Nanotopography as modulator of human mesenchymal stem cell function

Hierarchically Assembled Nanofiber Scaffold Guides Long Bone Regeneration by Promoting Osteogenic/Chondrogenic Differentiation of Endogenous Mesenchymal Stem Cells

Critical-sized segmental long bone defects represent a challenging clinical dilemma in the management of battlefield and trauma-related injuries. The residual bone marrow cavity of damaged long bones contains many bone marrow mesenchymal stem cells (BMSCs), which provide a substantial source of cells for bone repair. Thus, a three-dimensional (3D) vertically aligned nanofiber scaffold (VAS) is developed with long channels and large pore size. The pore of VAS toward the bone marrow cavity after transplantation, enables the scaffolds to recruit BMSCs from the bone marrow cavity to the defect area. In vivo, it is found that VAS can significantly shorten gap distance and promote new bone formation compared to the control and collagen groups after 4 and 8 weeks of implantation. The single-cell sequencing results discovered that the 3D nanotopography of VAS can promote BMSCs differentiation to chondrocytes and osteoblasts, and up-regulate related gene expression, resulting in enhancing the activities of bone regeneration, endochondral ossification, bone trabecula formation, bone mineralization, maturation, and remodeling. The Alcian blue and bone morphogenetic protein 2 (BMP-2) immunohistochemical staining verified significant cartilage formation and bone formation in the VAS group, corresponding to the single-cell sequencing results. The study can inspire the design of next-generation scaffolds for effective long-bone regeneration is expected by the authors.

Progress in the application of graphene and its derivatives to osteogenesis

As bone and joint injuries from various causes become increasingly prominent, how to effectively reconstruct and repair bone defects presents a difficult problem for clinicians and researchers. In recent years, graphene and its derivatives have been the subject of growing body of research and have been found to promote the proliferation and osteogenic differentiation of stem cells. This provides a new idea for solving the clinical problem of bone defects. However, as as numerous articles address various aspects and have not been fully systematized, there is an urgent need to classify and summarize them. In this paper, for the first time, the effects of graphene and its derivatives on stem cells in solution, in 2D and 3D structures and in vivo and their possible mechanisms are reviewed, and the cytotoxic effects of graphene and its derivatives were summarized and analyzed. The toxicity of graphene and its derivatives is further reviewed. In addition, we suggest possible future development directions of graphene and its derivatives in bone tissue engineering applications to provide a reference for further clinical application.

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.

Dissecting Physical and Biochemical Effects in Nanotopographical Regulation of Cell Behavior

Regulating cell behavior using nanotopography has been widely implemented. To facilitate cell adhesion, physical nanotopography is usually coated with adhesive proteins such as fibronectin (FN). However, the confounding effects of physical and biochemical cues of nanotopography hinder the understanding of nanotopography in regulating cell behavior, which ultimately limits the biomedical applications of nanotopography. To delineate the roles of the physical and biochemical cues in cell regulation, we fabricate substrates that have either the same physical nanotopography but different biochemical (FN) nanopatterns or identical FN nanopatterns but different physical nanotopographies. We then examine the influences of physical and biochemical cues of nanotopography on spreading, nuclear deformation, mechanotransduction, and function of human mesenchymal stem cells (hMSCs). Our results reveal that physical topographies, especially nanogratings, dominantly control cell spreading, YAP localization, proliferation, and differentiation of hMSCs. However, biochemical FN nanopatterns affect hMSC elongation, YAP intracellular localization, and lamin a/c (LAMAC) expression. Furthermore, we find that physical nanogratings induce nanoscale curvature of nuclei at the basal side, which attenuates the osteogenic differentiation of hMSCs. Collectively, our study highlights the dominant effect of physical nanotopography in regulating stem cell functions, while suggesting that fine-tuning of cell behavior can be achieved through altering the presentation of biochemical cues on substrate surfaces.

Biomimetic Mechanically Strong One-Dimensional Hydroxyapatite/Poly(d,l-lactide) Composite Inducing Formation of Anisotropic Collagen Matrix

Natural bone is a complex composite, consisting predominantly of collagen and hydroxyapatite (HA), which form a highly organized, hierarchical structure from the nano- to the macroscale. Because of its biphasic, anisotropic, ultrafine structural design, bone tissue possesses excellent mechanical properties. Herein, inspired by the composition and microstructure of natural bone, a biphasic composite consisting of highly aligned strontium/copper-doped one-dimensional hydroxyapatite (Sr/Cu-doped 1D HA) and poly(d,l-lactide) (PDLA) was developed. The presence and alignment of Sr/Cu-doped 1D HA crystals resulted in mechanical reinforcement of the polymer matrix, including compressive and tensile strength and modulus, fracture toughness, swelling resistance, and long-term structural stability. The compressive strength, tensile strength, and Young's modulus of the biomimetic composite were comparable to that of cortical bone. Biologically, the biomimetic composite showed a sustained release of the incorporated Sr and Cu ions, facilitated mineral deposition from simulated body fluid, and supported attachment, proliferation, and alkaline phosphatase activity of human mesenchymal stromal cells (hMSCs). Moreover, the highly aligned Sr/Cu-doped 1D HA crystals in the 3D porous scaffolds induced the alignment of hMSCs and secretion of an anisotropic collagen fiber matrix in 3D. The biomimetic Sr/Cu-doped 1D HA/PDLA composite presented here contributes to the current efforts aiming at the design and development of load-bearing bioactive synthetic bone graft substitutes. Moreover, the biomimetic composite may serve as a 3D platform for studying cell-extracellular matrix interactions in bone tissue.

Robust three-dimensional nanotube-in-micropillar array electrodes to facilitate size independent electroporation in blood cell therapy

Blood is an attractive carrier for plasmid and RNA-based medicine in cell therapy. Electroporation serves as a favorable delivery tool for simple operation, quick internalization, minimum cell culture involvement, and low contamination risk. However, the delivery outcome of electroporation heavily depends on the treated cells such as their type, size, and orientation to the electric field, not ideal for highly heterogeneous blood samples. Herein, a new electroporation system was developed towards effective transfection to cells in blood regardless of their large diversity. By coupling replica molding and infiltration-coating processes, we successfully configured a three-dimensional electrode comprised of a polymer micropillar array on which carbon nanotubes (CNTs) are partially embedded. During electroporation, cells sag between micropillars and deform to form a conformal contact with their top and side surfaces. The implanted CNTs not only provide a robust conductive coating for polymer micropattern but also have their protruded ends face the cell membrane vertically everywhere with maximum transmembrane potential. Regardless of their largely varied sizes and random dispersion, both individual blood cell type and whole blood samples were effectively transfected with plasmid DNA (85% after 24 h and 95% after 72 h, or 2.5-3.0 folds enhancement). High-dose RNA probes were also introduced, which regulate better the expression levels of exogenous and endogenous genes in blood cells. Besides its promising performance on non-viral delivery routes to cell-related studies and therapy, the involved new fabrication method also provides a convenient and effective way to construct flexible electronics with stable micro/nano features on the surface.

