E-cadherin adhesion dynamics as revealed by an accelerated force ramp are dependent upon the presence of α-catenin

Tissue remodeling and shape changes often rely on force-induced cell rearrangements occurring via cell-cell contact dynamics. Epithelial cell-cell contact shape changes are particularly dependent upon E-cadherin adhesion dynamics which are directly influenced by cell-generated and external forces. While both the mobility of E-cadherin adhesions and their adhesion strength have been reported before, it is not clear how these two aspects of E-cadherin adhesion dynamics are related. Here, using magnetic pulling cytometry, we applied an accelerated force ramp on the E-cadherin adhesion between an E-cadherin-coated magnetic microbead and an epithelial cell to ascertain this relationship. Our approach enables the determination of the adhesion strength and force-dependent mobility of individual adhesions, which revealed a direct correlation between these key characteristics. Since α-catenin has previously been reported to play a role in both E-cadherin mobility and adhesion strength when studied independently, we also probed epithelial cells in which α-catenin has been knocked out. We found that, in the absence of α-catenin, E-cadherin adhesions not only had lower adhesion strength, as expected, but were also more mobile. We observed that α-catenin was required for the recovery of strained cell-cell contacts and propose that the adhesion strength and force-dependent mobility of E-cadherin adhesions act in tandem to regulate cell-cell contact homeostasis. Our approach introduces a method which relates the force-dependent adhesion mobility to adhesion strength and highlights the morphological role played by α-catenin in E-cadherin adhesion dynamics.

Oyster-inspired carbon dots-functionalized silica and dialdehyde chitosan to fabricate a soy protein adhesive with high strength, mildew resistance, and long-term water resistance

Developing multifunctional adhesives with exceptional cold-pressing strength, water resistance, toughness, and mildew resistance remains challenging. Herein, inspired by oysters, a multifunctional organic-inorganic hybrid soybean meal (SM)-based adhesive was fabricated by incorporating amino-modified carbon dots functionalized silica nanoparticles (CDs@SiO2) and dialdehyde chitosan (DCS) into SM matrix. DCS effectively enhanced the interface interactions of organic-inorganic phases and the rigid nanofillers CDs@SiO2 uniformly dispersed in the SM matrix, which provided energy dissipation to improve the adhesive's toughness. Owing to the stiff skeleton structure and enhanced crosslinking density, the crosslinker-modified SM (MSM)/DCS/CDs@SiO2-2 wood adhesive exhibited outstanding cold-pressing strength (0.74 MPa), wet shear strength (1.36 MPa), and long-term water resistance (49 d). Additionally, the resultant adhesive showed superior antimildew and antibacterial properties benefiting from the introduction of DCS. Intriguingly, the fluorescent properties endowed by carbon dots further broadened the application of adhesives for realizing security testing. This study opens a new pathway for the synthesis of multifunctional biomass adhesives in industrial and household applications.

Sounding a New Era in Biomechanics with Acoustic Force Spectroscopy

The acoustic force spectroscopy (AFS) tool was recently introduced as a novel tool for probing mechanical properties of biomolecules, expanding the application of sound waves to high-throughput quantification of the mechanical properties of single cells. By using controlled acoustic forces in the piconewton to nanonewton range, tens to hundreds of cells functionalized by attached microspheres can simultaneously be stretched and tracked in real-time with sub millisecond time response. Since its first application, several studies have demonstrated the potential and versatility of the AFS for high-throughput measurements of force-induced molecular mechanisms, revealing insight into cellular biomechanics and mechanobiology at the molecular level. In this chapter, we describe the operation of the AFS starting with the underlying physical principles, followed by a run-down of experimental considerations, and finally leading to applications in molecular and cellular biology.

Interfacial mechanical properties of tetrahydrofuran hydrate-solid surfaces: Implications for hydrate management

Understanding the interfacial mechanical properties between hydrate and solids is vital to designing and fabricating surfaces for hydrate management. Herein, the role of the surface wettability, the type of solid substrate and temperature on the interfacial adhesion properties of tetrahydrofuran (THF) hydrate and ice were examined by force analysis based shearing measurements and molecular dynamics (MD) simulations. The results showed that the adhesion strength of THF hydrate and ice on silica varies with the compositions of coating, and the adhesion strength of ice is larger than that of THF hydrate for all investigated solid substrates. Particularly, in contrast to a linear relationship between 1 + cosθr and hydrate adhesion on organic silanes/thiols/polymer surfaces, the hydrate adhesion on the coated inorganic glass surfaces is enhanced as a function of 1 + cosθr, in which θr is the receding contact angle. MD simulations uncovered that the adhesion strength of ice on solid substrates is dominated by the quasi-liquid water layer, however, that of hydrate is governed not only by the quasi-liquid layer but also newly formed unconventional clathrate cages. This study provides new insights and perspectives into the hydrate adhesion on solid surfaces, which is of help to develop hydrate-phobic coatings for advanced hydrate management.

