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 µε. 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.

Enhancement of quasi-static compression strength for aluminum closed cell foam blocks shielded by aluminum tubes

Aluminum closed cell foam blocks are created with a volume of 1 inch³ which consist of aluminum foam parts shielded with part of aluminum tube and in some types reinforced with inner aluminum tubes. Blocks have been made to overcome some existing problems in metallic foam used to protect some applications parts from impacts as a sacrificial part. Metallic foam has three main categories sandwich panels, filled tubes and corrugated sheets. Quasi-static compression tests have been applied on 12 blocks with different shapes and compared with pure aluminum foam blocks as a reference. Results display the enhancement of mechanical properties of blocks like yield strength (S_Y), crushing strength (S_c) and densification strength (S_d), compression at strain 70%, as well as absorbed energy (area of compression under the curve). The highest value for yield strength (5.87 MPa) was registered for Finger phalanxes cube block (FP-0.1 Sq.). While the highest value for densification strength (21.7 MPa) was registered for spine cylinder block (SV8-0.17 C25). The registered results for samples apparent the highest value for energy dissipation density (E_dd) is 40.52 J/in³ (91% enhancement) and crushing strength (8.61 MPa) was registered for Finger phalanx cylinder block (FP-0.17 C25). The lowest value for E_dd is 14.16 J/in³ (less than pure aluminum foam block value by 33%), S_Y = 0.42 MPa, Sc = 3.21 MPa, and S_d = 4.46 MPa, registered for thin wall Ear canal cylinder block (EC8-0.075 C26.5). Best mechanical properties had been achieved for Finger phalanx cylinder block (FP-0.17 C25) and spine cylinder block (SV8-0.17 C25).

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.

Damage in a Distal Radius Fracture Model Treated With Locked Volar Plating After Simulated Postoperative Loading

PURPOSE

"Damage" is an engineering term defining a period between a state of material perfection and the onset of crack initiation. Clinically, it is a loss of fixation due to microstructural breakdown, indirectly measured as a reduction of stiffness of the bone-implant construct, normalized by the cross-sectional area and length of the bone. The purpose of this study was to characterize damage in a cadaver model of extra-articular distal radius fracture with dorsal comminution treated using 2-column volar distal radius plates.

METHODS

Ten matched distal radii were randomly divided into 2 groups: group I specimens were treated with a volar distal radius plate with an independent, 2-tiered scaffold design; group II specimens (contralateral limbs) were treated with a volar plate with a single-head design for enhanced ulnar buttressing. Specimens were cyclically loaded to simulate a 6-month postoperative load-bearing period. We report damage after a defined protocol of cyclical loading and load to failure simulating a fall on an outstretched hand.

RESULTS

Group II specimens experienced more damage under cyclic loading conditions than group I specimens. Group I specimens were stiffer than group II specimens under load-to-failure conditions. Ultimate force at failure in group I and group II specimens was not different. Specimens failed by plate bending (group I, n = 6/10; group II, n = 2/10) and fracture of the lunate facet (group I, n = 4/10; group II, n = 8/10).

CONCLUSIONS

Group I specimens had less screw cutout at the lunate facet than group II specimens under cyclic loading as indicated by lower damage measures and fewer facet fractures during load-to-failure testing. The overall strength of the construct is not affected by plate design.

CLINICAL RELEVANCE

Microstructural damage or a loss of fixation due to an overly rigid volar plate design may cause malunion or nonunion of fracture fragments and lead to bone-implant instability.

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.

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.