3D Printing, Ink Casting and Micromachined Lamination (3D PICLμM): A Makerspace Approach to the Fabrication of Biological Microdevices

Microneedles: materials, fabrication, and biomedical applications

The microneedles have attracted great interests for a wide range of transdermal biomedical applications, such as biosensing and drug delivery, due to the advantages of being painless, semi-invasive, and sustainable. The ongoing challenges are the materials and fabrication methods of the microneedles in order to obtain a specific shape, configuration and function of the microneedles to achieve a target biomedical application. Here, this review would introduce the types of materials of the microneedles firstly. The hardness, Young's modulus, geometric structure, processability, biocompatibility and degradability of the microneedles are explored as well. Then, the fabrication methods for the solid and hollow microneedles in recent years are reviewed in detail, and the advantages and disadvantages of each process are analyzed and compared. Finally, the biomedical applications of the microneedles are reviewed, including biosensing, drug delivery, body fluid extraction, and nerve stimulation. It is expected that this work provides the fundamental knowledge for developing new microneedle devices, as well as the applications in a variety of biomedical fields.

Microfluidics for diagnosis and treatment of cardiovascular disease

Cardiovascular disease (CVD), a type of circulatory system disease related to the lesions of the cardiovascular system, has become one of the main diseases that endanger human health. Currently, the clinical diagnosis of most CVDs relies on a combination of imaging technology and blood biochemical test. However, the existing technologies for diagnosis of CVDs still have limitations in terms of specificity, detection range, and cost. In order to break through the current bottleneck, microfluidic with the advantages of low cost, simple instruments and easy integration, has been developed to play an important role in the early prevention, diagnosis and treatment of CVDs. Here, we have reviewed the recent various applications of microfluidic in the clinical diagnosis and treatment of CVDs, including microfluidic devices for detecting CVD markers, the cardiovascular models based on microfluidic, and the microfluidic used for CVDs drug screening and delivery. In addition, we have briefly looked forward to the prospects and challenges of microfluidics in diagnosis and treatment of CVDs.

Plotter Cut Stencil Masks for the Deposition of Organic and Inorganic Materials and a New Rapid, Cost Effective Technique for Antimicrobial Evaluations

Plotter cutters in stencil mask prototyping are underutilized but have several advantages over traditional MEMS techniques. In this paper we investigate the use of a conventional plotter cutter as a highly effective benchtop tool for the rapid prototyping of stencil masks in the sub-250 μm range and characterize patterned layers of organic/inorganic materials. Furthermore, we show a new diagnostic monitoring application for use in healthcare, and a potential replacement of the Standard Kirby-Bauer Diffusion Antibiotic Resistance tests was developed and tested on both Escherichia coli and Xanthomonas alfalfae as pathogens with Oxytetracycline, Streptomycin and Kanamycin. We show that the reduction in area required for the minimum inhibitory concentration tests; allow for three times the number of tests to be performed within the same nutrient agar Petri dish, demonstrated both theoretically and experimentally resulting in correlations of R ≈ 0.96 and 0.985, respectively for both pathogens.

High-throughput microbead assay system with a portable, cost-effective Wi-Fi imaging module, and disposable multi-layered microfluidic cartridges for virus and microparticle detection, and tracking

In recent years biomedical scientific community has been working towards the development of high-throughput devices that allow a reliable, rapid and parallel detection of several strains of virus or microparticles simultaneously. One of the complexities of this problem lies on the rapid prototyping of new devices and wireless rapid detection of small particles and virus alike. By reducing the complexity of microfluidics microfabrication and using economic materials along with makerspace tools (Avra Kundu, Ausaf, and Rajaraman 2018) it is possible to provide an affordable solution to both the problems of high-throughput devices and detection technologies. We present the development of a wireless, standalone device and disposable microfluidics chips that rapidly generate parallel readouts for selected, possible virus variants from a nasal or saliva sample, based on motorized and non-motorized microbeads detection, and imaging processing of the motion tracks of these beads in micrometers. Microbeads and SARS-CoV-2 COVID-19 Delta variant were tested as proof-of-concept for testing the microfluidic cartridges and wireless imaging module. The Microbead Assay (MA) system kit consists of a WiFi readout module, a microfluidic chip, and a sample collection/processing sub-system. Here, we focus on the fabrication and characterization of the microfluidic chip to multiplex various micrometer-sized beads for economic, disposable, and simultaneous detection of up to six different viruses, microparticles or variants in a single test, and data collection using a commercially available, WiFi-capable, and camera integrated device (Fig. 1).

