Substrate Adhesion Research Articles

First person – Ignasi Casanellas

ABSTRACT First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping researchers promote themselves alongside their papers. Ignasi Casanellas is first author on ‘ Substrate adhesion determines migration during mesenchymal cell condensation in chondrogenesis’, published in JCS. Ignasi conducted the research described in this article while a PhD student in Josep Samitier's lab at the Institute for Bioengineering of Catalonia, Barcelona, Spain. He is now a postdoctoral scholar in the lab of Medha Pathak at University of California, Irvine, USA, where he is developing in vitro systems to understand how mechanical environmental inputs guide stem cell functions during tissue formation.

Bio-based polybenzoxazines coatings for efficient marine antifouling

It is a subject of great practical significance and challenge to endow marine coatings with both excellent bacterial killing and antifouling properties. In this work, a series of bio-based organic coatings demonstrating high antibacterial rate, strong algae-killing ability and satisfied real-sea fouling resistance were reported. The main-chain type benzoxazine (MCBZ) resins were prepared from the renewable daidzein and furfurylamine, together with polyetheramine, long aliphatic chain primary amines, and paraformaldehyde. By adjusting the amines, the overall performance of synthesized MCBZs could be manipulated. Results indicated that the low surface energy of obtained MCBZ could prevent fouling adhesion, and the synergistic effect of long alkyl chains and daidzein led to the efficient anti-fouling. Notably, besides the low curing temperature of 200 °C, excellent processing property and good substrate adhesion (5.02 MPa), poly (12-fu-MCBZ) also possessed 94.5 % antibacterial rate, 100 % algae-killing ability and excellent real-sea antifouling performance. This work provides us a new strategy to solve the marine biological pollution using renewable raw materials.

Energy harvesting properties of the Nafion thin films

In this report, energy harvesting properties of Nafion films were investigated using piezoionic generator (PIOG) and triboelectric generator (TEG) devices. Nafion films were prepared by simple doctor blade deposition of a Nafion ionomer solution onto the aluminum electrode. The Nafion films were characterized for their surface morphology, composition, and crystallinity. Furthermore, the Nafion film exhibited strong substrate adhesion, a smooth surface, and amorphous nature. The deposited Nafion film was used directly as an active layer to fabricate the PIOG and TEG devices with ITO electrodes. Output voltages of ∼450 mV and ∼1.9 V have been observed for the PIOG and TEG devices against biomechanical energy. The maximum instantaneous power produced by these devices is approximately ∼0.205 μW cm−2, and ∼0.128 μW cm−2 for the PIOG and TEG, respectively. The PIOG performance can be further improved using Nafion composite films. Similarly, the TEG performance can be enhanced with other friction layers such as PVDF, PDMS, PMMA, and PVC films instead of ITO. Therefore, the proposed nanogenerators can be used as touch sensors and energy sources for wearable electronic devices in the future.

Detailed analysis of particle–substrate interaction based on a centrifugal method

• Experiments to remove particles adhering to inclined substrates in a centrifuge. • Analyses using point-mass and rigid-body models. • Elucidation of the particle removal mechanism based on rolling rather than friction. • Determination of particle–substrate adhesion force and effective contact radius. • Estimation of the removal fraction curves at different inclination angles. The interaction between particles and inclined substrates in a centrifuge was investigated theoretically and experimentally. First, the balance of the force acting on a particle adhering to the substrate, with an inclination angle from 0 to 90° to the horizontal, was formulated separately in the normal and tangential directions. The adhesion force was then derived based on the point-mass model as a function of the angular velocity. Next, the balance of the moments of the forces acting on a particle adhering to the substrate was formulated; theoretical equations for the adhesion force and the effective contact radius were then derived from the angular velocities, obtained at any two inclination angles, based on the rigid-body model. Finally, the removal fraction curves of spherical/nonspherical particles with median diameters of less than 10 µm were experimentally obtained by increasing the angular velocity at each inclination angle. The experimentally obtained angular velocities were substituted into the theoretical equations to compare the point-mass and rigid-body models. The effects of the particle shape on the adhesion force and effective contact radius and that of the inclination angle on the removal fraction curves based on the theoretical equation were also investigated.

