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Stem cells respond to nanoscale cues from the extracellular matrix or culture substrates by altering cell adhesion, which can in turn define their fate. This Review discusses how stem cell adhesion and differentiation are influenced by surface nanotopography, with a particular focus on integrin–matrix interactions and cell-adhesion-mediated signalling processes. Stem cells respond to nanoscale surface features, with changes in cell growth and differentiation mediated by alterations in cell adhesion. The interaction of nanotopographical features with integrin receptors in the cells' focal adhesions alters how the cells adhere to materials surfaces, and defines cell fate through changes in both cell biochemistry and cell morphology. In this Review, we discuss how cell adhesions interact with nanotopography, and we provide insight as to how materials scientists can exploit these interactions to direct stem cell fate and to understand how the behaviour of stem cells in their niche can be controlled. We expect knowledge gained from the study of cell–nanotopography interactions to accelerate the development of next-generation stem cell culture materials and implant interfaces, and to fuel discovery of stem cell therapeutics to support regenerative therapies.

There is currently an unmet need for the supply of autologous, patient-specific stem cells for regenerative therapies in the clinic. Mesenchymal stem cell differentiation can be driven by the material/cell interface suggesting a unique strategy to manipulate stem cells in the absence of complex soluble chemistries or cellular reprogramming. However, so far the derivation and identification of surfaces that allow retention of multipotency of this key regenerative cell type have remained elusive. Adult stem cells spontaneously differentiate in culture, resulting in a rapid diminution of the multipotent cell population and their regenerative capacity. Here we identify a nanostructured surface that retains stem-cell phenotype and maintains stem-cell growth over eight weeks. Furthermore, the study implicates a role for small RNAs in repressing key cell signalling and metabolomic pathways, demonstrating the potential of surfaces as non-invasive tools with which to address the stem cell niche. On standard tissue culture platforms, mesenchymal stem cells tend to spontaneously differentiate with the loss of multi-lineage potential. Now, a robust and reproducible nanotopographical platform has been shown to maintain stem cell phenotype and promote stem cell growth over several months whilst implicating mechanisms for the observed stem cell behaviour

A key tenet of bone tissue engineering is the development of scaffold materials that can stimulate stem cell differentiation in the absence of chemical treatment to become osteoblasts without compromising material properties. At present, conventional implant materials fail owing to encapsulation by soft tissue, rather than direct bone bonding. Here, we demonstrate the use of nanoscale disorder to stimulate human mesenchymal stem cells (MSCs) to produce bone mineral in vitro , in the absence of osteogenic supplements. This approach has similar efficiency to that of cells cultured with osteogenic media. In addition, the current studies show that topographically treated MSCs have a distinct differentiation profile compared with those treated with osteogenic media, which has implications for cell therapies.

Preterm infants with very low birthweight are at serious risk for necrotizing enterocolitis. To functionally analyse the principles of three successful preventive NEC regimens, we characterize fecal samples of 55 infants (<1500 g, n  = 383, female = 22) longitudinally (two weeks) with respect to gut microbiome profiles (bacteria, archaea, fungi, viruses; targeted 16S rRNA gene sequencing and shotgun metagenomics), microbial function, virulence factors, antibiotic resistances and metabolic profiles, including human milk oligosaccharides (HMOs) and short-chain fatty acids (German Registry of Clinical Trials, No.: DRKS00009290). Regimens including probiotic Bifidobacterium longum subsp. infantis NCDO 2203 supplementation affect microbiome development globally, pointing toward the genomic potential to convert HMOs. Engraftment of NCDO 2203 is associated with a substantial reduction of microbiome-associated antibiotic resistance as compared to regimens using probiotic Lactobacillus rhamnosus LCR 35 or no supplementation. Crucially, the beneficial effects of Bifidobacterium longum subsp. infantis NCDO 2203 supplementation depends on simultaneous feeding with HMOs. We demonstrate that preventive regimens have the highest impact on development and maturation of the gastrointestinal microbiome, enabling the establishment of a resilient microbial ecosystem that reduces pathogenic threats in at-risk preterm infants. Here, the authors comparatively analyze the impact of three successful clinical preventive interventions against NEC in preterm, VLBW infants and demonstrate a major impact of especially probiotic-based strategies on the development and maturation of the gut microbiome.

Mesenchymal stem cells (MSCs) interact with their surroundings via integrins, which link to the actin cytoskeleton and translate physical cues into biochemical signals through mechanotransduction. N-cadherins enable cell-cell communication and are also linked to the cytoskeleton. This crosstalk between integrins and cadherins modulates MSC mechanotransduction and fate. Here we show the role of this crosstalk in the mechanosensing of viscosity using supported lipid bilayers as substrates of varying viscosity. We functionalize these lipid bilayers with adhesion peptides for integrins (RGD) and N-cadherins (HAVDI), to demonstrate that integrins and cadherins compete for the actin cytoskeleton, leading to an altered MSC mechanosensing response. This response is characterised by a weaker integrin adhesion to the environment when cadherin ligation occurs. We model this competition via a modified molecular clutch model, which drives the integrin/cadherin crosstalk in response to surface viscosity, ultimately controlling MSC lineage commitment. The crosstalk between cell-cell and cell-matrix adhesions regulates stem cell fate. Here, the authors reveal a critical role for matrix viscosity in controlling this crosstalk, which they explain via a modified molecular clutch model.

