Using nanotopography and metabolomics to identify biochemical effectors of multipotency

Nanotopography Influences Host-Pathogen Quorum Sensing and Facilitates Selection of Bioactive Metabolites in Mesenchymal Stromal Cells and Pseudomonas aeruginosa Co-Cultures

Orthopedic implant-related bacterial infections and resultant antibiotic-resistant biofilms hinder implant-tissue integration and failure. Biofilm quorum sensing (QS) communication determines the pathogen colonization success. However, it remains unclear how implant modifications and host cells are influenced by, or influence, QS. High aspect ratio nanotopographies have shown to reduce biofilm formation of Pseudomonas aeruginosa, a sepsis causing pathogen with well-defined QS molecules. Producing such nanotopographies in relevant orthopedic materials (i.e., titanium) allows for probing QS using mass spectrometry-based metabolomics. However, nanotopographies can reduce host cell adhesion and regeneration. Therefore, we developed a polymer (poly(ethyl acrylate), PEA) coating that organizes extracellular matrix proteins, promoting bioactivity to host cells such as human mesenchymal stromal cells (hMSCs), maintaining biofilm reduction. This allowed us to investigate how hMSCs, after winning the race for the surface against pathogenic cells, interact with the biofilm. Our approach revealed that nanotopographies reduced major virulence pathways, such as LasR. The enhanced hMSCs support provided by the coated nanotopographies was shown to suppress virulence pathways and biofilm formation. Finally, we selected bioactive metabolites and demonstrated that these could be used as adjuncts to the nanostructured surfaces to reduce biofilm formation and enhance hMSC activity. These surfaces make excellent models to study hMSC-pathogen interactions and could be envisaged for use in novel orthopedic implants.

Hybrid Micro-/Nanoprotein Platform Provides Endocrine-like and Extracellular Matrix-like Cell Delivery of Growth Factors

Protein materials are versatile tools in diverse biomedical fields. Among them, artificial secretory granules (SGs), mimicking those from the endocrine system, act as mechanically stable reservoirs for the sustained release of proteins as oligomeric functional nanoparticles. Only validated in oncology, the physicochemical properties of SGs, along with their combined drug-releasing and scaffolding abilities, make them suitable as smart topographies in regenerative medicine for the prolonged delivery of growth factors (GFs). Thus, considering the need for novel, safe, and cost-effective materials to present GFs, in this study, we aimed to biofabricate a protein platform combining both endocrine-like and extracellular matrix fibronectin-derived (ECM-FN) systems. This approach is based on the sustained delivery of a nanostructured histidine-tagged version of human fibroblast growth factor 2. The GF is presented onto polymeric surfaces, interacting with FN to spontaneously generate nanonetworks that absorb and present the GF in the solid state, to modulate mesenchymal stromal cell (MSC) behavior. The results show that SGs-based topographies trigger high rates of MSCs proliferation while preventing differentiation. While this could be useful in cell therapy manufacture demanding large numbers of unspecialized MSCs, it fully validates the hybrid platform as a convenient setup for the design of biologically active hybrid surfaces and in tissue engineering for the controlled manipulation of mammalian cell growth.

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.

Mechanotransducive surfaces for enhanced cell osteogenesis, a review

Novel strategies employing mechano-transducing materials eliciting biological outcomes have recently emerged for controlling cellular behaviour. Targeted cellular responses are achieved by manipulating physical, chemical, or biochemical modification of material properties. Advances in techniques such as nanopatterning, chemical modification, biochemical molecule embedding, force-tuneable materials, and artificial extracellular matrices are helping understand cellular mechanotransduction. Collectively, these strategies manipulate cellular sensing and regulate signalling cascades including focal adhesions, YAP-TAZ transcription factors, and multiple osteogenic pathways. In this minireview, we are providing a summary of the influence that these materials, particularly titanium-based orthopaedic materials, have on cells. We also highlight recent complementary methodological developments including, but not limited to, the use of metabolomics for identification of active biomolecules that drive cellular differentiation.

Three-dimensional bioprinted GelMA/GO composite hydrogel for stem cell osteogenic differentiation both in vitro and in vivo

In this study, we evaluated the use of graphene oxide (GO) mixed with methyl methacrylate gelatin (GelMA) for the construction of a microenvironmental implant to repair bone defects in orthopedic surgery. A scaffold containing a GelMA/GO composite with mesenchymal stem cells (MSCs) was constructed using three-dimensional bioprinting. The survival and osteogenic capacity of MSCs in the composite bioink were evaluated using cell viability and proliferation assays, osteogenesis-related gene expression analysis, and implantation under the skin of nude mice. The printing process had little effect on cell viability. We found that GO enhanced cell proliferation but had no significant effect on cell viability. In vitro experiments suggested that GO promoted material-cell interactions and the expression of osteogenesis-related genes. In vivo experiments showed that GO decreased the degradation time of the material and increased calcium nodule deposition. In contrast to pure GelMA, the addition of GO created a suitable microenvironment to promote the differentiation of loaded exogenous MSCs in vitro and in vivo, providing a basis for the repair of bone defects.

Regulation Mechanisms and Maintenance Strategies of Stemness in Mesenchymal Stem Cells

Stemness pertains to the intrinsic ability of mesenchymal stem cells (MSCs) to undergo self-renewal and differentiate into multiple lineages, while simultaneously impeding their differentiation and preserving crucial differentiating genes in a state of quiescence and equilibrium. Owing to their favorable attributes, including uncomplicated isolation protocols, ethical compliance, and ease of procurement, MSCs have become a focal point of inquiry in the domains of regenerative medicine and tissue engineering. As age increases or ex vivo cultivation is prolonged, the functionality of MSCs decreases and their stemness gradually diminishes, thereby limiting their potential therapeutic applications. Despite the existence of several uncertainties surrounding the comprehension of MSC stemness, considerable advancements have been achieved in the clarification of the potential mechanisms that lead to stemness loss, as well as the associated strategies for stemness maintenance. This comprehensive review provides a systematic overview of the factors influencing the preservation of MSC stemness, the molecular mechanisms governing it, the strategies for its maintenance, and the therapeutic potential associated with stemness. Finally, we underscore the obstacles and prospective avenues in present investigations, providing innovative perspectives and opportunities for the preservation and therapeutic utilization of MSC stemness.

