Micro-CT based finite element modelling and experimental characterization of the compressive mechanical properties of 3-D zirconia scaffolds for bone tissue engineering.

The present study aims at developing a computational framework with experimental validation to determine the mechanical properties of zirconia foams for bone tissue engineering. A micro-CT based finite element model that allows characterizing the mechanical property of such cellular structures is developed. Micro-CT images are filtered to vanish noises and smooth boundaries before constructing 3D zirconia foams using an adaptive Body-Centered Cubic background lattice. In addition to micro-CT images, the local material property at the scaffold struts is measured using a micro-indentation test, which shows a considerable difference with that of common zirconia owing to the manufacturing process. The computational model also takes the plastic deformation of material into account employing the Voce law, a nonlinear isotropic hardening law, as well as Von-mises yield criterion. Zirconia foams with different pore sizes are manufactured using the replica method and their mechanical properties determined experimentally. Such experimental outcomes are to validate and demonstrate the capability of the developed model, which can be used for pre-operational evaluations and preclinical tests of zirconia scaffolds. The stress magnitude and distribution within the scaffold as well as plastic strains and flow stress of the zirconia scaffold are computed and analysed. Using the proposed approach, a deep insight into the association of macroscopic behaviour of the scaffold to microscopic features, e.g. strut waviness, Plateau border, thickness variation of cells, irregularity, microstructural variability, imperfections and strut's material property associated with to the manufacturing procedure, can be gained.

Y-TZP/porcelain graded dental restorations design for improved damping behavior - A study on damping capacity and dynamic Young's modulus.

The development of dental restorative materials that mimic tooth-like properties provided by graded structures, aesthetics and properties such as strength, damping capacity and the ability for a continuous remodeling according to the biomechanical solicitation is a great challenge. In this work, damping capacity and dynamic Young's modulus of Y-TZP/porcelain composites for all-ceramic dental restorations were studied. These mechanical properties were assessed by dynamic mechanical analyses (DMA) at frequencies of 1, 5 and 10 Hz, over a temperature ranging from 0 to 60 °C, simulating extreme conditions when a cold or hot drink is experienced. The results showed that porcelain and porcelain-matrix composites exhibited higher damping capacity while Y-TZP and Y-TZP-matrix composites presented higher dynamic Young's modulus. Furthermore, while damping capacity is strongly influenced by the temperature, no significant difference in dynamic Young's modulus was found. For both damping and modulus properties, no significant influence of frequency was found for the tested materials. Based on the obtained results and also on the known advantages of the graded Y-TZP/porcelain structures over traditional bi-layer solutions (e.g., improved bending strength, enhanced mechanical and thermal stress distribution), a novel design of all-ceramic restoration with damping capacity has been proposed at the end of this study. A positive impact on the long-term performance of these all-ceramic restorations may be expected.

Sliding behavior of zirconia porous implant surfaces against bone.

Different zirconia porous layers were produced on zirconia dense zirconia substrates by slip casting using powder with different mean sizes: 40 µm (Z40), 70 µm (Z70), and 100 µm (Z100). The dynamic and static coefficients of friction against bovine femoral bone, mimicking the implantation process, were conducted using a ball-on-flat reciprocating sliding tribometer under 3 N of normal load. Additionally, the porous layers were assessed with regard to their low temperature degradation (aging). Results revealed that the porous layers were able to keep their integrity during the sliding testes against bone, with no zirconia particles being transferred to the bone. Results did not show significant differences (p > 0.05) in kinetic and static COF values for Z40, Z70, Z100, and GRAD specimens, ranging from 0.53 to 0.77 and 0.65 to 0.90, respectively. The aging tests revealed that all surfaces were prone to low temperature degradation (~49% of monoclinic content after 18 h). In conclusion, the cohesive integrity of the layers and relatively high COF observed reveled that zirconia porous layers may be considered for replacing the current implant surfaces, and are expected to improve their primary stability. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1113-1121, 2019.

Polymer coatings based on sulfonated-poly-ether-ether-ketone films for implant dentistry applications.

