Fused deposition modeling (FDM) is a widely implemented manufacturing technique typically used for rapid prototyping of custom components or geometries. Unfortunately, FDM printers are often limited by build volume, print quality, and print time. Build volume is traditionally fixed, such that components larger than a given printer volume must be printed separately as segmented components, and subsequently bonded to one another. Beyond the limitations of the build volume, the quality of prints is another key concern. The components that make up a larger 3D printer often cannot produce the fidelity of a smaller precise printer, thus limiting the device to solely larger components. Print time is also a function of the previous limitations; a faster print will typically have lower quality and a smaller print will often print quicker. This project seeks to address the limitations of a traditional FDM printer through the development of a modular 3D printer. Standard 3D printers operate with a rigid metal frame that inhibits the freedom to increase the print volume. The design proposed would allow a 3D printer to expand or contract in build volume while also allowing the user to customize needs depending on requirements of print fidelity or print time. The modularity further allows for compact storage and the ability to be transported for on-site prints, which would be particularly useful for wearables and orthopedic adjustments for athletics or within the medical field. In fact, compact storage size to maximum expanded printer size aims to be a 1 to 10 ratio. The design is self-printing, in that frame components are manufactured from the printer itself, to elongate the dimensions, without sacrificing print fidelity. Any desired build volume can be easily accommodated by printing additional frame components. Such a design is ideal for custom wearables or large-scale projects where a rigid printer structure occupies excessive space. This could prove especially useful for astronauts where cargo shipments are dependent on volume and mass or in fields where custom-fitted wearables are required, such as in athletics or the medical field.

Ambient environmental effects can often interfere with transducers and affect the accuracy of sensor readings. A typical method of compensating for temperature in strain measurements is to construct a full-bridge Wheatstone circuit. The objective of this study was to design patterned nanocomposites deposited onto fabric substrates to form a materials-based Wheatstone bridge circuit that could automatically compensate for unwanted ambient effects. Motion Tape (i.e., a self-adhesive, elastic-fabric-based nanocomposite sensor) specimens with patterned nanocomposite elements and conductive traces were designed to form a full-bridge circuit. The results showed that their strain sensing response was not adversely affected by concurrent temperature effects.

Cellulose is attractive for in fabricating renewable triboelectric nanogenerators (TENGs) due to its lightweight, flexibility, renewability, and biodegradability. However, the insufficient functional groups and weak polarization on the surface restrict its progress towards high-performance TENGs. Therefore, this research has developed flexible environment-friendly TENGs with significant output performance based on polyvinyl alcohol (PVA)/graphene oxide (GO) and cellulose films. Furthermore, the specific contact surface area of the films is improved by patterning rectangular dots using a photolithography technique. Moreover, the concentration of GO, size of friction layers, and thickness are optimized in terms of triboelectric output performance. The scanning electron microscope is used to observe the surface morphology of the prepared TENGs films. We believe that the fabricated TENGs have the potential to be applied for self-powered biomedical applications.

3D printing, commonly referred to as additive manufacturing (AM), is a rapid technique of making three-dimensional structures from a computer-based design model. Various materials have been used to manufacture 3D structures for different engineering applications, including synthetic and natural materials. In the case of natural materials for 3D printing, nanocellulose gain much attention as a feedstock material for AM techniques due to its high strength, lightweight, and biocompatibility. However, the mechanical properties exhibited in high concentration nanocellulose printed 3D structures are unsatisfactory, as demonstrated in their building blocks due to drying issues. Therefore, this research aims to optimize the proper drying conditions for 3D printed high concentration nanocellulose structures. The 3D printed structures are dried at different humidity and temperature conditions and evaluated their mechanical properties. The scanning electron microscope is utilized to observe the morphology of 3D printed high concentration nanocellulose structures. The research results will significantly help nanocellulose-based industries to overcome the drying issues in 3D printed high concentration nanocellulose structures.

Strong and tough cellulose nanofibers (CNF) are in high demand in the field of polymer composites. Recently, researchers have successfully employed different alignment techniques such as wet spinning, stretching, electric field, and magnetic field alignment to improve the mechanical properties of CNFs. However, none of these techniques were capable to achieve the goal of tensile strength above 600MPa. Herein, we utilize a high-performance bio-based hydrogen-bonded polyvinyl alcohol-citric acid-lignin (H-PCL) resin synthesized by our research group to functionalize CNFs via coating and blending techniques followed by post-heat treatment at 180℃ for esterification of resin. The esterified poly (vinyl alcohol)-citric acid-lignin resin (E-PCL)-CNF fibers were characterized and discovered to exhibit a dramatic increase in mechanical properties. Moreover, E-PCL/CNF fibers also possess high hydrophobicity and high thermal stability. These exceptional and impressive properties of E-PCL/CNF make them an ideal candidate for all-green fiber-reinforced polymer composites and in other structural applications.

