Nanotopographical Modulation of Cell Function through Nuclear Deformation

Human Skeletal Stem Cell Response to Multiscale Topography Induced by Large Area Electron Beam Irradiation Surface Treatment

The healthcare socio-economic environment is irreversibly changing as a consequence of an increasing aging population, consequent functional impairment, and patient quality of life expectations. The increasing complexity of ensuing clinical scenarios compels a critical search for novel musculoskeletal regenerative and replacement strategies. While joint arthroplasty is a highly effective treatment for arthritis and osteoporosis, further innovation and refinement of uncemented implants are essential in order to improve implant integration and reduce implant revision rate. This is critical given financial restraints and the drive to improve cost-effectiveness and quality of life outcomes. Multi-scale modulation of implant surfaces, offers an innovative approach to enhancement in implant performance. In the current study, we have examined the potential of large area electron beam melting to alter the surface nanotopography in titanium alloy (Ti6Al4V). We evaluated the in vitro osteogenic response of human skeletal stem cells to the resultant nanotopography, providing evidence of the relationship between the biological response, particularly Collagen type I and Osteocalcin gene activation, and surface nanoroughness. The current studies demonstrate osteogenic gene induction and morphological cell changes to be significantly enhanced on a topography Ra of ~40 nm with clinical implications therein for implant surface treatment and generation.

Wet electrospun alginate/gelatin hydrogel nanofibers for 3D cell culture

Convergence of biological and biofabrication approaches is necessary to progress new biomaterials promoting three-dimensional (3D) cell growth and maturation towards tissue regeneration and integration. Here, we have developed a novel approach to fabricate 3D macroporous, alginate/gelatin hydrogel nanofibers (Alg/GelF-MA), which provide superior cell adhesion, motility, proliferation and maturation. The electrospinning process greatly depends on the ionic strength and viscoelastic behavior of the solution. The polyelectrolyte nature of alginate favors intramolecular bundles over intermolecular entanglement, which hinders its electrospinnability. Electrospinning of alginate was achieved by the aid of a supporting polymer, polyethylene oxide and a surfactant, Pluronic®F127. Furthermore, the Ca²⁺-mediated coagulation process of alginate was realized in situ during wet electrospinning, where the rapid physical crosslink-ability of alginate was applied in conjunction with the jet entrance into the wet electrospinning collector, a coagulation bath. Consequently, the rapid formation of Ca²⁺-alginate complex stabilized the nanofiber morphology. The low surface tension of the non-solvent ethanol used in the bath prevented fibers from dense packing, thus allowing the generation of 3D macroporous structure favoring cell motility. The subsequent UV-mediated chemical crosslinking further stabilized the gelatin content in the Alg/GelF-MA hydrogel nanofibers. It is demonstrated that the Alg/GelF-MA nanofibers with low cytotoxicity (below 10%) supported an over 8-fold proliferation of mesenchymal stem cells over 5 weeks and supported the maturation of human iPSC-derived ventricular cardiomyocytes, which significantly outperform the cell encapsulated bulk GelF-MA hydrogel. The work provides an insight for rational design and development of 3D cell culture matrix for advancement of stem cell therapy and tissue regeneration.

Regulation of Mesenchymal Stem Cell Differentiation by Nanopatterning of Bulk Metallic Glass

Mesenchymal stem cell (MSC) differentiation is regulated by surface modification including texturing, which is applied to materials to enhance tissue integration. Here, we used Pt57.5Cu14.7Ni5.3P22.5 bulk metallic glass (Pt-BMG) with nanopatterned surfaces achieved by thermoplastic forming to influence differentiation of human MSCs. Pt-BMGs are a unique class of amorphous metals with high strength, elasticity, corrosion resistance, and an unusual plastic-like processability. It was found that flat and nanopattened Pt-BMGs induced osteogenic and adipogenic differentiation, respectively. In addition, osteogenic differentiation on flat BMG exceeded that observed on medical grade titanium and was associated with increased formation of focal adhesions and YAP nuclear localization. In contrast, cells on nanopatterned BMGs exhibited rounded morphology, formed less focal adhesions and had mostly cytoplasmic YAP. These changes were preserved on nanopatterns made of nanorods with increased stiffness due to shorter aspect ratios, suggesting that MSC differentiation was primarily influenced by topography. These observations indicate that both elemental composition and nanotopography can modulate biochemical cues and influence MSCs. Moreover, the processability and highly tunable nature of Pt-BMGs enables the creation of a wide range of surface topographies that can be reproducibly and systematically studied, leading to the development of implants capable of engineering MSC functions.

