Effect of bias voltage and temperature on lifetime of wireless neural interfaces with Al ₂O₃ and parylene bilayer encapsulation

Tunable theranostics: innovative strategies in combating oral cancer

Objective

This study aims to assess and compare the potential of advanced nano/micro delivery systems, including quantum dots, carbon nanotubes, magnetic nanoparticles, dendrimers, and microneedles, as theranostic platforms for oral cancer. Furthermore, we seek to evaluate their respective advantages and disadvantages over the past decade.

Materials and Methods

A comprehensive literature search was performed using Google Scholar and PubMed, with a focus on articles published between 2013 and 2023. Search queries included the specific advanced delivery system as the primary term, followed by oral cancer as the secondary term (e.g., "quantum dots AND oral cancer," etc.).

Results

The advanced delivery platforms exhibited notable diagnostic and therapeutic advantages when compared to conventional techniques or control groups. These benefits encompassed improved tumor detection and visualization, enhanced precision in targeting tumors with reduced harm to neighboring tissues, and improved drug solubility and distribution, leading to enhanced drug absorption and tumor uptake.

Conclusion

The findings suggest that advanced nano/micro delivery platforms hold promise for addressing numerous challenges associated with chemotherapy. By enabling precise targeting of cancerous cells, these platforms have the potential to mitigate adverse effects on surrounding healthy tissues, thus encouraging the development of innovative diagnostic and therapeutic strategies for oral cancer.

Cancer Models on Chip: Paving the Way to Large-Scale Trial Applications

Cancer kills millions of individuals every year all over the world (Global Cancer Observatory). The physiological and biomechanical processes underlying the tumor are still poorly understood, hindering researchers from creating new, effective therapies. Inconsistent results of preclinical research, in vivo testing, and clinical trials decrease drug approval rates. 3D tumor-on-a-chip (ToC) models integrate biomaterials, tissue engineering, fabrication of microarchitectures, and sensory and actuation systems in a single device, enabling reliable studies in fundamental oncology and pharmacology. This review includes a critical discussion about their ability to reproduce the tumor microenvironment (TME), the advantages and drawbacks of existing tumor models and architectures, major components and fabrication techniques. The focus is on current materials and micro/nanofabrication techniques used to manufacture reliable and reproducible microfluidic ToC models for large-scale trial applications.

Impact of Non-Accelerated Aging on the Properties of Parylene C

The polymer Parylene combines a variety of excellent properties and, hence, is an object of intensive research for packaging applications, such as the direct encapsulation of medical implants. Moreover, in the past years, an increasing interest for establishing new applications for Parylene is observed. These include the usage of Parylene as a flexible substrate, a dielectric, or a material for MEMS, e.g., a bonding adhesive. The increasing importance of Parylene raises questions regarding the long-term reliability and aging of Parylene as well as the impact of the aging on the Parylene properties. Within this paper, we present the first investigations on non-accelerated Parylene C aging for a period of about five years. Doing so, free-standing Parylene membranes were fabricated to investigate the barrier properties, the chemical stability, as well as the optical properties of Parylene in dependence on different post-treatments to the polymer. These properties were found to be excellent and with only a minor age-related impact. Additionally, the mechanical properties, i.e., the Young's modulus and the hardness, were investigated via nano-indentation over the same period of time. For both mechanical properties only, minor changes were observed. The results prove that Parylene C is a highly reliable polymer for applications that needs a high long-term stability.

Recent Advances in Encapsulation of Flexible Bioelectronic Implants: Materials, Technologies, and Characterization Methods

Bioelectronic implantable systems (BIS) targeting biomedical and clinical research should combine long-term performance and biointegration in vivo. Here, recent advances in novel encapsulations to protect flexible versions of such systems from the surrounding biological environment are reviewed, focusing on material strategies and synthesis techniques. Considerable effort is put on thin-film encapsulation (TFE), and specifically organic-inorganic multilayer architectures as a flexible and conformal alternative to conventional rigid cans. TFE is in direct contact with the biological medium and thus must exhibit not only biocompatibility, inertness, and hermeticity but also mechanical robustness, conformability, and compatibility with the manufacturing of microfabricated devices. Quantitative characterization methods of the barrier and mechanical performance of the TFE are reviewed with a particular emphasis on water-vapor transmission rate through electrical, optical, or electrochemical principles. The integrability and functionalization of TFE into functional bioelectronic interfaces are also discussed. TFE represents a must-have component for the next-generation bioelectronic implants with diagnostic or therapeutic functions in human healthcare and precision medicine.

