Micropatterned Azopolymer Surfaces Modulate Cell Mechanics and Cytoskeleton Structure

Time and Space Modulation of Substrate Curvature to Regulate Cell Mechanical Identity

Recently, a variety of microenvironmental biophysical stimuli have been proved to play a crucial role in regulating cell functions. Among them, morpho-physical cues, like curvature, are emerging as key regulators of cellular behavior. Changes in substrate curvature have been shown to impact the arrangement of Focal Adhesions (FAs), influencing the direction and intensity of cytoskeleton generated forces and resulting in an overall alteration of cell mechanical identity. In their native environment, cells encounter varying degrees of substrate curvature, and in specific organs, they are exposed to dynamic changes of curvature due to periodic tissue deformation. However, the mechanism by which cells perceive substrate curvature remains poorly understood. To this aim, a micro-pneumatic device was designed and implemented. This device enables the controlled application of substrate curvature, both statically and dynamically. Employing a combined experimental and simulative approach, human adipose-derived stem cells were exposed to controlled curvature intensity and frequency. During this exposure, measurements were taken on FAs extension and orientation, cytoskeleton organization and cellular/nuclear alignment. The data clearly indicated a significant influence of the substrate curvature on cell adhesion processes. These findings contribute to a better understanding of the mechanisms through which cells perceive and respond to substrate curvature signals. STATEMENT OF SIGNIFICANCE: This work is our contribution to the comprehension of substrate curvature's function as a crucial regulator of cell adhesion at the scale of focal adhesions and cell mechanical identity. In recent years, a large body of knowledge is continuously growing providing comprehension of the role of various microenvironmental biophysical stimuli in regulating cell functions. Nevertheless, little is known about the role of substrate curvature, in particular, when cells are exposed to this stimulus in a dynamic manner. To address the role of substrate curvature on cellular behavior, a micro-pneumatic device was designed and implemented. This device enables the controlled application of substrate curvature, both statically and dynamically. The experiment data made it abundantly evident that the substrate curvature had a major impact on the mechanisms involved in cell adhesion.

Effects of Temperature Adaptation on the Metabolism and Physiological Properties of Sturgeon Fish Larvae Cell Line

This study investigated how Atlantic sturgeon cells respond to elevated temperatures, shedding light on the potential impacts of climate change on fish. Atlantic sturgeon (Acipenser oxyrinchus), an IUCN (International Union for Conservation of Nature) Red List species and evolutionarily related to paleonisiform species, may have considerable physiological adaptability, suggesting that this species may be able to cope with changing climatic conditions and higher temperatures. To test this hypothesis, the AOXlar7y cell line was examined at 20 °C (control) and at elevated temperatures of 25 °C and 28 °C. Parameters including proliferation, vitality, morphology, and gene expressions related to proliferation, stemness, and stress were evaluated. Additionally, to achieve a comprehensive understanding of cellular changes, mitochondrial and metabolic activities were assessed using Seahorse XF96. AOXlar7y cells adapted to 28 °C exhibited enhanced mitochondrial adaptability, plasticity, heightened cell proliferation, and increased hsp70 expression. Increased baseline respiration indicated elevated ATP demand, which is potentially linked to higher cell proliferation and heat stress defense. Cells at 28 °C also displayed elevated reserve respiration capacity, suggesting adaptation to energy demands. At 25 °C, AOXlar7y cells showed no changes in basal respiration or mitochondrial capacity, suggesting unchanged ATP demand compared to cells cultivated at 20 °C. Proliferation and glycolytic response to energy requirements were diminished, implying a connection between glycolysis inhibition and proliferation suppression. These research results indicate sturgeon cells are capable of withstanding and adapting to an 8 °C temperature increase. This cellular analysis lays a foundation for future studies aimed at a deeper understanding of fish cell physiological adaptations, which will contribute to a better knowledge of environmental threats facing Atlantic sturgeon and fish populations amid climate change.