The influence of finishing lines and margin location on enamel and dentin removal for indirect partial restorations: A micro-CT quantitative evaluation

ObjectivesThis in vitro research aimed to quantitatively evaluate the enamel and dentin tissue removal and the residual adhesion surface area (RAS) after different margin designs and locations for indirect partial restorations (IPR). MethodsA human molar was scanned using a Micro-CT and the STL file obtained was used to 3D-print 50 resin-tooth replicas. IPR standardized preparations were performed. The specimens were randomly assigned to 5 groups (n = 10), according to preparation and margin location to the dental equator (DE): 1) Rounded shoulder above the DE (SA); 2) Hollow chamfer above the DE (CA); 3) Butt joint above the DE (BJ); 4) Rounded shoulder below the DE (SB); 5) Chamfer below the DE (CB). Then, the tooth replicas were scanned and each STL file was aligned and superimposed to the original STL model file. Data of enamel and dentin volume removal and RAS were assessed and statistically analyzed (one-way ANOVA and Kruskal-Wallis tests for the two dental substrates respectively). Significance was set at p<0.05. ResultsDifferences in dental tissue reductions were related to the margin location. Above the equator, SA, CA, and BJ performed comparably (p>0.05). Below the equator, CB was significantly more conservative in enamel reduction than SB (p<0.05) and showed the highest enamel adhesive surface exposure among the tested preparations (p<0.05). ConclusionsWhen the preparation margin is placed above DE, BJ determines a greater exposure of dentin, reducing the adhesive surface in enamel. Below DE, SB seems to be more aggressive in terms of tissue removal compared to CB. Clinical SignificanceThe results of this in vitro study suggest that in teeth requiring partial restoration with the margin below the dental equator, a chamfer preparation would be more conservative than a shoulder preparation. When above the equator, preparations with flat designs would expose more dentine providing a worse substrate for adhesion.

PRELP Regulates Cell-Cell Adhesion and EMT and Inhibits Retinoblastoma Progression.

Simple SummaryMutation of the RB1 tumor suppressor gene is fundamental in retinoblastoma initiation and progression although its downstream mechanism has not been well elucidated. Here, we found that expression of proline/arginine-rich end leucine-rich repeat protein (PRELP) is strongly downregulated in human retinoblastoma and highly expressed in Müller glial cells in normal retina. Deletion of PRELP in mice resulted in retinal dysplasia associated with enhanced proliferation. mRNA expression profiling revealed that cancer pathways were strongly activated in PRELP−/− retina. Additionally, cell–cell adhesion was inhibited while epithelial mesenchymal transition (EMT) and inflammation were activated. On the other hand, application of PRELP protein to retinoblastoma cell lines enhances cell–cell and cell–substrate adhesion and inhibits anchorage independent growth by reversing EMT. These observations indicate that PRELP downregulation in human retinoblastoma can contribute cancer progression through regulation of cell adhesion and EMT suggested that PRELP application might be a novel strategy for retinoblastoma treatment.Retinoblastoma (RB) is the most common intraocular pediatric cancer. Nearly all cases of RB are associated with mutations compromising the function of the RB1 tumor suppressor gene. We previously demonstrated that PRELP is widely downregulated in various cancers and our in vivo and in vitro analysis revealed PRELP as a novel tumor suppressor and regulator of EMT. In addition, PRELP is located at chromosome 1q31.1, around a region hypothesized to be associated with the initiation of malignancy in RB. Therefore, in this study, we investigated the role of PRELP in RB through in vitro analysis and next-generation sequencing. Immunostaining revealed that PRELP is expressed in Müller glial cells in the retina. mRNA expression profiling of PRELP−/− mouse retina and PRELP-treated RB cells found that PRELP contributes to RB progression via regulation of the cancer microenvironment, in which loss of PRELP reduces cell–cell adhesion and facilitates EMT. Our observations suggest that PRELP may have potential as a new strategy for RB treatment.