Extended Barrier Lifetime of Partially Cracked Organic/Inorganic Multilayers for Compliant Implantable Electronics

Flexible and soft bioelectronics display conflicting demands on miniaturization, compliance, and reliability. Here, the authors investigate the design and performance of thin encapsulation multilayers against hermeticity and mechanical integrity. Partially cracked organic/inorganic multilayer coatings are demonstrated to display surprisingly year-long hermetic lifetime under demanding mechanical and environmental loading. The thin hermetic encapsulation is grown in a single process chamber as a continuous multilayer with dyads of atomic layer deposited (ALD) Al₂ O₃ -TiO₂ and chemical vapor deposited Parylene C films with strong interlayer adhesion. Upon tensile loading, tortuous diffusion pathways defined along channel cracks in the ALD oxide films and through tough Parylene films efficiently postpone the hermeticity failure of the partially cracked coating. The authors assessed the coating performance against prolonged exposure to biomimetic physiological conditions using coated magnesium films, platinum interdigitated electrodes, and optoelectronic devices prepared on stretchable substrates. Designed extension of the lifetime preventing direct failures reduces from over 5 years yet tolerates the lifetime of 3 years even with the presence of critical damage, while others will directly fail less than two months at 37 °C. This strategy should accelerate progress on thin hermetic packaging for miniaturized and compliant implantable electronics.

Feasibility of generating 90 Hz vibrations in remote implanted magnets

Limb amputation not only reduces the motor abilities of an individual, but also destroys afferent channels that convey essential sensory information to the brain. Significant efforts have been made in the area of upper limb prosthetics to restore sensory feedback, through the stimulation of residual sensory elements. Most of the past research focused on the replacement of tactile functions. On the other hand, the difficulties in eliciting proprioceptive sensations using either haptic or (neural) electrical stimulation, has limited researchers to rely on sensory substitution. Here we propose the myokinetic stimulation interface, that aims at restoring natural proprioceptive sensations by exploiting the so-called tendon illusion, elicited through the vibration of magnets implanted inside residual muscles. We present a prototype which exploits 12 electromagnetic coils to vibrate up to four magnets implanted in a forearm mockup. The results demonstrated that it is possible to generate highly directional and frequency-selective vibrations. The system proved capable of activating a single magnet, out of many. Hence, this interface constitutes a promising approach to restore naturally perceived proprioception after an amputation. Indeed, by implanting several magnets in independent muscles, it would be possible to restore proprioceptive sensations perceived as coming from single digits.

Enzymatically functionalized polyaniline thin films produced with one-step electrochemical immobilization and its application in glucose and urea potentiometric biosensors

Glucose and urea enzymatic biosensors were fabricated. One-step electrochemical immobilization process was used to produce thin polyaniline films with entrapped enzymes. Chronopotentiometric analysis, scanning electron microscopy, electrochemical impedance spectroscopy and optical reflectance spectroscopy were used to determine the structure-property relationship of the functionalized polymeric thin films. The device has a recognition stage connected to a potentiometric field-effect-transistor stage and is based on the measurement of microenvironment pH variation or locally produced ions. Optimization of biosensor fabrication and effective measurement conditions were performed. The optimized films presented sensitivity, linearity and detection range to glucose of 14.6 ± 0.4 mV/decade, 99.8% and from 10^-4 M to 10^-1 mol/L. Two different biosensors were produced based on the enzymatic reaction of urea with selectivity to ammonium or hydroxyl ions. For ammonium ion selective film, the sensor's parameters were 14.7 ± 0.9 mV/decade, 98.2% and from 10^-5 to 10^-1 mol/L. For the hydroxyl ion selective film, the same parameters were 7.4 ± 0.5 mV/decade, 98.1% and from 10^-5 to 10^-1 mol/L. The change in the oxidation state of the polymeric matrix explains: i) the large loss of functionality of glucose biosensor in time, ii) the conservation of functionality to the hydroxyl ions for urea biosensor and iii) the selectivity variation of the ammonium ion selective urea biosensor. The results indicate that the polymeric matrix has indeed changeable selectivity, what can be applied in different situations for biosensors production.

