Developing a Chemiresistive Gas Sensor Array for Simultaneous Detection of Ammonia and Carbon Dioxide Gases.

Chemiresistive polymer-based sensors are promising platforms for monitoring various gases and volatile organic compounds. While they offer appealing attributes, such as ease of fabrication, flexibility, and cost-effectiveness, most of these sensors have a nearly identical response to cross-reactive gases, such as ammonia (NH3) and carbon dioxide (CO2). Aiming to address the shortcomings of chemiresistive polymer-based sensors in selectivity and simultaneous measurements of cross-reactive gases, a chemiresistive sensor array was developed consisting of components sensitive to carbon dioxide and ammonia as well as a control segment to provide the baseline. The designed system demonstrated a wide detection range for both ammonia (ranging from 0.05 to 1000 ppm) and carbon dioxide (ranging from 103 to 106 ppm) at both room and low temperatures (e.g., 4 °C). Our results also demonstrate the ability of this sensor array for the simultaneous detection of carbon dioxide and ammonia selectively in the presence of other gases and volatile organic compounds. Finally, the array was used to monitor CO2/NH3 in real food samples to demonstrate the potential for real-world applications.

Chemiresistive Sensor for Enhanced CO2 Gas Monitoring.

Carbon dioxide (CO2) gas sensing and monitoring have gained prominence for applications such as smart food packaging, environmental monitoring of greenhouse gases, and medical diagnostic tests. Although CO2 sensors based on metal oxide semiconductors are readily available, they often suffer from limitations such as high operating temperatures (>250 °C), limited response at elevated humidity levels (>60% RH), bulkiness, and limited selectivity. In this study, we designed a chemiresistive sensor for CO2 detection to overcome these problems. The sensing material of this sensor consists of a CO2 switchable polymer based on N-3-(dimethylamino)propyl methacrylamide (DMAPMAm) and methoxyethyl methacrylate (MEMA) [P(D-co-M)], and diethylamine. The designed sensor has a detection range for CO2 between 103 and 106 ppm even at high humidity levels (>80% RH), and it is capable of differentiating ammonia at low concentrations (0.1-5 ppm) from CO2. The addition of diethylamine improved sensor performance such as selectivity, response/recovery time, and long-term stability. These data demonstrate the potential of using this sensor for the detection of food spoilage.

Ammonia detection: A pathway towards potential point-of-care diagnostics.

Invasive methods such as blood collection and biopsy are commonly used for testing liver and kidney function, which are painful, time-consuming, require trained personnel, and may not be easily accessible to people for their routine checkup. Early diagnosis of liver and kidney diseases can prevent severe symptoms and ensure better management of these patients. Emerging approaches such as breath and sweat analysis have shown potential as non-invasive methods for disease diagnosis. Among the many markers, ammonia is often used as a biomarker for the monitoring of liver and kidney functions. In this review we provide an insight into the production and expulsion of ammonia gas in the human body, the different diseases that could potentially use ammonia as biomarker and analytical devices such as chemiresistive gas sensors for non-invasive monitoring of this gas. The review also provides an understanding into the different materials, doping agents and substrates used to develop such multifunctional sensors. Finally, the current challenges and the possible future trends have been discussed.

Bioinspired polymeric heart valves: A combined in vitro and in silico approach.