Pulse-Modulated Radio-Frequency Alternating-Current-Driven Atmospheric-Pressure Glow Discharge for Continuous-Flow Synthesis of Silver Nanoparticles and Evaluation of Their Cytotoxicity toward Human Melanoma Cells

An innovative and environmentally friendly method for the synthesis of size-controlled silver nanoparticles (AgNPs) is presented. Pectin-stabilized AgNPs were synthesized in a plasma-reaction system in which pulse-modulated radio-frequency atmospheric-pressure glow discharge (pm-rf-APGD) was operated in contact with a flowing liquid electrode. The use of pm-rf-APGD allows for better control of the size of AgNPs and their stability and monodispersity. AgNPs synthesized under defined operating conditions exhibited average sizes of 41.62 ± 12.08 nm and 10.38 ± 4.56 nm, as determined by dynamic light scattering and transmission electron microscopy (TEM), respectively. Energy-dispersive X-ray spectroscopy (EDS) confirmed that the nanoparticles were composed of metallic Ag. Furthermore, the ξ-potential of the AgNPs was shown to be -43.11 ± 0.96 mV, which will facilitate their application in biological systems. Between 70% and 90% of the cancerous cells of the human melanoma Hs 294T cell line underwent necrosis following treatment with the synthesized AgNPs. Furthermore, optical emission spectrometry (OES) identified reactive species, such as NO, NH, N₂, O, and H, as pm-rf-APGD produced compounds that may be involved in the reduction of the Ag(I) ions.

Characterizations of hyaluronate-based terpolymeric hydrogel synthesized via free radical polymerization mechanism for biomedical applications

In the present study, a novel terpolymeric hydrogel was developed using sodium hyaluronate (HA), 2-hydroxyethyl acrylate (2-HEA), and poly(ethylene glycol) diacrylate (PEGDA) via free radical polymerization for biomedical applications. To achieve elasticity, swelling ability, porous architecture and sufficient gel strength, hyaluronate was chemically modified by grafting and crosslinking methods using 2-HEA and PEGDA, respectively. The structure and compositions of the fabricated terpolymer (HA-g-p(2-HEA)-x-PEGDA) were verified by FTIR, ¹H HR-MAS-NMR, and TGA analyses. The surface morphology and cross-section of the hydrogel was detected by SEM analysis. The gel nature of terpolymer in aqueous medium at 37 °C was confirmed from swelling study, and rheological experiment. Non-cytotoxicity and biocompatibility of the HA-g-p(2-HEA)-x-PEGDA hydrogel were ascertained by in vitro mouse osteoblastic cells (MC3T3) proliferation, and viability studies. Hematoxylin and eosin Y, and Masson's trichrome stainings were performed to show tissue regeneration ability on the prepared hydrogel. In vitro release results of proangiogenic drug-dimethyloxalylglycine (DMOG), and antibiotics-tetracycline (TCN) showed sustained release behaviour from the prepared hydrogel under different pHs at 37 °C. The mathematical models fitted data imply that both DMOG and TCN release follow first order kinetics, while, the release mechanism is primarily controlled by diffusion as well as erosion process. Finally, the novel biocompatible HA-g-p(2-HEA)-x-PEGDA gel, which showed sustained drugs release, and regeneration ability of extracellular matrix and collagen, could be employed in biomedical applications, especially, for the delivery of DMOG/TCN, and in tissue engineering.

