Microfabrication of engineered Lactococcus lactis biocarriers with genetically programmed immunorecognition probes for sensitive lateral flow immunoassay of antibiotic in milk and lake water

Micro/nanomaterials display considerable potential for increasing the sensitivity of lateral flow immunoassay (LFIA) by acting as 3D carriers for both antibodies and signals. The key to achieving high detection sensitivity depends on the probe's orientation on the material surface and its multivalent biomolecular interactions with targets. Here, we engineer Lactococcus lactis as the bacterial microcarrier (BMC) for a multivalent immunorecognition probe that was genetically programmed to display multifunctional components including a phage-screened single-chain variable fragment (scFv), an enhanced green fluorescent protein (eGFP), and a C-terminal peptidoglycan-binding domain (AcmA) anchored on BMC through the cell wall peptidoglycan. The innovative design of this biocarrier system, which incorporates a lab-on-a-chip microfluidic device, allows for the rapid and non-destructive self-assembly of the multivalent scFv-eGFP-AcmA@BMC probe, in which the 3D structure of BMC with a large peptidoglycan surface area facilitates the precisely orientated attachment and immobilization of scFv-eGFP-AcmA. This leads to a remarkable fluorescence aggregation amplification effect in LFIA, outperforming a monovalent 2D scFv-eGFP-AcmA probe for florfenicol detection. By designing a portable sensing device, we achieved an exceptionally low detection limit of 0.28 pg/mL and 0.21 pg/mL for florfenicol in lake water and milk sample, respectively. The successful microfabrication of this biocarrier holds potential to inspire innovative biohybrid designs for environment and food safety biosensing applications.

A review of the recent achievements and future trends on 3D printed microfluidic devices for bioanalytical applications

3D printing has revolutionized the manufacturing process of microanalytical devices by enabling the automated production of customized objects. This technology promises to become a fundamental tool, accelerating investigations in critical areas of health, food, and environmental sciences. This microfabrication technology can be easily disseminated among users to produce further and provide analytical data to an interconnected network towards the Internet of Things, as 3D printers enable automated, reproducible, low-cost, and easy fabrication of microanalytical devices in a single step. New functional materials are being investigated for one-step fabrication of highly complex 3D printed parts using photocurable resins. However, they are not yet widely used to fabricate microfluidic devices. This is likely the critical step towards easy and automated fabrication of sophisticated, complex, and functional 3D-printed microchips. Accordingly, this review covers recent advances in the development of 3D-printed microfluidic devices for point-of-care (POC) or bioanalytical applications such as nucleic acid amplification assays, immunoassays, cell and biomarker analysis and organs-on-a-chip. Finally, we discuss the future implications of this technology and highlight the challenges in researching and developing appropriate materials and manufacturing techniques to enable the production of 3D-printed microfluidic analytical devices in a single step.

Microfabrication-based engineering of biomimetic dentin-like constructs to simulate dental aging

Human dentin is a highly organized dental tissue displaying a complex microarchitecture consisting of micrometer-sized tubules encased in a mineralized type-I collagen matrix. As such, it serves as an important substrate for the adhesion of microbial colonizers and oral biofilm formation in the context of dental caries disease, including root caries in the elderly. Despite this issue, there remains a current lack of effective biomimetic in vitro dentin models that facilitate the study of oral microbial adhesion by considering the surface architecture at the micro- and nanoscales. Therefore, the aim of this study was to develop a novel in vitro microfabricated biomimetic dentin surface that simulates the complex surface microarchitecture of exposed dentin. For this, a combination of soft lithography microfabrication and biomaterial science approaches were employed to construct a micropitted PDMS substrate functionalized with mineralized type-I collagen. These dentin analogs were subsequently glycated with methylglyoxal (MGO) to simulate dentin matrix aging in vitro and analyzed utilizing an interdisciplinary array of techniques including atomic force microscopy (AFM), elemental analysis, and electron microscopy. AFM force-mapping demonstrated that the nanomechanical properties of the biomimetic constructs were within the expected biological parameters, and that mineralization was mostly predominated by hydroxyapatite deposition. Finally, dual-species biofilms of Streptococcus mutans and Candida albicans were grown and characterized on the biofunctionalized PDMS microchips, demonstrating biofilm-specific morphologic characteristics and confirming the suitability of this model for the study of early biofilm formation under controlled conditions. Overall, we expect that this novel biomimetic dentin model could serve as an in vitro platform to study oral biofilm formation or dentin-biomaterial bonding in the laboratory without the need for animal or human tooth samples in the future.

Highly Localized Chemical Sampling at Subsecond Temporal Resolution Enabled with a Silicon Nanodialysis Platform at Nanoliter per Minute Flows

Microdialysis (MD) is a versatile and powerful technique for chemical profiling of biological tissues and is widely used for quantification of neurotransmitters, neuropeptides, metabolites, biomarkers, and drugs in the central nervous system as well as in dermatology, ophthalmology, and pain research. However, MD performance is severely limited by fundamental tradeoffs between chemical sensitivity, spatial resolution, and temporal response. Here, by using wafer-scale silicon microfabrication, we develop and demonstrate a nanodialysis (ND) sampling probe that enables highly localized chemical sampling with 100 μm spatial resolution and subsecond temporal resolution at high recovery rates. These performance metrics, which are 100-1000× superior to existing MD approaches, are enabled by a 100× reduction of the microfluidic channel cross-section, a corresponding drastic 100× reduction of flow rates to exceedingly slow few nL/min flows, and integration of a nanometer-thin nanoporous membrane with high transport flux into the probe sampling area. Miniaturized ND probes may allow for the minimally invasive and highly localized sampling and chemical profiling in live biological tissues with high spatiotemporal resolution for clinical, biomedical, and pharmaceutical applications.

Low-cost, versatile, and highly reproducible microfabrication pipeline to generate 3D-printed customised cell culture devices with complex designs

Cell culture devices, such as microwells and microfluidic chips, are designed to increase the complexity of cell-based models while retaining control over culture conditions and have become indispensable platforms for biological systems modelling. From microtopography, microwells, plating devices, and microfluidic systems to larger constructs such as live imaging chamber slides, a wide variety of culture devices with different geometries have become indispensable in biology laboratories. However, while their application in biological projects is increasing exponentially, due to a combination of the techniques, equipment and tools required for their manufacture, and the expertise necessary, biological and biomedical labs tend more often to rely on already made devices. Indeed, commercially developed devices are available for a variety of applications but are often costly and, importantly, lack the potential for customisation by each individual lab. The last point is quite crucial, as often experiments in wet labs are adapted to whichever design is already available rather than designing and fabricating custom systems that perfectly fit the biological question. This combination of factors still restricts widespread application of microfabricated custom devices in most biological wet labs. Capitalising on recent advances in bioengineering and microfabrication aimed at solving these issues, and taking advantage of low-cost, high-resolution desktop resin 3D printers combined with PDMS soft lithography, we have developed an optimised a low-cost and highly reproducible microfabrication pipeline. This is thought specifically for biomedical and biological wet labs with not prior experience in the field, which will enable them to generate a wide variety of customisable devices for cell culture and tissue engineering in an easy, fast reproducible way for a fraction of the cost of conventional microfabrication or commercial alternatives. This protocol is designed specifically to be a resource for biological labs with limited expertise in those techniques and enables the manufacture of complex devices across the μm to cm scale. We provide a ready-to-go pipeline for the efficient treatment of resin-based 3D-printed constructs for PDMS curing, using a combination of polymerisation steps, washes, and surface treatments. Together with the extensive characterisation of the fabrication pipeline, we show the utilisation of this system to a variety of applications and use cases relevant to biological experiments, ranging from micro topographies for cell alignments to complex multipart hydrogel culturing systems. This methodology can be easily adopted by any wet lab, irrespective of prior expertise or resource availability and will enable the wide adoption of tailored microfabricated devices across many fields of biology.

