Two-terminal adaptive materials and circuit elements that mimic the signal processing, learning, and computing capabilities of biological synapses are essential for next-generation computing systems. To this end, we have recently developed resistive (ion channel) and capacitive (lipid bilayer) memory elements that mimic the composition, structure, and plasticity of biological synapses. Unlike solid-state counterparts, these biomolecular systems are low-power, analog, less noisy, biocompatible, and capable of exhibiting multiple timescales of short-term synaptic plasticity. However, lipid membranes lack structural stability and modularity necessary for a long-lasting adaptive material system. To address this issue, we propose the replacement of phospholipids with amphiphilic polymers to create artificial membranes, which have been demonstrated to be more durable than phospholipids. With the focus on memory capacitors, we demonstrate that polymeric bilayers can exhibit pinched hysteresis in the Q-v plane because of voltage-induced geometrical changes. Further, we demonstrate that the memcapacitive response is altered based on the surrounding oil medium; smaller oil molecules are retained at higher volume in the membrane, so that thicker bilayers have lower nominal capacitance but can vary this value by over 400%. Finally, we present a physics-based model that enables us to predict the device’s areal voltage-dependent response. Polymeric bilayers represent a significant enhancement in the field of soft-matter, geometrically-reconfigurable memcapacitors, and their highly customizable compositions will allow for a finely tuned electrical response that has a future in brain-inspired materials and circuits.

In this paper, a new prototype is proposed for accelerated orthodontic tooth treatment. In contrast to conventional methods, where heavy vibration generators are used, the proposed design is light and small and may remain into patient’s mouth without obstructing his daily activities. To do that, a PVDF Piezoelectric actuator layer is incorporated into a bio-compatible flexible structure which is to be excited by an external electric source. Generally, application of cyclic loading (vibration) reverses bone loss, stimulates bone mass, induces cranial growth, and accelerates tooth movement. This reduce the pain experience and discomfort associated with the treatment and also enhances the patient compliance with the treatment. Vibration has the advantage of minimal side effects in comparison to medicinal treatments. This configuration enables the operator to adjust the vibration frequency as well as the orthodontic force exerted on the tooth.

Controlled drug delivery (CDD) technology has received extensive attention in the past three decades due to numerous advantages of this technology when compared to the conventional methods. Despite recent efforts and substantial achievements, controlled drug releasing systems still face major challenges in practice, including chemical issues with synthesizing biocompatible drug containers and releasing the pharmaceutical compounds at the targeted location with a controlled time rate. In this work, we present experimentally-validated acoustic-thermoelastic mathematical modeling to show the feasibility of using shape memory polymers (SMPs) and focused ultrasound (FU) technology for designing a novel drug-delivery system. SMPs represent a new class of materials that have the ability of storing a temporary shape and returning to their permanent or original shape when subjected to external stimuli such as heat. FU is used as a trigger for noninvasively stimulating SMP-based drug capsules. FU has a superior capability to localize the heating effect, thus initiating the shape recovery process only in selected parts of the polymer. A multiphysics model is developed, which optimizes the design of a SMP-based CDD system using acoustic-thermoelastic analysis of a filament as the constituting base structure and quantifies its activation through FU. The analytical and numerical models are divided into three parts. The first part studies the acoustic behavior of SMPs using Khokhlov-Zabolotskaya-Kuznetsov (KZK) model. The equation solves for acoustic pressure field in a hybrid time-frequency domain using operator-splitting method and examines the effects of absorption, diffraction and nonlinear distortion on the propagating wave in the medium. The second part provides a numerical model based on Penne’s Bioheat equation to estimate the thermal field developed in SMPs as a result of focused acoustic pressure field. The third part provides a numerical framework to predict the mechanical stresses developed in SMPs under FU and consequent shape recovery. The mechanical model is formulated by a compressible neo-Hookean constitutive equation, which assumes the SMPs behave as a thermoelastic material and predicts the shape memory effect under FU. Experimental validation is performed using a FU transducer in a water tank. The recovery of thermally responsive SMPs under FU predicted by our model shows a good accordance with the experiments. The modeling results are used to optimize parameters such as nonlinear properties, input frequency, source power and dimensional effects to achieve maximum shape recovery.