Poly-ether-ether-ketone (PEEK) is one of the most important biocompatible polymers and its sulfonation has been studied for biomedical applications. The aim of the present study is to produce, to characterize and to assess bioactivity of PEEK coatings with sulfonated PEEK (SPEEK) films. Biomedical grade PEEK (Invibio®, Batch: D0602, grade: NI1) was functionalized using sulfuric acid 98%. SPEEK was dissolved into DMSO or into DMF, both at 10% mass/volume. PEEK bars (N = 18) and cylinders (N = 27) were manufactured by compression molding and heating. SPEEK/DMSO and SPEEK/DMF were drop casted at PEEK bars and dip coated at PEEK cylinders (PEEK + SPEEK/DMSO and PEEK + SPEEK/DMF). Characterization was performed through Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and contact angle measurements. Bioactivity was assessed by immersion of samples at SBF for 1, 7 and 21 days, followed by SEM, energy-dispersive analysis (EDX) and FTIR analysis. Statistical analysis was carried out by one-way analysis of variance (ANOVA) (p = 0.05). Characteristic bands of PEEK and SPEEK, were identified through FTIR spectrum analysis, while semicrystallinity was confirmed by XRD. PEEK + SPEEK/DMF showed more evident physicochemical modifications. PEEK + SPEEK/DMSO provided a more regular and hydrophobic surface, observed through SEM and contact angle measurements. SEM/EDX showed that precipitates of calcium were formed at PEEK + SPEEK/DMSO and PEEK + SPEEK/DMF at all experimental times, but materials were not considered bioactive. Interesting surface properties were achieved with SPEEK coatings but the production of SPEEK films at PEEK surface has to be further improved and biologically tested. Schematic diagram showing the methodology applied in this study to prepare PEEK and SPEEK samples, as well as the promising application of the material.

Inhibition of multi-species oral biofilm by bromide doped bioactive glass.

Bioactive glass is an attractive biomaterial that has shown excellent osteogenic and angiogenic effects for oral bone repairing procedures. However, anti-biofilm potential related to such biomaterial has not been completely validated, mainly against multi-species biofilms involved in early tissue infections. The aim of the present study was to evaluate the anti-biofilm effect of 58 S bioactive glass embedding calcium bromide compounds at different concentrations. Bioactive glass free or containing 5, or 10 wt % CaBr2 was synthesized by alkali sol-gel method and then characterized by physco-chemical analyses and scanning electron microscopy (SEM). Then, samples were tested by microbiological assays using optical density, real time q-PCR, and SEM. Bioactive glass particles showed accurate chemical composition and an angular shape with a bimodal size distribution ranging from 0.6 to 110 µm. The mean particle size was around 29 µm. Anti-biofilm effect was recorded for 5 wt % CaBr2 -doped bioactive glass against S. mitis, V. parvula, P. gingivais, S. gordoni, A. viscosus, F, nucleatum, P. gingivais. F. nucleatum, and P. gingivalis. Such species are involved in the biofilm structure related to infections on hard and soft tissues in the oral cavity. The incorporation of calcium bromide into bioactive glass can be a strategy to enhance the anti-biofilm potential of bioactive glasses for bone healing and infection treatment. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1994-2003, 2017.

Anti-biofilm properties of bioactive glasses embedding organic active compounds.

Bioactive glasses (BGs) are promising materials for bone repair due to their desirable properties such as osteoconductivity, biodegradability, angiogenic potential, and antibacterial activity. Ionic dissolution products from bioactive glasses increase the medium pH inhibiting surrounding bacteria proliferation. The activity of BGs against biofilm formation has been enhanced by incorporating organic antibacterial compounds. The aim of this review was to summarize evidence in literature which assesses the efficacy of antibacterial and anti-biofilm compounds embedded in bioactive glasses to prevent peri-implant infection during bone healing. A PubMed bibliographical research was carried out including articles published in the last 20 years. Most previous studies evaluated antibacterial efficiency in planktonic cultures but did not investigate biofilm inhibition, underestimating biofilm clinical relevance. Multifactorial features such as biocompatibility of embedded compounds, receptor site characteristics, and drug delivery efficiency have been found to influence the bioactive glass capability of acting both as an anti-biofilm agent and as a bone repairing biomaterial. Accordingly, further in vitro and in vivo studies are required to select the most promising anti-biofilm agents which should be incorporated into bioactive glasses to counteract biofilm proliferation, without inducing toxic effects on human cells, and with the added functionality of promoting bone regeneration. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 672-679, 2017.

Processing and strengthening of 58S bioactive glass-infiltrated titania scaffolds.

In this work, TiO2 ceramic scaffolds were fabricated by the replica method using polyurethane (PU) sponges. Suspensions with high solid content were used to achieve scaffolds with improved mechanical behavior. TiO2 ceramic suspensions were optimized by rheological studies using different additives. It was found that the composition with 0.5 wt % Darvan enhanced the covering of the sponge struts. PU sponges of 45 to 80 ppi (pore per inch) were well coated without clogging pores. A thermal treatment with varying holding times, temperatures and heating rates was adjusted. The influence of different pore sizes on mechanical strength was evaluated. It was possible to obtain TiO2 scaffolds with 90% porosity and high pore interconnectivity, having compressive strength exceeding 0.6 MPa. TiO2 scaffolds were filled up with a 58S bioactive glass suspension to impart bioactive character to the scaffolds. These hybrid structures presented mechanical strengthening of about 26-213% depending on their sponge porosity. The prediction for cells viability via zeta potential measures indicated that this hybrid material is very promising for scaffold application with -19 to -25 mV between pH of 7.35-7.45. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 590-600, 2017.