Background: Polymeric heart valves (PHVs) may address the limitations of mechanical and tissue valves in the treatment of valvular heart disease. In this study, a bioinspired valve was designed, assessed in silico, and validated by an in vitro model to develop a valve with optimum function for pediatric applications. Methods: A bioinspired heart valve was created computationally with leaflet curvature derived from native valve anatomies. A valve diameter of 18 mm was chosen to approach sizes suitable for younger patients. Valves of different thicknesses were fabricated via dip-coating with siloxane-based polyurethane and tested in a pulse duplicator for their hydrodynamic function. The same valves were tested computationally using an arbitrary Lagrangian-Eulerian plus immersed solid approach, in which the fluid-structure interaction between the valves and fluid passing through them was studied and compared with experimental data. Results: Computational analysis showed that valves of 110 to 200 µm thickness had effective orifice areas (EOAs) of 1.20 to 1.30 cm2, with thinner valves exhibiting larger openings. In vitro tests demonstrated that PHVs of similar thickness had EOAs of 1.05 to 1.35 cm2 and regurgitant fractions (RFs) <7%. Valves with thinner leaflets exhibited optimal systolic performance, whereas thicker valves had lower RFs. Conclusions: Bioinspired PHVs demonstrated good hydrodynamic performance that exceeded ISO 5840-2 standards. Both methods of analysis showed similar correlations between leaflet thickness and valve systolic function. Further development of this PHV may lead to enhanced durability and thus a more reliable heart valve replacement than contemporary options.

Synthesis and Evaluation of Functionalized Polyurethanes for pH-Responsive Delivery of Compounds in Chronic Wounds.

Chronic wounds, depending on the bacteria that caused the infection, can be associated with an extreme acidic or basic pH. Therefore, the application of pH-responsive hydrogels has been instigated for the delivery of therapeutics to chronic wounds. Herein, with the aim of developing a flexible pH-responsive hydrogel, we functionalized hydrophilic polyurethanes with either cationic (polyethylene imine) or anionic (succinic anhydride) moieties. A comprehensive physicochemical characterization of corresponding polymers was carried out. Particularly, when tested in aqueous buffers, the surface charge of hydrogel films was closely correlated with the pH of the buffers. The loading of the cationic and anionic hydrogel films with various compound models (bromophenol blue; negatively charged or Pyronin Y; positively charged) showed that the electrostatic forces between the polymeric backbone and the compound model will determine the ultimate release rate at any given pH. The potential application of these films for chronic wound drug delivery was assessed by loading them with an antibiotic (ciprofloxacin). In vitro bacterial culturing was performed using Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Results showed that at the same drug dosage, different release profiles achievable from cationic and anionic polyurethanes can yield different degrees of an antibacterial effect. Overall, our results suggest the potential application of cationic and anionic hydrophilic polyurethanes as flexible pH-responsive materials for the delivery of therapeutics to chronic wounds.

Pediatric pulmonary valve replacements: Clinical challenges and emerging technologies.

Congenital heart diseases (CHDs) frequently impact the right ventricular outflow tract, resulting in a significant incidence of pulmonary valve replacement in the pediatric population. While contemporary pediatric pulmonary valve replacements (PPVRs) allow satisfactory patient survival, their biocompatibility and durability remain suboptimal and repeat operations are commonplace, especially for very young patients. This places enormous physical, financial, and psychological burdens on patients and their parents, highlighting an urgent clinical need for better PPVRs. An important reason for the clinical failure of PPVRs is biofouling, which instigates various adverse biological responses such as thrombosis and infection, promoting research into various antifouling chemistries that may find utility in PPVR materials. Another significant contributor is the inevitability of somatic growth in pediatric patients, causing structural discrepancies between the patient and PPVR, stimulating the development of various growth-accommodating heart valve prototypes. This review offers an interdisciplinary perspective on these challenges by exploring clinical experiences, physiological understandings, and bioengineering technologies that may contribute to device development. It thus aims to provide an insight into the design requirements of next-generation PPVRs to advance clinical outcomes and promote patient quality of life.

Biopolymeric Coatings for Local Release of Therapeutics from Biomedical Implants.

The deployment of structures that enable localized release of bioactive molecules can result in more efficacious treatment of disease and better integration of implantable bionic devices. The strategic design of a biopolymeric coating can be used to engineer the optimal release profile depending on the task at hand. As illustrative examples, here advances in delivery of drugs from bone, brain, ocular, and cardiovascular implants are reviewed. These areas are focused to highlight that both hard and soft tissue implants can benefit from controlled localized delivery. The composition of biopolymers used to achieve appropriate delivery to the selected tissue types, and their corresponding outcomes are brought to the fore. To conclude, key factors in designing drug-loaded biopolymeric coatings for biomedical implants are highlighted.