Osteoinductive and antimicrobial mechanisms of graphene-based materials for enhancing bone tissue engineering

Graphene-based materials (GMs) have great application prospects in bone tissue engineering due to their osteoinductive ability and antimicrobial activity. GMs induce osteogenic differentiation through several mechanisms and pathways in bone tissue engineering. First of all, the surface and high hardness of the porous folds of graphene or graphene oxide (GO) can generate mechanical stimulation to initiate a cascade of reactions that promote osteogenic differentiation without any chemical inducers. In addition, change of the extracellular matrix (ECM), regulation of macrophage polarization, the oncostatin M (OSM) signaling pathway, the MAPK signaling pathway, the BMP signaling pathway, the Wnt/β-catenin signaling pathway, and other pathways are involved in GMs' regulation of osteogenesis. In bone tissue engineering, GMs prevent the formation of microbial biofilms mainly through preventing microbial adhesion and killing them. The former is mainly achieved by reducing surface free energy (SFE) and increasing hydrophobicity. The latter mainly includes oxidative stress and photothermal/photodynamic effects. Graphene and its derivatives (GDs) are mainly combined with bioactive ceramic materials, metal materials and macromolecular polymers to play an antimicrobial effect in bone tissue engineering. Concentration, number of layers, and type of GDs often affect the antimicrobial activity of GMs. In this paper, we reviewed relevant osteoinductive and antimicrobial mechanisms of GMs and their applications in bone tissue engineering.

The osteogenic differentiation of human bone marrow stromal cells induced by nanofiber scaffolds using bioinformatics

This article aims to investigate the mechanism of behaviors of human bone marrow stromal cells (hBMSCs) affected by scaffold structure combining Monte Carlo feature selection (MFCS), incremental feature selection (IFS) and support vector machine (SVM). The specific differentially expressed genes (DEGs) of hBMSCs cultured on nanofiber (NF) scaffolds and freeform fabrication (FFF) scaffolds were obtained. Key genes were screened from common genes between osteogenic DEGs and NF specific DEGs with MFCS, IFS and SVM. The results demonstrated that NF scaffolds induced hBMSCs to express more genes related to osteogenic differentiation. Finally, 16 key genes were identified among the common genes. The common genes were significantly enriched in Rap1 signaling pathway, extracellular matrix and ossification. The results in this study suggested that the gene expression of hBMSCs was sensitive to NF scaffolds and FFF scaffolds, and the osteogenic differentiation of hBMSCs could be enhanced by NF scaffolds.

Biomaterials with structural hierarchy and controlled 3D nanotopography guide endogenous bone regeneration

Biomaterials without exogenous cells or therapeutic agents often fail to achieve rapid endogenous bone regeneration with high quality. Here, we reported a class of three-dimensional (3D) nanofiber scaffolds with hierarchical structure and controlled alignment for effective endogenous cranial bone regeneration. 3D scaffolds consisting of radially aligned nanofibers guided and promoted the migration of bone marrow stem cells from the surrounding region to the center in vitro. These scaffolds showed the highest new bone volume, surface coverage, and mineral density among the tested groups in vivo. The regenerated bone exhibited a radially aligned fashion, closely recapitulating the scaffold's architecture. The organic phase in regenerated bone showed an aligned, layered, and densely packed structure, while the inorganic mineral phase showed a uniform distribution with smaller pore size and an even distribution of stress upon the simulated compression. We expect that this study will inspire the design of next-generation biomaterials for effective endogenous bone regeneration with desired quality.

Nanotopography-Modulated Epithelial Cell Collective Migration

Matrix nanotopography plays an essential role in regulating cell behaviors including cell proliferation, differentiation, and migration. While studies on isolated single cell migration along the nanostructural orientation have been reported for various cell types, there remains a lack of understanding of how nanotopography regulates the behavior of collectively migrating cells during processes such as epithelial wound healing. We demonstrated that collective migration of epithelial cells was promoted on nanogratings perpendicular to, but not on those parallel to, the wound-healing axis. We further discovered that nanograting-modulated epithelial migration was dominated by the adhesion turnover process, which was Rho-associated protein kinase activity-dependent, and the lamellipodia protrusion at the cell leading edge, which was Rac1-GTPase activity-dependent. This work provides explanations to the distinct migration behavior of epithelial cells on nanogratings, and indicates that the effect of nanotopographic modulations on cell migration is cell-type dependent and involves complex mechanisms.

Novel low shear 3D bioreactor for high purity mesenchymal stem cell production

Bone marrow derived human Mesenchymal Stem Cells (hMSCs) are an attractive candidate for regenerative medicine. However, their harvest can be invasive, painful, and expensive, making it difficult to supply the enormous amount of pure hMSCs needed for future allogeneic therapies. Because of this, a robust method of scaled bioreactor culture must be designed to supply the need for high purity, high density hMSC yields. Here we test a scaled down model of a novel bioreactor consisting of an unsubmerged 3D printed Polylactic Acid (PLA) lattice matrix wetted by culture media. The growth matrix is uniform, replicable, and biocompatible, enabling homogenous cell culture in three dimensions. The goal of this study was to prove that hMSCs would culture well in this novel bioreactor design. The system tested resulted in comparable stem cell yields to other cell culture systems using bone marrow derived hMSCs, while maintaining viability (96.54% ±2.82), high purity (>98% expression of combined positive markers), and differentiation potential.