Effect of Bias Voltage on Adhesion and Corrosion Resistance of Titanium Nitride Coated Stainless Steel Substrate

In this work, the adhesion and corrosion resistance of TiN coating by magnetron sputtering on stainless steel substrates under different bias voltages conditions (-50 V and-100 V) was investigated. AFM was used for surface roughness and grain size analysis, XRD for phase identification, Rockwell C for adhesion and nanoindentation for hardness and elastic modulus. According to AFM the coating deposited at-100V bias had decreased surface roughness, the value decreased from 2.7 nm (for-50V sample) to 1.8 nm, this was due to an etching like process which occurs when ions with higher energies start hitting the surface. The coated samples came under HF1 adhesion parameter which is the highest class of adhesion in the model on the basis of Rockwell C adhesion test. nanoindentation hardness and elastic modulus results of-50 V and-100V were found to be 224 GPa and 182 GPa, respectively and the value of hardness, 16 GPa and 22 GPa, respectively. The corrosion behavior of TiN coatings were studied in 3.5wt. % NaCl solutions using Tafel Extrapolation, Cyclic Polarization and Open Circuit Potential. It was noted on the basis of these corrosion tests that, as bias voltage is increased, it leads to the formation of more densely packed, fine grained columnar structures with less pores, which decreases the chances of corrosion. .

RNA sequencing-based identification of the regulatory mechanism of microRNAs, transcription factors, and corresponding target genes involved in vascular dementia.

Vascular dementia (VaD) is the second most common form of dementia with uncertain mechanisms and no effective treatments. microRNAs (miRNAs) and transcription factors (TFs) are considered regulatory factors of genes involved in many diseases. Therefore, this work investigated the aberrantly expressed miRNAs, TFs, corresponding target genes, and their co-regulatory networks in the cortex of rats with bilateral common carotid artery occlusion (2VO) to uncover the potential mechanism and biomarkers of VaD. Differentially expressed genes (DEGs), miRNAs (DEMs), and TFs (DETFs) were identified using RNA sequencing, and their interaction networks were constructed using Cytoscape. The results showed that rats with 2VO had declined cognitive abilities and neuronal loss in the cortex than sham rats. DEGs, DEMs, and DETFs were discriminated between rats with 2VO and sham rats in the cortex, as shown by the 13 aberrantly expressed miRNAs, 805 mRNAs, and 63 TFs. The miRNA-TF-target gene network was constructed, showing 523 nodes and 7237 edges. Five miRNAs (miR-5132-5p, miR-764-3p, miR-223-3p, miR-145-5p, and miR-122-5p), ten TFs (Mxi1, Nfatc4, Rxrg, Zfp523, Foxj2, Nkx6-1, Klf4, Klf5, Csrnp1, and Prdm6), and seven target genes (Serpine1, Nedd4l, Pxn, Col1a1, Plec, Trip12, and Tpm1) were chosen as the significant nodes to construct feed-forward loops (FFLs). Gene Ontology and pathway enrichment analysis revealed that these miRNA and TF-associated genes are mostly involved in the PI3K/Akt, neuroactive ligand–receptor interaction, calcium signaling, and Wnt signaling pathways, along with central locations around the cell membrane. They exert functions such as growth factor binding, integrin binding, and extracellular matrix structural constituent, with representative biological processes like vasculature development, cell–substrate adhesion, cellular response to growth factor stimulus, and synaptic transmission. Furthermore, the expression of three miRNAs (miR-145-5p, miR-122-5p, and miR-5132-5p), six TFs (Csrnp1, Klf4, Nfatc4, Rxrg, Foxj2, and Klf5), and five mRNAs (Serpine1, Plec, Nedd4l, Trip12, and Tpm1) were significantly changed in rats with VaD, in line with the outcome of RNA sequencing. In the potential FFL, miR-145-5p directly bound Csrnp1 and decreased its mRNA expression. These results might help the understanding of the underlying regulatory mechanisms of miRNA-TF-genes, providing potential therapeutic targets in VaD.

Bioactive Fibronectin-III10-DNA Origami Nanofibers Promote Cell Adhesion and Spreading.

