Microstructural, Mechanical, Corrosion and Cytotoxicity Characterization of Porous Ti-Si Alloys with Pore-Forming Agent.

Titanium and its alloys belong to the group of materials used in implantology due to their biocompatibility, outstanding corrosion resistance and good mechanical properties. However, the value of Young's modulus is too high in comparison with the human bone, which could result in the failure of implants. This problem can be overcome by creating pores in the materials, which, moreover, improves the osseointegration. Therefore, TiSi2 and TiSi2 with 20 wt.% of the pore-forming agent (PA) were prepared by reactive sintering and compared with pure titanium and titanium with the addition of various PA content in this study. For manufacturing implants (especially augmentation or spinal replacements), titanium with PA seemed to be more suitable than TiSi2 + 20 wt.% PA. In addition, titanium with 30 or 40 wt.% PA contained pores with a size allowing bone tissue ingrowth. Furthermore, Ti + 30 wt.% PA was more suitable material in terms of corrosion resistance; however, its Young's modulus was higher than that of the human bone while Ti + 40 wt.% PA had a Young's modulus close to the human bone.

A review of in vitro cell culture testing methods for bioactive glasses and other biomaterials for hard tissue regeneration.

Bioactive glasses are used to regenerate bone by a mechanism which involves surface degradation, the release of ions such as calcium, soluble silica and phosphate and the precipitation of a biomimetic apatite surface layer on the glass. One major area of bioactive glass research is the incorporation of therapeutically active ions to broaden the application range of these materials. When developing such new compositions, in vitro cell culture studies are a key part of their characterisation. However, parameters of cell culture studies vary widely, and depending on the intended use of bioactive glass compositions, different layouts, cell types and assays need to be used. The aim of this publication is to provide materials scientists, particularly those new to cell culture studies, with a tool for selecting the most appropriate assays to give insight into the properties of interest.

Interaction of MOPS buffer with glass-ceramic scaffold: Effect of (PO4 )3- ions in SBF on kinetics and morphology of formatted hydroxyapatite.

The international standard ISO 23317:2014 for the in vitro testing of inorganic biomaterials in simulated body fluid (SBF) uses TRIS buffer to maintain neutral pH. In our previous papers, we investigated the interaction of a glass-ceramic scaffold with TRIS and HEPES buffers. Both of them speeded up glass-ceramic dissolution and hydroxyapatite (HAp) precipitation, thereby demonstrating their unsuitability for the in vitro testing of highly reactive biomaterials. In this article, we tested MOPS buffer (3-[N-morpholino] propanesulfonic acid), another amino acid from the group of "Goods buffers". A highly reactive glass-ceramic scaffold (derived from Bioglass®) was exposed to SBF under static-dynamic conditions for 13/15 days. The kinetics and morphology of the newly precipitated HAp were studied using two different concentrations of (PO4 )3- ions in SBF. The pH value and the SiIV , Ca2+ , and (PO4 )3- concentrations in the SBF leachate samples were measured every day (AAS, spectrophotometry). The glass-ceramic scaffold was monitored by SEM/EDS, XRD, WD-XRF, and BET before and after 1, 3, 7, 11, and 13/15 days of exposure. As in the case of TRIS and HEPES, the preferential dissolution of the glass-ceramic crystalline phase (Combeite) was observed, but less intensively. The lower concentration of (PO4 )3- ions slowed down the kinetics of HAp precipitation, thereby causing the disintegration of the scaffold structure. This phenomenon shows that the HAp phase was predominately generated by the presence of (PO4 )3- ions in the SBF, not in the glass-ceramic material. Irrespective of this, MOPS buffer is not suitable for the maintenance of pH in SBF.

Interaction of HEPES buffer with glass-ceramic scaffold: Can HEPES replace TRIS in SBF?

