Fundamentals of Modern Manufacturing: Materials, Processes and Systems

High-performance electromagnetic interference (EMI) shielding materials with ultraflexibility, outstanding mechanical properties, and superior EMI shielding performances are highly desirable for mo

Ultraflexible and Mechanically Strong Double-Layered Aramid Nanofiber-Ti3C2Tx MXene/Silver Nanowire Nanocomposite Papers for High-Performance Electromagnetic Interference Shielding.

We use multispeckle dynamic light scattering to measure the dynamic structure factor, f(q,tau), of gels formed by aggregation of colloids. Although the gel is an elastic solid, f(q,tau) nearly completely decays on long time scales, with an unusual form, f(q, tau) approximately exp{-(tau/tau(f))(mu)}, with mu approximately 1.5 and with tau(f) proportional variant q(-1). A model for restructuring of the gel with aging correctly accounts for this behavior. Aging leads to a dramatic increase in tau(f); however, all data can be scaled on a single master curve, with tau(f) asymptotically growing linearly with age. This behavior is strikingly similar to that predicted for aging in disordered glassy systems, offering convincing proof of the universality of these concepts.

Universal Aging Features in the Restructuring of Fractal Colloidal Gels

High-performance and rapid response electrical heaters with ultraflexibility, superior heat resistance, and mechanical properties are highly desirable for the development of wearable devices, artificial intelligence, and high-performance heating systems in areas such as aerospace and the military. Herein, a facile and efficient two-step vacuum-assisted filtration followed by hot-pressing approach is presented to fabricate versatile electrical heaters based on the high-performance aramid nanofibers (ANFs) and highly conductive Ag nanowires (AgNWs). The resultant ANF/AgNW nanocomposite papers present ultraflexibility, extremely low sheet resistance (minimum Rs of 0.12 Ω/sq), and outstanding heat resistance (thermal degradation temperature above 500 °C) and mechanical properties (tensile strength of 285.7 MPa, tensile modulus of 6.51 GPa with a AgNW area fraction of 0.4 g/m2), benefiting from the partial embedding of AgNWs into the ANF substrate and the extensive hydrogen-bonding interactions. Moreover, the ANF/AgNW nanocomposite paper-based electrical heaters exhibit satisfyingly high heating temperatures (up to ∼200 °C) with rapid response time (10-30 s) at low AgNW area fractions and supplied voltages (0.5-5 V) and possess sufficient heating reliability, stability, and repeatability during the long-term and repeated heating and cooling cycles. Fully functional applications of the ANF/AgNW nanocomposite paper-based electrical heaters are demonstrated, indicating their excellent potential for emerging electronic applications such as wearable devices, artificial intelligence, and high-performance heating systems.

High-Performance and Rapid-Response Electrical Heaters Based on Ultraflexible, Heat-Resistant, and Mechanically Strong Aramid Nanofiber/Ag Nanowire Nanocomposite Papers

Lightweight, robust, and thin aerogel films with multifunctionality are highly desirable to meet the technological demands of current society. However, fabrication and application of these multifunctional aerogel films are still significantly underdeveloped. Herein, we demonstrate a multifunctional aerogel film composed of strong aramid nanofibers (ANFs), conductive carbon nanotubes (CNTs), and hydrophobic fluorocarbon (FC) resin. The obtained hybrid aerogel film exhibits large specific surface area (232.8 m2·g-1), high electrical conductivity (230 S·m-1), and excellent hydrophobicity (contact angle of up to 137.0°) with exceptional Joule heating performance and supreme electromagnetic interference (EMI) shielding efficiency. The FC coating renders the hydrophilic ANF/CNT aerogel films hydrophobic, resulting in an excellent self-cleaning performance. The high electrical conductivity enables a low-voltage-driven Joule heating property and an EMI shielding effectiveness (SE) of 54.4 dB in the X-band at a thickness of 568 μm. The specific EMI SE is up to 33528.3 dB·cm2·g-1, which is among the highest values of typical metal-, conducting-polymer-, or carbon-based composites. This multifunctional aerogel film holds great promise for smart garments, electromagnetic wave shielding, and personal thermal management systems.

Multifunctional Aramid Nanofiber/Carbon Nanotube Hybrid Aerogel Films.