ECM-Mimetic Nylon Nanofiber Scaffolds for Neurite Growth Guidance

Numerous nanostructured synthetic scaffolds mimicking the architecture of the natural extracellular matrix (ECM) have been described, but the polymeric nanofibers comprising the scaffold were substantially thicker than the natural collagen nanofibers of neural ECM. Here, we report neuron growth on electrospun scaffolds of nylon-4,6 fibers with an average diameter of 60 nm, which closely matches the diameter of collagen nanofibers of neural ECM, and compare their properties with the scaffolds of thicker 300 nm nanofibers. Previously unmodified nylon was not regarded as an independent nanostructured matrix for guided growth of neural cells; however, it is particularly useful for ultrathin nanofiber production. We demonstrate that, while both types of fibers stimulate directed growth of neuronal processes, ultrathin fibers are more efficient in promoting and accelerating neurite elongation. Both types of scaffolds also improved synaptogenesis and the formation of connections between hippocampal neurons; however, the mechanisms of interaction of neurites with the scaffolds were substantially different. While ultrathin fibers formed numerous weak immature β1-integrin-positive focal contacts localized over the entire cell surface, scaffolds of submicron fibers formed β1-integrin focal adhesions only on the cell soma. This indicates that the scaffold nanotopology can influence focal adhesion assembly involving various integrin subunits. The fabricated nanostructured scaffolds demonstrated high stability and resistance to biodegradation, as well as absence of toxic compound release after 1 month of incubation with live cells in vitro. Our results demonstrate the high potential of this novel type of nanofibers for clinical application as substrates facilitating regeneration of nervous tissue.

The effect of carbon nanotubes on osteogenic functions of adipose-derived mesenchymal stem cells in vitro and bone formation in vivo compared with that of nano-hydroxyapatite and the possible mechanism

It has been well recognized that the development and use of artificial materials with high osteogenic ability is one of the most promising means to replace bone grafting that has exhibited various negative effects. The biomimetic features and unique physiochemical properties of nanomaterials play important roles in stimulating cellular functions and guiding tissue regeneration. But efficacy degree of some nanomaterials to promote specific tissue formation is still not clear. We hereby comparatively studied the osteogenic ability of our treated multi-walled carbon nanotubes (MCNTs) and the main inorganic mineral component of natural bone, nano-hydroxyapatite (nHA) in the same system, and tried to tell the related mechanism. In vitro culture of human adipose-derived mesenchymal stem cells (HASCs) on the MCNTs and nHA demonstrated that although there was no significant difference in the cell adhesion amount between on the MCNTs and nHA, the cell attachment strength and proliferation on the MCNTs were better. Most importantly, the MCNTs could induce osteogenic differentiation of the HASCs better than the nHA, the possible mechanism of which was found to be that the MCNTs could activate Notch involved signaling pathways by concentrating more proteins, including specific bone-inducing ones. Moreover, the MCNTs could induce ectopic bone formation in vivo while the nHA could not, which might be because MCNTs could stimulate inducible cells in tissues to form inductive bone better than nHA by concentrating more proteins including specific bone-inducing ones secreted from M2 macrophages. Therefore, MCNTs might be more effective materials for accelerating bone formation even than nHA.

The Implication of Spatial Statistics in Human Mesenchymal Stem Cell Response to Nanotubular Architectures

INTRODUCTION

In recent years there has been ample interest in nanoscale modifications of synthetic biomaterials to understand fundamental aspects of cell-surface interactions towards improved biological outcomes. In this study, we aimed at closing in on the effects of nanotubular TiO2 surfaces with variable nanotopography on the response on human mesenchymal stem cells (hMSCs). Although the influence of TiO2 nanotubes on the cellular response, and in particular on hMSC activity, has already been addressed in the past, previous studies overlooked critical morphological, structural and physical aspects that go beyond the simple nanotube diameter, such as spatial statistics.

METHODS

To bridge this gap, we implemented an extensive characterization of nanotubular surfaces generated by anodization of titanium with a focus on spatial structural variables including eccentricity, nearest neighbour distance (NND) and Voronoi entropy, and associated them to the hMSC response. In addition, we assessed the biological potential of a two-tiered honeycomb nanoarchitecture, which allowed the detection of combinatory effects that this hierarchical structure has on stem cells with respect to conventional nanotubular designs. We have combined experimental techniques, ranging from Scanning Electron (SEM) and Atomic Force (AFM) microscopy to Raman spectroscopy, with computational simulations to characterize and model nanotubular surfaces. We evaluated the cell response at 6 hrs, 1 and 2 days by fluorescence microscopy, as well as bone mineral deposition by Raman spectroscopy, demonstrating substrate-induced differential biological cueing at both the short- and long-term.

RESULTS

Our work demonstrates that the nanotube diameter is not sufficient to comprehensively characterize nanotubular surfaces and equally important parameters, such as eccentricity and wall thickness, ought to be included since they all contribute to the overall spatial disorder which, in turn, dictates the overall bioactive potential. We have also demonstrated that nanotubular surfaces affect the quality of bone mineral deposited by differentiated stem cells. Lastly, we closed in on the integrated effects exerted by the superimposition of two dissimilar nanotubular arrays in the honeycomb architecture.

DISCUSSION

This work delineates a novel approach for the characterization of TiO2 nanotubes which supports the incorporation of critical spatial structural aspects that have been overlooked in previous research. This is a crucial aspect to interpret cellular behaviour on nanotubular substrates. Consequently, we anticipate that this strategy will contribute to the unification of studies focused on the use of such powerful nanostructured surfaces not only for biomedical applications but also in other technology fields, such as catalysis.

Tough Anisotropic Silk Nanofiber Hydrogels with Osteoinductive Capacity

Multiple physical cues such as hierarchical microstructures, topography, and stiffness influence cell fate during tissue regeneration. Yet, introducing multiple physical cues to the same biomaterial remains a challenge. Here, a synergistic cross-linking strategy was developed to fabricate protein hydrogels with multiple physical cues based on combinations of two types of silk nanofibers. β-sheet-rich silk nanofibers (BSNFs) were blended with amorphous silk nanofibers (ASNFs) to form composite nanofiber systems. The composites were transformed into tough hydrogels through horseradish peroxidase (HRP) cross-linking in an electric field, where ASNFs were cross-linked with HRP, while BSNFs were aligned by the electrical field. Anisotropic morphologies and higher stiffness of 120 kPa were achieved. These anisotropic hydrogels induced osteogenic differentiation and the aligned aggregation of stem cells in vitro while also exhibiting osteoinductive capacity in vivo. Improved tissue outcomes with the hydrogels suggest promising applications in bone tissue engineering, as the processing strategy described here provides options to form hydrogels with multiple physical cues.