Hierarchical micro-/nanotopography for tuning structures and mechanics of cells probed by atomic force microscopy

Extracellular matrix plays an important role in regulating the behaviors of cells, and utilizing matrix physics to control cell fate has been a promising way for cell and tissue engineering. However, the nanoscale situations taking place during the topography-regulated cell-matrix interactions are still not fully understood to the best of our knowledge. The invention of atomic force microscopy (AFM) provides a powerful tool to characterize the structures and properties of living biological systems under aqueous conditions with unprecedented spatial resolution. In this work, with the use of AFM, structural and mechanical dynamics of individual cells grown on micro-/nanotopographical surface were revealed. First, the microgroove patterned silicon substrates were fabricated by photolithography. Next, nanogranular topography was formed on microgroove substrates by cell culture medium protein deposition, which was visualized by in situ AFM imaging. The micro-/nanotopographical substrates were then used to grow two types of cells (3T3 cell or MCF-7 cell). AFM morphological imaging and mechanical measurements were applied to characterize the changes of cells grown on the micro-/nanotopographical substrates. The experimental results showed the significant alterations in cellular structures and cellular mechanics caused by micro-/nanotopography. The study provides a novel way based on AFM to unveil the native nanostructures and mechanical properties of cell-matrix interfaces with high spatial resolution in liquids, which will have potential impacts on the studies of topography-tuned cell behaviors.

Biological responses to physicochemical properties of biomaterial surface

Biomedical scientists use chemistry-driven processes found in nature as an inspiration to design biomaterials as promising diagnostic tools, therapeutic solutions, or tissue substitutes. While substantial consideration is devoted to the design and validation of biomaterials, the nature of their interactions with the surrounding biological microenvironment is commonly neglected. This gap of knowledge could be owing to our poor understanding of biochemical signaling pathways, lack of reliable techniques for designing biomaterials with optimal physicochemical properties, and/or poor stability of biomaterial properties after implantation. The success of host responses to biomaterials, known as biocompatibility, depends on chemical principles as the root of both cell signaling pathways in the body and how the biomaterial surface is designed. Most of the current review papers have discussed chemical engineering and biological principles of designing biomaterials as separate topics, which has resulted in neglecting the main role of chemistry in this field. In this review, we discuss biocompatibility in the context of chemistry, what it is and how to assess it, while describing contributions from both biochemical cues and biomaterials as well as the means of harmonizing them. We address both biochemical signal-transduction pathways and engineering principles of designing a biomaterial with an emphasis on its surface physicochemistry. As we aim to show the role of chemistry in the crosstalk between the surface physicochemical properties and body responses, we concisely highlight the main biochemical signal-transduction pathways involved in the biocompatibility complex. Finally, we discuss the progress and challenges associated with the current strategies used for improving the chemical and physical interactions between cells and biomaterial surface.

Quantitative Study of Morphological Features of Stem Cells onto Photopatterned Azopolymer Films

In the last decade, the use of photolithography for the fabrication of structured substrates with controlled morphological patterns that are able to interact with cells at micrometric and nanometric size scales is strongly growing. A promising simple and versatile microfabrication method is based on the physical mass transport induced by visible light in photosensitive azobenzene-containing polymers (or azopolymers). Such light-driven material transport produces a modulation of the surface of the azopolymer film, whose geometry is controlled by the intensity and the polarization distributions of the irradiated light. Herein, two anisotropic structured azopolymer films have been used as substrates to evaluate the effects of topological signals on the in vitro response of human mesenchymal stem cells (hMSCs). The light-induced substrate patterns consist of parallel microgrooves, which are produced in a spatially confined or over large-scale areas of the samples, respectively. The analysis of confocal optical images of the in vitro hMSC cells grown on the patterned films offered relevant information about cell morphology-i.e., nuclei deformation and actin filaments elongation-in relation to the geometry and the spatial extent of the structured area of substrates. The results, together with the possibility of simple, versatile, and cost-effective light-induced structuration of azopolymers, promise the successful use of these materials as anisotropic platforms to study the cell guidance mechanisms governing in vitro tissue formation.

Design of Collective Motions from Synthetic Molecular Switches, Rotors, and Motors

Precise control over molecular movement is of fundamental and practical importance in physics, biology, and chemistry. At nanoscale, the peculiar functioning principles and the synthesis of individual molecular actuators and machines has been the subject of intense investigations and debates over the past 60 years. In this review, we focus on the design of collective motions that are achieved by integrating, in space and time, several or many of these individual mechanical units together. In particular, we provide an in-depth look at the intermolecular couplings used to physically connect a number of artificial mechanically active molecular units such as photochromic molecular switches, nanomachines based on mechanical bonds, molecular rotors, and light-powered rotary motors. We highlight the various functioning principles that can lead to their collective motion at various length scales. We also emphasize how their synchronized, or desynchronized, mechanical behavior can lead to emerging functional properties and to their implementation into new active devices and materials.

