Edge-Functionalized Graphene/Polydimethylsiloxane Composite Films for Flexible Neural Cuff Electrodes.

The design of neural electrodes has changed in the past decade, driven mainly by the development of new materials that open the possibility of manufacturing electrodes with adaptable mechanical properties and promising electrical properties. In this paper, we report on the mechanical and electrochemical properties of a polydimethylsiloxane (PDMS) composite with edge-functionalized graphene (EFG) and demonstrate its potential for use in neural implants with the fabrication of a novel neural cuff electrode. We have shown that a 200 µm thick 1:1 EFG/PDMS composite film has a stretchability of up to 20%, a Young's modulus of 2.52 MPa, and a lifetime of more than 10000 mechanical cycles, making it highly suitable for interfacing with soft tissue. Electrochemical characterization of the EFG/PDMS composite film showed that the capacitance of the composite increased up to 35 times after electrochemical reduction, widening the electrochemical water window and remaining stable after soaking for 5 weeks in phosphate buffered saline. The electrochemically activated EFG/PDMS electrode had a 3 times increase in the charge injection capacity, which is more than double that of a commercial platinum-based neural cuff. Electrochemical and spectrochemical investigations supported the conclusion that this effect originated from the stable chemisorption of hydrogen on the graphene surface. The biocompatibility of the composite was confirmed with an in vitro cell culture study using mouse spinal cord cells. Finally, the potential of the EFG/PDMS composite was demonstrated with the fabrication of a novel neural cuff electrode, whose double-layered and open structured design increased the cuff stretchability up to 140%, well beyond that required for an operational neural cuff. In addition, the cuff design offers better integration with neural tissue and simpler nerve fiber installation and locking.

Biometric Recognition: A Systematic Review on Electrocardiogram Data Acquisition Methods.

In the last decades, researchers have shown the potential of using Electrocardiogram (ECG) as a biometric trait due to its uniqueness and hidden nature. However, despite the great number of approaches found in the literature, no agreement exists on the most appropriate methodology. This paper presents a systematic review of data acquisition methods, aiming to understand the impact of some variables from the data acquisition protocol of an ECG signal in the biometric identification process. We searched for papers on the subject using Scopus, defining several keywords and restrictions, and found a total of 121 papers. Data acquisition hardware and methods vary widely throughout the literature. We reviewed the intrusiveness of acquisitions, the number of leads used, and the duration of acquisitions. Moreover, by analyzing the literature, we can conclude that the preferable solutions include: (1) the use of off-the-person acquisitions as they bring ECG biometrics closer to viable, unconstrained applications; (2) the use of a one-lead setup; and (3) short-term acquisitions as they required fewer numbers of contact points, making the data acquisition of benefit to user acceptance and allow faster acquisitions, resulting in a user-friendly biometric system. Thus, this paper reviews data acquisition methods, summarizes multiple perspectives, and highlights existing challenges and problems. In contrast, most reviews on ECG-based biometrics focus on feature extraction and classification methods.

3D printed linear soft multi-mode actuators expanding robotic applications.

Soft pneumatic actuators can produce a range of motions and deliver a high force-to-mass ratio whilst offering intrinsic compliance. Presently, the majority of soft pneumatic actuators are used to create bending motions, with very few able to produce significant linear movements. Fewer can actively produce strains in multiple directions. The purpose of this study is to produce and characterize a novel 3D printed actuator which is capable of both extension and contraction under differential pressures. A new elastomeric resin was synthesized to be used on digital light projection (DLP) 3D printers. The presented pneumatic device, a linear soft multi-mode actuator (LSOMMA), is demonstrably scalable and provides a stable response over its lifetime of >10 000 cycles. The LSOMMA operates at low pressures, achieving full contraction and expansion at gauge pressures of -25 kPa and 75 kPa, respectively, corresponding to actuator strains of up to -50% and 37%. All actuators presented in this study had a rise time of less than 250 ms. The applications of these multi-mode actuators were demonstrated by developing a pipe-crawling robot capable of traversing horizontal, vertical, and bent sections of a pipe, and a ground locomotion robot capable of moving up to 652 mm min-1 and turn at 361° min-1. An untethered locomotion robot which could navigate multiple surface materials was assembled to demonstrate the potential of the developed technologies for autonomous robotic applications.

