Direct Contraction Force Measurements of Engineered Cardiac Tissue Constructs With Inotropic Drug Exposure

Contractility is one of the most crucial functions of the heart because it is directly related to the maintenance of blood perfusion throughout the body. Both increase and decrease in contractility may cause fatal consequences. Therefore, drug discovery would benefit greatly from reliable testing of candidate molecule effects on contractility capacity. In this study, we further developed a dual-axis piezoelectric force sensor together with our human cell–based vascularized cardiac tissue constructs for cardiac contraction force measurements. The capability to detect drug-induced inotropic effects was tested with a set of known positive and negative inotropic compounds of isoprenaline, milrinone, omecamtiv mecarbil, propranolol, or verapamil in different concentrations. Both positive and negative inotropic effects were measurable, showing that our cardiac contraction force measurement system including a piezoelectric cantilever sensor and a human cell–based cardiac tissue constructs has the potential to be used for testing of inotropic drug effects.

Self-assembled cellulose nanofiber-carbon nanotube nanocomposite films with anisotropic conductivity

In this study, a nanocellulose-based material showing anisotopic conductivity is introduced. The material has up to 1000 times higher conductivity along the dry-line boundary direction than along the radial direction. In addition to the material itself, the method to produce the material is novel and is based on the alignment of cationic cellulose nanofibers (c-CNFs) along the dry-line boundary of an evaporating droplet composed of c-CNFs in two forms and conductive multi-walled carbon nanotubes (MWCNTs). On the one hand, c-CNFs are used as a dispersant of MWCNTs, and on the other hand they are used as an additional suspension element to create the desired anisotropy. When the suspended c-CNF is left out, and the nanocomposite film is manufactured using the high energy sonicated c-CNF/MWCNT dispersion only, conductive anisotropy is not present but evenly conducting nanocomposite films are obtained. Therefore, we suggest that suspending additional c-CNFs in the c-CNF/MWCNT dispersion results in nanocomposite films with anisotropic conductivity. This is a new way to obtain nanocomposite films with substantial anisotropic conductivity.

Extrusion-Based Bioprinting of Multilayered Nanocellulose Constructs for Cell Cultivation Using In Situ Freezing and Preprint CaCl2 Cross-Linking

Extrusion-based bioprinting with a preprint cross-linking agent and an in situ cooling stage provides a versatile method for the fabrication of 3D structures for cell culture. We added varying amounts of calcium chloride as a precross-linker into native nanofibrillated cellulose (NFC) hydrogel prior to 3D bioprinting to fabricate structurally stable multilayered constructs without the need for a separate cross-linking bath. To further enhance their stability, we bioprinted the multilayered structures onto an in situ temperature-controlled printing stage at 25, 0, and -10 °C. The extruded and subsequently freeze-dried volumetric constructs maintained their structures after being immersed into a cell culture medium. The ability to maintain the shape after immersion in cell media is an essential feature for the fabrication of stem cell-based artificial organs. We studied the viability and distribution of mouse embryonic fibroblast cells into the hydrogels using luminescence technique and confocal microscopy. Adding CaCl2 increased the stability of the multilayered nanocellulose structures, making them suitable for culturing cells inside the 3D hydrogel environment. Lower stage temperature considerably improved the structural stability of the 3D printed structures, however, had no effect on cell viability.

Disposable Microfluidic Sensor Based on Nanocellulose for Glucose Detection

Point-of-care devices that are inexpensive, disposable, and environmentally friendly are becoming increasingly predominant in the field of biosensing and biodiagnostics. Here, microfluidics is a suitable option to endow portability and minimal reagent and material consumption. Nanocellulose is introduced to manufacture microfluidic channels and as a storage and immobilization compartment of glucose oxidase. Improved enzymatic activity retention is demonstrated in a simple and disposable point-of-care diagnostic unit that is able to detect glucose from fluid matrices at 0.1 × 10-3 m concentration and in less than 10 min. It is concluded that the patterning and fluidic technologies that are possible with nanocellulose enable easily scalable multianalyte designs.