Nanotopographical Cues Tune the Therapeutic Potential of Extracellular Vesicles for the Treatment of Aged Skeletal Muscle Injuries

Skeletal muscle regeneration relies on the tightly temporally regulated lineage progression of muscle stem/progenitor cells (MPCs) from activation to proliferation and, finally, differentiation. However, with aging, MPC lineage progression is disrupted and delayed, ultimately causing impaired muscle regeneration. Extracellular vesicles (EVs) have attracted broad attention as next-generation therapeutics for promoting tissue regeneration. As a next step toward clinical translation, strategies to manipulate EV effects on downstream cellular targets are needed. Here, we developed an engineering strategy to tune the therapeutic potential of EVs using nanotopographical cues. We found that EVs released by young MPCs cultured on flat substrates (fEVs) promoted the proliferation of aged MPCs while EVs released by MPCs cultured on nanogratings (nEVs) promoted myogenic differentiation. We then employed a bioengineered 3D muscle aging model to optimize the administration protocol and test the therapeutic potential of fEVs and nEVs in a high-throughput manner. We found that the sequential administration first of fEVs during the phase of MPC proliferative expansion (i.e., 1 day after injury) followed by nEV administration at the stage of MPC differentiation (i.e., 3 days after injury) enhanced aged muscle regeneration to a significantly greater extent than fEVs and nEVs delivered either in isolation or mixed. The beneficial effects of the sequential EV treatment strategy were further validated in vivo, as evidenced by increased myofiber size and improved functional recovery. Collectively, our study demonstrates the ability of topographical cues to tune EV therapeutic potential and highlights the importance of optimizing the EV administration strategy to accelerate aged skeletal muscle regeneration.

Nanotopography reveals metabolites that maintain the immunomodulatory phenotype of mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) are multipotent progenitor cells that are of considerable clinical potential in transplantation and anti-inflammatory therapies due to their capacity for tissue repair and immunomodulation. However, MSCs rapidly differentiate once in culture, making their large-scale expansion for use in immunomodulatory therapies challenging. Although the differentiation mechanisms of MSCs have been extensively investigated using materials, little is known about how materials can influence paracrine activities of MSCs. Here, we show that nanotopography can control the immunomodulatory capacity of MSCs through decreased intracellular tension and increasing oxidative glycolysis. We use nanotopography to identify bioactive metabolites that modulate intracellular tension, growth and immunomodulatory phenotype of MSCs in standard culture and during larger scale cell manufacture. Our findings demonstrate an effective route to support large-scale expansion of functional MSCs for therapeutic purposes.

Static and photoresponsive dynamic materials to dissect physical regulation of cellular functions

Recent progress in mechanobiology has highlighted the importance of physical cues, such as mechanics, geometry (size), topography, and porosity, in the determination of cellular activities and fates, in addition to biochemical factors derived from their surroundings. In this review, we will first provide an overview of how such fundamental insights are identified by synchronizing the hierarchical nature of biological systems and static materials with tunable physical cues. Thereafter, we will explain the photoresponsive dynamic biomaterials to dissect the spatiotemporal aspects of the dependence of biological functions on physical cues.

The influence of nanotopography on cell behaviour through interactions with the extracellular matrix – A review

Nanotopography presents an effective physical approach for biomaterial cell manipulation mediated through material-extracellular matrix interactions. The extracellular matrix that exists in the cellular microenvironment is crucial for guiding cell behaviours, such as determination of integrin ligation and interaction with growth factors. These interactions with the extracellular matrix regulate downstream mechanotransductive pathways, such as rearrangements in the cytoskeleton and activation of signal cascades. Protein adsorption onto nanotopography strongly influences the conformation and distribution density of extracellular matrix and, therefore, subsequent cell responses. In this review, we first discuss the interactive mechanisms of protein physical adsorption on nanotopography. Secondly, we summarise advances in creating nanotopographical features to instruct desired cell behaviours. Lastly, we focus on the cellular mechanotransductive pathways initiated by nanotopography. This review provides an overview of the current state-of-the-art designs of nanotopography aiming to provide better biomedical materials for the future.

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A comprehensive overview of nanotopography fabrication, and nanotopography regulates various cell behaviours.

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The interactive physical adsorption between nanotopography and extracellular matrix.

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Nanotopography initiates the cellular mechanotransductive pathways and downstream signalling cascades.

Bioactivation of 3D Cell-Imprinted Polydimethylsiloxane Surfaces by Bone Protein Nanocoating for Bone Tissue Engineering

Physical and chemical parameters that mimic the physiological niche of the human body have an influence on stem cell fate by creating directional signals to cells. Micro/nano cell-patterned polydimethylsiloxane (PDMS) substrates, due to their ability to mimic the physiological niche, have been widely used in surface modification. Integration of other factors such as the biochemical coating on the surface can achieve more similar microenvironmental conditions and promote stem cell differentiation to the target cell line. Herein, we investigated the effect of physical topography, chemical functionalization by acid bone lysate (ABL) nanocoating, and the combined functionalization of the bone proteins' nanocoated surface and the topographically modified surface. We prepared four distinguishing surfaces: plain PDMS, physically modified PDMS by 3D cell topography patterning, chemically modified PDMS with bone protein nanocoating, and chemically modified nano 3D cell-imprinted PDMS by bone proteins (ABL). Characterization of extracted ABL was carried out by Bradford staining and sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis, followed by the MTT assay for evaluation of cell viability on ABL-coated PDMS. Moreover, field emission scanning electron microscopy and profilometry were used for the determination of optimal coating thickness, and the appropriate coating concentration was identified and used in the study. The binding and retention of ABL to PDMS were confirmed by Fourier transform infrared spectroscopy and bicinchoninic acid assay. Sessile drop static water contact angle measurements on substrates showed that the combined chemical functionalization and nano 3D cell-imprinting on the PDMS surface improved surface wettability by 66% compared to plain PDMS. The results of ALP measurement, alizarin red S staining, immunofluorescence staining, and real-time PCR showed that the nano 3D cell-imprinted PDMS surface functionalized by extracted bone proteins, ABL, is able to guide the fate of adipose derived stem cellss toward osteogenic differentiation. Eventually, chemical modification of the cell-imprinted PDMS substrate by bone protein extraction not only improved the cell adhesion and proliferation but also contributed to the topographical effect itself and caused a significant synergistic influence on the process of osteogenic differentiation.

Modulated nanowire scaffold for highly efficient differentiation of mesenchymal stem cells

Background

Nanotopographical cues play a critical role as drivers of mesenchymal stem cell differentiation. Nanowire scaffolds, in this regard, provide unique and adaptable nanostructured surfaces with focal points for adhesion and with elastic properties determined by nanowire stiffness.

Results

We show that a scaffold of nanowires, which are remotely actuated by a magnetic field, mechanically stimulates mesenchymal stem cells. Osteopontin, a marker of osteogenesis onset, was expressed after cells were cultured for 1 week on top of the scaffold. Applying a magnetic field significantly boosted differentiation due to mechanical stimulation of the cells by the active deflection of the nanowire tips. The onset of differentiation was reduced to 2 days of culture based on the upregulation of several osteogenesis markers. Moreover, this was observed in the absence of any external differentiation factors.

