Thiol-ene-epoxy thermoset for low-temperature bonding to biofunctionalized microarray surfaces

Performance and biocompatibility of OSTEMER 322 in cell-based microfluidic applications

The Off-Stoichiometry Thiol-ene and Epoxy (OSTE+) polymer technology has been increasingly utilised in the field of microfluidics and lab-on-a-chip applications. However, the impact of OSTEMER polymers, specifically the OSTEMER 322 formulation, on cell viability has remained limited. In this work, we thoroughly explored the biocompatibility of this commercial OSTEMER formulation, along with various surface modifications, through a broad range of cell types, from fibroblasts to epithelial cells. We employed cell viability and confluence assays to evaluate the performance of the material and its modified variants in cell culturing. The properties of the pristine and modified OSTEMER were also investigated using surface characterization methods including contact angle, zeta potential, and X-ray photoelectron spectroscopy. Mass spectrometry analysis confirmed the absence of leaching constituents from OSTEMER, indicating its safety for cell-based applications. Our findings demonstrated that cell viability on OSTEMER surfaces is sufficient for typical cell culture experiments, suggesting OSTEMER 322 is a suitable material for a variety of cell-based assays in microfluidic devices.

Proteomics Methodologies: The Search of Protein Biomarkers Using Microfluidic Systems Coupled to Mass Spectrometry

Protein biomarkers have been the subject of intensive studies as a target for disease diagnostics and monitoring. Indeed, biomarkers have been extensively used for personalized medicine. In biological samples, these biomarkers are most often present in low concentrations masked by a biologically complex proteome (e.g., blood) making their detection difficult. This complexity is further increased by the needs to detect proteoforms and proteome complexity such as the dynamic range of compound concentrations. The development of techniques that simultaneously pre-concentrate and identify low-abundance biomarkers in these proteomes constitutes an avant-garde approach to the early detection of pathologies. Chromatographic-based methods are widely used for protein separation, but these methods are not adapted for biomarker discovery, as they require complex sample handling due to the low biomarker concentration. Therefore, microfluidics devices have emerged as a technology to overcome these shortcomings. In terms of detection, mass spectrometry (MS) is the standard analytical tool given its high sensitivity and specificity. However, for MS, the biomarker must be introduced as pure as possible in order to avoid chemical noise and improve sensitivity. As a result, microfluidics coupled with MS has become increasingly popular in the field of biomarker discovery. This review will show the different approaches to protein enrichment using miniaturized devices and the importance of their coupling with MS.

Recent Advances in Thermoplastic Microfluidic Bonding

Microfluidics is a multidisciplinary technology with applications in various fields, such as biomedical, energy, chemicals and environment. Thermoplastic is one of the most prominent materials for polymer microfluidics. Properties such as good mechanical rigidity, organic solvent resistivity, acid/base resistivity, and low water absorbance make thermoplastics suitable for various microfluidic applications. However, bonding of thermoplastics has always been challenging because of a wide range of bonding methods and requirements. This review paper summarizes the current bonding processes being practiced for the fabrication of thermoplastic microfluidic devices, and provides a comparison between the different bonding strategies to assist researchers in finding appropriate bonding methods for microfluidic device assembly.

Novel, Emerging Chip Models of the Blood-Brain Barrier and Future Directions

The use of microfluidic chips is now allowing for more advanced modelling of the blood-brain barrier (BBB) in vitro, recapitulating heterotypic interactions, 3D architecture, and physiological flow. This chapter will give an introduction to these new technologies and how they are being applied to model the BBB and neurovascular unit (NVU). A foundational understanding of the fluid dynamics germane to the effective use of these chips will be set and an overview of how physical phenomena at the microscale can be exploited to enable new possibilities to control the cell culture environment. The four main approaches to construct microfluidic blood vessel mimetics will be discussed with examples of how these techniques are being applied to model the BBB and more recently to study specific neurovascular disease processes. Finally, practical guidance will be given for researchers wishing to adopt these new techniques along with a summary of the challenges, limitations faced, and new opportunities opened up by these advanced cell culture systems.

