Modeling of three-dimensional innervated epidermal like-layer in a microfluidic chip-based coculture system

Advances in Microengineered Platforms for Skin Research

The skin plays a critical role in human physiology, acting both as a barrier to environmental insults and as a window to environmental stimuli. Disruption of this homeostasis leads to numerous skin disorders. Human and animal skin differ significantly, limiting the translational potential of animal-based investigations to advance therapeutics to human skin diseases. Hence, there is a critical need for physiologically relevant human skin models to explore novel treatment strategies. Recent advances in microfluidic technologies now allow design and generation of organ-on-chip devices that mimic critical features of tissue architecture. Skin-on-a-chip and microfluidic platforms hold promise as useful models for diverse dermatology applications. Compared with traditional in vitro models, microfluidic platforms offer improved control of fluid flow, which in turn allows precise manipulation of cell and molecular distribution. These properties enable the generation of multilayered in vitro models that mimic human skin structure while simultaneously offering superior control over nutrient and drug distribution. Researchers have used microfluidic platforms for a variety of applications in skin research, including epidermal-dermal cellular crosstalk, cell migration, mechanobiology, microbiome-immune response interactions, vascular biology, and wound healing. In this review, we comprehensively review state-of-the-art microfluidic models for skin research. We discuss the challenges and promise of current skin-on-a-chip technologies and provide a roadmap for future research in this active field.

Infrared imaging with visible light in microfluidic devices: the water absorption barrier

Infrared spectro-microscopy is a powerful technique for analysing chemical maps of cells and tissues for biomedical and clinical applications, yet the strong water absorption in the mid-infrared region is a challenge to overcome, as it overlaps with the spectral fingerprints of biological components. Microfluidic chips offer ultimate control over the water layer thickness and are increasingly used in infrared spectro-microscopy. However, the actual impact of the water layer thickness on the instrument's performance is often left to the experimentalist's intuition and the peculiarities of specific instruments. Aiming to experimentally test the amount of absorption introduced by water with varying layer thicknesses, we fabricated a set of microfluidic devices with three controlled chamber thicknesses, each comprising a simple test pattern made of a well-known photoresist SU-8. We employed two infrared spectro-microscopy methods for measurements. The first method involves using a standard FTIR microscope with a benchtop infrared light source. The second method is a quantum infrared microscopy technique, where infrared imaging is achieved by detecting correlated photons in the visible range. We demonstrated that both methods enable the measurement of the absorption spectrum in the mid-IR region, even in the presence of up to a 30 μm thick water layer on top of a sample pattern. Additionally, the Q-IR technique offers practical advantages over synchrotron-based FTIR, such as reduced complexity, cost, and ease of operation.

Control of Tissue Strain Is Essential for Enhanced Dermal Innervation in the Three-Dimensional Skin Engineering

Engineered skin models with sensory innervation are a growing and challenging field of research aimed at applications in regenerative medicine, biosensing, and drug screening. Researchers are attempting to fabricate innervated skin tissues using collagen sponges, cell culture inserts, and microfluidic devices to partially mimic the layered structure of the skin. However, innervation of the full-thickness skin model has not yet been achieved. Here, using the anchoring culture device we previously reported, which is a powerful tool to construct a full-thickness three-dimensional (3D) skin model with balanced tissue contraction forces, we drastically improved dermal layer innervation using a composite hydrogel of collagen and Matrigel (Coll:MG). To determine the preferable hydrogel matrix for neurite extension in the 3D skin construct, DRG neural spheroids were placed at the bottom of the dermal layer composed of various hydrogel scaffold, including type I collagen from different origins (dermis or tendon) and Coll:MG composite hydrogel with different compositions. We showed that the Coll:MG (2:1) composite hydrogel significantly increased vertical neurite extension in the dermal layer, concomitant with the reduced tissue shrinkage during the culture. In contrast, in the collagen-only hydrogel, neurite extension occurred mostly in the horizontal direction, and tissues sometimes detached from the anchors due to significant shrinkage, indicating that tissue shrinkage may affect the direction of neurite extension. To exemplify this idea, 3D skin constructed in the device was partially detached from the anchors to comply with the cell-induced tissue shrinkage and reduce the strain on the tissue. The data showed that the partial allowance of in-plane tissue strain remarkably increased vertical neurite extension compared to the control cultures. Collectively, our results strongly suggest that neurite extension angles can be modulated by adjusting the tissue strain during the culture. Our findings highlight the importance of controlling tissue strain for the advancement of an innervated skin model.