A Review of 3D-Printing of Microneedles

Microneedles are micron-sized devices that are used for the transdermal administration of a wide range of active pharmaceutics substances with minimally invasive pain. In the past decade, various additive manufacturing technologies have been used for the fabrication of microneedles; however, they have limitations due to material compatibility and bioavailability and are time-consuming and expensive processes. Additive manufacturing (AM), which is popularly known as 3D-printing, is an innovative technology that builds three-dimensional solid objects (3D). This article provides a comprehensive review of the different 3D-printing technologies that have the potential to revolutionize the manufacturing of microneedles. The application of 3D-printed microneedles in various fields, such as drug delivery, vaccine delivery, cosmetics, therapy, tissue engineering, and diagnostics, are presented. This review also enumerates the challenges that are posed by the 3D-printing technologies, including the manufacturing cost, which limits its viability for large-scale production, the compatibility of the microneedle-based materials with human cells, and concerns around the efficient administration of large dosages of loaded microneedles. Furthermore, the optimization of microneedle design parameters and features for the best printing outcomes is of paramount interest. The Food and Drug Administration (FDA) regulatory guidelines relating to the safe use of microneedle devices are outlined. Finally, this review delineates the implementation of futuristic technologies, such as artificial intelligence algorithms, for 3D-printed microneedles and 4D-printing capabilities.

A PDMS-based microneedle array electrode for long-term ECG recording

To acquire high-quality electrocardiogram (ECG) signals, traditional Ag/AgCl wet electrodes used together with conductive gel can effectively reduce electrode-skin interface impedance (EII) in a short term. However, their weaknesses of poor flexibility and instability can no longer meet the long-term monitoring requirements of intelligent wearable devices. Owing to the flexible dry electrode without conductive gel, it is a good choice to solve the critical problem on drying-out of conductive gel. Therefore, we develop a flexible microneedle array electrode (FMAE) based on polydimethylsiloxane (PDMS) substrate, which obtains reliable bioelectrical signals by way of penetrating into the stratum corneum (SC) of the skin. The fabrication process, including silicon mold, twice PDMS shape-transferring and encapsulation, has advantages of low cost, repeatable production and good biocompatibility. Afterwards, by comparing the performance with different electrodes, impedance test results indicate that the impedance of FMAE are smaller and more stable, and ECG tests in long term and at resting/jogging states also verify that FMAE can obtain durable, stable and reliable signals. In conclusion, FMAE is promising in long-term ECG monitoring.

Additive Manufacturing of a Miniature Functional Trocar for Eye Surgery

Stereolithography is emerging as a promising additive manufacturing technology for a range of applications in the medical domain. However, for miniature, medical devices such as those used in ophthalmic surgery, a number of production challenges arise due to the small size of the components. In this work, we investigate the challenges of creating sub-millimeter features for a miniature, functional trocar using Stereolithography. The trocar cannula system is used in eye surgery to facilitate a passage for other instruments. A standard trocar consists of a hollow cannula and a flexible check valve. The research was performed in two stages: in the first stage we investigated the effect of different materials and print settings on the current design of the cannula and the valve separately, and in the second stage we used these findings to optimize the design and production process. After the first investigation, it became apparent that even though the dimensions of the trocar are within the feature size range of Stereolithography, all hollow features tended to fuse shut during printing. This effect appeared regardless of the materials or print settings, and can be attributed to refraction of the laser source. In order to circumvent this, we identified two potential strategies: (1) increasing the negative space surrounding features; and (2) decreasing the surface area per layer. By applying these strategies, we tested a new design for the cannula and valve and managed to 3D print a functional trocar, which was tested in an artificial eye. The design of the 3D printed trocar allows for further personalization depending on the specific requirements of both patient and surgeon. The proposed strategies can be applied to different applications to create miniature features using Stereolithography.