Predicting gene expression using morphological cell responses to nanotopography

Cells respond in complex ways to their environment, making it challenging to predict a direct relationship between the two. A key problem is the lack of informative representations of parameters that translate directly into biological function. Here we present a platform to relate the effects of cell morphology to gene expression induced by nanotopography. This platform utilizes the ‘morphome’, a multivariate dataset of cell morphology parameters. We create a Bayesian linear regression model that uses the morphome to robustly predict changes in bone, cartilage, muscle and fibrous gene expression induced by nanotopography. Furthermore, through this model we effectively predict nanotopography-induced gene expression from a complex co-culture microenvironment. The information from the morphome uncovers previously unknown effects of nanotopography on altering cell–cell interaction and osteogenic gene expression at the single cell level. The predictive relationship between morphology and gene expression arising from cell-material interaction shows promise for exploration of new topographies.

The surface nanotopography of biomaterials direct cell behavior, but screening for desired effects is inefficient. Here, the authors introduce a platform that enables prediction of nanotopography-induced gene expression changes from changes in cell morphology, including in co-culture environments.

Enhanced osteogenic differentiation of human mesenchymal stromal cells as response to periodical microstructured Ti6Al4V surfaces

Titanium-based alloys, for example, Ti6Al4V, are frequently employed for load-bearing orthopedic and dental implants. Growth of new bone tissue and therefore osseointegration can be promoted by the implant's microtopography, which can lead to improved long-term stability of the implant. This study investigates the effect that an organized, periodical microstructure produced by an electron beam (EB) technique has on the viability, morphology, and osteogenic differentiation capacity of human mesenchymal stromal cells (hMSC) in vitro. The technique generates topographical features of 20 μm in height with varying distances of 80-240 μm. Applied alterations of the surface roughness and local alloy composition do not impair hMSC viability (>94%) or proliferation. A favorable growth of hMSC onto the structure peaks and well-defined focal adhesions of the analyzed cells to the electron beam microstructured surfaces is verified. The morphological adaptation of hMSC to the underlying topography is detected using a three-dimensional (3D) visualization. In addition to the morphological changes, an increase in the expression of osteogenic markers such as osteocalcin (up to 17-fold) and osteoprotegerin (up to sixfold) is observed. Taken together, these results imply that the proposed periodical microstucturing method could potentially accelerate and enhance osseointegration of titanium-based bone implants.

Transcriptomic profiling of neural stem cell differentiation on graphene substrates

Graphene exhibits excellent mechanical strength, electrical conductivity and good biocompatibility, which make it a suitable candidate as a neural interfacing material in regenerative medicine and tissue engineering. Graphene is reported to promote both of neural stem cells (NSCs) proliferation and differentiation. However, the transcriptomes of 2D graphene-regulated NSC differentiation have not yet been investigated. To identify candidate genes, on which graphene may affect, we used next-generation RNA sequencing to analyze the transcriptome of NSCs differentiated for 21 days on a graphene substrate. These NSCs displayed highly enriched and differentially expressed genes compared with traditional cell culture in vitro. Of these, we identified motor protein genes that might regulate NSC differentiation, including cytoplasmic dynein and axonemal dynein genes, Ccdc108, Dnah5, and Dnah11. Furthermore, we analyzed the cell signaling pathway genes that might regulate NSC differentiation, and we constructed a protein-protein interaction network for the genes that are differentially expressed in NSCs on graphene compared to commercial tissue culture polystyrene substrates. We have identified genes potentially regulating the differentiation and migration of NSCs on graphene substrates, and our findings provide mechanistic evidence for the biological activities of graphene, especially in view of graphene-stem cell interactions.

Directional Topography Influences Adipose Mesenchymal Stromal Cell Plasticity: Prospects for Tissue Engineering and Fibrosis

Introduction

Progenitor cells cultured on biomaterials with optimal physical-topographical properties respond with alignment and differentiation. Stromal cells from connective tissue can adversely differentiate to profibrotic myofibroblasts or favorably to smooth muscle cells (SMC). We hypothesized that myogenic differentiation of adipose tissue-derived stromal cells (ASC) depends on gradient directional topographic features.

Methods

Polydimethylsiloxane (PDMS) samples with nanometer and micrometer directional topography gradients (wavelength (w) = 464-10, 990 nm; amplitude (a) = 49-3, 425 nm) were fabricated. ASC were cultured on patterned PDMS and stimulated with TGF-β1 to induce myogenic differentiation. Cellular alignment and adhesion were assessed by immunofluorescence microscopy after 24 h. After seven days, myogenic differentiation was examined by immunofluorescence microscopy, gene expression, and immunoblotting.

Results

Cell alignment occurred on topographies larger than w = 1758 nm/a = 630 nm. The number and total area of focal adhesions per cell were reduced on topographies from w = 562 nm/a = 96 nm to w = 3919 nm/a = 1430 nm. Focal adhesion alignment was increased on topographies larger than w = 731 nm/a = 146 nm. Less myogenic differentiation of ASC occurred on topographies smaller than w = 784 nm/a = 209 nm.

Conclusion

ASC adherence, alignment, and differentiation are directed by topographical cues. Our evidence highlights a minimal topographic environment required to facilitate the development of aligned and differentiated cell layers from ASC. These data suggest that nanotopography may be a novel tool for inhibiting fibrosis.

Surface bioactivation of PEEK by neutral atom beam technology

Polyetheretherketone (PEEK) is an alternative to metallic implants and a material of choice in many applications, including orthopedic, spinal, trauma, and dental. While titanium (Ti) and Ti-alloys are widely used in many intraosseous implants due to its biocompatibility and ability to osseointegrate, negatives include stiffness which contributes to shear stress, radio-opacity, and Ti-sensitivity. Many surgeons prefer to use PEEK due to its biocompatibility, similar elasticity to bone, and radiolucency, however, due to its inert properties, it fails to fully integrate with bone. Accelerated Neutral Atom Beam (ANAB) technology has been successfully employed to demonstrate enhanced bioactivity of PEEK both in vitro and in vivo. In this study, we further characterize surfaces of PEEK modified by ANAB as well as elucidate attachment and genetic effects of dental pulp stem cells (DPSC) exposed to these surfaces. ANAB modification resulted in decreased contact angle at 72.9 ± 4.5° as compared to 92.4 ± 8.5° for control (p < 0.01) and a decreased average surface roughness, however with a nano-textured surface profile. ANAB treatment also increased the ability of DPSC attachment and proliferation with considerable genetic differences showing earlier progression towards osteogenic differentiation. This surface modification is achieved without adding a coating or changing the chemical composition of the PEEK material. Taken together, we show that ANAB processing of PEEK surface enhances the bioactivity of implantable medical devices without an additive or a coating.

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PEEK is a material of choice for biomaterials except that it is inert and does not integrate with bone.

