Penetration Barrier Research Articles

Electrical-Field-Driven Tunable Spectral Responses in a Broadband-Absorbing Perovskite Photodiode.

Controllably manipulating the spectral response of broadband-absorbing semiconductors is crucial for developing wavelength-selective optoelectronic devices. In this article, we report for the first time, the bias-dependent spectral responses for a metal-halide perovskite photodiode. Tunable external quantum efficiencies in the short- and long-wavelength regimes, and the full spectral range (ca. 300-800 nm) are observed when the device is operated under short-circuit, and forward and reverse bias conditions, respectively. This observation is understood by the interplay of wavelength-dependent penetration depth and barrier formation within the photodiode device stack. The general applicability of this concept is confirmed by a systematic study on a series of mixed-halide perovskite devices. These results suggest that the proposed concept allows as a promising platform and should inspire further exploration of multispectral responsive optoelectronic devices.

Mechanochemical Degrafting of a Surface-Tethered Poly(acrylic acid) Brush Promoted Etching of Its Underlying Silicon Substrate.

The stability of surface-tethered polyelectrolyte brushes has been investigated during the past few years. We have previously reported on the degrafting of poly(acrylic acid) (PAA) polymer brushes from flat silicon substrates. Here, we present a detailed study on the effects of NaCl concentration and the grafting density and molecular weight on the stability of PAA brushes during incubation in 0.1 M ethanolamine buffer (pH 9.0) solutions. Without NaCl in the buffer solution, the PAA brushes remain intact. Adding NaCl facilitates etching of the substrate due to accelerating dissolution of the top silica layer and promoting degrafting of the PAA chains. The PAA grafting density and molecular weight play an important role in the substrate etching by affecting the penetration barrier and local concentration of the etchants. We also tested the stability of self-assembled monolayers (SAMs) made of hydrophobic alkyltrichlorosilanes anchored on silicon substrates. The results demonstrated that the SAMs were too thin to protect the substrates from etching, in contrast to thick poly(methyl methacrylate) brushes. Our findings suggest that both polymer brushes (especially polyelectrolyte brushes) and SAMs anchored to silicon substrates may undergo erosion/etching on the substrates in basic environments, which compromises their stability and therefore jeopardizes their applications in coating, biosensing, and so forth.

The nano gold rush: Graphynes as atomic sieves for coinage and Pt-group transition metals

Graphyne two-dimensional materials have been envisaged as potential useful membranes for applications such as gases separation and water desalination with very high salt rejection rates. The graphyne acetylenic linkages length defines its acetylenic holes size, thus offering a way of tuning their membrane permeability. The present study evaluates, based on density functional theory simulations, the possible use of γ-graphyne, the graphyne with the smallest acetylenic hole, to sieve Transition Metal (TM) atoms. The systematic study comprises obtaining adsorption minima for the 30 3d, 4d, and 5d TMs along with transition states for the diffusion across the γ-graphyne layer. The study reveals very small penetration barriers, below 0.5 eV, for late 3d, Pt-group, and coinage metals, whereas water molecules are found to display high penetration energy barriers above 5 eV, even when accounting for possible γ-graphyne out-of-plane deformations facilitating the water trespassing. The adsorption energy distribution of the adsorbed TMs shows that Pd and Au sieving by γ-graphyne would be specially enhanced versus their anchoring on the γ-graphyne carbon framework, thus pointing γ-graphyne as a possible effective membrane to sieve, particularly, late transition metals.

Aggregation-induced emission with enhanced two-photon absorption of dicyanomethylene-benzopyran with polyether chain for blood-brain barrier penetration

The potential application of high-efficiency luminescent materials with aggregation-induced emission (AIE) behaviour for central nervous system functional imaging is a promising emerging field of research. Whereas, their brain penetration and actual blood-brain barrier crossing mechanism remained scarcely understood. Herein, we report three D-π-A chromophores (DCO1-3) with AIE characteristics and two-photon activities. In particular, one of the compounds DCO3 displays large two-photon absorption cross-sections of up to 880 GM with 90% water fraction (fw). Meanwhile, introduced polyether chains endow them with appropriate biocompatibility and potential for central nervous system targeting. Its blood-brain barrier (BBB) penetration capability was evaluated in the cell model, indicating promising transcytosis efficiency via microtubule trafficking. The results offer a comprehensive understanding of designing AIE fluorescent probes for further central nervous system transportation and imaging purpose.

