Direct laser writing for cardiac tissue engineering: a microfluidic heart on a chip with integrated transducers

Development of an electroconductive Heart-on-a-chip model to investigate cellular and molecular response of human cardiac tissue to gold nanomaterials

To date, various strategies have been developed to construct biomimetic and functional in vitro cardiac tissue models utilizing human induced pluripotent stem cells (hiPSCs). Among these approaches, microfluidic-based Heart-on-a-chip (HOC) models are promising, as they enable the engineering of miniaturized, physiologically relevant in vitro cardiac tissues with precise control over cellular constituents and tissue architecture. Despite significant advancements, previously reported HOC models often lack the electroconductivity features of the native human myocardium. In this study, we developed a 3D electroconductive HOC (referred to as eHOC) model through the co-culture of isogenic hiPSC-derived cardiomyocytes (hiCMs) and cardiac fibroblasts (hiCFs), embedded within an electroconductive hydrogel scaffold in a microfluidic-based chip system. Functional and gene expression analyses demonstrated that, compared to non-conductive HOC, the eHOC model exhibited enhanced contractile functionality, improved calcium transients, and increased expression of structural and calcium handling genes. The eHOC model was further leveraged to investigate the underlying electroconduction-induced pathway(s) associated with cardiac tissue development through single-cell RNA sequencing (scRNA-seq). Notably, scRNA-seq analyses revealed a significant downregulation of a set of cardiac genes, associated with the fetal stage of heart development, as well as upregulation of sarcomere- and conduction-related genes within the eHOC model. Additionally, upregulation of the cardiac muscle contraction and motor protein pathways were observed in the eHOC model, consistent with enhanced contractile functionality of the engineered cardiac tissues. Comparison of scRNA-seq data from the 3D eHOC model with published datasets of adult human hearts demonstrated a similar expression pattern of fetal- and adult-like cardiac genes. Overall, this study provides a unique eHOC model with improved biomimcry and organotypic features, which could be potentially used for drug testing and discovery, as well as disease modeling applications.

Nanofabrication for Nanophotonics

Nanofabrication, a pivotal technology at the intersection of nanoscale engineering and high-resolution patterning, has substantially advanced over recent decades. This technology enables the creation of nanopatterns on substrates crucial for developing nanophotonic devices and other applications in diverse fields including electronics and biosciences. Here, this mega-review comprehensively explores various facets of nanofabrication focusing on its application in nanophotonics. It delves into high-resolution techniques like focused ion beam and electron beam lithography, methods for 3D complex structure fabrication, scalable manufacturing approaches, and material compatibility considerations. Special attention is given to emerging trends such as the utilization of two-photon lithography for 3D structures and advanced materials like phase change substances and 2D materials with excitonic properties. By highlighting these advancements, the review aims to provide insights into the ongoing evolution of nanofabrication, encouraging further research and application in creating functional nanostructures. This work encapsulates critical developments and future perspectives, offering a detailed narrative on the state-of-the-art in nanofabrication tailored for both new researchers and seasoned experts in the field.

Organ-on-a-Chip Applications in Microfluidic Platforms

Microfluidic technology plays a crucial role in organ-on-a-chip (OoC) systems by replicating human physiological processes and disease states, significantly advancing biomedical research and drug discovery. This article reviews the design and fabrication processes of microfluidic devices. It also explores how these technologies are integrated into OoC platforms to simulate human physiological environments, highlighting key principles, technological advances, and diverse applications. Through case studies involving the simulation of multiple organs such as the heart, liver, and lungs, the article evaluates the impact of OoC systems' integrated microfluidic technology on drug screening, toxicity assessment, and personalized medicine. In addition, this article considers technical challenges, ethical issues, and future directions, and looks ahead to further optimizing the functionality and biomimetic precision of OoCs through innovation, emphasizing its critical role in promoting personalized medicine and precision treatment strategies.

Heart-on-a-chip: a revolutionary organ-on-chip platform for cardiovascular disease modeling

Heart-on-a-chip (HoC) devices have emerged as a powerful tool for studying the human heart's intricate functions and dysfunctions in vitro. Traditional preclinical models, such as 2D cell cultures model and animal model, have limitations in accurately predicting human response to cardiovascular diseases and treatments. The HoC approach addresses these shortcomings by recapitulating the microscale anatomy, physiology, and biomechanics of the heart, thereby providing a more clinically relevant platform for drug testing, disease modeling, and personalized therapy. Recent years have seen significant strides in HoC technology, driven by advancements in biomaterials, bioelectronics, and tissue engineering. Here, we first review the construction and on-chip detection in HoC. Then we introduce the current proceedings of in vitro models for studying cardiovascular diseases (CVD) based on the HoC platform, including ischemia and myocardial infarction, cardiac fibrosis, cardiac scar, myocardial hypertrophy and other CVD models. Finally, we discuss the future directions of HoC and related emerging technologies.