Hydrophilic competent and enhanced wet-bond strength castor oil-based bioadhesive for bone repair

Bone adhesive has been proved to be a promising alternative in the clinical treatment of bone repairs. However, the problems of unsatisfying bone-bonding strength, especially the bonding of cortical bone in vivo, and blocked bone tissue recovery remain barriers to clinical reparation. Benefit from dopamine-modified castor oil synthesized by an epoxy-modification method, a porous and two-component polyurethane adhesive (PUA) was prepared to overcome the current challenges encountered. The tailored surface morphology and open porosity of the adhesive layer can be obtained to meet the requirements of bone repair by tuning the fraction of the formulation. Furthermore, the incorporation of nano-hydroxyapatite improved the mechanical properties and osteocompatibility of the material. Compared with PUA without catechol groups, the introduction of catechol groups not only increased the adhesive strength from 0.28 ± 0.05 MPa to 0.58 ± 0.06 MPa under wet conditions but also enabled the enrichment of Ca2+ on the adhesive surface to promote bone regeneration. Besides, the cell culture experiments also indicated that PUAs show good biocompatibility and excellent adhesion to stem cells. Given its excellent wet adhesive strength and biocompatibility, this system demonstrated potential applications in orthopedic treatment.

Effects of hydrate inhibitors on the adhesion strengths of sintered hydrate deposits on pipe walls

The effects of hydrate inhibitors on the adhesion of sintered hydrate deposits on pipe walls are still unexplored. Herein, a custom-built adhesion strength measurement apparatus was utilized to quantify the adhesion strengths of sintered cyclopentane (CyC5) hydrate deposits with thermodynamic inhibitors (ethylene glycol, glycerol) and low-dosage inhibitors (dodecylbenzene sulfonic acid (DBSA), sorbitan oleate (Span 80)). It was found that the hydrate adhesion strengths decreased by 69.82%-97.06% and 40.24%-94.36% with the concentration of ethylene glycol and glycerol increased from 2 wt% to 6 wt%, respectively. For DBSA and Span 80, the hydrate adhesion strength increased with concentration less than 0.01 wt% due to the acceleration on hydrate growth. The further increment of concentration leads to a dramatic reduction in adhesion strengths. Furthermore, the relatively large deviations with the predicted strengths led to the discussions of the effects of change in hydrate formation rate, crystal morphology, and also the adaption of the fitting model. Two modified models were proposed to give a better prediction/explanation of the hydrate adhesion with thermodynamic inhibitors and low-dosage inhibitors, respectively. This work provides a fundamental understanding of the adhesion mechanism of hydrate deposits with hydrate inhibitors, which is important in advancing the management of hydrate formation for preventing plugging in pipelines.

Superhydrophobic versus SLIPS: Temperature dependence and the stability of ice adhesion strength

HYPOTHESIS

Ice adhesion to solids, being affected by the ice/solid intermolecular interactions and structure of ice surface layer is dependent on temperature, and ice surface layer equilibration time.

EXPERIMENTS

A new centrifugal method of shear ice adhesion strength measurement with accurate temperature control on each stage from ice formation on test surfaces to the adhesion measurement is applied to study ice adhesion to superhydrophobic and slippery surfaces. The determinative advantage of the developed method is related to monitoring in one experiment the ice detachment from numerous samples and accurate measuring the rotation frequency for each ice detachment.

FINDINGS

The following findings will be discussed.

The mechanisms of anti-icing properties degradation for slippery liquid-infused porous surfaces under shear stresses

HYPOTHESIS

Loss of anti-icing properties of slippery liquid-infused porous surfaces (SLIPS) in conditions of repetitive shear stresses is the intrinsic process related to peculiarities of SLIPS structure.