Conclusions

The magneto-mechanically modulated nanosurface enhanced the osteogenic differentiation capabilities of mesenchymal stem cells, and it provides a customizable tool for stem cell research and tissue engineering.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01488-5.

Cell-controlled dynamic surfaces for skeletal stem cell growth and differentiation

Skeletal stem cells (SSCs, or mesenchymal stromal cells typically referred to as mesenchymal stem cells from the bone marrow) are a dynamic progenitor population that can enter quiescence, self-renew or differentiate depending on regenerative demand and cues from their niche environment. However, ex vivo, in culture, they are grown typically on hard polystyrene surfaces, and this leads to rapid loss of the SSC phenotype. While materials are being developed that can control SSC growth and differentiation, very few examples of dynamic interfaces that reflect the plastic nature of the stem cells have, to date, been developed. Achieving such interfaces is challenging because of competing needs: growing SSCs require lower cell adhesion and intracellular tension while differentiation to, for example, bone-forming osteoblasts requires increased adhesion and intracellular tension. We previously reported a dynamic interface where the cell adhesion tripeptide arginine-glycine-aspartic acid (RGD) was presented to the cells upon activation by user-added elastase that cleaved a bulky blocking group hiding RGD from the cells. This allowed for a growth phase while the blocking group was in place and the cells could only form smaller adhesions, followed by an osteoblast differentiation phase that was induced after elastase was added which triggered exposure of RGD and subsequent cell adhesion and contraction. Here, we aimed to develop an autonomous system where the surface is activated according to the need of the cell by using matrix metalloprotease (MMP) cleavable peptide sequences to remove the blocking group with the hypothesis that the SSCs would produce higher levels of MMP as the cells reached confluence. The current studies demonstrate that SSCs produce active MMP-2 that can cleave functional groups on a surface. We also demonstrate that SSCs can grow on the uncleaved surface and, with time, produce osteogenic marker proteins on the MMP-responsive surface. These studies demonstrate the concept for cell-controlled surfaces that can modulate adhesion and phenotype with significant implications for stem cell phenotype modulation.

Mechano-Nanoarchitectonics: Design and Function

Mechanical stimuli have rather ambiguous and less-specific features among various physical stimuli, but most materials exhibit a certain level of responses upon mechanical inputs. Unexplored sciences remain in mechanical responding systems as one of the frontiers of materials science. Nanoarchitectonics approaches for mechanically responding materials are discussed as mechano-nanoarchitectonics in this review article. Recent approaches on molecular and materials systems with mechanical response capabilities are first exemplified with two viewpoints: i) mechanical control of supramolecular assemblies and materials and ii) mechanical control and evaluation of atom/molecular level structures. In the following sections, special attentions on interfacial environments for mechano-nanoarchitectonics are emphasized. The section entitled iii) Mechanical Control of Molecular System at Dynamic Interface describes coupling of macroscopic mechanical forces and molecular-level phenomena. Delicate mechanical forces can be applied to functional molecules embedded at the air-water interface where operation of molecular machines and tuning of molecular receptors upon macroscopic mechanical actions are discussed. Finally, the important role of the interfacial media are further extended to the control of living cells as described in the section entitled iv) Mechanical Control of Biosystems. Pioneering approaches on cell fate regulations at liquid-liquid interfaces are discussed in addition to well-known mechanobiology.

NMR Metabolomics Assessment of Osteogenic Differentiation of Adipose-Tissue-Derived Mesenchymal Stem Cells

This Article presents, for the first time to our knowledge, an untargeted nuclear magnetic resonance (NMR) metabolomic characterization of the polar intracellular metabolic adaptations of human adipose-derived mesenchymal stem cells during osteogenic differentiation. The use of mesenchymal stem cells (MSCs) for bone regeneration is a promising alternative to conventional bone grafts, and untargeted metabolomics may unveil novel metabolic information on the osteogenic differentiation of MSCs, allowing their behavior to be understood and monitored/guided toward effective therapies. Our results unveiled statistically relevant changes in the levels of just over 30 identified metabolites, illustrating a highly dynamic process with significant variations throughout the whole 21-day period of osteogenic differentiation, mainly involving amino acid metabolism and protein synthesis; energy metabolism and the roles of glycolysis, the tricarboxylic acid cycle, and oxidative phosphorylation; cell membrane metabolism; nucleotide metabolism (including the specific involvement of O-glycosylation intermediates and NAD⁺); and metabolic players in protective antioxidative mechanisms (such as glutathione and specific amino acids). Different metabolic stages are proposed and are supported by putative biochemical explanations for the metabolite changes observed. This work lays the groundwork for the use of untargeted NMR metabolomics to find potential metabolic markers of osteogenic differentiation efficacy.

Enhancement strategies for mesenchymal stem cells and related therapies

Cell therapy, particularly mesenchymal stem/stromal (MSC) therapy, has been investigated for a wide variety of disease indications, particularly those with inflammatory pathologies. However, recently it has become evident that the MSC is far from a panacea. In this review we will look at current and future strategies that might overcome limitations in efficacy. Many of these take their inspiration from stem cell niche and the mechanism of MSC action in response to the injury microenvironment, or from previous gene therapy work which can now benefit from the added longevity and targeting ability of a live cell vector. We will also explore the nascent field of extracellular vesicle therapy and how we are already seeing enhancement protocols for this exciting new drug. These enhanced MSCs will lead the way in more difficult to treat diseases and restore potency where donors or manufacturing practicalities lead to diminished MSC effect.

Nanotopography Sequentially Mediates Human Mesenchymal Stem Cell-Derived Small Extracellular Vesicles for Enhancing Osteogenesis

Engineered small extracellular vesicles (sEVs) are used as tools to enhance therapeutic efficacy. However, such application of sEVs is associated with several issues, including high costs and a high risk of tumorigenesis. Nanotopography has a greater influence on bone-related cell behaviors. However, whether nanotopography specifically mediate sEV content to perform particular biological functions remains unclear. Here, we demonstrate that selective nanotopography may be used to sequentially mediate human bone mesenchymal stem cell (hBMSC) sEVs to enhance the therapeutic efficacy of hBMSCs-EVs for osteogenesis. We subjected sEVs harvested from hBMSCs cultured on polished titanium plates (Ti) or nanotopographical titanium plates (Ti4) after 7, 14, and 21 d for RNA sequencing, and we found that there was no significant difference in sEV-miRNA expression after 7 d. Differentially expressed osteogenic-related microRNAs were founded after 14 days, and KEGG analysis indicated that the main microRNAs were associated with osteogenesis-related pathways, such as TGF-beta, AMPK, and FoxO. A significant difference was found in sEV-miRNAs expression after 21 d. We loaded sEV secreted from hBMSCs cultured on Ti4 after 21 d on 3D-printed porous PEEK scaffolds with poly dopamine (PDA) and found that such scaffolds showed superior osteogenic ability after 6- and 12-weeks. Here, we demonstrate the alkali- and heat-treated nanotopography with the ability of stimulating osteogenic differentiation of hBMSC can induce the secretion of pro-osteogenesis sEV, and we also found that sEVs meditate osteogenesis through miRNA. Thus, whether nanotopography has the ability to regulate other contents of sEVs such as proteins for enhancing osteogenesis needs further research. These findings may help us use nanotopography to extract sEVs for other biomedical applications, including cancer therapy.

