Metastable and Electronically Percolating Silver Nanowire-Polymer Composites by Spray Drying.

The factors that influence product development depend, amongst other things, on the type of product, the economic situation, the state of the art technology and various social and cultural trends. In modern era, often not the specs and costs are the decisive factors for purchasing a product, but aspects like design and brand personality. One of the reasons for this is the abundance of products of the same type for the same purpose. In fact, this is the current situation for dry powder inhalers (DPIs) although the self-congruity concept seems more applicable to the doctors who prescribe the inhalers than to the patients who are using them. For the early DPIs from the 1960s and 1970s the driving factor for development was the necessity of having an alternative for cholofluorocarbon (CFC) containing metered dose inhalers (MDIs). An important factor affecting their design could have been the desire to improve pulmonary drug delivery compared to that from MDIs, but unfortunately this oportunity was missed. Instead, available technology like hard gelatin capsules and adhesive ('ordered') mixtures were used and lung deposition remained more or less the same as from MDIs (only approx. 10% of the dose). After the capsule (and multi-dose reservoir) DPIs became more widely accepted and patents on inhaled drugs expired, consulting groups and generic manufacturers became more and more involved in the emerging DPI market, purely on an economic basis. This does not mean that there have not been developments yet aiming at improvement of the therapy with DPIs and various future applications may give a new boost to using new technology for dry powder inhalation.

The inhomogenous real-space electronic structure of gapless and gapped disordered bilayer graphene is calculated in the presence of quenched charge impurities. For gapped bilayer graphene, we find that for current experimental conditions the amplitude of the fluctuations of the screened disorder potential is of the order of (or often larger than) the intrinsic gap Δ induced by the application of a perpendicular electric field. We calculate the crossover chemical potential Δ(cr), separating the insulating regime from a percolative regime in which less than half of the area of the bilayer graphene sample is insulating. We find that most of the current experiments are in the percolative regime with Δ(cr)≪Δ. The huge suppression of Δ(cr) compared with Δ provides a possible explanation for the large difference between the theoretical band gap Δ and the experimentally extracted transport gap.

Nanofibrils are known to improve the cohesion of supraparticle (SP) assemblies. However, tailoring the morphology of SPs using nanofibrillar additives is not well developed. Herein, β-lactoglobulin amyloid nanofibrils (ANFs) are investigated as means to impart morphological control over the assembly process of spray-dried SPs composed of 10-100nm silica nanoparticles (SiNPs). Phytoglycogen (PG) and silver nanowires (AgNWs) are used to assess the influence of building block softness and aspect ratio, respectively. The results demonstrate that ANFs promote the onset of structural arrest during the particle consolidation enabling the preparation of corrugated SP morphologies. The critical ANF loading required to induce SP corrugation increases by roughly 1vol% for every 10-nm increase in SiNP diameter, while the ensuing ANF network density decreases with SiNP volume fraction and increases with SiNP diameter. Results imply that ANF length starts to become influential when it approaches the SiNP diameter. ANFs display a reduced effectiveness in altering soft PG SP morphology compared with hard SiNPs of comparable size. In SiNP-AgNW SPs, ANFs induce a toroid-to-corrugated morphology transformation for sufficiently large SPs and small SiNPs. The results illustrate that ANFs are effective additives for the morphological engineering of spray-dried SPs important for numerous applications.