EXPERIMENTS

The study of the evolution of the ice adhesion strength to superhydrophobic surfaces (SHS) and SLIPS during repetitive icing/de-icing cycles measured by a centrifugal method was supplemented with the estimation of change in capillary pressure inside the pores, and SEM analysis of the effect of multiple ice detachments on surface morphology.

FINDINGS

Obtained data indicated that although for freshly prepared SLIPS, the ice shear adhesion strength at -25 °C was several times lower than for SHS, repetitive icing-deicing cycles resulted in dramatic SLIPS degradation. In contrast, SHS showed weak degradation at least during 50 cycles. Additional to the depletion of an impregnating oil layer, other mechanisms of SLIPS degradation were hypothesized and tested. It was shown that lower capillary pressure required to displace air by water from the surface texture for SLIPSs compared to SHSs resulted in deeper water/ice penetration inside the grooves. The accelerated destruction of the mechanical texture caused by the Rehbinder effect constitutes another mechanism of SLIPSs degradation.

Self-healing epoxy coating synthesis by embedment of metal 2-methyl imidazole and acetylacetonate complexes with microcapsules

The restoration of mechanical properties is desired for creating the self-healing coatings with no corrosion capabilities. The encapsulation of epoxy resins is limited by various factors in urea and melamine formaldehyde microcapsules. An improved method was developed, where epoxy resin was encapsulated by individual wrapping of poly(melamine-formaldehyde) and poly(urea-formaldehyde) shell around emulsified epoxy droplets via oil-in-water emulsion polymerization method. The synthesized materials were characterized analytically. The curing of the epoxy was achieved by adding the [Ni/Co(2-MI)₆].2NO₃ as a latent hardener and iron acetylacetonate [Fe(acac)₃] as a latent accelerator. Isothermal and non-isothermal differential scanning calorimetric analysis revealed lower curing temperature (T_onset = 116 °C) and lower activation energies (Ea ≈ 69-75 kJ/mol). The addition of microcapsules and complexes did not adversely alter the flexural strength and flexural modulus of the epoxy coatings. The adhesion strength of neat coating decreased from 6310.8 ± 31 to 4720.9 ± 60 kPa and percent healing increased from 50.83 to 67.45% in the presence of acetylacetonate complex at 10 wt% of microcapsules.

Ultraviolet-C inactivation and hydrophobicity of Bacillus subtilis and Bacillus velezensis spores isolated from extended shelf-life milk

Bacterial spores are important in food processing due to their ubiquity, resistance to high temperature and chemical inactivation. This work aims to study the effect of ultraviolet C (UVC) on the spores of Bacillus subtilis and Bacillus velezensis at a molecular and individual level to guide in deciding on the right parameters that must be applied during the processing of liquid foods. The spores were treated with UVC using phosphate buffer saline (PBS) as a suspension medium and their lethality rate was determined for each sample. Purified spore samples of B. velezensis and B. subtilis were treated under one pass in a UVC reactor to inactivate the spores. The resistance pattern of the spores to UVC treatment was determined using dipicolinic acid (Ca-DPA) band of spectral analysis obtained from Raman spectroscopy. Flow cytometry analysis was also done to determine the effect of the UVC treatment on the spore samples at the molecular level. Samples were processed for SEM and the percentage spore surface hydrophobicity was also determined using the Microbial Adhesion to Hydrocarbon (MATH) assay to predict the adhesion strength to a stainless-steel surface. The result shows the maximum lethality rate to be 6.5 for B. subtilis strain SRCM103689 (B47) and highest percentage hydrophobicity was 54.9% from the sample B. velezensis strain LPL-K103 (B44). The difference in surface hydrophobicity for all isolates was statistically significant (P < 0.05). Flow cytometry analysis of UVC treated spore suspensions clarifies them further into sub-populations unaccounted for by plate counting on growth media. The Raman spectroscopy identified B4002 as the isolate possessing the highest concentration of Ca-DPA. The study justifies the critical role of Ca-DPA in spore resistance and the possible sub-populations after UVC treatment that may affect product shelf-life and safety. UVC shows a promising application in the inactivation of resistant spores though there is a need to understand the effects at the molecular level to design the best parameters during processing.