Interfacial engineering for biomolecule immobilisation in microfluidic devices

Microfluidic devices are used for various applications in biology and medicine. From on-chip modelling of human organs for drug screening and fast and straightforward point-of-care (POC) detection of diseases to sensitive biochemical analysis, these devices can be custom-engineered using low-cost techniques. The microchannel interface is essential for these applications, as it is the interface of immobilised biomolecules that promote cell capture, attachment and proliferation, sense analytes and metabolites or provide enzymatic reaction readouts. However, common microfluidic materials do not facilitate the stable immobilisation of biomolecules required for relevant applications, making interfacial engineering necessary to attach biomolecules to the microfluidic surfaces. Interfacial engineering is performed through various immobilisation mechanisms and surface treatment techniques, which suitably modify the surface properties like chemistry and energy to obtain robust biomolecule immobilisation and long-term storage stability suitable for the final application. In this review, we provide an overview of the status of interfacial engineering in microfluidic devices, covering applications, the role of biomolecules, their immobilisation pathways and the influence of microfluidic materials. We then propose treatment techniques to optimise performance for various biological and medical applications and highlight future areas of development.

Materials-based hair follicle engineering: Basic components and recent advances

The hair follicle (HF) is a significant skin appendage whose primary function is to produce the hair shaft. HFs are a non-renewable resource; skin damage or follicle closure may lead to permanent hair loss. Advances in biomaterials and biomedical engineering enable the feasibility of manipulating the HF-associated cell function for follicle reconstruction via rational design. The regeneration of bioengineered HF addresses the issue of limited resources and contributes to advancements in research and applications in hair loss treatment, HF development, and drug screening. Based on these requirements, this review summarizes the basic and recent advances in hair follicle regulation, including four components: acquisition of stem cells, signaling pathways, materials, and engineering methods. Recent studies have focused on efficiently combining these components and reproducing functionality, which would boost fabrication in HF rebuilding ex vivo, thereby eliminating the obstacles of transplantation into animals to promote mature development.

Modeling neuropathic pain in a dish

The study of pain mechanisms has advanced significantly with the development of innovative in vitro models. This chapter explores those already used in or potentially useful for neuropathic pain research, emphasizing the complementary roles of animal and human cellular models to enhance translational success. Traditional animal models have provided foundational insights into the neurobiology of pain and remain invaluable for understanding complex pain pathways. However, integrating human cellular models addresses the need for better replication of human nociceptors. The chapter details methodologies for culturing rodent and human primary sensory neurons, including isolation and culture techniques, advantages, and limitations. It highlights the application of these models in neuropathic pain research, such as identifying pain-associated receptors and ion channels. Recent advancements in using induced pluripotent stem cell (iPSC)-derived sensory neurons are also discussed. Finally, the chapter explores advanced in vitro models, including 2D co-cultures and 3D organoids, and their implications for studying neuropathic pain. These models offer significant advantages for drug screening and ethical research practices, providing a more accurate representation of human pain pathways and paving the way for innovative therapeutic strategies. Despite challenges such as limited access to viable human tissue and variability between samples, these in vitro models, alongside traditional animal models, are indispensable for advancing our understanding of neuropathic pain and developing effective treatments.

Characterization of AI-enhanced magnetophoretic transistors operating in a tri-axial magnetic field for on-chip bioparticle sorting

We demonstrate two general classes of magnetophoretic transistors, called the "trap" and the "repel-and-collect" transistors, capable of switching single magnetically labeled cells and magnetic particles between different paths in a microfluidic chamber. Compared with prior work on magnetophoretic transistors operating in a two-dimensional in-plane rotating field, the use of a tri-axial magnetic field has the fundamental advantages of preventing particle cluster formation and better syncing of single particles with the general operating clock. We use finite element methods to investigate the energy distribution on the chip surface and to predict the particle behavior at various device geometries. We then fabricate the proposed transistors and compare the experimental results with the simulation predictions. We found that with gate electrical currents of ~ 40 mA for a transistor with proper geometry, complete switching of magnetic particles with diameters in the range of 8-15 μm is achieved. We show that the device is reliable and works well at different magnetic field strengths (50-100 Oe) and frequencies (0.05-0.5 Hz). We also employed an image processing code with a trained convolutional neural network to automate the proposed transistors for identifying and sorting particles with various sizes and magnetic susceptibilities with accuracies higher than 98%. The proposed transistors can be used in designing novel magnetophoretic circuits for important applications in biomedical microdevices and single-cell biology.