Microfabrication of Gelatin Methacrylate/Hydroxyapatite Composites by Utilizing Alternate Soaking Process

To construct a complex three-dimensional (3D) structure mimicking bone microstructure, hydrogel models of polymerized gelatin methacrylate (pGelMA) were fabricated by using stereolithography and modified with hydroxyapatite (HAp) via an alternate soaking process (ASP) using a solution of calcium and phosphate ions. Fabricated pGelMA line models whose widths were designed as 100, 300, and 600 μm were modified with HAp by ASP by changing the immersion time and number of cycles. After ASP, all of the line models with widths of 100, 300, and 600 μm were successfully modified with HAp, and large amounts of HAp were covered with the fabricated models by increasing both the immersion time and the number of cycles in ASP. HAp was observed near the surface of the line model with a width of 600 μm after ASP at an immersion time of 10 s, while the entire model was modified with HAp using ASPs for longer immersion times. The adhesion and spread of mesenchymal stem cells (MSCs) on the pGelMA-HAp discs depended on the ASP conditions. Moreover, the HAp modification of 3D pyramid models without alteration of the microstructure was also conducted. This two-step fabrication method of first fabricating frameworks of hydrogel models by stereolithography and subsequently modifying the fabricated models with HAp will lead to the development of 3D cell culture systems to support bone grafts or to create biological niches, such as artificial bone marrow.

Breaking Barriers: Exploring Neurotransmitters through In Vivo vs. In Vitro Rivalry

Neurotransmitter analysis plays a pivotal role in diagnosing and managing neurodegenerative diseases, often characterized by disturbances in neurotransmitter systems. However, prevailing methods for quantifying neurotransmitters involve invasive procedures or require bulky imaging equipment, therefore restricting accessibility and posing potential risks to patients. The innovation of compact, in vivo instruments for neurotransmission analysis holds the potential to reshape disease management. This innovation can facilitate non-invasive and uninterrupted monitoring of neurotransmitter levels and their activity. Recent strides in microfabrication have led to the emergence of diminutive instruments that also find applicability in in vitro investigations. By harnessing the synergistic potential of microfluidics, micro-optics, and microelectronics, this nascent realm of research holds substantial promise. This review offers an overarching view of the current neurotransmitter sensing techniques, the advances towards in vitro microsensors tailored for monitoring neurotransmission, and the state-of-the-art fabrication techniques that can be used to fabricate those microsensors.

Recent advancements in Mg-based micromotors for biomedical and environmental applications

Synthetic micro/nanomotors have attracted considerable attention due to their promising potential in the field of biomedicine. Despite their great potential, major micromotors require chemical fuels or complex devices to generate external physical fields for propulsion. Therefore, for future practical medical and environmental applications, Mg-based micromotors that exhibit water-powered movement and thus eliminate the need for toxic fuels, and that display optimal biocompatibility and biodegradability, are attracting attention. In this review, we summarized the recent microarchitectural design of Mg-based micromotors for biomedical applications. We also highlight the mechanism for realizing their water-powered motility. Furthermore, recent biomedical and environmental applications of Mg-based micromotors are introduced. We envision that advanced Mg-based micromotors will have a profound impact in biomedicine.

Using Microtechnology and the Fourier Transform for the Analysis of Effective Activity Time in Professional Soccer

ABSTRACT

Oliva-Lozano, JM, Chmura, P, Granero-Gil, P, and Muyor, JM. Using microtechnology and the Fourier Transform for the analysis of effective activity time in professional soccer. J Strength Cond Res 37(12): 2491-2495, 2023-This study aimed to investigate the use of the fast Fourier transform (FFT) for the analysis of effective activity time in professional soccer by (a) exploring the relationship between this variable and standard external load parameters and (b) analyzing the effective activity time during official professional soccer matches. Twenty-six male players participated in the study. Each player was categorized as midfielder, central defender, full-back, wide-midfielder, or forward. Tracking systems based on inertial sensors (4 3D accelerometers, 3 3D gyroscopes, and 1 magnetometer), and global positioning systems technology were used to collect external load measures for 35 matches. Each match was analyzed considering 15-minute periods to explore the evolution of effective activity time during the matches. The extra time from each match was also included. Fast Fourier transform duration may be a representative variable of effective activity time, given the strong positive correlation with the external load variables ( p < 0.001). The linear regression analysis showed that the variables that significantly contributed to the model ( R2 = 0.97) were the total of steps and the distance covered. The mean effective activity time in soccer match play was ∼48.69 minutes. This time significantly changed depending on factors such as the period of the match ( F = 239.05; p < 0.001; ηp 2 = 0.60) or playing position ( F = 16.99; p < 0.001; ηp 2 = 0.06). The greatest effective activity time was observed for all playing positions in the 0'-15' period. However, the 60'-75' period showed the lowest effective activity times compared with the rest of the 15-minute periods for all positions except for forwards (75'-90'). From a practical standpoint, sports performance practitioners may consider these results to improve the individualization of training and match demands. Also, a more accurate indicator of exercise intensity may be obtained (e.g., multiplying the rating of perceived exertion by the effective activity time).

Transforming medical device biofilm control with surface treatment using microfabrication techniques

Biofilm deposition on indwelling medical devices and implanted biomaterials is frequently attributed to the prevalence of resistant infections in humans. Further, the nature of persistent infections is widely believed to have a biofilm etiology. In this study, the wettability of commercially available indwelling medical devices was explored for the first time, and its effect on the formation of biofilm was determined in vitro. Surprisingly, all tested indwelling devices were found to be hydrophilic, with surface water contact angles ranging from 60° to 75°. First, we established a thriving Candida albicans biofilm growth at 24 hours. in YEPD at 30°C and 37°C plus serum in vitro at Cyclic olefin copolymer (COC) modified surface, which was subsequently confirmed via scanning electron microscopy, while their cellular metabolic function was assessed using the XTT cell viability assay. Surfaces with patterned wettability show that a contact angle of 110° (hydrophobic) inhibits C. albicans planktonic and biofilm formation completely compared to robust growth at a contact angle of 40° (hydrophilic). This finding may provide a novel antimicrobial strategy to prevent biofilm growth and antimicrobial resistance on indwelling devices and prosthetic implants. Overall, this study provides valuable insights into the surface characteristics of medical devices and their potential impact on biofilm formation, leading to the development of improved approaches to control and prevent microbial biofilms and re-infections.

Microfabrication and lab-on-a-chip devices promotein vitromodeling of neural interfaces for neuroscience researches and preclinical applications

Neural tissues react to injuries through the orchestration of cellular reprogramming, generating specialized cells and activating gene expression that helps with tissue remodeling and homeostasis. Simplified biomimetic models are encouraged to amplify the physiological and morphological changes during neural regeneration at cellular and molecular levels. Recent years have witnessed growing interest in lab-on-a-chip technologies for the fabrication of neural interfaces. Neural system-on-a-chip devices are promisingin vitromicrophysiological platforms that replicate the key structural and functional characteristics of neural tissues. Microfluidics and microelectrode arrays are two fundamental techniques that are leveraged to address the need for microfabricated neural devices. In this review, we explore the innovative fabrication, mechano-physiological parameters, spatiotemporal control of neural cell cultures and chip-based neurogenesis. Although the high variability in different constructs, and the restriction in experimental and analytical access limit the real-life applications of microphysiological models, neural system-on-a-chip devices have gained considerable translatability for modeling neuropathies, drug screening and personalized therapy.

Silicon microfabrication technologies for biology integrated advance devices and interfaces

Miniaturization is the trend to manufacture ever smaller devices and this process requires knowledge, experience, understanding of materials, manufacturing techniques and scaling laws. The fabrication techniques used in semiconductor industry deliver an exceptionally high yield of devices and provide a well-established platform. Today, these miniaturized devices are manufactured with high reproducibility, design flexibility, scalability and multiplexed features to be used in several applications including micro-, nano-fluidics, implantable chips, diagnostics/biosensors and neural probes. We here provide a review on the microfabricated devices used for biology driven science. We will describe the ubiquity of the use of micro-nanofabrication techniques in biology and biotechnology through the fabrication of high-aspect-ratio devices for cell sensing applications, intracellular devices, probes developed for neuroscience-neurotechnology and biosensing of the certain biomarkers. Recently, the research on micro and nanodevices for biology has been progressing rapidly. While the understanding of the unknown biological fields -such as human brain- has been requiring more research with advanced materials and devices, the development protocols of desired devices has been advancing in parallel, which finally meets with some of the requirements of biological sciences. This is a very exciting field and we aim to highlight the impact of micro-nanotechnologies that can shed light on complex biological questions and needs.