Powering Implantable and Ingestible Electronics.

Implantable and ingestible biomedical electronic devices can be useful tools for detecting physiological and pathophysiological signals, and providing treatments that cannot be done externally. However, one major challenge in the development of these devices is the limited lifetime of their power sources. The state-of-the-art of powering technologies for implantable and ingestible electronics is reviewed here. The structure and power requirements of implantable and ingestible biomedical electronics are described to guide the development of powering technologies. These powering technologies include novel batteries that can be used as both power sources and for energy storage, devices that can harvest energy from the human body, and devices that can receive and operate with energy transferred from exogenous sources. Furthermore, potential sources of mechanical, chemical, and electromagnetic energy present around common target locations of implantable and ingestible electronics are thoroughly analyzed; energy harvesting and transfer methods befitting each energy source are also discussed. Developing power sources that are safe, compact, and have high volumetric energy densities is essential for realizing long-term in-body biomedical electronics and for enabling a new era of personalized healthcare.

Co-delivery of inhalable therapies: Controlling active ingredients spatial distribution and temporal release.

The management of respiratory diseases relies on the daily administration of multiple active pharmaceutical ingredients (APIs), leading to a lack of patient compliance and impaired quality of life. The frequency and dosage of the APIs result in increased side effects that further worsens the overall patient condition. Here, the manufacture of polymer-polymer core-shell microparticles for the sequential delivery of multiple APIs by inhalation delivery is reported. The microparticles, composed of biodegradable polymers silk fibroin (shell) and poly(L-lactic acid) (core), incorporating ciprofloxacin in the silk layer and ibuprofen (PLLA core) as the antibiotic and anti-inflammatory model APIs, respectively. The polymer-polymer core-shell structure and the spatial distribution of the APIs have been characterized using cutting-edge synchrotron macro ATR-FTIR technique, which was correlated with the respective API sequential release profiles. The APIs microparticles had a suitable size and aerosol properties for inhalation therapies (≤4.94 ± 0.21µm), with low cytotoxicity and immunogenicity in healthy lung epithelial cells. The APIs compartmentalization obtained by the microparticles not only could inhibit potential actives interactions but can provide modulation of the APIs release profiles via an inhalable single administration.

Smart-Responsive Colloidal Capsules as an Emerging Tool to Design a Multifunctional Lubricant Additive.

The microencapsulation technique has been proven as a powerful and flexible tool to design and develop a multifunctional additive for various applications. The significant characteristics of this technique center around the ability to control the release of the core active ingredients by tuning the porosity and the permeability of the shell. However, this original concept has faced a major roadblock in lubricant research since it causes a major breakage of the microcapsules (∼70%) under severe stressed-shearing conditions. The shell fragments generated from such unwanted events significantly influence the friction and wear performances of the counterpart, thus limiting the ongoing research of the microencapsulation technique in tribology. To solve such technical bottlenecks, we develop a new strategy of utilizing the microencapsulation technique which focuses on the smart responsiveness of the shell with the base lubricant and the synergy between the incorporated materials. In this study, the smart-responsive colloidal capsule has been developed based on our proposed concept that demonstrates outstanding performances in improving the lubricity of the conventional melt lubricant (by ∼70%) under hot metal working conditions. An unprecedented oxidation-reduction (by ∼93%) and the first instance of ultralow friction (0.07) at elevated temperatures (880 °C) have been initially achieved. This work opens a new avenue of customizing a multifunctional additive package by utilizing the smart colloidal capsules in lubrication science.

Design of polymeric core-shell carriers for combination therapies.