The integration of proteins with DNA nanotechnology would enable materials with diverse applications in biology, medicine, and engineering. Here, we describe a method for the incorporation of bioactive fibronectin domain proteins with DNA nanostructures using two orthogonal coiled-coil peptides. One peptide from each coiled-coil pair is attached to a DNA origami cuboid in a multivalent fashion by attaching the peptides to DNA handles. These structures can then be assembled into one-dimensional arrays through the addition of a fibronectin domain linker genetically fused with the complementary peptides to those on the origami. We validate array formation using two different self-assembly protocols and characterize the fibers by atomic force and electron microscopy. Finally, we demonstrate that surfaces coated with the protein-DNA nanofibers can serve as biomaterial substrates for fibroblast adhesion and spreading with the nanofibers showing enhanced bioactivity compared to that of the monomeric protein.

Effect of electrochemical treatment on substrate adhesion strength in the restoration of motor vehicle parts operating under hydroabrasive wear

Introduction. In the process of chrome plating of car parts, it is necessary to obtain high-quality chrome coatings with specified physical and mechanical properties. Therefore, electrochemical treatment before coating plays a crucial role in the formation of coatings with high contact strength and wear resistance. The study of the electrochemical treatment process will make it possible to develop recommendations for obtaining high-quality coatings when restoring vehicle parts.Materials and methods. To conduct reliable research, the necessary equipment was used, which made it possible to obtain data with the necessary accuracy. Also, modern data processing tools were used to carry out mathematical processing, which excluded the possibility of error and thereby obtain the dependences of factors with the necessary accuracy.Results. When using the developed new chromium plating electrolyte, it became necessary to conduct studies of the modes and time of electrochemical treatment before coating parts made of steels containing chromium and hardened to HRC 55-60 hardness. Based on the results obtained, it was found that the greatest adhesion strength will be when using electrochemical etching with a current density of 130-140 A/dm2 and a holding time of 60-70 s. It is also necessary to activate in the chrome plating solution itself with an anode current density of 70-80 A/dm2 and a time of 30-40 s, with a sharp switch to the chrome plating mode. Conclusions are drawn on the optimization of electrochemical surface treatment before chrome plating, in order to obtain the greatest adhesion to the substrate. Discussion and conclusion. As a result of the conducted studies of the electrochemical processing of the part before chrome plating, it was possible to obtain that when restoring parts operating under waterjet wear, it is necessary to observe the specified conditions for obtaining high-quality coatings with high adhesion strength while maintaining high physical and mechanical properties of the coating.

Ag NPs/PMMA nanocomposite as an efficient platform for fluorescence regulation of riboflavin.

The fluorescence detection platform has broad application in many fields. In this paper, we report a simple and efficient fluorescence detection platform based on the synergistic effects of Ag nanoparticles (Ag NPs) and polymethylmethacrylate (PMMA). Ag NPs were introduced to realize the plasmon enhancement fluorescence and a thin PMMA layer was used to adjust the distance between Ag NPs and riboflavin. The thin PMMA layer not only enhances the fluorescence by enhancing adhesion of substrate, but also optimizes the plasmon enhancement fluorescence effect by serving as the spacer. The fluorescence enhancement factor based on this platform shows a trend of increasing with the decrease of the concentration of riboflavin, and the detection of riboflavin is realized based on this feature, the lowest detectable concentration is as low as 0.27 µM. In addition to the detection based on plasmon enhancement fluorescence, the detection of riboflavin at low concentrations can also be realized by the shift and broadening of the fluorescence peak due to the Ag NPs. The combination of the two ways of plasmon enhancement fluorescence and shift of the fluorescence spectra is used for the detection of riboflavin. These results show that the platform has great potential applications in the field of detection and sensing.

Facile Preparation of Dual Functional Wearable Devices Based on Hindered Urea Bond-Integrated Reprocessable Polyurea and AgNWs