In Vitro Models for Peripheral Nerve Regeneration

Peripheral nerve injury (PNI) resulting in lesions is highly prevalent clinically, but current therapeutic approaches fail to provide satisfactory outcomes in many patients. While peripheral nerves have intrinsic regenerative capacity, the regenerative capabilities of peripheral nerves are often insufficient to restore full functionality. This highlights an unmet need for developing more effective strategies to repair damaged peripheral nerves and improve regenerative success. Consequently, researchers are actively exploring a variety of therapeutic strategies, encompassing the local delivery of trophic factors or bioactive molecules, the design of advanced biomaterials that interact with regenerating axons, and augmentation with nerve guidance conduits or complex prostheses. However, clinical translation of these technologies remains limited, emphasizing the need for continued research on peripheral nerve regeneration modalities that can enhance functional restoration. Experimental models that accurately recapitulate key aspects of peripheral nerve injury and repair biology can accelerate therapeutic development by enabling systematic testing of new techniques. Advancing regenerative therapies for PNI requires bridging the gap between basic science discoveries and clinical application. This review discusses different in vitro models of peripheral nerve injury and repair, including their advantages, limitations, and potential applications.

Bioprinted Multi-Composition Array Mimicking Tumor Microenvironments to Evaluate Drug Efficacy with Multivariable Analysis

Current organ-on-a-chip technologies confront limitations in effectively recapitulating the intricate in vivo microenvironments and accommodating diverse experimental conditions on a single device. Here, a novel approach for constructing a multi-composition tumor array on a single microfluidic device, mimicking complex transport phenomena within tumor microenvironments (TMEs) and allowing for simultaneous evaluation of drug efficacy across 12 distinct conditions is presented. The TME array formed by bioprinting on a microfluidic substrate consists of 36 individual TME models, each characterized by one of three different compositions and tested under four varying drug concentrations. Notably, the TME model exhibits precise compartmentalization, fostering the development of self-organized vascular endothelial barriers surrounding breast cancer spheroids affecting substance transport. Multivariable screening and analysis of diverse conditions, including model complexity, replicates, and drug concentrations, within a single microfluidic platform, highlight the synergistic potential of integrating bioprinting with microfluidics to evaluate drug responses across diverse TME conditions comprehensively.

In vitro models for studying implant-associated biofilms - A review from the perspective of bioengineering 3D microenvironments

Biofilm research has grown exponentially over the last decades, arguably due to their contribution to hospital acquired infections when they form on foreign body surfaces such as catheters and implants. Yet, translation of the knowledge acquired in the laboratory to the clinic has been slow and/or often it is not attempted by research teams to walk the talk of what is defined as 'bench to bedside'. We therefore reviewed the biofilm literature to better understand this gap. Our search revealed substantial development with respect to adapting surfaces and media used in models to mimic the clinical settings, however many of the in vitro models were too simplistic, often discounting the composition and properties of the host microenvironment and overlooking the biofilm-implant-host interactions. Failure to capture the physiological growth conditions of biofilms in vivo results in major differences between lab-grown- and clinically-relevant biofilms, particularly with respect to phenotypic profiles, virulence, and antimicrobial resistance, and they essentially impede bench-to-bedside translatability. In this review, we describe the complexity of the biological processes at the biofilm-implant-host interfaces, discuss the prerequisite for the development and characterization of biofilm models that better mimic the clinical scenario, and propose an interdisciplinary outlook of how to bioengineer biofilms in vitro by converging tissue engineering concepts and tools.