Particle engineering for co-delivery of drugs has the potential to combine multiple drugs with different pharmaceutical mechanisms within the same carrier, increasing the therapeutic efficiency while improving patient compliance. This work proposes a novel approach for producing polymer-polymer core-shell microparticles by multi-step processing of emulsion and spray drying. The particle core was obtained by an oil-in-water emulsion of poly(ε-caprolactone) (PCL) loaded with curcumin (CM), followed by the resuspension in poly(vinyl alcohol) (PVA) containing ciprofloxacin (CPx) forming the shell layer by spray-drying. The obtained core-shell particles showed an average size of 3.8 ± 1.2 µm, which is a suitable size for inhalation therapies. The spatial distribution of the drugs was studied using synchrotron-based macro attenuated total reflection Fourier transform infrared (macro ATR-FTIR) microspectroscopy to map the chemical distribution of the components within the particles and supported the presence of CM and CPx in the core and shell layers, respectively. The formation of the core-shell structure was further supported by the differences in the release profile of CM from these particles, when compared to the release profile observed for the single particle structure (PCL-CM). Both empty and drug-loaded carriers (up to 100 µg.mL-1) showed no cytotoxic effects on A549 cells while exhibiting the antibacterial activity of CPx against Gram-positive and Gram-negative bacteria. These polymer core-shell microparticles provide a promising route for the combination and sequential drug release therapies, with the potential to be used in inhalation therapies.

Low-Hysteresis and Ultrasensitive Microcellular Structures for Wearable Electronic Applications.

Wearable technologies offer the opportunity to record human physiological signals in real time, in a noninvasive way, and the data can be used to aid in the early detection of abnormal health conditions. Here, we demonstrate how the interconnected porosity can be used to increase the sensitivity and linearity of capacitive pressure sensors. The finite element analysis supports the experimental observation that the movement of air during the dynamic mechanical loading is responsible for the high sensitivity observed (0.18 ± 0.01 kPa-1) when compared with the solid poly(glycerol sebacate) sensor (0.0042 ± 0.0002 kPa-1). The porous sensors present strain insensitivity and remarkable linearity over the entire range of applied mechanical pressure (0-6 kPa), capable of detecting both static and dynamic mechanical stimuli (17 nm/s), and a response time of 50 ms, without evidence of fatigue or electrical hysteresis over 10,000 mechanical cycles. The outstanding features of the porous sensors can find a broad range of applications in real-time health monitoring, from demanding movements like walking/running, to small deformations resulting from breathing or heart beating. The ultrasensitive microcellular structures synthesized in this study can be applied to other types of sensing transductions to obtain tunable and function-specific sensors with high sensitivity.

Triboelectric Nanogenerator versus Piezoelectric Generator at Low Frequency (<4 Hz): A Quantitative Comparison.

Triboelectric nanogenerators (TENGs) and piezoelectric generators (PGs) are generally considered the two most common approaches for harvesting ambient mechanical energy that is ubiquitous in our everyday life. The main difference between the two generators lies in their respective working frequency range. Despite the remarkable progress, there has been no quantitative studies on the operating frequency band of the two generators at frequency values below 4 Hz, typical of human motion. Here, the two generators are systematically compared based on their energy harvesting capabilities below 4 Hz. Unlike PGs, the TENG demonstrates higher power performance and is almost independent of the operating frequency, making it highly efficient for multi-frequency operation. In addition, PGs were shown to be inapplicable for charging capacitors when a rectifier was attached to the system. The results of this work reveal the tremendous potential of flexible TENGs for harvesting energy at low frequency.

Intrinsic Effect of Nanoparticles on the Mechanical Rupture of Doubled-Shell Colloidal Capsule via In Situ TEM Mechanical Testing and STEM Interfacial Analysis.