In this work, we report rapid, high-resolution three-dimensional (3D) printing of piezoelectric composite structures via micro continuous liquid interface production (μCLIP). We formulated chemically functionalized, photo-curable resins using piezoelectric nanoparticles (PiezoNPs) such as barium titanate (BTO) and achieved 3D printings of high-resolution composite structures with piezoelectric performance comparable to other vat-polymerization-based works but come at drastically boosted speeds. Proof-of-concept demonstrations utilizing the composite further validate its capability in a variety of flexible and wearable sensing applications.

Functional neuroimaging techniques are becoming mandatory tools for neuroscience research and brain disorders medical therapy, respectively. Electrical Impedance Tomography (EIT) has been impressed neuroscientists for its advantages of fast, radiation-free, and low-cost brain visualization method. Implementation of EIT on neuroimaging requires high performance data acquisition system which significantly depends on analog and digital electronic circuitry to achieve high and improve signal to noise ratio (SNR). A proposed EIT system based on high performance digital signal processor (DSP) has been successfully designed and developed for first prototype. A precise data acquisition unit that provides 24-bit 16 channels simultaneously sampling up to 100ksps was integrated into the system alongside with stable and biocompatible stimulation analog current source. Simulation of analog circuitry was constructed using PSPICE software. The proposed EIT system was designed using Cadence PCB Editor software to acquire compact integration requirements with all EIT components on a single circuit board. Evaluation of the proposed EIT system was conducted in a neural simulated environment phantom experiment. With this proposed system, EIT study on neural activity recording and neuroimaging has potentials to accelerate both in speed and performance to approach real-time imaging.

This study involves implantable flexible polymer-based probes where these microelectrodes would then be used later for neural recordings in vivo, using rodents as test subjects. Neural electrodes are used for medical purposes to record action potential or local field potential that comes from brain activity. Flexible polymer-based probes are used in order to reduce the effects of glial scars that come from surgery, also the polymer has high mechanical strengths, high dielectric, and good biocompatibility. Fabricating and studying the effects of impedance is the key part of this experiment for data accusation of these electrodes. Impedance that has a good signal-to-noise ratio is the goal in this research. Later, the impedance data that is collected from the working electrode over a wide range of frequencies would then be fitted using a CH Instrument and/or ZSimWin to create an equivalent integrated circuit (IC) model that mimics the real experiment to get a deeper understanding on its electrical properties. For the preparation of polymer-based electrodes, Tungsten electrodes and Carbon electrodes were tested with Phosphate-buffered saline (PBS) solution which completed the circuit. By having to test two different electrodes, Data acquisition was the next step to see which electrode give the best result.

Conductive self-healing (SH) hydrogels have been receiving significant attention benefiting from the behavior of living tissue to improve the design of health monitoring systems and soft robotics with the ability of repairing damages autonomously. Herein, we propose a novel approach of high-resolution 3D printing of ion-conductive SH hydrogel realized by high-speed continuous printing of interpenetrating polymer network (IPN) hydrogel based on physical crosslinking of poly(vinyl alcohol) combined with chemical/ionic crosslinking of acrylic acid and ferric chloride. The 3D printed hydrogel can fully recover the mechanical properties after 12 h without any external stimulus, and the ionic conductivity enables strain and pressure sensing capabilities.

By having the capability of shape-shifting, shape memory polymer is widely used on different kind of applications. One of the actuator configurations is made into a tubular shape actuator. Several methods have been developed to heat the SMP tube, such as blowing hot air and flowing through heated liquid. However, these methods aren’t robust since it is difficult to control the exact temperature on the component. To solve this problem, silver paint coating had been used to make the SMP tube conductive and actuated by using Joule heating. Although silver paint coating seems to work well, it isn’t mechanically robust. Over time, the coating develops cracks once the spring go through multiple extensions and contractions. These micro cracks will enlarge over time and render spring useless. In order to improve the SMP patterned tube into electrical controllable, a carbon nanotube (CNT) composite SMP was developed. Background, fabrication and electrical and mechanical characterization of this newly developed composite will be presented. Multidirectional movement of a actuator will be demonstrated.