From Scan to Simulation-A Novel Workflow for Developing Bioinspired Heart Valves.

Current heart valve replacements lack durability and prolonged performance, especially in pediatric patients. In part, these problems may be attributed to the materials chosen for these constructs, but another important contributing factor is the design of the valve, as this dictates hemodynamic performance and impacts leaflet stresses which may accelerate structural valve deterioration. Most current era bioprosthetic valves adhere to a fundamental design where flat leaflets are supported by commissural posts, secured to a sewing ring. This overall design strategy is effective, but functionality and durability can be improved by incorporating features of the native valve geometry. This paper presents a novel workflow for developing and analyzing bio-inspired valve designs computationally. The leaflet curvature was defined using a mathematical equation whose parameters were derived from the three-dimensional model of a native sheep pulmonary valve obtained via microcomputed tomography. Finite element analysis was used to screen the various valve designs proposed in this study by assessing the effect of leaflet thickness, Young's modulus, and height/curvature on snap-through (where leaflets bend against their original curvature), geometric orifice area (GOA) and the stress in the leaflets. This workflow demonstrated benefits for valve designs with leaflet thicknesses between 0.1 and 0.3 mm, Young's moduli less than 50 MPa, and elongated leaflets with higher curvatures. The proposed workflow brings substantial efficiency gains at the design stage, minimizing manufacturing and animal testing during iterative improvements, and offers a bridge between in vitro and more complex in silico studies in the future.

Electrical Response of Poly(N-[3-(dimethylamino)Propyl] Methacrylamide) to CO2 at a Long Exposure Period.

Amine-functionalized polymers (AFPs) are able to react with carbon dioxide (CO2) and are therefore useful in CO2 capture and sensing. To develop AFP-based CO2 sensors, it is critical to examine their electrical responses to CO2 over long periods of time, so that the device can be used consistently for measuring CO2 concentration. To this end, we synthesized poly(N-[3-(dimethylamino)propyl] methacrylamide) (pDMAPMAm) by free radical polymerization and tested its ability to behave as a CO2-responsive polymer in a transducer. The electrical response of this polymer to CO2 upon long exposure times was measured in both the aqueous and solid phases. Direct current resistance measurement tests on pDMAPMAm films printed along with the silver electrodes in the presence of CO2 at various concentrations reveal a two-region electrical response. Upon continuous exposure to different CO2 flow rates (at a constant pressure of 0.2 MPa), the resistance first decreased over time, reaching a minimum, followed by a gradual increase with further exposure to CO2. A similar trend is observed when CO2 is introduced to an aqueous solution of pDMAPMAm. The in situ monitoring of pH suggests that the change in resistance of pDMAPMAm can be attributed to the protonation of tertiary amine groups in the presence of CO2. This two-region response of pDMAPMAm is based on a proton-hopping mechanism and a change in the number of free amines when pDMAPMAm is exposed to various levels of CO2.

Flexible Sensors for Hydrogen Peroxide Detection: A Critical Review.

Hydrogen peroxide (H2O2) is a common chemical used in many industries and can be found in various biological environments, water, and air. Yet, H2O2 in a certain range of concentrations can be hazardous and toxic. Therefore, it is crucial to determine its concentration at different conditions for safety and diagnostic purposes. This review provides an insight about different types of sensors that have been developed for detection of H2O2. Their flexibility, stability, cost, detection limit, manufacturing, and challenges in their applications have been compared. More specifically the advantages and disadvantages of various flexible substrates that have been utilized for the design of H2O2 sensors were discussed. These substrates include carbonaceous substrates (e.g., reduced graphene oxide films, carbon cloth, carbon, and graphene fibers), polymeric substrates, paper, thin glass, and silicon wafers. Many of these substrates are often decorated with nanostructures composed of Pt, Au, Ag, MnO2, Fe3O4, or a conductive polymer to enhance the performance of sensors. The impact of these nanostructures on the sensing performance of resulting flexible H2O2 sensors has been reviewed in detail. In summary, the detection limits of these sensors are within the range of 100 nM-1 mM, which makes them potentially, but not necessarily, suitable for applications in health, food, and environmental monitoring. However, the required sample volume, cost, ease of manufacturing, and stability are often neglected compared to other detection parameters, which hinders sensors' real-world application. Future perspectives on how to address some of the substrate limitations and examples of application-driven sensors are also discussed.

