Use of nanoscale mechanical stimulation for control and manipulation of cell behaviour

Non-viral gene delivery to human mesenchymal stem cells: a practical guide towards cell engineering

In recent decades, human mesenchymal stem cells (hMSCs) have gained momentum in the field of cell therapy for treating cartilage and bone injuries. Despite the tri-lineage multipotency, proliferative properties, and potent immunomodulatory effects of hMSCs, their clinical potential is hindered by donor variations, limiting their use in medical settings. To address this challenge, gene delivery technologies have emerged as a promising approach to modulate the phenotype and commitment of hMSCs towards specific cell lineages, thereby enhancing osteochondral repair strategies. This review provides a comprehensive overview of current non-viral gene delivery approaches used to engineer MSCs, highlighting key factors such as the choice of nucleic acid or delivery vector, transfection strategies, and experimental parameters. Additionally, it outlines various protocols and methods for qualitative and quantitative evaluation of their therapeutic potential as a delivery system in osteochondral regenerative applications. In summary, this technical review offers a practical guide for optimizing non-viral systems in osteochondral regenerative approaches. hMSCs constitute a key target population for gene therapy techniques. Nevertheless, there is a long way to go for their translation into clinical treatments. In this review, we remind the most relevant transfection conditions to be optimized, such as the type of nucleic acid or delivery vector, the transfection strategy, and the experimental parameters to accurately evaluate a delivery system. This survey provides a practical guide to optimizing non-viral systems for osteochondral regenerative approaches.

Vibropolyfection: coupling polymer-mediated gene delivery to mechanical stimulation to enhance transfection of adherent cells

BACKGROUND

With the success of recent non-viral gene delivery-based COVID-19 vaccines, nanovectors have gained some public acceptance and come to the forefront of advanced therapies. Unfortunately, the relatively low ability of the vectors to overcome cellular barriers adversely affects their effectiveness. Scientists have thus been striving to develop ever more effective gene delivery vectors, but the results are still far from satisfactory. Therefore, developing novel strategies is probably the only way forward to bring about genuine change. Herein, we devise a brand-new gene delivery strategy to boost dramatically the transfection efficiency of two gold standard nucleic acid (NA)/polymer nanoparticles (polyplexes) in vitro.

RESULTS

We conceived a device to generate milli-to-nanoscale vibrational cues as a function of the frequency set, and deliver vertical uniaxial displacements to adherent cells in culture. A short-lived high-frequency vibrational load (t = 5 min, f = 1,000 Hz) caused abrupt and extensive plasmalemma outgrowths but was safe for cells as neither cell proliferation rate nor viability was affected. Cells took about 1 hr to revert to quasi-naïve morphology through plasma membrane remodeling. In turn, this eventually triggered the mechano-activated clathrin-mediated endocytic pathway and made cells more apt to internalize polyplexes, resulting in transfection efficiencies increased from 10-to-100-fold. Noteworthy, these results were obtained transfecting three cell lines and hard-to-transfect primary cells.

CONCLUSIONS

In this work, we focus on a new technology to enhance the intracellular delivery of NAs and improve the transfection efficiency of non-viral vectors through priming adherent cells with a short vibrational stimulation. This study paves the way for capitalizing on physical cell stimulation(s) to significantly raise the effectiveness of gene delivery vectors in vitro and ex vivo.

Mechanical Behaviour Evaluation of Porous Scaffold for Tissue-Engineering Applications Using Finite Element Analysis

In recent years, finite element analysis (FEA) models of different porous scaffold shapes consisting of various materials have been developed to predict the mechanical behaviour of the scaffolds and to address the initial goals of 3D printing. Although mechanical properties of polymeric porous scaffolds are determined through FEA, studies on the polymer nanocomposite porous scaffolds are limited. In this paper, FEA with the integration of material designer and representative volume elements (RVE) was carried out on a 3D scaffold model to determine the mechanical properties of boron nitride nanotubes (BNNTs)-reinforced gelatin (G) and alginate (A) hydrogel. The maximum stress regions were predicted by FEA stress distribution. Furthermore, the analysed material model and the boundary conditions showed minor deviation (4%) compared to experimental results. It was noted that the stress regions are detected at the zone close to the pore areas. These results indicated that the model used in this work could be beneficial in FEA studies on 3D-printed porous structures for tissue engineering applications.