Conductive Cellulose based Foam Formed 3D Shapes-From Innovation to Designed Prototype

In this article, we introduce for the first time, a method to manufacture cellulose based electrically conductive non-woven three-dimensional (3D) structures using the foam forming technology. The manufacturing is carried out using a minimum amount of processing steps, materials, and hazardous chemicals. The optimized solution applies a single surfactant type and a single predefined portion for the two main processing steps: (1) the dispersing of nanocellulose (NC) and carbon nanotubes (CNT) and (2) the foam forming process. The final material system has a concentration of the used surfactant that is not only sufficient to form a stable and homogeneous nanoparticle dispersion, but it also results in stable foam in foam forming. In this way, the advantages of the foam forming process can be maximized for this application. The cellulose based composite material has a highly even distribution of CNTs over the NC network, resulting a conductivity level of 7.7 S/m, which increased to the value 8.0 S/m after surfactant removal by acetone washing. Also, the applicability and a design product case 'Salmiakki' were studied where the advantages of the material system were validated for a heating element application.

High Bending-Mode Sensitivity of Printed Piezoelectric Poly(vinylidenefluoride-co-trifluoroethylene) Sensors

Printable piezoelectric sensors were fabricated on a flexible polyethylene terephthalate (PET) substrate. Solution-processed piezoelectric poly(vinylidenefluoride-co-trifluoroethylene) ink was used as an active layer. Evaporated silver on PET was used as the bottom electrode and the painted silver glue as the top electrode. The sensors were poled using a high dc electric field from 25 to 65 MV m^-1, yielding piezoelectric normal direction sensitivities up to 25 pC N^-1. Bending-mode sensitivities showed values up to 200 nC N^-1, which is 4 orders of magnitude larger than the force sensitivity in the normal direction. The high bending-mode sensitivities suggest suitability for detecting small forces, such as single fiber bonds or cardiomyocyte cell-beating force.

Effect of Surfactant Type and Sonication Energy on the Electrical Conductivity Properties of Nanocellulose-CNT Nanocomposite Films

We present a detailed study on the influence of sonication energy and surfactant type on the electrical conductivity of nanocellulose-carbon nanotube (NFC-CNT) nanocomposite films. The study was made using a minimum amount of processing steps, chemicals and materials, to optimize the conductivity properties of free-standing flexible nanocomposite films. In general, the NFC-CNT film preparation process is sensitive concerning the dispersing phase of CNTs into a solution with NFC. In our study, we used sonication to carry out the dispersing phase of processing in the presence of surfactant. In the final phase, the films were prepared from the dispersion using centrifugal cast molding. The solid films were analyzed regarding their electrical conductivity using a four-probe measuring technique. We also characterized how conductivity properties were enhanced when surfactant was removed from nanocomposite films; to our knowledge this has not been reported previously. The results of our study indicated that the optimization of the surfactant type clearly affected the formation of freestanding films. The effect of sonication energy was significant in terms of conductivity. Using a relatively low 16 wt. % concentration of multiwall carbon nanotubes we achieved the highest conductivity value of 8.4 S/cm for nanocellulose-CNT films ever published in the current literature. This was achieved by optimizing the surfactant type and sonication energy per dry mass. Additionally, to further increase the conductivity, we defined a preparation step to remove the used surfactant from the final nanocomposite structure.