Interconnectivity of components in three-dimensional networks (3DNs) is essential for stress transfer in hydrogels, aerogels, and composites. Entanglement of nanoscale components in the network relies on weak short-range intermolecular interactions. The intrinsic stiffness and rod-like geometry of nanoscale components limit the cohesive energy of the physical crosslinks in 3DN materials. Nature realizes networked gels differently using components with extensive branching. Branched aramid nanofibers (BANFs) mimicking polymeric components of biological gels were synthesized to produce 3DNs with high efficiency stress transfer. Individual BANFs are flexible, with the number of branches controlled by base strength in the hydrolysis process. The extensive connectivity of the BANFs allows them to form hydro- and aerogel monoliths with an order of magnitude less solid content than rod-like nanocomponents. Branching of nanofibers also leads to improved mechanics of gels and nanocomposites.

Branched Aramid Nanofibers.

Despite the promise of additive manufacturing (AM) to bring unprecedented agility and design freedom to manufactured components, structural applications remain largely out of reach due to material restrictions – notably the lack of a mature AM process for reinforced thermoset composites. AM is also hindered by process-induced defects such as porosity and unfavorable microstructure. This research shows that a direct write AM process for epoxy / chopped carbon fiber composites can simultaneously achieve a high degree of fiber alignment and low degree of porosity, obtaining 90% of the theoretical tensile modulus and 66% of the theoretical tensile strength for a fully aligned composite. These values exceed those of compression molded properties for the same material. Transverse properties of AM samples were roughly half of the longitudinal properties but showed no statistically significant difference from the matrix material, suggesting that the process may not adversely affect microstructure. The addition of only 5.5 vol% carbon fiber more than doubled the strength and stiffness of the neat epoxy, and more than tripled the properties of ABS thermoplastic while achieving a higher glass transition temperature. Flexural properties show similar trends. SEM and CT imaging shows that fiber orientation is largely maintained in the print direction and cross-section micrographs show there is sufficient local material flow during deposition to achieve low porosity.

Mechanical Properties of Printed Epoxy-Carbon Fiber Composites

Skeletal muscle function, which is essential in the human body, can be lost due to injury, trauma, or diseases such as muscular dystrophy, prompting the need for in vitro models of human skeletal muscle tissue. In vitro tissue models are indispensable in performing quantitative studies of injury and disease progression as well as in providing sources of tissue for potential regenerative medicine therapies. An ideal bioengineered model of skeletal muscle should promote myoblast (muscle cell precursor) alignment as well as subsequent myoblast fusion into mature, multinucleated muscle cells known as myotubes. Accordingly, we report the development of an engineered protein biomaterial that promotes the alignment and fusion of primary human myoblasts into organized and differentiated myotubes. Furthermore, these aligned human myotubes exhibit markers of functional maturation including organization of sarcomeres (the force-generating apparatus within muscle) and induced contractility upon electrical stimulation.

Protein-Engineered Biomaterials to Generate Human Skeletal Muscle Mimics

Extrusion-based additive manufacturing methods, such as direct-write of carbon fiber-reinforced epoxy inks, have become an attractive route toward development of structural composites in recent yea...

In Operando Monitoring of Dynamic Recovery in 3D-Printed Thermoset Nanocomposites by XPCS.

OBJECTIVE The goal of this analysis was to define temporal and geographic trends in the surgical treatment of Chiari malformation Type I (CM-I) in a large, privately insured health care network. METHODS The authors examined de-identified insurance claims data from a large, privately insured health care network of over 58 million beneficiaries throughout the United States for the period between 2001 and 2014 for all patients undergoing surgical treatment of CM-I. Using a combination of International Classification of Diseases (ICD) diagnosis codes and Current Procedural Terminology (CPT) codes, the authors identified CM-I and associated diagnoses and procedures over a 14-year period, highlighting temporal and geographic trends in the performance of CM-I decompression (CMD) surgery as well as commonly associated procedures. RESULTS There were 2434 surgical procedures performed for CMD among the beneficiaries during the 14-year interval; 34% were performed in patients younger than 20 years of age. The rate o...

https://thejns.org/downloadpdf/journals/j-neurosurg-pediatr/19/2/article-p208.pdf

Kyle Johnson

Papers

Branched Aramid Nanofibers.

Mechanical Properties of Printed Epoxy-Carbon Fiber Composites

Protein-Engineered Biomaterials to Generate Human Skeletal Muscle Mimics

In Operando Monitoring of Dynamic Recovery in 3D-Printed Thermoset Nanocomposites by XPCS.

Trends in surgical treatment of Chiari malformation Type I in the United States