An international standard (ISO: 23317:2014) exists for the in vitro testing of inorganic biomaterials in simulated body fluid (SBF). This standard uses TRIS buffer to maintain neutral pH in SBF, but in our previous paper, we showed that the interaction of a tested glass-ceramic material with TRIS can produce false-positive results. In this study, we evaluated whether the HEPES buffer, which also belongs to the group of Good´s buffers, would be more suitable for SBF. We compared its suitability in two media: SBF with HEPES and demineralized water with HEPES. The tested scaffold (45S5 bioactive glass-based) was exposed to the media under a static-dynamic arrangement (solutions were replaced on a daily basis) for 15 days. Leachate samples were collected daily for the analysis of Ca2+ ions and Si (AAS), (PO4 )3- ions (UV-VIS), and to measure pH. The glass-ceramic scaffold was analyzed by SEM/EDS, XRD, and WD-XRF before and after 0.3, 1, 3, 7, 11, and 15 days of exposure. Our results confirmed the rapid selective dissolution of the glass-ceramic crystalline phase (Combeite) containing Ca2+ ions due to the presence of HEPES, hydroxyapatite supersaturation being reached within 24 h in both solutions. These new results suggest that, like TRIS, HEPES buffer is not suitable for the in vitro testing of highly reactive inorganic biomaterials (glass, glass-ceramics). The ISO standard for such tests requires revision, but HEPES is not a viable alternative to TRIS buffer. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 143-152, 2018.

Is non-buffered DMEM solution a suitable medium for in vitro bioactivity tests?

Several laboratories had tested bioactivity of the materials in commercially available solution DMEM (Dulbecco's Modified Eagle's Medium) that is normally used for cultivation of cell cultures. The objective of this work was to find out whether it is possible to replace TRIS-buffered SBF currently used for bioactivity tests with the non-buffered DMEM solution. To understand the role of the organic part of the DMEM solution in the process of crystallization, we have prepared non-buffered solution simulating only its inorganic part (identified as I-solution). It was found that under static-dynamic test conditions calcite (CaCO3) and the amorphous phase of calcium phosphate (ACP) formed on the surface of the glass-ceramic (45S5 bioactive glass based) scaffold exposed to both solutions. Additionally, halite (NaCl) formed at the beginning of exposure to DMEM. Hydroxyapatite phase was not detected on the surface in either non-buffered solution. Organic components contained in the DMEM solution failed to prevent formation of crystalline phases. The present results indicate that it is not recommendable to use DMEM for bioactivity tests of glass-ceramic materials due to its low concentration of Ca2+ ions, high concentration of HCO3 - ions and the necessity to maintain sterile environment during the test.

TRIS buffer in simulated body fluid distorts the assessment of glass-ceramic scaffold bioactivity.

The paper deals with the characterisation of the bioactive phenomena of glass-ceramic scaffold derived from Bioglass® (containing 77 wt.% of crystalline phases Na(2)O·2CaO·3SiO(2) and CaO·SiO(2) and 23 wt.% of residual glass phase) using simulated body fluid (SBF) buffered with tris-(hydroxymethyl) aminomethane (TRIS). A significant effect of the TRIS buffer on glass-ceramic scaffold dissolution in SBF was detected. To better understand the influence of the buffer, the glass-ceramic scaffold was exposed to a series of in vitro tests using different media as follows: (i) a fresh liquid flow of SBF containing tris (hydroxymethyl) aminomethane; (ii) SBF solution without TRIS buffer; (iii) TRIS buffer alone; and (iv) demineralised water. The in vitro tests were provided under static and dynamic arrangements. SBF buffered with TRIS dissolved both the crystalline and residual glass phases of the scaffold and a crystalline form of hydroxyapatite (HAp) developed on the scaffold surface. In contrast, when TRIS buffer was not present in the solutions only the residual glassy phase dissolved and an amorphous calcium phosphate (Ca-P) phase formed on the scaffold surface. It was confirmed that the TRIS buffer primarily dissolved the crystalline phase of the glass-ceramic, doubled the dissolving rate of the scaffold and moreover supported the formation of crystalline HAp. This significant effect of the buffer TRIS on bioactive glass-ceramic scaffold degradation in SBF has not been demonstrated previously and should be considered when analysing the results of SBF immersion bioactivity tests of such systems.