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  • Open access
  • 114 Reads
Isolation and Identification of Cytotoxic Compounds Present in Biomaterial Life®

Introduction: Direct pulp capping consists of a minimally invasive procedure in which a material is placed directly over the exposed pulp to maintain dental vitality. Previous studies found that the Lifeâ biomaterial presented high cytotoxicity and cell death in vitro. This study aims to identify which Life® constituents are responsible for the proliferation and viability decrease in odontoblast-like cells (MDPC-23).

The aqueous media conditioned with Life® was submitted to liquid-liquid extraction with ethyl acetate. Cells were treated with both organic and inorganic fractions, and further MTT assays were carried out to evaluate metabolic activity. The toxic compounds were determined by nuclear magnetic resonance spectroscopy (1HNMR and 13CNMR) and gas chromatography coupled with mass spectrometry (GC-MS).

Results and Discussion: The organic phase showed a significant decrease in metabolic activity. On the other hand, no cytotoxic effect was observed with the inorganic fraction. From the spectroscopic analysis, the organic extract was identified as a mixture of isomers (ortho/para/meta) of N-ethyl-toluenesulfonamide. For the first time, the phase and compound associated with Lifeâ induced cell death were determined. Given this biomaterial's moderate clinical success, our results support the development of new materials with improved biocompatibility characteristics.

Conclusions: The toxicity of biomaterial Life® in MDPC-23 cells was confirmed. N-ethyl-toluenesulfonamide was identified as the toxic agent. Although it is no longer considered a gold standard, this biomaterial remains widely used in clinical practice. However, based on our results, its application is not recommended.

  • Open access
  • 115 Reads
Effects of Incorporation of Marine Derived Hydroxyapatite on the Microhardness and Surface Roughness of Two Glass-ionomer Cements

Background: The aim of this study was to evaluate the effects of incorporation of hydroxyapatite (HA) derived from cuttlefish bone on the microhardness (MH) and surface roughness (SR) of chemically cured, Fuji IX GP Extra and resin-modified glass-ionomer cement, Fuji II LC (GC Corporation, Tokyo, Japan). Methods: There were 4 groups for each GIC: one group without the addition of HA particles and three experimental groups with the addition of 2, 5 and 10 wt% HA. A sectional Teflon molds (8 mm diameter × 2 mm deep) were used to prepare 10 samples per group (n=80). The specimens were stored in distilled water at 37°C for 7 days before testing. The SR was measured using a contact type profilometer and the MH was measured with a Vickers micro-hardness tester at a load of 980 g for 15 s. Statistical analysis was performed using one-way ANOVA with Tukey post-hoc test. Results and Conclusion: Fuji II modified with 10 wt.% HA showed most favorable results with respect to MH. Comparison of materials with respect to SR showed that there is a difference between them (p <0.0001; ANOVA test). Fuji II and Fuji IX modified with HA showed higher surface roughness values which should be considered.

  • Open access
  • 81 Reads
Acoustic emission for evaluating the performance of steel fiber reinforced concrete

Steel fiber reinforcement in concrete strongly enhances its ductility and toughness. This is basically due to the additional fracture mechanisms and energy to overcome the interlocking and adhesion between the fibers and the cementitious matrix. The enhancement of the final properties is measured by mechanical tests and can be assessed only at the end of loading. These processes can be well monitored by acoustic emission (AE) indices offering real-time characterization of the material’s performance much earlier than the final failure or the termination of loading. In this study, steel fiber reinforced concrete (SFRC) beams were tested in bending with simultaneous AE monitoring. Tests conducted independently in different laboratories confirm that the AE behavior at low load levels is very indicative of the amount of reinforcement and consequently, of the final mechanical properties. The reason is that the reinforcement phase is activated through shear stresses in the interphase, a mechanism that is more profound in the presence of higher fiber content, and correspondingly is absent in plain unreinforced material. This finding opens the way to characterize the effectiveness of reinforcement with just a proof loading at less than 20% of the final load bearing capacity.

