Conventional silica-based aerogels are among the most promising materials considering their special properties, such as extremely low thermal conductivity (~15 mW/mK) and low-density (∼0.003–0.5 ...g.cm−3) as well as high surface area (500–1200 m2. g−1). However, they have relatively low mechanical properties and entail extensive and energy-consuming processing steps. Silica-based aerogels are mostly fragile and possess minimal mechanical properties as well as a long processing procedure which hinders their application range. The key point in improving the mechanical properties of such a material is to increase the connectivity in the aerogel backbone. Several methods of mechanical improvement of silica-based aerogels have been explored by researchers such as (i) use of flexible silica precursors in silica gel backbone, (ii) surface-crosslinking of silica particles with a polymer, (iii) prolonged aging step in different solutions, (iv) distribution of flexible nanofillers into the silica solution prior to gelation, and, most recently, (v) polymerizing the silica precursor prior to gelation.
The polymerized silica precursor, as in the most recent approach, can be gelled either by binodal decomposition (nucleation and growth), resulting in a particulate structure, or by spinodal decomposition, resulting in a non-particulate structure. By optimizing the material composition and processing conditions of materials, the aerogel can be tailored with different functional capabilities.
This review paper presents a literature survey of precursor modification toward increased connectivity in the backbone, and the synthesis of inorganic and hybrid systems containing siloxane in the backbone of the silica-based aerogels and its composite version with carbon nanofillers. This review also explains the novel properties and applications of these material systems in a wide area. The relationship among the materials-processing-structure-properties in these kinds of aerogels is the most important factor in the development of aerogel products with given morphologies (particulate, fiber-like, or non-particulate) and their resultant properties. This approach to advancing precursor systems leads to the next-generation, multifunctional silica-based aerogel materials.
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•An overview on conventional chemistry and synthesis methods of silica-based aerogels is given.•An overview on trending and the most recent synthesis methods of silica-based aerogels is given.•A literature survey of precursor modification toward increased connectivity in the backbone is given.•A literature survey on methods for multifunctionality and mechanical enhancement of silica-based aerogels is given.•A literature survey on precursor enhancement with carbonaceous material is given.
Tissue engineering using cardiomyocytes derived from human pluripotent stem cells holds a promise to revolutionize drug discovery, but only if limitations related to cardiac chamber specification and ...platform versatility can be overcome. We describe here a scalable tissue-cultivation platform that is cell source agnostic and enables drug testing under electrical pacing. The plastic platform enabled on-line noninvasive recording of passive tension, active force, contractile dynamics, and Ca2+ transients, as well as endpoint assessments of action potentials and conduction velocity. By combining directed cell differentiation with electrical field conditioning, we engineered electrophysiologically distinct atrial and ventricular tissues with chamber-specific drug responses and gene expression. We report, for the first time, engineering of heteropolar cardiac tissues containing distinct atrial and ventricular ends, and we demonstrate their spatially confined responses to serotonin and ranolazine. Uniquely, electrical conditioning for up to 8 months enabled modeling of polygenic left ventricular hypertrophy starting from patient cells.
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•Positive force frequency and post-rest potentiation are achieved in human tissues•Engineered atrial and ventricular tissues have distinct electrophysiology and drug responses•Atrio-ventricular tissues show spatially confined drug responses•Long-term electrical conditioning enables polygenic cardiac disease modeling
A scalable cardiac tissue cultivation platform enables assessment of multiple parameters of atrial and ventricular tissue function, drug testing, and disease modeling.
•Double crosslinked chitin aerogels were prepared by supercritical drying.•Poly(ethylene glycol) diglycidyl ether (EGDE) induced the etherification of chitin.•The double crosslinked chitin aerogels ...increased the mechanical properties.•The incorporation of EGDE changed the internal morphology of porous aerogels.•Excessive amount of EGDE caused the emulsion effect and macroporou structure.
In this study, we introduced a novel double crosslinked chitin aerogel via etherification with EGDE for mechanical reinforcement. Samples with different EGDE: chitin weight ratios from 0 to 1.5:1 were fabricated through chitin dissolution in KOH/urea aqueous solution, ethanol neutralization and washing, and supercritical CO2 drying. Both the physical and chemical crosslinking maintained the high porosity and light weight of chitin aerogels. The morphology under SEM has shown the close-ended and denser fibrils alignment for EGDE crosslinked aerogels and the mesoporous and macroporous structure induced by emulsion effect from excessive EGDE. FTIR characterization was conducted for chemical structure analysis. Compressive testing showed an increase of 247 % compressive strength at 10 % strain and 243 % modulus could be achieved at 1.0 EGDE samples. TGA results revealed a delayed thermal degradation for the chemically crosslinked samples. This study demonstrates EGDE an effective chemical crosslinker for reinforced chitin aerogels.