<p>Bone tissue engineering and synthetic biomineralization are two widely researched areas, the principles of which have been combined from time to time in efforts to develop replacement materials for natural bone grafts. Nacre has been studied as a prospective bone graft material owing to its mechanical strength being comparable to that of natural bone. The extraordinary mechanical strength of nacre is attributed to its nanostructure. The McGrath research group developed a synthetic biomineralization method, herein called the McGrath method, that can be used to effectively replicate the elements of nacre’s nanostructure in 2D biopolymer systems in laboratory conditions. Here, the applicability of the McGrath method in translating the calcium carbonate-based mineralization achieved in 2D films onto 3D printed chitosan hydrogel-based scaffolds is investigated. Thereby, enabling the fabrication of 3D chitosan-calcium carbonate composites with properties sought in the context of prospective load-bearing bone grafts. In this work, considering the importance of interconnected porosity in an in vivo environment, nozzle extrusion-based 3D printing was employed to develop 3D structures with interconnected macropores, essentially imitating the porous structure of bone. The applicability of chitosan hydrogels as the printing ink in a custom-designed 3D printer was evaluated and quantified through rheological studies. The printing parameters and an appropriate experimental protocol were devised to fabricate stable 3D chitosan hydrogel-based scaffolds featuring physically crosslinked-layered structure with interconnected macropores. The effect of various drying techniques on retaining this porous structure in dried scaffolds and their swelling behaviour when soaked in a physiologically relevant solvent were explored using various techniques including cryo-scanning electron microscopy. The strategies required to mineralize the as-fabricated 3D chitosan hydrogel-based scaffolds via the McGrath method, such that the mineralization achieved within the 3D scaffolds is similar to that obtained within 2D films, were elucidated. This included the use of polyacrylic acid (PAA), a crystal growth modifier. PAA has previously been shown to be important in achieving a pancake-like calcium carbonate formation, comprised of laterally growing nanoparticle aggregates which form in association with the organic matrix, in 2D films; such structures are observed in the early stages of nacre formation. By modulating the period of exposure of the 3D scaffolds to the mineralization solutions and the concentrations of these solutions, it was found that 3D composites with up to 40% calcium carbonate content and varying crystal morphology could be fabricated using this mineralization method. Importantly, it was observed that the calcium carbonate crystallites were intricately associated with the organic hydrogel matrix. This is another essential element observed in biomineral systems. Various techniques such as scanning electron microscopy (SEM), thermogravimetric analysis (TGA), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were employed for structural and compositional characterisation of the final composites. The prospect of fabricating 3D chitosan-calcium carbonate composites via a single-step method using chitosan hydrogel preloaded with calcium carbonate crystallites as the printing ink in our custom-designed 3D printer was also investigated. This method was studied as a faster and less labour-intensive alternative to developing composites via the two-step method devised in this research whereby 3D hydrogel-based scaffolds are printed first and then mineralized via the McGrath method. The advantages and disadvantages of the two fabrication techniques are compared. The two-step fabrication method was found to be superior in terms of the properties explored and desired in the composite. The behaviour of the chitosan hydrogel-based scaffolds and composites fabricated using the McGrath method, under different stress and strain regimes were also investigated. Mechanical tests performed on air-dried chitosan hydrogel-based scaffolds and composites showed that the compressive modulus, strength and indentation hardness values obtained were within the same order of magnitude as that of trabecular bone. Data from uniaxial compression tests showed that the yield, ultimate strength and compressive modulus of the 3D scaffolds vary with the total mineral content, morphology and size of the resultant crystallites in the composite. Composites with very low mineral content (~7% CaCO₃ content) showed the best mechanical properties under uniaxial compressive stress (approximately 0.37 GPa compressive modulus, 26 MPa yield strength, and 31 MPa ultimate strength). Nanoindentation tests showed that the nanoscale hardness and indentation modulus increased upon mineralization of the scaffolds but did not vary significantly as a function of the extent of mineralization. Dynamic mechanical analysis showed that the scaffolds (both mineralized and non-mineralized) can effectively dissipate stress without complete fracture when subjected to dynamic compressions within physiologically relevant loading frequencies (1 - 15 Hz) irrespective of the mineral content. The individual responses vary with loading frequency. Having ascertained the structural and mechanical attributes of the fabricated materials, their capacity to enable osteoblast cell attachment and proliferation was explored. Alamar Blue assay and confocal microscopy performed at various time points for samples exposed to in vitro cultured osteoblasts showed that chitosan hydrogel-based scaffolds and composites are biologically non-toxic and facilitate cell adhesion and proliferation. Furthermore, when osteoblasts were incubated with composites with low CaCO₃ content, the number of cells increased significantly within 14 days. The results of this research confirm that 3D printed chitosan hydrogel-based composites fabricated using the McGrath mineralization method featuring various structural and compositional imitations of bone and nacre shows considerable potential as future bone grafts materials.</p>

Comparative study of Hot-Melt Extrusion, spray drying, and KinetiSol® processing to formulate a poorly water-soluble and thermolabile drug.

