A Low-Cost Method to Prepare Biocompatible Filaments with Enhanced Physico-Mechanical Properties for FDM 3D Printing.

BACKGROUND: Fused Deposition Modelling (FDM) 3D printing has received much interest as a fabrication method in the medical and pharmaceutical industry due to its accessibility and cost-effectiveness. A low-cost method to produce biocompatible and biodegradable filaments can improve the usability of FDM 3D printing for biomedical applications. OBJECTIVES: The feasibility of producing low-cost filaments suitable for FDM 3D printing via single screw and twin-screw hot melt extrusion was explored. METHODS: A single-screw extruder and a twin-screw extruder were used to produce biocompatible filaments composed of varying concentrations of polyethylene glycol (PEG) at 10%, 20%, 30% w/w and polylactic acid (PLA) 90%, 80% and 70% w/w, respectively. DSC, TGA and FTIR were employed to investigate the effect of PEG on the PLA filaments. RESULTS: The presence of PEG lowered the processing temperature of the formulation compositions via melt-extrusion, making it suitable for pharmaceutical applications. The use of PEG can lower the melting point of the PLA polymer to 170°C, hence lowering the printing temperature. PEG can also improve the plasticity of the filaments, as the rupture strain of twin-screw extruded filaments increased up to 10-fold as compared to the commercial filaments. Advanced application of FTIR analysis confirmed the compatibility and miscibility of PEG with PLA. CONCLUSION: Twin-screw extrusion is more effective in producing a polymeric mixture of filaments as the mixing is more homogenous. The PEG/PLA filament is suitable to be used in 3D printing of medical or pharmaceutical applications such as medical implants, drug delivery systems, or personalised tablets.

Flexible Temperature Sensor Integration into E-Textiles Using Different Industrial Yarn Fabrication Processes.

Textiles enhanced with thin-film flexible sensors are well-suited for unobtrusive monitoring of skin parameters due to the sensors' high conformability. These sensors can be damaged if they are attached to the surface of the textile, also affecting the textiles' aesthetics and feel. We investigate the effect of embedding flexible temperature sensors within textile yarns, which adds a layer of protection to the sensor. Industrial yarn manufacturing techniques including knit braiding, braiding, and double covering were utilised to identify an appropriate incorporation technique. The thermal time constants recorded by all three sensing yarns was <10 s. Simultaneously, effective sensitivity only decreased by a maximum of 14% compared to the uncovered sensor. This is due to the sensor being positioned within the yarn instead of being in direct contact with the measured surface. These sensor yarns were not affected by bending and produced repeatable measurements. The double covering method was observed to have the least impact on the sensors' performance due to the yarn's smaller dimensions. Finally, a sensing yarn was incorporated in an armband and used to measure changes in skin temperature. The demonstrated textile integration techniques for flexible sensors using industrial yarn manufacturing processes enable large-scale smart textile fabrication.

Buckled Thin-Film Transistors and Circuits on Soft Elastomers for Stretchable Electronics.

Although recent progress in the field of flexible electronics has allowed the realization of biocompatible and conformable electronics, systematic approaches which combine high bendability (<3 mm bending radius), high stretchability (>3-4%), and low complexity in the fabrication process are still missing. Here, we show a technique to induce randomly oriented and customized wrinkles on the surface of a biocompatible elastomeric substrate, where Thin-Film Transistors (TFTs) and circuits (inverter and logic NAND gates) based on amorphous-IGZO are fabricated. By tuning the wavelength and the amplitude of the wrinkles, the devices are fully operational while bent to 13 µm bending radii as well as while stretched up to 5%, keeping unchanged electrical properties. Moreover, a flexible rectifier is also realized, showing no degradation in the performances while flat or wrapped on an artificial human wrist. As proof of concept, transparent TFTs are also fabricated, presenting comparable electrical performances to the nontransparent ones. The extension of the buckling approach from our TFTs to circuits demonstrates the scalability of the process, prospecting applications in wireless stretchable electronics to be worn or implanted.

A wearable bluetooth LE sensor for patient monitoring during MRI scans.