Towards the development of sensation-enabled skin substitutes

Recent advances in cell and biofabrication technologies have contributed to the development of complex human organs. In particular, several skin substitutes are being generated using tissue engineering and regenerative medicine (TERM) technologies. However, recent studies mainly focus on the restoration of the dermis and epidermis layers rather than the regeneration of a fully functional innervated skin organ. Innervation is a critical step in functional tissue repair which has been overlooked in the current TERM studies. In the current study, we highlight the importance of sensation in the skin as the largest sensory organ in the human body. In large non-healing skin wounds, the skin sensation is severely diminished or completely lost and ultimately lead to chronic pain and wound healing process interruption. Current therapeutics for restoring skin sensation after trauma are limited. Recent regenerative medicine-based studies could successfully induce neural networks in skin substitutes, but the effectiveness of these technologies in enhancing sensory capability needs further investigation.

Modeling of the brain-lung axis using organoids in traumatic brain injury: an updated review

Clinical outcome after traumatic brain injury (TBI) is closely associated conditions of other organs, especially lungs as well as degree of brain injury. Even if there is no direct lung damage, severe brain injury can enhance sympathetic tones on blood vessels and vascular resistance, resulting in neurogenic pulmonary edema. Conversely, lung damage can worsen brain damage by dysregulating immunity. These findings suggest the importance of brain-lung axis interactions in TBI. However, little research has been conducted on the topic. An advanced disease model using stem cell technology may be an alternative for investigating the brain and lungs simultaneously but separately, as they can be potential candidates for improving the clinical outcomes of TBI.In this review, we describe the importance of brain-lung axis interactions in TBI by focusing on the concepts and reproducibility of brain and lung organoids in vitro. We also summarize recent research using pluripotent stem cell-derived brain organoids and their preclinical applications in various brain disease conditions and explore how they mimic the brain-lung axis. Reviewing the current status and discussing the limitations and potential perspectives in organoid research may offer a better understanding of pathophysiological interactions between the brain and lung after TBI.

Review: 3D cell models for organ-on-a-chip applications

Two-dimensional (2D) cultures do not fully reflect the human organs' physiology and the real effectiveness of the used therapy. Therefore, three-dimensional (3D) models are increasingly used in bioanalytical science. Organ-on-a-chip systems are used to obtain cellular in vitro models, better reflecting the human body's in vivo characteristics and allowing us to obtain more reliable results than standard preclinical models. Such 3D models can be used to understand the behavior of tissues/organs in response to selected biophysical and biochemical factors, pathological conditions (the mechanisms of their formation), drug screening, or inter-organ interactions. This review characterizes 3D models obtained in microfluidic systems. These include spheroids/aggregates, hydrogel cultures, multilayers, organoids, or cultures on biomaterials. Next, the methods of formation of different 3D cultures in Organ-on-a-chip systems are presented, and examples of such Organ-on-a-chip systems are discussed. Finally, current applications of 3D cell-on-a-chip systems and future perspectives are covered.

Hybrid Printing of Fully Integrated Microfluidic Devices for Biosensing

The advent of 3D printing has facilitated the rapid fabrication of microfluidic devices that are accessible and cost-effective. However, it remains a challenge to fabricate sophisticated microfluidic devices with integrated structural and functional components due to limited material options of existing printing methods and their stringent requirement on feedstock material properties. Here, a multi-materials multi-scale hybrid printing method that enables seamless integration of a broad range of structural and functional materials into complex devices is reported. A fully printed and assembly-free microfluidic biosensor with embedded fluidic channels and functionalized electrodes at sub-100 µm spatial resolution for the amperometric sensing of lactate in sweat is demonstrated. The sensors present a sensitive response with a limit of detection of 442 nm and a linear dynamic range of 1-10 mm, which are performance characteristics relevant to physiological levels of lactate in sweat. The versatile hybrid printing method offers a new pathway toward facile fabrication of next-generation integrated devices for broad applications in point-of-care health monitoring and sensing.

A layered cancer-on-a-chip system for anticancer drug screening and disease modeling

Recent advances in the development of microfluidic systems for the culture of complex and three-dimensional cell, tissue, and organ models allow their use in toxicity studies and mimicking many diseases. These types of in vitro models are important because of the huge advantages over standard two-dimensional cell cultures: better mimicking of in vivo conditions and more reliable response to the tested drugs. This report presents a new approach to modeling skin cancer (melanoma-on-a-chip) and breast cancer (breast cancer-on-a-chip) using the microfluidic systems. We designed a microfluidic device to co-culture cancer cells with non-malignant cells, which are the main component of the cancer microenvironment. In the construction of the microsystem, we used a scaffold in the form of a porous membrane made of poly(ethylene terephthalate), which enables the regular and reproducible arrangement of cells in the culture and maintains intercellular communication. To demonstrate the functionality of the microsystem, we used it to analyze the effectiveness of photodynamic therapy in the treatment of melanoma and chemotherapy in the treatment of breast cancer. The developed microsystem can be successfully used to model cancer diseases, especially with a layered arrangement of cells in the cancerous tissue, such as melanoma, ductal breast cancer, or breast cancer metastases to the skin.