Substrate topography interacts with substrate stiffness and culture time to regulate mechanical properties and smooth muscle differentiation of mesenchymal stem cells

Substrate stiffness and topography are two powerful means by which mesenchymal stem cells (MSCs) activities can be modulated. The effects of substrate stiffness on the MSCs mechanical properties were investigated previously, however, the role of substrate topography in this regard is not yet well understood. Moreover, in vessel wall, these two physical cues act simultaneously to regulate cellular function, hence it is important to investigate their cooperative effects on cellular activity. Herein, we investigated the combined effects of substrate stiffness, substrate topography and culture time on the mechanical behavior of MSCs. The MSCs were cultured on the stiff and soft substrates with or without micro-grooved topography for 10 days and their viscoelastic properties and smooth muscle (SM) gene expression were investigated on days 2, 6 and 10. In general, substrate topography significantly interacted with substrate stiffness as well as culture time in the modulation of cell viscoelastic behavior and SM gene expression. The micro-grooved, stiff substrates resulted in the maximum cell stiffness and gene expression of α-actin and h1-calponin, and these values were detected to be minimum in the smooth, soft substrates. The findings can be helpful in the mechano-regulation of MSCs for vascular tissue engineering applications.

Atomic Force Microscopy in Characterizing Cell Mechanics for Biomedical Applications: A Review

Cell mechanics is a novel label-free biomarker for indicating cell states and pathological changes. The advent of atomic force microscopy (AFM) provides a powerful tool for quantifying the mechanical properties of single living cells in aqueous conditions. The wide use of AFM in characterizing cell mechanics in the past two decades has yielded remarkable novel insights in understanding the development and progression of certain diseases, such as cancer, showing the huge potential of cell mechanics for practical applications in the field of biomedicine. In this paper, we reviewed the utilization of AFM to characterize cell mechanics. First, the principle and method of AFM single-cell mechanical analysis was presented, along with the mechanical responses of cells to representative external stimuli measured by AFM. Next, the unique changes of cell mechanics in two types of physiological processes (stem cell differentiation, cancer metastasis) revealed by AFM were summarized. After that, the molecular mechanisms guiding cell mechanics were analyzed. Finally the challenges and future directions were discussed.

Fabrication of Patterned Thermoresponsive Microgel Strips on Cell-Adherent Background and Their Application for Cell Sheet Recovery

Interfaces between materials and cells play a critical role in cell biomedical applications. Here, a simple, robust, and cost-effective method is developed to fabricate patterned thermoresponsive poly(N-isopropylacrylamide-co-styrene) microgel strips on a polyethyleneimine-precoated, non-thermoresponsive cell-adherent glass coverslip. The aim is to investigate whether cell sheets could be harvested from these cell-adherent surfaces patterned with thermoresponsive strips comprised of the microgels. We hypothesize that if the cell-to-cell interaction is strong enough to retain the whole cell sheet from disintegration, the cell segments growing on the thermoresponsive strips may drag the cell segments growing on the cell-adherent gaps to detach, ending with a whole freestanding and transferable cell sheet. Critical value concerning the width of the thermoresponsive strip and its ratio to the non-thermoresponsive gap may exist for cell sheet recovery from this type of surface pattern. To obtain this critical value, a series of strip patterns with various widths of thermoresponsive strip and non-thermoresponsive gap were prepared using negative microcontact printing technology, with COS7 fibroblast cells being used to test the growth and detachment. The results unraveled that COS7 cells preferentially attached and proliferated on the cell-adherent, non-thermoresponsive gaps to form patterned cell layers and that they subsequently proliferated to cover the microgel strips to form a confluent cell layer. Intact COS7 cell sheets could be recovered when the width of the thermoresponsive strip is no smaller than that of the non-thermoresponsive gap. Other cells such as HeLa, NIH3T3, 293E, and L929 could grow similarly; that is, they showed initial preference to the non-thermoresponsive gaps and then migrated to cover the entire patterned surface. However, it was difficult to detach them as cell sheets due to the weak interactions within the cell layers formed. In contrast, when COS7 and HeLa cells were cultured successively, they formed the cocultured cell layer that could be detached together. These freestanding patterned cell sheets could lead to the development of more elaborate tumor models for drug targeting and interrogation.

Light-responsive polymer brushes: active topographic cues for cell culture applications

Azopolymer brushes were patterned using interference lithography and erased using ultrasonication. This substrate was able to induce cell orientation.