Sorption of Neuropsychopharmaca in Microfluidic Materials for In Vitro Studies

Sorption (i.e., adsorption and absorption) of small-molecule compounds to polydimethylsiloxane (PDMS) is a widely acknowledged phenomenon. However, studies to date have largely been conducted under atypical conditions for microfluidic applications (lack of perfusion, lack of biological fluids, etc.), especially considering biological studies such as organs-on-chips where small-molecule sorption poses the largest concern. Here, we present an in-depth study of small-molecule sorption under relevant conditions for microphysiological systems, focusing on a standard geometry for biological barrier studies that find application in pharmacokinetics. We specifically assess the sorption of a broad compound panel including 15 neuropsychopharmaca at in vivo concentration levels. We consider devices constructed from PDMS as well as two material alternatives (off-stoichiometry thiol-ene-epoxy, or tape/polycarbonate laminates). Moreover, we study the much neglected impact of peristaltic pump tubing, an essential component of the recirculating systems required to achieve in vivo-like perfusion shear stresses. We find that the choice of the device material does not have a significant impact on the sorption behavior in our barrier-on-chip-type system. Our PDMS observations in particular suggest that excessive compound sorption observed in prior studies is not sufficiently described by compound hydrophobicity or other suggested predictors. Critically, we show that sorption by peristaltic tubing, including the commonly utilized PharMed BPT, dominates over device sorption even on an area-normalized basis, let alone at the typically much larger tubing surface areas. Our findings highlight the importance of validating compound dosages in organ-on-chip studies, as well as the need for considering tubing materials with equal or higher care than device materials.

Photoclick Chemistry: A Bright Idea

At its basic conceptualization, photoclick chemistry embodies a collection of click reactions that are performed via the application of light. The emergence of this concept has had diverse impact over a broad range of chemical and biological research due to the spatiotemporal control, high selectivity, and excellent product yields afforded by the combination of light and click chemistry. While the reactions designated as "photoclick" have many important features in common, each has its own particular combination of advantages and shortcomings. A more extensive realization of the potential of this chemistry requires a broader understanding of the physical and chemical characteristics of the specific reactions. This review discusses the features of the most frequently employed photoclick reactions reported in the literature: photomediated azide-alkyne cycloadditions, other 1,3-dipolarcycloadditions, Diels-Alder and inverse electron demand Diels-Alder additions, radical alternating addition chain transfer additions, and nucleophilic additions. Applications of these reactions in a variety of chemical syntheses, materials chemistry, and biological contexts are surveyed, with particular attention paid to the respective strengths and limitations of each reaction and how that reaction benefits from its combination with light. Finally, challenges to broader employment of these reactions are discussed, along with strategies and opportunities to mitigate such obstacles.

Lung on a Chip Development from Off-Stoichiometry Thiol-Ene Polymer

Current in vitro models have significant limitations for new respiratory disease research and rapid drug repurposing. Lung on a chip (LOAC) technology offers a potential solution to these problems. However, these devices typically are fabricated from polydimethylsiloxane (PDMS), which has small hydrophobic molecule absorption, which hinders the application of this technology in drug repurposing for respiratory diseases. Off-stoichiometry thiol–ene (OSTE) is a promising alternative material class to PDMS. Therefore, this study aimed to test OSTE as an alternative material for LOAC prototype development and compare it to PDMS. We tested OSTE material for light transmission, small molecule absorption, inhibition of enzymatic reactions, membrane particle, and fluorescent dye absorption. Next, we microfabricated LOAC devices from PDMS and OSTE, functionalized with human umbilical vein endothelial cell (HUVEC) and A549 cell lines, and analyzed them with immunofluorescence. We demonstrated that compared to PDMS, OSTE has similar absorption of membrane particles and effect on enzymatic reactions, significantly lower small molecule absorption, and lower light transmission. Consequently, the immunofluorescence of OSTE LOAC was significantly impaired by OSTE optical properties. In conclusion, OSTE is a promising material for LOAC, but optical issues should be addressed in future LOAC prototypes to benefit from the material properties.

