Automation Highlights from the Literature

Abstract

Microfluidic platforms have become great tools for biomedical fields. However, microfluidic fabrication can be costly and time-consuming. The utilization of three-dimensional (3D) printing technologies has greatly enhanced the ability to iterate and build functional devices with unique functions. However, the ability to directly fabricate structure within exiting microfluidic devices is lacking and prevents 3D printing from becoming a more useful tool for microfluidics. To address this issue, Liu et al. introduce a projection-based method for direct 3D printing within microfluidic architectures. A variable-height micromixer (VHM) is fabricated using projection 3D printing combined with soft lithography. Theoretical and flow experiments demonstrate that altering the local z heights of VHM improved mixing at lower flow rates than simple geometries. Following device printing, complex, user-defined cell-laden scaffolds are directly printed inside the VHM, which further improves the functionality of the device. The authors believe utilization of this ability to produce 3D tissue models within a microfluidic system could offer a unique platform for medical diagnostics and disease modeling. (Liu, J.; et al., Lab Chip 2016, 16, 1430–1438) A challenge for tissue engineering is producing 3D, vascularized cellular constructs of clinically relevant size, shape, and structural integrity. Kang et al. report an integrated tissue–organ printer (ITOP) that can fabricate stable, human-scale tissue constructs of any shape. The authors achieve mechanical stability by printing cell-laden hydrogels together with biodegradable polymers in integrated patterns anchored on sacrificial hydrogels. The correct shape of the tissue construct is achieved by representing clinical imaging data as a computer model of the anatomical defect and translating the model into a program that controls the motions of the printer nozzles, which dispense cells to discrete locations. The authors further incorporate microchannels into the tissue constructs to facilitate diffusion of nutrients to printed cells, thereby overcoming the diffusion limit of 100–200 μm for cell survival in engineered tissues. With this novel ITOP, Kang et al. are able to fabricate various tissues, such as mandible and calvarial bone, cartilage, and skeletal muscle. The authors are continuing to investigate the production of tissues for human applications and the building of more complex tissues and solid organs. (Kang, H.-W.; et al., Nat. Biotechnol. 2016, 34, 312–319) Bioinspired organ-level in vitro platforms become important tools for fundamental research, drug discovery, and personalized health care. Models for nervous system research are particularly interesting due to the complexity of neurological phenomena and challenges associated with developing targeted treatment of neurological disorders. Johnson et al. introduce an additive manufacturing-based approach in the form of a bioinspired, customizable 3D printed nervous system-on-a-chip (3DNSC) for the study of viral infection in the nervous system. The authors utilize microextrusion 3D printing to enable assembly of biomimetic scaffold components (microchannels and compartmented chambers) for the alignment of axonal networks and spatial organization of cellular components. The functionality of the in vitro platform is validated by the physiologically relevant studies of nervous system infection using the multiscale biomimetic device. With this chip, the authors show that Schwann cells participate in axon-to-cell viral spread but appear refractory to infection, exhibiting a multiplicity of infection (MOI) of 1.4 genomes per cell. Johnson et al. believe these results demonstrate that 3D printing is a valuable approach for the prototyping of a customized model of nervous system-on-a-chip technology. (Johnson, B. N.; et al., Lab Chip 2016, 16, 1393–1400) The brain is an enormously complex organ structured into various regions of layered tissue. Researchers have attempted to study the brain by modeling the architecture using two-dimensional (2D) in vitro cell culturing methods. While those platforms attempt to mimic the in vivo environment, they do not truly resemble the 3D microstructure of neuronal tissues. Development of an accurate in vitro model of the brain remains a significant obstacle to our understanding of the functioning of the brain at the tissue or organ level. To address these obstacles, Lozano et al. demonstrate a new method for bioprinting 3D brainlike structures consisting of discrete layers of primary neural cells encapsulated in hydrogels. Brainlike structures are constructed using a bio-ink consisting of a novel peptide-modified biopolymer, gellan gum-RGD (RGD-GG), combined with primary cortical