Dermal Delivery of the High-Molecular-Weight Drug Tacrolimus by Means of Polyglycerol-Based Nanogels.

Polyglycerol-based thermoresponsive nanogels (tNGs) have been shown to have excellent skin hydration properties and to be valuable delivery systems for sustained release of drugs into skin. In this study, we compared the skin penetration of tacrolimus formulated in tNGs with a commercial 0.1% tacrolimus ointment. The penetration of the drug was investigated in ex vivo abdominal and breast skin, while different methods for skin barrier disruption were investigated to improve skin permeability or simulate inflammatory conditions with compromised skin barrier. The amount of penetrated tacrolimus was measured in skin extracts by liquid chromatography tandem-mass spectrometry (LC-MS/MS), whereas the inflammatory markers IL-6 and IL-8 were detected by enzyme-linked immunosorbent assay (ELISA). Higher amounts of tacrolimus penetrated in breast as compared to abdominal skin or in barrier-disrupted as compared to intact skin, confirming that the stratum corneum is the main barrier for tacrolimus skin penetration. The anti-proliferative effect of the penetrated drug was measured in skin tissue/Jurkat cells co-cultures. Interestingly, tNGs exhibited similar anti-proliferative effects as the 0.1% tacrolimus ointment. We conclude that polyglycerol-based nanogels represent an interesting alternative to paraffin-based formulations for the treatment of inflammatory skin conditions.

Numerical analysis of the SOC factor variations’ influence on the autonomy of an electric vehicle

Electric vehicles are considered to be the immediate solution to drastically reduce the pollutant emissions from the road transport sector. However, one of the barriers of the massive penetration of the automotive market by electric vehicles is related to consumer/driver anxiety linked to the autonomy of electric vehicles. Autonomy depends directly on the battery technology that equips the electric vehicle, and from this point of view, the technology based on Li-Ion electrochemistry is the most accepted. This article presents a study by numerical simulation methods on the functional performance (autonomy) of an electric vehicle equipped with three different types of batteries (LiCoO2, LiFePO4, and a classic Acid-lead), as they have a low battery energetic charge. The obtained results showed that there are differences between the various technologies considered, the most efficient one being the LiCoO2 battery type.

Successful treatment of acute experimental toxoplasmosis by spiramycin-loaded chitosan nanoparticles

Spiramycin-metronidazole and spiramycin-loaded chitosan (CS) nanoparticles (NPs) were tested in comparison with the current spiramycin treatment of T.gondii concerning tissue penetration and blood brain barrier (BBB) passage. Swiss Albino mice were inoculated intraperitoneally with 2500 T. gondii tachyzoites RH strain and were divided into experimental and control groups. The experimental groups orally received CS NPs, spiramycin, spiramycin-metronidazole, spiramycin-loaded CS NPs 400 mg/kg and spiramycin-loaded CS NPs 100 mg/kg. Drug efficacy was assessed by mice survival time, mortality rate, parasite load in different organs and morphological study of the tachyzoites movement by light microscope and the ultra-structure by SEM. The results revealed that the maximum survival time of more than 200 days with no mortality on the sacrifice day (8th) was observed in mice receiving spiramycin-loaded NPs. Spiramycin-loaded NPs showed the highest significant percent reduction of tachyzoites (about 90% reduction) in liver, spleen and brain as compared to the other used drugs denoting successful bypass of BBB. Light microscopy of the treated peritoneal tachyzoites showed sluggish tachyzoites movement while the NPs caused loss of their movement. SEM of the treated tachyzoites were more mutilated and some of them appeared rupturing in those receiving CS NPs and spiramycin-loaded NPs. In conclusion, spiramycin-loaded NPs showed the highest efficiency in the treatment of acute toxoplasmosis. The non-toxic nature and the anti-parasitic effect of both CS and spiramycin make the use of spiramycin-loaded CS NPs a potential material for treatment of human toxoplasmosis.

Variation in Immune Defense Shapes Disease Outcomes in Laboratory and Wild Daphnia.