A recent achievement in the droplet interface bilayer (DIB) technique is the ability to link multiple lipid-encased aqueous droplets in an oil medium to construct a membrane-based network. Highly flexible, efficient and durable compared to other lipid bilayer modeling techniques, these systems establish a framework for the creation of biocompatible and stimuli-responsive smart materials with applications ranging from biosensing to reliable micro-actuation. Incorporating ferrofluids droplets into this platform has proven to accelerate the networks’ building mechanism through remote magnetic-control of the droplets movement and has reduced the likelihood of failure during the pre-network-completion phase. Additionally, ferrofluid drops may be placed in the final network structure as they are macroscopically homogenous and behave as single phased liquids. Due to their paramagnetic characteristics, no residual magnetization is observed in the ferrofluid upon removal of the external magnetic field, allowing for simple control of the magnetically responsive droplets. Aside from the ferrofluids reliability in contact-free manipulation of bilayer networks, this work shows a different feature of having such hybrid ferrofluid-water DIB networks: magnetic-sensibility and actuation. Once pre-structured mixed networks are formed, a magnetic source is used to generate various magnetic fields in the vicinity of the DIB webs; changes in structural responses are then observed and used to induce protein channel gating in DIB networks channeling the functionality of a switch. Tailored architectures are accordingly evaluated and their suitability for the creation of microfluidic-magneto sensors and actuators is assessed.

Additive manufacturing ( i.e. 3D printing) has only recently be shown as a well-established technology to create complex shapes and porous structures from different biocompatible metal powder such as titanium, nitinol, and stainless steel alloys. This allows for manufacturing bone fixation hardware with patient-specific geometry and properties (e.g. density and mechanical properties) directly from CAD files. Superelastic NiTi is one of the most biocompatible alloys with high shock absorption and biomimetic hysteresis behavior. More importantly, NiTi has the lowest stiffness (36–68 GPa) among all biocompatible alloys [1]. The stiffness of NiTi can further be reduced, to the level of the cortical bone (10–31.2 GPa), by introducing engineered porosity using additive manufacturing [2–4]. The low level of fixation stiffness allows for bone to receive a stress profile close to that of healthy bone during the healing period. This enhances the bone remodeling process (Wolf’s Law) which primarily driven by the pattern of stress. Also, this match in the stiffness of bone and fixation mitigates the problem of stress shielding and detrimental stress concentrations. Stress shielding is a known problem for the currently in-use Ti-6Al-4V fixation hardware. The high stiffness of Ti-6Al-4V (112 GPa) compared to bone results in the absence of mechanical loading on the adjacent bone that causes loss of bone mass and density and subsequently bone/implant failure. We have proposed additively manufactured porous NiTi fixation hardware with a patient-specific stiffness to be used for the mandibular reconstructive surgery (MRS). In MRS, the use of metallic fixation hardware and double barrel fibula graft is the standard methodology to restore the mandible functionality and aesthetic. A validated finite element model was developed from a dried cadaveric mandible using CT scan data. The model simulated a patient’s mandible after mandibular reconstructive surgery to compare the performance of the conventional Ti-6Al-4V fixation hardware with the proposed one (porous superelastic NiTi fixation plates). An optimized level of porosity was determined to match the NiTi equivalent stiffness to that of a resected bone, then it was imposed to the simulated fixation plates. Moreover, the material property of superelastic NiTi was simulated by using a validated customized code. The code was calibrated by using DSC analysis and mechanical tests on several prepared bulk samples of Ni-rich NiTi. The model was run under common activities such as chewing by considering different levels of the applied fastening torques on screws. The results show a higher level of stress distribution on mandible cortical bone in the case of using NiTi fixation plates. Based on wolf’s law it can lead to a lower level of stress shielding on the grafted bone and over time bone can remodel itself. Moreover, the results suggest an optimum fastening torque for fastening the screws for the superelastic fixations causes more normal distribution of stress on the bone similar to that for the healthy mandible. Finally, we successfully fabricated the stiffness-matched porous NiTi fixation plates using selective laser melting technique, and they were mounted on the dried cadaveric mandible used to create the finite element model.