neurons. The ink is optimized for a modified reactive printing process and was developed for use in traditional cell culturing facilities without the need for extensive bioprinting equipment. Furthermore, the peptide modification of the gellan gum hydrogel has a profound positive effect on primary cell proliferation and network formation. The neural cell viability combined with the support of neural network formation demonstrates the cell supportive nature of the matrix. The facile ability to form discrete cell-containing layers validates the application of this novel printing technique to form complex, layered, and viable 3D cell structures. The authors believe these brainlike structures offer the opportunity to reproduce more accurate 3D in vitro microstructures, with applications ranging from cell behavior studies to improving the understanding of brain injuries and neurodegenerative diseases. (Lozano, R.; et al., Biomaterials 2015, 67, 264–273) Alessandri et al. report a microfluidic device that generates submillimetric hollow hydrogel spheres, encapsulating cells and coated internally with a layer of reconstituted extracellular matrix (ECM) of a few microns thick. The spherical capsules, composed of alginate hydrogel, originate from the spontaneous instability of a multilayered jet formed by coextrusion using a coaxial flow device. The authors provide a simple design to manufacture this device using a digital light processing (DLP) 3D printer. Further, the authors demonstrate how the inner wall of the capsules can be decorated with a continuous ECM layer that is anchored to the alginate gel and mimics the basal membrane of a cellular niche. Finally, the authors use this approach to encapsulate human neural stem cells (hNSC) derived from human induced pluripotent stem cells (hIPSC), which are further differentiated into neurons within the capsules with negligible loss of viability. Altogether, Alessandri et al. show that these capsules may serve as cell microcontainers compatible with complex cell culture conditions and applications, and believe these developments advance the field of research and biomedical applications of the cell encapsulation technology. (Alessandri, K.; et al., Lab Chip 2016, 16, 1593–1604) Conformal bioelectronics enable wearable, noninvasive, health monitoring platforms. Rim et al. demonstrate a simple and straightforward method for producing thin, sensitive In2O3-conformal biosensors based on field-effect transistors using facile solution-based processing. The authors apply a one-step coating via aqueous In2O3 solution to achieve ultrathin (3.5 nm), high-density, uniform films over large areas. These conformal In2O3-based biosensors on ultrathin polyimide films display good device performance, low mechanical stress, and highly conformal contact, which are great features suitable for artificial skin with complex curvilinear surfaces or even artificial eyes. pH sensors can be achieved by immobilizing In2O3 field-effect transistors with self-assembled monolayers of NH2-terminated silanes. Glucose sensors can be achieved by functionalizing the In2O3 field-effect transistors with glucose oxidase. Rim et al. believe this conformal ultrathin field-effect transistor biosensor represents new opportunities for future wearable human technologies. (Rim, Y. S.; et al., ACS Nano 2015, 9, 12174–12181) Stretchable electrochemical sensors are useful tools that provide important chemical information on living bodies. Liu et al. report a new method for synthesizing Au nanotubes (NTs) with large aspect ratios to construct an effective stretchable electrochemical sensor. An interlacing network of Au NTs provide the sensor with desirable stability against mechanical deformation, and Au nanostructures provide excellent electrochemical performance and biocompatibility. This makes possible the real-time electrochemical monitoring of mechanically sensitive cells on the sensor in both stretching-free and stretching states, as well as sensing of the inner lining of blood vessels. The authors believe this sensor has great potential in electrochemical detection within the living body and can open new opportunities for stretchable electrochemical sensors in biological exploration. (Liu, Y. L.; et al., Angew. Chem. Int. Ed. 2016, 55, 4537–4541) The progress of smart skin technology presents great opportunities for artificial intelligence. Resolution enhancement and energy conservation need to be addressed in order to further improve the perception and standby time of robots. Shi et al. present a novel self-powered analog smart skin for detecting contact location and velocity of an object, based on a single-electrode contact electrification effect and planar electrostatic induction. Using an analog localizing method, the resolution of this 2D smart skin can