Welcome to SmARTextiles Lab

At the beginning of my tenure at NC State my research focus was mainly on process simulation as it relates to ring spinning and over-end unwinding. Initially, I worked with my colleague at the college, Profs. Subhash Batra and M. Zeidman.  Later the team also included Prof. Barrie Fraser of the School of Mathematics and Statistics of the University of Sydney. In ring spinning, we developed analytical and subsequently computational models to explain the shape, tension distribution, and stability of the balloon as a function of the spinning geometry bobbin radius, balloon height, etc.), traveler mass, and speed with or without consideration of air-drag. The theory was finally modified to show the effects of the control ring.   In unwinding, we provided a theoretical framework using a regular perturbation expansion to approximate the time dependence of the moving boundary condition (at the unwinding point).  The method helped explain the relationship between yarn movements on and off the package during unwinding and thereby obtain the solution of the problem with appropriate continuity between solutions. The research results published in twelve papers are considered some of the most important in this area.

The first of my notable research collaborations is that with Prof. Richard Spontak, of the Chemical and Biomolecular Engineering Department of NC State. My interaction with Prof. Spontak began in mid-2005 after I returned from an SPIE conference on polymer actuators and invited Prof. Spontak to a casual lunch-time conversation on my interest in the evolving research area of dielectric electroactive polymers and textiles. The discussion soon produced two significant research grants (NSF and National Textile Center), and many years of intense and very productive collaborative work on exploring the electroactive behavior of nanostructued elastomer gels. It led to the development of a new class of electroactive dielectric elastomers, thermoplastic elastomer gels that are readily tunable to a wide spectrum of electromechanical properties. The materials we developed, exhibit high levels of actuation strain (up to ~300% area strain) under relatively low electric fields (as low as ~20 V/m) with negligible strain hysteresis and comparable energy density, efficiency, and damping as human muscles. We demonstrated the use of nanostructured polymers whose properties can be broadly tailored by varying copolymer characteristics or blend composition represents an innovative and tunable avenue to reduced-field actuation for advanced engineering, biomimetic, and biomedical applications. Along the way, the research produced four doctoral dissertations, and 12 peer-reviewed research papers in high impact journals.

The second example comes from my research collaboration with Prof. Alper Bozkurt of the ECE department on the study of fiber-based electronics. Once again, I initiated the conversation with Prof. Bozkurt on some of my ideas in the emerging field of electronic textiles (e-textiles) back in 2011. Once the research ideas took shape and we began generating some data, we received funding from NC State’s Chancellor’s Innovation Fund and two back-to-back research grants from the NSF. The second NSF grant had two additional PIs, one from NC State and the other from UNC, Chapel Hill. In this ongoing research, we are developing a transformative technology through the design of a multimodal and multifunctional sensor array formed within a woven fabric structure using extrusion printed bicomponent fibers. Our fibers are able to measure tactile (compressive), tensile, shear deformations, as well as wetness of the fiber assembly through capacitive and/or resistive measurement. The exceptional strength of our approach is in its facile scalability and its potential to manufacture from a wide variety of materials using simple and time-tested industrial processes. Our sensory fibers can be manufactured using commercial bicomponent melt extrusion systems and can be easily assembled into sensor arrays using a commercial roll-to-roll weaving process, thus allowing a simple, cheap, yet robust sensing platform for high-performance, large-area e-textile sensors. We currently have five doctoral students working on the project, and we have already published eight peer-reviewed research papers.

More recently, I have made the study of biomimetic actuation and control the central focus of my research. Movement and morphing in biological systems provide insights into the materials and mechanisms that may enable the development of advanced engineering structures. The nastic motion of plants in response to environmental stimuli, e.g., the rapid closure of the Venus flytrap’s leaves, utilizes snap-through instabilities originating from anisotropic deformation of plant tissues. In contrast, ballistic tongue projection of chameleon is attributed to direct mechanical energy transformation by stretching elastic tissues in advance of rapid projection to achieve higher speed and power output. In this instance, I began working with Prof. Douglas P. Holmes of the Department of Mechanical Engineering, Boston University at the beginning of 2016. Prof. Holmes is a well-known expert in the mechanics of slender and soft structures like rods, plates, and shells. Our primary objective in this research has been to utilize electrically active polymers for the controlled deformation and buckling of thin structures to control shape fluid flow. We believe a fundamental understanding of the bistability and control of these shapes will open up new opportunities in textile-based devices and systems for comfort and protection. In a recently published work, we demonstrated a bioinspired trilayered bistable all-polymer laminate containing dielectric elastomers (DEs) is reported, which double as both structural and active materials. It is demonstrated that the prestress and laminating strategy induces tunable bistability, while the electromechanical response of the DE-film enables reversible shape transition and morphing. Electrical actuation of bistable structures obviates the need for continuous application of electric field to sustain their transformed state. The experimental results are qualitatively consistent with our theoretical analyses of prestrain-dependent shape and bistability.

The research is aimed at developing appropriate technology necessary to produce three-dimensional molded garments to produce low-cost combat uniforms with effective barrier characteristics, using minimal joining. The system being developed is called Robotic Fiber Assembly and Control (RFAC) system. RFAC system will allow the incorporation of fibers, powders, or other appropriate additives into the garment systems. The additives may identify, measure, absorb, and/or deactivate chemical/biological agents. In the RFAC system deposition of melt-blown fibers on an appropriate mold is controlled by a six-axis industrial robot. The system allows precise control of fiber orientation distribution, fiber diameter distributions, and pore size distribution.

Fiber actuators are capable of dimensional change under the applied electrical field. Dielectric elastomer-based prototype fiber actuators have been developed using commercially available dielectric elastomer tubes and by applying appropriate compliant electrodes to the inner cavity and outer walls of these tubes. The force and displacement generated by such actuators have been studied under different isometric conditions and as a function of the applied electric field. The actuation characteristics such as axial strains, radial strains, and actuation blocking forces produced in the prototype upon actuation were studied. Actuation strain and blocking force are strongly influenced by the applied prestrain and have a parabolic relationship to the applied electric field. High actuation strains (>50%) are currently afforded by dielectric elastomers at relatively high electric fields (>50 V/µm). A new class of electroactive polymers, suitable for fiber formation, have been developed by incorporating low-volatility, aliphatic-rich solvent into a nanostructured triblock copolymer yielding physically crosslinked micellar networks that exhibit excellent displacement under an external electric field. Ultrahigh areal actuation strains (>200%) at significantly reduced electric fields (<40 V/µm) has been achieved.

Fabric-based electrical circuits are fundamental to electronic textile products of the future. The objective of the current research is to develop fabric-based electrical circuits by interlacing conducting and non-conducting threads into woven textile structures for civilians as well as military applications. Wired interconnections between different devices attached to the conducting elements of these circuits are made by weaving conductive threads so that they follow desired electrical circuit designs. In a woven electrically conductive network, routing of electrical signals is achieved by the formation of effective electrical interconnects and disconnects. Resistance welding is identified as one of the most effective means of producing crossover point interconnects and disconnects. These circuits are evaluated for signal integrity issues (crosstalk, etc.). Two new thread structures – coaxial and twisted Pair copper threads to minimize cross talk have been developed and evaluated. Significant reductions in crosstalk were obtained with the coaxial and twisted pair thread structures when compared with bare copper thread or insulated conductive threads.