Pozzolan Based 3D Printing Composites: From the Formulation Till the Final Application in the Precision Irrigation Field

A new eco-composite polymer for material extrusion fabrication based on fine fraction pozzolan waste was developed. In addition, the composite materials obtained were used to produce a self-watering pot with complex geometry and a permeable porous part to regulate the passage of water from the storage area to the roots of the plant. Moreover, the system was devised with a cover characterized by a UV-B barrier film. The results have shown the possibility of the 3D printing of complex geometric parts as microporous structures or thin films using a composite based on poly lactic acid (PLA) and pozzolan. The pozzolan has an effect of reinforcement for the composite and at the same time improves the cohesion between the layers of the part during printing.

Robocasting of Single and Multi-Functional Calcium Phosphate Scaffolds and Its Hybridization with Conventional Techniques: Design, Fabrication and Characterization

In this work, dense, porous, and, for the first time, functionally-graded bi-layer scaffolds with a cylindrical geometry were produced from a commercially available hydroxyapatite powder using the robocasting technique. The bi-layer scaffolds were made of a dense core part attached to a surrounding porous part. Subsequently, these bi-layer robocast scaffolds were joined with an outer shell of an antibacterial porous polymer layer fabricated by solvent casting/salt leaching techniques, leading to hybrid ceramic-polymer scaffolds. The antibacterial functionality was achieved through the addition of silver ions to the polymer layer. All the robocast samples, including the bi-layer ones, were first characterized through scanning electron microscopy observations, mechanical characterization in compression and preliminary bioactivity tests. Then, the hybrid bi-layer ceramic-polymer scaffolds were characterized through antimicrobial tests. After sintering at 1300 °C for 3 h, the compressive strengths of the structures were found to be equal to 29 ± 4 MPa for dense samples and 7 ± 4 MPa for lattice structures with a porosity of 34.1%. Bioactivity tests performed at 37 °C for 4 weeks showed that the precipitated layer on the robocast samples contained octacalcium phosphate. Finally, it was evidenced that the hybrid structure was effective in releasing antibacterial Ag+ ions to the surrounding medium showing its potential efficiency in limiting Staphylococcus aureus proliferation during surgery.

A novel design, analysis and 3D printing of Ti-6Al-4V alloy bio-inspired porous femoral stem

The current study is proposing a design envelope for porous Ti-6Al-4V alloy femoral stems to survive under fatigue loads. Numerical computational analysis of these stems with a body-centered-cube (BCC) structure is conducted in ABAQUS. Femoral stems without shell and with various outer dense shell thicknesses (0.5, 1.0, 1.5, and 2 mm) and inner cores (porosities of 90, 77, 63, 47, 30, and 18%) are analyzed. A design space (envelope) is derived by using stem stiffnesses close to that of the femur bone, maximum fatigue stresses of 0.3σys in the porous part, and endurance limits of the dense part of the stems. The Soderberg approach is successfully employed to compute the factor of safety Nf > 1.1. Fully porous stems without dense shells are concluded to fail under fatigue load. It is thus safe to use the porous stems with a shell thickness of 1.5 and 2 mm for all porosities (18–90%), 1 mm shell with 18 and 30% porosities, and 0.5 mm shell with 18% porosity. The reduction in stress shielding was achieved by 28%. Porous stems incorporated BCC structures with dense shells and beads were successfully printed.

Structural and aggregate composition features of southern variant natural forest edaphotopes of Ukrainian steppe zone