Perfluorooctylbromide nanoparticles for ultrasound imaging and drug delivery

Perfluorooctylbromide nanoparticles (PFOB NPs) are a type of multifunctional nanotechnology that has been studied for various medical applications. Commercial ultrasound contrast agents (UCAs) suffer from the following limitations: short half-lives in vivo, high background signal and restricted distribution in the vascular circulation due to their micrometer dimensions. PFOB NPs are new potential UCAs that persist for long periods in the circulatory system, possess a relatively stable echogenic response without increasing the background signal and exhibit lower acoustic attenuation than commercial UCAs. Furthermore, PFOB NPs may also serve as drug delivery vehicles in which drugs are dissolved in the outer lipid or polymer layer for subsequent delivery to target sites in site-targeted therapy. The use of PFOB NPs as carriers has the potential advantage of selectively delivering payloads to the target site while improving visualization of the site using ultrasound (US) imaging. Unfortunately, the application of PFOB NPs to the field of ultrasonography has been limited because of the low intensity of US reflection. Numerous researchers have realized the potential use of PFOB NPs as UCAs and thus have developed alternative approaches to apply PFOB NPs in ultrasonography. In this article, we review the latest approaches for using PFOB NPs to enhance US imaging in vivo. In addition, this article emphasizes the application of PFOB NPs as promising drug delivery carriers for cancer and atherosclerosis treatments, as PFOB NPs can transport different drug payloads for various applications with good efficacy. We also note the challenges and future study directions for the application of PFOB NPs as both a delivery system for therapeutic agents and a diagnostic agent for ultrasonography.

Enhanced retinal pigment epithelium (RPE) regeneration using curcumin/alginate hydrogels: In vitro evaluation

The retinal pigment epithelium (RPE) plays a significant role in retaining structural integrity of eye. Factors such as reduction in cell regeneration due to aging and physical injury pose a major hurdle in RPE regeneration. In this study, we exploited the use of alginate (AGT) incorporated with Curcumin (CCI) forming a hydrogel based system CCI/AGT. The fabricated hydrogel could anchor RPE cell in it. In vitro cell analysis revealed that the CCI/AGT hydrogel shows good biocompatibility, enhanced cell growth ability and higher ECM formation compared to the pure AGT hydrogel. In particular, the presence of CCI in the hydrogels enhances the cells proliferation of the 23% respect to the pure alginate. Also the expression of crucial genes for retina functions and matrix production were positively affected by CCI presence, with an increment of 45% for RPE65, 32% for CRALBP and 26% for Collagen type 1. In vitro tests demonstrated the potential application of CCI/AGT hydrogels for transplantation under the sub-retinal space acting as a cell delivery vehicle and also their capability to provide an appropriate environment for RPE regeneration. These results suggest that CCI/AGT hydrogel could be translated into a potential surgical graft for biological implantation of retinal tissue engineering.

Study on the morphological and biocompatible properties of chitosan grafted silk fibre reinforced PVA films for tissue engineering applications

The current study delineates the preparation of novel chitosan grafted silk fibre reinforced Poly (vinyl alcohol) (PVA) composite films with desirable properties. Although silk fibroin has been extensively used for various biomedical applications, its properties could be further re-tailored for its suitability in the field of regenerative medicine. Chitosan was successfully grafted over silk, via acylation with succinic anhydride and thereby the fibres were incised and used for the preparation of the films. The grafted silk fibre reinforced PVA films were subjected to FTIR studies, microscopic analysis by atomic force microscopy (AFM) and optical microscopy techniques, X-ray diffraction (XRD) analysis and further evaluated for in vitro biocompatibility studies. The composite films demonstrated improved surface roughness with increasing concentration of the fibre and its dispersion in the polymer matrix was observed. Furthermore, in vitro biocompatibility and cellular behaviour such as adhesion and proliferation of mouse fibroblasts as well as astrocyte cells was studied and the results showed improved proliferative activity, when compared to the pristine PVA films. These results were further supported by the results confirmed by MTT assay demonstrating the films to be non-toxic. The efficiency and feasibility of the films to be used for tissue engineering, was further evaluated by haemocompatibility studies using human erythrocytes, thus making them a potential material to be used for biomedical applications.

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.

Harnessing Nanotopography to Enhance Osseointegration of Clinical Orthopedic Titanium Implants-An in Vitro and in Vivo Analysis

Despite technological advancements, further innovations in the field of orthopedics and bone regeneration are essential to meet the rising demands of an increasing aging population and associated issues of disease, injury and trauma. Nanotopography provides new opportunities for novel implant surface modifications and promises to deliver further improvements in implant performance. However, the technical complexities of nanotopography fabrication and surface analysis have precluded identification of the optimal surface features to trigger osteogenesis. We herein detail the osteoinductive potential of discrete nanodot and nanowire nanotopographies. We have examined the ability of modified titanium and titanium alloy (Ti64) surfaces to induce bone-specific gene activation and extracellular matrix protein expression in human skeletal stem cells (SSCs) in vitro, and de novo osteogenic response within a murine calvarial model in vivo. This study provides evidence of enhanced osteogenic response to nanowires 300 surface modifications, with important implications for clinical orthopedic application.