Rapid Assessment of Surface Markers on Cancer Cells Using Immuno-Magnetic Separation and Multi-frequency Impedance Cytometry for Targeted Therapy

The rapid qualitative assessment of surface markers on cancer cells can allow for point-of-care prediction of patient response to various cancer drugs. Preclinical studies targeting cells with an antibody to "activated" matriptase conjugated to a potent toxin show promise as a selective treatment for a variety of solid tumors. In this paper, we implemented a novel technique for electrical detection of proteins on surfaces of cancer cells using multi-frequency microfluidic impedance cytometry. The biosensor, consists of two gold microelectrodes on a glass substrate embedded in a PDMS microfluidic channel, is used in conjugation with immuno-magnetic separation of cancer cells, and is capable of differentiating between bare magnetic beads, cancer cells and bead-cell aggregates based on their various impedance and frequency responses. We demonstrated proof-of-concept based on detection of "activated" matriptase proteins on the surface of cultured Mantle cells.

Implantable electrical stimulation bioreactor with liquid crystal polymer-based electrodes for enhanced bone regeneration at mandibular large defects in rabbit

The osseous regeneration of large bone defects is still a major clinical challenge in maxillofacial and orthopedic surgery. Previous studies demonstrated that biphasic electrical stimulation (ES) stimulates bone formation; however, polyimide electrode should be removed after regeneration. This study presents an implantable electrical stimulation bioreactor with electrodes based on liquid crystal polymer (LCP), which can be permanently implanted due to excellent biocompatibility to bone tissue. The bioreactor was implanted into a critical-sized bone defect and subjected to ES for one week, where bone regeneration was evaluated four weeks after surgery using micro-CT. The effect of ES via the bioreactor was compared with a sham control group and a positive control group that received recombinant human bone morphogenetic protein (rhBMP)-2 (20 μg). New bone volume per tissue volume (BV/TV) in the ES and rhBMP-2 groups increased to 132% (p < 0.05) and 174% (p < 0.01), respectively, compared to that in the sham control group. In the histological evaluation, there was no inflammation within the bone defects and adjacent to LCP in all the groups. This study showed that the ES bioreactor with LCP electrodes could enhance bone regeneration at large bone defects, where LCP can act as a mechanically resistant outer box without inflammation. Graphical abstract To enhance bone regeneration, a bioreactor comprising collagen sponge and liquid crystal polymer-based electrode was implanted in the bone defect. Within the defect, electrical current pulses having biphasic waveform were applied from the implanted bioreactor.

An Injectable Neural Stimulation Electrode Made from an In-Body Curing Polymer/Metal Composite

Implanted neural stimulation and recording devices hold vast potential to treat a variety of neurological conditions, but the invasiveness, complexity, and cost of the implantation procedure greatly reduce access to an otherwise promising therapeutic approach. To address this need, a novel electrode that begins as an uncured, flowable prepolymer that can be injected around a neuroanatomical target to minimize surgical manipulation is developed. Referred to as the Injectrode, the electrode conforms to target structures forming an electrically conductive interface which is orders of magnitude less stiff than conventional neuromodulation electrodes. To validate the Injectrode, detailed electrochemical and microscopy characterization of its material properties is performed and the feasibility of using it to stimulate the nervous system electrically in rats and swine is validated. The silicone-metal-particle composite performs very similarly to pure wire of the same metal (silver) in all measures, including exhibiting a favorable cathodic charge storage capacity (CSCC ) and charge injection limits compared to the clinical LivaNova stimulation electrode and silver wire electrodes. By virtue of its simplicity, the Injectrode has the potential to be less invasive, more robust, and more cost-effective than traditional electrode designs, which could increase the adoption of neuromodulation therapies for existing and new indications.