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.

Janus 3D printed dynamic scaffolds for nanovibration-driven bone regeneration

The application of physical stimuli to cell cultures has shown potential to modulate multiple cellular functions including migration, differentiation and survival. However, the relevance of these in vitro models to future potential extrapolation in vivo depends on whether stimuli can be applied “externally”, without invasive procedures. Here, we report on the fabrication and exploitation of dynamic additive-manufactured Janus scaffolds that are activated on-command via external application of ultrasounds, resulting in a mechanical nanovibration that is transmitted to the surrounding cells. Janus scaffolds were spontaneously formed via phase-segregation of biodegradable polycaprolactone (PCL) and polylactide (PLA) blends during the manufacturing process and behave as ultrasound transducers (acoustic to mechanical) where the PLA and PCL phases represent the active and backing materials, respectively. Remote stimulation of Janus scaffolds led to enhanced cell proliferation, matrix deposition and osteogenic differentiation of seeded human bone marrow derived stromal cells (hBMSCs) via formation and activation of voltage-gated calcium ion channels.

Fabrication of dynamic, reversible and biocompatible scaffolds with non-invasive external triggers has so far been limited. Here, the authors report on the creation of 3D printed scaffolds with Janus structure that produce nanovibrations when exposed to ultrasound, promoting bone regeneration.

Biophysical phenotyping of mesenchymal stem cells along the osteogenic differentiation pathway

Mesenchymal stem cells represent an important resource, for bone regenerative medicine and therapeutic applications. This review focuses on new advancements and biophysical tools which exploit different physical and chemical markers of mesenchymal stem cell populations, to finely characterize phenotype changes along their osteogenic differentiation process. Special attention is paid to recently developed label-free methods, which allow monitoring cell populations with minimal invasiveness. Among them, quantitative phase imaging, suitable for single-cell morphometric analysis, and nanoindentation, functional to cellular biomechanics investigation. Moreover, the pool of ion channels expressed in cells during differentiation is discussed, with particular interest for calcium homoeostasis.Altogether, a biophysical perspective of osteogenesis is proposed, offering a valuable tool for the assessment of the cell stage, but also suggesting potential physiological links between apparently independent phenomena.

Regulation of gene transfection by cell size, shape and elongation on micropatterned surfaces

Gene transfection has been widely studied due to its potential applications in tissue repair and gene therapy. Many studies have focused on designing gene carriers and developing novel transfection techniques. However, the influence of cell size, shape and elongation on gene transfection has rarely been investigated. In this study, poly(vinyl alcohol)-micropatterned surfaces were prepared to precisely manipulate the size, shape and elongation of mesenchymal stem cells, and the influences of these factors on gene transfection were investigated. Cell size showed a significant influence on gene transfection. Elongation could affect the gene transfection of large cells but not small cells. Cells with a large spreading area and high aspect ratio showed high transfection with exogenous plasmid DNA. In particular, the transfection efficiency was the highest in micropatterned cells with a spreading area of 5024 μm2 and an aspect ratio of 8 : 1. In contrast, cell shape had no significant influence on gene transfection. The different influences of cell size, shape and elongation were correlated with their respective impacts on cytoskeletal structures, cellular nanoparticle uptake and DNA synthesis. Cells with a large size and elongated morphology showed well-organized actin filaments with a high cellular modulus, therefore promoting cellular nanoparticle uptake and DNA synthesis. Cells with different shapes showed similarities in actin filament organization, cellular modulus, uptake capacity and DNA synthesis. The results suggest the importance of cell size and elongation in exogenous gene transfection and should provide useful information for gene transfection and gene therapy.