Polydopamine surface functionalization of 3D printed resin material for enhanced polystyrene adhesion towards insulation layers for 3D microelectrode arrays (3D MEAs)

3D printing involves the use of photopolymerizable resins, which are toxic and typically have incompatible properties with materials such as polystyrene (PS), which present limitations for biomedical applications. We present a method to dramatically improve the poor adhesion between the PS insulative layer on 3D printed Microelectrode Array (MEA) substrates by functionalizing the resin surface with polydopamine (PDA), a mussel-inspired surface chemistry derivative. A commercial 3D printing prepolymer resin, FormLabs Clear (FLC), was printed using a digital light processing (DLP) printer and then surface functionalized with PDA by alkali-induced aqueous immersion deposition and self-polymerization. It was observed that the adhesion of the PS to FLC was improved due to the precision emanating from the DLP method and further improved after the functionalization of DLP printed substrates with PDA at 1, 12, and 24 h time intervals. The adhesion of PS was evaluated through scotch tape peel testing and instron measurements of planar substrates and incubation testing with qualitative analysis of printed culture wells. The composition and topology of the samples were studied to understand how the properties of the surface change after PDA functionalization and how this contributes to the overall improvement in PS adhesion. Furthermore, the surface energies at each PDA deposition time were calculated from contact angle studies as it related to adhesion. Finally, biocompatibility assays of the newly modified surfaces were performed using mouse cardiac cells (HL-1) to demonstrate the biocompatibility of the PDA functionalization process. PDA surface functionalization of 3D DLP printed FLC resin resulted in a dramatic improvement of thin film PS adhesion and proved to be a biocompatible solution for improving additive manufacturing processes to realize biosensors such as in vitro MEAs.

3D printing involves the use of toxic photopolymerizable resins which typically have incompatible properties with polystyrene for biomedical applications. Herein, we use 3D printing tricks and polydopamine to dramatically improve adhesion.

The Role of Soft Robotic Micromachines in the Future of Medical Devices and Personalized Medicine

Developments in medical device design result in advances in wearable technologies, minimally invasive surgical techniques, and patient-specific approaches to medicine. In this review, we analyze the trajectory of biomedical and engineering approaches to soft robotics for healthcare applications. We review current literature across spatial scales and biocompatibility, focusing on engineering done at the biotic-abiotic interface. From traditional techniques for robot design to advances in tunable material chemistry, we look broadly at the field for opportunities to advance healthcare solutions in the future. We present an extracellular matrix-based robotic actuator and propose how biomaterials and proteins may influence the future of medical device design.

Rapid Makerspace Microfabrication and Characterization of 3D Microelectrode Arrays (3D MEAs) for Organ-on-a-Chip Models

Integrated sensors in "on-a-chip" in vitro cellular models are a necessity for granularity in data collection required for advanced biosensors. As these models become more complex, the requirement for the integration of electrogenic cells is apparent. Interrogation of such cells, whether alone or within a connected cellular framework, are best achieved with microelectrodes, in the form of a microelectrode array (MEA). Makerspace microfabrication has thus far enabled novel and accessible approaches to meet these demands. Here, resin-based 3D printing, selective multimodal laser micromachining, and simple insulation strategies, define an approach to highly customizable and "on-demand" in vitro 3D MEA-based biosensor platforms. The scalability of this approach is aided by a novel makerspace microfabrication assisted technique denoted using the term Hypo-Rig. The MEA utilizes custom-defined metal microfabricated microelectrodes transitioned from planar (2D) to 3D using the Hypo-Rig. To simulate this transition process, COMSOL modeling is utilized to estimate transitionary forces and angles (with respect to normal). Practically, the Hypo-Rig demonstrated a force of ~40N, as well as a consistent 70° average angular transitionary performance which matched well with the COMSOL model. To illustrate the scalability potential, 3 × 3, 6 × 6, and 8 × 8 versions of the device were fabricated and characterized. The 3D MEAs, demonstrated impedance and phase measurements in the biologically relevant 1 kHz range of 45.4 kΩ, and -34.6° respectively, for polystyrene insulated, ~70μm sized microelectrodes.