A pre‐designed functional π‐conjugated nanoporous covalent organic frameworks (COFs) are suggested to develop a high‐performance electrode for electroactive ionic soft actuators. In-depth structural characterization confirm the structural integrity of the developed active materials. Nanoporous structural configuration of COFs acted as nanoreactors for boosting the transportation and accommodation of oppositely charged ions in presence of available electrolytes during the switching of an alternating current input signal. As a results, the soft electroactive actuators show fast rise times, short phase delays, strong blocking force, high bending displacement, and ultralong durability.

Artificial muscles have been used in various applications, from small to large scale robots, especially bio-inspired robots. Among many types of artificial muscles, shape memory alloy (SMA), which can be actuated through heating and cooling, have the advantage of generating high force with large deformation, thus many studies have been conducted on their application as artificial muscles. However, limited actuation speed and bandwidth of shape memory alloy was troublesome for long time due to remarkably slow cooling rate compared to the heating. While some applications used active cooling components such as heavy and bulky air or liquid pumps, they depreciated the merit of SMA being lightweight and shape-conformable. Therefore, in this work, we focused on increasing cooling rate under natural cooling by maximizing thermal dissipation of SMA. Specifically, Cu nanowire with high thermal conductivity was directly grown on the surface of SMA which resulted with increasing the surface area of the SMA for facile heat dissipation. Accelerated cooling of Cu nanowire grown SMA showed faster actuation compared to the bare SMA, and it was successfully applied to biomimetic with enhanced working speed.

A triboelectric energy harvester with a long-lasting and steady output was developed by using an escapement mechanism to induce a much larger torque after storing the irregular input motion as elastic energy in a spiral torsion spring. The escapement mechanism-based triboelectric nanogenerator (EM-TENG) consists of the spiral torsion spring, escapement part, and a torsional resonator for regular operation and frequency up-conversion using freestanding mode interdigitated electrodes. Under only 5 s of input motion, the EM-TENG produces long-lasting and steady output power for 110 s by using the escapement mechanism.

Due to environmental concerns, replacing conventional synthetic materials with eco-friendly bio-based materials is receiving much attention from academic and industrial research. As the most abundant polymer among several bio-based materials, cellulose is widely used to produce bio-based porous materials that have been used in various applications, including packaging, thermal insulation and sound absorption. Different processing methods have been used to prepare nanocellulosic porous materials but the specific requirement and time consuming process limit the use of these methods for large-scale production. Further, the use of toxic and expensive inorganic or synthetic blowing agents or crosslinking agents limits the applications of these porous materials. Therefore, to overcome these drawbacks, we used an environmentally friendly, time-saving, economical process to produce bio-based cellulose nanofiber (CNF) foam using bio-based nontoxic and inexpensive citric acid as a green crosslinking agent. The foam is prepared by homogenizer followed by freezing, solvent exchange and oven drying. The prepared foam indicates low shrinkage and has a very low density. The foam shows a highly porous structure (more than 98% porosity) and the morphology of the foam is examined by SEM. The FTIR study confirms the covalent crosslinking, and the foam shows high compressive modulus and strength.

Recently, extrusion-based 3D printing has been widely used to manufacture precise and accurate 3D structures with high nanocellulose concentrations due to excellent materials flow control and system stability. With the extrusion-based 3D printing technique, the main challenges for precision and accuracy in high concentration nanocellulose 3D printed structures are proper printing parameters and appropriate adhesion between printed layers. Therefore, this study aims to improve the adhesion between high content nanocellulose printed layers by blending different lignin concentrations and optimizing the twin-screw extruder printing parameters. The lignin concentrations are optimized in nanocellulose paste by assessing the mechanical properties, shape retention, and shrinkage of 3D printed structures. To ease shape retention, the 3D printed structures are dried at controlled humidity (45%) and temperature (25oC). The surface morphology of the 3D printed structures is observed by scanning electron microscope.

Graphene is a proper selection for triboelectric nanogenerators (TENGs) because of its outstanding properties such as high electrical conductivity, specific surface area, aspect ratio, mechanical strength, flexibility, and transparency. In addition, Polydimethylsiloxane (PDMS) is a triboelectric material that is transparent, flexible, and biocompatible. Nanogenerators based on graphene has several advantages over other nanogenerators including flexibility, simplicity, and structural stability. Graphene/PDMS nanocomposites can be made with good electrical and mechanical properties for use in TENGs. In the present research work, Graphene/PDMS nanocomposites with varying amounts of graphene (0, 0.05, 0.5, 1, and 1.5 wt.%) have been synthesized. The effect of chemical composition and surface modification on the properties of nanocomposites, including transparency, roughness, and contact angle has been investigated. Comparison of these results revealed the optimized nanocomposite for application in TENGs