  • Open access
  • 74 Reads
Early performance of mortars prepared with binary and ternary binders exposed to a real exposure class XC4 Mediterranean climate environment

At present, the reduction of CO2 emissions due to the cement manufacture is an important field of study. In this line, the production of commercial cements consisting of binary binders is relatively common. However, the manufacture of commercial cements made with ternary binders is still very low, at least in Spain. In these binders, clinker is partially replaced by two additions, and the synergetic effect of both additions can also improve the behavior of cement-based materials.

In this work, it has been studied the short-term effects of the exposure to a real in-situ environment in the microstructure and properties of mortars prepared with different binders. The in-situ condition consisted of exposing the samples to a Mediterranean climate environment in an inland location sited in Alicante province (Spain), but not too far away from the coast (10 km approximately). This location would accomplish the specifications of exposure class XC4 (corrosion induced by carbonation, cyclic wet and dry) defined by the Eurocode 2.

Reference mortars were prepared with ordinary Portland cement without additions. A binary binder was also studied, incorporating 30% limestone, as well as two ternary binders, with addition 15% limestone and 15% fly ash, and 15% limestone and 15% ground granulated blast furnace slag, respectively. The microstructure has been analyzed using mercury intrusion porosimetry, electrical resistivity and scanning electron microscopy. Absorption after immersion and mechanical strengths have also been studied. According to the results obtained, mortars with ternary binders showed a good behavior in the short-term compared to reference mortars.

  • Open access
  • 87 Reads
Effects in the short-term of combining an eco-friendly slag cement and several lightweight aggregates in relation to the microstructure and water ingress ability of mortars

Improving the sustainability of the construction sector is now a major issue. In order to reach more eco-friendly buildings and structures, the use of cements which incorporate additions as clinker replacement has reached a great development. Furthermore, the use of lightweight aggregates has a great interest regarding the sustainability of construction industry. Among other advantages, they lead to a lessening in the density of cement-based materials, increasing their thermal resistance and producing a reduction of dead loads in the construction elements.

In this research, it has been studied the effects at early hardening ages of combining a sustainable cement with high content of ground granulated blast furnace slag (type CEM III/B) and different lightweight aggregates in the microstructure and durability of mortars. In these mortars, the 50% of the volume of the sand has been replaced by lightweight aggregates, such as natural cork, expanded cork and expanded clay. Reference mortars with an ordinary Portland cement (type CEM I) has also been prepared, as well as mortars without lightweight aggregates. The samples were kept submerged in water until the testing age. The microstructure has been studied using mercury intrusion porosimetry and scanning electron microscopy. Regarding the durability, the ingress of water is one of the main ways through which the aggressive substances can go into the materials. Therefore, in this work several parameters related to water absorption have been also determined. According to the results obtained, the incorporation of slag improved the performance of the mortars with the studied lightweight aggregates.

  • Open access
  • 137 Reads
A Novel Layer Sharing-based Incremental Learning via Bayesian Optimization

Incremental learning means the methodology that continuously uses sequential input data to extend the existing network’s knowledge. The layer sharing algorithm is one of the representative methods which leverages general knowledge by sharing some initial layers of the existing network. In this algorithm, estimating how much initial convolutional layers of the existing network can be shared as the fixed feature extractors for incremental learning should be solved. However, the existing algorithm selects the sharing configurations through not a proper optimization strategy but a brute force manner. Accordingly, it has to search for all possible sharing layer cases, leading to high computational complexity. To solve this problem, we firstly define this problem as a discrete combinatorial optimization problem. However, this problem is a non-convex and non-differential optimization problem which can not be solved using the gradient descent algorithm or other convex optimization methods, even though these are the powerful optimization techniques. Thus, we propose a novel efficient incremental learning algorithm based on Bayesian optimization, which guarantees the global convergence in a non-convex and non-differential optimization problem. And the proposed algorithm can adaptively find the optimal number of sharing layers via adjusting the threshold accuracy parameter in the proposed loss function. The proposed method produces the global optimal sharing layer number in only 6 iterations without searching for all possible layer cases in experimental results. Hence, the proposed method can find the global optimal sharing layer and achieve both high combined accuracy and low computational complexity.