Host susceptibility may be critical for the spread of infectious disease, and understanding its basis is a goal of ecological immunology. Here, we employed a series of mechanistic tests to evaluate four factors commonly assumed to influence host susceptibility: parasite exposure, barriers to infection, immune responses, and body size. We tested these factors in an aquatic host-parasite system (Daphnia dentifera and the fungal parasite, Metschnikowia bicuspidata) using both laboratory-reared and field-collected hosts. We found support for each factor as a driver of infection. Elevated parasite exposure, which occurs through consumption of infectious fungal spores, increased a host's probability of infection. The host's gut epithelium functioned as a barrier to infection, but in the opposite manner from which we predicted: thinner anterior gut epithelia were more resistant to infectious spores than thick epithelia. This relationship may be mediated by structural attributes associated with epithelial cell height. Fungal spores that breached the host's gut barrier elicited an intensity-dependent hemocyte response that decreased the probability of infection for some Daphnia. Although larger body sizes were associated with increased levels of spore ingestion, larger hosts also had lower frequencies of parasite attack, less penetrable gut barriers, and stronger hemocyte responses. After investigating which mechanisms underlie host susceptibility, we asked: do these four factors contribute equally or asymmetrically to the outcome of infection? An information-theoretic approach revealed that host immune defenses (barriers and immune responses) played the strongest roles in mediating infection outcomes. These two immunological traits may be valuable metrics for linking host susceptibility to the spread of infectious disease.

DESIGNING A GUIDELINE FOR GREEN ROOF SYSTEM IN MALAYSIA

Green roof system is widely implemented because of its environmental and economic benefits and aesthetic value to a building. There are numerous successful green roof projects, both extensive and intensive in Malaysia. However, there is no specific technical guideline for the planning, design and construction of green roof system catered to the climate and background of Malaysia. The aim of the research is to propose and develop a technical guideline of extensive green roof system in Malaysia on the planning, design and construction aspects of vegetation, substrate, filter, drainage and root penetration barrier. Comparative literature review of guidelines from Hong Kong, Singapore and Sydney were leveraged upon to propose an appropriate guideline for Malaysia’s market. In-depth interviews were carried out with green roof experts to collect feedbacks on the proposed guideline in the validation stage. The output from this research will conceptualise a framework for a technical guideline for future implementation of green roof systems in Malaysia.

Real-time observation of self-interstitial reactions on an atomically smooth silicon surface

Self-diffusion and impurity diffusion both play crucial roles in the fabrication of semiconductor nanostructures with high surface-to-volume ratios. However, experimental studies of bulk-surface reactions of point defects in semiconductors are strongly hampered by extremely low concentrations and difficulties in the visualization of single point defects in the crystal lattice. Herein we report the first real-time experimental observation of the self-interstitial reactions on a large atomically smooth silicon surface. We show that non-equilibrium self-interstitials generated in silicon bulk during gold diffusion in the temperature range 860–1000 °C are annihilated at the (111) surface, producing the net mass flux of silicon from the bulk to the surface. The kinetics of the two-dimensional islands formed by self-interstitials are dominated by the reactions at the atomic step edges. The activation energy for the interaction of self-interstitials with the surface and energy barrier for gold penetration into the silicon bulk through the surface are estimated. These results demonstrating that surface morphology can be profoundly affected by surface-bulk reactions should have important implications for the development of nanoscale fabrication techniques.

Carbon-Doped TiO2 Activated by X-Ray Irradiation for the Generation of Reactive Oxygen Species to Enhance Photodynamic Therapy in Tumor Treatment.

Traditional photodynamic therapy (PDT) is limited by the penetration depth of visible light. Although the light source has been changed to near infrared, infrared light is unable to overcome the penetration barrier and it is only effective at the surface of the tumors. In this study, we used X-ray as a light source for deep-seated tumor treatment. A particle with a narrow band gap when exposed to soft X-rays would produce reactive oxygen species (ROS) to kill tumor cell, with less damage to the normal tissues. Anatase TiO2 has been studied as a photosensitizer in PDT. In the experiment, C was doped into the anatase lattice at an optimum atomic ratio to make the band gap narrower, which would be activated by X-ray to produce more ROS and kill tumor cells under stress. The results showed that the synthesized TiO2:C particles were identified as crystal structures of anatase. The synthesized particles could be activated effectively by soft X-rays to produce ROS, to degrade methylene blue by up to 30.4%. Once TiO2:C was activated by X-ray irradiation, the death rate of A549 cells in in vitro testing was as high as 16.57%, on day 2. In the animal study, the tumor size gradually decreased after treatment with TiO2:C and exposure to X-rays on day 0 and day 8. On day 14, the tumor declined to nearly half of its initial volume, while the tumor in the control group was twice its initial volume. After the animal was sacrificed, blood, and major organs were harvested for further analysis and examination, with data fully supporting the safety of the treatment. Based on the results of the study, we believe that TiO2:C when exposed to X-rays could overcome the limitation of penetration depth and could improve PDT effects by inhibiting tumor growth effectively and safely, in vivo.