Emerging Encapsulation Technologies for Long-Term Reliability of Microfabricated Implantable Devices

The development of reliable long-term encapsulation technologies for implantable biomedical devices is of paramount importance for the safe and stable operation of implants in the body over a period of several decades. Conventional technologies based on titanium or ceramic packaging, however, are not suitable for encapsulating microfabricated devices due to their limited scalability, incompatibility with microfabrication processes, and difficulties with miniaturization. A variety of emerging materials have been proposed for encapsulation of microfabricated implants, including thin-film inorganic coatings of Al2O3, HfO2, SiO2, SiC, and diamond, as well as organic polymers of polyimide, parylene, liquid crystal polymer, silicone elastomer, SU-8, and cyclic olefin copolymer. While none of these materials have yet been proven to be as hermetic as conventional metal packages nor widely used in regulatory approved devices for chronic implantation, a number of studies have demonstrated promising outcomes on their long-term encapsulation performance through a multitude of fabrication and testing methodologies. The present review article aims to provide a comprehensive, up-to-date overview of the long-term encapsulation performance of these emerging materials with a specific focus on publications that have quantitatively estimated the lifetime of encapsulation technologies in aqueous environments.

Hydrogel Printing Based on UV-Induced Projection for Cell-Based Microarray Fabrication

A considerable number of studies have focused on fabrication of hydrogel microstructures due to its wide applications in tissue engineering, drug delivery, and extracellular matrix construction. Here, we introduce a hydrogel printing method based on UV-induced projection via a digital micromirror device (DMD). Arbitrary microstructures could be fabricated within few seconds (<3) by modulating UV projection using DMD as digital dynamic masks instead of a physical mask, which also offers a high degree of flexibility and repeatability. Furthermore, the ability of PEGDA film to hinder cell adhesion makes it possible to control area over which cells attach.

Chronic softening spinal cord stimulation arrays

OBJECTIVE

We sought to develop a cervical spinal cord stimulator for the rat that is durable, stable, and does not perturb the underlying spinal cord.

APPROACH

We created a softening spinal cord stimulation (SCS) array made from shape memory polymer (SMP)-based flexible electronics. We developed a new photolithographic process to pattern high surface area titanium nitride (TiN) electrodes onto gold (Au) interconnects. The thiol-ene acrylate polymers are stiff at room temperature and soften following implantation into the body. Durability was measured by the duration the devices produced effective stimulation and by accelerated aging in vitro. Stability was measured by the threshold to provoke an electromyogram (EMG) muscle response and by measuring impedance using electrochemical impedance spectroscopy (EIS). In addition, spinal cord modulation of motor cortex potentials was measured. The spinal column and implanted arrays were imaged with MRI ex vivo, and histology for astrogliosis and immune reaction was performed.

MAIN RESULTS

For durability, the design of the arrays was modified over three generations to create an array that demonstrated activity up to 29 weeks. SCS arrays showed no significant degradation over a simulated 29 week period of accelerated aging. For stability, the threshold for provoking an EMG rose in the first few weeks and then remained stable out to 16 weeks; the impedance showed a similar rise early with stability thereafter. Spinal cord stimulation strongly enhanced motor cortex potentials throughout. Upon explantation, device performance returned to pre-implant levels, indicating that biotic rather than abiotic processes were the cause of changing metrics. MRI and histology showed that softening SCS produced less tissue deformation than Parylene-C arrays. There was no significant astrogliosis or immune reaction to either type of array.

SIGNIFICANCE

Softening SCS arrays meet the needs for research-grade devices in rats and could be developed into human devices in the future.

