Mimicking dynamic in vivo environments with stimuli-responsive materials for cell culture

Photoresponsive Hydrogels for Tissue Engineering

Hydrophilic and biocompatible hydrogels are widely applied as ideal scaffolds in tissue engineering. The "smart" gelation material can alter its structural, physiochemical, and functional features in answer to various endo/exogenous stimuli to better biomimic the endogenous extracellular matrix for the engineering of cells and tissues. Light irradiation owns a high spatial-temporal resolution, complete biorthogonal reactivity, and fine-tunability and can thus induce physiochemical reactions within the matrix of photoresponsive hydrogels with good precision, efficiency, and safety. Both gel structure (e.g., geometry, porosity, and dimension) and performance (like conductivity and thermogenic or mechanical properties) can hence be programmed on-demand to yield the biochemical and biophysical signals regulating the morphology, growth, motility, and phenotype of engineered cells and tissues. Here we summarize the strategies and mechanisms for encoding light-reactivity into a hydrogel and demonstrate how fantastically such responsive gels change their structure and properties with light irradiation as desired and thus improve their applications in tissue engineering including cargo delivery, dynamic three-dimensional cell culture, and tissue repair and regeneration, aiming to provide a basis for more and better translation of photoresponsive hydrogels in the clinic.

Advances and challenges in organ-on-chip technology: toward mimicking human physiology and disease in vitro

Organs-on-chips have been tissues or three-dimensional (3D) mini-organs that comprise numerous cell types and have been produced on microfluidic chips to imitate the complicated structures and interactions of diverse cell types and organs under controlled circumstances. Several morphological and physiological distinctions exist between traditional 2D cultures, animal models, and the growing popular 3D cultures. On the other hand, animal models might not accurately simulate human toxicity because of physiological variations and interspecies metabolic capability. The on-chip technique allows for observing and understanding the process and alterations occurring in metastases. The present study aimed to briefly overview single and multi-organ-on-chip techniques. The current study addresses each platform's essential benefits and characteristics and highlights recent developments in developing and utilizing technologies for single and multi-organs-on-chips. The study also discusses the drawbacks and constraints associated with these models, which include the requirement for standardized procedures and the difficulties of adding immune cells and other intricate biological elements. Finally, a comprehensive review demonstrated that the organs-on-chips approach has a potential way of investigating organ function and disease. The advancements in single and multi-organ-on-chip structures can potentially increase drug discovery and minimize dependency on animal models, resulting in improved therapies for human diseases.

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.

Biofabrication methods for reconstructing extracellular matrix mimetics

In the human body, almost all cells interact with extracellular matrices (ECMs), which have tissue and organ-specific compositions and architectures. These ECMs not only function as cellular scaffolds, providing structural support, but also play a crucial role in dynamically regulating various cellular functions. This comprehensive review delves into the examination of biofabrication strategies used to develop bioactive materials that accurately mimic one or more biophysical and biochemical properties of ECMs. We discuss the potential integration of these ECM-mimics into a range of physiological and pathological in vitro models, enhancing our understanding of cellular behavior and tissue organization. Lastly, we propose future research directions for ECM-mimics in the context of tissue engineering and organ-on-a-chip applications, offering potential advancements in therapeutic approaches and improved patient outcomes.

Static and Dynamic: Evolving Biomaterial Mechanical Properties to Control Cellular Mechanotransduction

The extracellular matrix (ECM) is a highly dynamic system that constantly offers physical, biological, and chemical signals to embraced cells. Increasing evidence suggests that mechanical signals derived from the dynamic cellular microenvironment are essential controllers of cell behaviors. Conventional cell culture biomaterials, with static mechanical properties such as chemistry, topography, and stiffness, have offered a fundamental understanding of various vital biochemical and biophysical processes, such as cell adhesion, spreading, migration, growth, and differentiation. At present, novel biomaterials that can spatiotemporally impart biophysical cues to manipulate cell fate are emerging. The dynamic properties and adaptive traits of new materials endow them with the ability to adapt to cell requirements and enhance cell functions. In this review, an introductory overview of the key players essential to mechanobiology is provided. A biophysical perspective on the state-of-the-art manipulation techniques and novel materials in designing static and dynamic ECM-mimicking biomaterials is taken. In particular, different static and dynamic mechanical cues in regulating cellular mechanosensing and functions are compared. This review to benefit the development of engineering biomechanical systems regulating cell functions is expected.

A Near-Infrared Mechanically Switchable Elastomeric Film as a Dynamic Cell Culture Substrate

Commercial static cell culture substrates can usually not change their physical properties over time, resulting in a limited representation of the variation in biomechanical cues in vivo. To overcome this limitation, approaches incorporating gold nanoparticles to act as transducers to external stimuli have been employed. In this work, gold nanorods were embedded in an elastomeric matrix and used as photothermal transducers to fabricate biocompatible light-responsive substrates. The nanocomposite films analysed by lock-in thermography and nanoindentation show a homogeneous heat distribution and a greater stiffness when irradiated with NIR light. After irradiation, the initial stiffness values were recovered. In vitro experiments performed during NIR irradiation with NIH-3T3 fibroblasts demonstrated that these films were biocompatible and cells remained viable. Cells cultured on the light stiffened nanocomposite exhibited a greater proliferation rate and stronger focal adhesion clustering, indicating increased cell-surface binding strength.