With the advancement of material science and electronic technology, wearable devices have been integrated into daily lives, no longer just a stirring idea in science fiction. In the future, robust multifunctionalized wearable devices with low cost and long-term service life are urgently required. However, preparing multifunctional wearable devices robust enough to resist harsh conditions using a commercially available raw material through a simple process still remains challenging. In this work, reprocessable polyurea (HUBTPU) with a hard segment of hindered urea bonds (HUBs) and a soft segment of polyether is synthesized via a facile one-pot method. The robust dual functional wearable devices were obtained by simply spray-coating silver nanowires (AgNWs) on HUBTPU elastomer substrates. Due to the dynamic combination and decomposition of the HUBs and hydrogen bonds at 130 °C, the robust elastomer demonstrates favorable adhesion to various substrates. Especially, the partially embedded AgNW structure is also achieved by using ethanol as a spray solvent. The adhesion of HUBTPU substrates and embedded structure leads to stronger interfacial adhesion and stability compared to non-adhesive substrates. The as-obtained HUBTPU electrodes are able to be heated to 115 °C by applying a low voltage and sensing the strain deformation caused by human movement, which means that the electrodes are endowed with both electrical heating capability and strain sensing functionality. Therefore, this strategy reveals a potential way to prepare multifunctional wearable devices using other conductive particles and adhesive functional polymer substrates.

Silicone low surface energy antifouling coating modified by zwitterionic side chains with strong substrate adhesion

Silicone fouling release coatings were receiving increasing concern due to of their eco-friendly properties. However, their poor fouling resistance capability and mechanical properties limited the applications. Herein, we reported a type of silicone low surface energy coating with zwitterionic side chains and the carbamates group was introduced into the Si-O main chain. The carbamates groups and zwitterions provided strong substrate adhesion up to 2.0 MPa through hydrogen bond and ion interaction which also endowed the good mechanical properties higher than 6.0 MPa. The coating had a low surface energy less than 30 mJ·m−2, and exhibited good fouling release properties in the range of 0.3–0.5 MPa. Also, zwitterions gave the coating excellent fouling resistance properties. The bioassays showed that the anti-bacterial efficiency of PDMS-zPDEM-14 coating against Pseudomonas sp. was 94.86%, the coating could inhibit the formation of biofilm (the coverage area was only 13.64%) and effectively prevent the adhesion of diatoms (the density of adhered diatoms was 107 cells/mm2) This work had promising applications in low surface energy marine antifouling coating and interfaces of biomaterials.

Identification of Candidate Therapeutic Target Genes and Profiling of Tumor-Infiltrating Immune Cells in Pancreatic Cancer via Integrated Transcriptomic Analysis.

Pancreatic cancer (PC) has a dismal prognosis despite advancing scientific and technological knowledge. The exploration of novel genes is critical to improving current therapeutic measures. This research is aimed at selecting hub genes that can act as candidate therapeutic target genes and as prognostic biomarkers in PC. Gene expression profiles of datasets GSE101448, GSE15471, and GSE62452 were extracted from the GEO database. The “limma” package was performed to select differentially expressed genes (DEGs) between PC and normal tissue samples in each dataset. Robust rank aggregation (RRA) algorithm was conducted to integrate multiple expression profiles and identify robust DEGs. GO analysis and KEGG analysis were conducted to identify the functional correlation of the DEGs. The CIBERSORT algorithm was conducted to estimate the immune cell composition of each tissue sample. STRING and Cytoscape were used to establish the protein-protein interaction (PPI) network. The cytoHubba plugin in Cytoscape was performed to identify hub genes. Survival analysis based on hub gene expression was performed with clinical information from TCGA database. 566 robust DEGs (338 upregulated genes and 226 downregulated genes) were identified. Tumor tissue had a higher infiltration of resting dendritic cells and tumor-associated macrophages (TAM), including M0, M1, and M2 macrophages, while infiltration levels of B memory cells, plasma cells, T cells CD8, T follicular helper cells, and NK cells in normal tissue were relatively higher. GO terms and KEGG pathway analysis results revealed enrichment in tumor-associated pathways, including the extracellular matrix organization, cell−substrate adhesion cytokine−cytokine receptor interaction, calcium signaling pathway, and glycine, serine, and threonine metabolism, to name a few. Finally, FN1, MSLN, PLAU, and VCAN were selected as hub genes. High expression of FN1, MSLN, PLAU, and VCAN in PC significantly correlated with poor prognosis. Integrated transcriptomic analysis was used to provide new insights into PC pathogenesis. FN1, MSLN, PLAU, and VCAN may be considered as novel biomarkers of PC.

Nanoscale MXene Interlayer and Substrate Adhesion for Lubrication: A Density Functional Theory Study.