A Materials Roadmap to Functional Neural Interface Design

Advancement in neurotechnologies for electrophysiology, neurochemical sensing, neuromodulation, and optogenetics are revolutionizing scientific understanding of the brain while enabling treatments, cures, and preventative measures for a variety of neurological disorders. The grand challenge in neural interface engineering is to seamlessly integrate the interface between neurobiology and engineered technology, to record from and modulate neurons over chronic timescales. However, the biological inflammatory response to implants, neural degeneration, and long-term material stability diminish the quality of interface overtime. Recent advances in functional materials have been aimed at engineering solutions for chronic neural interfaces. Yet, the development and deployment of neural interfaces designed from novel materials have introduced new challenges that have largely avoided being addressed. Many engineering efforts that solely focus on optimizing individual probe design parameters, such as softness or flexibility, downplay critical multi-dimensional interactions between different physical properties of the device that contribute to overall performance and biocompatibility. Moreover, the use of these new materials present substantial new difficulties that must be addressed before regulatory approval for use in human patients will be achievable. In this review, the interdependence of different electrode components are highlighted to demonstrate the current materials-based challenges facing the field of neural interface engineering.

Bubble removal with the use of a vacuum pressure generated by a converging-diverging nozzle

Bubbles are an intrinsic problem in microfluidic devices and they can appear during the initial filling of the device or during operation. This report presents a generalizable technique to extract bubbles from microfluidic networks using an adjacent microfluidic negative pressure network over the entire microfluidic channel network design. We implement this technique by superimposing a network of parallel microchannels with a vacuum microfluidic channel and characterize the bubble extraction rates as a function of negative pressure applied. In addition, we generate negative pressure via a converging-diverging (CD) nozzle, which only requires inlet gas pressure to operate. Air bubbles generated during the initial liquid filling of the microfluidic network are removed within seconds and their volume extraction rate is calculated. This miniaturized vacuum source can achieve a vacuum pressure of 7.23 psi which corresponds to a bubble extraction rate of 9.84 pL/s, in the microfluidic channels we characterized. Finally, as proof of concept it is shown that the bubble removal system enables bubble removal on difficult to fill microfluidic channels such as circular or triangular shaped channels. This method can be easily integrated into many microfluidic experimental protocols.

Accelerated life-test methods and results for implantable electronic devices with adhesive encapsulation

We have developed and applied new methods to estimate the functional life of miniature, implantable, wireless electronic devices that rely on non-hermetic, adhesive encapsulants such as epoxy. A comb pattern board with a high density of interdigitated electrodes (IDE) could be used to detect incipient failure from water vapor condensation. Inductive coupling of an RF magnetic field was used to provide DC bias and to detect deterioration of an encapsulated comb pattern. Diodes in the implant converted part of the received energy into DC bias on the comb pattern. The capacitance of the comb pattern forms a resonant circuit with the inductor by which the implant receives power. Any moisture affects both the resonant frequency and the Q-factor of the resonance of the circuitry, which was detected wirelessly by its effects on the coupling between two orthogonal RF coils placed around the device. Various defects were introduced into the comb pattern devices to demonstrate sensitivity to failures and to correlate these signals with visual inspection of failures. Optimized encapsulation procedures were validated in accelerated life tests of both comb patterns and a functional neuromuscular stimulator under development. Strong adhesive bonding between epoxy and electronic circuitry proved to be necessary and sufficient to predict 1 year packaging reliability of 99.97% for the neuromuscular stimulator.

Facile modulation of cell adhesion to a poly(ethylene glycol) diacrylate film with incorporation of polystyrene nano-spheres

Poly(ethylene glycol) diacrylate (PEGDA) is a common hydrogel that has been actively investigated for various tissue engineering applications owing to its biocompatibility and excellent mechanical properties. However, the native PEGDA films are known for their bio-inertness which can hinder cell adhesion, thereby limiting their applications in tissue engineering and biomedicine. Recently, nano composite technology has become a particularly hot topic, and has led to the development of new methods for delivering desired properties to nanomaterials. In this study, we added polystyrene nano-spheres (PS) into a PEGDA solution to synthesize a nano-composite film and evaluated its characteristics. The experimental results showed that addition of the nanospheres to the PEGDA film not only resulted in modification of the mechanical properties and surface morphology but further improved the adhesion of cells on the film. The tensile modulus showed clear dependence on the addition of PS, which enhanced the mechanical properties of the PEGDA-PS film. We attribute the high stiffness of the hybrid hydrogel to the formation of additional cross-links between polymeric chains and the nano-sphere surface in the network. The effect of PS on cell adhesion and proliferation was evaluated in L929 mouse fibroblast cells that were seeded on the surface of various PEGDA-PS films. Cells density increased with a larger PS concentration, and the cells displayed a spreading morphology on the hybrid films, which promoted cell proliferation. Impressively, cellular stiffness could also be modulated simply by tuning the concentration of nano-spheres. Our results indicate that the addition of PS can effectively tailor the physical and biological properties of PEGDA as well as the mechanical properties of cells, with benefits for biomedical and biotechnological applications.