In vivo safety and efficacy testing of a thermally triggered injectable hydrogel scaffold for bone regeneration and augmentation in a rat model

Bone loss resulting from degenerative diseases and trauma is a significant clinical burden which is likely to grow exponentially with the aging population. In a number of conditions where pre-formed materials are clinically inappropriate an injectable bone forming hydrogel could be beneficial. The development of an injectable hydrogel to stimulate bone repair and regeneration would have broad clinical impact and economic benefit in a variety of orthopedic clinical applications.

We have previously reported the development of a Laponite^® crosslinked pNIPAM-co-DMAc (L-pNIPAM-co-DMAc) hydrogel delivery system, loaded with hydroxyapatite nanoparticles (HAPna), which was capable of inducing osteogenic differentiation of mesenchymal stem cells (MSCs) without the need for additional growth factors in vitro. However to enable progression towards clinical acceptability, biocompatibility and efficacy of the L-pNIPAM-co-DMAc hydrogel to induce bone repair in vivo must be determined.

Biocompatibility was evaluated by subcutaneous implantation for 6 weeks in rats, and efficacy to augment bone repair was evaluated within a rat femur defect model for 4 weeks. No inflammatory reactions, organ toxicity or systemic toxicity were observed. In young male rats where hydrogel was injected, defect healing was less effective than sham operated controls when rat MSCs were incorporated. Enhanced bone healing was observed however, in aged exbreeder female rats where acellular hydrogel was injected, with increased deposition of collagen type I and Runx2. Integration of the hydrogel with surrounding bone was observed without the need for delivered MSCs; native cell infiltration was also seen and bone formation was observed within all hydrogel systems investigated.

This hydrogel can be delivered directly into the target site, is biocompatible, promotes increased bone formation and facilitates migration of cells to promote integration with surrounding bone, for safe and efficacious bone repair.

Nanotherapeutics: An insight into healthcare and multi-dimensional applications in medical sector of the modern world

In recent years nanotechnology has revolutionized the healthcare strategies and envisioned to have a tremendous impact to offer better health facilities. In this context, medical nanotechnology involves design, fabrication, regulation, and application of therapeutic drugs and devices having a size in nano-range (1-100 nm). Owing to the revolutionary implications in drug delivery and gene therapy, nanotherapeutics has gained increasing research interest in the current medical sector of the modern world. The areas which anticipate benefits from nano-based drug delivery systems are cancer, diabetes, infectious diseases, neurodegenerative diseases, blood disorders and orthopedic problems. The development of nanotherapeutics with multi-functionalities has considerable potential to fill the lacunae existing in the present therapeutic domain. Nanomedicines in the field of cancer management have enhanced permeability and retention of drugs thereby effectively targeting the affected tissues. Polymeric conjugates of asparaginase, polymeric micelles of paclitaxel have been recmended for various types of cancer treatment .The advancement of nano therapeutics and diagnostics can provide the improved effectiveness of the drug with less or no toxicity concerns. Similarly, diagnostic imaging is having potential future applications with newer imaging elements at nano level. The newly emerging field of nanorobotics can provide new directions in the field of healthcare. In this article, an attempt has been made to highlight the novel nanotherapeutic potentialities of polymeric nanoparticles, nanoemulsion, solid lipid nanoparticle, nanostructured lipid carriers, dendrimers, nanocapsules and nanosponges based approaches. The useful applications of these nano-medicines in the field of cancer, nutrition, and health have been discussed in details. Regulatory and safety concerns along with the commercial status of nanosystems have also been presented. In summary, a successful translation of emerging nanotherapeutics into commercial products may lead to an expansion of biomedical science. Towards the end of the review, future perspectives of this important field have been introduced briefly.

