Cognizant Fiber-Reinforced Polymer Composites Incorporating Seamlessly Integrated Sensing and Computing Circuitry.

Structural fiber-reinforced polymer (FRP) composite materials consisting of a polymer matrix reinforced with layers of high-strength fibers are used in numerous applications, including but not limited to spacecraft, vehicles, buildings, and bridges. Researchers in the past few decades have suggested the necessary integration of sensors (e.g., fiber optic sensors) in polymer composites to enable health monitoring of composites' performance over their service lives. This work introduces an innovative cognizant composite that can self-sense, compute, and implement decisions based on sensed values. It is a critical step towards smart, resilient infrastructure. We describe a method to fabricate textile sensors with flexible circuitry and a microcontroller within the polymer composite, enabling computational operations to take place in the composite without impacting its integrity. A microstructural investigation of the sensors showed that the amount of oxidative agent and soaking time of the fabric play a major role in the adsorption of polypyrrole (PPy) on fiberglass (FG). XPS results showed that the 10 g ferric chloride solution with 6 h of soaking time had the highest degree of protonation (28%) and, therefore, higher adsorption of PPy on FG. A strain range of 30% was achieved by examining different circuitry and sensor designs for their resistance and strain resolution under mechanical loading. A microcontroller was added to the circuit and then embedded within a composite material. This composite system was tested under flexural loading to demonstrate its self-sensing, computing, and actuation capabilities. The resulting cognizant composite demonstrated the ability to read resistance values and measure strain using the embedded microcontroller and autonomously actuate an LED light when the strain exceeds a predefined limit of 2000 µÎµ. The application of the proposed FRP system would provide in situ monitoring of structural composite components with autonomous response capabilities, as well as reduce manufacturing, production, and maintenance costs.

Development and Characterization of a Sustainable Bio-Polymer Concrete with a Low Carbon Footprint.

Polymer concrete (PC) has been used to replace cement concrete when harsh service conditions exist. Polymers have a high carbon footprint when considering their life cycle analysis, and with increased climate change concerns and the need to reduce greenhouse gas emission, bio-based polymers could be used as a sustainable alternative binder to produce PC. This paper examines the development and characterization of a novel bio-polymer concrete (BPC) using bio-based polyurethane used as the binder in lieu of cement, modified with benzoic acid and carboxyl-functionalized multi-walled carbon nanotubes (MWCNTs). The mechanical performance, durability, microstructure, and chemical properties of BPC are investigated. Moreover, the effect of the addition of benzoic acid and MWCNTs on the properties of BPC is studied. The new BPC shows relatively low density, appreciable compressive strength between 20-30 MPa, good tensile strength of 4 MPa, and excellent durability resistance against aggressive environments. The new BPC has a low carbon footprint, 50% lower than ordinary Portland cement concrete, and can provide a sustainable concrete alternative in infrastructural applications.

Titanium mesh as a low-profile alternative for tension-band augmentation in patella fracture fixation: A biomechanical study.

OBJECTIVES: We performed a simple biomechanical study to compare the fixation strength of titanium mesh with traditional tension-band augmentation, which is a standard treatment for transverse patella fractures. We hypothesised that titanium mesh augmentation is not inferior in fixation strength to the standard treatment. METHODS: Twenty-four synthetic patellae were tested. Twelve were fixed with stainless steel wire and parallel cannulated screws. Twelve were fixed with parallel cannulated screws, augmented with anterior titanium mesh and four screws. A custom test fixture was developed to simulate a knee flexed to 90°. A uniaxial force was applied to the simulated extensor mechanism at this angle. A non-inferiority study design was used to evaluate ultimate force required for failure of each construct as a measure of fixation strength. Stiffness of the bone/implant construct, fracture gap immediately prior to failure, and modes of failure are also reported. RESULTS: The mean difference in force at failure was -23.0 N (95% CI: -123.6 to 77.6N) between mesh and wire constructs, well within the pre-defined non-inferiority margin of -260 N. Mean stiffness of the mesh and wire constructs were 19.42 N/mm (95% CI: 18.57-20.27 N/mm) and 19.49 N/mm (95% CI: 18.64-20.35 N/mm), respectively. Mean gap distance for the mesh constructs immediately prior to failure was 2.11 mm (95% CI: 1.35-2.88 mm) and 3.87 mm (95% CI: 2.60-5.13 mm) for wire constructs. CONCLUSIONS: Titanium mesh augmentation is not inferior to tension-band wire augmentation when comparing ultimate force required for failure in this simplified biomechanical model. Results also indicate that stiffness of the two constructs is similar but that the mesh maintains a smaller fracture gap prior to failure. The results of this study indicate that the use of titanium mesh plating augmentation as a low-profile alternative to tension-band wiring for fixation of transverse patella fractures warrants further investigation.