The discovery of Pickering emulsion templated assembly enables the design of a hybrid colloidal capsule with engineered properties. However, the underlying mechanisms by which nanoparticles affect the mechanical properties of the shell are poorly understood. Herein, in situ mechanical compression on the transmission electron microscope and aberration-corrected scanning transmission microscope are unprecedentedly implemented to study the intrinsic effect of nanoparticles on the mechanical properties of the calcium carbonate (CaCO3 )-decorated silica (SiO2 ) colloidal capsule. The stiff and brittle nature of the colloidal capsule is due to the interfacial chemical bonding between the CaCO3 nanoparticles and SiO2 inner shell. Such bonding strengthens the mechanical strength of the SiO2 shell (166 ± 14 nm) from the colloidal capsule compared to the thicker single SiO2 shell (310 ± 70 nm) from the silica hollow sphere. At elevated temperature, this interfacial bonding accelerates the formation of the single calcium silicate shell, causing shell morphology transformation and yielding significantly enhanced mechanical strength by 30.9% and ductility by 94.7%. The superior thermal durability of the heat-treated colloidal capsule holds great potential for the fabrication of the functional additives that can be applied in the wide range of applications at elevated temperatures.

Environmentally Friendly and Biodegradable Ultrasensitive Piezoresistive Sensors for Wearable Electronics Applications.

Highly sensitive, flexible sensors that can be manufactured with minimum environmental footprint and be seamlessly integrated into wearable devices are required for real-time tracking of complex human movement, gestures, and health conditions. This study reports on how biodegradation can be used to enhance the sensitivity and electromechanical performance of piezoresistive sensors. Poly(glycerol sebacate) (PGS) elastomeric porous sensor was synthesized and blended with multiwall carbon nanotubes (MWCNTs) and sodium chloride (NaCl). Because of their unique porous characteristics, a single linear behavior over a large range of pressures (≤8 kPa) and an increase in their sensitivity from 0.12 ± 0.03 kPa-1 up to 8.00 ± 0.20 kPa-1 was achieved after 8 weeks in a simulated body fluid media. They can detect very low pressures (100 Pa), with negligible hysteresis, reliability, long lifetime (>200 000 cycles), short response time (≤20 ms), and high force sensitivity (≤4 mN). The characteristics of the developed foam sensors match the sensing characteristics of the human finger to pave the way toward low-footprint wearable devices for applications including human movement and condition monitoring, recreation, health and wellness, virtual reality, and tissue engineering.

Mechanical performance of elastomeric PGS scaffolds under dynamic conditions.

In developing novel scaffolds, addressing mechanical properties is essential especially when future applications involve cyclic mechanical loading. Therefore, it is important to understand the behaviour of its physical properties with the evolution of its weight loss. Poly(glycerol sebacate) (PGS) is a promising material for tissue and biomedical engineering applications due to its biocompatibility, biodegradability and mechanical properties. To understand the impact of the hydrolytic degradation on the density, cross-linking degree and porosity; scaffolds with an average porosity of 93 ±â€¯2% were synthetized by salt leaching technique and submitted to hydrolytic degradation. The scaffold showed a Young modulus of 17.3 ±â€¯3.4 kPa, with a negligible energy loss during the mechanical solicitation. Moreover, a weight loss of 28 ±â€¯2% followed by an increase in the swelling ratio of the scaffold was observed after 8 weeks of hydrolytic degradation. When submitted to cyclic mechanical loading-unloading, the PGS scaffolds present an outstanding fatigue behaviour under dry and wet conditions, with a remarkable resilience to the cyclic mechanical solicitation, and even after 1000 mechanical cycles, the construct was able to recover to its initial geometry. Overall, the PGS scaffolds demonstrate promising mechanical properties for biomedical applications, especially under dynamic conditions.

An Intrinsically Non-flammable Electrolyte for High-Performance Potassium Batteries.

Potassium-ion batteries are promising for low-cost and large-scale energy storage applications, but the major obstacle to their application is the lack of safe and effective electrolytes. A phosphate-based fire retardant such as triethyl phosphate is now shown to work as a single solvent with potassium bis(fluorosulfonyl)imide at 0.9 m, in contrast to previous Li and Na systems where phosphates cannot work at low concentrations. This electrolyte is optimized at 2 m, where it exhibits the advantages of low cost, low viscosity, and high conductivity, as well as the formation of a uniform and robust salt-derived solid-electrolyte interphase layer, leading to non-dendritic K-metal plating/stripping with Coulombic efficiency of 99.6 % and a highly reversible graphite anode.