Due to the sensitive relations between aerogel physical, thermal, and mechanical properties, improving the polyimide aerogels performance requires understanding of their structure to properties ...relations, along with introducing a robust method to tailor aerogels properties to achieve the optimum performance. Given this background, this work extensively studies the structure to properties relations of pyromellitic dianhydride (PMDA) and biphenyl-tetracarboxylic acid dianhydride (BPDA) backbone polyimide aerogels at varying hybrid diamine fractions. Based on the results, combination of rigid and flexible diamine monomers at varying fractions successfully tailored the properties of the hybrid diamine polyimide aerogels. Also, physical, thermal, and mechanical properties of the two aerogel backbones presented a tendency to the hybrid diamine monomers fraction. However, the opposite trends of the two backbones suggested that, rather than the diamine or dianhydride monomers individually, their network structure and bonding nature would define the aerogel behavior. Furthermore, this work shows that the shrinkage and morphology are the two main parameters, those describe the aerogels properties. Therefore, tailoring these two parameters can provide aerogels with optimum performance. The fabricated aerogels presented wide range of properties with the maximum observed open cell content of 96.6% and compression modulus of 16.9 MPa along with the effective thermal conductivity and density as low as 32.5 mW/mK and 0.056 g/cm3, respectively.
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•Study on structure to properties relations of hybrid diamine polyimide aerogels.•Tailoring hybrid polyimide aerogels properties by altering the diamine fraction.•Hybrid aerogels by combining a rigid and a flexible diamine monomer.•The shrinkage and morphology are the main parameters, defining aerogels properties.
When we think of "soft" in terms of socially assistive robots (SARs), it is mainly in reference to the soft outer shells of these robots, ranging from robotic teddy bears to furry robot pets. ...However, soft robotics is a promising field that has not yet been leveraged by SAR design. Soft robotics is the incorporation of smart materials to achieve biomimetic motions, active deformations, and responsive sensing. By utilizing these distinctive characteristics, a new type of SAR can be developed that has the potential to be safer to interact with, more flexible, and uniquely uses novel interaction modes (colors/shapes) to engage in a heighted human-robot interaction. In this perspective article, we coin this new collaborative research area as SoftSAR. We provide extensive discussions on just how soft robotics can be utilized to positively impact SARs, from their actuation mechanisms to the sensory designs, and how valuable they will be in informing future SAR design and applications. With extensive discussions on the fundamental mechanisms of soft robotic technologies, we outline a number of key SAR research areas that can benefit from using unique soft robotic mechanisms, which will result in the creation of the new field of SoftSAR.
Polymeric composites have the potential to replace current electronic packaging and improve thermal management of electronics to open the way for further size shrinkage. Such composites need to ...provide high thermal conductivity and high electrical resistivity while possessing suitable mechanical properties. This paper reports the study of thermal behavior of arranged and random network of hexagonal boron nitride (hBN) in composite with different polymers. Thermal barrier factors and possible solutions to reduce the effect of these factors are thoroughly investigated. Thermal behavior of hBN filler network in composite with different polymers as well as the possibility of using green (bio-based) polymers as the matrix have been studied. Fully bio-based, partially bio-based and petroleum based composites are compared to investigate the effect of different polymer matrices on thermal properties of composites. Designed high thermally conductive and electrically insulative composites are expected to possess unique properties. This includes being lightweight, injection moldable, low coefficients of thermal expansion, eco-friendly, and with proper service temperature and mechanical properties. Such composites will result in more compact, lighter and cheaper electronics with higher performance, by avoiding the use of electrical fans, heat sinks and other methods of heat dissipation.