Improved Strength and Toughness of Carbon Woven Fabric Composites with Functionalized MWCNTs.

This investigation examines the role of carboxyl functionalized multi-walled carbon nanotubes (COOH-MWCNTs) in the on- and off-axis flexure and the shear responses of thin carbon woven fabric composite plates. The chemically functionalized COOH-MWCNTs were used to fabricate epoxy nanocomposites and, subsequently, carbon woven fabric plates to be tested on flexure and shear. In addition to the neat epoxy, three loadings of COOH-MWCNTs were examined: 0.5 wt%, 1.0 wt% and 1.5 wt% of epoxy. While no significant statistical difference in the flexure response of the on-axis specimens was observed, significant increases in the flexure strength, modulus and toughness of the off-axis specimens were observed. The average increase in flexure strength and flexure modulus with the addition of 1.5 wt% COOH-MWCNTs improved by 28% and 19%, respectively. Finite element modeling is used to demonstrate fiber domination in on-axis flexure behavior and matrix domination in off-axis flexure behavior. Furthermore, the 1.5 wt% COOH-MWCNTs increased the toughness of carbon woven composites tested on shear by 33%. Microstructural investigation using Fourier Transform Infrared Spectroscopy (FTIR) proves the existence of chemical bonds between the COOH-MWCNTs and the epoxy matrix.

Mechanical and Electrical Characterization of Entangled Networks of Carbon Nanofibers.

Entangled networks of carbon nanofibers are characterized both mechanically and electrically. Results for both tensile and compressive loadings of the entangled networks are presented for various densities. Mechanically, the nanofiber ensembles follow the micromechanical model originally proposed by van Wyk nearly 70 years ago. Interpretations are given on the mechanisms occurring during loading and unloading of the carbon nanofiber components.

A cadaver model that investigates irreducible metacarpophalangeal joint dislocation.

PURPOSE: Controversy exists over the pathologic anatomy of irreducible dorsal metacarpophalangeal (MCP) dislocation. The aim of this work is to develop a cadaveric model of MCP joint dislocation that closely simulates the clinical situation and to study the structures around the MCP joint and their contribution to irreducibility of the dislocation. METHODS: Nine fresh-frozen cadaveric specimens were amputated at the radiocarpal joint and stabilized in a specially formulated fixture. The dislocation was created by an impact load delivered by a servohydraulic testing machine, at a displacement rate of 1000 mm/s and with a maximum displacement of 60 mm. An irreducible dislocation was successfully created in 6 index fingers. An attempt at closed reduction was followed by a dissection of the dislocated joint. RESULTS: In the 6 examined specimens, the flexor tendons were ulnar to the joint in all cases, the radial digital nerve was superficial (5 cases) or radial (5 cases) to the metacarpal head, and the lumbrical was usually radial (5 of 6 cases) to the joint. Division of the superficial transverse metacarpal ligaments, natatory ligaments, flexor tendons, or lumbricals does not aid reduction of the dislocation. Division of the volar plate was necessary for reduction of the dislocation in all 6 cases, whereas division of the deep transverse metacarpal ligaments does not allow reduction of the dislocation. CONCLUSIONS: We present a model for creating an irreducible MCP joint dislocation using an impact load that simulates the clinical situation. The volar plate is the primary structure preventing reduction of the dislocation. Division of the deep transverse metacarpal ligament is not effective in reducing the dislocation. The flexor tendons, lumbricals, superficial transverse metacarpal ligament and natatory ligaments do not contribute to irreducibility. The anatomy of the structures surrounding the MCP joint is variable, and careful dissection to prevent iatrogenic injuries is mandatory.