Understanding the interlayer interaction at the nanoscale in two-dimensional (2D) transition metal carbides and nitrides (MXenes) is important to improve their exfoliation/delamination process and application in (nano)-tribology. The layer–substrate interaction is also essential in (nano)-tribology as effective solid lubricants should be resistant against peeling-off during rubbing. Previous computational studies considered MXenes’ interlayer coupling with oversimplified, homogeneous terminations while neglecting the interaction with underlying substrates. In our study, Ti-based MXenes with both homogeneous and mixed terminations are modeled using density functional theory (DFT). An ad hoc modified dispersion correction scheme is used, capable of reproducing the results obtained from a higher level of theory. The nature of the interlayer interactions, comprising van der Waals, dipole–dipole, and hydrogen bonding, is discussed along with the effects of MXene sheet’s thickness and C/N ratio. Our results demonstrate that terminations play a major role in regulating MXenes’ interlayer and substrate adhesion to iron and iron oxide and, therefore, lubrication, which is also affected by an external load. Using graphene and MoS2 as established references, we verify that MXenes’ tribological performance as solid lubricants can be significantly improved by avoiding −OH and −F terminations, which can be done by controlling terminations via post-synthesis processing.

Efficient TADF-based blue OLEDs with 100% stretchability using titanium particle-embedded indium zinc oxide mesh electrodes

A highly stretchable and transparent electrode is a key element for realizing stretchable organic light-emitting diodes (SOLEDs). To date, several reports have been made on this issue; however, a sufficiently high mechanical stability (i.e., 100% stretchability) has not yet been demonstrated. Herein, we propose a titanium particle-embedded indium zinc oxide (Ti/IZO) mesh electrode fabricated on a Norland optical adhesive (NOA) substrate for the realization of mechanically robust and efficient SOLEDs. Initially, the geometry of the Ti/IZO mesh electrode is optimized based on the simulation and experimental results, which provides a high transmittance (92.5% at 480 nm), low sheet resistance (22.1 Ω/sq), and excellent mechanical stability (no substantial loss under 100% strain; only a 20% resistance change after 1000 stretching cycles), along with a work function of approximately 5.0 eV. Next, Ti/IZO mesh-based thermally activated delayed-fluorescence blue SOLEDs fabricated on NOA substrate are transferred onto prestretched 3 M VHB tape for mechanical testing. Interestingly, the devices stably operate under 100% tensile strain and exhibit an external quantum efficiency of 13.2%, which is 30 and 29% higher than those of devices with IZO and indium tin oxide planar electrodes, respectively. The reduced waveguide mode at the interface and increased outcoupling via corrugated metal islands are attributed to the observed improvement in performance.

Exploring the Effect of Pt Addition on the Fracture Behavior of CrN Coatings by Finite Element Simulation

Previous research confirmed that Pt addition induced a prominent refinement effect of CrN coating, resulting in an enhanced conductivity and corrosion resistance. In this work, a detailed finite element simulation and scratch test were employed to calculate and characterize the fracture failure behaviors (stress distribution, crack damage process, critical coating load, and coating–substrate adhesion energy) of CrN coatings with different Pt contents. Simulation results showed that the synergistic action of dynamic scratch load and extrusion load induced the fracture of the coatings. S11 and S22 caused transverse cracks in the CrN coating, S11 caused longitudinal cracks in the CrN-Pt coating and CrN-3Pt coatings, S22 led to the inclined propagation of cracks in these coatings, and S11 and S22 jointly induced the separation of the coating from the substrate. The doping Pt element in the CrN coating will make the coating easier to fracture and reduce the adhesion strength between the coating and substrate. Scratch test results revealed that adding Pt into the CrN coating will make this coating easier to fracture and cause more serious damage; the simulation results are in good accordance with the scratch test characterizations. The current founding provided a comprehensive understanding for the fracture damage mechanism of Pt-doped nitride coatings.