The speed and acceleration of the ball carrier and tackler into contact during front-on tackles in rugby league

The aim was to use a combination of video analysis and microtechnology (10 Hz global positioning system [GPS]) to quantify and compare the speed and acceleration of ball-carriers and tacklers during the pre-contact phase (contact - 0.5s) of the tackle event during rugby league match-play. Data were collected from 44 professional male rugby league players from two Super League clubs across two competitive matches. Tackle events were coded and subject to three stages of inclusion criteria to identify front-on tackles. 10 Hz GPS data was synchronised with video to extract the speed and acceleration of the ball-carrier and tackler into each front-on tackle (n = 214). Linear mixed effects models (effect size [ES], confidence intervals, p-values) compared differences. Overall, ball-carriers (4.73 ± 1.12 m∙s-1) had greater speed into front-on tackles than tacklers (2.82 ± 1.07 m∙s-1; ES = 1.69). Ball-carriers accelerated (0.67 ± 1.01 m∙s-2) into contact whilst tacklers decelerated (-1.26 ± 1.36 m∙s-2; ES = 1.74). Positional comparisons showed speed was greater during back vs. back (ES = 0.66) and back vs. forward (ES = 0.40) than forward vs. forward tackle events. Findings can be used to inform strategies to improve performance and player welfare.

Flexible Organic Electronic Ion Pump Fabricated Using Inkjet Printing and Microfabrication for Precision In Vitro Delivery of Bupivacaine

The organic electronic ion pump (OEIP) is an on-demand electrophoretic drug delivery device, that via electronic to ionic signal conversion enables drug delivery without additional pressure or volume changes. The fundamental component of OEIPs is their polyelectrolyte membranes which are shaped into ionic channels that conduct and deliver ionic drugs, with high spatiotemporal resolution. The patterning of these membranes is essential in OEIP devices and is typically achieved using laborious microprocessing techniques. Here, the development of an inkjet printable formulation of polyelectrolyte is reported, based on a custom anionically functionalized hyperbranched polyglycerol (i-AHPG). This polyelectrolyte ink greatly simplifies the fabrication process and is used in the production of free-standing OEIPs on flexible polyimide (PI) substrates. Both i-AHPG and the OEIP devices are characterized, exhibiting favorable iontronic characteristics of charge selectivity and the ability to transport aromatic compounds. Further, the applicability of these technologies is demonstrated by the transport and delivery of the pharmaceutical compound bupivacaine to dorsal root ganglion cells with high spatial precision and effective nerve blocking, highlighting the applicability of these technologies for biomedical scenarios.

Vat photopolymerization 3D printed microfluidic devices for organ-on-a-chip applications

Organs-on-a-chip, or OoCs, are microfluidic tissue culture devices with micro-scaled architectures that repeatedly achieve biomimicry of biological phenomena. They are well positioned to become the primary pre-clinical testing modality as they possess high translational value. Current methods of fabrication have facilitated the development of many custom OoCs that have generated promising results. However, the reliance on microfabrication and soft lithographic fabrication techniques has limited their prototyping turnover rate and scalability. Additive manufacturing, known commonly as 3D printing, shows promise to expedite this prototyping process, while also making fabrication easier and more reproducible. We briefly introduce common 3D printing modalities before identifying two sub-types of vat photopolymerization - stereolithography (SLA) and digital light processing (DLP) - as the most advantageous fabrication methods for the future of OoC development. We then outline the motivations for shifting to 3D printing, the requirements for 3D printed OoCs to be competitive with the current state of the art, and several considerations for achieving successful 3D printed OoC devices touching on design and fabrication techniques, including a survey of commercial and custom 3D printers and resins. In all, we aim to form a guide for the end-user to facilitate the in-house generation of 3D printed OoCs, along with the future translation of these important devices.

Bubble-Based Microrobots with Rapid Circular Motions for Epithelial Pinning and Drug Delivery

Remotely powered microrobots are proposed as next-generation vehicles for drug delivery. However, most microrobots swim with linear trajectories and lack the capacity to robustly adhere to soft tissues. This limits their ability to navigate complex biological environments and sustainably release drugs at target sites. In this work, bubble-based microrobots with complex geometries are shown to efficiently swim with non-linear trajectories in a mouse bladder, robustly pin to the epithelium, and slowly release therapeutic drugs. The asymmetric fins on the exterior bodies of the microrobots induce a rapid rotational component to their swimming motions of up to ≈150 body lengths per second. Due to their fast speeds and sharp fins, the microrobots can mechanically pin themselves to the bladder epithelium and endure shear stresses commensurate with urination. Dexamethasone, a small molecule drug used for inflammatory diseases, is encapsulated within the polymeric bodies of the microrobots. The sustained release of the drug is shown to temper inflammation in a manner that surpasses the performance of free drug controls. This system provides a potential strategy to use microrobots to efficiently navigate large volumes, pin at soft tissue boundaries, and release drugs over several days for a range of diseases.

Multicellular dynamics on structured surfaces: Stress concentration is a key to controlling complex microtissue morphology on engineered scaffolds

Tissue engineers have utilised a variety of three-dimensional (3D) scaffolds for controlling multicellular dynamics and the resulting tissue microstructures. In particular, cutting-edge microfabrication technologies, such as 3D bioprinting, provide increasingly complex structures. However, unpredictable microtissue detachment from scaffolds, which ruins desired tissue structures, is becoming an evident problem. To overcome this issue, we elucidated the mechanism underlying collective cellular detachment by combining a new computational simulation method with quantitative tissue-culture experiments. We first quantified the stochastic processes of cellular detachment shown by vascular smooth muscle cells on model curved scaffolds and found that microtissue morphologies vary drastically depending on cell contractility, substrate curvature, and cell-substrate adhesion strength. To explore this mechanism, we developed a new particle-based model that explicitly describes stochastic processes of multicellular dynamics, such as adhesion, rupture, and large deformation of microtissues on structured surfaces. Computational simulations using the developed model successfully reproduced characteristic detachment processes observed in experiments. Crucially, simulations revealed that cellular contractility-induced stress is locally concentrated at the cell-substrate interface, subsequently inducing a catastrophic process of collective cellular detachment, which can be suppressed by modulating cell contractility, substrate curvature, and cell-substrate adhesion. These results show that the developed computational method is useful for predicting engineered tissue dynamics as a platform for prediction-guided scaffold design. STATEMENT OF SIGNIFICANCE: Microfabrication technologies aiming to control multicellular dynamics by engineering 3D scaffolds are attracting increasing attention for modelling in cell biology and regenerative medicine. However, obtaining microtissues with the desired 3D structures is made considerably more difficult by microtissue detachments from scaffolds. This study reveals a key mechanism behind this detachment by developing a novel computational method for simulating multicellular dynamics on designed scaffolds. This method enabled us to predict microtissue dynamics on structured surfaces, based on cell mechanics, substrate geometry, and cell-substrate interaction. This study provides a platform for the physics-based design of micro-engineered scaffolds and thus contributes to prediction-guided biomaterials design in the future.

Photolithographic microfabrication of hydrogel clefts for cell invasion studies

Invasion of migrating cells into surrounding tissue plays a key role in cancer metastasis and immune response. In order to assess invasiveness, most in vitro invasion assays measure the degree to which cells migrate between microchambers that provide a chemoattractant gradient across a polymeric membrane with defined pores. However, in real tissue cells experience soft, mechanically deformable microenvironments. Here we introduce RGD-functionalized hydrogel structures that present pressurized clefts for invasive migration of cells between reservoirs maintaining a chemotactic gradient. Using UV-photolithography, equally spaced blocks of polyethylene glycol-norbornene (PEG-NB) hydrogels are formed, which subsequently swell and close the interjacent gaps. The swelling ratio and final contours of the hydrogel blocks were determined using confocal microscopy confirming a swelling induced closure of the structures. The velocity profile of cancer cells transmigrating through the clefts, which we name 'sponge clamp', is found to depend on the elastic modulus as well as the gap size between the swollen blocks. The 'sponge clamp' discriminates the invasiveness of two distinct cell lines, MDA-MB-231 and HT-1080. The approach provides soft 3D-microstructures mimicking invasion conditions in extracellular matrix.