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Neutral atom beam technology (ANAB) is a surface modification technique that modifies the surface at a nano-scale level and makes the surface more hydrophilic.

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Increased cell attachment and proliferation is seen on ANAB-treated PEEK.

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Dental pulp stem cells differentiate towards osteoblast when grown on ANAB-treated PEEK.

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ANAB makes PEEK bioactive.

Bulk poly(N-isopropylacrylamide) (PNIPAAm) thermoresponsive cell culture platform: toward a new horizon in cell sheet engineering

In contrast to the conventional ‘grafting’-based thermoresponsive cell culture platform, we first developed a bulk form of thermoresponsive cell culture platform for attaching/detaching diverse types and origins of the cell sheets in different shape.

Topographically Defined, Biodegradable Nanopatterned Patches to Regulate Cell Fate and Acceleration of Bone Regeneration

If only allowed to proceed naturally, the bone-healing process can take several weeks, months, or even years depending on the injury size. In terms of bone-healing speed, many studies have been conducted investigating the deliverance of various growth factors of implantable biomaterials to shorten the time for bone regeneration. However, there may be side effects such as nerve pain, infection, or ectopic bone formation. As an alternative method, we focused on biophysical guidance, which provided similar topographical cues to the cellular environment to recruit host cells for bone defect healing. In this study, we hypothesized that aligned nanotopographical features have enhanced osteoblast recruitment, migration, and differentiation without external stimuli. We designed and fabricated a biodegradable poly(lactic- co-glycolic acid) nanopatterned patch using simple solvent casting and capillary force lithography. We confirmed that a biodegradable nanopatterned patch (BNP) accelerated the migration of osteoblasts according to the orientation of the patterned direction. These highly aligned osteoblasts may contribute to in vitro osteogenic differentiation, such as alkaline phosphate activity, mineralization, and calcium deposition, compared to the biodegradable flat patch (BFP). To demonstrate bone defect healing by BNP guidance in vivo, we implanted either whole or bridge BNP on the critical size defect of mouse calvarial ( ø 4 mm) or tibia bone (3 × 7 mm²). Only the BNP-treated group showed faster new bone formation and compact bone regeneration at the calvarial or tibia bone defect area compared to BFP at 4 or 8 weeks. Bridge BNP guided, in particular, the regeneration of new bone formation along the parallel direction of nanopatterned substrates. Here, we show that a BNP with biophysical guidance should be suitable for use in bone tissue regeneration through accelerated migration of the intact host cell.

Nanoengineered, cell-derived extracellular matrix influences ECM-related gene expression of mesenchymal stem cells

Background

Human mesenchymal stem cells (hMSCs) are, due to their pluripotency, useful sources of cells for stem cell therapy and tissue regeneration. The phenotypes of hMSCs are strongly influenced by their microenvironment, in particular the extracellular matrix (ECM), the composition and structure of which are important in regulating stem cell fate. In reciprocal manner, the properties of ECM are remodeled by the hMSCs, but the mechanism involved in ECM remodeling by hMSCs under topographical stimulus is unclear. In this study, we therefore examined the effect of nanotopography on the expression of ECM proteins by hMSCs by analyzing the quantity and structure of the ECM on a nanogrooved surface.

Methods

To develop the nanoengineered, hMSC-derived ECM, we fabricated the nanogrooves on a coverglass using a UV-curable polyurethane acrylate (PUA). Then, hMSCs were cultivated on the nanogrooves, and the cells at the full confluency were decellularized. To analyze the effect of nanotopography on the hMSCs, the hMSCs were re-seeded on the nanoengineered, hMSC-derived ECM.

Results

hMSCs cultured within the nano-engineered hMSC-derived ECM sheet showed a different pattern of expression of ECM proteins from those cultured on ECM-free, nanogrooved surface. Moreover, hMSCs on the nano-engineered ECM sheet had a shorter vinculin length and were less well-aligned than those on the other surface. In addition, the expression pattern of ECM-related genes by hMSCs on the nanoengineered ECM sheet was altered. Interestingly, the expression of genes for osteogenesis-related ECM proteins was downregulated, while that of genes for chondrogenesis-related ECM proteins was upregulated, on the nanoengineered ECM sheet.

Conclusions

The nanoengineered ECM influenced the phenotypic features of hMSCs, and that hMSCs can remodel their ECM microenvironment in the presence of a nanostructured ECM to guide differentiation into a specific lineage.

Electronic supplementary material

The online version of this article (10.1186/s40824-018-0141-y) contains supplementary material, which is available to authorized users.

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.

Control of cell behaviour through nanovibrational stimulation: nanokicking

Mechanical signals are ubiquitous in our everyday life and the process of converting these mechanical signals into a biological signalling response is known as mechanotransduction. Our understanding of mechanotransduction, and its contribution to vital cellular responses, is a rapidly expanding field of research involving complex processes that are still not clearly understood. The use of mechanical vibration as a stimulus of mechanotransduction, including variation of frequency and amplitude, allows an alternative method to control specific cell behaviour without chemical stimulation (e.g. growth factors). Chemical-independent control of cell behaviour could be highly advantageous for fields including drug discovery and clinical tissue engineering. In this review, a novel technique is described based on nanoscale sinusoidal vibration. Using finite-element analysis in conjunction with laser interferometry, techniques that are used within the field of gravitational wave detection, optimization of apparatus design and calibration of vibration application have been performed. We further discuss the application of nanovibrational stimulation, or 'nanokicking', to eukaryotic and prokaryotic cells including the differentiation of mesenchymal stem cells towards an osteoblast cell lineage. Mechanotransductive mechanisms are discussed including mediation through the Rho-A kinase signalling pathway. Optimization of this technique was first performed in two-dimensional culture using a simple vibration platform with an optimal frequency and amplitude of 1 kHz and 22 nm. A novel bioreactor was developed to scale up cell production, with recent research demonstrating that mesenchymal stem cell differentiation can be efficiently triggered in soft gel constructs. This important step provides first evidence that clinically relevant (three-dimensional) volumes of osteoblasts can be produced for the purpose of bone grafting, without complex scaffolds and/or chemical induction. Initial findings have shown that nanovibrational stimulation can also reduce biofilm formation in a number of clinically relevant bacteria. This demonstrates additional utility of the bioreactor to investigate mechanotransduction in other fields of research.This article is part of a discussion meeting issue 'The promises of gravitational-wave astronomy'.