3D printing as a transformative tool for microneedle systems: Recent advances, manufacturing considerations and market potential

The present review aims at identifying the key progress points that have been made on the use of 3D printing to manufacture microneedles in the past 3 years. The advances in the field of photopolymerization and extrusion-based 3D printing are outlined. The study revealed that the printing resolution and the material properties are the two critical parameters that have the most influential effect on the outcome of every microneedle printing endeavour. Finally, the authors attempt to estimate the impact of 3D printing on the transdermal drug delivery market.

Fabrication of hollow microneedles using liquid crystal display (LCD) vat polymerization 3D printing technology for transdermal macromolecular delivery

The present study aimed to fabricate a hollow microneedle device consisting of an array and a reservoir by means of 3D printing technology for transdermal peptide delivery. Hollow microneedles (HMNs) were fabricated using a biocompatible resin material, while PLA filament was used for the reservoirs. The fabricated microdevice was characterized by means of optical microscopy, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), contact angle measurements and leakage inspection studies to ensure the passageway of liquid formulations. Mechanical failure and penetration tests were carried out and supported by Finite Element Analysis (FEA). The cytocompatibility of the microneedle arrays was assessed to human keratinocytes (HaCaT). Finally, the transport of the model peptide octreotide acetate across artificial membranes was assessed in Franz cells using the aforementioned HMN design.

Recent advances in three-dimensional microelectrode array technologies for in vitro and in vivo cardiac and neuronal interfaces

Three-dimensional microelectrode arrays (3D MEAs) have emerged as promising tools to detect electrical activities of tissues or organs in vitro and in vivo, but challenges in achieving fast, accurate, and versatile monitoring have consistently hampered further advances in analyzing cell or tissue behaviors. In this review, we discuss emerging 3D MEA technologies for in vitro recording of cardiac and neural cellular electrophysiology, as well as in vivo applications for heart and brain health diagnosis and therapeutics. We first review various forms of recent 3D MEAs for in vitro studies in context of their geometry, materials, and fabrication processes as well as recent demonstrations of 3D MEAs to monitor electromechanical behaviors of cardiomyocytes and neurons. We then present recent advances in 3D MEAs for in vivo applications to the heart and the brain for monitoring of health conditions and stimulation for therapy. A brief overview of the current challenges and future directions of 3D MEAs are provided to conclude the review.

Fabrication and Characterization of 3D Printed, 3D Microelectrode Arrays for Interfacing with a Peripheral Nerve-on-a-Chip

We present a nontraditional fabrication technique for the realization of three-dimensional (3D) microelectrode arrays (MEAs) capable of interfacing with 3D cellular networks in vitro. The technology uses cost-effective makerspace microfabrication techniques to fabricate the 3D MEAs with 3D printed base structures with the metallization of the microtowers and conductive traces being performed by stencil mask evaporation techniques. A biocompatible lamination layer insulates the traces for realization of 3D microtower MEAs (250 μm base diameter, 400 μm height). The process has additionally been extended to realize smaller electrodes (30 μm × 30 μm) at a height of 400 μm atop the 3D microtower using laser micromachining of an additional silicon dioxide (SiO₂) insulation layer. A 3D microengineered, nerve-on-a-chip in vitro model for recording and stimulating electrical activity of dorsal root ganglion (DRG) cells has further been integrated with the 3D MEA. We have characterized the 3D electrodes for electrical, chemical, electrochemical, biological, and chip hydration stability performance metrics. A decrease in impedance from 1.8 kΩ to 670 Ω for the microtower electrodes and 55 to 39 kΩ for the 30 μm × 30 μm microelectrodes can be observed for an electrophysiologically relevant frequency of 1 kHz upon platinum electroless plating. Biocompatibility assays on the components of the system resulted in a large range (∼3%-70% live cells), depending on the components. Fourier-transform infrared (FTIR) spectra of the resin material start to reveal possible compositional clues for the resin, and the hydration stability is demonstrated in in-vitro-like conditions for 30 days. The fabricated 3D MEAs are rapidly produced with minimal usage of a cleanroom and are fully functional for electrical interrogation of the 3D organ-on-a-chip models for high-throughput of pharmaceutical screening and toxicity testing of compounds in vitro.