Multiple lipid encased water droplets may be linked together in oil to form large networks of droplet interface bilayers thus creating a new class of stimuli-responsive materials for applications in sensing, actuation, drug delivery, and tissue engineering. While single droplet interface bilayers have been extensively studied, comparatively little is known about their interaction in large networks. One particular problem of interest is understanding the impact of the coalescence of two neighboring droplets on the overall structural integrity of the network. Here, we propose a computational modeling scheme that predicts and characterizes the mechanical properties of the multiple lipid bilayer interfaces within the droplet network upon intentional coalescence of adjacent droplets. Droplet networks with tailored architectures are synthesized with the aid of magnetic motor droplets containing a biocompatible ferrofluid. The equilibrium configuration of the droplet networks is compared to computational prediction which defines the overall stability by summing the interfacial energies. Once the networks are completed, failure in selected membranes is induced. As the targeted droplets coalesce together, the equilibrium structure of the network is altered and the remaining droplets may shift to new configurations dictated by their minimized mechanical energies.

ZnO based polymer composite materials are of great interest because of their excellent electrical, optical, semiconductor and biocompatible properties. In this study, we synthesize anisotropic composites of aligned ZnO rods in polydimethylsiloxane (PDMS) elastomer and study their dielectric properties as a function of applied electric field and frequency. Submicron ZnO rods are synthesized using an inexpensive, high yield chemical route. Washed and purified ZnO rods are then aligned in uncured PDMS at different electric field and frequency. We find that under electric field, ZnO rotates with their long axis in the direction of the electric field and before coalescing form chains in the silicone elastomer. From the optical microscopy images and in situ dielectric measurements, the best alignment parameters are found at 4 kV/mm and 10 kHz. These conditions are then selected to prepare aligned ZnO-PDMS composites. Complete curing of composites is confirmed using dynamic mechanical analysis (DMA). Our results show that aligned ZnO in uncured PDMS exhibit higher dielectric permittivity compared to random dispersion with the same composition. For the cured ZnO-PDMS composites, dielectric permittivity increases by 80% compared to random composites.

This work explores incorporating ferrofluids with droplet interface bilayer (DIB) membranes. Ferrofluids contain magnetic nanoparticles in solution with a stabilizing surfactant, providing a magnetically-responsive fluid. These fluids allow for remote mechanical manipulation of ferrofluid droplets through magnetic fields, and will allow for better control over the characteristics of networks of stimuli-responsive cellular membranes created through by DIB technique. This work involves several phases. First, a suitable biocompatible ferrofluid is synthesized, containing a neutral pH and a biocompatible surfactant. Once a proper ferrofluid is identified, it is tested as the aqueous phase for the creation of DIB membranes. Interfacial membranes between ferrofluid droplets are created and compared to non-ferrofluid DIB membranes. The interfacial membrane between two ferrofluid droplets was tested for leakage and stability, and the electrical characteristics of the interfacial membrane were studied and compared to non-ferrofluid DIB membranes. Once it is confirmed that the ferrofluid droplets do not negatively interfere with the formation of the artificial cellular membranes through the electrical measurements, the magnetically-responsive nature of the ferrofluid droplets are used to form large networks of DIB membranes through a simple magnetic field. These networks are easy to assemble and may be remotely manipulated, providing a significant step towards the rapid and simple assembly of DIB networks advancing towards the tissue scale.

Mandibular segmental defect reconstruction is most often necessitated by tumor resection, trauma, infection, or osteoradionecrosis. The standard of care treatment for mandibular segmental defect repair involves using metallic plates to immobilize fibula grafts, which replace the resected portion of mandible. Surgical grade 5 titanium (Ti-6Al-4V) is commonly used to fabricate the fixture plate due to its low density, high strength, and high biocompatibility. One of the potential problems with mandibular reconstruction is stress shielding caused by a stiffness mismatch between the Titanium fixation plate and the remaining mandible bone and the bone grafts. A highly stiff fixture carries a large portion of the load (e.g., muscle loading and bite force), therefore the surrounding mandible would undergo reduced stress. As a result the area receiving less strain would remodel and may undergo significant resorption. This process may continue until the implant fails. To avoid stress shielding it is ideal to use fixtures with stiffness similar to that of the surrounding bone. Although Ti-6Al-4V has a lower stiffness (110 GPa) than other common materials (e.g., stainless steel, tantalum), it is still much stiffer than the cancellous (1.5–4.5 GPa) and cortical portions of the mandible (17.6–31.2 GPa). As a solution, we offer a nitinol in order to reduce stiffness of the fixation hardware to the level of mandible. To this end, we performed a finite element analysis to look at strain distribution in a human mandible in three different cases: I) healthy mandible, II) resected mandible treated with a Ti-6Al-4V bone plate, III) resected mandible treated with a nitinol bone plate. In order to predict the implant’s success, it is useful to simulate the stress-strain trajectories through the treated mandible. This work covers a modeling approach to confirm superiority of nitinol for mandibular reconstruction. Our results show that the stress-strain trajectories of the mandibular reconstruction using nitinol fixation is closer to normal than if grade 5 surgical titanium fixation is used.