The natural forests of the southern variant of the steppe zone of Ukraine (according to the classification of O. L. Belgard) are located on the territory of the former porous part of the Dnieper. The properties of edaphotopes of these forests were studied in detail by the staff of the Comprehensive expedition of the Oles Honchar Dnipro National University for the study of forests in the steppe zone of Ukraine (A. P. Travleev, N. A. Bilova, A. A. Dubina, K. M. Bozhko). However, there are no data on the structural and aggregate composition of the genetic horizons of edaphotopes of natural forests of the southern variant of the steppe zone of Ukraine, established by classical methods of determination. This work is devoted to the coverage of these features. As a result of research it is established that the best conditions for the formation of structural aggregates are characteristic of the upper horizons of all studied soils and especially for the forest chernozem in the conditions of northern exposure. The highest content of agronomically valuable structural aggregates is characterized by forest chernozem in the conditions of northern exposure of the ravine, the lowest – meadow-forest soil of thalweg, and forest chernozem in the conditions of southern exposure occupies an intermediate value. The eluvial horizons of ravine edaphotopes differ most contrastingly from the illuvial horizons in the conditions of northern and southern exposures. Eluvial horizons are characterized by a reduced fraction content of > 10 mm and increased values ​​of the structural coefficient compared to illuvial horizons. In the thalweg, these differences are not so clear. The upper horizons have an increased content of water-resistant fraction size > 5 mm compared to the horizons below. With depth in all studied edaphotopes there is an increase in the content of the fraction size < 0.25 mm with depth. Among the upper horizons, the highest content of water-resistant fraction size > 5 mm and the lowest content of fraction < 0.25 mm differs meadow-forest soil in thalweg conditions. Very close to the meadow-forest soil in terms of the values ​​of the respective fractions is forest chernozem in the conditions of northern exposure. Forest chernozem in the conditions of southern exposure differs by the lowest content of water-resistant fraction size > 5 mm and the highest content of fraction size < 0.25 mm among all studied soils. Eluvial horizons of forest chernozems of northern and southern exposures differ from illuvial horizons by reduced content of water-resistant fractions of > 5 and 5–3 mm. The eluvial horizons of the meadow-forest soil of the thalweg differ from the illuvial horizon by a sharp decrease in the content of the water-resistant fraction of 1–0.5 mm. A comparative analysis of the structural and aggregate composition of the studied edaphotopes revealed that the best conditions for the formation of agronomically valuable fractions are characteristic of the forest chernozem of the northern exposure. As a result of comparing the characteristics of eluvial and illuvial horizons, it was found that the change of eluvial process to illuvial is accompanied by a sharp decrease in forest chernozems content of agronomically valuable fractions during dry sieving, as well as an increase in water resistance. In meadow-forest soils, this transition is characterized by a sharp decrease in the content of agronomically valuable fractions in the illuvial horizon during wet sieving compared to the eluvial horizon.

TORTUOSIMETRIC OPERATOR FOR COMPLEX POROUS MEDIA CHARACTERIZATION

Geometric tortuosity is one of the foremost topological characteristics of porous media. Despite the various definitions in the literature, to our knowledge, they are all linked to an arbitrary propagation direction. This article proposes a novel topological descriptor, named M-tortuosity, by giving a more straightforward definition, describing the data regardless of physicochemical processes. M-tortuosity, based on the concept of geometric tortuosity, is a scalable descriptor, meaning that information of several dimensions (scalar, histograms, 3D maps) is available. It is applicable on complex disconnected structures without any arbitrary definition of entry and exit. Topological information can be represented by aggregation into a unique scalar descriptor for classification purposes. It is extended by iterative erosions to take into account porous structure narrowness, especially bottleneck effects. This new descriptor, called M-tortuosity-by-iterative-erosions, describes tortuosity of the porous part as seen by a spherical particle of given size walking along the network. Boolean models are used to simulate different porous media structures in order to test the proposed characterization.

Metallic skeletons as reinforcement of new composite materials applied in orthopaedics and dentistry

Purpose: The article concerns the development of completely new groups of composite materials that can be used to produce functional replacements for damaged bones or teeth. Design/methodology/approach: A selective laser sintering was used to produce the reinforcement of those materials from titanium and its Ti6Al4V alloy in the form of skeletons with pores with adjustable geometric features. The matrix of those materials is either air or crystallised from the liquid AlSi12 or AlSi7Mg0.3 alloys condition after prior vacuum infiltration or human osteoblast cells from the hFOB 1.19 (Human ATCC - CRL - 11372) culture line. Findings: The porous material may be used for the non-biodegradable scaffold. After implantation into the body in the form of an implant-scaffold one, it allows the natural cells of the patient to grow into the pores of the implant, and it fuses with the bone or the appropriate tissue over time. The essential part of the implant-scaffold is the porous part inseparably connected with the core of solid materials. Into pores can grow living cells. Research limitations/implications: Biological-engineering composite materials in which natural cells were cultured in the pores in the laboratory next are combined as an artificial material with the natural cells of the patient in his/her body. Practical implications: The hybrid technologies of the all group of those materials were obtained and optimised. Numerous structure research was carried out using the most modern research methods of contemporary materials engineering, and mechanical tests and biological research involving the cultivation of natural cells were realised. Originality/value: The results of the research indicate the accuracy of the idea of implementing a new group of biological-engineering materials and the wide possibilities of their application in regenerative medicine.

