Solid Foam Research Articles

Navigation versus experience: providing training in accurate lumbar pedicle screw positioning

PurposeAccurate placement of spinal pedicle screws (PS) is mandatory for good primary segmental stabilization allowing consequent osseous fusion, requiring judgmental experience developed during a long training process. Computer navigation offers permanent visual control during screw manipulation and has been shown to significantly lower the risk of pedicle perforation. This study aims to evaluate whether safety, accuracy, and judgmental skills in screw placement, comparable to an experienced surgeon, can be developed during training using computer navigation.MethodsLumbosacral PS were placed in 18 patients in a prospective setting, in one segment side with conventional fluoroscopy by a senior spine-surgeon, and computer navigated on the other side by a trainee without prior experience in the technique. At the beginning and at the end of the study, PS were placed freehand in solid foam models by the trainee. PS placement time, intraoperative placement revisions, PS placement accuracy on postoperative CT scans, and postoperative complications were assessed.ResultsSignificant improvement of trainee’s PS placement accuracy (Sclafani score 8.2–8.83; p = 0.006) and time (13.3–6.8 min per screw; p = 0.005) to a similar level as the experienced surgeon state (5.2–4.1 min per screw; p = 0.39) was explored; similar improvement was explored in the foam models. The number of intraoperative placement revisions kept on a low level for surgeon (3.3–0.0%) and trainee (5.1–2.6%) during the whole study, no postoperative complications occurred.ConclusionNavigated PS insertion allows safe teaching from the early beginning of surgical training, due to steady intraoperative control on PS placement. Adequacy of PS placement is similar to screws placed by an experienced surgeon. Progress in judgmental skills in screw placement can be gained rapidly by the trainee, which can also be transferred to non-computer navigated PS placement.

Automated Continuous Production Line of Parts Made of Metallic Foams

The paper presents an automated continuous production line (7 m × 1.5 m × 1 m) of high-quality metallic foams using a powder metallurgical method. This continuous production line was used to obtain metal foam parts and/or components by heating the foamable precursor material at melting temperatures close to the temperature of the metallic matrix and cooling the formed liquid metallic foam (in liquid state), which then results in a solid closed-cell metallic foam. This automated continuous production line is composed of a continuous foaming furnace, a cooling sector and a robotic system. This installation has enabled a technological breakthrough with many improvements solving some technical problems and eliminating the risks and dangers related to the safety of workers due to the high temperatures involved in this process. The whole process becomes automatic without any need for human intervention.

Laser forming of sandwich panels with metal foam cores

Over the past decade, laser forming has been effectively used to bend various metal foams, opening the possibility of applying these unique materials in new engineering applications. The purpose of the study was to extend laser forming to bend sandwich panels consisting of metallic facesheets joined to a metal foam core. Metal foam sandwich panels combine the excellent shock-absorption properties and low weight of metal foam with the wear resistance and strength of metallic facesheets, making them desirable for many applications in fields such as aerospace, the automotive industry, and solar power plants. To better understand the bending behavior of metal foam sandwich panels, as well as the impact of laser forming on the material properties, the fundamental mechanisms that govern bending deformation during laser forming were analyzed. It was found that the well-established bending mechanisms that separately govern solid metal and metal foam laser forming still apply to sandwich panel laser forming. However, two mechanisms operate in tandem, and a separate mechanism is responsible for the deformation of the solid facesheet and the foam core. From the bending mechanism analysis, it was concluded on the maximum achievable bending angle and the overall efficiency of the laser forming process at different process conditions. Throughout the analysis, experimental results were complemented by numerical simulations that were obtained using two finite element models that followed different geometrical approaches.

Foams as carrier systems for pharmaceuticals and cosmetics

Foams are becoming more and popular in several areas of our lives, including pharmaceutics and cosmetics. They are colloid systems where gas is dispersed in liquid phase Active ingredient bearing pharmaceutical foams are traditionally applied topically (dermal, local rectal, vaginal), but formulations for other delivery routes (e.g. nanosystems parenterally, solid foams orally) are also available. Numerous advantages are attached to foams when compared to traditional vehicles, resulting in increased patient compliance. Amongst others, the suitable composition contributes to quick, oily residue‑free and convenient application even on large or hairy areas, as well as to good drug transfer rate.