Omics Technologies for High-Throughput-Screening of Cell-Biomaterial Interactions

Recent research effort in biomaterial development has largely focused on engineering bio-instructive materials to stimulate specific cell signaling. Assessing the biological performance of these materials using time-consuming and trial-and-error traditional...

Materials-driven fibronectin assembly on nanoscale topography enhances mesenchymal stem cell adhesion, protecting cells from bacterial virulence factors and preventing biofilm formation

Post-operative infection is a major complication in patients recovering from orthopaedic surgery. As such, there is a clinical need to develop biomaterials for use in regenerative surgery that can promote mesenchymal stem cell (MSC) osteospecific differentiation and that can prevent infection caused by biofilm-forming pathogens. Nanotopographical approaches to pathogen control are being identified, including in orthopaedic materials such as titanium and its alloys. These topographies use high aspect ratio nanospikes or nanowires to prevent bacterial adhesion but these features also significantly reduce MSC adhesion and activity. Here, we use a poly (ethyl acrylate) (PEA) polymer coating on titanium nanowires to spontaneously organise fibronectin (FN) and to deliver bone morphogenetic protein 2 (BMP2) to enhance MSC adhesion and osteospecific signalling. Using a novel MSC-Pseudomonas aeruginosa co-culture, we show that the coated nanotopographies protect MSCs from cytotoxic quorum sensing and signalling molecules, enhance MSC adhesion and osteoblast differentiation and reduce biofilm formation. We conclude that the PEA polymer-coated nanotopography can both support MSCs and prevent pathogens from adhering to a biomaterial surface, thus protecting from biofilm formation and bacterial infection, and supporting osteogenic repair.

Nanovibrational stimulation inhibits osteoclastogenesis and enhances osteogenesis in co-cultures

Models of bone remodelling could be useful in drug discovery, particularly if the model is one that replicates bone regeneration with reduction in osteoclast activity. Here we use nanovibrational stimulation to achieve this in a 3D co-culture of primary human osteoprogenitor and osteoclast progenitor cells. We show that 1000 Hz frequency, 40 nm amplitude vibration reduces osteoclast formation and activity in human mononuclear CD14⁺ blood cells. Additionally, this nanoscale vibration both enhances osteogenesis and reduces osteoclastogenesis in a co-culture of primary human bone marrow stromal cells and bone marrow hematopoietic cells. Further, we use metabolomics to identify Akt (protein kinase C) as a potential mediator. Akt is known to be involved in bone differentiation via transforming growth factor beta 1 (TGFβ1) and bone morphogenetic protein 2 (BMP2) and it has been implicated in reduced osteoclast activity via Guanine nucleotide-binding protein subunit α13 (Gα13). With further validation, our nanovibrational bioreactor could be used to help provide humanised 3D models for drug screening.

Graphene oxide-functionalized nanocomposites promote osteogenesis of human mesenchymal stem cells via enhancement of BMP-SMAD1/5 signaling pathway

Biomaterials that can harness the intrinsic osteogenic potential of stem cells offer a promising strategy to accelerate bone regeneration and repair. Previously, we had used methacrylated gelatin (GelMA)-based scaffolds to achieve bone formation from human mesenchymal stem cells (hMSCs). In this study, we aimed to further enhance hMSC osteogenesis by incorporating graphene oxide (GO)-based nanosheets into GelMA. In vitro results showed high viability and metabolic activities in hMSCs encapsulated in the newly developed nanocomposites. Incorporation of GO markedly increased mineralization within hMSC-laden constructs, which was further increased by replacing GO with silica-coated graphene oxide (SiGO). Mechanistic analysis revealed that the nanosheet enhanced the production, retention, and biological activity of endogenous bone morphogenetic proteins (BMPs), resulting in robust osteogenesis in the absence of exogenous osteoinductive growth factors. Specifically, the osteoinductive effect of the nanosheets was abolished by inhibiting the BMP signaling pathway with LDN-193189 treatment. The bone formation potential of the technology was further tested in vivo using a mouse subcutaneous implantation model, where hMSCs-laden GO/GelMA and SiGO/GelMA samples resulted in bone volumes 108 and 385 times larger, respectively, than the GelMA control group. Taken together, these results demonstrate the biological activity and mechanism of action of GO-based nanosheets in augmenting the osteogenic capability of hMSCs, and highlights the potential of leveraging nanomaterials such as GO and SiGO for bone tissue engineering applications.

Stem Cell Niche Microenvironment: Review

The cornea comprises a pool of self-regenerating epithelial cells that are crucial to preserving clarity and visibility. Limbal epithelial stem cells (LESCs), which live in a specialized stem cell niche (SCN), are crucial for the survival of the human corneal epithelium. They live at the bottom of the limbal crypts, in a physically enclosed microenvironment with a number of neighboring niche cells. Scientists also simplified features of these diverse microenvironments for more analysis in situ by designing and recreating features of different SCNs. Recent methods for regenerating the corneal epithelium after serious trauma, including burns and allergic assaults, focus mainly on regenerating the LESCs. Mesenchymal stem cells, which can transform into self-renewing and skeletal tissues, hold immense interest for tissue engineering and innovative medicinal exploration. This review summarizes all types of LESCs, identity and location of the human epithelial stem cells (HESCs), reconstruction of LSCN and artificial stem cells for self-renewal.