3D printing technology as innovative solutions for biomedical applications

3D printing was once predicted to be the third industrial revolution. Today, the use of 3D printing is found across almost all industries. This article discusses the latest 3D printing applications in the biomedical industry.

Biocompatibility of Blank, Post-Processed and Coated 3D Printed Resin Structures with Electrogenic Cells

The widespread adaptation of 3D printing in the microfluidic, bioelectronic, and Bio-MEMS communities has been stifled by the lack of investigation into the biocompatibility of commercially available printer resins. By introducing an in-depth post-printing treatment of these resins, their biocompatibility can be dramatically improved up to that of a standard cell culture vessel (99.99%). Additionally, encapsulating resins that are less biocompatible with materials that are common constituents in biosensors further enhances the biocompatibility of the material. This investigation provides a clear pathway toward developing fully functional and biocompatible 3D printed biosensor devices, especially for interfacing with electrogenic cells, utilizing benchtop-based microfabrication, and post-processing techniques.

SeedEZ™ Interdigitated Electrodes and Multifunctional Layered Biosensor Composites (MLBCs): A Paradigm Shift in the Development of In Vitro BioMicrosystems

We have developed a new technology for the realization of composite biosensor systems, capable of measuring electrical and electrophysiological signals from electrogenic cells, using SeedEZ™ 3D cell culture-scaffold material. This represents a paradigm-shift for BioMEMS processing; 'Biology-Microfabrication' versus the standard 'Microfabrication-Biology' approach. An Interdigitated Electrode (IDE) developed on the 3D cell-scaffold was used to successfully monitor acute cardiomyocyte growth and controlled population decline. We have further characterized processability of the 3D scaffold, demonstrated long-term biocompatibility of the scaffold with various cell lines and developed a multifunctional layered biosensor composites (MLBCs) using SeedEZ™ and other biocompatible substrates for future multilayer sensor integration.

Capabilities and limitations of 3D printed microserpentines and integrated 3D electrodes for stretchable and conformable biosensor applications

We explore the capabilities and limitations of 3D printed microserpentines (µserpentines) and utilize these structures to develop dynamic 3D microelectrodes for potential applications in in vitro, wearable, and implantable microelectrode arrays (MEAs). The device incorporates optimized 3D printed µserpentine designs with out-of-plane microelectrode structures, integrated on to a flexible Kapton® package with micromolded PDMS insulation. The flexibility of the optimized, printed µserpentine design was calculated through effective stiffness and effective strain equations, so as to allow for analysis of various designs for enhanced flexibility. The optimized, down selected µserpentine design was further sputter coated with 7-70 nm-thick gold and the performance of these coatings was studied for maintenance of conductivity during uniaxial strain application. Bending/conforming analysis of the final devices (3D MEAs with a Kapton® package and PDMS insulation) were performed to qualitatively assess the robustness of the finished device toward dynamic MEA applications. 3D microelectrode impedance measurements varied from 4.2 to 5.2 kΩ during the bending process demonstrating a small change and an example application with artificial agarose skin composite model to assess feasibility for basic transdermal electrical recording was further demonstrated.

Makerspace microfabrication of a stainless steel 3D microneedle electrode array (3D MEA) on a glass substrate for simultaneous optical and electrical probing of electrogenic cells

Microfabrication and assembly of 3D MEA based on a glass-stainless steel platform is shown utilizing non-traditional “Makerspace Microfabrication” techniques featuring cost-effective, rapid fabrication and an assorted biocompatible material palette.