Freeze Casting is a Facile Method to Create Solid Solution Alloy Foams: Cu–Ni Alloy Foams via Freeze Casting

Porous metals have attracted great attention for their functional and structural applications; however, they often possess limited applicability in their pure form for the areas requiring decent strength and corrosion resistance. In this study, pure copper (Cu), pure nickel (Ni), and Cu–Ni alloy foams with five different compositions are successfully fabricated using freeze casting, resulting in open‐pore structures with varied porosity (from 55% to 75%). Their varied morphologies and crystal sizes are compared, and the lattice parameters and crystal sizes are calculated. The corrosion resistance of the synthesized Cu–Ni alloy foams is superior to those of the pure Cu and Ni foams. The weight loss rate of the Cu7Ni3 alloy foam is six times and five times slower than those of the pure Ni and pure Cu foams in a sulfuric corrosive environment, respectively. The yield strength of Cu7Ni3 alloy foam (53 ± 2% porosity) is 72 ± 2 MPa and its yield strength when normalized by the Gibson‐Ashby model is the largest with a value of up to 852 ± 3 MPa. The elastic modulus and hardness values are varied in the range of 73.4–152.4 GPa and 1.6–4.7 GPa, respectively, depending on the composition of the alloy foam.

Simulation of bubble growth during the foaming process and mechanics of the solid foam

Elastomeric foams are widely used in different types of applications where different material properties are of interest in each application. All of these properties are governed by the microstructure and the properties of the material matrix. Studying the evolution of the microstructure experimentally is extremely challenging. Thus, here we use direct numerical simulations to gain an insight into the changes that happen from the creation of the gas bubbles in the liquid state, until the solidification into a cellular morphology. Furthermore, the resulting microstructure is then used directly in simulations of solid mechanical testing to determine the mechanical properties of the foam. The matrix fluid is assumed to be Newtonian and incompressible. A linear elastic isotropic material model for the solidified polymer was used to obtain the solid foam properties. The foam was described by a representative volume element (RVE), where a small number of bubbles was randomly distributed. Using this approach, the RVE can describe the bulk behavior of the foam, while remaining computationally tractable. Microstructures with volumes fraction of over 90% (2D) and 45% (3D) are accurately captured. In addition, the influence that the bubble growth rate and the initial bubble distribution of the fluid simulations have on the solid foam properties was studied.

Macroporous hybrid Pickering foams based on carbon nanotubes and cellulose nanocrystals

The association of nanoparticles with complementary properties to produce hybrids is an underestimated way to develop multifunctional original architectures. This strategy is used to prepare simple, low‐cost, and environmentally friendly method to fabricate ultra-low density alveolar foam reinforced with carbon nanotubes (CNTs). This paper investigates the ability of cellulose nanocrystals (CNCs) to produce highly stable oil-in-water Pickering emulsions and to efficiently disperse carbon nanotubes in water to form three-dimensional macroporous conductive foam. It is shown that both single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) are strongly linked to CNCs by non-covalent interactions, preserving the intrinsic properties of both nanoparticles. Homogeneous surfactant-free emulsions with a droplet diameter of 6 µm are produced. Once concentrated, they can form stable high internal phase emulsions. Incorporating CNTs into these CNC-based emulsions was shown to improve their rheological properties. Freeze-drying the concentrated emulsions produces ultra-low density solid foams (14 mg·cm−3) with several levels of porosity controlled by the emulsification step. Loading CNCs with only 2–4 wt% of CNTs, decreases the electrical resistivity of the foam to 104 Ω cm in high relative humidity. The mechanical and electrical properties are studied and discussed in light of the resulting specific foam structure.