Encapsulation of silver nanowire networks by atomic layer deposition for indium-free transparent electrodes

In this study, chemical treatment (CT; oxidation–reduction method) and physical treatment (HP; hot-pressing methods) were applied to improve the performance of silver nanowire (AgNW)-derived electrodes on a glass or flexible polyethylene terephthalate (PET) substrate. The four-point probe method, UV-Vis spectroscopy and scanning electron microscopy (SEM) were used to measure the properties of AgNW electrodes and compare them with those of indium tin oxide (ITO) electrodes for exploring the possibility of using CT- and HP-based AgNW electrodes for polymer solar cell (PSC) applications. Using the CT or HP method, the sheet resistance of electrodes decreased to lower than 40 Ω sq−1 with an average high transmittance of more than 80%. Furthermore, HP reduced the surface roughness of AgNWs, which solved the inter-electrode short circuiting problem for devices. We studied the performance of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) and zinc oxide-based PSC devices. The power conversion efficiency of HP-AgNW-derived poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl] (PTB7-Th):[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) devices was 7.83%, which was slightly lower than the performance of the device using ITO (8.03%) as a substrate. After a bend test (100 times) at a 2-cm curvature radius, the efficiency of AgNW/PET-derived PSCs was more than 70%. The performance of PSCs made with AgNWs and ITO electrodes is comparable, but the cost of using AgNWs for electrodes is much lower; therefore, HP-derived AgNWs demonstrate great potential for optoelectronic applications.

The paper deals with development and characterization of 3D sandwich composite structures reinforced with newly-designed multi-cell flat-knitted spacer fabrics in terms of compressive behaviour and Poisson’s ratio. Multi-cell spacer knitted preforms was produced on a computerized flat knitting machine. 3D composite samples with three different cross-sectional geometries were prepared via vacuum assisted resin transfer moulding method. Quasi-static compressive experiments were carried out on the prepared 3D composite samples. The Poisson’s ratio of re-entrant 3D knitted composite varied between -6 and -1, which clearly points to existence of auxetic behaviour of the samples. The re-entrant 3D composites also demonstrated the highest initial slope and area under the compression force-displacement curve than spear-head or hexagonal composite structures which refer to higher energy absorbing capacity. The Poisson’s ratio of 3D regular hexagonal knitted composites at small strain was usually 4 which gradually decreased to 1.6 as the exerted compressive strain increased. Additionally, 3D spear-head knitted composite having zero Poisson’s ratio was also developed.

Electrically conductive silver nanowires-filled methylcellulose composite transparent films with high mechanical properties

The construction of 3D networks enhanced filler utilization in conductive composites, but heat‐induced liquefaction of solid epoxy resins hindered internal 3D structure formation. This study prepared semi‐cured epoxy particles (S‐E12‐RGs) by mixing and pre‐curing E12 epoxy with a curing agent. S‐E12‐RGs were combined with liquid epoxy E51, curing additives, and ethylenediamine‐modified nickel‐coated graphite (ENCG), and then hot‐pressed into 3D composites. The crosslinking of S‐E12‐RGs prevented ENCG's inward migration, which promoted its selective dispersion in the E51 phase. With only 15 wt% nickel‐coated graphite (NCG), the conductivity increased by 7 orders of magnitude compared to direct filling. At 25 wt% ENCG, the composites achieved a conductivity of 23.81 S/m, a thermal conductivity of 0.557 W/(m K), and an EMI shielding of 35 dB. Furthermore, DMA‐digital multimeter analysis showed that ΔR/R0 was less than 0.27 from 35 to 70°C at 0.1–50 Hz, which demonstrated excellent operational stability.Highlights A 3D network was formed in the thermosetting matrix via specific methods. The cross‐linked S‐E12‐RGs promoted ENCG's selective dispersion in the E51 phase. The composite exhibited high electrical conductivity at low filler content. The material maintained stability within a specific temperature and frequency range.

We review recent new avenues for controlling two-dimensional (2D) self-assembly stabilized by non-covalent interactions. The use of host–guest architectures has opened new pathways for supramolecular self-assembly in two dimensions by immobilizing molecules of interest in 2D nano-porous networks. We also describe how a judicious choice of guest molecule can induce effective changes in host templates. These transformations could enable full control of 2D self-assembly with nanoscale precision, by tuning parameters such as stoichiometry, geometry and non-covalent interactions. This approach is of paramount importance for understanding changes of dimensionality and subsequently the formation of 2D and 3D supramolecular networks and ordered films that can be used as active materials for applications (e.g., electronic devices).

