass-ceramics for applications in tissue engineering scaffolds.

Electrospinning, Nanofibers, Bioglass®, Polyhydroxyalkanoates, Tissue engineering

In this work, mechanical properties of a β-Ti alloy Gum Metal (Ti–23Nb–0.7Ta–2.0Zr–1.2O at.%, free of cytotoxic content), which was fabricated at Toyota Central Research&Development Laboratories, Inc., were investigated. It was confirmed that Gum Metal is characterized by a low Young's modulus (around 60 GPa), high strength (over 1000 MPa) and a large range of reversible deformation, which are important features in the context of potential implant applications. Moreover, a comprehensive assessment of biocompatibility was realized. Properties of Gum Metal were contrasted with those of Ti-6Al-4V (ELI) which was taken as reference. Surface conditions, such as topography, roughness and structural composition, were analyzed. Evaluation of biocompatibility for the alloys was performed by cell attachment and spreading analysis after predefined cell culture periods. Gum Metal presented excellent properties, what makes it a goodcandidate for implant applications.

Gum Metal, titanium alloy, biocompatibility, implant applications