Thermally drawn biodegradable fibers with tailored topography for biomedical applications.

There is a growing demand for polymer fiber scaffolds for biomedical applications and tissue engineering. Biodegradable polymers such as polycaprolactone have attracted particular attention due to their applicability to tissue engineering and optical neural interfacing. Here we report on a scalable and inexpensive fiber fabrication technique, which enables the drawing of PCL fibers in a single process without the use of auxiliary cladding. We demonstrate the possibility of drawing PCL fibers of different geometries and cross-sections, including solid-core, hollow-core, and grooved fibers. The solid-core fibers of different geometries are shown to support cell growth, through successful MCF-7 breast cancer cell attachment and proliferation. We also show that the hollow-core fibers exhibit a relatively stable optical propagation loss after submersion into a biological fluid for up to 21 days with potential to be used as waveguides in optical neural interfacing. The capacity to tailor the surface morphology of biodegradable PCL fibers and their non-cytotoxicity make the proposed approach an attractive platform for biomedical applications and tissue engineering.

Performance Optimization of Polymer Fibre Actuators for Soft Robotics.

Analytical modeling of soft pneumatic actuators constitutes a powerful tool for the systematic design and characterization of these key components of soft robotics. Here, we maximize the quasi-static bending angle of a soft pneumatic actuator by optimizing its cross-section for a fixed positive pressure inside it. We begin by formulating a general theoretical framework for the analytical calculation of the bending angle of pneumatic actuators with arbitrary cross-sections, which is then applied to an actuator made of a circular polymer tube and an asymmetric patch in the shape of a hollow-cylinder sector on its outer surface. It is shown that the maximal bending angle of this actuator can be achieved using a wide range of patches with different optimal dimensions and approximately the same cross-sectional area, which decreases with pressure. We also calculate the optimal dimensions of thin and small patches in thin pneumatic actuators. Our analytical results lead to clear design guidelines, which may prove useful for engineering and optimization of the key components of soft robotics with superior features.

Facile Development of a Fiber-Based Electrode for Highly Selective and Sensitive Detection of Dopamine.

A facile one-step method was used to create a selective and sensitive electrode for dopamine (DA) detection based upon a stainless steel (SS) filament substrate and reduced graphene oxide (rGO). The electrode successfully and selectively detects DA in the presence of uric acid and ascorbic acid without the need for a Nafion coating. The proposed electrode is easy to fabricate, low-cost, flexible, and strong. The rGO-SS electrode could also be incorporated into a three-dimensional braided structure enabling DA detection in a two-electrode fiber system. The sensor is an excellent candidate for production of an affordable, robust, and flexible wearable and portable sensor and expands the application of textiles in point of care diagnostic devices.

Life-Saving Threads: Advances in Textile-Based Analytical Devices.

Novel approaches that incorporate electrofluidic and microfluidic technologies are reviewed to illustrate the translation of traditional enclosed structures into open and accessible textile based platforms. Through the utilization of on-fiber and on-textile microfluidics, it is possible to invert the typical enclosed capillary column or microfluidic "chip" platform, to achieve surface accessible efficient separations and fluid handling, while maintaining a microfluidic environment. The open fiber/textile based fluidics approach immediately provides new possibilities to interrogate, manipulate, redirect, extract, characterize, and quantify solutes and target species at any point in time during such processes as on-fiber electrodriven separations. This approach is revolutionary in its simplicity and provides many potential advantages not otherwise afforded by the more traditional enclosed platforms.