Electromagnetic interference (EMI) shielding materials with silver nanowires (AgNWs) have been widely reported to deal with electromagnetic radiation pollution. However, few studies focus on the effect of the spatial distribution of the AgNWs on the shielding performance of materials. In this work, poly(vinylidene fluoride) (PVDF)/AgNW hybrid electrospun membranes were prepared through dip‐coating and spray‐coating of AgNWs, respectively, and the morphology features and EMI shielding effectiveness (SE) of dip‐coated and spray‐coated hybrid membranes were investigated. The results show that the AgNWs in dip‐coated samples form three‐dimensional (3D) networks and those in spray‐coated samples form a two‐dimensional (2D) layer. EMI SE of dip‐coated sample is higher than that of the spray‐coated sample at the same area density of AgNWs, though the electrical conductivity of the spray‐coated sample can be higher than that of the dip‐coated sample. At 900 mg/m2 for area density of AgNWs, EMI SE of the dip‐coated sample can reach 58.7 dB, and EMI SE of the spray‐coated sample does not exceed 33.4 dB owing to that the 3D AgNW networks formed by dip‐coating are beneficial for multiple reflection and interfacial polarization. A higher concentration of AgNW dispersion for dip‐coating leads to a more excellent EMI shielding performance, and the specific SE of the sample by dip‐coating in 0.5 wt% AgNW dispersion can reach 6.62 × 104 dB˙cm2/g due to the high SE of 107.2 dB and low density and thickness. These results reveal the effect of the structure of the AgNW networks on the EMI shielding performance of the hybrid membrane.

In this study, caprine forestomach native collagen (CFNC) isolated from rumen tissues is reported for the first time with subsequent surface modifications with varying concentrations of silver nanowires (AgNWs). Accordingly, CFNC/AgNWs scaffolds were prepared to be used as suitable wound healing dressing materials through a sequential isolation and decellularization process, followed by step-wise AgNW surface modification and ultraviolet (UV) crosslinking. The significant outcomes of this research highlight that CFNC/AgNWs scaffolds exhibit a highly porous three-dimensional (3D) network structure with favourable physicochemical characteristics. Also, the comprehensive tensile testing demonstrated that there were changes in mechanical properties based on the AgNW content. The CFNC/AgNWs scaffolds also exhibited strong antibacterial action against E. coli and S. aureus in a dose-dependent manner. The release of Ag+ ions from CFNC/AgNWs scaffolds exhibited a slow and sustained release pattern over an extended period of time. The cell-biomaterial interaction studies on CFNC/AgNWs scaffolds using L929 fibroblast cells showed dose-dependent and time-dependent toxicity when the concentration exceeded above 1 mg mL-1. The cytotoxicity is mainly due to the higher concentration of Ag+ ions which initiates cell death through lipid peroxidation and causes cell membrane damage. The biocompatibility test results serve as a reference point to select the optimal dosage of AgNWs with balanced antibacterial and biocompatibility properties. Thus, the developed CFNC/AgNWs scaffolds will serve as a versatile wound dressing material similar to other metallic or conjugated reconstituted collagen systems with the added benefit of strong antimicrobial properties, and as a biomimetic xenograft for skin regeneration.

Fabrication of three-dimensional metal-graphene network phase change composite for high thermal conductivity and suppressed subcooling phenomena

Random networks offer fertile ground for achieving complexity and criticality, both crucial for an unconventional computing paradigm inspired by biological brains' features. In this work, characterizing and modeling different electrical transport regimes of self‐assemblies of silver nanowires (AgNWs) are focused. As percolation plays an essential role in such a scenario, a broad range of areal density coverage is examined. Close‐to‐percolation realizations (usually used to demonstrate neuromorphic computing capabilities) have high pristine resistance and require an electrical activation. Until now, highly conductive over‐percolated systems (commonly used in electrode fabrication technology) have not been thoroughly considered for hardware‐based neuromorphic applications, even though biological systems exhibit such an extremely high degree of interconnections. Here, it is shown that high current densities in over‐percolated low‐resistance AgNW networks induce a fuse‐type process, allowing a switching operation. Such electro‐fusing discriminates between weak and robust NW‐to‐NW links and enhances the role of filamentary junctions. Their reversible resistive switching enable different conductive paths exhibiting linear I–V features. Both percolation regimes are experimentally studied and proposed a model comprising two types of junctions that can describe, through numerical simulations, the overall behavior and observed phenomenology. These findings reveal a potential interplay of functionalities of neuromorphic systems and transparent electrodes.