Using encrusting bryozoan adhesion to evaluate the efficacy of fouling-release marine coatings

Biofouling communities are spatiotemporally diverse, underscoring the need to assess fouling-release (FR) coating performance against common biofouling taxa at multiple field sites. Adhesion strength assessments of FR coatings incorporate few taxa into standardized protocols. This study tested the feasibility of incorporating existing ASTM barnacle protocols on tubeworms and encrusting bryozoans (EB). Additionally, trends in adhesion strength among these taxa were compared at two field sites. EB adhesion at both field sites showed consistent results and adhesion strength followed the same trend: tubeworms > barnacles >EB. Testing EB adhesion was feasible and enhanced assessments of FR coatings by increasing the diversity of assessed taxa.

Biomarkers to quantify cell migration characteristics

Background

Because cell movement is primarily driven by the connection between F-actin and integrin through a physical linkage, cellular elasticity and adhesion strength have been considered as biomarkers of cell motility. However, a consistent set of biomarkers that indicate the potential for cell motility is still lacking.

Methods

In this work, we characterize a phenotype of cell migration in terms of cellular elasticity and adhesion strength, which reveals the interdependence of subcellular systems that mediate optimal cell migration.

Results

Stiff cells weakly adhered to the substrate revealed superior motility, while soft cell migration with strong adhesion was relatively inhibited. The spatial distribution and amount of F-actin and integrin were highly variable depending on cell type, but their density exhibited linear correlations with cellular elasticity and adhesion strength, respectively.

Conclusions

The densities of F-actin and integrin exhibited linear correlations with cellular elasticity and adhesion strength, respectively, therefore, they can be considered as biomarkers to quantify cell migration characteristics.

Enhanced interfacial adhesion and osseointegration of anodic TiO2 nanotube arrays on ultra-fine-grained titanium and underlying mechanisms

The poor adhesion of anodic TiO₂ nanotubes (TNTs) arrays on titanium (Ti) substrates adversely affects applications in many fields especially biomedical engineering. Herein, an efficient strategy is described to improve the adhesion strength of TNTs by performing grain refinement in the underlying Ti substrate via high-pressure torsion processing, as a larger number of grain boundaries can provide more interfacial mechanical anchorage. This process also improves the biocompatibility and osseointegration of TNTs by increasing the surface elastic modulus. The TNTs in length of 0.4 µm have significantly larger adhesion strength than the 2.0 µm long ones because the shorter TNTs experience less interfacial internal stress. However, post-anodization annealing reduces the fluorine concentration in TNTs and adhesion strength due to the formation of interfacial cavities during crystallization. The interfacial structure of TNTs/Ti system and the mechanism of adhesion failures are further investigated and discussed. STATEMENT OF SIGNIFICANCE: Self-assembled TiO₂ nanotubes (TNTs) prepared by electrochemical anodization have a distinct morphology and superior properties, which are commonly used in photocatalytic systems, electronic devices, solar cells, sensors, as well as biomedical implants. However, the poor adhesion between the TNTs and Ti substrate has hampered wider applications. Here in this study, we describe an efficient strategy to improve the adhesion strength of TNTs by performing grain refinement in the underlying Ti substrate via high-pressure torsion (HPT) processing. The interfacial structure of TNTs/Ti system and the mechanism of adhesion failure are systematically studied and discussed. Our findings not only develop the knowledge of TNTs/Ti system, but also provide new insights into the design of Ti-based implants for orthopedic applications.

A novel hybrid technique to fabricate silicon-based micro-implants with near defect-free quality for neuroprosthetics application

This paper introduces a new hybrid microfabrication technique which combines ultra-precision micro-milling and a ductile sacrificial material deposition process to fabricate a silicon-based implant for neuroprosthetics applications with near defect-free quality at several hundreds of micrometres in thickness. The sacrificial materials can influence the quality of silicon during machining. The cutting mechanism and feasibility of the hybrid technique are studied by molecular dynamics (MD) simulations and experiments. Due to the complexity of modelling PMMA and SU-8 structures in MD environment, only copper was modelled as the simulation is intended to understand the performance of using a ductile sacrificial layer structure in silicon machining. MD analysis shows that the reduced stress intensity and subsurface damage were mainly attributed to workpiece plasticity enhancement, where its mechanism was contributed by better deformability of the ductile sacrificial layer and enhanced thermal softening from the heat generated by the high interfacial stress between the sacrificial layer and silicon substrate. Despite the MD simulation and experiment having different machining scale in terms of cutting parameters, phenomenal behaviours of the cutting performance when observed under the experimental conditions are in good agreement with simulation. Experimental verification shows that near defect-free quality was achieved at large cutting depth of 150 μm when silicon is coated either with PMMA or SU-8. An exemplary implant structure was also fabricated to better demonstrate the hybrid technique's capability. In addition, the hybrid technique will be beneficial for low volume high customisation applications as it is a serial process.