Multiscale Biofabrication: Integrating Additive Manufacturing with DNA-Programmable Self-Assembly

Structure and hierarchical organization are crucial elements of biological systems and are likely required when engineering synthetic biomaterials with life-like behavior. In this context, additive manufacturing techniques like bioprinting have become increasingly popular. However, 3D bioprinting, as well as other additive manufacturing techniques, show limited resolution, making it difficult to yield structures on the sub-cellular level. To be able to form macroscopic synthetic biological objects with structuring on this level, manufacturing techniques have to be used in conjunction with biomolecular nanotechnology. Here, a short overview of both topics and a survey of recent advances to combine additive manufacturing with microfabrication techniques and bottom-up self-assembly involving DNA, are given.

Organs-on-a-chip: a union of tissue engineering and microfabrication

We review the emergence of the new field of organ-on-a-chip (OOAC) engineering, from the parent fields of tissue engineering and microfluidics. We place into perspective the tools and capabilities brought into the OOAC field by early tissue engineers and microfluidics experts. Liver-on-a-chip and heart-on-a-chip are used as two case studies of systems that heavily relied on tissue engineering techniques and that were amongst the first OOAC models to be implemented, motivated by the need to better assess toxicity to human tissues in preclinical drug development. We review current challenges in OOAC that often stem from the same challenges in the parent fields, such as stable vascularization and drug absorption.

Microfluidic Organ-on-A-chip: A Guide to Biomaterial Choice and Fabrication

Organ-on-A-chip (OoAC) devices are miniaturized, functional, in vitro constructs that aim to recapitulate the in vivo physiology of an organ using different cell types and extracellular matrix, while maintaining the chemical and mechanical properties of the surrounding microenvironments. From an end-point perspective, the success of a microfluidic OoAC relies mainly on the type of biomaterial and the fabrication strategy employed. Certain biomaterials, such as PDMS (polydimethylsiloxane), are preferred over others due to their ease of fabrication and proven success in modelling complex organ systems. However, the inherent nature of human microtissues to respond differently to surrounding stimulations has led to the combination of biomaterials ranging from simple PDMS chips to 3D-printed polymers coated with natural and synthetic materials, including hydrogels. In addition, recent advances in 3D printing and bioprinting techniques have led to the powerful combination of utilizing these materials to develop microfluidic OoAC devices. In this narrative review, we evaluate the different materials used to fabricate microfluidic OoAC devices while outlining their pros and cons in different organ systems. A note on combining the advances made in additive manufacturing (AM) techniques for the microfabrication of these complex systems is also discussed.

Laser Micromachining of Bone as a Tool for Studying Bone Marrow Biology

The bone marrow (BM) has traditionally been a difficult tissue to access because it is embedded deep within the bone matrix. It is home to the hematopoietic stem cells (HSCs) that give rise to all blood cells in the body. It is also the site of origin for malignant blood cells such as leukemia and multiple myeloma, as well as a frequent site of metastasis for many solid tumors including prostate and breast cancer. The following chapter describes how laser micromachining of bone can be used to improve both optical and physical access to the BM. For example, laser thinning of the overlying bone can improve optical access, enabling deeper imaging into the BM as well as enhancing optical resolution by reducing scattering and aberration. Laser micromachining can also be used to provide physical access into the BM by creating access ports for micropipette insertion and delivery of cells to precise locations in the BM, as well as for the extraction of BM cells and interstitial fluid, all under image guidance. This chapter provides a detailed protocol for installing a laser-micromachining capability for users with an existing multiphoton microscope. Additionally, we briefly outline how such a system improves the optical resolution during imaging as well as its potential use to study injury response.

3D microfabrication by applying the laser-induced bubble method to the thermoset polymer PDMS using a conventional nanosecond laser

We recently developed a microfabrication technique [microfabrication using laser-induced bubble (microFLIB)] and applied it to polydimethylsiloxane (PDMS), a thermoset polymer. The technique enabled the rapid fabrication of a microchannel on a PDMS substrate and selective metallization of the channel via subsequent plating; however, the technique was limited to surface microfabrication. Therefore, we explored the feasibility of three-dimensional (3D) microFLIB of PDMS using a nanosecond laser. In the experiment, a laser beam was focused inside pre-curing liquid PDMS and was scanned both perpendicular and parallel to the laser-beam axis to generate a 3D line of laser-induced bubbles. In the microFLIB processing, the shape of the created bubbles was retained in the pre-curing PDMS for more than 24 h; thus, the line of bubbles generated by the perpendicular laser scanning successfully produced a 3D hollow transverse microchannel inside the PDMS substrate after subsequent thermal curing. In addition, a through-hole with an aspect ratio greater than ∼200 was easily fabricated in the PDMS substrate by parallel laser scanning. The fabrication of a 3D microfluidic device comprising two open reservoirs in a PDMS substrate was also demonstrated for biochip applications.

Digital manufacturing for accelerating organ-on-a-chip dissemination and electrochemical biosensing integration

Organ on-a-chip (OoC) is a promising technology that aims to recapitulate human body pathophysiology in a more precise way to advance in drug development and complex disease understanding. However, the presence of OoC in biological laboratories is still limited and mainly restricted to laboratories with access to cleanroom facilities. Besides, the current analytical methods employed to extract information from the organ models are endpoint and post facto assays which makes it difficult to ensure that during the biological experiment the cell microenvironment, cellular functionality and behaviour are controlled. Hence, the integration of real-time biosensors is highly needed and requested by the OoC end-user community to provide insight into organ function and responses to stimuli. In this context, electrochemical sensors stand out due to their advantageous features like miniaturization capabilities, ease of use, automatization and high sensitivity and selectivity. Electrochemical sensors have been already successfully miniaturized and employed in other fields such as wearables and point-of-care devices. We have identified that the explanation for this issue may be, to a large extent, the accessibility to microfabrication technologies. These fields employ preferably digital manufacturing (DM), which is a more accessible microfabrication approach regardless of funding and facilities. Therefore, we envision that a paradigm shift in microfabrication that adopts DM instead of the dominating soft lithography for the in-lab microfabrication of OoC devices will contribute to the dissemination of the field and integration of the promising real-time sensing.

High Throughput Omnidirectional Printing of Tubular Microstructures from Elastomeric Polymers

Bioelastomers are extensively used in biomedical applications due to their desirable mechanical strength, tunable properties, and chemical versatility; however, three-dimensional (3D) printing bioelastomers into microscale structures has proven elusive. Herein, a high throughput omnidirectional printing approach via coaxial extrusion is described that fabricates perfusable elastomeric microtubes of unprecedently small inner diameter (350-550 µm) and wall thickness (40-60 µm). The versatility of this approach is shown through the printing of two different polymeric elastomers, followed by photocrosslinking and removal of the fugitive inner phase. Designed experiments are used to tune the microtube dimensions and stiffness to match that of native ex vivo rat vasculature. This approach affords the fabrication of multiple biomimetic shapes resembling cochlea and kidney glomerulus and affords facile, high-throughput generation of perfusable structures that can be seeded with endothelial cells for biomedical applications. Post-printing laser micromachining is performed to generate micro-sized holes (520 µm) in the tube wall to tune microstructure permeability. Importantly, for organ-on-a-chip applications, the described approach takes only 3.6 min to print microtubes (without microholes) over an entire 96-well plate device, in contrast to comparable hole-free structures that take between 1.5 and 6.5 days to fabricate using a manual 3D stamping approach.