Shape memory polymers (SMP) are a class of stimuli-responsive materials that are able to respond to external stimulus such as heat by altering their shape. Bio-compatible SMPs have a number of advantages over existing SMP materials and are being studied extensively for biomedical and clinical applications. Polymer blending has proved to be an effective method to improve the mechanical properties of polymers (such as tensile strength and toughness) as well as shape memory properties. In this study, we investigate the effect of blending two bio compatible polymers, thermoplastic polyurethane (TPU), a polymer with a high toughness and percent elongation, and poly-lactic acid (PLA), a stiff and strong polymer. The thermal, mechanical and thermo-mechanical (shape memory) properties of TPU/PLA blends were characterized in the following weight percent compositions: 80/20, 65/35, and 50/50 TPU/PLA. The TPU/PLA SMP blending was achieved with melt-blending and the tensile samples were fabricated with compression molding. The mechanical properties of each blend were studied at three different temperatures. The following thermo-mechanical (or shape memory) properties were also studied at each temperature: the shape fixity rate (R f ), shape recovery rate (R r ) and the effect of recovery temperature on the shape memory behavior. The microstructure of the polymer blends were investigated with an environmental scanning electron microscope (SEM). The results showed that the glass transition temperatures of the blends were similar to pure PLA. The toughness of the SMP blend increased with increasing TPU concentration and the tensile strength of the blend increased with PLA composition. The shape fixity rate of the TPU/PLA blend increased with increasing TPU content and the shape recovery rate increased with increasing deformation and recovery temperature. The various TPU/PLA SMP blends characterized in this study have the potential to be developed further for specific biomedical and clinical applications.

Design and actuation modes of IntraVAD assistive device for end stage congestive heart failure patients are discussed in this paper. Flexibility, biocompatibility and coupled behavior of Ionic Polymer Metal Composites and Shape Memory Alloys allow replicating the motion of natural heart to address the cardiac deficiency. The squeezing motion of the heart is approximated by propulsion mechanism of a jelllyfish, while the rising-twisting motion of the heart is augmented by upward-downward motion of a cone shaped structure. These motion mechanisms may be combined or used separately, in order to create various blood flow regimes and provide different levels of support for each individual. Not only as actuators, but SMAs and IPMCs may be utilized as sensors to provide feedback from instantaneous status of the device to the controller. A device embodiment is introduced and followed by discussion on IPMC and antagonistic two-way SMA actuators in order to explain how actuation modes are delivered.

Shape memory alloys (SMA) have received widespread attention from researchers in various fields of engineering sciences due to their exceptional properties of shape memory and superelasticity. NiTi equiatomic alloys among other SMA, show acceptable biocompatibility to be implemented in biomedical applications. Applications of NiTi in biomedical areas specifically orthopedics, demonstrate its unique performance which is not achievable with conventional materials. Pedicle screws, which are used as an anchoring point for implanting spinal instrumentations in spinal fracture and deformity treatments, entail a major drawback; i.e. loosening and back-out. The strength of screw contact with the surrounding bone diminishes as the bone degrades due to osteoporosis. A “ Smart ” pedicle screw design was developed to address this issue which uses NiTi superelastic-shape memory coils wrapped around it. The smart assembly consists of external superelastic tubing which is responsible for expanding the designed protrusions when they reach body temperature; also an internal shape memory wire inserted into the tubing is sought to retract the assembly when locally heated to above body temperature. The whole assembly was modeled as a beam structure in COMSOL Multiphysics Finite Element software. The behavior of shape memory alloy was defined in the software via its Partial Differential Equation (PDE) module. The SMA model has is a Tanaka-based model and is capable of capturing shape memory effect, superelasticity and hysteresis behavior, and partial transformation in both positive and negative directions. This 1D model was further modified to be included in a 3D framework such that it makes it possible for simulation of a beam under bending. The functionality of the smart screw design can be studied via this FEM model as a future work and the outcomes of the simulation can be compared with experimental tests on the prepared sample of the screw comprising NiTi tubing and wires.