Constrained Adherable Area of Nanotopographic Surfaces Promotes Cell Migration through the Regulation of Focal Adhesion via Focal Adhesion Kinase/Rac1 Activation

Cell migration is crucial in physiological and pathological processes such as embryonic development and wound healing; such migration is strongly guided by the surrounding nanostructured extracellular matrix. Previous studies have extensively studied the cell migration on anisotropic nanotopographic surfaces; however, only a few studies have reported cell migration on isotropic nanotopographic surfaces. We herein, for the first time, propose a novel concept of adherable area on cell migration using isotropic nanopore surfaces with sufficient nanopore depth by adopting a high aspect ratio. As the pore size of the nanopore surface was controlled to 200, 300, and 400 nm in a fixed center-to-center distance of 480 nm, it produced 86, 68, and 36% of adherable area, respectively, on the fabricated surface. A meticulous investigation of the cell migration in response to changes in the constrained adherable area of the nanotopographic surface showed 1.4-, 1.5-, and 1.6-fold increase in migration speeds and a 1.4-, 2-, and 2.5-fold decrease in the number of focal adhesions as the adherable area was decreased to 86, 68, and 36%, respectively. Furthermore, a strong activation of FAK/Rac1 signaling was observed to be involved in the promoted cell migration. These results suggest that the reduced adherable area promotes cell migration through decreasing the FA formation, which in turn upregulates FAK/Rac1 activation. The findings in this study can be utilized to control the cell migration behaviors, which is a powerful tool in the research fields involving cell migration such as promoting wound healing and tissue repair.

Human mesenchymal stem cell basal membrane bending on gratings is dependent on both grating width and curvature

The topography of the extracellular substrate provides physical cues to elicit specific downstream biophysical and biochemical effects in cells. An example of such a topographical substrate is periodic gratings, where the dimensions of the periodic gratings influence cell morphology and directs cell differentiation. We first develop a novel sample preparation technique using Spurr's resin to allow for cross-sectional transmission electron microscopy imaging of cells on grating grooves, and observed that the plasma membrane on the basal surface of these cells can deform and bend into grooves between the gratings. We postulate that such membrane bending is an important first step in eliciting downstream effects. Thus, we use a combination of image analysis and mathematical modeling to explain the extent of bending of basal membrane into grooves. We show that the extent to which the basal membrane bends into grooves depends on both groove width and angle of the grating ridge. Our model predicts that the basal membrane will bend into grooves when they are wider than 1.9 µm in width. The existence of such a threshold may provide an explanation for how the width of periodic gratings may bring about cellular downstream effects, such as cell proliferation or differentiation.

Influence of diameter of fiber membrane scaffolds on the biocompatibility of hPDL mesenchymal stromal cells

This study evaluated the influence in the biocompatibility of human periodontal ligament (hPDL) mesenchymal stromal cell onto poly lactic-acid (PLA) films and PLA fiber membrane. Fiber scaffold was prepared via air jet spinning (AJS) from PLA solutions (6, 7, and 10%) and analyzed using SEM, AFM and FTIR. Biocompatibility was evaluated by adhesion, proliferation and cell-material interaction. PLA film exhibited a smooth and homogenously surface topography in comparison with random orientation of PLA fiber with roughness structure where diameter size depends on PLA solution. Moreover, cell adhesion; proliferation and cell-material interaction has the best respond on random orientation nanofiber of 10, followed by 7, and 6% of PLA in comparison with PLA films. It could be concluded that AJS is an attractive alternative technique for manufacture fiber scaffolds with a tunable random orientation geometry of fibers that allow to produce interconnected porous formed by nanometric fiber diameter structures that could be a potential scaffold for periodontal tissue engineering applications.

Biomimetic oyster shell-replicated topography alters the behaviour of human skeletal stem cells

The regenerative potential of skeletal stem cells provides an attractive prospect to generate bone tissue needed for musculoskeletal reparation. A central issue remains efficacious, controlled cell differentiation strategies to aid progression of cell therapies to the clinic. The nacre surface from Pinctada maxima shells is known to enhance bone formation. However, to date, there is a paucity of information on the role of the topography of P. maxima surfaces, nacre and prism. To investigate this, nacre and prism topographical features were replicated onto polycaprolactone and skeletal stem cell behaviour on the surfaces studied. Skeletal stem cells on nacre surfaces exhibited an increase in cell area, increase in expression of osteogenic markers ALP (p < 0.05) and OCN (p < 0.01) and increased metabolite intensity (p < 0.05), indicating a role of nacre surface to induce osteogenic differentiation, while on prism surfaces, skeletal stem cells did not show alterations in cell area or osteogenic marker expression and a decrease in metabolite intensity (p < 0.05), demonstrating a distinct role for the prism surface, with the potential to maintain the skeletal stem cell phenotype.

Influence of patterned titanium coatings on polarization of macrophage and osteogenic differentiation of bone marrow stem cells

Biomaterial surface topography plays a vital role in the osteointegration of implants by regulating the early cell responses and tissue growth-in. However, most of the previous researches focused on the effects of osteogenic cells, only a little is known about the immune cells which dominate osteogenesis after implanting. In this paper, patterned titanium coatings were fabricated and the effects of surface topography on the macrophage behaviors were investigated. On patterned titanium surface, macrophages preferred to polarize to M2, while macrophages on traditional titanium coatings presented higher M1 polarization. Nearly 70% higher expression of anti-inflammatory genes, including interleukin-4, interleukin-10, interleukin-1ra, and arginase, were detected on the patterned titanium coatings. While the pro-inflammatory genes, such as interleukin-1β, interleukin-6, tumor necrosis factor-α, interferon-γ, and inducible nitric oxide synthase were notably depressed. Up-regulation of the osteoinductive cytokines were also detected on the patterned coatings, which indicated advantageous osteogenic microenvironment provided by macrophages. Immunomodulation effect on osteogenesis was also investigated in this study. Stimulated with RAW cells/patterned coatings conditioned medium, bone marrow stem cells presented nearly 1.5 fold higher expression of osteogenic genes and more mineralization nodules than the traditional sprayed Ti coatings. All these results suggested that modulating materials with a patterned surface might be a valuable strategy to endow the implants with favorable osteoimmunomodulatory properties.