Polymeric nanoparticles targeting Sialyl-Tn in gastric cancer: A live tracking under flow conditions

Drug delivery using nanoparticles (NPs) represents a potential approach for therapy in cancer, such gastric cancer (GC) due to their targeting ability and controlled release properties. The use of advanced nanosystems that deliver anti-cancer drugs specifically to tumor cells may strongly rely on the expression of cancer-associated targets. Glycans aberrantly expressed by cancer cells are attractive targets for such delivery strategy. Sialylated glycans, such as Sialyl-Tn (STn) are aberrantly expressed in several epithelial tumors, including GC, being a potential target for a delivery nanosystem. The aim of this study was the development of NPs surface-functionalized with a specific antibody targeting the STn glycan and further evaluate this nanosystem effectiveness regarding its specificity and recognition capacity. Our results showed that the NPs surface-functionalized with anti-STn antibody efficiently are recognized by cells displaying the cancer-associated STn antigen under static and live cell monitoring flow conditions. This uncovers the potential use of such NPs for drug delivery in cancer. However, flow exposure was disclosed as an important biomechanical parameter to be taken into consideration. Here we presented an innovative and successful methodology to live track the NPs targeting STn antigen under shear stress, simulating the physiological flow. We demonstrate that unspecific binding of NPs agglomerates did not occur under flow conditions, in contrast with static assays. This robust approach can be applied for in vitro drug studies, giving valuable insights for in vivo studies.

A bead-based method for high-throughput mapping of the sequence- and force-dependence of T cell activation

Adaptive immunity relies on T lymphocytes that use αβ T cell receptors (TCRs) to discriminate among peptides presented by major histocompatibility complex molecules (pMHCs). Identifying pMHCs capable of inducing robust T cell responses will not only enable a deeper understanding of the mechanisms governing immune responses but could also have broad applications in diagnosis and treatment. T cell recognition of sparse antigenic pMHCs in vivo relies on biomechanical forces. However, in vitro screening methods test potential pMHCs without force and often at high (nonphysiological) pMHC densities and thus fail to predict potent agonists in vivo. Here, we present a technology termed BATTLES (biomechanically assisted T cell triggering for large-scale exogenous-pMHC screening) that uses biomechanical force to initiate T cell triggering for peptides and cells in parallel. BATTLES displays candidate pMHCs on spectrally encoded beads composed of a thermo-responsive polymer capable of applying shear loads to T cells, facilitating exploration of the force- and sequence-dependent landscape of T cell responses. BATTLES can be used to explore basic T cell mechanobiology and T cell-based immunotherapies.

A trio of biological rhythms and their relevance in rhythmic mechanical stimulation of cell cultures

The primary aim of this article is to provide a biological rhythm model based on previous theoretical and experimental findings to promote more comprehensive studies of rhythmic mechanical stimulation of cell cultures, which relates to tissue engineering and regenerative medicine fields. Through an interdisciplinary approach where different standpoints from biology and musicology are combined, we explore some of the core rhythmic features of biological and cellular rhythmic processes and present them as a trio model that aims to afford a basic but fundamental understanding of the connections between various biological rhythms. It is vital to highlight such links since rhythmic mechanical stimulation and its effect on cell cultures are vastly underexplored even though the cellular response to mechanical stimuli (mechanotransduction) has been studied widely and relevant experimental evidence suggests mechanotransduction processes are rhythmic.

4D Materials with Photoadaptable Properties Instruct and Enhance Intestinal Organoid Development

Intestinal organoids are self-organized tissue constructs, grown in vitro, that resemble the structure and function of the intestine and are often considered promising as a prospective platform for drug testing and disease modeling. Organoid development in vitro is typically instructed by exogenous cues delivered from the media, but cellular responses also depend on properties of the surrounding microenvironmental niche, such as mechanical stiffness and extracellular matrix (ECM) ligands. In recent years, synthetic hydrogel platforms have been engineered to resemble the in vivo niche, with the goal of generating physiologically relevant environments that can promote mature and reproducible organoid development. However, a few of these approaches consider the importance of intestinal organoid morphology or how morphology changes during development, as cues that may dictate organoid functionality. For example, intestinal organoids grown in vitro often lack the physical boundary conditions found in vivo that are responsible for shaping a collection of cells into developmentally relevant morphologies, resulting in organoids that often differ in structure and cellular organization from the parent organ. This disconnect relates, in part, to a lack of appropriate adaptable and programmable materials for cell culture, especially those that enable control over colony growth and differentiation in space and time (i.e., 4D materials). We posit that the future of organoid culture platforms may benefit from advances in photoadaptable chemistries and integration into biomaterials scaffolds, thereby allowing greater user-directed control over both the macro- and microscale material properties. In this way, synthetic materials can begin to better replicate changes in the ECM during development or regeneration in vivo. Recapitulation of cellular and tissue morphological changes, along with an appreciation for the appropriate developmental time scales, should help instruct the next generation of organoid models to facilitate predictable outcomes.

Profiling the responsiveness of focal adhesions of human cardiomyocytes to extracellular dynamic nano-topography

Focal adhesion complexes function as the mediators of cell-extracellular matrix interactions to sense and transmit the extracellular signals. Previous studies have demonstrated that cardiomyocyte focal adhesions can be modulated by surface topographic features. However, the response of focal adhesions to dynamic surface topographic changes remains underexplored. To study this dynamic responsiveness of focal adhesions, we utilized a shape memory polymer-based substrate that can produce a flat-to-wrinkle surface transition triggered by an increase of temperature. Using this dynamic culture system, we analyzed three proteins (paxillin, vinculin and zyxin) from different layers of the focal adhesion complex in response to dynamic extracellular topographic change. Hence, we quantified the dynamic profile of cardiomyocyte focal adhesion in a time-dependent manner, which provides new understanding of dynamic cardiac mechanobiology.