This paper presents a working prototype of a wearable patient monitoring device capable of recording the heart rate, blood oxygen saturation, surface temperature and humidity during an magnetic resonance imaging (MRI) experiment. The measured values are transmitted via Bluetooth low energy (LE) and displayed in real time on a smartphone on the outside of the MRI room. During 7 MRI image acquisitions of at least 1 min and a total duration of 25 min no Bluetooth data packets were lost. The raw measurements of the light intensity for the photoplethysmogram based heart rate measurement shows an increased noise floor by 50LSB (least significant bit) during the MRI operation, whereas the temperature and humidity readings are unaffected. The device itself creates a magnetic resonance (MR) signal loss with a radius of 14 mm around the device surface and shows no significant increase in image noise of an acquired MRI image due to its radio frequency activity. This enables continuous and unobtrusive patient monitoring during MRI scans.

Biomimetic Microelectronics for Regenerative Neuronal Cuff Implants.

Smart biomimetics, a unique class of devices combining the mechanical adaptivity of soft actuators with the imperceptibility of microelectronics, is introduced. Due to their inherent ability to self-assemble, biomimetic microelectronics can firmly yet gently attach to an inorganic or biological tissue enabling enclosure of, for example, nervous fibers, or guide the growth of neuronal cells during regeneration.

Design and simulation of a 800 Mbit/s data link for magnetic resonance imaging wearables.

This paper presents the optimization of electronic circuitry for operation in the harsh electro magnetic (EM) environment during a magnetic resonance imaging (MRI) scan. As demonstrator, a device small enough to be worn during the scan is optimized. Based on finite element method (FEM) simulations, the induced current densities due to magnetic field changes of 200 T s(-1) were reduced from 1 × 10(10) A m(-2) by one order of magnitude, predicting error-free operation of the 1.8V logic employed. The simulations were validated using a bit error rate test, which showed no bit errors during a MRI scan sequence. Therefore, neither the logic, nor the utilized 800 Mbit s(-1) low voltage differential swing (LVDS) data link of the optimized wearable device were significantly influenced by the EM interference. Next, the influence of ferro-magnetic components on the static magnetic field and consequently the image quality was simulated showing a MRI image loss with approximately 2 cm radius around a commercial integrated circuit of 1×1 cm(2). This was successively validated by a conventional MRI scan.

Wafer-scale design of lightweight and transparent electronics that wraps around hairs.

Electronics on very thin substrates have shown remarkable bendability, conformability and lightness, which are important attributes for biological tissues sensing, wearable or implantable devices. Here we propose a wafer-scale process scheme to realize ultra flexible, lightweight and transparent electronics on top of a 1-µm thick parylene film that is released from the carrier substrate after the dissolution in water of a polyvinyl- alcohol layer. The thin substrate ensures extreme flexibility, which is demonstrated by transistors that continue to work when wrapped around human hairs. In parallel, the use of amorphous oxide semiconductor and high-K dielectric enables the realization of analogue amplifiers operating at 12 V and above 1 MHz. Electronics can be transferred on any object, surface and on biological tissues like human skin and plant leaves. We foresee a potential application as smart contact lenses, covered with light, transparent and flexible devices, which could serve to monitor intraocular pressure for glaucoma disease.

High performance flexible electronics for biomedical devices.

Plastic electronics is soft, deformable and lightweight and it is suitable for the realization of devices which can form an intimate interface with the body, be implanted or integrated into textile for wearable and biomedical applications. Here, we present flexible electronics based on amorphous oxide semiconductors (a-IGZO) whose performance can achieve MHz frequency even when bent around hair. We developed an assembly technique to integrate complex electronic functionalities into textile while preserving the softness of the garment. All this and further developments can open up new opportunities in health monitoring, biotechnology and telemedicine.

Fabrication and transfer of flexible few-layers MoS2 thin film transistors to any arbitrary substrate.