A reductionist approach to determine the effect of cell-cell contact on human epidermal stem cell differentiation

The balance between stem cell renewal and differentiation is determined by the interplay between intrinsic cellular controls and extrinsic factors presented by the microenvironment, or ‘niche’. Previous studies on cultured human epidermis have utilised suspension culture and restricted cell spreading to investigate regulation of differentiation in single keratinocytes. However, keratinocytes are typically adherent to neighbouring cells in vivo. We therefore developed experimental models to investigate the combined effects of cell-ECM adhesion and cell-cell contact. We utilized lipid-modified oligonucleotides to form clusters of keratinocytes which were subsequently placed in suspension to induce terminal differentiation. In this experimental model cell-cell contact had no effect on suspension-induced differentiation of keratinocytes. We next developed a high-throughput platform for robust geometrical confinement of keratinocytes to hexagonal ECM-coated islands permitting direct cell-cell contact between single cells. As in the case of circular islands, differentiation was stimulated on the smallest single hexagonal islands. However, the percentage of involucrin-positive cells on small bowtie islands was significantly lower than on single islands, demonstrating that cell-cell contact reduced differentiation in response to decreased substrate adhesion. None of the small bowtie islands contained two involucrin-positive cells. Rather, if one cell was involucrin-positive the other was involucrin-negative. This suggests that there is intrinsic asymmetry in the effect of cell-cell contact in decreasing differentiation. Thus, our reductionist approaches provide new insights into the effect of the niche on keratinocyte differentiation. Statement of significanceStem cell behaviour is regulated by a combination of external signals, including the nature of the adhesive substrate and cell-cell interactions. An understanding of how different signals are integrated creates the possibility of developing new biomaterials to promote tissue regeneration and broaden our understanding of skin diseases such as eczema and psoriasis, in which stem cell proliferation and differentiation are perturbed. In this study we have applied two methods to engineer intercellular adhesion of human epidermal stem cells, one involving lipid-modified DNA and the other involving hexagonal micropatterns. We show that the effect of cell-cell adhesion depends on cell-substrate adhesion and uncover evidence that two cells in equivalent environments can nevertheless behave differently.

Transepithelial potential difference governs epithelial homeostasis by electromechanics

Studies of electric effects in biological systems, from the work on action potential to studies on limb regeneration or wound healing, commonly focus on transitory behaviour and not on addressing the question of homeostasis. Here we use a microfluidic device to study how the homeostasis of confluent epithelial tissues is modified when a transepithelial potential difference that is different from the natural one is imposed on an epithelial layer. When the field direction matches the natural one, we can restore perfect confluence in an epithelial layer turned defective either by E-cadherin knockout or by weakening the cell–substrate adhesion; additionally, the tissue pushes on the substrate with kilopascal stress, inducing active-cell response such as death and differentiation. When the field is opposite, the tissue pulls with similar strengths, whereas homeostasis is destroyed by the perturbation of junctional actin and cell shapes, increased cell division rate and formation of mounds. Most of these observations can be quantitatively explained by an electrohydrodynamic theory involving local cytoplasmic electro-osmotic flows. We expect this work to motivate further studies on the long-time effects of electromechanical pathways with important tissue engineering applications. Epithelial tissues such as those in the gut or skin are strongly polar, generating electric fields that play a role in wound healing and nutrient transport. Changing the field direction in a layer of tissue disrupts its homeostatic stability.

Measurement of the interfacial strain energy release rate of adhesively bonded structures with metallic substrates before and after water ageing

The aim of the presented work is to propagate cracks at interfaces between adhesive joints and metallic substrates and to measure the Strain Energy Release Rate (SERR). In order to propagate at a specific interface and not cohesively, a specific specimen was developed, based on a modification of the Tapered Double Cantilever Beam (TDCB) specimen. In particular, the dimensions of one substrate were reduced to create an asymmetry in the specimen and drive the propagation path towards one interface. The authors present experimental results showing repetitive interfacial failures and a procedure to evaluate the SERR. The non-linear behaviour responsible of non-linear deformation in the substrate was taken into account in the calculations of the SERR. Through a numerical inverse method using Finite Element Analysis (FEA) and Cohezive Zone Modelling (CZM), the SERR was calculated for an epoxy based structural adhesive at the interface with a stainless-steel substrate. Then, the procedure was carried out to measure the interfacial SERR after different ageing times.