Report of the Assay Guidance Workshop on 3-Dimensional Tissue Models for Antiviral Drug Development

The National Center for Advancing Translational Sciences (NCATS) Assay Guidance Manual (AGM) Workshop on 3D Tissue Models for Antiviral Drug Development, held virtually on 7-8 June 2022, provided comprehensive coverage of critical concepts intended to help scientists establish robust, reproducible, and scalable 3D tissue models to study viruses with pandemic potential. This workshop was organized by NCATS, the National Institute of Allergy and Infectious Diseases, and the Bill and Melinda Gates Foundation. During the workshop, scientific experts from academia, industry, and government provided an overview of 3D tissue models' utility and limitations, use of existing 3D tissue models for antiviral drug development, practical advice, best practices, and case studies about the application of available 3D tissue models to infectious disease modeling. This report includes a summary of each workshop session as well as a discussion of perspectives and challenges related to the use of 3D tissues in antiviral drug discovery.

Fabrication and Validation of a 3D Portable PEGDA Microfluidic Chip for Visual Colorimetric Detection of Captured Breast Cancer Cells

To guide therapeutic strategies and to monitor the state changes in the disease, a low-cost, portable, and easily fabricated microfluidic-chip-integrated three-dimensional (3D) microchamber was designed for capturing and analyzing breast cancer cells. Optimally, a colorimetric sensor array was integrated into a microfluidic chip to discriminate the metabolites of the cells. The ultraviolet polymerization characteristic of poly(ethylene glycol) diacrylate (PEGDA) hydrogel was utilized to rapidly fabricate a three-layer hydrogel microfluidic chip with the designed structure under noninvasive 365 nm laser irradiation. 2-Hydroxyethyl methacrylate (HEMA) was added to the prepolymer in order to increase the adhesive capacity of the microchip's surface for capturing cells. 1-Vinyl-2-pyrrolidone (NVP) was designed to improve the toughness and reduce the swelling capacity of the hydrogel composite. A non-toxic 3D hydrogel microarray chip (60 mm × 20 mm × 3 mm) with low immunogenicity and high hydrophilicity was created to simulate the real physiological microenvironment of breast tissue. The crisscross channels were designed to ensure homogeneous seeding density. This hydrogel material displayed excellent biocompatibility and tunable physical properties compared with traditional microfluidic chip materials and can be directly processed to obtain the most desirable microstructure. The feasibility of using a PEGDA hydrogel microfluidic chip for the real-time online detection of breast cancer cells' metabolism was confirmed using a specifically designed colorimetric sensor array with 16 kinds of porphyrin, porphyrin derivatives, and indicator dyes. The results of the principal component analysis (PCA), the hierarchical cluster analysis (HCA), and the linear discriminant analysis (LDA) suggest that the metabolic liquids of different breast cells can be easily distinguished with the developed PEGDA hydrogel microfluidic chip. The PEGDA hydrogel microfluidic chip has potential practicable applicability in distinguishing normal and cancerous breast cells.

Recent Methods for Modifying Mechanical Properties of Tissue-Engineered Scaffolds for Clinical Applications

The limited regenerative capacity of the human body, in conjunction with a shortage of healthy autologous tissue, has created an urgent need for alternative grafting materials. A potential solution is a tissue-engineered graft, a construct which supports and integrates with host tissue. One of the key challenges in fabricating a tissue-engineered graft is achieving mechanical compatibility with the graft site; a disparity in these properties can shape the behaviour of the surrounding native tissue, contributing to the likelihood of graft failure. The purpose of this review is to examine the means by which researchers have altered the mechanical properties of tissue-engineered constructs via hybrid material usage, multi-layer scaffold designs, and surface modifications. A subset of these studies which has investigated the function of their constructs in vivo is also presented, followed by an examination of various tissue-engineered designs which have been clinically translated.