Deformation Field in Diametrically Loaded Soft Cylinders

Deformation fields at the surface of diametrically squeezed shallow cylinders in the large deformation regime are measured experimentally and numerically for different material behaviour in the large deformation regime. By means of a digital image correlation method optimized for large displacements, strain fields are measured and compared with finite element simulations. Assuming a neo-Hookean behaviour for cylinders made of rubber silicone, the strain field is found to be in quantitative agreement with non-linear finite element simulations up to the highest deformations reached in our experiments (15%). For materials that follow an elastoplastic constitutive law, agreement is lost after few percents of deformation and location of the strain field differences are identified up to strains as high as 30%. Strain field evolution is also measured for solid foam cylinders up to 60% of global deformation strain. This method that can be applied to a broad variety of materials, even in the occurrence of large deformations, provides a way to study quantitatively local features of the mechanical contact.

Composite Roofing of PIR Sandwich Panels: Numerical and Experimental Approach

The PIR panels are composite elements made of an inner core of poly-iso-cyanurate (PIR) solid foam injected between two external sheets of fabric or polypropylene. When testing composite samples having such structure the obtained results (in terms of compression and bending resistances) usually reach relatively high levels. This suggests a possible use of panels in applications under distributed loading and not only as simple thermos-insulating layers. A large range of applications thus derives, i.e. cladding of timber roofing, sloping support for hydro-insulation in flat concrete roofs, or hydro-insulation support for trapezoidal sheeting for flat or even curved roofs. The paper presents an experimental and numerical study on two practical cases, i.e. flat concrete roofs and trapezoidal sheets roofs respectively. Standard testing of samples, taken from the composite core and from the membrane, have been performed in the frame of present investigation together with testing of some composite samples in compression and bending. Typical roof loading as gravity (dead + snow) load or wind suction have been analysed in the numerical simulation (reproducing the test arrangement) in order to assess panel response and to evaluate the practical applicability of these composites. Conclusions on stress distribution and deflections both under gravity and uplift load are presented. The high resistance of PIR composite panels (well beyond design loads calculated by the code) is confirmed, clearly indicating their practical applicability in the cases under study. This also meets the producer requirements who intends to obtain in the future an official agreement allowing to supply these particular composite solutions using PIR on the market.

Experimental Study on A Sloshing Mitigation Concept Using Floating Layers of Solid Foam Elements

A sloshing mitigation concept taking advantage of floating layers of solid foam elements is proposed in the present study. Physical experiments are carried out in a liquid tank to investigate the hydrodynamic mechanism of this concept. Effects of the foam-layer thickness, excitation amplitude, and excitation frequency on the sloshing properties are analyzed in detail. It is found that the floating layers of solid foam elements do not evidently affect the fundamental natural sloshing frequency of the liquid tank evidently among the considered cases. At the resonant condition, the maximum wave height and dynamic pressure are greatly reduced as the foam-layer thickness increases. Higher-order pressure components on the tank side gradually vanish with the increase of the foam-layer thickness. Cases with different excitation amplitudes are also analyzed. The phenomenon is observed when the wave breaking in the tank can be suppressed by solid foam elements.

Micromixing efficiency in a multiphase reactor with a foam block stirrer

ABSTRACTA rotating foam reactor (RFR), which comprises a solid foam block stirrer as opposed to the agitator blade in stirred tanks, has recently received a significant amount of research interest due to its high mass transfer rates. For a deeper insight into the RFR the work herein investigated the micromixing efficiency of the RFR in terms of segregation index (Xs) using the iodide‐iodate reaction system. The effects of various operating parameters including injection time, rotational speed, acid concentration, volume of liquid, volumetric ratio, and gas flow rate on segregation index were systematically examined. Results showed that the segregation index remained constant when injection time exceeded 100 s. Moreover, the Xs increased with an increase in acid concentration but decreased with an increase in rotational speed, volume of liquid, volumetric ratio, and gas flow rate. Micromixing time was also calculated based on the incorporation model and was established to range from 1.1 × 10−3–4.5 × 10−2 s, which is much shorter than that of conventional reactors. The results herein demonstrate that an RFR exhibits excellent micromixing efficiency and has a significant potential for use in chemical industries.