Nano-sunscreens - a double-edged sword in protecting consumers from harm: viewing Australian regulatory policies through the lenses of the European Union.

Nanotechnology has the potential to bring about revolutionary changes in manufacturing products, including sunscreens. However, a knowledge gap between benefits and detriments of engineered nano-materials used in sunscreens exists, which gives rise to safety concerns. This article is concerned with the protection of consumers without impairing the embellishment of this promising technology. It is widely argued that the harm associated with nano-sunscreens may only occur under certain conditions related mainly to users skin vulnerability, which can be avoided by informed and careful use of such a product. We thus recognize the need for fostering the growth of nanotech simultaneously with preventing potential harm. We revisit the Australian sunscreens regulatory policies, which embrace a "wait and see" approach, through the lens of regulatory policies in the European Union (EU) that are influenced by a "precautionary principle." We highlight the importance of informing consumers about the sunscreen they are using and recommend that product labels should disclose the presence of nano-ingredients in line with the EU disclosure requirements. This will allow users to carefully apply the product in order to avoid any potential harm and to protect manufacturers from possible costly litigation in future. This can be achieved through a combined collaborative effort of regulators, supply chain entities, and end users.

Synthesis of methotrexate-loaded tantalum pentoxide-poly(acrylic acid) nanoparticles for controlled drug release applications.

Over the past decade, there has been increasing interest in the use of multifunctional nanoparticles (NPs) for cancer treatment. Of importance are systems that can deliver drugs at a sustained rate to target cancer cells, which can result in higher efficiency and reduced systemic toxicity. In this study, we present the route for the synthesis of tantalum pentoxide (Ta2O5) NPs with a particle size of 27 nm that were individually coated with poly(acrylic acid) (PAA) with a different layer thickness of 2-8 nm by in-situ polymerization of the acrylic acid monomer. The capability of Ta2O5-PAA to provide anatomical contrast-enhancing features has been demonstrated via computed tomography. The Ta2O5-PAA conjugate was further loaded with methotrexate, and the drug release was observed for a total of 72 h at a pH of 3.6, 5.4, 7.4, and 9.4. While the different layer thicknesses did not influence the drug release kinetics, a decrease in pH of the release medium resulted in a slower drug release. The developed nanocomposite particles present a great potential as a theranostic system for biomedical applications.

Reusable Flexible Concentric Electrodes Coated With a Conductive Graphene Ink for Electrotactile Stimulation.

Electrotactile stimulation is a highly promising technique for providing sensory feedback information for prosthetics. To this aim, disposable electrodes which are predominantly used result in a high environmental and financial cost when used over a long period of time. In addition, disposable electrodes are limited in their size and configurations. This paper presents an alternative approach based on a 3D printed reusable flexible concentric electrode coated with a conductive graphene ink. Here, we have characterized the electrode and demonstrated its effective performance in electrotactile stimulation and sensory feedback for robotic prosthetic hands.

Development of ciprofloxacin-loaded poly(vinyl alcohol) dry powder formulations for lung delivery.