Irreversible Thermal Expansion of Replicated Aluminium Foam

There was found irreversible thermal expansion of large items made of the replicated aluminium foam during the extraction of soluble filler from Al-NaCl composite. Sources of the phenomena were investigated. The expansion is discovered to be caused by incomplete contraction of the porous metal due to oxidation of its internal porous surface during thermal cycling with air and water presence. Significant role of oxide film defects in the expansion process was exposed. There was gained information on dependencies of the irreversible thermal expansion on temperature of the extraction process and metal foam pore size. Measurements of the expansion dynamics showed its finite character. It was also noted that the expansion is limited by the thermal expansion coefficient of used alloy. Finally correction coefficients were obtained that, being applied to nominal sizes of a porous part, compensates the expansion.

An Overview of Powder Metallurgy (PM) Method for Porous Nickel Titanium Shape Memory Alloy (SMA)

NiTi is categorized as a Shape Memory Alloy (SMA) that has been commercially studied and used in biomedical industry due to two main unique properties, Pseudoelastic (PE) and Shape Memory Effect (SME). Combined with biomimetic properties to human bone, NiTi has the potential to be applied as implants by engineered manufacturing process. The common manufacturing by casting has some challenges in order to obtain intrinsic and miscellaneous design of NiTi parts leash to explore more using powder metallurgy (PM) method that expected to get the porous structure. This paper aims to provide an overview of processing NiTi by conventional PM method which could contribute in focusing porous part that suits for biomedical and implants.

Reliability Evaluations of an Offshore Platform With Partial Porous Cylinders due to Wave and Seismic Forces

In the present study, the partial porous cylinder, which is composed of a porous part located near free surface and a rigid part bounded top and bottom by impermeable end caps, is suggested to reduce the effect of wave forces. In order to calculate the wave force acting on the partial porous cylinder the fluid domain is divided into three regions, and the scattering wave in each fluid region is expressed by an Eigen-function expansion method. Applying Darcy’s law to the porous boundary condition, the effect of porosity can be simplified. Using the wave and the seismic forces, the dynamic response evaluations of the offshore platform with partial porous cylinders are carried out through the modal analysis and the substructure method based on the effect of soil-structure interaction. The displacement and the bending stress at critical structure members are computed using the Monte Carlo Simulation (MCS). Using the reliability index based on the results from MCS, the reliability evaluations of the offshore platform with partial porous cylinders are examined.

Fabrication of Functionally Graded ZTA Ceramics Using a Novel Combination of Freeze Casting and Electrophoretic Deposition

Functionally graded zirconia toughened alumina (ZTA) ceramics have been fabricated from aqueous suspension with an open porous and aligned lamellae structure on one side and a dense layer on the other side. A novel combination of two processes has been merged to achieve such graded structures, i.e. unidirectional freeze casting and electrophoretic deposition (EPD). A custom-designed apparatus has been built in which a controlled double side cooling has been realized in conjunction with the possibility to introduce an electric field over the ceramic slurry prior to the freezing process. A square wave pulsed DC voltage has been used in the EPD process in order to avoid electrolysis of water. Suitable duty cycle of applied pulse voltage could gain bubble-free deposition. The thickness of the dense layer is controlled by tuning voltage, duty of cycle, pulse width and deposition time. It was shown that thicknesses up to 500μm could be achieved. The microstructure of the porous part is controlled by adjusting the temperature during the freezing process. Using temperatures between -1 and -25°C the channel width changed from 220 to 40μm, respectively.