The overall purpose of this study was to analyze multi-source energy harvesters for creation of a rechargeable onboard power system, capable of supplying 5–50mW of intermittent power at a system mass of less than one gram, to be placed on a cyborg MAV (CMAV). To recharge the system, three sources of available ambient energy with respect to the application were explored, solar, thermal, and kinetic. Evaluations were performed based on magnitudes of available energy from each source, mass, dimension, and biocompatible constraints for each of the transducers, and specific power output of each energy harvester. Conclusions of this research show the magnitudes of the performance for photo-voltaic, thermoelectric, piezoelectric, and electromagnetic transducers weighing less than one gram. In addition, issues related to combining these multi-sourced energy harvesters into a collective power system are discussed.

Cellulose Electro-Active Paper (EAPap) has been discovered as a smart material that can be used as a sensor and actuator [1]. It has many advantages in terms of low voltage operation, light weight, low power consumption, low cost, biocompatibility and biodegradability. EAPap is made with cellulose paper coated with thin electrodes. EAPap shows a reversible and reproducible bending movement as well as longitudinal displacement under electric field. The out-of-plane bending deformation is useful for achieving flapping wings, micro-insect robots, and smart wall papers. On the other hand, in-plane strains, such as extension and contraction of EAPap materials are also promising for artificial muscle applications. The actuation principle of cellulose EAPap bending actuator is known to be a combination of piezoelectric effect and ion migration effect. This paper presents further investigation of cellulose EAPap for actuator, sensor and MEMS devices. Piezoelectricity is one of major actuating mechanism of cellulose EAPap. Cellulose is a complex anisotropic material. Aligning cellulose fibers in the fabrication process is a critical parameter to improve mechanical and electromechanical properties of EAPap such as stiffness, strength, piezoelectricity and so on. Cotton cellulose fibers are dissolved into a solution using NaOH/urea and DMAc/LiCl methods. In the later method, the dissolution and shaping of cellulose can be carried out by DMAc/LiCl. Cellulose pulp was mixed with lithium chloride (LiCl) and dehydrated by heating. After adding DMAc (N, N-dimethylacetamide) to the mixture, swell it in room temperature. By heating it a solution formation can be obtained. There are some issues on eliminating solvent and ions and regenerating a pure cellulose films. The material processing all about EAPap has been introduced [2, 3]. Wet drawn stretching method is used in the fabrication process of cellulose film to increase its mechanical and electromechanical properties. This wet-drawn cellulose EAPap is termed as Piezo-Paper. Cellulose EAPap material can be customized to satisfy the material requirement for specific applications. Piezo-Paper can be used for strain sensors, vibration sensors, ultrasonic transducers, SAW devices, speakers, microphones, stack actuators, bending actuators and MEMS devices. Figure 1 shows some applications. Piezoelectric charge constant of Piezo-Paper is 70 pC/N. Details of piezoelectric characteristics of Piezo-Paper and its applications are presented in this paper. Micro-fabrication on cellulose EAPap has many applications, for example, MEMS sensors, e-Paper, thin film transistor (TFT), and even microwave-driven EAPap actuator. To develop microwave-driven EAPap actuator, rectenna (rectifying antenna) has been developed [4]. Rectenna can rectify microwaves and feed dc power without wire. Thus, this technology has many applications. To fabricate the rectenna array on cellulose EAPap, micro patterning of metallic layer and Schottky diode fabrication were studied. The Schottky diode fabrication gives the possibility of TFT on cellulose sheet. Advancing from this technology, SAW (Surface Acoustic Wave) device fabrication for humidity sensor is possible. The devices fabrication along with the characterization and their demonstration will be shown. Cellulose EAPap technology will bring the dream of flying magic paper into real world in the near future.