The mechanical properties of monodisperse foam scaffolds

Tissue engineering scaffolds provide mechanical supports and microenvironment for cells to grow in the third dimensionality (3D). Inspired by the recent advance to fabricate monodisperse foam scaffold by self-assembly of monodisperse liquid foam created by the microfluidic method, we investigated the mechanical properties of an open-cell solid foam with pores packed in the face-centered cubic (FCC) structure. We first characterized the microstructural geometry of solid foam with different porosities made by the microfluidic technique. We then developed both analytical and finite element method (FEM) models based on the measured geometric features. We computed mechanical parameters such as the elastic modulus, Poisson's ratio, and the shear modulus. Finally, we performed mechanical measurements of FCC solid foam fabricated by a 3D printer. All experimental, analytical, and numerical results show good agreement, which validate the FEM models.

Computational Analysis of Nonuniform Expansion in Polyurethane Foams.

This paper computationally investigates heterogeneity in the distribution of foam fraction in chemically expanding blown polyurethane foam. The experimentally observed disparity in the volumes of expanded foam when an equal mass of the foaming mixture was injected into tubes of different dimensions motivated this study. To understand this phenomenon, attributed to local variations in the thermal and rheological properties of the expanding system, we explore available data from free-rise foam-expansion experiments in different geometries. Inspired by the mathematical framework for the microstructure modelling of bubble growth in viscous liquids, we study the reacting mixture as a continuum and formulate appropriate mathematical models that account for spatial inhomogeneity in the foam-expansion process. The nonlinear coupled system of partial differential equations governing flow was numerically solved using finite-volume techniques, and the associated results are presented and discussed with graphical illustrations. The proximity of the foaming-mixture core to the external environment and the thickness of a thermal-diffusion layer formed near the bounding geometry was seen to influence the distribution of the foam fraction. Our simulations showed an average spatial variation of about 1.1% in the distribution of solid foam fraction from the walls to the core, as verified with data from CT scan analysis of the expanded foam. This also reflects the distribution of void fraction in the foam matrix. The models were validated with experimental data, and our results favourably compared with the experiment observations.

Edible solid foams as porous substrates for inkjet-printable pharmaceuticals

The aim of this study was to investigate new porous flexible substrates, i.e., solid foams that would serve as a carrier with a high ink absorption potential for inkjet printable pharmaceuticals. Propranolol hydrochloride was used as a model active pharmaceutical ingredient (API). Pharmaceutically approved and edible cellulose derivatives and gums together with different additives were evaluated as a base for the substrate. Different methods for preparation of a solid foam such as freeze-drying, vacuum oven drying and drying at room temperature were explored. Only freeze-drying of the polymeric solutions resulted in the desired porous and flexible, but mechanically stable, soft sponge-like substrates with hydroxypropyl methylcellulose (HPMC)-based solid foams being the most suitable for the use in continuous inkjet printing. The plasticized HPMC foams had a superior absorption capacity and fast penetration speed for the different solvents due to the open cell pore structure and higher porosity as compared to nonplasticized additive-free foams, although, the latter were less hygroscopic. The produced solid foams were well suited for inkjet printing of high volumes of API-containing ink. The inkjet-printed API was immediately released from the dosage forms upon contact with the dissolution medium. This work demonstrates that the fabricated solid foams, based on plasticized HPMC, show a great potential as porous carriers in the fabrication of high dose dosage forms by inkjet printing.