Hydrophilic surface modification of coronary stent using an atmospheric pressure plasma jet for endothelialization

The first two authors contributed equally to this study. Bioactivity and cell adhesion properties are major factors for fabricating medical devices such as coronary stents. The aim of this study was to evaluate the advantages of atmospheric-pressure plasma jet in enhancing the biocompatibility and endothelial cell-favorites. The experimental objects were divided into before and after atmospheric-pressure plasma jet treatment with the ratio of nitrogen:argon = 3:1, which is similar to air. The treated surfaces were basically characterized by means of a contact angle analyzer for the activation property on their surfaces. The effect of atmospheric-pressure plasma jet on cellular response was examined by endothelial cell adhesion and XTT analysis. It was difficult to detect any changeable morphology after atmospheric-pressure plasma jet treatment on the surface. The roughness was increased after atmospheric-pressure plasma jet treatment compared to nonatmospheric-pressure plasma jet treatment (86.781 and 7.964 nm, respectively). The X-ray photoelectron spectroscopy results showed that the surface concentration of the C–O groups increased slightly from 6% to 8% after plasma activation. The contact angle dramatically decreased in the atmospheric-pressure plasma jet treated group (22.6 ± 15.26°) compared to the nonatmospheric-pressure plasma jet treated group (72.4 ± 15.26°) ( n = 10, p < 0.05). The effect of the increment in hydrophilicity due to the atmospheric-pressure plasma jet on endothelial cell migration and proliferation was 85.2% ± 12.01% and 34.2% ± 2.68%, respectively, at 7 days, compared to the nonatmospheric-pressure plasma jet treated group (58.2% ± 11.44% in migration, n = 10, p < 0.05). Taken together, the stent surface could easily obtain a hydrophilic property by the atmospheric-pressure plasma jet method. Moreover, the atmospheric-pressure plasma jet might affect re-endothelialization after stenting.

Modulation of PEI-Mediated Gene Transfection through Controlling Cytoskeleton Organization and Nuclear Morphology via Nanogrooved Topographies

The effect of nanotopographies on cell adhesion, migration, proliferation, differentiation, and/or apoptosis have been studied over the last two decades. However, the effect of nanotopography on gene transfection of adhered cells is far from understood. One key phenomenon of using nanotopography is mimicry of native cell morphology in vitro such as in alignment of skeletal myoblasts on nanogrooves. The formation of focal adhesions, the cytoskeleton, and the morphology of cell nuclei are altered by underlying nanogrooves, but the role of these changes in gene transfection are not well understood. In this study, C2C12 skeletal myoblasts were transfected using polyethylenimine (PEI)/DNA complexes on nanogrooved patterns of two groove widths (400 and 800 nm) at three depths (50 nm and 400 or 500 nm). The results showed that the deep nanogrooved surfaces (i.e., 400/400 and 800/500) induced formation of aligned, parallel F-actin and elongated nucleus morphology. Gene transfection was also reduced on the deep nanogrooved surfaces. Disruption of F-actin organization using Cytochalasin D (Cyto-D) restored the nuclear morphology accompanied by higher transfection efficiency, demonstrating that the reduction in gene expression on deep nanogrooves was due to cytoskeletal stretching and nucleus elongation. Spatiotemporal images of fluorescent-labeled PEI/DNA complexes showed that endocytosis of PEI/DNA complexes was retarded and DNA trafficking into the cell nucleus was reduced. This study demonstrates for the first time the important role of cytoskeletal organization and nuclear morphology in PEI-mediated gene transfection to skeletal myoblasts using nanogrooved patterns. These findings are informative for in vitro studies and could potentially be useful in in vivo intramuscular (IM) administration.

Bone marrow stem cells-derived extracellular matrix is a promising material

The extracellular matrix(ECM), which is primarily composed of collagens and proteoglycans, plays a key role in cell proliferation, differentiation, and migration and interactions between cells. In this study, we produced chitosan/gelatin/bone marrow stem cells-derived extracellular matrix(C/G/BMSCs-dECM) scaffolds via lyophilization and cross-linking, and chitosan/gelatin(C/G) scaffolds were used as controls. For the C/G/BMSCs-dECM scaffolds, the average pore size was 289.17 ± 80.28 μm; the average porosity was 89.25 ± 3.75%; the average compressive modulus was 0.82 ± 0.07 MPa; and the average water uptake ratio was 13.81 ± 1.00. In vitro, the C/G/BMSCs-dECM scaffolds promoted bone marrow stem cells(BMSCs) attachment and proliferation. Moreover, improved osteogenic differentiation was observed for these scaffolds. Thus, C/G/BMSCs-dECM is a promising material for bone tissue engineering.