Two novel, origami-inspired, metamaterials were designed, mechanically tested, and modelled. One novel origami model was folded using a triangular based crease pattern and the other was folded using ...a rectangular based crease pattern. The origami-inspired metamaterial sheets were fabricated from polylactic acid using fused deposition additive manufacturing. Several configurations, parameterized by varying the fold angle, were mechanically tested under compression and impact loads. It was found that the specific elastic compression modulus of these novel designs was higher, ranging from 594 MPa/kg to 926 MPa/kg, than existing origami-inspired structures made based on the popular Ron-Resch design, which had specific elastic compression moduli between 15 MPa/kg to 365 MPa/kg. A finite element model further analysed the stress distribution of the core structures under compression loads. The impact testing results showed that the pattern of the tessellated cores affected the amount of impact force transferred through the samples, whereas the fold angle of the origami-inspired design had little impact on the results. The rectangular structure was shown to transfer approximately 50–75% of the force transferred by the triangular structure under impact loads.
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•Two novel, origami-inspired, tessellated patterns were designed for use as light-weight cores in sandwich structures.•Compressions tests showed that increasing fold angle improved the metamaterials’ resistance to compression loads.•The elastic compression moduli of both new designs were higher than that of existing Miura-ori and Ron Resch designs.•The ability to absorb impact force was dependant on the tessellated design pattern and independent of the origami fold angle.
In recent decades, the development and optimization of supercapacitors have garnered a great deal of attention for the reason that it is a promising method to store energy and supply power to the ...wireless sensors and portable electronics. Therefore, carbon nanotube (CNT) and zinc oxide (ZnO) based supercapacitors are reported in this paper for high-performance energy storage. The electrodes with different contents of ZnO and CNT are obtained by orderly depositing carbon nanofiber (CNF), ZnO and CNT nano-materials on tissue substrates through the method of suction filtration. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and electrochemical testing are carried out in the experiments to characterize the composition, morphology and electrochemical performance of the electrodes. Results show that the increase in the content of CNT will enhance capacitive performance. While for ZnO, the capacitive performance of the electrodes will firstly increase and then decrease with the increase of the content. Furthermore, the largest areal capacitance obtained in the experiment at a scan rate of 50 mV/s is 14.6 mF/cm2. Finally, the sensing ability of the electrode is demonstrated by output voltage under finger tapping testing due to the piezoelectricity of ZnO.
This paper presents a novel aerogel-based Triboelectric Nanogenerator (TENG) which shows a superior performance for energy harvesting and sensing applications. Polyimide-based aerogel film with ...varying open-cell content level is developed to be used as the main contact material for the TENG. The fabricated aerogel film is fully characterized to reveal the chemical and mechanical properties of the developed material. It is shown the use of Polyimide aerogel film remarkably enhances the performance of the TENG compared to a TENG with fully dense Polyimide layer with no porosity. This enhancement is due to the increase on the effective surface area, charge generation inside the open-cells of the aerogel, and increase on the relative capacitance of the TENG device. The effect of varying porosity from zero to 70% of open-cell content reveals that the aerogel film with 50% shows the highest performance where the peak open-circuit voltage of 40V and peak short-circuit current of 5 μA are obtained. These values are higher than those of the TENG with simple Polyimide layer with an order of magnitude. Finally, the performance of proposed TENG under resistive loads and capacitors are tested. Thus, this work presents an effective method for high performance TENG.
In this paper, we originally report an approach for cantilever piezoelectric energy harvesters (PEHs) for frequency tuning and performance improvement. The proposed scheme implements embedment of ...revolute joint(s) into PEH structure. We investigated two ways of embedment: the prior one is to replace the clamped edge partially with a joint and the other is to incorporate joint(s) into the substrate plane. Introducing joint mechanism reduces stiffness of the harvester, leading to more intense vibration and higher voltage of the piezoelectric element. We conducted FEA to validate hypothetical stiffness reduction by deriving resonant frequency considering parameters of joint width, length and number. Furthermore, experimental studies were conducted to compare open-circuit voltages in the frequency domain, power generation and capacitor-charging capabilities. The resonant frequencies from experiments display a good agreement with those from our simulation estimations. The embedded joint(s) effectively lowers resonant frequency by ∼43.1%. The output voltage of jointed cases increases ∼71.2 V, 2.83 times as high as that of the counterpart case. The mean power of the jointed cases reaches 0.49 mW, 7.3 times as high as that of the counterpart case. Furthermore, experimental charging results indicate remarkable improvement in charging capabilities regarding much higher charging rates and higher saturated voltage.
•Original study of favorable effects of joints on piezoelectric energy harvesters.•Embedded joints can effectively tune the resonant frequency of the harvester.•A 630% output power improvement due to the joint embedment.•Much higher charging rates and voltages in charging performance of capacitors.
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