Ship hull in-water cleaning and its effects on fouling-control coatings

Today, ship hull fouling is managed through fouling-control coatings, complemented with in-water cleaning. During cleaning, coating damage and wear must be avoided, for maximum coating lifetime and reduced antifoulant release. When possible, cleaning should target early stages of fouling, using minimal forces. However, such forces, and their effects on coatings, have not yet been fully quantified. In this one-year study, minimal cleaning forces were determined using a newly-designed immersed waterjet. The results show that bi-monthly/monthly cleaning, with maximum wall shear stress up to ∼1.3 kPa and jet stagnation pressure ∼0.17 MPa, did not appear to cause damage or wear on either the biocidal antifouling (AF) or the biocide-free foul-release (FR) coatings. The AF coating required bi-monthly cleanings to keep fouling to incipient slime (time-averaged results), while the FR coating had a similar fouling level even without cleaning. The reported forces may be used in matching cleaning parameters to the adhesion strength of the early stages of fouling.

An Evaluation Approach of Cell Viability Based on Cell Detachment Assay in a Single-Channel Integrated Microfluidic Chip

Due to the heterogeneity of cancer cell populations, the traditional evaluation approach of cell viability based on the cell counting assay is quite inaccurate for the dose-response test of anticancer drugs, cell toxicology assays, and other biochemical stimulations. In this paper, an evaluation approach of cell viability based on the cell detachment assay in a single-channel integrated microfluidic chip is proposed to improve the accuracy of cell viability assessment. The electrodes are coated by fibronectin for specific cell adhesion, and it is biologically significant to study the cell detachment assay in vitro. The maximum number of cells that can be detected by this sensor is about 10⁵ cells (overgrowing), while the minimum is about 100 cells. This method is calibrated with the half-maximal inhibitory concentration assay, and the results show that the cell viability calculated by adhesion strength is more accurate than that evaluated using the cell counting assay. Meanwhile, the shear rate is transformed into shear stress for the comparability among the results in other papers. The most sensitive frequency is also determined as 1 kHz according to normalized impedance. Besides, the impedance of cell adhesion affected by different shear stresses is monitored to study the optimized plan for long-term culture of cells in the integrated microfluidic chip prepared for the cell detachment assay. Adhesion strength τ₂₅, which is the magnitude of shear stress needed to detach 75% of cell population, is introduced to describe the cell adhesion forces. It is calculated and normalized based on the cell detachment assay to evaluate cell viability. The relative errors of the cell detachment method compared with those of the cell counting method decrease by 0.637 (0% FBS), 0.586 (0.5% FBS), and 0.342 (2% FBS).

Towards an absolute scale for adhesion strength of ship hull microfouling

In-water ships' hull cleaning enables significant fuel savings through removal of marine fouling from surfaces. However, cleaning may also shorten the lifetime of hull coatings, with a subsequent increase in the colonization and growth rate of fouling organisms. Deleterious effects of cleaning would be minimized by matching cleaning forces to the adhesion strength of the early stages of fouling, or microfouling. Calibrated waterjets are routinely used to compare different coatings in terms of the adhesion strength of microfouling. However, an absolute scale is lacking for translating such results into cleaning forces, which are of interest for the design and operation of hull cleaning devices. This paper discusses how such forces can be determined using computational fluid dynamics. Semi-empirical formulae are derived for forces under immersed waterjets, where the normal and tangential components of wall forces are given as functions of different flow parameters. Nozzle translation speed is identified as a parameter for future research, as this may affect cleaning efficacy.

Synergistic effects of VE-TPGS and riboflavin in crosslinking of dentine

OBJECTIVE

Effect of d-alpha-tocopheryl poly(ethyleneglycol)-1000-succinate (VE-TPGS) with riboflavin-5'-phosphate solution on crosslinking of dentine collagen was investigated to analyze collagen's structural integrity.