Lecithin Microemulsion Lipogels Versus Conventional Gels for Skin Targeting of Terconazole: In Vitro, Ex Vivo, and In Vivo Investigation

Topical treatment of fungal infections has several superiorities over oral treatment. However, the greatest challenge for dermal delivery is the stratum corneum which is considered an effective barrier for penetration of most antifungal drugs into deeper skin layers. Terconazole (Tr), which is the first marketed triazole antifungal, was reported to be one of the most active azoles against vaginal candidiasis. Nevertheless, our work group is the first to investigate the potential of Tr in the treatment of skin mycosis via integration into lecithin microemulsion-based lipogels (LMBGs). The microemulsion regions of the investigated systems were detected through ternary phase diagrams. The in vitro characterization studies revealed promising physicochemical merits for the selected LMBGs as well as satisfactory in vitro antifungal activity. The current research work was endeavored to investigate the potential of such novel Tr-loaded LMBGs in comparison with conventional gels. Ex vivo permeation and retention studies in addition to in vivo deposition study showed a significant improvement in the permeability of Tr through animal skin from LMBGs compared to other conventional gels. Furthermore, the optimized microemulsion lipogel proved to be safe and a nonirritant to experimental animals through the acute sensitivity study and histological skin examination. Overall, lecithin-based microemulsion lipogels of different composition confirmed their potential as interesting nanocarriers for skin delivery of terconazole compared to current therapy.

Effect of Nanoparticles Surface Charge on the Arabidopsis thaliana (L.) Roots Development and Their Movement into the Root Cells and Protoplasts.

Increasing usage of gold nanoparticles (AuNPs) in different industrial areas inevitably leads to their release into the environment. Thus, living organisms, including plants, may be exposed to a direct contact with nanoparticles (NPs). Despite the growing amount of research on this topic, our knowledge about NPs uptake by plants and their influence on different developmental processes is still insufficient. The first physical barrier for NPs penetration to the plant body is a cell wall which protects cytoplasm from external factors and environmental stresses. The absence of a cell wall may facilitate the internalization of various particles including NPs. Our studies have shown that AuNPs, independently of their surface charge, did not cross the cell wall of Arabidopsis thaliana (L.) roots. However, the research carried out with using light and transmission electron microscope revealed that AuNPs with different surface charge caused diverse changes in the root’s histology and ultrastructure. Therefore, we verified whether this is only the wall which protects cells against particles penetration and for this purpose we used protoplasts culture. It has been shown that plasma membrane (PM) is not a barrier for positively charged (+) AuNPs and negatively charged (−) AuNPs, which passage to the cell.

Investigating the Effectiveness of Emulsified Acid on Sandstone Formation under High Temperature Conditions

Acid stimulation supports the oil and gas industry as a versatile mean in enhanced oil recovery to fulfil the world energy demand. Although hydrochloric acid can significantly improve the reservoir permeability, its rapid reaction rate at high temperature has created a barrier for acid penetration. Subsequently, emulsified acid has slowly gain its popularity due to its retardation effect which allows deeper penetration of acid into the formation and achieves minimal corrosion issues. Nonetheless, emulsified acid has rarely applied on sandstone formation. Since a large portion of reservoirs are made up of sandstone, the effects of emulsified acid on sandstone under high temperature conditions should be studied to unlock the effective usage of emulsified acid in restoring the hydrocarbon recovery from the potential sandstone reservoirs. Besides, it is also crucial to explore cheaper and greener substitute to formulate innovative emulsified acid in minimizing the high acidizing budget along with environmental concerns. In this project, 10 different emulsified acid combinations are prepared using hydrofluoric acid, hydrochloric acid, phosphoric acid, formic acid, acetic acid, cationic surfactant, diesel and waste oil. The pre-flush treatment (5 % CH3COOH: 10 % HCl) is followed by the main flush (emulsified acids) saturation for 3 days. The thermal stability of emulsified acids and their effect on the Berea sandstone properties are evaluated. Major outcome is that the emulsified acids have the capability to remain stable at 275 °F up to 6 hours with uniform and fine droplet size. It is also proven that most of the emulsified acids can improve the porosity and permeability of Berea sandstone core samples except for HF: H3PO4. Regardless of the types of oil used for emulsified acid formulation, HF: HCl acid combination shows the best performance enhancement for both diesel-based and waste oil-based emulsified acids. In sandstone acidizing, emulsified acid dissolves the minerals and create acid transport pathway with close connectivity between pore spaces, causing the formation of large and conductive channels within the rock. Hence, these positive results clearly reflect on the feasibility of emulsified acid application in sandstone matrix acidizing and the effectiveness of waste oil as a replacement fluid for diesel.