Microfluidic platforms for monitoring cardiomyocyte electromechanical activity

Cardiovascular diseases account for ~40% of global deaths annually. This situation has revealed the urgent need for the investigation and development of corresponding drugs for pathogenesis due to the complexity of research methods and detection techniques. An in vitro cardiomyocyte model is commonly used for cardiac drug screening and disease modeling since it can respond to microphysiological environmental variations through mechanoelectric feedback. Microfluidic platforms are capable of accurate fluid control and integration with analysis and detection techniques. Therefore, various microfluidic platforms (i.e., heart-on-a-chip) have been applied for the reconstruction of the physiological environment and detection of signals from cardiomyocytes. They have demonstrated advantages in mimicking the cardiovascular structure and function in vitro and in monitoring electromechanical signals. This review presents a summary of the methods and technologies used to monitor the contractility and electrophysiological signals of cardiomyocytes within microfluidic platforms. Then, applications in common cardiac drug screening and cardiovascular disease modeling are presented, followed by design strategies for enhancing physiology studies. Finally, we discuss prospects in the tissue engineering and sensing techniques of microfluidic platforms.

3D Bioprinting for Engineered Tissue Constructs and Patient-Specific Models: Current Progress and Prospects in Clinical Applications

Advancements in bioprinting technology are driving the creation of complex, functional tissue constructs for use in tissue engineering and regenerative medicine. Various methods, including extrusion, jetting, and light-based bioprinting, have their unique advantages and drawbacks. Over the years, researchers and industry leaders have made significant progress in enhancing bioprinting techniques and materials, resulting in the production of increasingly sophisticated tissue constructs. Despite this progress, challenges still need to be addressed in achieving clinically relevant, human-scale tissue constructs, presenting a hurdle to widespread clinical translation. However, with ongoing interdisciplinary research and collaboration, the field is rapidly evolving and holds promise for personalized medical interventions. Continued development and refinement of bioprinting technologies have the potential to address complex medical needs, enabling the development of functional, transplantable tissues and organs, as well as advanced in vitro tissue models.

Recent Advances in Polymer Science and Fabrication Processes for Enhanced Microfluidic Applications: An Overview

This review explores significant advancements in polymer science and fabrication processes that have enhanced the performance and broadened the application scope of microfluidic devices. Microfluidics, essential in biotechnology, medicine, and chemical engineering, relies on precise fluid manipulation in micrometer-sized channels. Recent innovations in polymer materials, such as flexible, biocompatible, and structurally robust polymers, have been pivotal in developing advanced microfluidic systems. Techniques like replica molding, microcontact printing, solvent-assisted molding, injection molding, and 3D printing are examined, highlighting their advantages and recent developments. Additionally, the review discusses the diverse applications of polymer-based microfluidic devices in biomedical diagnostics, drug delivery, organ-on-chip models, environmental monitoring, and industrial processes. This paper also addresses future challenges, including enhancing chemical resistance, achieving multifunctionality, ensuring biocompatibility, and scaling up production. By overcoming these challenges, the potential for widespread adoption and impactful use of polymer-based microfluidic technologies can be realized.

MicroBundlePillarTrack: A Python package for automated segmentation, tracking, and analysis of pillar deflection in cardiac microbundles

Movies of human induced pluripotent stem cell (hiPSC)-derived engineered cardiac tissue (microbundles) contain abundant information about structural and functional maturity. However, extracting these data in a reproducible and high-throughput manner remains a major challenge. Furthermore, it is not straightforward to make direct quantitative comparisons across the multiple in vitro experimental platforms employed to fabricate these tissues. Here, we present "MicroBundlePillarTrack," an open-source optical flow-based package developed in Python to track the deflection of pillars in cardiac microbundles grown on experimental platforms with two different pillar designs ("Type 1" and "Type 2" design). Our software is able to automatically segment the pillars, track their displacements, and output time-dependent metrics for contractility analysis, including beating amplitude and rate, contractile force, and tissue stress. Because this software is fully automated, it will allow for both faster and more reproducible analyses of larger datasets and it will enable more reliable cross-platform comparisons as compared to existing approaches that require manual steps and are tailored to a specific experimental platform. To complement this open-source software, we share a dataset of 1,540 brightfield example movies on which we have tested our software. Through sharing this data and software, our goal is to directly enable quantitative comparisons across labs, and facilitate future collective progress via the biomedical engineering open-source data and software ecosystem.