A 3D-printed microfluidic-enabled hollow microneedle architecture for transdermal drug delivery

Embedding microfluidic architectures with microneedles enables fluid management capabilities that present new degrees of freedom for transdermal drug delivery. To this end, fabrication schemes that can simultaneously create and integrate complex millimeter/centimeter-long microfluidic structures and micrometer-scale microneedle features are necessary. Accordingly, three-dimensional (3D) printing techniques are suitable candidates because they allow the rapid realization of customizable yet intricate microfluidic and microneedle features. However, previously reported 3D-printing approaches utilized costly instrumentation that lacked the desired versatility to print both features in a single step and the throughput to render components within distinct length-scales. Here, for the first time in literature, we devise a fabrication scheme to create hollow microneedles interfaced with microfluidic structures in a single step. Our method utilizes stereolithography 3D-printing and pushes its boundaries (achieving print resolutions below the full width half maximum laser spot size resolution) to create complex architectures with lower cost and higher print speed and throughput than previously reported methods. To demonstrate a potential application, a microfluidic-enabled microneedle architecture was printed to render hydrodynamic mixing and transdermal drug delivery within a single device. The presented architectures can be adopted in future biomedical devices to facilitate new modes of operations for transdermal drug delivery applications such as combinational therapy for preclinical testing of biologic treatments.

Precision Vascular Delivery of Agrochemicals with Micromilled Microneedles (µMMNs)

We demonstrate use of makerspace techniques involving subtractive microtechnologies to fabricate micromilled microneedles (µMMNs) of stainless steel (SS) for precise delivery of agrochemicals into vascular bundles of plant tissue. Precision delivery is of immense importance for systemic pathogen control in specific areas of plant tissue. Optimization of the micromilling allows for selective removal of SS at the microscale and the microfabrication of a 5 × 5 array of µMMNs having both base width and height of 500 µm to enable precise puncture into the stem of citrus saplings. Atomic Absorption Spectroscopy reveals up to 7.5× increase in the uptake of a therapeutic cargo while Scanning Electron Microscopy reveals that specific sites of the vascular bundle; either xylem or the phloem can be uniquely targeted with customized µMMNs. Such rapid and cost-effective customization with intricate designs along with scalability is enabled by makerspace microfabrication. Additionally, a 19 × 20 array of micromilled mesoneedles has been fabricated and affixed to a paint roller as an applicator system for real-world field testing outside the laboratory. Initial results indicate reliable behavior of the applicator system and the technique can be applied to the systemic delivery of agrochemicals while conserving the loss of the agrochemical with increased application efficiency.

A rapid and low-cost fabrication and integration scheme to render 3D microfluidic architectures for wearable biofluid sampling, manipulation, and sensing

The large-scale deployment of wearable bioanalytical devices for general population longitudinal monitoring necessitates rapid and high throughput manufacturing-amenable fabrication schemes that render disposable, low-cost, and mechanically flexible microfluidic modules capable of performing a variety of bioanalytical operations within a compact footprint. The spatial constraints of previously reported wearable bioanalytical devices (with microfluidic operations confined to 2D), their lack of biofluid manipulation capability, and the complex and low-throughput nature of their fabrication process inherently limit the diversity and frequency of end-point assessments and prevent their deployment at large scale. Here, we devise a simple, scalable, and low-cost "CAD-to-3D Device" fabrication and integration scheme, which renders 3D and complex microfluidic architectures capable of performing biofluid sampling, manipulation, and sensing. The devised scheme is based on laser-cutting of tape-based substrates, which can be programmed at the software-level to rapidly define microfluidic features such as a biofluid collection interface, microchannels, and VIAs (vertical interconnect access), followed by the vertical assembly of pre-patterned layers to realize the final device. To inform the utility of our fabrication scheme, we demonstrated three representative devices to perform sweat collection (with visualizable secretion profile), sample filtration, and simultaneous biofluid actuation and sensing (using a sandwiched-interface). Our devised scheme can be adapted for the fabrication and manufacturing of current and future wearable bioanalytical devices, which in turn will catalyze the large-scale production and deployment of such devices for general population health monitoring.