Light-Driven Reversible Shaping of Individual Azopolymeric Micro-Pillars

Azopolymers are known to exhibit a strong light responsivity known as athermal photofluidization. Although the underlying physics is still under debate, athermal photofluidization has been demonstrated to trigger mass-migration according to the polarization of a proper illumination light. Here, a polymer blend is proposed wherein a commercial azo-polyelectrolyte is mixed with a passive polymer. The blend is patterned as an array of micro-pillars that are individually exposed to visible laser illumination. Thanks to the interplay between the two blend components, a reversible and controlled deformation of the micro-pillars by periodically tuning the laser polarization in time is demonstrated. A reduced mobility of the azo-compound allows to repeatibly elongate and rotate micro-pillars along specific directions, with no significant material flow outisde the initial volume and no significant degradation of the structure morphology over several cycles. The proposed work suggests new degrees of freedom in controlling the mechanical features of micro-patterned light-responsive materials that can be usefully exploited in many application fields.

Effects of methotrexate on the viscoelastic properties of single cells probed by atomic force microscopy

Methotrexate is a commonly used anti-cancer chemotherapy drug. Cellular mechanical properties are fundamental parameters that reflect the physiological state of a cell. However, so far the role of cellular mechanical properties in the actions of methotrexate is still unclear. In recent years, probing the behaviors of single cells with the use of atomic force microscopy (AFM) has contributed much to the field of cell biomechanics. In this work, with the use of AFM, the effects of methotrexate on the viscoelastic properties of four types of cells were quantitatively investigated. The inhibitory and cytotoxic effects of methotrexate on the proliferation of cells were observed by optical and fluorescence microscopy. AFM indenting was used to measure the changes of cellular viscoelastic properties (Young's modulus and relaxation time) by using both conical tip and spherical tip, quantitatively showing that the stimulation of methotrexate resulted in a significant decrease of both cellular Young's modulus and relaxation times. The morphological changes of cells induced by methotrexate were visualized by AFM imaging. The study improves our understanding of methotrexate action and offers a novel way to quantify drug actions at the single-cell level by measuring cellular viscoelastic properties, which may have potential impacts on developing label-free methods for drug evaluation.

A comparative study of photoinduced deformation in azobenzene containing polymer films

In this paper two groups supporting different views on the mechanism of light induced polymer deformation argue about the respective underlying theoretical conceptions, in order to bring this interesting debate to the attention of the scientific community. The group of Prof. Nicolae Hurduc supports the model claiming that the cyclic isomerization of azobenzenes may cause an athermal transition of the glassy azobenzene containing polymer into a fluid state, the so-called photo-fluidization concept. This concept is quite convenient for an intuitive understanding of the deformation process as an anisotropic flow of the polymer material. The group of Prof. Svetlana Santer supports the re-orientational model where the mass-transport of the polymer material accomplished during polymer deformation is stated to be generated by the light-induced re-orientation of the azobenzene side chains and as a consequence of the polymer backbone that in turn results in local mechanical stress, which is enough to irreversibly deform an azobenzene containing material even in the glassy state. For the debate we chose three polymers differing in the glass transition temperature, 32 °C, 87 °C and 95 °C, representing extreme cases of flexible and rigid materials. Polymer film deformation occurring during irradiation with different interference patterns is recorded using a homemade set-up combining an optical part for the generation of interference patterns and an atomic force microscope for acquiring the kinetics of film deformation. We also demonstrated the unique behaviour of azobenzene containing polymeric films to switch the topography in situ and reversibly by changing the irradiation conditions. We discuss the results of reversible deformation of three polymers induced by irradiation with intensity (IIP) and polarization (PIP) interference patterns, and the light of homogeneous intensity in terms of two approaches: the re-orientational and the photo-fluidization concepts. Both agree in that the formation of opto-mechanically induced stresses is a necessary prerequisite for the process of deformation. Using this argument, the deformation process can be characterized either as a flow or mass transport.

Photoinduced change in the shape of azobenzene-based molecular glass particles fixed in agar gel

A new photomechanical phenomenon was observed, in which azobenzene-based molecular glass particles fixed in an isotropic agar gel environment became elongated and formed string-like structures upon being irradiated with a linearly polarized laser beam.

Azo-polymers photofluidisation – a transient state of matter emulated by molecular motors

In the present paper we propose a new phenomenological model of inscription based on a particular state of matter induced by continuous laser irradiation.