Fabricating hierarchical micro and nano structures on implantable Co-Cr-Mo alloy for tissue engineering by one-step laser ablation

Surface texturing is one of the effective strategies to improve bioactivity of implantable materials. In this study, hierarchical micro and nano structure (HMN) were fabricated on Co-Cr-Mo alloy substrate by a movable picosecond laser irradiation. Respectively, microgrooves with nano ripples and islands were produced on Co-Cr-Mo alloy by low and high laser power density. X-ray diffraction apparatus (XRD) phase analysis illustrated that substrate was in the phase of γ- face-centered cubic structure (FCC) before laser treatment, while it was in ε-hexagonal closest packing structure (HCP) phase dominant after laser treatment. Cell adhesion and proliferation studies showed that the HMN surface exhibits enhanced adhesion of MC3TC-E1 osteoblast and promoted cell activity. Analyzing of the morphology of osteoblast cells indicated cells were in high ratio of elongation on the HMN surface, while they mainly kept in round shape on the polished surface. Results indicated the formation of hierarchical structure on Co-Cr-Mo alloy was able to improve biological performances, suggesting the potential application in cobalt based orthopedic implants.

Biomechanical Regulation of Mesenchymal Stem Cells for Cardiovascular Tissue Engineering

Mesenchymal stem cells (MSCs) are an appealing potential therapy for vascular diseases; however, many challenges remain in their clinical translation. While the use of biochemical, pharmacological, and substrate-mediated treatments to condition MSCs has been subjected to intense investigation, there has been far less exploration of using these treatments in combination with applied mechanical force for conditioning MSCs toward vascular phenotypes. This review summarizes the current understanding of the use of applied mechanical forces to differentiate MSCs into vascular cells and enhance their therapeutic potential for cardiovascular disease. First recent work on the use of material-based mechanical cues for differentiation of MSCs into vascular and cardiovascular phenotypes is examined. Then a summary of the studies using mechanical stretch or shear stress in combination with biochemical treatments to enhance vascular phenotypes in MSCs is presented.

The Functional Response of Mesenchymal Stem Cells to Electron-Beam Patterned Elastomeric Surfaces Presenting Micrometer to Nanoscale Heterogeneous Rigidity

Cells directly probe and respond to the physicomechanical properties of their extracellular environment, a dynamic process which has been shown to play a key role in regulating both cellular adhesive processes and differential cellular function. Recent studies indicate that stem cells show lineage-specific differentiation when cultured on substrates approximating the stiffness profiles of specific tissues. Although tissues are associated with a range of Young's modulus values for bulk rigidity, at the subcellular level, tissues are comprised of heterogeneous distributions of rigidity. Lithographic processes have been widely explored in cell biology for the generation of analytical substrates to probe cellular physicomechanical responses. In this work, it is shown for the first time that that direct-write e-beam exposure can significantly alter the rigidity of elastomeric poly(dimethylsiloxane) substrates and a new class of 2D elastomeric substrates with controlled patterned rigidity ranging from the micrometer to the nanoscale is described. The mechanoresponse of human mesenchymal stem cells to e-beam patterned substrates was subsequently probed in vitro and significant modulation of focal adhesion formation and osteochondral lineage commitment was observed as a function of both feature diameter and rigidity, establishing the groundwork for a new generation of biomimetic material interfaces.

Mechanically dynamic PDMS substrates to investigate changing cell environments

Mechanics of the extracellular matrix (ECM) play a pivotal role in governing cell behavior, such as cell spreading and differentiation. ECM mechanics have been recapitulated primarily in elastic hydrogels, including with dynamic properties to mimic complex behaviors (e.g., fibrosis); however, these dynamic hydrogels fail to introduce the viscoelastic nature of many tissues. Here, we developed a two-step crosslinking strategy to first form (via platinum-catalyzed crosslinking) networks of polydimethylsiloxane (PDMS) and then to increase PDMS crosslinking (via thiol-ene click reaction) in a temporally-controlled manner. This photoinitiated reaction increased the compressive modulus of PDMS up to 10-fold within minutes and was conducted under cytocompatible conditions. With stiffening, cells displayed increased spreading, changing from ∼1300 to 1900 μm² and from ∼2700 to 4600 μm² for fibroblasts and mesenchymal stem cells, respectively. In addition, higher myofibroblast activation (from ∼2 to 20%) for cardiac fibroblasts was observed with increasing PDMS substrate stiffness. These results indicate a cellular response to changes in PDMS substrate mechanics, along with a demonstration of a mechanically dynamic and photoresponsive PDMS substrate platform to model the dynamic behavior of ECM.

Control of Cell Alignment and Morphology by Redesigning ECM-Mimetic Nanotopography on Multilayer Membranes

Inspired by native extracellular matrix (ECM) together with the multilevel architecture observed in nature, a material which topography recapitulates topographic features of the ECM and the internal architecture mimics the biological materials organization is engineered. The nanopatterned design along the XY plane is combined with a nanostructured organization along the Z axis on freestanding membranes prepared by layer-by-layer deposition of chitosan and chondroitin sulfate. Cellular behavior is monitored using two different mammalian cell lines, fibroblasts (L929) and myoblasts (C2C12), in order to perceive the response to topography. Viability, proliferation, and morphology of L929 are sensitively controlled by topography; also differentiation of C2C12 into myotubes is influenced by the presence of nanogrooves. This kind of nanopatterned structure has also been associated with strong cellular alignment. To the best of the knowledge, it is the first time that such a straightforward and inexpensive strategy is proposed to produce nanopatterned freestanding multilayer membranes. Controlling cellular alignment plays a critical role in many human tissues, such as muscles, nerves, or blood vessels, so these membranes can be potentially useful in specific tissue regeneration strategies.

Correlation of focal adhesion assembly and disassembly with cell migration on nanotopography

Selective cell adhesion is desirable to control cell growth and migration on biomedical implants. Mesenchymal cell migration is regulated through focal adhesions (FAs) and can be modulated by their microenvironment, including changes in surface topography. We use the Number and Molecular Brightness (N&B) imaging analysis to provide a unique perspective on FA assembly and disassembly. This imaging analysis generates a map of real-time fluctuations of protein monomers, dimers, and higher order aggregates of FA proteins, such as paxillin during assembly and disassembly. We show a dynamic view of how nanostructured surfaces (nanoline gratings or nanopillars) regulate single molecular dynamics. In particular, we report that the smallest nanopillars (100 nm spacing) gave rise to a low population of disassembling adhesion clusters of ∼2 paxillin proteins whereas the larger nanopillars (380 nm spacing) gave rise to a much larger population of larger disassembling clusters of ∼3-5 paxillin proteins. Cells were more motile on the smaller nanopillars (spaced 100-130 nm apart) compared to all other surfaces studied. Thus, physical nanotopography influences cell motility, adhesion size, and adhesion assembly and disassembly. We report for the first time, with single molecular detection, how nanotopography influences cell motility and protein reorganization in adhesions.