Direct laser writing-enabled 3D printing strategies for microfluidic applications

Over the past decade, additive manufacturing-or "three-dimensional (3D) printing"-has attracted increasing attention in the Lab on a Chip community as a pathway to achieve sophisticated system architectures that are difficult or infeasible to fabricate via conventional means. One particularly promising 3D manufacturing technology is "direct laser writing (DLW)", which leverages two-photon (or multi-photon) polymerization (2PP) phenomena to enable high geometric versatility, print speeds, and precision at length scales down to the 100 nm range. Although researchers have demonstrated the potential of using DLW for microfluidic applications ranging from organ on a chip and drug delivery to micro/nanoparticle processing and soft microrobotics, such scenarios present unique challenges for DLW. Specifically, microfluidic systems typically require macro-to-micro fluidic interfaces (e.g., inlet and outlet ports) to facilitate fluidic loading, control, and retrieval operations; however, DLW-based 3D printing relies on a micron-to-submicron-sized 2PP volume element (i.e., "voxel") that is poorly suited for manufacturing these larger-scale fluidic interfaces. In this Tutorial Review, we highlight and discuss the four most prominent strategies that researchers have developed to circumvent this trade-off and realize macro-to-micro interfaces for DLW-enabled microfluidic components and systems. In addition, we consider the possibility that-with the advent of next-generation commercial DLW printers equipped with new dynamic voxel tuning, print field, and laser power capabilities-the overall utility of DLW strategies for Lab on a Chip fields may soon expand dramatically.

Advances in cardiac tissue engineering and heart-on-a-chip

Recent advances in both cardiac tissue engineering and hearts-on-a-chip are grounded in new biomaterial development as well as the employment of innovative fabrication techniques that enable precise control of the mechanical, electrical, and structural properties of the cardiac tissues being modelled. The elongated structure of cardiomyocytes requires tuning of substrate properties and application of biophysical stimuli to drive its mature phenotype. Landmark advances have already been achieved with induced pluripotent stem cell-derived cardiac patches that advanced to human testing. Heart-on-a-chip platforms are now commonly used by a number of pharmaceutical and biotechnology companies. Here, we provide an overview of cardiac physiology in order to better define the requirements for functional tissue recapitulation. We then discuss the biomaterials most commonly used in both cardiac tissue engineering and heart-on-a-chip, followed by the discussion of recent representative studies in both fields. We outline significant challenges common to both fields, specifically: scalable tissue fabrication and platform standardization, improving cellular fidelity through effective tissue vascularization, achieving adult tissue maturation, and ultimately developing cryopreservation protocols so that the tissues are available off the shelf.

MicroBundleCompute: Automated segmentation, tracking, and analysis of subdomain deformation in cardiac microbundles

Advancing human induced pluripotent stem cell derived cardiomyocyte (hiPSC-CM) technology will lead to significant progress ranging from disease modeling, to drug discovery, to regenerative tissue engineering. Yet, alongside these potential opportunities comes a critical challenge: attaining mature hiPSC-CM tissues. At present, there are multiple techniques to promote maturity of hiPSC-CMs including physical platforms and cell culture protocols. However, when it comes to making quantitative comparisons of functional behavior, there are limited options for reliably and reproducibly computing functional metrics that are suitable for direct cross-system comparison. In addition, the current standard functional metrics obtained from time-lapse images of cardiac microbundle contraction reported in the field (i.e., post forces, average tissue stress) do not take full advantage of the available information present in these data (i.e., full-field tissue displacements and strains). Thus, we present "MicroBundleCompute," a computational framework for automatic quantification of morphology-based mechanical metrics from movies of cardiac microbundles. Briefly, this computational framework offers tools for automatic tissue segmentation, tracking, and analysis of brightfield and phase contrast movies of beating cardiac microbundles. It is straightforward to implement, runs without user intervention, requires minimal input parameter setting selection, and is computationally inexpensive. In this paper, we describe the methods underlying this computational framework, show the results of our extensive validation studies, and demonstrate the utility of exploring heterogeneous tissue deformations and strains as functional metrics. With this manuscript, we disseminate "MicroBundleCompute" as an open-source computational tool with the aim of making automated quantitative analysis of beating cardiac microbundles more accessible to the community.