Evaluation of Dry Electrodes in Canine Heart Rate Monitoring

The functionality of three dry electrocardiogram electrode constructions was evaluated by measuring canine heart rate during four different behaviors: Standing, sitting, lying and walking. The testing was repeated (n = 9) in each of the 36 scenarios with three dogs. Two of the electrodes were constructed with spring-loaded test pins while the third electrode was a molded polymer electrode with Ag/AgCl coating. During the measurement, a specifically designed harness was used to attach the electrodes to the dogs. The performance of the electrodes was evaluated and compared in terms of heartbeat detection coverage. The effect on the respective heart rate coverage was studied by computing the heart rate coverage from the measured electrocardiogram signal using a pattern-matching algorithm to extract the R-peaks and further the beat-to-beat heart rate. The results show that the overall coverage ratios regarding the electrodes varied between 45–95% in four different activity modes. The lowest coverage was for lying and walking and the highest was for standing and sitting.

Engineering and Characterization of Bacterial Nanocellulose Films as Low Cost and Flexible Sensor Material

Some bacterial strains such as Komagataeibacter xylinus are able to produce cellulose as an extracellular matrix. In comparison to wood-based cellulose, bacterial cellulose (BC) holds interesting properties such as biodegradability, high purity, water-holding capacity, and superior mechanical and structural properties. Aiming toward improvement in BC production titer and tailored alterations to the BC film, we engineered K. xylinus to overexpress partial and complete bacterial cellulose synthase operon that encodes activities for BC production. The changes in cell growth, end metabolite, and BC production titers from the engineered strains were compared with the wild-type K. xylinus. Although there were no significant differences between the growth of wild-type and engineered strains, the engineered K. xylinus strains demonstrated faster BC production, generating 2-4-fold higher production titer (the highest observed titer was obtained with K. xylinus-bcsABCD strain producing 4.3 ± 0.46 g/L BC in 4 days). The mechanical and structural characteristics of cellulose produced from the wild-type and engineered K. xylinus strains were analyzed with a stylus profilometer, in-house built tensile strength measurement system, a scanning electron microscope, and an X-ray diffractometer. Results from the profilometer indicated that the engineered K. xylinus strains produced thicker BC films (wild type, 5.1 μm, and engineered K. xylinus strains, 6.2-10.2 μm). Scanning electron microscope revealed no principal differences in the structure of the different type BC films. The crystallinity index of all films was high (from 88.6 to 97.5%). All BC films showed significant piezoelectric response (5.0-20 pC/N), indicating BC as a promising sensor material.

Testing and comparing of film-type sensor materials in measurement of plantar pressure distribution

Simple in-shoe sensors based on film-type sensor materials were developed in this study. Three sensor materials were tested: polyvinylidenefluoride (PVDF), cellulose nanofibrils (CNF) and ElectroMechanical Film (EMFi). Plantar pressure distributions of a subject were measured with the developed in-shoe sensors; each consisting of three sensor channels (lateral and medial metatarsal heads and heel). In addition, piezoelectric sensor sensitivities and crosstalk between the sensor channels were determined. Differences between the tested film-type materials and measured plantar pressure distribution signals were studied.

Cellulose Nanofibril Film as a Piezoelectric Sensor Material

Self-standing films (45 μm thick) of native cellulose nanofibrils (CNFs) were synthesized and characterized for their piezoelectric response. The surface and the microstructure of the films were evaluated with image-based analysis and scanning electron microscopy (SEM). The measured dielectric properties of the films at 1 kHz and 9.97 GHz indicated a relative permittivity of 3.47 and 3.38 and loss tangent tan δ of 0.011 and 0.071, respectively. The films were used as functional sensing layers in piezoelectric sensors with corresponding sensitivities of 4.7-6.4 pC/N in ambient conditions. This piezoelectric response is expected to increase remarkably upon film polarization resulting from the alignment of the cellulose crystalline regions in the film. The CNF sensor characteristics were compared with those of polyvinylidene fluoride (PVDF) as reference piezoelectric polymer. Overall, the results suggest that CNF is a suitable precursor material for disposable piezoelectric sensors, actuators, or energy generators with potential applications in the fields of electronics, sensors, and biomedical diagnostics.