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Cardiac dynamic mechanobiology can be investigated by integrating programmable smart biomaterials and human induced pluripotent stem cells.

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The tBA-co-BA based shape memory polymer with polyelectrolyte multilayer coating is able to achieve an on-demand flat-to-wrinkle surface topographic transition.

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The responsiveness of cardiomyocyte's focal adhesions to extracellular dynamic nano-topography was profiled for both peripheral focal adhesions and sarcomere-linked costameres.

Cell-Traction-Triggered On-Demand Electrical Stimulation for Neuron-Like Differentiation

Electromechanical interaction of cells and extracellular matrix are ubiquitous in biological systems. Understanding the fundamentals of this interaction and feedback is critical to design next-generation electroactive tissue engineering scaffold. Herein, based on elaborately modulating the dynamic mechanical forces in cell microenvironment, the design of a smart piezoelectric scaffold with suitable stiffness analogous to that of collagen for on-demand electrical stimulation is reported. Specifically, it generated a piezoelectric potential, namely a piezopotential, to stimulate stem cell differentiation with cell traction as a loop feedback signal, thereby avoiding the unfavorable effect of early electrical stimulation on cell spreading and adhesion. This is the first time to adapt to the dynamic microenvironment of cells and meet the electrical stimulation of cells in different states by a constant scaffold, diminishing the cumbersomeness of inducing material transformation or trigging by an external stimulus. This in situ on-demand electrical stimulation based on cell-traction-mediated piezopotential paves the way for smart scaffolds design and future bioelectronic therapies.

Regulation of stem cell fate using nanostructure-mediated physical signals

One of the major issues in tissue engineering is regulation of stem cell differentiation toward specific lineages. Unlike biological and chemical signals, physical signals with adjustable properties can be applied to stem cells in a timely and localized manner, thus making them a hot topic for research in the fields of biomaterials, tissue engineering, and cell biology. According to the signals sensed by cells, physical signals used for regulating stem cell fate can be classified into six categories: mechanical, light, thermal, electrical, acoustic, and magnetic. In most cases, external macroscopic physical fields cannot be used to modulate stem cell fate, as only the localized physical signals accepted by the surface receptors can regulate stem cell differentiation via nanoscale fibrin polysaccharide fibers. However, surface receptors related to certain kinds of physical signals are still unknown. Recently, significant progress has been made in the development of functional materials for energy conversion. Consequently, localized physical fields can be produced by absorbing energy from an external physical field and subsequently releasing another type of localized energy through functional nanostructures. Based on the above concepts, we propose a methodology that can be utilized for stem cell engineering and for the regulation of stem cell fate via nanostructure-mediated physical signals. In this review, the combined effect of various approaches and mechanisms of physical signals provides a perspective on stem cell fate promotion by nanostructure-mediated physical signals. We expect that this review will aid the development of remote-controlled and wireless platforms to physically guide stem cell differentiation both in vitro and in vivo, using optimized stimulation parameters and mechanistic investigations while driving the progress of research in the fields of materials science, cell biology, and clinical research.

Magnetic field tuning of mechanical properties of ultrasoft PDMS-based magnetorheological elastomers for biological applications

We report tuning of the moduli and surface roughness of magnetorheological elastomers (MREs) by varying applied magnetic field. Ultrasoft MREs are fabricated using a physiologically relevant commercial polymer, Sylgard™ 527, and carbonyl iron powder (CIP). We found that the shear storage modulus, Young's modulus, and root-mean-square surface roughness are increased by ~41×, ~11×, and ~11×, respectively, when subjected to a magnetic field strength of 95.5 kA m-1. Single fit parameter equations are presented that capture the tunability of the moduli and surface roughness as a function of CIP volume fraction and magnetic field strength. These magnetic field-induced changes in the mechanical moduli and surface roughness of MREs are key parameters for biological applications.

The emerging technology of biohybrid micro-robots: a review

Abstract

In the past few decades, robotics research has witnessed an increasingly high interest in miniaturized, intelligent, and integrated robots. The imperative component of a robot is the actuator that determines its performance. Although traditional rigid drives such as motors and gas engines have shown great prevalence in most macroscale circumstances, the reduction of these drives to the millimeter or even lower scale results in a significant increase in manufacturing difficulty accompanied by a remarkable performance decline. Biohybrid robots driven by living cells can be a potential solution to overcome these drawbacks by benefiting from the intrinsic microscale self-assembly of living tissues and high energy efficiency, which, among other unprecedented properties, also feature flexibility, self-repair, and even multiple degrees of freedom. This paper systematically reviews the development of biohybrid robots. First, the development of biological flexible drivers is introduced while emphasizing on their advantages over traditional drivers. Second, up-to-date works regarding biohybrid robots are reviewed in detail from three aspects: biological driving sources, actuator materials, and structures with associated control methodologies. Finally, the potential future applications and major challenges of biohybrid robots are explored.