Aptamer-based Field-Effect Biosensor for Tenofovir Detection

During medical treatment it is critical to maintain the circulatory concentration of drugs within their therapeutic range. A novel biosensor is presented in this work to address the lack of a reliable point-of-care drug monitoring system in the market. The biosensor incorporates high selectivity and sensitivity by integrating aptamers as the recognition element and field-effect transistors as the signal transducer. The drug tenofovir was used as a model small molecule. The biointerface of the sensor is a binary self-assembled monolayer of specific thiolated aptamer and 6-mercapto-1-hexanol (MCH), whose ratio was optimized by electrochemical impedance spectroscopy measurements to enhance the sensitivity towards the specific target. Surface plasmon resonance, performed under different buffer conditions, shows optimum specific and little non-specific binding in phosphate buffered saline. The dose-response behavior of the field-effect biosensor presents a linear range between 1 nM and 100 nM of tenofovir and a limit of detection of 1.2 nM. Two non-specific drugs and one non-specific aptamer, tested as stringent control candidates, caused negligible responses. The applications were successfully extended to the detection of the drug in human serum. As demonstrated by impedance measurements, the aptamer-based sensors can be used for real-time drug monitoring.

High-Throughput Fabrication and Modular Assembly of 3D Heterogeneous Microscale Tissues

3D hydrogel microstructures that encapsulate cells have been used in broad applications in microscale tissue engineering, personalized drug screening, and regenerative medicine. Recent technological advances in microstructure assembly, such as bioprinting, magnetic assembly, microfluidics, and acoustics, have enabled the construction of designed 3D tissue structures with spatially organized cells in vitro. However, a bottleneck exists that still hampers the application of microtissue structures, due to a lack of techniques that combined high-throughput fabrication and flexible assembly. Here, a versatile method for fabricating customized microstructures and reorganizing building blocks composed of functional components into a combined single geometric shape is demonstrated. The arbitrary microstructures are dynamically synthesized in a microfluidic device and then transferred to an optically induced electrokinetics chip for manipulation and assembly. Moreover, building blocks containing different cells can be arranged into a desired geometry with specific shape and size, which can be used for microscale tissue engineering.

Quantification of Type, Timing, and Extent of Cell Body and Nucleus Deformations Caused by the Dimensions and Hydrophilicity of Square Prism Micropillars

Novel digital analysis strategies are developed for the quantification of changes in the cytoskeletal and nuclear morphologies of mesenchymal stem cells cultured on micropillars. Severe deformations of nucleus and distinct conformational changes of cell body ranging from extensive elongation to branching are visualized and quantified. These deformations are caused mainly by the dimensions and hydrophilicity of the micropillars.

A method for measuring the attachment strength of the cestode Hymenolepis diminuta to the rat intestine

A unique adaptation of many internal parasites of mammals is their ability to stay in the intestine for extended periods of time and resist the normal peristaltic movements and forces that push and expel material. To better understand parasite adhesion behaviour and replicate their attachment method in medical devices, an experiment was designed and performed using the rat tapeworm, Hymenolepis diminuta. The experiment employed a tensile test machine and a digital scale and was designed to calculate the attachment strength of the scolex to the mucosa through the change of the value of the digital scale during the tensile test. The attachment force of H. diminuta is 0.021 ± 0.011 g. This method could be applied in studies of parasite biomechanics and the results may help medical device researchers to better mimic the unique functional morphology of this species of parasite.