METHODS

VE-TPGS was added to RF-solution, at RF/VE-TPGS (w/w) ratios of 0.125/0.250 and 0.125/0.500. Demineralized dentine beams were used (10wt.% phosphoric acid), rinsed using deionized-water and analysed using ELISA (Human MMP2 ELISA; Human CTSK/Cathepsin-K for MMP2 and Cathepsin K analysis). AFM of dentine collagen-fibrils structure was done before and after dentine specimens' placement in mineralization solution and tested after 14days in artificial saliva/collagenase (AS/Co) solution. The specimens were tested after 24h in mineralization solution for surface/bulk elastic modulus. Nano-indentation was carried out for each specimen on intertubular-dentine with lateral spacing of 400nm. Reduced elastic-modulus and nano-hardness were calculated and collagen content was determined using hydroxyproline-assay. Micro-Raman were performed. TEM was carried out to study structural variations of dentine-collagen in artificial-saliva (collagenase). Data were presented as mean±standard deviation and analyzed by SPSS v.15, by analysis of variance.

RESULTS

Synergetic effect of VE-TPGS was observed with RF through higher structural integrity of dentine collagen-fibrils shown by TEM/AFM. Superior surface/bulk mechanical stability was shown by nano-indentation/mechanical testing. Improvement in collagenase degradation resistance for hydroxyproline release was observed and lower endogenous-protease release of MMP-2/Cathepsin-K. Raman-analysis analysed chemical interactions between RF and collagen confirming structural-integrity of collagen fibrils after crosslinking. After 24h mineralization, AFM showed mineral depositions in close association with dentine-collagen fibrils with RF/VE-TPGS formulations.

SIGNIFICANCE

Potential synergetic effect of RF/VE-TPGS was observed by reflection of higher structural integrity and conformational-stability of dentine-collagen fibrils.

Dual-functioning peptides discovered by phage display increase the magnitude and specificity of BMSC attachment to mineralized biomaterials

Design of biomaterials for cell-based therapies requires presentation of specific physical and chemical cues to cells, analogous to cues provided by native extracellular matrices (ECM). We previously identified a peptide sequence with high affinity towards apatite (VTKHLNQISQSY, VTK) using phage display. The aims of this study were to identify a human MSC-specific peptide sequence through phage display, combine it with the apatite-specific sequence, and verify the specificity of the combined dual-functioning peptide to both apatite and human bone marrow stromal cells. In this study, a combinatorial phage display identified the cell binding sequence (DPIYALSWSGMA, DPI) which was combined with the mineral binding sequence to generate the dual peptide DPI-VTK. DPI-VTK demonstrated significantly greater binding affinity (1/K_D) to apatite surfaces compared to VTK, phosphorylated VTK (VTK_phos), DPI-VTK_phos, RGD-VTK, and peptide-free apatite surfaces (p < 0.01), while significantly increasing hBMSC adhesion strength (τ₅₀, p < 0.01). MSCs demonstrated significantly greater adhesion strength to DPI-VTK compared to other cell types, while attachment of MC3T3 pre-osteoblasts and murine fibroblasts was limited (p < 0.01). MSCs on DPI-VTK coated surfaces also demonstrated increased spreading compared to pre-osteoblasts and fibroblasts. MSCs cultured on DPI-VTK coated apatite films exhibited significantly greater proliferation compared to controls (p < 0.001). Moreover, early and late stage osteogenic differentiation markers were elevated on DPI-VTK coated apatite films compared to controls. Taken together, phage display can identify non-obvious cell and material specific peptides to increase human MSC adhesion strength to specific biomaterial surfaces and subsequently increase cell proliferation and differentiation. These new peptides expand biomaterial design methodology for cell-based regeneration of bone defects. This strategy of combining cell and material binding phage display derived peptides is broadly applicable to a variety of systems requiring targeted adhesion of specific cell populations, and may be generalized to the engineering of any adhesion surface.

Surface phosphonation enhances hydroxyapatite coating adhesion on polyetheretherketone and its osseointegration potential

Polyetheretherketone (PEEK) has excellent mechanical properties, biocompatibility, chemical resistance and radiolucency, making it suitable for use as orthopedic implants. However, its surface is hydrophobic and bioinert, and surface modification is required to improve its bioactivity. In this work, we showed that grafting phosphonate groups via diazonium chemistry enhances the bioactivity of PEEK. Decreased contact angle indicated reduced hydrophobicity as a result of the treatment and X-ray photoelectron spectroscopy (XPS) confirmed the attachment of phosphonate groups to the surface. The surface treatment not only accelerated hydroxyapatite (HA) deposition after immersion in simulated body fluid but also significantly increased the adhesion strength of HA particles on PEEK. MC3T3-E1 cell viability, metabolic activity and deposition of calcium-containing minerals were also enhanced by the phosphonation. After three months of implantation in a critical size calvarial defect model, a fibrous capsule surrounded untreated PEEK while no fibrous capsule was observed around the treated PEEK. Instead, mineral deposition was observed in the region between the treated PEEK implant and underlying bone. This work introduces a simple method to improve the potential of PEEK-based orthopedic implants.