Reducing Results Variance in Lifespan Machines: An Analysis of the Influence of Vibrotaxis on Wild-Type Caenorhabditis elegans for the Death Criterion

Nowadays, various artificial vision-based machines automate the lifespan assays of C. elegans. These automated machines present wider variability in results than manual assays because in the latter worms can be poked one by one to determine whether they are alive or not. Lifespan machines normally use a “dead or alive criterion” based on nematode position or pose changes, without poking worms. However, worms barely move on their last days of life, even though they are still alive. Therefore, a long monitoring period is necessary to observe motility in order to guarantee worms are actually dead, or a stimulus to prompt worm movement is required to reduce the lifespan variability measure. Here, a new automated vibrotaxis-based method for lifespan machines is proposed as a solution to prompt a motion response in all worms cultured on standard Petri plates in order to better distinguish between live and dead individuals. This simple automated method allows the stimulation of all animals through the whole plate at the same time and intensity, increasing the experiment throughput. The experimental results exhibited improved live-worm detection using this method, and most live nematodes (>93%) reacted to the vibration stimulus. This method increased machine sensitivity by decreasing results variance by approximately one half (from ±1 individual error per plate to ±0.6) and error in lifespan curve was reduced as well (from 2.6% to 1.2%).

Integrated design and fabrication strategies for biomechanically and biologically functional PLA/β-TCP nanofiber reinforced GelMA scaffold for tissue engineering applications

We present an integrated design and fabrication strategy for the development of hierarchically structured biomechanically and biologically functional tissue scaffold. An integration of β-TCP incorporated fluffy type nanofibers and biodegradable interpenetrating gelatin-hydrogel networks (IGN) result in biomimetic tissue engineered constructs with fully tunable properties that can match specific tissue requirements. FESEM images showed that nanofibers were efficiently assembled into an orientation of IGN without disturbing its pore architecture. The pore architecture, compressive stiffness and modulus, swelling, and the biological properties of the composite constructs can be tailored by adjusting the composition of nanofiber content with respect to IGN. Experimental results of cell proliferation assay and confocal microscopy imaging showed that the as-fabricated composite constructs exhibit excellent ability for MC3T3-E1 cell proliferation, infiltration and growth. Furthermore, β-TCP incorporated functionalized nanofiber enhanced the biomimetic mineralization, cell infiltration and cell proliferation. Within two weeks of cell-seeding, the composite construct exhibited enhanced osteogenic performance (Runx2, osterix and ALP gene expression) compared to pristine IGN hydrogel scaffold. Our integrated design and fabrication approach enables the assembly of nanofiber within IGN architecture, laying the foundation for biomimetic scaffold.

Design, Implementation, and Validation of a Piezoelectric Device to Study the Effects of Dynamic Mechanical Stimulation on Cell Proliferation, Migration and Morphology

Cell functions and behavior are regulated not only by soluble (biochemical) signals but also by biophysical and mechanical cues within the cells' microenvironment. Thanks to the dynamical and complex cell machinery, cells are genuine and effective mechanotransducers translating mechanical stimuli into biochemical signals, which eventually alter multiple aspects of their own homeostasis. Given the dominant and classic biochemical-based views to explain biological processes, it could be challenging to elucidate the key role that mechanical parameters such as vibration, frequency, and force play in biology. Gaining a better understanding of how mechanical stimuli (and their mechanical parameters associated) affect biological outcomes relies partially on the availability of experimental tools that may allow researchers to alter mechanically the cell's microenvironment and observe cell responses. Here, we introduce a new device to study in vitro responses of cells to dynamic mechanical stimulation using a piezoelectric membrane. Using this device, we can flexibly change the parameters of the dynamic mechanical stimulation (frequency, amplitude, and duration of the stimuli), which increases the possibility to study the cell behavior under different mechanical excitations. We report on the design and implementation of such device and the characterization of its dynamic mechanical properties. By using this device, we have performed a preliminary study on the effect of dynamic mechanical stimulation in a cell monolayer of an epidermal cell line (HaCaT) studying the effects of 1 Hz and 80 Hz excitation frequencies (in the dynamic stimuli) on HaCaT cell migration, proliferation, and morphology. Our preliminary results indicate that the response of HaCaT is dependent on the frequency of stimulation. The device is economic, easily replicated in other laboratories and can support research for a better understanding of mechanisms mediating cellular mechanotransduction.