Three-Dimensional Printing of Abrasive, Hard, and Thermally Conductive Synthetic Microdiamond-Polymer Composite Using Low-Cost Fused Deposition Modeling Printer.

A relative lack of printable materials with tailored functional properties limits the applicability of three-dimensional (3D) printing. In this work, a diamond-acrylonitrile butadiene styrene (ABS) composite filament for use in 3D printing was created through incorporation of high-pressure and high-temperature (HPHT) synthetic microdiamonds as a filler. Homogenously distributed diamond composite filaments, containing either 37.5 or 60 wt % microdiamonds, were formed through preblending the diamond powder with ABS, followed by subsequent multiple fiber extrusions. The thermal conductivity of the ABS base material increased from 0.17 to 0.94 W/(m·K), more than five-fold following incorporation of the microdiamonds. The elastic modulus for the 60 wt % microdiamond containing composite material increased by 41.9% with respect to pure ABS, from 1050 to 1490 MPa. The hydrophilicity also increased by 32%. A low-cost fused deposition modeling printer was customized to handle the highly abrasive composite filament by replacing the conventional (stainless-steel) filament feeding gear with a harder titanium gear. To demonstrate improved thermal performance of 3D printed devices using the new composite filament, a number of composite heat sinks were printed and characterized. Heat dissipation measurements demonstrated that 3D printed heat sinks containing 60 wt % diamond increased the thermal dissipation by 42%.

Conductive Tough Hydrogel for Bioapplications.

Biocompatible conductive tough hydrogels represent a new class of advanced materials combining the properties of tough hydrogels and biocompatible conductors. Here, a simple method, to achieve a self-assembled tough elastomeric composite structure that is biocompatible, conductive, and with high flexibility, is reported. The hydrogel comprises polyether-based liner polyurethane (PU), poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(4-styrenesulfonate) (PSS), and liquid crystal graphene oxide (LCGO). The polyurethane hybrid composite (PUHC) containing the PEDOT:PSS, LCGO, and PU has a higher electrical conductivity (10×), tensile modulus (>1.6×), and yield strength (>1.56×) compared to respective control samples. Furthermore, the PUHC is biocompatible and can support human neural stem cell (NSC) growth and differentiation to neurons and supporting neuroglia. Moreover, the stimulation of PUHC enhances NSC differentiation with enhanced neuritogenesis compared to unstimulated cultures. A model describing the synergistic effects of the PUHC components and their influence on the uniformity, biocompatibility, and electromechanical properties of the hydrogel is presented.

Enhanced physicochemical properties of polydimethylsiloxane based microfluidic devices and thin films by incorporating synthetic micro-diamond.

Synthetic micro-diamond-polydimethylsiloxane (PDMS) composite microfluidic chips and thin films were produced using indirect 3D printing and spin coating fabrication techniques. Microfluidic chips containing up to 60 wt% micro-diamond were successfully cast and bonded. Physicochemical properties, including the dispersion pattern, hydrophobicity, chemical structure, elasticity and thermal characteristics of both chip and films were investigated. Scanning electron microscopy indicated that the micro-diamond particles were embedded and interconnected within the bulk material of the cast microfluidic chip, whereas in the case of thin films their increased presence at the polymer surface resulted in a reduced hydrophobicity of the composite. The elastic modulus increased from 1.28 for a PDMS control, to 4.42 MPa for the 60 wt% composite, along with a three-fold increase in thermal conductivity, from 0.15 to 0.45 W m-1 K-1. Within the fluidic chips, micro-diamond incorporation enhanced heat dissipation by efficient transfer of heat from within the channels to the surrounding substrate. At a flow rate of 1000 µL/min, the gradient achieved for the 60 wt% composite chip equalled a 9.8 °C drop across a 3 cm long channel, more than twice that observed with the PDMS control chip.