Microenvironment complexity and matrix stiffness regulate breast cancer cell activity in a 3D in vitro model

Three-dimensional (3D) cell cultures represent fundamental tools for the comprehension of cellular phenomena both in normal and in pathological conditions. In particular, mechanical and chemical stimuli play a relevant role on cell fate, cancer onset and malignant evolution. Here, we use mechanically-tuned alginate hydrogels to study the role of substrate elasticity on breast adenocarcinoma cell activity. The hydrogel elastic modulus (E) was measured via atomic force microscopy (AFM) and a remarkable range (150-4000 kPa) was obtained. A breast cancer cell line, MCF-7, was seeded within the 3D gels, on standard Petri and alginate-coated dishes (2D controls). Cells showed dramatic morphological differences when cultured in 3D versus 2D, exhibiting a flat shape in both 2D conditions, while maintaining a circular, spheroid-organized (cluster) conformation within the gels, similar to those in vivo. Moreover, we observed a strict correlation between cell viability and substrate elasticity; in particular, the number of MCF-7 cells decreased constantly with increasing hydrogel elasticity. Remarkably, the highest cellular proliferation rate, associated with the formation of cell clusters, occurred at two weeks only in the softest hydrogels (E = 150-200 kPa), highlighting the need to adopt more realistic and a priori defined models for in vitro cancer studies.

Polymerase chain reaction in microfluidic devices

The invention of the polymerase chain reaction (PCR) has caused a revolution in molecular biology, giving access to a method of amplifying deoxyribonucleic acid (DNA) molecules across several orders of magnitude. Since the first application of PCR in a microfluidic device was developed in 1998, an increasing number of researchers have continued the development of microfluidic PCR systems. In this review, we introduce recent developments in microfluidic-based space and time domain devices as well as discuss various designs integrated with multiple functions for sample preparation and detection. The development of isothermal nucleic acid amplification and digital PCR microfluidic devices within the last five years is also highlighted. Furthermore, we introduce various commercial microfluidic PCR devices.

Bio-syncretic tweezers actuated by microorganisms: modeling and analysis

Advancements in micro-/nano-technology have led to the development of micro-manipulators. However, some challenges remain; for instance, the efficiency, precision and flexibility of micro-manipulators restrain their applications. This paper proposes a bio-tweezer system to flexibly manipulate micro-objects with bio-actuation via local light-induced high-concentration microorganisms in two different manipulation modes: light-spot induced mode and geometric shape-induced mode. Depending on the shape of micro-objects, either 2-dimensional translation or 1-dimensional rotation can be achieved. Based on the Langevin equation, a mathematical model considering both hydrodynamics and mimicked Brownian motion is proposed to analyze the bio-manipulation performance of the microorganisms; the model was validated by experiments to translate micro-particles in a two-dimensional plane and to rotate a micro-gear structure around its axis. This paper will aid in the development of micro-manipulators and the quantitative understanding of micro-/nano-manipulation actuated by microorganisms.

Advances in digital polymerase chain reaction (dPCR) and its emerging biomedical applications

Since the invention of polymerase chain reaction (PCR) in 1985, PCR has played a significant role in molecular diagnostics for genetic diseases, pathogens, oncogenes and forensic identification. In the past three decades, PCR has evolved from end-point PCR, through real-time PCR, to its current version, which is the absolute quantitive digital PCR (dPCR). In this review, we first discuss the principles of all key steps of dPCR, i.e., sample dispersion, amplification, and quantification, covering commercialized apparatuses and other devices still under lab development. We highlight the advantages and disadvantages of different technologies based on these steps, and discuss the emerging biomedical applications of dPCR. Finally, we provide a glimpse of the existing challenges and future perspectives for dPCR.