Graphic abstract

Electrospun Shape Memory Polymer Micro-/Nanofibers and Tailoring Their Roles for Biomedical Applications

Shape memory polymers (SMPs) as a relatively new class of smart materials have gained increasing attention in academic research and industrial developments (e.g., biomedical engineering, aerospace, robotics, automotive industries, and smart textiles). SMPs can switch their shape, stiffness, size, and structure upon being exposed to external stimuli. Electrospinning technique can endow SMPs with micro-/nanocharacteristics for enhanced performance in biomedical applications. Dynamically changing micro-/nanofibrous structures have been widely investigated to emulate the dynamical features of the ECM and regulate cell behaviors. Structures such as core-shell fibers, developed by coaxial electrospinning, have also gained potential applications as drug carriers and artificial blood vessels. The clinical applications of micro-/nanostructured SMP fibers include tissue regeneration, regulating cell behavior, cell growth templates, and wound healing. This review presents the molecular architecture of SMPs, the recent developments in electrospinning techniques for the fabrication of SMP micro-/nanofibers, the biomedical applications of SMPs as well as future perspectives for providing dynamic biomaterials structures.

Dynamic azopolymeric interfaces for photoactive cell instruction

The ability to affect a wide range of biophysical properties through the use of light has led to the development of dynamic cell instructive materials. Using photoresponsive materials such as azopolymers, smart systems that use external, minimally damaging, light irradiation can be used to trigger specific surface morpho-physical properties in the presence of living cells. The interaction of light with an azopolymer film induces a mass migration phenomenon, allowing a variety of topographic patterns to be embossed on the polymeric film. Photoisomerization induces conformational changes at the molecular and macroscopic scale, resulting in light-induced variations of substrate morphological, physical, and mechanical properties. In this review, we discuss the photoactuation of azopolymeric interfaces to provide guidelines for the engineering and design of azopolymer films. Laser micropatterning for the modulation of azopolymer surfaces is examined as a way to diversify the capabilities of these polymers in cellular systems. Mass migration effects induced by azopolymer switching provides a foundation for performing a broad range of cellular manipulation techniques. Applications of azopolymers are explored in the context of dynamic culture systems, gaining insight into the complex processes involved in dynamic cell-material interactions. The review highlights azopolymers as a candidate for various applications in cellular control, including cell alignment, migration, gene expression, and others. Recent advances have underlined the importance of these systems in applications regarding three-dimensional cell culture and stem cell morphology. Azopolymers can be used not only to manipulate cells but also to probe for mechanistic studies of cellular crosstalk in response to chemical and mechanical stimuli.

Spatiotemporal regulation of dynamic cell microenvironment signals based on an azobenzene photoswitch

Dynamic biochemical and biophysical signals of cellular matrix define and regulate tissue-specific cell functions and fate. To recapitulate this complex environment in vitro, biomaterials based on structural- or degradation-tunable polymers have emerged as powerful platforms for regulating the "on-demand" cell-material dynamic interplay. As one of the most prevalent photoswitch molecules, the photoisomerization of azobenzene demonstrates a unique advantage in the construction of dynamic substrates. Moreover, the development of azobenzene-containing biomaterials is particularly helpful in elucidating cells that adapt to a dynamic microenvironment or integrate spatiotemporal variations of signals. Herein, this minireview, places emphasis on the research progress of azobenzene photoswitches in the dynamic regulation of matrix signals. Some techniques and material design methods have been discussed to provide some theoretical guidance for the rational and efficient design of azopolymer-based material platforms. In addition, considering that the UV-light response of traditional azobenzene photoswitches is not conducive to biological applications, we have summarized the recent approaches to red-shifting the light wavelength for azobenzene activation.

Photoactive Interfaces for Spatio-Temporal Guidance of Mesenchymal Stem Cell Fate

Patterned surfaces have proved effective in guiding stem cells commitment to a specific lineage by presenting highly ordered biophysical/biochemical cues at the cellmaterial interface. Their potency in controlling cell fate can be significantly empowered by encoding logic of space and time control of signal presentation. Here, azopolymeric photoactive interfaces are proposed to present/withdraw morphophysical signals to living cells using a green light trigger in a non-invasive spatio-temporal controlled way. To assess the potency of these dynamic platforms in controlling cell decision and fate, topography changes are actuated by light at specific times to reverse the fate of otherwise committed human mesenchymal stem cells (hMSC) toward osteoblastic lineage. It is first proved by dynamic change from ordered parallel patterning to flat or grid surfaces, that it is possible to induce cyclic cellular and nuclear stretches. Furthermore, by culturing hMSCs on a specific pattern known to prime them toward osteoblast lineage, the possibility to reroute or reverse stem cell fate decision by dynamic modulation of morphophysical signal is proved. To conclude, dynamic topographies can control the spatial conformation of hMSCs, modulate lineage reversal even after several weeks of culture and redirect lineage specification in response to light-induced changes in the microenvironment.

Poly(N-isopropylacrylamide) based thin microgel films for use in cell culture applications

Poly(N-isopropylacrylamide) (PNIPAm) is widely used to fabricate cell sheet surfaces for cell culturing, however copolymer and interpenetrated polymer networks based on PNIPAm have been rarely explored in the context of tissue engineering. Many complex and expensive techniques have been employed to produce PNIPAm-based films for cell culturing. Among them, spin coating has demonstrated to be a rapid fabrication process of thin layers with high reproducibility and uniformity. In this study, we introduce an innovative approach to produce anchored smart thin films both thermo- and electro-responsive, with the aim to integrate them in electronic devices and better control or mimic different environments for cells in vitro. Thin films were obtained by spin coating of colloidal solutions made by PNIPAm and PAAc nanogels. Anchoring the films to the substrates was obtained through heat treatment in the presence of dithiol molecules. From analyses carried out with AFM and XPS, the final samples exhibited a flat morphology and high stability to water washing. Viability tests with cells were finally carried out to demonstrate that this approach may represent a promising route to integrate those hydrogels films in electronic platforms for cell culture applications.