Metabolomic Applications in Stem Cell Research: a Review

This review describes the use of metabolomics to study stem cell (SC) characteristics and function, excluding SCs in cancer research, suited to a fully dedicated text. The interest in employing metabolomics in SC research has consistently grown and emphasis is, here, given to developments reported in the past five years. This text informs on the existing methodologies and their complementarity regarding the information provided, comprising untargeted/targeted approaches, which couple mass spectrometry or nuclear magnetic resonance spectroscopy with multivariate analysis (and, in some cases, pathway analysis and integration with other omics), and more specific analytical approaches, namely isotope tracing to highlight particular metabolic pathways, or in tandem microscopic strategies to pinpoint characteristics within a single cell. The bulk of this review covers the existing applications in various aspects of mesenchymal SC behavior, followed by pluripotent and neural SCs, with a few reports addressing other SC types. Some of the central ideas investigated comprise the metabolic/biological impacts of different tissue/donor sources and differentiation conditions, including the importance of considering 3D culture environments, mechanical cues and/or media enrichment to guide differentiation into specific lineages. Metabolomic analysis has considered cell endometabolomes and exometabolomes (fingerprinting and footprinting, respectively), having measured both lipid species and polar metabolites involved in a variety of metabolic pathways. This review clearly demonstrates the current enticing promise of metabolomics in significantly contributing towards a deeper knowledge on SC behavior, and the discovery of new biomarkers of SC function with potential translation to in vivo clinical practice.

Probing cell metabolism on insulin like growth factor(IGF)-1/tumor necrosis factor(TNF)-α and chargeable polymers co-immobilized conjugates

Cell culturing on different synthetic biomaterials would reprogram cell metabolism for adaption to their living conditions because such alterations in cell metabolism were necessary for cellular functions on them. Here we used metabolomics to uncover metabolic changes when liver cells were cultured on insulin-like growth factor (IGF)/tumor necrosis factor-α (TNF-α) and chargeable polymers co-modified biomaterials with the aim to explain their modulating effects on cell metabolism. The results showed that cell metabolism on IGF-1/TNF-α co-immobilized conjugates was significantly regulated according to their scatterings on the score plot of principal component analysis. Specifically, cell metabolisms were reprogrammed to the higher level of pyrimidine metabolism, β-alanine metabolism, and pantothenate and CoA biosynthesis, and the lower level of methionine salvage pathway in order to promote cell growth on IGF/TNF-α co-modified surface. Furthermore, cell senescence on PSt-PAAm-IGF/TNF-α surface was delayed through the regulation of branch amino acid metabolism and AMPK signal pathway. The research showed that metabolomics had great potential to uncover the molecular interaction between biomaterials and seeded cells, and provide the insights about cell metabolic reprogramming on IGF/TNF-α co-modified conjugates for cell growth.

The use of nanovibration to discover specific and potent bioactive metabolites that stimulate osteogenic differentiation in mesenchymal stem cells

Bioactive metabolites have wide-ranging biological activities and are a potential source of future research and therapeutic tools. Here, we use nanovibrational stimulation to induce osteogenic differentiation of mesenchymal stem cells, in the absence of off-target, nonosteogenic differentiation. We show that this differentiation method, which does not rely on the addition of exogenous growth factors to culture media, provides an artifact-free approach to identifying bioactive metabolites that specifically and potently induce osteogenesis. We first identify a highly specific metabolite, cholesterol sulfate, an endogenous steroid. Next, a screen of other small molecules with a similar steroid scaffold identified fludrocortisone acetate with both specific and highly potent osteogenic-inducing activity. Further, we implicate cytoskeletal contractility as a measure of osteogenic potency and cell stiffness as a measure of specificity. These findings demonstrate that physical principles can be used to identify bioactive metabolites and then enable optimization of metabolite potency can be optimized by examining structure-function relationships.

The influence of the morphology of titania and hydroxyapatite on the proliferation and osteogenic differentiation of human mesenchymal stem cells

Herein, the proliferation and osteogenic potential of human mesenchymal stem cells (hMSCs) on the disordered and ordered porous morphology of the titania surface and titania surface modified by hydroxyapatite (HA) are compared for the first time. In 5 days, the MTT-assay showed that the ordered porous morphology of electrochemically fabricated titania nanotubes (TNT) and TNT with chemically deposited hydroxyapatite (TNT–HA) was favorable for stem cell proliferation. In 14 days, RT-qPCR demonstrated that the disordered porous morphology of the sonochemically produced titania mesoporous surface (TMS) and TMS modified by the chemical deposition of HA (TMS–HA) led to the differentiation of hMSCs into the osteogenic direction in the absence of osteogenic inductors. These results originate from the mechanism of mechanotransduction, which sheds a light on the interaction of mesenchymal stem cells with the porous interface through focal adhesion, regulating the expression of genes determining stem cell self-renewal and osteogenic differentiation. The strong focal adhesion of hMSCs adjusted by the disordered TMS and TMS–HA is enough to induce osteogenic differentiation with the delay of cellular self-renewal. The weak focal adhesion of hMSCs tuned by the ordered TNT and TNT–HA affects only cellular self-renewal. The present research makes a new contribution to nanomedicine and engineering of porous implant interfaces for the replacement of bone injuries.

Herein, the proliferation and osteogenic potential of human mesenchymal stem cells (hMSCs) on the disordered and ordered porous morphology of the titania surface and titania surface modified by hydroxyapatite (HA) are compared for the first time.

A Metabolomics-Based Approach to Identify Lineage Guiding Molecules in Pericyte Cultures

We report the use of self-assembled peptide (F₂/S) hydrogels and cellular metabolomics to identify a number of innate molecules that are integral to the metabolic processes which drive cellular differentiation of multipotent pericyte stem cells. The culture system relies solely on substrate mechanics to induce differentiation in the absence of traditional differentiation media and therefore is a non-invasive approach to assessing cellular behavior at the molecular level and identifying key metabolites in this process. This novel approach demonstrates that simple metabolites can provide an alternative means to direct stem cell differentiation and that biomaterials can be used to identify them simply and quickly.

Designing topographically textured microparticles for induction and modulation of osteogenesis in mesenchymal stem cell engineering

Mesenchymal stem cells are the focus of intense research in bone development and regeneration. The potential of microparticles as modulating moieties of osteogenic response by utilizing their architectural features is demonstrated herein. Topographically textured microparticles of varying microscale features are produced by exploiting phase-separation of a readily soluble sacrificial component from polylactic acid. The influence of varying topographical features on primary human mesenchymal stem cell attachment, proliferation and markers of osteogenesis is investigated. In the absence of osteoinductive supplements, cells cultured on textured microparticles exhibit notably increased expression of osteogenic markers relative to conventional smooth microparticles. They also exhibit varying morphological, attachment and proliferation responses. Significantly altered gene expression and metabolic profiles are observed, with varying histological characteristics in vivo. This study highlights how tailoring topographical design offers cell-instructive 3D microenvironments which allow manipulation of stem cell fate by eliciting the desired downstream response without use of exogenous osteoinductive factors.