Polymeric microparticles are micro carriers for the sustained drug delivery of drugs in the lungs, used as alternatives to the use of established excipients. This study aims to develop and characterize inhalable ciprofloxacin (CPx)-loaded poly(vinyl alcohol) (PVA) microparticles by a single-step spray-drying procedure. The optimization of the processing parameters was achieved by an orthogonal design of the most relevant processing parameters (polymer concentration, feed rate and inlet temperature). The obtained spray-dried particles showed a drug encapsulation efficiency higher than 90%. Furthermore, PVA-CPx formulations, with drug contents up to 10 wt%, showed a morphology and size suitable for inhalation, with a sustained release profile over 24 h. Data from Fourier transformed infra-red spectroscopy and differential scanning calorimetry indicated absence of interaction between the polymer matrix and the drug. Aerodynamic assessment of PVA-CPx 10 wt% was determined by the next generation impactor (NGI), using spray-dried CPx as a control. The results showed improved values of mass median aerodynamic diameter (5.06±0.10µm) and a fine particle fraction (39.78±0.98%) when comparing with the CPx alone (5.33±0.39µm and 30.43±1.38%). This study highlights the potential of spray-dried PVA microparticles as drug carriers for lung local delivery of antibiotics.

Effect of multi-walled carbon nanotubes on the cross-linking density of the poly(glycerol sebacate) elastomeric nanocomposites.

Processing conditions deeply affect the mechanical, chemical and biological properties of elastomeric based nanocomposites. In this work, multi-walled carbon nanotubes (MWCNTs) were dispersed in poly(glycerol sebacate) (PGS) prepolymer, followed by curing under vacuum at 120 °C. It was observed an increase of the water contact angle with the amount of MWCNTs added, as well as the tensile strength and Young modulus, without compromising the elastomeric behaviour of the pristine PGS matrix. The cross-linking degree was determined by the Flory-Rehner swelling method and through the mechanical rubber elasticity model, and an increase of more than six-fold was observed, which demonstrates the chemical conjugation between the MWCNTs and the PGS polymer chains, resulting in stiff and elastomeric nanocomposites. Finally, in vitro cell culture of adult mouse hypothalamus neurons A59 cells showed good support for cell viability and stimulation for axons and dendrites growth. The unique features of these nanocomposites make them promise for biomedical applications, as soft tissue substrates with tailored mechanical properties.

Modeling and Experimental Evaluation of Bending Behavior of Soft Pneumatic Actuators Made of Discrete Actuation Chambers.

In this article, we have established an analytical model to estimate the quasi-static bending displacement (i.e., angle) of the pneumatic actuators made of two different elastomeric silicones (Elastosil M4601 with a bulk modulus of elasticity of 262 kPa and Translucent Soft silicone with a bulk modulus of elasticity of 48 kPa-both experimentally determined) and of discrete chambers, partially separated from each other with a gap in between the chambers to increase the magnitude of their bending angle. The numerical bending angle results from the proposed gray-box model, and the corresponding experimental results match well that the model is accurate enough to predict the bending behavior of this class of pneumatic soft actuators. Further, by using the experimental bending angle results and blocking force results, the effective modulus of elasticity of the actuators is estimated from a blocking force model. The numerical and experimental results presented show that the bending angle and blocking force models are valid for this class of pneumatic actuators. Another contribution of this study is to incorporate a bistable flexible thin metal typified by a tape measure into the topology of the actuators to prevent the deflection of the actuators under their own weight when operating in the vertical plane.

Antibacterial and Antifungal Activity of Poly(Lactic Acid)-Bovine Lactoferrin Nanofiber Membranes.

Antimicrobial materials have become relevant for local therapies preventing microbial resistance induced by systemic antibiotic treatments. This work reports the development of electrospun poly(lactic acid) (PLLA) nanofiber membranes loaded with bovine lactoferrin (bLF) up to 20 wt%. The membranes present smooth and nondefective fibers with mean diameters between 717 ± 197 and 495 ± 127 nm, and an overall porosity of ≈80%. The hydrophobicity of the PLLA membranes is reduced by the presence of bLF. The release profile of bLF correlates with an anomalous transport model, with 17.7 ± 3.6% being released over 7 weeks. The nanofiber mats show no cytotoxicity on human skin fibroblasts and even promote cell proliferation after short exposure periods. Furthermore, the developed membranes display antifungal activity against Aspergillus nidulans by inhibiting spore germination and mycelial growth. These results evidence the strong potential of bLF-PLLA nanofiber membranes to be used as antifungal dressings.