One-step large-scale deposition of salt-free DNA origami nanostructures

DNA origami nanostructures have tremendous potential to serve as versatile platforms in self-assembly -based nanofabrication and in highly parallel nanoscale patterning. However, uniform deposition and reliable anchoring of DNA nanostructures often requires specific conditions, such as pre-treatment of the chosen substrate or a fine-tuned salt concentration for the deposition buffer. In addition, currently available deposition techniques are suitable merely for small scales. In this article, we exploit a spray-coating technique in order to resolve the aforementioned issues in the deposition of different 2D and 3D DNA origami nanostructures. We show that purified DNA origamis can be controllably deposited on silicon and glass substrates by the proposed method. The results are verified using either atomic force microscopy or fluorescence microscopy depending on the shape of the DNA origami. DNA origamis are successfully deposited onto untreated substrates with surface coverage of about 4 objects/mm(2). Further, the DNA nanostructures maintain their shape even if the salt residues are removed from the DNA origami fabrication buffer after the folding procedure. We believe that the presented one-step spray-coating method will find use in various fields of material sciences, especially in the development of DNA biochips and in the fabrication of metamaterials and plasmonic devices through DNA metallisation.

Preparation of Supercapacitors on Flexible Substrates with Electrodeposited PEDOT/Graphene Composites

Composite films consisting of poly(3,4-ethylenedioxythiophene) (PEDOT) and graphene oxide (GO) were electrochemically polymerized by electrooxidation of EDOT in ionic liquid (BMIMBF4) onto flexible electrode substrates. Two polymerization approaches were compared, and the cyclic voltammetry (CV) method was found to be superior to potentiostatic polymerization for the growth of PEDOT/GO films. After deposition, incorporated GO was reduced to rGO by a rapid electrochemical method of repetitive cathodic potential cycling, without using any reducing reagents. The films were characterized in 3-electrode configuration in BMIMBF4. Symmetric supercapacitors with aqueous electrolyte were assembled from the composite films and characterized through cyclic voltammetry and galvanostatic discharge tests. It was shown that PEDOT/rGO composites have better capacitive properties than pure PEDOT or the unreduced composite film. The cycling stability of the supercapacitors was also tested, and the results indicate that the specific capacitance still retains well over 90% of the initial value after 2000 consecutive charging/discharging cycles. The supercapacitors were demonstrated as energy storages in a room light energy harvester with a printed organic solar cell and printed electrochromic display. The results are promising for the development of energy-autonomous, low-power, and disposable electronics.

Direct conductance measurements of short single DNA molecules in dry conditions

We present a study of electronic transport in short (12-base-pair) DNA duplexes covalently bonded (via thiol groups) to two gold electrodes obtained by a mechanically controllable break junction (MCJB) technique in dry conditions. A large number of DNA junctions have been repeatedly formed in order to obtain a conductance histogram that reveals a peak which corresponds to the conductance of a single DNA molecule. We observed that the conductivity of a DNA increases upon increasing the content of G:C base pairs in the duplex. With our method we are able to obtain a reliable value of a single DNA conductance and subsequently measure its current-voltage (I-V) characteristics. In contrast to the electronic transport measurements performed with long DNA sequences (hundreds of base pairs) where the obtained conductance values vary a lot with environmental conditions, our values obtained for the short DNA sequences are consistent with the values reported for comparable sequences in aqueous solution.

Carbon nanotubes as electrodes for dielectrophoresis of DNA

Dielectrophoresis can potentially be used as an efficient trapping tool in the fabrication of molecular devices. For nanoscale objects, however, the Brownian motion poses a challenge. We show that the use of carbon nanotube electrodes makes it possible to apply relatively low trapping voltages and still achieve high enough field gradients for trapping nanoscale objects, e.g., single molecules. We compare the efficiency and other characteristics of dielectrophoresis between carbon nanotube electrodes and lithographically fabricated metallic electrodes, in the case of trapping nanoscale DNA molecules. The results are analyzed using finite element method simulations and reveal information about the frequency-dependent polarizability of DNA.