Microfluidic Lab-on-a-Chip for Studies of Cell Migration under Spatial Confinement

Understanding cell migration is a key step in unraveling many physiological phenomena and predicting several pathologies, such as cancer metastasis. In particular, confinement has been proven to be a key factor in the cellular migration strategy choice. As our insight in the field improves, new tools are needed in order to empower biologists’ analysis capabilities. In this framework, microfluidic devices have been used to engineer the mechanical and spatial stimuli and to investigate cellular migration response in a more controlled way. In this work, we will review the existing technologies employed in the realization of microfluidic cellular migration assays, namely the soft lithography of PDMS and hydrogels and femtosecond laser micromachining. We will give an overview of the state of the art of these devices, focusing on the different geometrical configurations that have been exploited to study specific aspects of cellular migration. Our scope is to highlight the advantages and possibilities given by each approach and to envisage the future developments in in vitro migration studies under spatial confinement in microfluidic devices.

Neural microprobe modelling and microfabrication for improved implantation and mechanical failure mitigation

Careful design and material selection are the most beneficial strategies to ensure successful implantation and mitigate the failure of a neural probe in the long term. In order to realize a fully flexible implantable system, the probe should be easily manipulated by neuroscientists, with the potential to bend up to 90°. This paper investigates the impact of material choice, probe geometry, and crucially, implantation angle on implantation success through finite-element method simulations in COMSOL Multiphysics followed by cleanroom microfabrication. The designs introduced in this paper were fabricated using two polyimides: (i) PI-2545 as a release layer and (ii) photodefinable HD-4110 as the probe substrate. Four different designs were microfabricated, and the implantation tests were compared between an agarose brain phantom and lamb brain samples. The probes were scanned in a 7 T PharmaScan MRI coil to investigate potential artefacts. From the simulation, a triangular base and 50 µm polymer thickness were identified as the optimum design, which produced a probe 57.7 µm thick when fabricated. The probes exhibit excellent flexibility, exemplified in three-point bending tests performed with a DAGE 4000Plus. Successful implantation is possible for a range of angles between 30° and 90°. This article is part of the theme issue 'Advanced neurotechnologies: translating innovation for health and well-being'.

Low-cost rapid prototyping and assembly of an open microfluidic device for a 3D vascularized organ-on-a-chip

Reconstruction of 3D vascularized microtissues within microfabricated devices has rapidly developed in biomedical engineering, which can better mimic the tissue microphysiological function and accurately model human diseases in vitro. However, the traditional PDMS-based microfluidic devices suffer from the microfabrication with complex processes and usage limitations of either material properties or microstructure design, which drive the demand for easy processing and more accessible devices with a user-friendly interface. Here, we present an open microfluidic device through a rapid prototyping method by laser cutting in a cost-effective manner with high flexibility and compatibility. This device allows highly efficient and robust hydrogel patterning under a liquid guiding rail by spontaneous capillary action without the need for surface treatment. Different vascularization mechanisms including vasculogenesis and angiogenesis were performed to construct a 3D perfusable microvasculature inside a tissue chamber with various shapes under different microenvironment factors. Furthermore, as a proof-of-concept we have created a vascularized spheroid by placing a monoculture spheroid into the central through-hole of this device, which formed angiogenesis between the spheroid and microvascular network. This open microfluidic device has great potential for mass customization without the need for complex microfabrication equipment in the cleanroom, which can facilitate studies requiring high-throughput and high-content screening.

Review of Dielectrophoretic Manipulation of Micro and Nanomaterials: Fundamentals, Recent Developments, and Challenges

This paper reviews the state-of-the-art methods of dielectrophoresis for micro- and nanomaterial manipulation. Dielectrophoresis is a well-known technique for material manipulation using a nonuniform electric field. This field can apply a force to dielectric materials and move them toward a predefined location. Controlling the pattern of the electric field and its intensity, achieved by a specific arrangement of electrodes or insulators, along with the dielectric properties of the materials allows a variety of manipulation functions including trapping, separation, and transportation. The development of microfabrication techniques has significantly improved the research quality in the field of dielectrophoresis for precisely manipulating micro and nanomaterials. Later, the advent of microfluidic devices provided an excellent platform for reliable and practical devices. Modifying the shape, geometry, and material of the electrodes, isolating the electrodes from the sample, incorporating a particular arrangement of insulators within the electric field, and monitoring the operation in situ are some of the methods utilized for overcoming common problems in dielectrophoretic devices or the problems associated with a specific sample and the manipulation function. The goal of the research in this field is to design practical, high throughput, and inexpensive devices that reliably manipulate micro and nanomaterials. Accordingly, this review aims to represent latest findings and advancements in the field of dielectrophoresis. In particular, the working principles, technical implementation details, current status, and the issues and challenges of dielectrophoretic devices for electrode-based and insulator-based dielectrophoresis in terms of operation and fabrication are discussed.

Hybrid fabrication of multimodal intracranial implants for electrophysiology and local drug delivery

New fabrication approaches for mechanically flexible implants hold the key to advancing the applications of neuroengineering in fundamental neuroscience and clinic. By combining the high precision of thin film microfabrication with the versatility of additive manufacturing, we demonstrate a straight-forward approach for the prototyping of intracranial implants with electrode arrays and microfluidic channels. We show that the implant can modulate neuronal activity in the hippocampus through localized drug delivery, while simultaneously recording brain activity by its electrodes. Moreover, good implant stability and minimal tissue response are seen one-week post-implantation. Our work shows the potential of hybrid fabrication combining different manufacturing techniques in neurotechnology and paves the way for a new approach to the development of multimodal implants.

Simple and Robust Microfabrication of Polymeric Piezoelectric Resonating MEMS Mass Sensors

Resonating MEMS mass sensors are microdevices with broad applications in fields such as bioscience and biochemistry. Their advantageous surface-to-volume ratio makes their resonant frequency highly sensitive to variations in their mass induced by surface depositions. Recent global challenges, such as water quality monitoring or pandemic containment, have increased the need for low-cost (even disposable), rapidly fabricated microdevices as suitable detectors. Resonant MEMS mass sensors are among the best candidates. This paper introduces a simple and robust fabrication of polymeric piezoelectric resonating MEMS mass sensors. The microfabrication technology replaces the traditional layer-by-layer micromachining techniques with laser micromachining to gain extra simplicity. Membrane-based resonant sensors have been fabricated to test the technology. Their characterization results have proven that the technology is robust with good reproducibility (around 2% batch level variations in the resonant frequency). Initial tests for the MEMS mass sensors’ sensitivity have indicated a sensitivity of 340 Hz/ng. The concept could be a starting point for developing low-cost MEMS sensing solutions for pandemic control, health examination, and pollution monitoring.

Microfabricated cantilevers for parallelized cell-cell adhesion measurements

Single-cell adhesion measured with atomic force microscopy (AFM) offers outstanding time and force resolution and allows the investigation of many important phenomena with unmatched precision. However, this technique suffers from serious practical limitations that hinder its effective application to a broader set of situations. Here we propose a different strategy based on the fabrication of large cantilevers and on the culture of the cells directly on them. Cantilevers are fabricated by standard micromachining, with an active area of 300 × 300 µm. A wedged structure is created so that the cantilever surface lies parallel to the substrate when mounted on an AFM system, so that the adhesion measurement probes the whole surface area at the same time. Thanks to the large area, cells can be seeded and grown on the cantilevers the day before the experiment, and let recover to optimal condition for the experiment. We used Human Embryonic Kidney cells, HEK 293A, to demonstrate the measurement of adhesion forces of up to 100 cells in parallel, and obtain a straightforward measurement of the average single cell adhesion energy. Our approach can improve significantly the cell-cell and cell-substrate adhesion statistics, reduce the experiment time and allow the investigation of the adhesion properties of cells that do not grow well in solution or on low adherent substrates, or that develop their characteristic features only after several hours or days of culture on a solid and adherent substrate.