be achieved at 1.9 mm with only four terminals, which significantly reduces the terminal number of smart skins. This new design gives rise to remarkable sensitivity of this smart skin, which is sufficient to perceive the perturbation of a honeybee. In addition, thanks to a triboelectric mechanism, an extra power supply is unnecessary for this smart skin. The authors believe their design solves the problems of powering and connecting wires for smart skins, and with microstructured poly(dimethylsiloxane) films and silver nanowire electrodes, this can be a great solution for analog skin with transparency, flexibility, and high sensitivity. (Shi, M.; et al., ACS Nano 2016, 10, 4083–4091) Currently, there is a practical limitation on frequent breath monitoring due to lack of convenient and low-cost breath monitoring systems. To address this challenge, Güder et al have developed a novel paper-based moisture sensor system that takes advantage of the hygroscopic character of paper to measure patterns and rates of respiration. This is achieved by converting the changes in humidity of the paper, as a result of inhalation/exhalation, to electric signals. An ionic conductivity sensor is incorporated into the paper sensor, allowing the sensor to measure changing humidity. The paper sensor can be easily integrated with a facial mask. By combining the paper sensor with other electronic components, the authors are able to easily collect data concerning respiration and transmit the data to a smartphone, computer, or cloud for analysis. The authors believe this novel approach provides a more accessible and practical method of recording and analyzing patterns of breathing. (Güder, F.; et al., Angew. Chem. Int. Ed. 2016, 55, 5727–5732) For sputum analysis, it is critical to transfer inflammatory cells from liquefied sputum samples to a culture medium or buffer solution because this step separates inflammatory cells from the presence of residual dithiothreitol (DTT), a reagent that is needed for sputum liquefaction but causes reduced cell viability and interference with further sputum analyses. Li et al. report a new approach for transferring inflammatory cells using standing surface acoustic waves (SSAWs). In particular, the authors exploit the acoustic radiation force generated from an SSAW field to actively transfer inflammatory cells from a solution containing residual DTT to a buffer solution. The viability and integrity of the inflammatory cells are maintained during the acoustofluidic-based cell transfer process. This approach removes residual DTT and facilitates immunophenotyping of major inflammatory cells from sputum samples. It also enables cell transfer in a continuous flow, which aids the development of an automated, integrated system for on-chip sputum processing and analysis. (Li, S.; et al., Anal. Chem. 2016, DOI: 10.1021/acs.analchem.5b03383) The Gram-positive bacterium Staphylococcus aureus is a major pathogen responsible for a variety of infectious diseases ranging from cellulitis to more serious conditions, such as septic arthritis and septicemia. Timely treatment with appropriate antibiotic therapy is essential to ensure clinical defervescence and to prevent further complications, such as infective endocarditis or organ impairment due to septic shock. To date, initial antibiotic choice is empirical, using a best guess of likely organism and sensitivity, due to the lack of rapid identification methods for bacteria. Current culture-based methods can take as long as 5 days to identify the causative bacterial pathogen and its antibiotic sensitivity. To tackle this problem, Abeyrathne et al. have developed a rapid biosensor based on interdigitated electrodes to detect the presence of S. aureus and ascertain its sensitivity to flucloxacillin in just 2 h. The proposed method is label-free and uses nonfaradic measurements. The authors claim this is the first study to successfully employ interdigitated electrodes for the rapid detection of antibiotic resistance, and believe this method has important implications for faster definitive antibiotic treatment and more rapid clinical response to treatment. (Abeyrathne, C. D.; et al., Analyst 2016, 141, 1922–1929) Extracellular vesicles, including exosomes, are nanoscale membrane particles that carry molecular information on parental cells. They are being pursued as promising biomarkers for cancer diagnosis. Jeong et al. present a novel sensor technology for rapid, on-site exosome screening. The sensor is based on an integrated magnetoelectrochemical assay: exosomes are immunomagnetically captured from patient samples and profiled through electrochemical reaction. By combining magnetic enrichment and enzymatic amplification, the approach enables highly sensitive, cell-specific exosome detection and sensor miniaturization