Geometry and length control of 3D engineered heart tissues using direct laser writing

Geometry and mechanical characteristics of the environment surrounding the Engineered Heart Tissues (EHT) affect their structure and function. Here, we employed a 3D tissue culture platform fabricated using two-photon direct laser writing with a high degree of accuracy to control parameters that are relevant to EHT maturation. Using this platform, we first explore the effects of geometry based on two distinct shapes: a rectangular seeding well with two attachment sites, and a stadium-like seeding well with six attachment sites that are placed symmetrically along hemicylindrical membranes. The former geometry promotes uniaxial contraction of the tissues; the latter additionally induces diagonal fiber alignment. We systematically increase the length of the seeding wells for both configurations and observe a positive correlation between fiber alignment at the center of the EHTs and tissue length. With increasing length, an undesirable thinning and "necking" also emerge, leading to the failure of longer tissues over time. In the second step, we optimize the stiffness of the seeding wells and modify some of the attachment sites of the platform and the seeding parameters to achieve tissue stability for each length and geometry. Furthermore, we use the platform for electrical pacing and calcium imaging to evaluate the functional dynamics of EHTs as a function of frequency.

Hydrogel-Sheathed hiPSC-Derived Heart Microtissue Enables Anchor-Free Contractile Force Measurement

In vitro reconstruction of highly mature engineered heart tissues (EHTs) is attempted for the selection of cardiotoxic drugs suitable for individual patients before administration. Mechanical contractile force generated in the EHTs is known to be a critical indicator for evaluating the EHT response. However, measuring contractile force requires anchoring the EHT in a tailored force-sensing cell culture chamber, causing technical difficulties in the stable evaluation of contractile force in long-term culture. This paper proposes a hydrogel-sheathed human induced pluripotent stem cell (hiPSC)-derived heart microtissue (H3 M) that can provide an anchor-free contractile force measurement platform in commonly used multi-well plates. The contractile force associated with tissue formation and drug response is calculated by motion tracking and finite element analysis on the bending angle of the hydrogel sheath. From the experiment of the drug response, H3 M is an excellent drug screening platform with high sensitivity and early testing capability compared to conventionally anchored EHT. This unique platform would be useful and versatile for regenerative therapy and drug discovery research in EHT.

Recent advances in soluble decellularized extracellular matrix for heart tissue engineering and organ modeling

Despite the advent of tissue engineering (TE) for the remodeling, restoring, and replacing damaged cardiovascular tissues, the progress is hindered by the optimal mechanical and chemical properties required to induce cardiac tissue-specific cellular behaviors including migration, adhesion, proliferation, and differentiation. Cardiac extracellular matrix (ECM) consists of numerous structural and functional molecules and tissue-specific cells, therefore it plays an important role in stimulating cell proliferation and differentiation, guiding cell migration, and activating regulatory signaling pathways. With the improvement and modification of cell removal methods, decellularized ECM (dECM) preserves biochemical complexity, and bio-inductive properties of the native matrix and improves the process of generating functional tissue. In this review, we first provide an overview of the latest advancements in the utilization of dECM in in vitro model systems for disease and tissue modeling, as well as drug screening. Then, we explore the role of dECM-based biomaterials in cardiovascular regenerative medicine (RM), including both invasive and non-invasive methods. In the next step, we elucidate the engineering and material considerations in the preparation of dECM-based biomaterials, namely various decellularization techniques, dECM sources, modulation, characterizations, and fabrication approaches. Finally, we discuss the limitations and future directions in fabrication of dECM-based biomaterials for cardiovascular modeling, RM, and clinical translation.

Ultra-resolution scalable microprinting

Projection micro stereolithography (PµSL) is a digital light processing (DLP) based printing technique for producing structured microparts. In this approach there is often a tradeoff between the largest object that can be printed and the minimum feature size, with higher resolution generally reducing the overall extent of the structure. The ability to produce structures with high spatial resolution and large overall volume, however, is immensely important for the creation of hierarchical materials, microfluidic devices and bioinspired constructs. In this work, we report a low-cost system with 1 µm optical resolution, representing the highest resolution system yet developed for the creation of micro-structured parts whose overall dimensions are nevertheless on the order of centimeters. To do so, we examine the limits at which PµSL can be applied at scale as a function of energy dosage, resin composition, cure depth and in-plane feature resolution. In doing so we develop a unique exposure composition approach that allows us to greatly improve the resolution of printed features. This ability to construct high-resolution scalable microstructures has the potential to accelerate advances in emerging areas, including 3D metamaterials, tissue engineering and bioinspired constructs.