Reduction of Pseudomonas aeruginosa biofilm formation through the application of nanoscale vibration

Bacterial biofilms pose a significant burden in both healthcare and industrial environments. With the limited effectiveness of current biofilm control strategies, novel or adjunctive methods in biofilm control are being actively pursued. Reported here, is the first evidence of the application of nanovibrational stimulation (nanokicking) to reduce the biofilm formation of Pseudomonas aeruginosa. Nanoscale vertical displacements (approximately 60 nm) were imposed on P. aeruginosa cultures, with a significant reduction in biomass formation observed at frequencies between 200 and 4000 Hz at 24 h. The optimal reduction of biofilm formation was observed at 1 kHz, with changes in the physical morphology of the biofilms. Scanning electron microscope imaging of control and biofilms formed under nanovibrational stimulation gave indication of a reduction in extracellular matrix (ECM). Quantification of the carbohydrate and protein components of the ECM was performed and showed a significant reduction at 24 h at 1 kHz frequency. To model the forces being exerted by nanovibrational stimulation, laser interferometry was performed to measure the amplitudes produced across the Petri dish surfaces. Estimated peak forces on each cell, associated with the nanovibrational stimulation technique, were calculated to be in the order of 10 pN during initial biofilm formation. This represents a potential method of controlling microbial biofilm formation in a number of important settings in industry and medical related processes.

Design, construction and characterisation of a novel nanovibrational bioreactor and cultureware for osteogenesis

In regenerative medicine, techniques which control stem cell lineage commitment are a rapidly expanding field of interest. Recently, nanoscale mechanical stimulation of mesenchymal stem cells (MSCs) has been shown to activate mechanotransduction pathways stimulating osteogenesis in 2D and 3D culture. This has the potential to revolutionise bone graft procedures by creating cellular graft material from autologous or allogeneic sources of MSCs without using chemical induction. With the increased interest in mechanical stimulation of cells and huge potential for clinical use, it is apparent that researchers and clinicians require a scalable bioreactor system that provides consistently reproducible results with a simple turnkey approach. A novel bioreactor system is presented that consists of: a bioreactor vibration plate, calibrated and optimised for nanometre vibrations at 1 kHz, a power supply unit, which supplies a 1 kHz sine wave signal necessary to generate approximately 30 nm of vibration amplitude, and custom 6-well cultureware with toroidal shaped magnets incorporated in the base of each well for conformal attachment to the bioreactor’s magnetic vibration plate. The cultureware and vibration plate were designed using finite element analysis to determine the modal and harmonic responses, and validated by interferometric measurement. This helps ensure that the vibration plate and cultureware, and thus collagen and MSCs, all move as a rigid body, avoiding large deformations close to the resonant frequency of the vibration plate and vibration damping beyond the resonance. Assessment of osteogenic protein expression was performed to confirm differentiation of MSCs after initial biological experiments with the system, as well as atomic force microscopy of the 3D gel constructs during vibrational stimulation to verify that strain hardening of the gel did not occur. This shows that cell differentiation was the result of the nanovibrational stimulation provided by the bioreactor alone, and that other cell differentiating factors, such as stiffening of the collagen gel, did not contribute.

Zero-dimensional, one-dimensional, two-dimensional and three-dimensional biomaterials for cell fate regulation

The interaction of biological cells with artificial biomaterials is one of the most important issues in tissue engineering and regenerative medicine. The interaction is strongly governed by physical and chemical properties of the materials and displayed with differentiated cellular behaviors, including cell self-renewal, differentiation, reprogramming, dedifferentiation, or transdifferentiation as a result. A number of engineered biomaterials with micro- or nano-structures have been developed to mimic structural components of cell niche and specific function of extra cellular matrix (ECM) over past two decades. In this review article, we briefly introduce the fabrication of biomaterials and their classification into zero-dimensional (0D), one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) ones. More importantly, the influence of different biomaterials on inducing cell self-renewal, differentiation, reprogramming, dedifferentiation, and transdifferentiation was discussed based on the progress at 0D, 1D, 2D and 3D levels, following which the current research limitations and research perspectives were provided.