Hurdles to uptake of mesenchymal stem cells and their progenitors in therapeutic products

Twenty-five years have passed since the first clinical trial utilising mesenchymal stomal/stem cells (MSCs) in 1995. In this time academic research has grown our understanding of MSC biochemistry and our ability to manipulate these cells in vitro using chemical, biomaterial, and mechanical methods. Research has been emboldened by the promise that MSCs can treat illness and repair damaged tissues through their capacity for immunomodulation and differentiation. Since 1995, 31 therapeutic products containing MSCs and/or progenitors have reached the market with the level of in vitro manipulation varying significantly. In this review, we summarise existing therapeutic products containing MSCs or mesenchymal progenitor cells and examine the challenges faced when developing new therapeutic products. Successful progression to clinical trial, and ultimately market, requires a thorough understanding of these hurdles at the earliest stages of in vitro pre-clinical development. It is beneficial to understand the health economic benefit for a new product and the reimbursement potential within various healthcare systems. Pre-clinical studies should be selected to demonstrate efficacy and safety for the specific clinical indication in humans, to avoid duplication of effort and minimise animal usage. Early consideration should also be given to manufacturing: how cell manipulation methods will integrate into highly controlled workflows and how they will be scaled up to produce clinically relevant quantities of cells. Finally, we summarise the main regulatory pathways for these clinical products, which can help shape early therapeutic design and testing.

On the Interaction between 1D Materials and Living Cells

One-dimensional (1D) materials allow for cutting-edge applications in biology, such as single-cell bioelectronics investigations, stimulation of the cellular membrane or the cytosol, cellular capture, tissue regeneration, antibacterial action, traction force investigation, and cellular lysis among others. The extraordinary development of this research field in the last ten years has been promoted by the possibility to engineer new classes of biointerfaces that integrate 1D materials as tools to trigger reconfigurable stimuli/probes at the sub-cellular resolution, mimicking the in vivo protein fibres organization of the extracellular matrix. After a brief overview of the theoretical models relevant for a quantitative description of the 1D material/cell interface, this work offers an unprecedented review of 1D nano- and microscale materials (inorganic, organic, biomolecular) explored so far in this vibrant research field, highlighting their emerging biological applications. The correlation between each 1D material chemistry and the resulting biological response is investigated, allowing to emphasize the advantages and the issues that each class presents. Finally, current challenges and future perspectives are discussed.

Biological Effects of Polyrotaxane Surfaces on Cellular Responses of Fibroblast, Preosteoblast and Preadipocyte Cell Lines

Biointerfaces based on polyrotaxane (PRX), consisting of α-cyclodextrins (α-CDs) threaded on a poly(ethylene glycol) (PEG) chain, are promising functionalized platforms for culturing cells. PRXs are characterized by the molecular mobility of constituent molecules where the threading α-CDs can move and rotate along the PEG chain. Taking advantage of this mobility, we have previously succeeded in demonstrating the regulation of cellular responses, such as cellular adhesion, proliferation, and differentiation. In the present study, we investigated differences in the cellular responses to PRX surfaces versus commercially available tissue culture polystyrene (TCPS) surfaces using fibroblasts, preosteoblasts, and preadipocytes. PRX surfaces were found to more significantly promote cellular proliferation than the TCPS surfaces, regardless of the cell type. To identify the signaling pathways involved in the activation of cellular proliferation, a DNA microarray analysis was performed. PRX surfaces showed a significant increase in the integrin-mediated cell adhesion and focal adhesion pathways. Furthermore, PRX surfaces also promoted osteoblast differentiation more than TCPS. These results suggest that structural features of PRX surfaces act as mechanical cues to dominate cellular proliferation and differentiation.

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.

Bone marrow niche crosses paths with BMPs: a road to protection and persistence in CML

Chronic myeloid leukaemia (CML) is a paradigm of precision medicine, being one of the first cancers to be treated with targeted therapy. This has revolutionised CML therapy and patient outcome, with high survival rates. However, this now means an ever-increasing number of patients are living with the disease on life-long tyrosine kinase inhibitor (TKI) therapy, with most patients anticipated to have near normal life expectancy. Unfortunately, in a significant number of patients, TKIs are not curative. This low-level disease persistence suggests that despite a molecularly targeted therapeutic approach, there are BCR-ABL1-independent mechanisms exploited to sustain the survival of a small cell population of leukaemic stem cells (LSCs). In CML, LSCs display many features akin to haemopoietic stem cells, namely quiescence, self-renewal and the ability to produce mature progeny, this all occurs through intrinsic and extrinsic signals within the specialised microenvironment of the bone marrow (BM) niche. One important avenue of investigation in CML is how the disease highjacks the BM, thereby remodelling this microenvironment to create a niche, which enables LSC persistence and resistance to TKI treatment. In this review, we explore how changes in growth factor levels, in particular, the bone morphogenetic proteins (BMPs) and pro-inflammatory cytokines, impact on cell behaviour, extracellular matrix deposition and bone remodelling in CML. We also discuss the challenges in targeting LSCs and the potential of dual targeting using combination therapies against BMP receptors and BCR-ABL1.

Engineering Biomaterials with Micro/Nanotechnologies for Cell Reprogramming

Cell reprogramming is a revolutionized biotechnology that offers a powerful tool to engineer cell fate and function for regenerative medicine, disease modeling, drug discovery, and beyond. Leveraging advances in biomaterials and micro/nanotechnologies can enhance the reprogramming performance in vitro and in vivo through the development of delivery strategies and the control of biophysical and biochemical cues. In this review, we present an overview of the state-of-the-art technologies for cell reprogramming and highlight the recent breakthroughs in engineering biomaterials with micro/nanotechnologies to improve reprogramming efficiency and quality. Finally, we discuss future directions and challenges for reprogramming technologies and clinical translation.

Customizable, engineered substrates for rapid screening of cellular cues

Biophysical cues robustly direct cell responses and are thus important tools for in vitro and translational biomedical applications. High throughput platforms exploring substrates with varying physical properties are therefore valuable. However, currently existing platforms are limited in throughput, the biomaterials used, the capability to segregate between different cues and the assessment of dynamic responses. Here we present a multiwell array (3 × 8) made of a substrate engineered to present topography or rigidity cues welded to a bottomless plate with a 96-well format. Both the patterns on the engineered substrate and the well plate format can be easily customized, permitting systematic and efficient screening of biophysical cues. To demonstrate the broad range of possible biophysical cues examinable, we designed and tested three multiwell arrays to influence cardiomyocyte, chondrocyte and osteoblast function. Using the multiwell array, we were able to measure different cell functionalities using analytical modalities such as live microscopy, qPCR and immunofluorescence. We observed that grooves (5 μm in size) induced less variation in contractile function of cardiomyocytes. Compared to unpatterned plastic, nanopillars with 127 nm height, 100 nm diameter and 300 nm pitch enhanced matrix deposition, chondrogenic gene expression and chondrogenic maintenance. High aspect ratio pillars with an elastic shear modulus of 16 kPa mimicking the matrix found in early stages of bone development improved osteogenic gene expression compared to stiff plastic. We envisage that our bespoke multiwell array will accelerate the discovery of relevant biophysical cues through improved throughput and variety.