Structured light enables biomimetic swimming and versatile locomotion of photoresponsive soft microrobots

Microorganisms move in challenging environments by periodic changes in body shape. In contrast, current artificial microrobots cannot actively deform, exhibiting at best passive bending under external fields. Here, by taking advantage of the wireless, scalable and spatiotemporally selective capabilities that light allows, we show that soft microrobots consisting of photoactive liquid-crystal elastomers can be driven by structured monochromatic light to perform sophisticated biomimetic motions. We realize continuum yet selectively addressable artificial microswimmers that generate travelling-wave motions to self-propel without external forces or torques, as well as microrobots capable of versatile locomotion behaviours on demand. Both theoretical predictions and experimental results confirm that multiple gaits, mimicking either symplectic or antiplectic metachrony of ciliate protozoa, can be achieved with single microswimmers. The principle of using structured light can be extended to other applications that require microscale actuation with sophisticated spatiotemporal coordination for advanced microrobotic technologies.

Approaches to a cortical vision prosthesis: implications of electrode size and placement

OBJECTIVE

In order to move forward with the development of a cortical vision prosthesis, the critical issues in the field must be identified.

APPROACH

To begin this process, we performed a brief review of several different cortical and retinal stimulation techniques that can be used to restore vision.

MAIN RESULTS

Intracortical microelectrodes and epicortical macroelectrodes have been evaluated as the basis of a vision prosthesis. We concluded that an important knowledge gap necessitates an experimental in vivo performance evaluation of microelectrodes placed on the surface of the visual cortex. A comparison of the level of vision restored by intracortical versus epicortical microstimulation is necessary. Because foveal representation in the primary visual cortex involves more cortical columns per degree of visual field than does peripheral vision, restoration of foveal vision may require a large number of closely spaced microelectrodes. Based on previous studies of epicortical macrostimulation, it is possible that stimulation via surface microelectrodes could produce a lower spatial resolution, making them better suited for restoring peripheral vision.

SIGNIFICANCE

The validation of epicortical microstimulation in addition to the comparison of epicortical and intracortical approaches for vision restoration will fill an important knowledge gap and may have important implications for surgical strategies and device longevity. It is possible that the best approach to vision restoration will utilize both epicortical and intracortical microstimulation approaches, applying them appropriately to different visual representations in the primary visual cortex.

Loop-Mediated Isothermal Amplification (LAMP) for Rapid Detection and Quantification of Dehalococcoides Biomarker Genes in Commercial Reductive Dechlorinating Cultures KB-1 and SDC-9

Real-time quantitative PCR (qPCR) protocols specific to the reductive dehalogenase (RDase) genes vcrA, bvcA, and tceA are commonly used to quantify Dehalococcoides spp. in groundwater from chlorinated solvent-contaminated sites. In this study, loop-mediated isothermal amplification (LAMP) was developed as an alternative approach for the quantification of these genes. LAMP does not require a real-time thermal cycler (i.e., amplification is isothermal), allowing the method to be performed using less-expensive and potentially field-deployable detection devices. Six LAMP primers were designed for each of three RDase genes (vcrA, bvcA, and tceA) using Primer Explorer V4. The LAMP assays were compared to conventional qPCR approaches using plasmid standards, two commercially available bioaugmentation cultures, KB-1 and SDC-9 (both contain Dehalococcoides species). DNA was extracted over a growth cycle from KB-1 and SDC-9 cultures amended with trichloroethene and vinyl chloride, respectively. All three genes were quantified for KB-1, whereas only vcrA was quantified for SDC-9. A comparison of LAMP and qPCR using standard plasmids indicated that quantification results were similar over a large range of gene concentrations. In addition, the quantitative increase in gene concentrations over one growth cycle of KB-1 and SDC-9 using LAMP was comparable to that of qPCR. The developed LAMP assays for vcrA and tceA genes were validated by comparing quantification on the Gene-Z handheld platform and a real-time thermal cycler using DNA isolated from eight groundwater samples obtained from an SDC-9-bioaugmented site (Tulsa, OK). These assays will be particularly useful at sites subject to bioaugmentation with these two commonly used Dehalococcoides species-containing cultures.

Regulation of breast cancer cell behaviours by the physical microenvironment constructed via projection microstereolithography

A considerable number of studies have examined how intrinsic factors regulate breast cancer cell behaviours; however, physical microenvironmental cues may also modulate cellular morphology, proliferation, and migration and mechanical properties.