Recently, transition metal dichalcogenides (TMDCs) have attracted interest thanks to their large field effective mobility (>100 cm(2)/V · s), sizable band gap (around 1-2 eV), and mechanical properties, which make them suitable for high performance and flexible electronics. In this paper, we present a process scheme enabling the fabrication and transfer of few-layers MoS2 thin film transistors from a silicon template to any arbitrary organic or inorganic and flexible or rigid substrate or support. The two-dimensional semiconductor is mechanically exfoliated from a bulk crystal on a silicon/polyvinyl alcohol (PVA)/polymethyl methacrylane (PMMA) stack optimized to ensure high contrast for the identification of subnanometer thick flakes. Thin film transistors (TFTs) with structured source/drain and gate electrodes are fabricated following a designed procedure including steps of UV lithography, wet etching, and atomic layer deposited (ALD) dielectric. Successively, after the dissolution of the PVA sacrificial layer in water, the PMMA film, with the devices on top, can be transferred to another substrate of choice. Here, we transferred the devices on a polyimide plastic foil and studied the performance when tensile strain is applied parallel to the TFT channel. We measured an electron field effective mobility of 19 cm(2)/(V s), an I(on)/I(off)ratio greater than 10(6), a gate leakage current as low as 0.3 pA/µm, and a subthreshold swing of about 250 mV/dec. The devices continue to work when bent to a radius of 5 mm and after 10 consecutive bending cycles. The proposed fabrication strategy can be extended to any kind of 2D materials and enable the realization of electronic circuits and optical devices easily transferrable to any other support.

Textile integrated sensors and actuators for near-infrared spectroscopy.

Being the closest layer to our body, textiles provide an ideal platform for integrating sensors and actuators to monitor physiological signals. We used a woven textile to integrate photodiodes and light emitting diodes. LEDs and photodiodes enable near-infrared spectroscopy (NIRS) systems to monitor arterial oxygen saturation and oxygenated and deoxygenated hemoglobin in human tissue. Photodiodes and LEDs are mounted on flexible plastic strips with widths of 4 mm and 2 mm, respectively. The strips are woven during the textile fabrication process in weft direction and interconnected with copper wires with a diameter of 71 µm in warp direction. The sensor textile is applied to measure the pulse waves in the fingertip and the changes in oxygenated and deoxygenated hemoglobin during a venous occlusion at the calf. The system has a signal-to-noise ratio of more than 70 dB and a system drift of 0.37% ± 0.48%. The presented work demonstrates the feasibility of integrating photodiodes and LEDs into woven textiles, a step towards wearable health monitoring devices.

In tube integrated electronic nose system on a flexible polymer substrate.

The fabrication of electronic devices, such as gas sensors on flexible polymer substrates, enables the use of electronics in applications where conventional devices on stiff substrates could not be used. We demonstrate the development of a new intra-tube electronic-nose (e-nose) gas sensor device with multiple sensors fabricated and integrated on a flexible substrate. For this purpose, we developed a new method of fabricating a sensor array of four gas sensors on a flexible polymer substrate. The method allowed the use of lithography techniques to pattern different polymers with a broad range of solubility parameters. Conductive polymer composites were used as a gas sensitive layer due to the high stretchability of the material. Each of the 30 e-nose devices on one substrate was designed to fit on a polymer strip with a width of 2 mm. A single e-nose strip was successfully integrated into the inlet tube of a gas-measurement apparatus with an inner-tube diameter of 3 mm. Using the e-nose, we were able to differentiate between four different volatile solvent vapors. The tube-integrated e-nose outperformed a chamber-integrated e-nose of the same type in terms of response time and flow-rate influences. The sensor array inside the tube showed a faster response time and detected short pulses of analyte exposure compared to the same sensor array outside of the tube. We measured gas flow rates from 1,000 to 30 sccm without significant changes in sensor performance using this intra-tube e-nose prototype. The tube could be bent to radii < 15 mm with a sensor performance similar to an unbent sensor.

Locally reinforced polymer-based composites for elastic electronics.

A promising approach to fabricating elastic electronic systems involves processing thin film circuits directly on the elastic substrate by standard photolithography. Thin film devices are generally placed onto stiffer islands on the substrate surface to protect devices from excessive strain while still achieving a globally highly deformable system. Here we report a new method to achieve island architectures by locally reinforcing polymeric substrates at the macro- and microscale using magnetically responsive anisotropic microparticles. We demonstrate that the resulting particle-reinforced elastic substrates can be made smooth enough for the patterning and successful operation of thin film transistors with transfer characteristics comparable to state-of-the-art devices.