The neurotoxicity of Nε-(carboxymethyl)lysine in food processing by a study based on animal and organotypic cell culture

Nε-(carboxymethyl)lysine (CML) is a potentially noxious compound that is causing widespread concern due to its use in various food products. In this study, we investigated CML neurotoxicity via an in vivo experiment with mice, and an in vitro experiment using a 3D microvascular network model (with human brain vascular endothelial cell and human astrocyte) that simulated the blood-brain barrier. We found that CML could induce cell survival status variations, and histopathological changes to the brain. In addition, CML increased levels of oxidative stress, prompted the protein expression of the receptor for advanced glycation end-products (RAGE). CML up-regulated both the gene expression of RAGE, the activating protein-1 (AP-1), the inflammatory cytokines Interleukin-6 (IL-6), vascular cell adhesion molecule1 (VCAM-1), monocyte chemotactic protein1 (MCP-1). We, therefore, postulated that CML has the potential to deleteriously affect the nervous system through oxidative stress and that activation of the p38 MAPK-AP-1 signaling pathway might be implicated in this pathological process.

Cell adhesion control by photoinduced LCST shift of PNIPAAm-based brush scaffolds

Cell adhesion was markedly regulated on spiropyran-containing PNIPAAm-based brush scaffolds by photoinduced LCST shift across a standard culture temperature.

Temperature-Induced Mechanomodulation of Interpenetrating Networks of Star Poly(ethylene glycol)-Heparin and Poly(N-isopropylacrylamide)

Thermoresponsive interpenetrating networks (IPNs) were prepared by sequential synthesis of a biohybrid network of star-shaped poly(ethylene glycol) [starPEG] and heparin and a poly(N-isopropylacrylamide)-polymer network. Amide bond formation was used for cross-linking of the starPEG-heparin network and photo-cross-linking with N,N'-methylenebis(acrylamide) was applied for the formation of the second polymer network. Both networks were linked by chain entanglements and hydrogen bonds only. The obtained sequential IPNs (seq-IPNs) showed temperature-dependent network properties as reflected by swelling and elasticity data as well as by the release of glycosaminoglycan-binding growth factors. The elastic modulus of the seq-IPNs was found to be amplified up to 50-fold upon temperature change from 22 to 37 °C compared to the intrinsic elastic moduli of the two combined networks. The heparin concentration (as well as the complexation of growth factors with the hydrogel-contained heparin) was demonstrated to be variably independent from the mechanical properties (elastic moduli) of the hydrogels. Illustrating the usability of the developed seq-IPN platform for cell fate control, the thermo-modulation of the release of vascular endothelial growth factor (VEGF) and bone morphogenetic protein 2 (BMP-2) is shown as well as the osteogenic differentiation of human mesenchymal stem cells exposed to stiff and BMP-2 releasing seq-IPNs.

Tunable and Reversible Substrate Stiffness Reveals a Dynamic Mechanosensitivity of Cardiomyocytes

New directions in material applications have allowed for the fresh insight into the coordination of biophysical cues and regulators. Although the role of the mechanical microenvironment on cell responses and mechanics is often studied, most analyses only consider static environments and behavior, however, cells and tissues are themselves dynamic materials that adapt in myriad ways to alterations in their environment. Here, we introduce an approach, through the addition of magnetic inclusions into a soft poly(dimethylsiloxane) elastomer, to fabricate a substrate that can be stiffened nearly instantaneously in the presence of cells through the use of a magnetic gradient to investigate short-term cellular responses to dynamic stiffening or softening. This substrate allows us to observe time-dependent changes, such as spreading, stress fiber formation, Yes-associated protein translocation, and sarcomere organization. The identification of temporal dynamic changes on a short time scale suggests that this technology can be more broadly applied to study targeted mechanisms of diverse biologic processes, including cell division, differentiation, tissue repair, pathological adaptations, and cell-death pathways. Our method provides a unique in vitro platform for studying the dynamic cell behavior by better mimicking more complex and realistic microenvironments. This platform will be amenable to future studies aimed at elucidating the mechanisms underlying mechanical sensing and signaling that influence cellular behaviors and interactions.

Indoor nanoscale particulate matter-induced coagulation abnormality based on a human 3D microvascular model on a microfluidic chip

BACKGROUND

A growing body of evidence shows that indoor concentrations of airborne particles are often higher than is typically encountered outdoors. Since exposure to indoor PM2.5 is thought to be associated with cardiovascular disease, the health impacts of indoor air pollution need to be explored. Based on animal models, ambient particulate matter has been proved to promote coagulation which is very likely involved in the pathogenic development of cardiovascular disease. However, animal models are insufficient to predict what will happen with any certainty in humans. For this reason, the precise pathogenic mechanisms behind the development of cardiovascular disease in humans have not yet been determined.

RESULTS

We generated a 3D functional human microvascular network in a microfluidic device. This model enables human vascular endothelial cells to form tissue-like microvessels that behave very similarly to human blood vessels. The perfusable microvasculature allows the delivery of particles introduced into these generated human-like microvessels to follow the fluid flow. This exposure path effectively simulates the dynamic movement of airborne nanoscale particles (ANPs) within human vessels. In this study, we first identified the existence of ANPs in indoor air pollution. We then showed that ANPs could activate endothelial cells via ROS induced inflammation, and further resulted in abnormal expression of the coagulation factors (TF, TM and t-PA) involved in coagulation cascades. In addition, we found that a protein could cover ANPs, and this biointeraction could interfere with heparan sulfate (HS). Human organotypic 3D microvessel models provide a bridge for how research outcomes can translate to humans.