Simulation of the effects of different substrates, temperature, and substrate roughness on the mechanical properties of Al2O3 coating as tritium penetration barrier

Residual thermal stress in the system is a serious problem that affects the application of tritium permeation barrier coatings in fusion reactors. The stress not only determines the adhesion between coating and substrate, but also changes the properties of the material. In this study, finite element analysis was used to investigate the relationship between the residual thermal stress and the mechanical properties of Al2O3 tritium penetration barrier systems. Moreover, the residual thermal stress influenced by factors such as different substrates, temperature, and substrate roughness was also analyzed. The calculation showed that the hardness and elastic modulus increased with increasing compressive stress. However, the hardness and elastic modulus decreased with increasing tensile stress. The systems composed of Al2O3 coatings and different substrates exhibited different trends in mechanical properties. As the temperature increased, the hardness and the elastic modulus increased in an Al2O3/316L stainless steel system; the trend was opposite in an Al2O3/Si system. Apart from this, the roughness of the substrate surface in the system could magnify the change in hardness and elastic modulus of the coating. Results showed that all these factors led to variation in the mechanical properties of Al2O3 tritium permeation barrier systems. Thus, the detailed reasons for the changes in mechanical properties of these materials need to be analyzed.

Programmable Electrofabrication of Porous Janus Films with Tunable Janus Balance for Anisotropic Cell Guidance and Tissue Regeneration

AbstractJanus films with controlled pore structures can be particularly important in diverse applications. There remains a challenge for simple, rapid, and scalable fabrication methods to control Janus balance (JB) including the thickness of the individual face as well as porosity and pore size. Here the electrofabrication of a porous Janus film with controlled Janus balance from aminopolysaccharide chitosan under the salt effect is reported. Sequential deposition of chitosan under programmable salt environment and electrochemical conditions enables construction of Janus films with precisely controlled Janus balance. Bioactive partially soluble calcium phosphate (CaP) salts can also generate porous structure in Janus film. It is specifically reported that a chitosan/hydroxyl apatite (HAp) composite Janus film can serve as an effective scaffold for guided bone regeneration. The dense layer functions to provide mechanical support and serves as a barrier for fibrous connective tissue penetration. The porous composite layer functions to provide the microenvironment for osteogenesis. In vivo studies using a rat calvarial defect model confirm the beneficial features of this Janus composite for guided bone regeneration. These results suggest the potential of electrofabrication as a simple and scalable platform technology to tune the self‐organization of soft matter for a range of emerging applications.

Transferrin Receptor‐Mediated Sequential Intercellular Nanoparticles Relay for Tumor Deep Penetration and Sonodynamic Therapy

AbstractSonodynamic therapy overcomes the tissue penetration barrier of photo‐activated therapeutics, whereas the poor tumor penetration of sonosensitizers largely lowers therapeutic effectiveness. Here, a brand‐new strategy for achieving tumor deep penetration is developed by exploiting the cellular recycling transferrin (Tf). Specifically, a new type of nanosonosensitizer self‐assembled from Tf and organic sonosensitizer protoporphyrin IX is first designed, which exhibits expected biosafety, stability, and ultrasound‐activated cytotoxic reactive oxygen species (ROS) production capability ensuring in vivo administration. More importantly, the nanosonosensitizers inherit the unique transferrin receptor (TfR)‐mediated endocytosis and exocytosis behaviors of Tf, enabling specific binding to TfR‐overexpressed tumor cells and thereafter TfR‐mediated sequential intercellular delivery of nanosonosensitizers. Consequently, tumor deep delivery of sonosensitizers is achieved in TfR‐overexpressed HeLa tumors, which is considerably beneficial for desired tumor‐suppression effect with ROS‐mediated sonodynamic therapy protocol. Such a TfR‐mediated sequential intercellular relay strategy offers an innovative concept for the deep delivery of nanomedicines in tumors.