High-Throughput Continuous-Flow Separation in a Micro Free-Flow Electrophoresis Glass Chip Based on Laser Microfabrication

Micro free-flow electrophoresis (μFFE) provides a rapid and straightforward route for the high-performance online separation and purification of targeted liquid samples in a mild manner. However, the facile fabrication of a μFFE device with high throughput and high stability remains a challenge due to the technical barriers of electrode integration and structural design for the removal of bubbles for conventional methods. To address this, the design and fabrication of a high-throughput μFFE chip are proposed using laser-assisted chemical etching of glass followed by electrode integration and subsequent low-temperature bonding. The careful design of the height ratio of the separation chamber and electrode channels combined with a high flow rate of buffer solution allows the efficient removal of electrolysis-generated bubbles along the deep electrode channels during continuous-flow separation. The introduction of microchannel arrays further enhances the stability of on-chip high-throughput separation. As a proof-of-concept, high-performance purification of fluorescein sodium solution with a separation purity of ~97.9% at a voltage of 250 V from the mixture sample solution of fluorescein sodium and rhodamine 6G solution is demonstrated.

MXene-Sponge Based High-Performance Piezoresistive Sensor for Wearable Biomonitoring and Real-Time Tactile Sensing

Electrode microfabrication technologies such as lithography and deposition have been widely applied in wearable electronics to boost interfacial coupling efficiency and device performance. However, a majority of these approaches are restricted by expensive and complicated processing techniques, as well as waste discharge. Here, helium plasma irradiation is employed to yield a molybdenum microstructured electrode, which is constructed into a flexible piezoresistive pressure sensor based on a Ti₃ C₂ T_x nanosheet-immersed polyurethane sponge. This electrode engineering strategy enables the smooth transition between sponge deformation and MXene interlamellar displacement, giving rise to high sensitivity (1.52 kPa^-1 ) and good linearity (r²  = 0.9985) in a wide sensing range (0-100 kPa) with a response time of 226 ms for pressure detection. In addition, both the experimental characterization and finite element simulation confirm that the hierarchical structures modulated by pore size, plasma bias, and MXene concentration play a crucial role in improving the sensing performance. Furthermore, the as-developed flexible pressure sensor is demonstrated to measure human radial pulse, detect finger tapping, foot stomping, and perform object identification, revealing great feasibility in wearable biomonitoring and health assessment.

Micromachined Optical Fiber Sensors for Biomedical Applications

Optical fibers revolutionized the rate of information reception and transmission in telecommunications. The revolution has now extended to the field of physicochemical sensing. Optical fiber sensors (OFSs) have found a multitude of applications, spanning from structural health monitoring to biomedical and clinical measurements due to their unique physical and functional advantages, such as small dimensions, light weight, immunity to electromagnetic interference, high sensitivity and resolution, multiplexing, and remote operation. OFSs generally rely on the detection of measurand-induced changes in the optical properties of the light propagating in the fiber, where the OFS essentially functions as the conduit and physical link between the probing light waves and the physicochemical parameters under investigation. Several advanced micromachining techniques have been developed to optimize the structure of OFSs, thus improving their sensing performance. These techniques include fusion splicing, tapering, polishing, and more complicated femtosecond laser micromachining methods. This chapter discusses and reviews the most recent developments in micromachined OFSs specifically for biomedical applications. Step-by-step procedures for several optical fiber micromachining techniques are detailed.

A Tri-Channel Oxide Transistor Concept for the Rapid Detection of Biomolecules Including the SARS-CoV-2 Spike Protein

Solid-state transistor sensors that can detect biomolecules in real time are highly attractive for emerging bioanalytical applications. However, combining upscalable manufacturing with the required performance remains challenging. Here, an alternative biosensor transistor concept is developed, which relies on a solution-processed In₂ O₃ /ZnO semiconducting heterojunction featuring a geometrically engineered tri-channel architecture for the rapid, real-time detection of important biomolecules. The sensor combines a high electron mobility channel, attributed to the electronic properties of the In₂ O₃ /ZnO heterointerface, in close proximity to a sensing surface featuring tethered analyte receptors. The unusual tri-channel design enables strong coupling between the buried electron channel and electrostatic perturbations occurring during receptor-analyte interactions allowing for robust, real-time detection of biomolecules down to attomolar (am) concentrations. The experimental findings are corroborated by extensive device simulations, highlighting the unique advantages of the heterojunction tri-channel design. By functionalizing the surface of the geometrically engineered channel with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody receptors, real-time detection of the SARS-CoV-2 spike S1 protein down to am concentrations is demonstrated in under 2 min in physiological relevant conditions.

3D-to-3D Microscale Shape-Morphing from Configurable Helices with Controlled Chirality

Tunable and reconfigurable materials with autonomic shape transformation in response to the environment have emerged as one of the most promising approaches for a variety of biomedical applications, such as tissue engineering, biosensing, and in vivo biomedical devices. Currently, it is still quite challenging to fabricate soft, microscaled 3D shape-reconfigurable structures due to either complicated microfabrication or limited microscale photopolymerization-based printing approaches to enable adaptive shape transformation. Here, a one-step photo-cross-linking approach has been demonstrated to obtain a 3D-to-3D morphological transformable microhelix from a self-rolled hydrogel microsheet, resulting in chirality conversion. It was enabled by a custom-designed "hard" stripe/"soft" groove topography on the microsheets for introducing, which introduced both in-planar and out-of-planar anisotropies. Both experiment and simulation confirmed that a stripe/groove geometry can effectively control the 3D transformation by activating in-planar or/and out-of-planar mismatch stress within the microsheets, resulting in switching of the rolling direction between perpendicular/parallel to the length of the stripe. Furthermore, versatile 3D microconstructs with the ability to transform between two distinct 3D configurations have been achieved based on controlled rolling of microhelices, demonstrated as "windmill"-to-"T-cross" and "cylinder"-to-"scroll" transformations and dynamic blossoming of biomimetic orchids. In contrast to conventional 2D-to-3D micro-origami, we have successfully demonstrated an approach for fabricating microscale, all-soft-material-based constructs with autonomic 3D-to-3D structural transformation, which presents an opportunity for designing more complex hydrogel-based microrobotics.

Fabrication of sharp-edged 3D microparticles via folded PDMS microfluidic channels

3D microparticles have promising applications in self-assembly, biomedical engineering, mechanical engineering, etc. The shape of microparticles plays a significant role in their functionalities. Although numerous investigations have been conducted to tailor the shape of microparticles, the diversity is still limited, and it remains a challenge to fabricate 3D microparticles with sharp edges. Here, we present a facile approach that combines a folded PDMS channel and orthogonal projection lithography for shaping sharp-edged 3D microparticles. By adjusting the number and the length of channel sides, both regular and irregular polyhedral cross-sections of the folded channel can be obtained. UV light with diverse patterns is applied vertically as the second shape controlling factor. A variety of 3D microparticles are obtained with sharp edges, which are potential templates for micromachining tools and abrasives. Some sharp-edged microparticles are assembled into 2D and 3D mesoscale structures, which demonstrates their prospective applications in self-assembly, tissue engineering, etc.

Nanostructured Shell-Layer Artificial Antibody with Fluorescence-Tagged Recognition Sites for the Trace Detection of Heavy Metal Ions by Self-Reporting Microsensor Arrays

Herein, a strategy for a metal ion-imprinted artificial antibody with recognition sites tagged by fluorescein was carried out to construct the selective sites with a sensitive optical response signal to the specific metal ion. The synthesized silica nanoparticles were modified by the derivative residue group of 3-aminopropyltriethoxysilane conjugated with a 4-chloro-7-nitro-1,2,3-benzoxadiazole (NBD-Cl) molecule through the hydrolysis and condensation reactions. The as-prepared silica nanoparticles were encapsulated by metal ion (Cu²⁺, Cd²⁺, Hg²⁺, and Pb²⁺)-imprinted polymers with nanostructured layers through the copolymerization of ethyl glycol dimethyl methacrylate (EGDMA) as a cross-linker, AIBN as an initiator, metal ions as template molecules, AA as a functional monomer, and acetonitrile as a solvent. The layers of molecular imprinted polymers (MIPs) with a core-shell structure removed template molecules by EDTA-2Na to retain the cavities and spatial sizes to match the imprinted metal ions. The microsensor arrays were achieved by the self-assembly technique of SiO₂@MIP nanoparticles on the etched silicon wafer with regular dot arrays. The nanostructured-shell layers with fluorescence-tagged recognition sites rebound metal ions by the driving force of concentration difference demonstrates the high selective recognition and sensitive detection to heavy metal ions through the decline of fluorescence intensity. The LOD concentration for four metal ions is down to 10^-9 mol·L^-1. The method will provide biomimetic synthesis, analyte screen, and detection of highly dangerous materials in the environment for theoretical foundation and technological support.