Optimization of makerspace microfabrication techniques and materials for the realization of planar, 3D printed microelectrode arrays in under four days

Conventional two-dimensional microelectrode arrays (2D MEAs) in the market involve long manufacturing timeframes, have cleanroom requirements, and need to be assembled from multiple parts to obtain the final packaged device. For MEAs to be “used and tossed”, manufacturing has to be moved from the cleanroom to makerspaces. In order to enable makerspace fabricated MEAs comparable to conventional MEAs, the microfabrication processes must be optimized to have similar electrical properties along with biocompatibility and number of recording sites. This work presents a makerspace microfabricated 2D MEA having electrode densities up to a commercially popular 8 × 8 array, all fabricated under four days. Additive manufacturing-based realization of the MEA devices provides immense flexibility in terms of meeting distinct design requirements. A unique non-planar MEA having meso-scale electrodes on the top side of a chip transitioning to traces onto the bottom side through electrical vias is presented in this work. This allows for (a) monolithic integration of a culture well for devices having up to a 6 × 6 MEA array, (b) selective electroplating of the meso-scale electrodes (500 μm diameter) defined by silver ink casting followed by pulsed electroplating of gold or platinum without any masking procedure, (c) casting of a uniform and planar insulation layer via a novel process of confined precision spin coating (CPSC) of SU-8 which acts as a biocompatible insulation atop the meso-scale electrodes; and (d) selective laser micromachining to define the 50 μm × 50 μm microelectrodes. For an 8 × 8 array, the culture well and MEA chip framework are 3D printed as two separate parts and sealed together with a biocompatible epoxy as in commercially available MEAs. The fabricated MEAs have an average 1 kHz impedance of 36.8 kΩ/16 kΩ with a double layer capacitance of 400 nF cm⁻²/520 nF cm⁻² for nano-porous platinum/nano-gold which is comparable to the state-of-art commercially available 2D MEAs. Additionally, it was found out that our 3D printing-based process compares very favorably with traditional glass MEAs in terms of design to device while representing a dramatic reduction in cost, timeline for fabrication, reduction in the number of steps and the need for sophisticated microfabrication and packaging equipment.

“Makerspace microfabrication” with the use of simple tools and materials is used to demonstrate the realization of 2D microelectrode arrays (MEAs) having a density of up to 8 × 8 MEAs in under four days which are comparable to conventional MEAs.

Advanced electronic skin devices for healthcare applications

Electronic skin, a kind of flexible electronic device and system inspired by human skin, has emerged as a promising candidate for wearable personal healthcare applications. Wearable electronic devices with skin-like properties will provide platforms for continuous and real-time monitoring of human physiological signals such as tissue pressure, body motion, temperature, metabolites, electrolyte balance, and disease-related biomarkers. Transdermal drug delivery devices can also be integrated into electronic skin to enhance its non-invasive, real-time dynamic therapy functions. This review summarizes the recent progress in electronic skin devices for applications in human health monitoring and therapy systems as well as several potential mass production technologies such as inkjet printing and 3D printing. The opportunities and challenges in broadening the applications of electronic skin devices in practical healthcare are also discussed.

Three-Dimensional (3D) Printed Microneedles for Microencapsulated Cell Extrusion

Cell-hydrogel based therapies offer great promise for wound healing. The specific aim of this study was to assess the viability of human hepatocellular carcinoma (HepG2) cells immobilized in atomized alginate capsules (3.5% (w/v) alginate, d = 225 µm ± 24.5 µm) post-extrusion through a three-dimensional (3D) printed methacrylate-based custom hollow microneedle assembly (circular array of 13 conical frusta) fabricated using stereolithography. With a jetting reliability of 80%, the solvent-sterilized device with a root mean square roughness of 158 nm at the extrusion nozzle tip (d = 325 μm) was operated at a flowrate of 12 mL/min. There was no significant difference between the viability of the sheared and control samples for extrusion times of 2 h (p = 0.14, α = 0.05) and 24 h (p = 0.5, α = 0.05) post-atomization. Factoring the increase in extrusion yield from 21.2% to 56.4% attributed to hydrogel bioerosion quantifiable by a loss in resilience from 5470 (J/m³) to 3250 (J/m³), there was no significant difference in percentage relative payload (p = 0.2628, α = 0.05) when extrusion occurred 24 h (12.2 ± 4.9%) when compared to 2 h (9.9 ± 2.8%) post-atomization. Results from this paper highlight the feasibility of encapsulated cell extrusion, specifically protection from shear, through a hollow microneedle assembly reported for the first time in literature.