Advances in microfluidic in vitro systems for neurological disease modeling

Neurological disorders are the leading cause of disability and the second largest cause of death worldwide. Despite significant research efforts, neurology remains one of the most failure-prone areas of drug development. The complexity of the human brain, boundaries to examining the brain directly in vivo, and the significant evolutionary gap between animal models and humans, all serve to hamper translational success. Recent advances in microfluidic in vitro models have provided new opportunities to study human cells with enhanced physiological relevance. The ability to precisely micro-engineer cell-scale architecture, tailoring form and function, has allowed for detailed dissection of cell biology using microphysiological systems (MPS) of varying complexities from single cell systems to "Organ-on-chip" models. Simplified neuronal networks have allowed for unique insights into neuronal transport and neurogenesis, while more complex 3D heterotypic cellular models such as neurovascular unit mimetics and "Organ-on-chip" systems have enabled new understanding of metabolic coupling and blood-brain barrier transport. These systems are now being developed beyond MPS toward disease specific micro-pathophysiological systems, moving from "Organ-on-chip" to "Disease-on-chip." This review gives an outline of current state of the art in microfluidic technologies for neurological disease research, discussing the challenges and limitations while highlighting the benefits and potential of integrating technologies. We provide examples of where such toolsets have enabled novel insights and how these technologies may empower future investigation into neurological diseases.

Thiol-Ene Based Polymers as Versatile Materials for Microfluidic Devices for Life Sciences Applications

While there is a steady growth in the number of microfluidics applications, the search for an optimal material that delivers the diverse characteristics needed for the numerous tasks is still nowhere close to being settled. Often overlooked and still underrepresented, the thiol-ene family of polymer materials has an enormous potential for applications in organs-on-a-chip, droplet productions, microanalytics, and point of care testing. In this review, the main characteristics of the thiol-ene materials are given, and advantages and drawbacks with respect to their potential in microfluidic chip fabrication are critically assessed. Select applications, which exploit the versatility of the thiol-ene polymers, are presented and discussed. It is concluded that, in particular, the rapid prototyping possibility combined with the material's resulting mechanical strength, solvent resistance, and biocompatibility, as well as the inherently easy surface functionalization, are strong factors to make thiol-ene polymers strong contenders for promising future materials for many biological, clinical, and technical lab-on-a-chip applications.

A compression transmission device for the evaluation of bonding strength of biocompatible microfluidic and biochip materials and systems

Bonding of a variety of inorganic and organic polymers as multi-layered structures is one of the main challenges for biochip production even to date, since the chemical nature of these materials often does not allow easy and straight forward bonding and proper sealing. After selection of an appropriate method to bond the chosen materials to form a complex biochip, function and stability of bonding either requires qualitative burst tests or expensive mechanical multi-test stations, that often do not have the right adaptors to clamp biochip slides without destruction. Therefore, we have developed a simple and inexpensive bonding test based on 3D printed transmission elements that translate compressive forces via manual compression, hand press or hydraulic press compression into shear and tensile force. Mechanical stress simulations showed that design of the bonding geometry and size must be considered for bonding tests since the stress distribution thus bonding strength heavily varies with size but also with geometry. We demonstrate the broad applicability of our 3D printed bonding test system by testing the most frequent bonding strategies in combination with the respective most frequently used biochip material in a force-to-failure study. All evaluated materials are biocompatible and used in cell-based biochip devices. This study is evaluating state-of-the-art bonding approaches used for sealing of microfluidic biochips including adhesive bonding, plasma bonding, solvent bonding as well as bonding mediated by amino-silane monolayers or even functional thiol-ene epoxy biochip materials that obviate intermediate adhesive layers.

Magnetic micropump embedded in contact lens for on-demand drug delivery

In this paper, we report a thin magnetic micropump embedded in contact lens, which is capable of on-demand one-directional drug delivery. The proposed micropump can be actuated by the external magnetic field whenever needed without the need of battery. A micro check valve was integrated with the micropump for one-directional drug delivery from the micropump to the post-lens tear film. With actuation of the external magnetic field, the micro check valve is opened, and on-demand drug release can be realized. On the contrary, without an external magnetic field, the micro check valve is closed, and the undesired drug diffusion can be prevented. Through the control of the strength and the frequency of the magnetic field pulse, on-demand drug release and controlled dose can be realized.