CONCLUSIONS

The 3D human microvessel model was used to determine the physiological responses of human vessels to ANP stimulation. Based on the obtained data, we concluded that ANPs not only disrupts normal coagulation functions, but also act directly on anticoagulant factors in human vessels. These experimental observations provide a potential biological explanation for the epidemiologically established link between ANPs and coagulation abnormality. This organ-on-chip model may provide a bridge from in vitro results to human responses.

Recent advances in the design of injectable hydrogels for stem cell-based therapy

The recent advances in the design of injectable hydrogels for stem cell delivery, especially for in vivo applications, are overviewed in this review.

Cyclic Stiffness Modulation of Cell-Laden Protein-Polymer Hydrogels in Response to User-Specified Stimuli including Light

Although mechanical signals presented by the extracellular matrix are known to regulate many essential cell functions, the specific effects of these interactions, particularly in response to dynamic and heterogeneous cues, remain largely unknown. Here, we introduce a modular semisynthetic approach to create protein-polymer hydrogel biomaterials that undergo reversible stiffening in response to user-specified inputs. Employing a novel dual-chemoenzymatic modification strategy, we create fusion protein-based gel crosslinkers that exhibit stimuli-dependent intramolecular association. Linkers based on calmodulin yield calcium-sensitive materials, while those containing the photosensitive LOV2 (light, oxygen, and voltage sensing domain 2) protein give phototunable constructs whose moduli can be cycled on demand with spatiotemporal control about living cells. We exploit these unique materials to demonstrate the significant role that cyclic mechanical loading plays on fibroblast-to-myofibroblast transdifferentiation in three-dimensional (3D) space. Our moduli-switchable materials should prove useful for studies in mechanobiology, providing new avenues to probe and direct matrix-driven changes in 4D cell physiology.

3D Spatiotemporal Mechanical Microenvironment: A Hydrogel-Based Platform for Guiding Stem Cell Fate

Stem cells hold great promise for widespread biomedical applications, for which stem cell fate needs to be well tailored. Besides biochemical cues, accumulating evidence has demonstrated that spatiotemporal biophysical cues (especially mechanical cues) imposed by cell microenvironments also critically impact on the stem cell fate. As such, various biomaterials, especially hydrogels due to their tunable physicochemical properties and advanced fabrication approaches, are developed to spatiotemporally manipulate biophysical cues in vitro so as to recapitulate the 3D mechanical microenvironment where stem cells reside in vivo. Here, the main mechanical cues that stem cells experience in their native microenvironment are summarized. Then, recent advances in the design of hydrogel materials with spatiotemporally tunable mechanical properties for engineering 3D the spatiotemporal mechanical microenvironment of stem cells are highlighted. These in vitro engineered spatiotemporal mechanical microenvironments are crucial for guiding stem cell fate and their potential biomedical applications are subsequently discussed. Finally, the challenges and future perspectives are presented.

Trinity of Three-Dimensional (3D) Scaffold, Vibration, and 3D Printing on Cell Culture Application: A Systematic Review and Indicating Future Direction

Cell culture and cell scaffold engineering have previously developed in two directions. First can be 'static into dynamic', with proven effects that dynamic cultures have benefits over static ones. Researches in this direction have used several mechanical means, like external vibrators or shakers, to approximate the dynamic environments in real tissue, though such approaches could only partly address the issue. Second, can be '2D into 3D', that is, artificially created three-dimensional (3D) passive (also called 'static') scaffolds have been utilized for 3D cell culture, helping external culturing conditions mimic real tissue 3D environments in a better way as compared with traditional two-dimensional (2D) culturing. In terms of the fabrication of 3D scaffolds, 3D printing (3DP) has witnessed its high popularity in recent years with ascending applicability, and this tendency might continue to grow along with the rapid development in scaffold engineering. In this review, we first introduce cell culturing, then focus 3D cell culture scaffold, vibration stimulation for dynamic culture, and 3DP technologies fabricating 3D scaffold. Potential interconnection of these realms will be analyzed, as well as the limitations of current 3D scaffold and vibration mechanisms. In the recommendation part, further discussion on future scaffold engineering regarding 3D vibratory scaffold will be addressed, indicating 3DP as a positive bridging technology for future scaffold with integrated and localized vibratory functions.

Sweet Switch: Sugar-Responsive Bioactive Surfaces Based on Dynamic Covalent Bonding

Smart bioactive surfaces that can modulate interactions with biological systems are of great interest. In this work, a surface with switchable bioactivity in response to sugars has been developed. It is based on dynamic covalent bonding between phenylboronic acid (PBA) and secondary hydroxyls on the "wide" rim of β-cyclodextrin (β-CD). The system reported consists of gold surface modified with PBA-containing polymer brushes and a series of functional β-CD derivatives conjugated to diverse bioactive ligands (CD-X). CD-X molecules are attached to the surface to give specified bioactivity such as capture of a specific protein or killing of attached bacteria. Subsequent treatment with cis-diol containing biomolecules having high affinity for PBA (e.g. fructose) leads to the release of CD-X together with the captured proteins, killed bacteria, and so forth from the surface. The surface bioactivity is thereby "turned off". Effectively, this constitutes an on-off bioactivity switch in a mild and noninvasive way, which has the potential in the design of dynamic bioactive surfaces for biomedical applications.