Basic Guide to Multilayer Microfluidic Fabrication with Polyimide Tape and Diode Laser

For normal operations, microfluidic devices typically require an external source of pressure to deliver fluid flow through the microchannel. This requirement limits their use for benchtop research activities in a controlled static environment. To exploit the full potential of the miniaturization and portability of microfluidic platforms, passively driven capillary microfluidic devices have been developed to completely remove the need for an external pressure source. Capillary microfluidics can be designed to perform complex tasks by designing individual components of the device. These components, such as the stop valve and trigger valve, operate through changes in microchannel dimensions and aspect ratios. A direct, maskless fabrication protocol that allows the precise fabrication of microchannels and other microfluidic components is introduced here. A diode laser and polyimide tape on a PMMA substrate are the only components needed to start fabrication. By varying the laser power used and the number of laser repetitions, various depths and widths of the microchannel can be quickly created to meet specific needs. As an example of a functional unit, a trigger valve was fabricated and tested, as proof of the validity of the fabrication protocol.

Stress-induced birefringence in 3D direct laser written micro-optics

3D direct laser writing is a widely used technology to create different nano- and micro-optical devices for various purposes. However, one big issue is the shrinking of the structures during polymerization, which results in deviations from the design and in internal stress. While the deviations can be compensated by adapting the design, the internal stress remains and induces birefringence. In this Letter, we successfully demonstrate the quantitative analysis of stress-induced birefringence in 3D direct laser written structures. After presenting the measurement setup based on a rotating polarizer and an elliptical analyzer, we characterize the birefringence of different structures and writing modes. We further investigate different photoresists and the implications for 3D direct laser written optics.

Microfluidic Organ-on-a-Chip System for Disease Modeling and Drug Development

An organ-on-a-chip is a device that combines micro-manufacturing and tissue engineering to replicate the critical physiological environment and functions of the human organs. Therefore, it can be used to predict drug responses and environmental effects on organs. Microfluidic technology can control micro-scale reagents with high precision. Hence, microfluidics have been widely applied in organ-on-chip systems to mimic specific organ or multiple organs in vivo. These models integrated with various sensors show great potential in simulating the human environment. In this review, we mainly introduce the typical structures and recent research achievements of several organ-on-a-chip platforms. We also discuss innovations in models applied to the fields of pharmacokinetics/pharmacodynamics, nano-medicine, continuous dynamic monitoring in disease modeling, and their further applications in other fields.

Simultaneous measurement of contractile force and field potential of dynamically beating human iPS cell-derived cardiac cell sheet-tissue with flexible electronics

Human induced pluripotent stem (iPS) cell-derived cardiomyocytes are used for in vitro pharmacological and pathological studies worldwide. In particular, the functional assessment of cardiac tissues created from iPS cell-derived cardiomyocytes is expected to provide precise prediction of drug effects and thus streamline the process of drug development. However, the current format of electrophysiological and contractile assessment of cardiomyocytes on a rigid substrate is not appropriate for cardiac tissues that beat dynamically. Here, we show a novel simultaneous measurement system for contractile force and extracellular field potential of iPS cell-derived cardiac cell sheet-tissues using 500 nm-thick flexible electronic sheets. It was confirmed that the developed system is applicable for pharmacological studies and assessments of excitation-contraction coupling-related parameters, such as the electro-mechanical window. Our results indicate that flexible electronics with cardiac tissue engineering provide an advanced platform for drug development. This system will contribute to gaining new insight in pharmacological study of human cardiac function.

Mechanical Strain-Enabled Reconstitution of Dynamic Environment in Organ-on-a-Chip Platforms: A Review

Organ-on-a-chip (OOC) uses the microfluidic 3D cell culture principle to reproduce organ- or tissue-level functionality at a small scale instead of replicating the entire human organ. This provides an alternative to animal models for drug development and environmental toxicology screening. In addition to the biomimetic 3D microarchitecture and cell-cell interactions, it has been demonstrated that mechanical stimuli such as shear stress and mechanical strain significantly influence cell behavior and their response to pharmaceuticals. Microfluidics is capable of precisely manipulating the fluid of a microenvironment within a 3D cell culture platform. As a result, many OOC prototypes leverage microfluidic technology to reproduce the mechanically dynamic microenvironment on-chip and achieve enhanced in vitro functional organ models. Unlike shear stress that can be readily generated and precisely controlled using commercial pumping systems, dynamic systems for generating proper levels of mechanical strains are more complicated, and often require miniaturization and specialized designs. As such, this review proposes to summarize innovative microfluidic OOC platforms utilizing mechanical actuators that induce deflection of cultured cells/tissues for replicating the dynamic microenvironment of human organs.