  • Open access
  • 78 Reads
Influence of geometry on the Acoustic Emission activity of Composite Plates

The acoustic emission (AE) monitoring technique has proven its suitability in characterizing the condition of materials and structures. In composites for construction and repair, several developments have recently been emerged involving mainly fracture mode evaluation based on the waveform parameters. However, the propagation distance, the size and the shape of the specimens strongly influence the recorded signals. Although the effect of wave propagation distance has been studied, the influence of the lateral dimension of the plate (width) has not been given proper attention, not allowing the extrapolation of results obtained from small coupons to large scale plates. The study examines wave propagation from actual AE sources as well as artificial ones in textile-reinforced cement (TRC) plates highlighting the strong differences in the results that are attributed just to the shape and size of the specimens even though the source of emission is unchanged. The aim is to highlight that the interpretation of AE trends should be firmly connected to the shape and size of the specimens.

  • Open access
  • 51 Reads
Reinforcement effectiveness in composites evaluated by low load acoustic emission

Fiber reinforcement is well known to dominate the post-cracking behavior of composites. The fibers’ contribution is also important however, at the pre-peak stage as they restrain cracking. The sensitivity of AE, enables characterization in the micro-scale even during this pre-cracking regime and before serious damage evolves. This study focuses on parameters obtained at low level of loading before cracks appear in any measurable form in the material. As model materials, additively manufactured fibrous polymer composites and cementitious composites are used, showing that the content and the effectiveness of the reinforcement phase and the properties of the fiber/matrix interphase are reflected on the early AE activity allowing projections to the final mechanical properties.

  • Open access
  • 95 Reads

Acoustic emission (AE) is commonly applied in laboratory and in-situ for structural condition evaluation of materials. Its advantages concern the non-invasive and safe application, while the developments in sensors’ technology and signal analysis, make it a suitable technique for monitoring of the structural condition. Concerning cementitious composite plates, AE parameters have proven its potential to characterize not only the fracture mode but also the developing strain field before visible damage evolves. Matrix cracking events are recorded as relatively short elastic signals occupying high frequencies while debonding between layers or fiber pull-out result in longer signals with lower frequency content. However, the capacity of the technique is not fully exploited in-situ mainly because of factors that mask the original source information. Wave propagation distance and exact path, reflections, dispersion due to plate geometry and heterogeneity usually result in attenuating the signal and elongating it in time domain. These factors change the received AE waveform and therefore, may complicate the evaluation outside laboratory where the sample dimensions are usually larger. In this study, textile reinforced cement plates with different widths and curvatures are loaded in bending with concurrent AE monitoring. The aim is to evaluate the influence of the geometry in order to check if conclusions based on laboratory small straight specimens can be upgraded to larger scales and different geometries.

  • Open access
  • 62 Reads
Acoustic emission for identification of the dominant stress component in polymer composites at early loads

Carbon Fiber Reinforced Polymer (CFRP) composites are broadly used in many engineering applications. Their inherent anisotropy due to different fiber orientations in the individual layers can be considered an advantage since the maximum strength of the composite component can be designated in preferential loading directions. However, this anisotropy leads to multiaxial stress conditions at the same time, complicating the damage sequence and the mechanical response of CFRPs. Identification of these multiaxial conditions at early loading stages is of paramount importance in order to predict the upcoming structural response of the material. Acoustic Emission (AE) is applied in this study to various CFRP composite laminates with different stacking sequences, in which different multiaxial conditions are generated. Laminates consisting of 30o off-axis plies are characterized by dominant shear stresses, whereas in laminates with 60o layers transverse normal stresses govern the stress state. Through quasi-static and incremental loading, it is shown through this research work that certain AE features can be used in order to identify the dominant stress component rather than just the occurring damage mode even at early loading stages, before severe fracture influences the mechanical capacity of the material. This is of great importance in cases that detrimental shear stresses are generated in the material, leading to important interlaminar delaminations and mechanical deterioration. AE can be used in this direction in order to predict the upcoming damage modes and to take the necessary measures to avoid final catastrophic failure.