Wet-spinning fabrication of shear-patterned alginate hydrogel microfibers and the guidance of cell alignment

Native tissue is naturally comprised of highly-ordered cell-matrix assemblies in a multi-hierarchical way, and the nano/submicron alignment of fibrous matrix is found to be significant in supporting cellular functionalization. In this study, a self-designed wet-spinning device appended with a rotary receiving pool was used to continuously produce shear-patterned hydrogel microfibers with aligned submicron topography. The process that the flow-induced shear force reshapes the surface of hydrogel fiber into aligned submicron topography was systematically analysed. Afterwards, the effect of fiber topography on cellular longitudinal spread and elongation was investigated by culturing rat neuron-like PC12 cells and human osteosarcoma MG63 cells with the spun hydrogel microfibers, respectively. The results suggested that the stronger shear flow force would lead to more distinct aligned submicron topography on fiber surface, which could induce cell orientation along with fiber axis and therefore form the cell-matrix dual-alignment. Finally, a multi-hierarchical tissue-like structure constructed by dual-oriented cell-matrix assemblies was fabricated based on this wet-spinning method. This work is believed to be a potentially novel biofabrication scheme for bottom-up constructing of engineered linear tissue, such as nerve bundle, cortical bone, muscle and hepatic cord.

Improved Antithrombotic Function of Oriented Endothelial Cell Monolayer on Microgrooves

Achievement of an endothelial cell (EC) monolayer (re-endothelialization) on the vascular implant surface with competent and functioning features is critical for long-term safety after implantation. Oriented EC monolayer is beneficial to improve endothelial function such as enhanced athero-resistant property. However, the information about antithrombotic property of oriented EC monolayer is limited. Here, we used the microgrooved polydimethylsiloxane substrates to guide EC orientation and obtain oriented EC monolayer. The effects of anisotropic topography on EC behaviors and antithrombotic function of the EC monolayer were then evaluated. Our data demonstrated that ECs responded to grooves in a size-dependent way as shown in oriented cell cytoskeleton and nuclei, enhanced directed migration, and overall velocity. Furthermore, compared to the EC monolayer on the flat surface, the oriented EC monolayer formed on the grooved substrates exhibited improved antithrombotic capability as indicated by higher expression of functional related genes, production of prostacyclin and tissue plasminogen activator, and prolonged activated coagulation time. The improvement of antithrombotic function was especially notable on the smaller-size groove. These findings reveal the responses of ECs to varisized topography and antithrombotic function of the oriented EC monolayer, providing insights into optimal design of vascular implants.

Nonmonotonic Self-Deformation of Cell Nuclei on Topological Surfaces with Micropillar Array

Cells respond to the mechanical signals from their surroundings and integrate physiochemical signals to initiate intricate mechanochemical processes. While many studies indicate that topological features of biomaterials impact cellular behaviors profoundly, little research has focused on the nuclear response to a mechanical force generated by a topological surface. Here, we fabricated a polymeric micropillar array with an appropriate dimension to induce a severe self-deformation of cell nuclei and investigated how the nuclear shape changed over time. Intriguingly, the nuclei of mesenchymal stem cells (MSCs) on the poly(lactide-co-glycolide) (PLGA) micropillars exhibited a significant initial deformation followed by a partial recovery, which led to an "overshoot" phenomenon. The treatment of cytochalasin D suppressed the recovery of nuclei, which indicated the involvement of actin cytoskeleton in regulating the recovery at the second stage of nuclear deformation. Additionally, we found that MSCs exhibited different overshoot extents from their differentiated lineage, osteoblasts. These findings enrich the understanding of the role of the cell nucleus in mechanotransduction. As the first quantitative report on nonmonotonic kinetic process of self-deformation of a cell organelle on biomaterials with unique topological surfaces, this study sheds new insight into cell-biomaterial interactions.

Carbon Nanotubes Induced Fibrogenesis on Nanostructured Substrates

While the rapidly evolving nanotechnology has shown promise in electronics, energy, healthcare and many other fields, there is an increasing concern about the adverse health consequences of engineered nanomaterials. To accurately evaluate the toxicity of nanomaterials, in vitro models incorporated with in vivo microenvironment characteristics are desirable. This study aims to delineate the influence of nanotopography on fibrogenic response of normal human lung fibroblasts to multi-walled carbon nanotubes (MWCNTs). Nanoscale gratings and pillars of various heights were fabricated on polydimethylsiloxane substrates. Cell spreading and biomechanics were measured, and fibrogenic responses including proliferation, collagen production and reactive oxygen species generation of the fibroblasts grown on the nanostructured substrates in response to MWCNTs were assessed. It was observed that the cells could be largely stretched on shallow nanogratings, leading to stiffer cytoskeleton and nucleus, enhanced cell proliferation and collagen production, and consequently, toxic response sensitivity of the fibroblasts was undermined. In contrast, the cell spreading and stiffness could be reduced using tall, isotropic nanopillars, which significantly improved the cell toxic sensitivity to the MWCNTs. In addition to highlighting the significant influence of cell-nanotopography interactions on cell sensing CNTs, this study contributed to development of physiologically relevant in vitro models for nanotoxicology study.