Designing stem cell niches for differentiation and self-renewal

Mesenchymal stem cells, characterized by their ability to differentiate into skeletal tissues and self-renew, hold great promise for both regenerative medicine and novel therapeutic discovery. However, their regenerative capacity is retained only when in contact with their specialized microenvironment, termed the stem cell niche Niches provide structural and functional cues that are both biochemical and biophysical, stem cells integrate this complex array of signals with intrinsic regulatory networks to meet physiological demands. Although, some of these regulatory mechanisms remain poorly understood or difficult to harness with traditional culture systems. Biomaterial strategies are being developed that aim to recapitulate stem cell niches, by engineering microenvironments with physiological-like niche properties that aim to elucidate stem cell-regulatory mechanisms, and to harness their regenerative capacity in vitro In the future, engineered niches will prove important tools for both regenerative medicine and therapeutic discoveries.

Phage-Based Artificial Niche: The Recent Progress and Future Opportunities in Stem Cell Therapy

Self-renewal and differentiation of stem cells can be the best option for treating intractable diseases in regenerative medicine, and they occur when these cells reside in a special microenvironment, called the "stem cell niche." Thus, the niche is crucial for the effective performance of the stem cells in both in vivo and in vitro since the niche provides its functional cues by interacting with stem cells chemically, physically, or topologically. This review provides a perspective on the different types of artificial niches including engineered phage and how they could be used to recapitulate or manipulate stem cell niches. Phage-based artificial niche engineering as a promising therapeutic strategy for repair and regeneration of tissues is also discussed.

An engineered cell-imprinted substrate directs osteogenic differentiation in stem cells

A cell-imprinted poly(dimethylsiloxane)/hydroxyapatite nanocomposite substrate was fabricated to engage topographical, mechanical, and chemical signals to stimulate and boost stem cell osteogenic differentiation. The physicochemical properties of the fabricated substrates, with nanoscale resolution of osteoblast morphology, were probed using a wide range of techniques including scanning electron microscopy, atomic force microscopy, dynamic mechanical thermal analysis, and water contact angle measurements. The osteogenic differentiation capacity of the cultured stem cells on these substrates was probed by alizarin red staining, ALP activity, osteocalcin measurements, and gene expression analysis. The outcomes revealed that the concurrent roles of the surface patterns and viscoelastic properties of the substrate provide the capability of directing stem cell differentiation toward osteogenic phenotypes. Besides the physical and mechanical effects, we found that the chemical signaling of osteoinductive hydroxyapatite nanoparticles, embedded in the nanocomposite substrates, could further improve and optimize stem cell osteogenic differentiation.

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'.

Improved osseointegration properties of hierarchical microtopographic/nanotopographic coatings fabricated on titanium implants

Background

Titanium (Ti) implants are extensively used in reconstructive surgery and orthopedics. However, the intrinsic inertness of untreated Ti implants usually results in insufficient osseointegration. In order to improve the osteoconductivity properties of the implants, they are coated with hierarchical microtopographic/nanotopographic coatings employing the method of molecular layering of atomic layer deposition (ML-ALD).

Results

The analysis of the fabricated nanostructured relief employing scanning electron microscopy, atomic force microscopy, and electron spectroscopy for chemical analysis clearly demonstrated the formation of the nanotopographic (<100 nm) and microtopographic (0.1–0.5 μm) titano-organic structures on the surface of the nanograined Ti implants. Subsequent coincubation of the MC3T3-E1 mouse osteoblasts on the microtopographic/nanotopographic surface of the implants resulted in enhanced osteogenic cell differentiation (the production of alkaline phosphatase, osteopontin, and osteocalcin). In vivo assessment of the osseointegrative properties of the microtopographically/nanotopographically coated implants in a model of below-knee amputation in New Zealand rabbits demonstrated enhanced new bone formation in the zone of the bone–implant contact (as measured by X-ray study) and increased osseointegration strength (removal torque measurements).

Conclusion

The fabrication of the hierarchical microtopographic/nanotopographic coatings on the nanograined Ti implants significantly improves the osseointegrative properties of the intraosseous Ti implants. This effect could be employed in both translational and clinical studies in orthopedic and reconstructive surgery.

From supramolecular polymers to multi-component biomaterials

The most striking and general property of the biological fibrous architectures in the extracellular matrix (ECM) is the strong and directional interaction between biologically active protein subunits. These fibers display rich dynamic behavior without losing their architectural integrity. The complexity of the ECM taking care of many essential properties has inspired synthetic chemists to mimic these properties in artificial one-dimensional fibrous structures with the aim to arrive at multi-component biomaterials. Due to the dynamic character required for interaction with natural tissue, supramolecular biomaterials are promising candidates for regenerative medicine. Depending on the application area, and thereby the design criteria of these multi-component fibrous biomaterials, they are used as elastomeric materials or hydrogel systems. Elastomeric materials are designed to have load bearing properties whereas hydrogels are proposed to support in vitro cell culture. Although the chemical structures and systems designed and studied today are rather simple compared to the complexity of the ECM, the first examples of these functional supramolecular biomaterials reaching the clinic have been reported. The basic concept of many of these supramolecular biomaterials is based on their ability to adapt to cell behavior as a result of dynamic non-covalent interactions. In this review, we show the translation of one-dimensional supramolecular polymers into multi-component functional biomaterials for regenerative medicine 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.

Development of a Virtual Cell Model to Predict Cell Response to Substrate Topography

Cells can sense and respond to changes in the topographical, chemical, and mechanical information in their environment. Engineered substrates are increasingly being developed that exploit these physical attributes to direct cell responses (most notably mesenchymal stem cells) and therefore control cell behavior toward desired applications. However, there are very few methods available for robust and accurate modeling that can predict cell behavior prior to experimental evaluations, and this typically means that many cell test iterations are needed to identify best material features. Here, we developed a unifying computational framework to create a multicomponent cell model, called the "virtual cell model" that has the capability to predict changes in whole cell and cell nucleus characteristics (in terms of shape, direction, and even chromatin conformation) on a range of cell substrates. Modeling data were correlated with cell culture experimental outcomes in order to confirm the applicability of the virtual cell model and demonstrating the ability to reflect the qualitative behavior of mesenchymal stem cells. This may provide a reliable, efficient, and fast high-throughput approach for the development of optimized substrates for a broad range of cellular applications including stem cell differentiation.