Miniaturized probe on polymer SU-8 with array of individually addressable microelectrodes for electrochemical analysis in neural and other biological tissues

An SU-8 probe with an array of nine, individually addressable gold microband electrodes (100 μm long, 4 μm wide, separated by 4-μm gaps) was photolithographically fabricated and characterized for detection of low concentrations of chemicals in confined spaces and in vivo studies of biological tissues. The probe's shank (6 mm long, 100 μm wide, 100 μm thick) is flexible, but exhibits sufficient sharpness and rigidity to be inserted into soft tissue. Laser micromachining was used to define probe geometry by spatially revealing the underlying sacrificial aluminum layer, which was then etched to free the probes from a silicon wafer. Perfusion with fluorescent nanobeads showed that, like a carbon fiber electrode, the probe produced no noticeable damage when inserted into rat brain, in contrast to damage from an inserted microdialysis probe. The individual addressability of the electrodes allows single and multiple electrode activation. Redox cycling is possible, where adjacent electrodes serve as generators (that oxidize or reduce molecules) and collectors (that do the opposite) to amplify signals of small concentrations without background subtraction. Information about electrochemical mechanisms and kinetics may also be obtained. Detection limits for potassium ferricyanide in potassium chloride electrolyte of 2.19, 1.25, and 2.08 μM and for dopamine in artificial cerebral spinal fluid of 1.94, 1.08, and 5.66 μM for generators alone and for generators and collectors during redox cycling, respectively, were obtained.

Robust Pressure Sensor in SOI Technology with Butterfly Wiring for Airfoil Integration

Current research in the field of aviation considers actively controlled high-lift structures for future civil airplanes. Therefore, pressure data must be acquired from the airfoil surface without influencing the flow due to sensor application. For experiments in the wind and water tunnel, as well as for the actual application, the requirements for the quality of the airfoil surface are demanding. Consequently, a new class of sensors is required, which can be flush-integrated into the airfoil surface, may be used under wet conditions-even under water-and should withstand the harsh environment of a high-lift scenario. A new miniature silicon on insulator (SOI)-based MEMS pressure sensor, which allows integration into airfoils in a flip-chip configuration, is presented. An internal, highly doped silicon wiring with "butterfly" geometry combined with through glass via (TGV) technology enables a watertight and application-suitable chip-scale-package (CSP). The chips were produced by reliable batch microfabrication including femtosecond laser processes at the wafer-level. Sensor characterization demonstrates a high resolution of 38 mVV^-1 bar^-1. The stepless ultra-smooth and electrically passivated sensor surface can be coated with thin surface protection layers to further enhance robustness against harsh environments. Accordingly, protective coatings of amorphous hydrogenated silicon nitride (a-SiN:H) and amorphous hydrogenated silicon carbide (a-SiC:H) were investigated in experiments simulating environments with high-velocity impacting particles. Topographic damage quantification demonstrates the superior robustness of a-SiC:H coatings and validates their applicability to future sensors.

A Portable Micro-Gas Chromatography with Integrated Photonic Crystal Slab Sensors on Chip

The miniaturization of gas chromatography (GC) systems has made it possible to utilize the analytical technique in various on-site applications to rapidly analyze complex gas samples. Various types of miniaturized sensors have been developed for micro-gas chromatography (µGC). However, the integration of an appropriate detector in µGC systems still faces a significant challenge. We present a solution to the problem through integration of µGC with photonic crystal slab (PCS) sensors using transfer printing technology. This integration offers an opportunity to utilize the advantages of optical sensors, such as high sensitivity and rapid response time, and at the same time, compensate for the lack of detection specificity from which label-free optical sensors suffer. We transfer printed a 2D defect free PCS on a borofloat glass, bonded it to a silicon microfluidic gas cell or directly to a microfabricated GC column, and then coated it with a gas responsive polymer. Realtime spectral shift in Fano resonance of the PCS sensor was used to quantitatively detect analytes over a mass range of three orders. The integrated µGC–PCS system was used to demonstrate separation and detection of a complex mixture of 10 chemicals. Fast separation and detection (4 min) and a low detection limit (ng) was demonstrated.

Point-of-critical-care diagnostics for sepsis enabled by multiplexed micro and nanosensing technologies

Sepsis is responsible for the highest economic and mortality burden in critical care settings around the world, prompting the World Health Organization in 2018 to designate it as a global health priority. Despite its high universal prevalence and mortality rate, a disproportionately low amount of sponsored research funding is directed toward diagnosis and treatment of sepsis, when early treatment has been shown to significantly improve survival. Additionally, current technologies and methods are inadequate to provide an accurate and timely diagnosis of septic patients in multiple clinical environments. For improved patient outcomes, a comprehensive immunological evaluation is critical which is comprised of both traditional testing and quantifying recently proposed biomarkers for sepsis. There is an urgent need to develop novel point-of-care, low-cost systems which can accurately stratify patients. These point-of-critical-care sensors should adopt a multiplexed approach utilizing multimodal sensing for heterogenous biomarker detection. For effective multiplexing, the sensors must satisfy criteria including rapid sample to result delivery, low sample volumes for clinical sample sparring, and reduced costs per test. A compendium of currently developed multiplexed micro and nano (M/N)-based diagnostic technologies for potential applications toward sepsis are presented. We have also explored the various biomarkers targeted for sepsis including immune cell morphology changes, circulating proteins, small molecules, and presence of infectious pathogens. An overview of different M/N detection mechanisms are also provided, along with recent advances in related nanotechnologies which have shown improved patient outcomes and perspectives on what future successful technologies may encompass. This article is categorized under: Diagnostic Tools > Biosensing.

Fabrication and characterization of an antibacterial chitosan/silk fibroin electrospun nanofiber loaded with a cationic peptide for wound-dressing application

Wound infections are still problematic in many cases and demand new alternatives for current treatment strategies. In recent years, biomaterials-based wound dressings have received much attention due to their potentials and many studies have been performed based on them. Accordingly, in this study, we fabricated and optimized an antibacterial chitosan/silk fibroin (CS/SF) electrospun nanofiber bilayer containing different concentrations of a cationic antimicrobial peptide (AMP) for wound dressing applications. The fabricated CS/SF nanofiber was fully characterized and compared to the electrospun silk fibroin and electrospun chitosan alone in vitro. Then, the release rate of different concentrations of peptide (16, 32, and 64 µg/ml) from peptide-loaded CS/SF nanofiber was investigated. Finally, based on cytotoxic activity, the antibacterial activity of scaffolds containing 16 and 32 µg/ml of the peptide was evaluated against standard and multi-drug resistant strains of Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa isolated from burn patients. The peptide-loaded CS/SF nanofiber displayed appropriate mechanical properties, high water uptake, suitable biodegradation rate, a controlled release without cytotoxicity on Hu02 human foreskin fibroblast cells at the 16 and 32 µg/ml concentrations of peptide. The optimized CS/SF containing 32 μg/ml peptide showed strong antibacterial activity against all experimental strains from standard to resistance. The results showed that the fabricated antimicrobial nanofiber has the potential to be applied as a wound dressing for infected wound healing, although further studies are needed in vivo.