Biophysical Regulation of Cell Behavior-Cross Talk between Substrate Stiffness and Nanotopography

The stiffness and nanotopographical characteristics of the extracellular matrix (ECM) influence numerous developmental, physiological, and pathological processes in vivo. These biophysical cues have therefore been applied to modulate almost all aspects of cell behavior, from cell adhesion and spreading to proliferation and differentiation. Delineation of the biophysical modulation of cell behavior is critical to the rational design of new biomaterials, implants, and medical devices. The effects of stiffness and topographical cues on cell behavior have previously been reviewed, respectively; however, the interwoven effects of stiffness and nanotopographical cues on cell behavior have not been well described, despite similarities in phenotypic manifestations. Herein, we first review the effects of substrate stiffness and nanotopography on cell behavior, and then focus on intracellular transmission of the biophysical signals from integrins to nucleus. Attempts are made to connect extracellular regulation of cell behavior with the biophysical cues. We then discuss the challenges in dissecting the biophysical regulation of cell behavior and in translating the mechanistic understanding of these cues to tissue engineering and regenerative medicine.

Artificial Slanted Nanocilia Array as a Mechanotransducer for Controlling Cell Polarity

We present a method to induce cell directional behavior using slanted nanocilia arrays. NIH-3T3 fibroblasts demonstrated bidirectional polarization in a rectangular arrangement on vertical nanocilia arrays and exhibited a transition from a bidirectional to a unidirectional polarization pattern when the angle of the nanocilia was decreased from 90° to 30°. The slanted nanocilia guided and facilitated spreading by allowing the cells to contact the sidewalls of the nanocilia, and the directional migration of the cells opposed the direction of the slant due to the anisotropic bending stiffness of the slanted nanocilia. Although the cells recognized the underlying anisotropic geometry when the nanocilia were coated with fibronectin, collagen type I, and Matrigel, the cells lost their directionality when the nanocilia were coated with poly-d-lysine and poly-l-lysine. Furthermore, although the cells recognized geometrical anisotropy on fibronectin coatings, pharmacological perturbation of PI3K-Rac signaling hindered the directional elongation of the cells on both the slanted and vertical nanocilia. Furthermore, myosin light chain II was required for the cells to obtain polarized morphologies. These results indicated that the slanted nanocilia array provided anisotropic contact guidance cues to the interacting cells. The polarization of cells was controlled through two steps: the recognition of underlying geometrical anisotropy and the subsequent directional spreading according to the guidance cues.

Integrin β1 activation by micro-scale curvature promotes pro-angiogenic secretion of human mesenchymal stem cells

A cell culture substrate with micro-scale surface curvature promotes β1 integrin activation and pro-angiogenic secretion of mesenchymal stem cells.

Size Specific Transfection to Mammalian Cells by Micropillar Array Electroporation

Electroporation serves as a promising non-viral gene delivery approach, while its current configuration carries several drawbacks associated with high-voltage electrical pulses and heterogeneous treatment on individual cells. Here we developed a new micropillar array electroporation (MAE) platform to advance the electroporation-based delivery of DNA and RNA probes into mammalian cells. By introducing well-patterned micropillar array texture on the electrode surface, the number of pillars each cell faces varies with its plasma membrane surface area, despite their large population and random locations. In this way, cell size specific electroporation is conveniently carried out, contributing to a 2.5~3 fold increase on plasmid DNA transfection and an additional 10–55% transgene knockdown with siRNA probes, respectively. The delivery efficiency varies with the number and size of micropillars as well as their pattern density. As MAE works like many single cell electroporation are carried out in parallel, the electrophysiology response of individual cells is representative, which has potentials to facilitate the tedious, cell-specific protocol screening process in current bulk electroporation (i.e., electroporation to a large population of cells). Its success might promote the wide adoption of electroporation as a safe and effective non-viral gene delivery approach needed in many biological research and clinical treatments.

Modulation of human multipotent and pluripotent stem cells using surface nanotopographies and surface-immobilised bioactive signals: A review

The ability to control the interactions of stem cells with synthetic surfaces is proving to be effective and essential for the quality of passaged stem cells and ultimately the success of regenerative medicine. The stem cell niche is crucial for stem cell self-renewal and differentiation. Thus, mimicking the stem cell niche, and here in particular the extracellular matrix (ECM), in vitro is an important goal for the expansion of stem cells and their applications. Here, surface nanotopographies and surface-immobilised biosignals have been identified as major factors that control stem cell responses. The development of tailored surfaces having an optimum nanotopography and displaying suitable biosignals is proposed to be essential for future stem cell culture, cell therapy and regenerative medicine applications. While early research in the field has been restricted by the limited availability of micro- and nanofabrication techniques, new approaches involving the use of advanced fabrication and surface immobilisation methods are starting to emerge. In addition, new cell types such as induced pluripotent stem cells (iPSCs) have become available in the last decade, but have not been fully understood. This review summarises significant advances in the area and focuses on the approaches that are aimed at controlling the behavior of human stem cells including maintenance of their self-renewal ability and improvement of their lineage commitment using nanotopographies and biosignals. More specifically, we discuss developments in biointerface science that are an important driving force for new biomedical materials and advances in bioengineering aiming at improving stem cell culture protocols and 3D scaffolds for clinical applications. Cellular responses revolve around the interplay between the surface properties of the cell culture substrate and the biomolecular composition of the cell culture medium. Determination of the precise role played by each factor, as well as the synergistic effects amongst the factors, all of which influence stem cell responses is essential for future developments. This review provides an overview of the current state-of-the-art in the design of complex material surfaces aimed at being the next generation of tools tailored for applications in cell culture and regenerative medicine.

STATEMENT OF SIGNIFICANCE

This review focuses on the effect of surface nanotopographies and surface-bound biosignals on human stem cells. Recently, stem cell research attracts much attention especially the induced pluripotent stem cells (iPSCs) and direct lineage reprogramming. The fast advance of stem cell research benefits disease treatment and cell therapy. On the other hand, surface property of cell adhered materials has been demonstrated very important for in vitro cell culture and regenerative medicine. Modulation of cell behavior using surfaces is costeffective and more defined. Thus, we summarise the recent progress of modulation of human stem cells using surface science. We believe that this review will capture a broad audience interested in topographical and chemical patterning aimed at understanding complex cellular responses to biomaterials.