A highly resistant structure between the cuticle and the cortex of human hair. II. CARB, a penetration barrier.

We previously reported that a chemically resistant structure is present at the interface between the cuticle and the cortex of human hair. The goal of this study was to identify the position of that structure and to clarify its barrier ability. Untreated, partially and completely decuticled hair fibres were characterized. The correlation between the number of cuticle layers and the penetration depth of a dye into the cortex was microscopically investigated. In addition, similar measurements were performed using hair with a denatured cell membrane complex. The penetration depth of the dye into the cortex showed no statistically significant correlation with the number of cuticle layers in the case of partially decuticled hair fibres (the number of cuticle layers ranged from one to four). Penetration of the dye proceeded drastically just when the last cuticle layer was lost, but denaturation of the cell membrane complex did not affect the depth of penetration. That suggested that the penetration barrier at the interface between the cuticle and the cortex is not the cell membrane complex, but rather is the resistant structure previously reported. It was observed that a thin layer structure is located beneath the endocuticle of the innermost cuticle cell layer, only in the range where the cuticle borders the cortex. It is thought that this is the structure in question. These results demonstrate that a highly resistant structure located at the interface between the cuticle and the cortex of human hair acts as a penetration barrier. We propose that structure be named CARB, cuticle anchored resistant base.

Experimental study of the penetration of oxygen and deuterium atoms into porous water ice

Context. Many interstellar molecules are thought to form on dust grains. In particular, hydrogenation is one of the major mechanisms of the formation of mantle ice. To date it is not clear if H atoms can penetrate the bulk of the ice mantle or if it only has chemical activity on the accessible surface of grains. Aims. We wish to study the efficiency of atoms deposited on the outer surface of the amorphous solid water to penetrate into the ice bulk. Methods. NO molecules react with O and H atoms. They are easily detected by infrared (IR) spectroscopy. These two properties make this molecule an ideal chemical tracer for the penetration of O and H atoms through water ice. In our experiments we first deposited a NO undercoat and covered this layer (at 40 K) with a variable amount of water ice. Then, we exposed this undercoat to D (10 K) or O (40 K) atoms, and we followed the NO consumption and the products that appeared via IR signatures, and we finally analyzed the desorption of all species through a temperature-programmed desorption technique. We experimentally characterize the accessible surface of the ice and provide a model to interpret quantitatively our measurements. Results. Water ice limits the destruction of tracer NO molecules. The thicker the ice, the more NO remains unreacted. H and O atoms lead to the same amount of NO consumption, pointing out that access to reactants for these two different atoms is identical. We discuss different possible scenarios of NO localization (in and/or on the ice) and determine how this affects our observables (IR data and desorption profiles). Conclusions. In our experimental conditions, it is not possible to measure any atom penetration through the bulk of the ice. The surface diffusion followed by reaction with NO or by self-reaction (i.e., H + H → H2) is faster than bulk diffusion. We propose lower limit values for penetration barriers. Therefore the building of astrophysical ice mantles should be mostly driven by surface reactivity.

Customers’ Current Preferences in E-commerce and Possible Dominance of Social Media Marketplace in the Industry

Technological advancement and internet development have significantly contributed to more comfortable and innovative services. The e-commerce industry has become tough and full of competition. Technologies and the internet reduce barriers of penetration into new markets. Social media, which is a vivid example of internet development, has already penetrated the e-commerce industry. However, the business environment is rapidly changing and requires constant analysis to anticipate prospective threats or opportunities. Therefore, this paper refers to the analysis of customers’ current preferences. Questionnaires were distributed to 83 participants to analyze preferences and to evaluate possible dominance of “Facebook Marketplace” in the e-commerce industry. According to the results, provision of high protection is overly required. Online sales network should act as an intermediary, in order to provide refund guarantees an official verification, which is not provided by ‘Facebook Marketplace”. The survey was conducted in a country were “Facebook Marketplace” was not available, and it was impossible to identify practical challenges of the marketplace.