Thin-film microfabrication and intraoperative testing ofµECoG and iEEG depth arrays for sense and stimulation

Objective.Intracranial neural recordings and electrical stimulation are tools used in an increasing range of applications, including intraoperative clinical mapping and monitoring, therapeutic neuromodulation, and brain computer interface control and feedback. However, many of these applications suffer from a lack of spatial specificity and localization, both in terms of sensed neural signal and applied stimulation. This stems from limited manufacturing processes of commercial-off-the-shelf (COTS) arrays unable to accommodate increased channel density, higher channel count, and smaller contact size.Approach.Here, we describe a manufacturing and assembly approach using thin-film microfabrication for 32-channel high density subdural micro-electrocorticography (µECoG) surface arrays (contacts 1.2 mm diameter, 2 mm pitch) and intracranial electroencephalography (iEEG) depth arrays (contacts 0.5 mm × 1.5 mm, pitch 0.8 mm × 2.5 mm). Crucially, we tackle the translational hurdle and test these arrays during intraoperative studies conducted in four humans under regulatory approval.Main results.We demonstrate that the higher-density contacts provide additional unique information across the recording span compared to the density of COTS arrays which typically have electrode pitch of 8 mm or greater; 4 mm in case of specially ordered arrays. Our intracranial stimulation study results reveal that refined spatial targeting of stimulation elicits evoked potentials with differing spatial spread.Significance.Thin-film,μECoG and iEEG depth arrays offer a promising substrate for advancing a number of clinical and research applications reliant on high-resolution neural sensing and intracranial stimulation.

Cervical lesion assessment using real-time microendoscopy image analysis in Brazil: The CLARA study

We conducted a prospective evaluation of the diagnostic performance of high-resolution microendoscopy (HRME) to detect cervical intraepithelial neoplasia (CIN) in women with abnormal screening tests. Study participants underwent colposcopy, HRME and cervical biopsy. The prospective diagnostic performance of HRME using an automated morphologic image analysis algorithm was compared to that of colposcopy using histopathologic detection of CIN as the gold standard. To assess the potential to further improve performance of HRME image analysis, we also conducted a retrospective analysis assessing performance of a multi-task convolutional neural network to segment and classify HRME images. One thousand four hundred eighty-six subjects completed the study; 435 (29%) subjects had CIN Grade 2 or more severe (CIN2+) diagnosis. HRME with morphologic image analysis for detection of CIN Grade 3 or more severe diagnoses (CIN3+) was similarly sensitive (95.6% vs 96.2%, P = .81) and specific (56.6% vs 58.7%, P = .18) as colposcopy. HRME with morphologic image analysis for detection of CIN2+ was slightly less sensitive (91.7% vs 95.6%, P < .01) and specific (59.7% vs 63.4%, P = .02) than colposcopy. Images from 870 subjects were used to train a multi-task convolutional neural network-based algorithm and images from the remaining 616 were used to validate its performance. There were no significant differences in the sensitivity and specificity of HRME with neural network analysis vs colposcopy for detection of CIN2+ or CIN3+. Using a neural network-based algorithm, HRME has comparable sensitivity and specificity to colposcopy for detection of CIN2+. HRME could provide a low-cost, point-of-care alternative to colposcopy and biopsy in the prevention of cervical cancer.

Electrochemistry in an optical fiber microcavity - optical monitoring of electrochemical processes in picoliter volumes

In this work, we demonstrate a novel method for multi-domain analysis of properties of analytes in volumes as small as picoliters, combining electrochemistry and optical measurements. A microcavity in-line Mach-Zehnder interferometer (μIMZI) obtained in a standard single-mode optical fiber using femtosecond laser micromachining was able to accommodate a microelectrode and optically monitor electrochemical processes inside the fiber. The interferometer shows exceptional sensitivity to changes in the optical properties of analytes in the microcavity. We show that the optical readout follows the electrochemical reactions. Here, the redox probe (ferrocenedimethanol) undergoing reactions of oxidation and reduction changes the optical properties of the analyte (refractive index and absorbance) that are monitored using the μIMZI. Measurements have been supported by numerical analysis of both optical and electrochemical phenomena. On top of the capability of the approach to perform analysis on a microscale, the difference between oxidized and reduced forms in the near-infrared region can be measured using the μIMZI, which is hardly possible using other optical techniques. The proposed multi-domain concept is a promising approach for highly reliable and ultrasensitive chemo- and biosensing.

Self-Assembled Permanent Micro-Magnets in a Polymer-Based Microfluidic Device for Magnetic Cell Sorting

Magnetophoresis-based microfluidic devices offer simple and reliable manipulation of micro-scale objects and provide a large panel of applications, from selective trapping to high-throughput sorting. However, the fabrication and integration of micro-scale magnets in microsystems involve complex and expensive processes. Here we report on an inexpensive and easy-to-handle fabrication process of micrometer-scale permanent magnets, based on the self-organization of NdFeB particles in a polymer matrix (polydimethylsiloxane, PDMS). A study of the inner structure by X-ray tomography revealed a chain-like organization of the particles leading to an array of hard magnetic microstructures with a mean diameter of 4 µm. The magnetic performance of the self-assembled micro-magnets was first estimated by COMSOL simulations. The micro-magnets were then integrated into a microfluidic device where they act as micro-traps. The magnetic forces exerted by the micro-magnets on superparamagnetic beads were measured by colloidal probe atomic force microscopy (AFM) and in operando in the microfluidic system. Forces as high as several nanonewtons were reached. Adding an external millimeter-sized magnet allowed target magnetization and the interaction range to be increased. Then, the integrated micro-magnets were used to study the magnetophoretic trapping efficiency of magnetic beads, providing efficiencies of 100% at 0.5 mL/h and 75% at 1 mL/h. Finally, the micro-magnets were implemented for cell sorting by performing white blood cell depletion.

Fabrication of Topographically Controlled Electrospun Scaffolds to Mimic the Stem Cell Microenvironment in the Dermal-Epidermal Junction

The use of microfabrication techniques for the development of innovative constructs for tissue regeneration is a growing area of research. This area comprises both manufacturing and biological approaches for the development of smart materials aiming to control and direct cell behavior to enhance tissue healing. Many groups have focused their efforts on introducing complexity within these innovative constructs via the inclusion of nano- and microtopographical cues mimicking physical and biological aspects of the native stem cell niche. Specifically, in the area of skin tissue engineering, seminal work has reported replicating the microenvironments located in the dermal-epithelial junction, which are known as rete ridges. The rete ridges are key for both stem cell control and the physiological performance of the skin. In this work, we have introduced complexity within electrospun membranes to mimic the morphology of the rete ridges in the skin. We designed and tested three different patterns, characterized them, and explored their performance in vitro, using 3D skin models. One of the studied patterns (pattern B) was shown to aid in the development of an in vitro rite-ridgelike skin model that resulted in the expression of relevant epithelial markers such as collagen IV and integrin β1. In summary, we have developed a new skin model including synthetic rete-ridgelike structures that replicate both morphology and function of the native dermal-epidermal junction and that offer new insights for the development of smart skin tissue engineering constructs.

A reusable single-cell patterning strategy based on an ultrathin metal microstencil

The ability to arrange distinct cells in specific, predefined patterns at single-cell resolution can have broad applications in cell-based assays and play an important role in facilitating interdisciplinary research for researchers in various fields. However, most existing methods for single-cell patterning are based on the complicated lithography-based microfabrication process, and require professional skills. Thus, exploiting convenient and universal strategies of single-cell preparation while maintaining high-throughput single-cell patterning remains a challenge. Here, we describe a simple approach for rapid and high-efficiency single-cell patterning using an ultrathin metal microstencil (UTmS) and common tools available in any laboratory. In this work, ultrathin steel microstencil plates with only 5 μm thickness could be fabricated with laser drilling and achieve single-cell prototyping on an arbitrary planar substrate under gravity-induced natural sedimentation without requiring additional fixation, reaction pools, and centrifugation procedures. In this method, the UTmS is reusable and single-cell occupancy could easily reach approximately 88% within 30 min on fibronectin-modified substrates under gravity-induced natural sedimentation, and no significant effect on cell viability was observed. To verify this method, the real-time and heterogeneous study of calcium release and apoptosis behaviors of single cells was carried out based on this new strategy. To our knowledge, it is the first time that a UTmS with 5 μm thickness is directly applied to facilitate the micropatterning of high-resolution single cells, which is valuable for researchers in different fields owing to its user-friendly operation.