and scale-up for high-throughput measurements. The authors demonstrate this concept by implementing a portable, eight-channel device for screening extracellular vesicles in plasma samples from ovarian cancer patients. The sensor achieves simultaneous profiling of multiple protein markers within an hour, outperforming conventional methods in assay sensitivity and speed. (Jeong, S.; et al., ACS Nano 2016, 10, 1802–1809) Gunda et al. report a new chemical composition for rapid detection of Escherichia coli with readily available enzymatic substrates. The authors use a novel hydrogel-based porous matrix to encapsulate the optimized chemical compounds and incorporate it within a readily available plunger–tube assembly. The performance of the new chemical composition is evaluated with different kinds of bacteria and metallic and ionic interferences, and optimized for rapid and specific detection of E. coli. According to the authors, advantages of this new system include its efficiency, rapid speed, and field deployability. The system is applied in field testing of water samples, and rapid detection of E. coli concentrations of 4 × 106 to 4 × 105 CFU mL–1 within 5 min and 4 × 104 to 400 CFU mL–1 within 60 min is achieved. (Gunda, N. S. K.; et al., Analyst 2016, 141, 2920–2929) Priye et al. introduce a drone-based mobile biochemical analysis platform for rapid field deployment of nucleic acid–based diagnostics. This is achieved by combining a consumer-class quadcopter drone with a low-power, single-heater isothermal PCR system. The PCR system can be operated using a standard 5 V USB source via battery, solar, or hand-crank action. Time-resolved fluorescence detection and quantification is achieved using a smartphone camera and integrated image analysis app. Standard sample preparation is enabled by leveraging the drone’s motors as centrifuges via 3D printed snap-on attachments. These techniques make it possible a complete DNA/RNA analysis system that costs less than $50. This system is rugged and versatile, enabling pinpoint deployment of sophisticated diagnostics to distributed field sites. The capability of the system is demonstrated by successfully performing an in-flight replication of S. aureus and λ-phage DNA targets in less than 20 min. The authors believe the ability to perform rapid in-flight assays with smartphone connectivity eliminates delays between sample collection and analysis, which opens new application areas of drones beyond cargo transport and imaging. (Priye, A.; et al. Anal. Chem. 2016, 88, 4651–4660) Wang et al. report on a smartphone spectrometer for colorimetric biosensing applications. The spectrometer is built on an integrated grating substrate coupled with a smartphone’s built-in light-emitting diode flash and camera. The authors show how this simple design allows detection of glucose and, in conjunction with peptide-functionalized gold nanoparticles, the detection of human cardiac troponin I (Wang, Y.; et al., Analyst 2016, 141, 3233–3238) Rico-Yuste et al. introduce disposable color-changing polymeric films for quantifying the freshness of beer, which can be read by a smartphone-based reader. These films target furfural, a beer freshness indicator. The films are prepared by radical polymerization of 4-vinylaniline, which is a furfural-sensitive indicator monomer, 2-hydroxymethyl methacrylate (comonomer), and ethylene dimethyl methacrylate (cross-linker). The sensing mechanism is based on the Stenhouse reaction in which aniline and furfural react in acidic media and generate a deep red cyanine derivative. This derivative absorbs light at 537 nm, which is visible to the naked eye. The colorimetric response can then be monitored and quantified using a smartphone camera. A linear response to furfural in beer is obtained in the 39–500 μg L–1 range and the detection limit is 12 μg L–1, which represent a significant improvement to other well-established colorimetric or chromatographic methods. These novel films are highly selective to furfural, and no cross-reactivity has been observed from other volatile compounds generated during beer aging. A smartphone app was developed to measure the red, green, blue (RGB) color coordinates of the sensing membranes after exposure to the beer. Following data processing, the signals are converted into concentration values by preloaded calibration curves. The authors apply this method to determination of furfural in pale lager beers with different storage times at room temperature. A linear correlation (r > 0.995) between the storage time and the furfural concentration in the samples is achieved. The film sensor results are validated by high-performance liquid chromatography (HPLC). (Rico-Yuste, A.; et al., Anal. Chem. 2016, 88, 3959–3966) The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.