Titanium (Ti) plays a predominant role as the material of choice in orthopaedic and dental implants. Despite the majority of Ti implants having long-term success, premature failure due to unsuccessful osseointegration leading to aseptic loosening is still too common. Recently, surface topography modification and biological/non-biological coatings have been integrated into orthopaedic/dental implants in order to mimic the surrounding biological environment as well as reduce the inflammation/infection that may occur. In this review, we summarize the impact of various Ti coatings on cell behaviour both in vivo and in vitro. First, we focus on the Ti surface properties and their effects on osteogenesis and then on bacterial adhesion and viability. We conclude from the current literature that surface modification of Ti implants can be generated that offer both osteoinductive and antimicrobial properties.

Background Recent studies have shown that the maternal gut microbiota can regulate placental growth, particularly the transport region, in association with fetal growth. However, the specific role of certain microorganisms in modulating the hormonal production of the placenta, which is critical for supporting fetal development and maintaining a healthy pregnancy, remains largely unexplored. In this context, the objective of this study is to determine whether the maternal colonisation with the early life gut bacterium Bifidobacterium breve UCC2003 regulates placental endocrine function. Methods Pregnant germ-free mice were colonized with or without Bifidobacterium breve UCC2003 (BIF) during pregnancy. The endocrine region of the placenta (junctional zone, Jz) was collected to assess its metabolic profile using metabolomics, the expression of key nutrient uptake genes, hormones and synthetic genes by qPCR, and proteome using LC-MS/MS. Results BIF colonised dams had increased lactate and taurine concentrations in the placental Jz. BIF presence was also associated with upregulated expression of nutrient carriers, particularly those involved in large neutral amino acid and monocarboxylate uptake (e.g., Slc7a8 and Slc16a4 ). Additionally, key hormones, such as prolactins and pregnancy-specific glycoproteins, were upregulated. The Jz proteome was changed in BIF colonised dams, with over 400 proteins dysregulated. Pathway analysis revealed more than 150 biological processes were altered, including transcriptional activity, protein synthesis, cell cycle progression, and metabolic regulation. Proteins regulated by BIF in the placental Jz were correlated with fetal growth and nutrient levels (namely glucose). Notably, maternal-associated BIF reduced the number of fetal resorptions (early fetal loss). Conclusions In germ-free mice, maternal-associated gut Bifidobacterium breve UCC2003 regulates placental endocrine capacity, by altering its metabolic profile and ability to produce endocrine factors. This study provides the first clear evidence that the maternal gut microbiota not only influences placental transport function, but also regulates its endocrine outputs. Graphical Abstract

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. Mesenchymal Stromal Cells are hard to expand whilst retaining immunomodulatory properties due to spontaneous differentiation and ageing in culture. Here, the authors describe a mechanotransductive link between metabolism and functional activity and identify bioactive metabolites to expand functional MSCs at cell therapy scale.

Long-term reconstituting haematopoietic stem cells (LT-HSCs) are used to treat blood disorders via stem cell transplantation. The very low abundance of LT-HSCs and their rapid differentiation during in vitro culture hinders their clinical utility. Previous developments using stromal feeder layers, defined media cocktails, and bioengineering have enabled HSC expansion in culture, but of mostly short-term HSCs and progenitor populations at the expense of naive LT-HSCs. Here, we report the creation of a bioengineered LT-HSC maintenance niche that recreates physiological extracellular matrix organisation, using soft collagen type-I hydrogels to drive nestin expression in perivascular stromal cells (PerSCs). We demonstrate that nestin, which is expressed by HSC-supportive bone marrow stromal cells, is cytoprotective and, via regulation of metabolism, is important for HIF-1α expression in PerSCs. When CD34 +ve HSCs were added to the bioengineered niches comprising nestin/HIF-1α expressing PerSCs, LT-HSC numbers were maintained with normal clonal and in vivo reconstitution potential, without media supplementation. We provide proof-of-concept that our bioengineered niches can support the survival of CRISPR edited HSCs. Successful editing of LT-HSCs ex vivo can have potential impact on the treatment of blood disorders. The ability to maintain blood stem cells (HSCs) in vitro would allow us to provide better therapies for blood diseases. Here, the authors report that polymer-organised extracellular proteins, coupled to soft environments mimicking bone marrow stiffness, allow stromal cells to maintain HSCs in vitro.

The neonatal developmental window represents a key time for establishment of the gut microbiota. First contact with these microbes within the infant gastrointestinal tract signifies the start of a critical mutualistic relationship, which is central for short- and longer-term health. Recent research has provided insights into the origin of these microbial pioneers, how they are maintained within the gut environment, and how factors such as antibiotics or preterm birth may disrupt the succession of beneficial microbes.  The acquisition, colonisation, and maintenance of the early life microbiota, and subsequent interactions with the host is a rapidly developing research area. In this review we explore some of these key topics which have been illuminated by recent research, and we highlight some of the important unresolved questions which currently limit our overall understanding of the neonatal gut microbiome.