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.

Expanding Nanopatterned Substrates Using Stitch Technique for Nanotopographical Modulation of Cell Behavior

Substrate nanotopography has been shown to be a potent modulator of cell phenotype and function. To dissect nanotopography modulation of cell behavior, a large area of nanopatterned substrate is desirable so that enough cells can be cultured on the nanotopography for subsequent biochemical and molecular biology analyses. However, current nanofabrication techniques have limitations to generate highly defined nanopatterns over a large area. Herein, we present a method to expand nanopatterned substrates from a small, highly defined nanopattern to a large area using stitch technique. The method combines multiple techniques, involving soft lithography to replicate poly(dimethylsiloxane) (PDMS) molds from a well-defined mold, stitch technique to assemble multiple PDMS molds to a single large mold, and nanoimprinting to generate a master mold on polystyrene (PS) substrates. With the PS master mold, we produce PDMS working substrates and demonstrate nanotopographical modulation of cell spreading. This method provides a simple, affordable yet versatile avenue to generate well-defined nanopatterns over large areas, and is potentially extended to create micro-/nanoscale devices with hybrid components.

Nanotopography promoted neuronal differentiation of human induced pluripotent stem cells

Inefficient neural differentiation of human induced pluripotent stem cells (hiPSCs) motivates recent investigation of the influence of biophysical characteristics of cellular microenvironment, in particular nanotopography, on hiPSC fate decision. However, the roles of geometry and dimensions of nanotopography in neural lineage commitment of hiPSCs have not been well understood. The objective of this study is to delineate the effects of geometry, feature size and height of nanotopography on neuronal differentiation of hiPSCs. HiPSCs were seeded on equally spaced nanogratings (500 and 1000nm in linewidth) and hexagonally arranged nanopillars (500nm in diameter), each having a height of 150 or 560nm, and induced for neuronal differentiation in concert with dual Smad inhibitors. The gratings of 560nm height reduced cell proliferation, enhanced cytoplasmic localization of Yes-associated protein, and promoted neuronal differentiation (up to 60% βIII-tubulin⁺ cells) compared with the flat control. Nanograting-induced cell polarity and cytoplasmic YAP localization were shown to be critical to the induced neural differentiation of hiPSCs. The derived neuronal cells express MAP2, Tau, glutamate, GABA and Islet-1, indicating the existence of multiple neuronal subtypes. This study contributes to the delineation of cell-nanotopography interactions and provides the insights into the design of nanotopography configuration for pluripotent stem cell neural lineage commitment.

Adhesion-based tumor cell capture using nanotopography

Circulating tumor cells (CTCs) shed from primary tumors, transport through the blood stream to distant sites, and cause 90% of cancer deaths. Although different techniques have been developed to isolate CTCs for cancer detection, diagnosis and treatment, the heterogeneity of expression of the target antigen and the significant size variance in CTCs limit clinical applications of antibody- and size-based isolation techniques. Cell adhesion using nanotopography has been suggested as a promising approach to isolate CTCs independent of surface marker expression or size of CTCs. However, the nanotopographies studied are mainly nanopillars; the influence of other nanotopography such as nanogratings and their dimensions on tumor cell capture remains to be investigated. This study examined capture performance of several cancer cell lines of different types, surface marker expression and metastatic status on nanotopographies of various geometries and dimensions without antibody conjugation. The cancer cells exhibited differential capture performance on the nanotopographies with an efficiency up to 52%. Compared with flat surfaces and isotropic, discrete nanopillars, nanogratings favored cancer cell adhesion, thus improving the capture efficiency. The influence of nanotopography height studied, on the other hand, was less significant. This study provides useful information to optimize nanotopography for further improvement of CTC capture efficiency.