Mixed Copolymer Adlayers Allowing Reversible Thermal Control of Single Cell Aspect Ratio

Dynamic guidance of living cells is achieved by fine-tuning and spatiotemporal modulation on artificial polymer layers enabling reversible peptide display. Adjustment of surface composition and interactions is obtained by coadsorption of mixed poly(lysine) derivatives, grafted with either repellent PEG, RGD adhesion peptides, or T-responsive poly(N-isopropylacrylamide) strands. Deposition of mixed adlayers provides a straightforward mean to optimize complex substrates, which is here implemented to achieve (1) thermal control of ligand accessibility and (2) adjustment of relative adhesiveness between adjacent micropatterns, while preserving cell attachment during thermal cycles. The reversible polarization of HeLa cells along orthogonal stripes mimics guidance along natural matrices.

Three-Dimensional Microstructured Azobenzene-Containing Gelatin as a Photoactuable Cell Confining System

In materials science, there is a considerable interest in the fabrication of highly engineered biomaterials that can interact with cells and control their shape. In particular, from the literature, the role played by physical cell confinement in cellular structural organization and thus in the regulation of its functions has been well-established. In this context, the addition of a dynamic feature to physically confining platforms aiming at reproducing in vitro the well-known dynamic interaction between the cells and their microenvironment would be highly desirable. To this aim, we have developed an advanced gelatin-based hydrogel that can be finely micropatterned by two-photon polymerization and stimulated in a controlled way by light irradiation thanks to the presence of an azobenzene cross-linker. Light-triggered expansion of gelatin microstructures induced an in-plane nuclear deformation of physically confined NIH-3T3 cells. The microfabricated photoactuable gelatin shown in this work paves the way to new "dynamic" caging culture systems that can find applications, for example, as "engineered stem cell niches".

Dynamic alterations of hepatocellular function by on-demand elasticity and roughness modulation

Temporal elasticity and roughness modulation with temperature-responsive poly(ε-caprolactone) induced the alternation of hepatocellular function dynamically.

Tailored Approaches in Drug Development and Diagnostics: From Molecular Design to Biological Model Systems

Approaches to increase the efficiency in developing drugs and diagnostics tools, including new drug delivery and diagnostic technologies, are needed for improved diagnosis and treatment of major diseases and health problems such as cancer, inflammatory diseases, chronic wounds, and antibiotic resistance. Development within several areas of research ranging from computational sciences, material sciences, bioengineering to biomedical sciences and bioimaging is needed to realize innovative drug development and diagnostic (DDD) approaches. Here, an overview of recent progresses within key areas that can provide customizable solutions to improve processes and the approaches taken within DDD is provided. Due to the broadness of the area, unfortunately all relevant aspects such as pharmacokinetics of bioactive molecules and delivery systems cannot be covered. Tailored approaches within (i) bioinformatics and computer-aided drug design, (ii) nanotechnology, (iii) novel materials and technologies for drug delivery and diagnostic systems, and (iv) disease models to predict safety and efficacy of medicines under development are focused on. Current developments and challenges ahead are discussed. The broad scope reflects the multidisciplinary nature of the field of DDD and aims to highlight the convergence of biological, pharmaceutical, and medical disciplines needed to meet the societal challenges of the 21st century.

Functional and Biomimetic Materials for Engineering of the Three-Dimensional Cell Microenvironment

The cell microenvironment has emerged as a key determinant of cell behavior and function in development, physiology, and pathophysiology. The extracellular matrix (ECM) within the cell microenvironment serves not only as a structural foundation for cells but also as a source of three-dimensional (3D) biochemical and biophysical cues that trigger and regulate cell behaviors. Increasing evidence suggests that the 3D character of the microenvironment is required for development of many critical cell responses observed in vivo, fueling a surge in the development of functional and biomimetic materials for engineering the 3D cell microenvironment. Progress in the design of such materials has improved control of cell behaviors in 3D and advanced the fields of tissue regeneration, in vitro tissue models, large-scale cell differentiation, immunotherapy, and gene therapy. However, the field is still in its infancy, and discoveries about the nature of cell-microenvironment interactions continue to overturn much early progress in the field. Key challenges continue to be dissecting the roles of chemistry, structure, mechanics, and electrophysiology in the cell microenvironment, and understanding and harnessing the roles of periodicity and drift in these factors. This review encapsulates where recent advances appear to leave the ever-shifting state of the art, and it highlights areas in which substantial potential and uncertainty remain.

Nanofiber-structured hydrogel yarns with pH-response capacity and cardiomyocyte-drivability for bio-microactuator application

Polymeric hydrogels have great potential in soft biological micro-actuator applications. However, inappropriate micro-architecture, non-anisotropy, weak biomechanics, and inferior response behaviors limit their development. In this study, we designed and manufactured novel polyacrylonitrile (PAN)-based hydrogel yarns composed with uniaxially aligned nanofibers. The nanofibrous hydrogel yarns possessed anisotropic architecture and robust mechanical properties with flexibility, and could be assembled into defined scaffold structures by subsequent processes. The as-prepared hydrogel yarns showed excellent pH response behaviors, with around 100% maximum length and 900% maximum diameter changes, and the pH response was completed within several seconds. Moreover, the hydrogel yarns displayed unique cell-responsive abilities to promote the cell adhesion, proliferation, and smooth muscle differentiation of human adipose derived mesenchymal stem cells (HADMSC). Chicken cardiomyocytes were further seeded onto our nanofibrous hydrogel yarns to engineer living cell-based microactuators. Our results demonstrated that the uniaxially aligned nanofibrous networks within the hydrogel yarns were the key characteristics leading to the anisotropic organization of cardiac cells, and improved sarcomere organization, mimicking the cardiomyocyte bundles in the native myocardium. The construct is capable of sustaining spontaneous cardiomyocyte pumping behaviors for 7days. Our PAN-based nanofibrous hydrogel yarns are attractive for creating linear microactuators with pH-response capacity and biological microactuators with cardiomyocyte-drivability.