Nanoscale Mechanical Stimulation Method for Quantifying C. elegans Mechanosensory Behavior and Memory

Withdrawal escape response of C. elegans to nonlocalized vibration is a useful behavioral paradigm to examine mechanisms underlying mechanosensory behavior and its memory-dependent change. However, there are very few methods for investigating the degree of vibration frequency, amplitude and duration needed to induce behavior and memory. Here, we establish a new system to quantify C. elegans mechanosensory behavior and memory using a piezoelectric sheet speaker. In the system, we can flexibly change the vibration properties at a nanoscale displacement level and quantify behavioral responses under each vibration property. This system is an economic setup and easily replicated in other laboratories. By using the system, we clearly detected withdrawal escape responses and confirmed habituation memory. This system will facilitate the understanding of physiological aspects of C. elegans mechanosensory behavior in the future.

Strain and Vibration in Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are multipotent cells capable of differentiating into any mesenchymal tissue, including bone, cartilage, muscle, and fat. MSC differentiation can be influenced by a variety of stimuli, including environmental and mechanical stimulation, scaffold physical properties, or applied loads. Numerous studies have evaluated the effects of vibration or cyclic tensile strain on MSCs towards developing a mechanically based method of differentiation, but there is no consensus between studies and each investigation uses different culture conditions, which also influence MSC fate. Here we present an overview of the response of MSCs to vibration and cyclic tension, focusing on the effect of various culture conditions and strain or vibration parameters. Our review reveals that scaffold type (e.g., natural versus synthetic; 2D versus 3D) can influence cell response to vibration and strain to the same degree as loading parameters. Hence, in the efforts to use mechanical loading as a reliable method to differentiate cells, scaffold selection is as important as method of loading.

Stepwise morphological changes and cytoskeletal reorganization of human mesenchymal stem cells treated by short-time cyclic uniaxial stretch

This study aimed to investigate stepwise remodeling of human mesenchymal stem cells (hMSCs) in response to cyclic stretch through rearrangement and alignment of cells and cytoskeleton regulation toward smooth muscle cell (SMC) fate in different time spans. Image analysis techniques were utilized to calculate morphological parameters. Cytoskeletal reorganization was observed by investigating F-actin filaments using immunofluorescence staining, and expression level of contractile SMC markers was followed by a quantitative polymerase chain reaction method. Applying cyclic uniaxial stretch on cultured hMSCs, utilizing a costume-made device, led to alteration in fractal dimension (FD) and cytoskeleton structure toward continuous alignment and elongation of cells by elevation of strain duration. Actin filaments became more aligned perpendicular to the axis of mechanical stretch by increasing uniaxial loading duration. At first, FD met a significant decrease in 4 h loading duration then increased significantly by further loading up to 16 h, followed by another decrease up to 1 d of uniaxial stretching. HMSCs subjected to 24 h cyclic uniaxial stretching significantly expressed early and intermediate contractile SM markers. It was hypothesized that the increase in FD after 4 h while cells continuously became more aligned and elongated was due to initiation of change in phenotype that influenced arrangement of cells. At this point, change in cell phenotype started leading to change in morphology while mechanical loading still caused cell alignment and rearrangement. Results can be helpful when optimized engineered cells are needed based on mechanical condition for functional engineered tissue and cell therapy.

Ex-Vivo Tissues Engineering Modeling for Reconstructive Surgery Using Human Adult Adipose Stem Cells and Polymeric Nanostructured Matrix

The major challenge for stem cell translation regenerative medicine is the regeneration of damaged tissues by creating biological substitutes capable of recapitulating the missing function in the recipient host. Therefore, the current paradigm of tissue engineering strategies is the combination of a selected stem cell type, based on their capability to differentiate toward committed cell lineages, and a biomaterial, that, due to own characteristics (e.g., chemical, electric, mechanical property, nano-topography, and nanostructured molecular components), could serve as active scaffold to generate a bio-hybrid tissue/organ. Thus, effort has been made on the generation of in vitro tissue engineering modeling. Here, we present an in vitro model where human adipose stem cells isolated from lipoaspirate adipose tissue and breast adipose tissue, cultured on polymeric INTEGRA^® Meshed Bilayer Wound Matrix (selected based on conventional clinical applications) are evaluated for their potential application for reconstructive surgery toward bone and adipose tissue. We demonstrated that human adipose stem cells isolated from lipoaspirate and breast tissue have similar stemness properties and are suitable for tissue engineering applications. Finally, the overall results highlighted lipoaspirate adipose tissue as a good source for the generation of adult adipose stem cells.