Bulk Photodriven CO2 Conversion through TiO2@Si(HIPE) Monolithic Macrocellular Foams

AbstractOperating photo‐induced reactions exclusively on catalyst surfaces while not exploiting the full catalyst volume generates a major footprint penalty for the photocatalytic reactor and leads to an inefficient use of the catalytic material. Photonic investigations clearly show that the solid foams have a strongly multidiffusive character, with photons being significantly trapped within the sample cores while addressing a photon mean free path lt = 20.1 ± 1.3 µm. This 3D process both greatly limits back‐reactions and promotes outstanding selectivity toward methane (around 80%) generation, and even ethane (around 18%) through C‐C coupling reaction, with residual carbon monoxide and dihydrogen contents (around 2%). Silica–titania TiO2@Si(HIPE) self‐standing macrocellular catalysts lead to optimal efficient thicknesses up to 20 times those of powders, thereby enhancing the way for real 3D‐photodriven catalytic processes above the millimeter scale and up to a 6 mm thickness. A rather simple Langmuir–Hinshelwood based kinetic model is proposed which highlights the strong dependence of photocatalytic reaction rates on light scattering and the crucial role on oxidation back‐reactions. In addition, a strong correlation between light attenuation coefficient and photon mean free path and median pore aperture diameter is demonstrated, offering thus a tool for photocatalytic behavior prediction.

Soft lamellar solid foams from ice-templating of self-assembled lipid hydrogels: organization drives the mechanical properties

Ice-templating soft self-assembled lipid hydrogels with different morphologies (fibrous vs. lamellar) of comparable elastic properties result in macroporous solids with extremely different mechanical properties.

Ultrasound transmission through monodisperse 2D microfoams.

While the acoustic properties of solid foams have been abundantly characterized, sound propagation in liquid foams remains poorly understood. Recent studies have investigated the transmission of ultrasound through three-dimensional polydisperse liquid foams (Pierre et al., 2013, 2014, 2017). However, further progress requires to characterize the acoustic response of better-controlled foam structures. In this work, we study experimentally the transmission of ultrasounds through a single layer of monodisperse bubbles generated by microfluidics techniques. In such a material, we show that the sound velocity is only sensitive to the gas phase. Nevertheless, the structure of the liquid network has to be taken into account through a transfer parameter analogous to the one in a layer of porous material. Finally, we observe that the attenuation cannot be explained by thermal dissipation alone, but is compatible with viscous dissipation in the gas pores of the monolayer.

Removal of Textile Dyes Present in Effluents by Adsorption in Polyurethane Foams Derived from Vegetable Oil

Large amounts of effluents, some even untreated, used in the dyeing in-dustries are dumped into natural water provoking a huge environmental impact daily. The Analytical Chemistry and Polymer Technology Group from the University of Sao Paulo in Sao Carlos, Brazil developed the polyurethane foam. It is a unique type of foam produced from vegetable oil—a renewable natural raw material. The objective of the research was to verify the effectiveness of adsorption of textile dyes in effluents through the polyurethane foam derived from vegetable oil. The dye samples collected from an industry in the dying segment in the city of Passos, Minas Gerais State, Brazil, were prepared in various predetermined concentrations. The percolation in thermostatic glass column containing polyurethane foam derived from vegetable oil was used as analytical method, with known mass, pressed in the form of powder between two solid foam disks containing two millimeters of thickness.

Kinetics of azodicarbonamide decomposition in the presence of an initiator for obtaining solid foams

Kinetics of azodicarbonamide decomposition in the presence of an initiator for obtaining solid foams

FORMULATION AND EVALUATION OF HERBAL SHAMPOO

Aim and Objective: The aim of this present study is to prepare and formulate an herbal shampoo and to assess its physiochemical function that emphasis on safety, efficacy, eliminating harmful synthetic ingredient, and substitute with safe natural ingredients.Methods: The formulation of shampoo using the extracts of Emblica officinalis, Hibiscus rosa-sinensis, Acacia concinna, Sapindus indica, Eclipta prostrata, Aloe barbadensis, and Cassia auriculata in different proportions. Evaluation of organoleptic, physicochemical, and performance tests in terms of visual assessment, wetting time test, pH, assurance of solid contents, surface tension, detergency, dirt dispersion, conditioning performance, foam volume, and stability was performed.Results: The created cleanser was clear and good appealing. It demonstrated good froth stability, detergency, good cleansing, small bubble size, low surface strain, and execution of good conditioning.Conclusion: The physicochemical evaluation of the formulated shampoo showed ideal results. However, to improve its quality, productperformance, and safety, further development was required.