A nanoporous titanium surface promotes the maturation of focal adhesions and formation of filopodia with distinctive nanoscale protrusions by osteogenic cells

While topography is a key determinant of the cellular response to biomaterials, the mechanisms implicated in the cell-surface interactions are complex and still not fully elucidated. In this context, we have examined the effect of nanoscale topography on the formation of filopodia, focal adhesions, and gene expression of proteins associated with cell adhesion and sensing. Commercially pure titanium discs were treated by oxidative nanopatterning with a solution of H₂SO₄/H₂O₂ 50:50 (v/v). Scanning electron microscopy and atomic force microscopy characterizations showed that this facile chemical treatment efficiently creates a unique nanoporous surface with a root-mean-square roughness of 11.5nm and pore diameter of 20±5nm. Osteogenic cells were cultured on polished (control) and nanotextured discs for periods of 6, 24, and 72h. Immunofluorescence analysis revealed increases in the adhesion formation per cell area, focal adhesion length, and maturity on the nanoporous surface. Gene expression for various focal adhesion markers, including paxillin and talin, and different integrins (e.g. α1, β1, and α5) was also significantly increased. Scanning electron microscopy revealed the presence of more filopodia on cells grown on the nanoporous surface. These cell extensions displayed abundant and distinctive nanoscale lateral protrusions of 10-15nm diameter that molded the nanopore walls. Together the increase in the focal adhesions and abundance of filopodia and associated protrusions could contribute to strengthening the adhesive interaction of cells with the surface, and thereby, alter the nanoscale biomechanical relationships that trigger cellular cascades that regulate cell behavior.

STATEMENT OF SIGNIFICANCE

Oxidative patterning was exploited to create a unique three-dimensional network of nanopores on titanium surfaces. Our study illustrates how a facile chemical treatment can be advantageously used to modulate cellular behavior. The nanoscale lateral protrusions on filopodia elicited by this surface are novel adhesive structures. Altogether, the increases in focal adhesion, length, maturity, and filopodia with distinctive lateral protrusions could substantially increase the contact area and adhesion strength of cells, thereby promoting the activation of cellular signaling cascades that may explain the positive osteogenic outcomes previously achieved with this surface. Such physicochemical cueing offers a simple attractive alternative to the use of bioactive agents for guiding tissue repair/regeneration around implantable metals.

Confined Sandwichlike Microenvironments Tune Myogenic Differentiation

Sandwichlike (SW) cultures are engineered as a multilayer technology to simultaneously stimulate dorsal and ventral cell receptors, seeking to mimic cell adhesion in three-dimensional (3D) environments in a reductionist manner. The effect of this environment on cell differentiation was investigated for several cell types cultured in standard growth media, which promotes proliferation on two-dimensional (2D) surfaces and avoids any preferential differentiation. First, murine C2C12 myoblasts showed specific myogenic differentiation. Human mesenchymal stem cells (hMSCs) of adipose and bone marrow origin, which can differentiate toward a wider variety of lineages, showed again myodifferentiation. Overall, this study shows myogenic differentiation in normal growth media for several cell types under SW conditions, avoiding the use of growth factors and cytokines, i.e., solely by culturing cells within the SW environment. Mechanistically, it provides further insights into the balance between integrin adhesion to the dorsal substrate and the confinement imposed by the SW system.

Nacre Topography Produces Higher Crystallinity in Bone than Chemically Induced Osteogenesis

It is counterintuitive that invertebrate shells can induce bone formation, yet nacre, or mother of pearl, from marine shells is both osteoinductive and osteointegrative. Nacre is composed of aragonite (calcium carbonate) and induces production of vertebrate bone (calcium phosphate). Exploited by the Mayans for dental implants, this remarkable phenomenon has been confirmed in vitro and in vivo, yet the characteristic of nacre that induces bone formation remains unknown. By isolating nacre topography from its inherent chemistry in the production of polycaprolactone (PCL) nacre replica, we show that, for mesenchymal stem cells, nacre topography is osteoinductive. Gene expression of specific bone marker proteins, osteopontin, osteocalcin, osteonectin, and osterix, is increased 10-, 2-, 1.7-, and 1.8-fold, respectively, when compared to planar PCL. Furthermore, we demonstrate that bone tissue that forms in response to the physical topographical features of nacre has a higher crystallinity than bone formed in response to chemical cues with a full width half-maximum for PO₄^3- Raman shift of 7.6 ± 0.7 for mineral produced in response to nacre replica compared to a much broader 34.6 ± 10.1 in response to standard osteoinductive medium. These differences in mineral product are underpinned by differences in cellular metabolism. This observation can be exploited in the design of bone therapies; a matter that is most pressing in light of a rapidly aging human population.

Electroactive BaTiO3 nanoparticle-functionalized fibrous scaffolds enhance osteogenic differentiation of mesenchymal stem cells

It has been proven that the surface topographic cues of fiber arrangement can induce osteogenic differentiation of mesenchymal stem cells. However, this effect alone is weak and insufficient to meet the needs of regenerative medicine. In this work, electroactivity concept was introduced to enhance the osteoinductivity of fibrous scaffolds. The randomly oriented and aligned electroactive fibrous scaffolds of poly-(l-lactic acid) (PLLA) with incorporation of ferroelectric ceramic BaTiO₃ (BTO) nanoparticles (NPs) were fabricated by electrospinning. Physicochemical properties, including fiber morphology, microstructure, composition, thermal stability, surface roughness, and surface wettability, of these fibrous scaffolds were studied. The dielectric properties of the scaffolds were evaluated. The results showed that the randomly oriented BTO/PLLA composite fibrous scaffolds had the highest dielectric permittivity of 1.19, which is of the same order of magnitude as the natural bone. The combined effects of fiber orientation and electrical activity on the osteogenic responses of bone marrow mesenchymal stem cells (BM-MSCs) were specifically investigated. Randomly oriented composite fibrous scaffolds significantly promoted polygonal spreading and encouraged early osteogenic differentiation in BM-MSCs, whereas aligned composite fibrous scaffolds promoted cell elongation and discouraged osteogenic differentiation. These results evidenced that randomly fiber orientation and biomimetic electric activity have combining effects on osteogenic differentiation of BM-MSCs. Our findings indicate that coupling effects of multi-physical properties should be paid more attention to mimic the microenvironment for enhancing osteogenic differentiation of BM-MSCs.