STATEMENT OF SIGNIFICANCE

A mechanically robust polyacrylonitrile-based nanofibrous hydrogel yarn is fabricated by using a modified electrospinning setup in combination with chemical modification processes. The as-prepared hydrogel yarn possesses a uniaxially aligned nanofiber microarchitecture and supports a rapid, pH-dependent expansion/contraction response within a few seconds. Embryonic cardiomyocytes-seeded hydrogel yarn improves the sarcomere organization and mimics the cardiomyocyte bundles in the native myocardium, which sustains spontaneous cardiomyocyte pumping behaviors. The nanofibrous hydrogel yarn has several advantages over traditional bulk hydrogel scaffolds in terms of robust biomechanics, anisotropic aligned architecture, and superior pH response behaviors. Our nanofibrous hydrogel yarn holds the potential to be developed into novel linear and biological microactuators for various biomedical applications.

Mechanotransduction and Growth Factor Signalling to Engineer Cellular Microenvironments

Engineering cellular microenvironments involves biochemical factors, the extracellular matrix (ECM) and the interaction with neighbouring cells. This progress report provides a critical overview of key studies that incorporate growth factor (GF) signalling and mechanotransduction into the design of advanced microenvironments. Materials systems have been developed for surface-bound presentation of GFs, either covalently tethered or sequestered through physico-chemical affinity to the matrix, as an alternative to soluble GFs. Furthermore, some materials contain both GF and integrin binding regions and thereby enable synergistic signalling between the two. Mechanotransduction refers to the ability of the cells to sense physical properties of the ECM and to transduce them into biochemical signals. Various aspects of the physics of the ECM, i.e. stiffness, geometry and ligand spacing, as well as time-dependent properties, such as matrix stiffening, degradability, viscoelasticity, surface mobility as well as spatial patterns and gradients of physical cues are discussed. To conclude, various examples illustrate the potential for cooperative signalling of growth factors and the physical properties of the microenvironment for potential applications in regenerative medicine, cancer research and drug testing.

Dynamically Tunable Cell Culture Platforms for Tissue Engineering and Mechanobiology

Human tissues are sophisticated ensembles of many distinct cell types embedded in the complex, but well-defined, structures of the extracellular matrix (ECM). Dynamic biochemical, physicochemical, and mechano-structural changes in the ECM define and regulate tissue-specific cell behaviors. To recapitulate this complex environment in vitro, dynamic polymer-based biomaterials have emerged as powerful tools to probe and direct active changes in cell function. The rapid evolution of polymerization chemistries, structural modulation, and processing technologies, as well as the incorporation of stimuli-responsiveness, now permit synthetic microenvironments to capture much of the dynamic complexity of native tissue. These platforms are comprised not only of natural polymers chemically and molecularly similar to ECM, but those fully synthetic in origin. Here, we review recent in vitro efforts to mimic the dynamic microenvironment comprising native tissue ECM from the viewpoint of material design. We also discuss how these dynamic polymer-based biomaterials are being used in fundamental cell mechanobiology studies, as well as towards efforts in tissue engineering and regenerative medicine.

A bioreactor with an electro-responsive elastomeric membrane for mimicking intestinal peristalsis

This study describes an actuated bioreactor which mimics the pulsatile contractile motion of the intestinal barrier using electro-responsive elastomers as smart materials that undergo deformation upon electrical stimulation. The device consists of an annular dielectric elastomer actuator working as a radial artificial muscle able to rhythmically contract and relax a central cell culture well. The bioreactor maintained up to 4 h of actuation at a frequency of 0.15 Hz and a strain of 8%-10%, to those of the cyclic contraction and relaxation of the small intestine. In vitro tests demonstrated that the device was biocompatible and cell-adhesive for Caco-2 cells, which formed a confluent monolayer following 21 days of culture in the central well. In addition, cellular adhesion and cohesion were maintained after 4 h of continuous cyclic strain. These preliminary results encourage further investigations on the use of dielectric elastomer actuation as a versatile technology that might overcome the limitations of commercially available pneumatic driving systems to obtain bioreactors that can cyclically deform cell cultures in a biomimetic fashion.

Capturing extracellular matrix properties in vitro: Microengineering materials to decipher cell and tissue level processes

Rapid advances in biology have led to the establishment of new fields with tremendous translational potential including regenerative medicine and immunoengineering. One commonality to these fields is the need to extract cells for manipulation in vitro; however, results obtained in laboratory cell culture will often differ widely from observations made in vivo. To more closely emulate native cell biology in the laboratory, designer engineered environments have proved a successful methodology to decipher the properties of the extracellular matrix that govern cellular decision making. Here, we present an overview of matrix properties that affect cell behavior, strategies for recapitulating important parameters in vitro, and examples of how these properties can affect cell and tissue level processes, with emphasis on leveraging these tools for immunoengineering.