STATEMENT OF SIGNIFICANCE

We have introduced phosphonate groups on the surface of PEEK substrates using diazonium chemistry. Our results show that the treatment not only increased the adhesion strength of hydroxyapatite particles deposited on PEEK in vitro by approximately 40% compared to unmodified PEEK, but also improved the metabolic activity and mineralization of MC3T3-E1 cells. When implanted in cranial defects in rats, the phosphonate coating enhanced the osseointegration of PEEK by successfully preventing the formation of a fibrous capsule and favoring mineral deposition between the implant and the surrounding bone. This work introduces a simple method to improve the potential of PEEK-based orthopedic implants, particularly those with complex shapes.

Enhancing the adhesion strength of micro electroforming layer by ultrasonic agitation method and the application

Micro electroforming is widely used for fabricating micro metal devices in Micro Electro Mechanism System (MEMS). However, there is the problem of poor adhesion strength between micro electroforming layer and substrate. This dramatically influences the dimensional accuracy of the device. To solve this problem, ultrasonic agitation method is applied during the micro electroforming process. To explore the effect of the ultrasonic agitation on the adhesion strength, micro electroforming experiments were carried out under different ultrasonic power (0W, 100W, 150W, 200W, 250W) and different ultrasonic frequencies (0kHz, 40kHz, 80kHz, 120kHz, 200kHz). The effects of the ultrasonic power and the ultrasonic frequency on the micro electroforming process were investigated by polarization method and alternating current (a.c.) impedance method. The adhesion strength between the electroforming layer and the substrate was measured by scratch test. The compressive stress of the electroforming layer was measured by X-ray Diffraction (XRD) method. The crystallite size of the electroforming layer was measured by Transmission Electron Microscopy (TEM) method. The internal contact surface area of the electroforming layer was measured by cyclic voltammetry (CV) method. The experimental results indicate that the ultrasonic agitation can decrease the polarization overpotential and increase the charge transfer process. Generally, the internal contact surface area is increased and the compressive stress is reduced. And then the adhesion strength is enhanced. Due to the different depolarization effects of the ultrasonic power and the ultrasonic frequency, the effects on strengthening the adhesion strength are different. When the ultrasonic agitation is 200W and 40kHz, the effect on strengthening the adhesion strength is the best. In order to prove the effect which the ultrasonic agitation can improve the adhesion strength of the micro devices, micro pillar arrays were fabricated under ultrasonic agitation (200W, 40kHz). The experimental results show that the residual rate of the micro pillar arrays is increased about 17% by ultrasonic agitation method. This work contributes to fabricating the electroforming layer with large adhesion strength.

Cell adhesion strength from cortical tension - an integration of concepts

Morphogenetic mechanisms such as cell movement or tissue separation depend on cell attachment and detachment processes, which involve adhesion receptors as well as the cortical cytoskeleton. The interplay between the two components is of stunning complexity. Most strikingly, the binding energy of adhesion molecules is usually too small for substantial cell-cell attachment, pointing to a main deficit in our present understanding of adhesion. In this Opinion article, I integrate recent findings and conceptual advances in the field into a coherent framework for cell adhesion. I argue that active cortical tension is best viewed as an integral part of adhesion, and propose on this basis a non-arbitrary measure of adhesion strength - the tissue surface tension of cell aggregates. This concept of adhesion integrates heterogeneous molecular inputs into a single mechanical property and simplifies the analysis of attachment-detachment processes. It draws attention to the enormous variation of adhesion strengths among tissues, whose origin and function is little understood.

Effects of ultrasonic agitation on adhesion strength of micro electroforming Ni layer on Cu substrate

Micro electroforming is an important technology, which is widely used for fabricating micro metal devices in MEMS. The micro metal devices have the problem of poor adhesion strength, which has dramatically influenced the dimensional accuracy of the devices and seriously limited the development of the micro electroforming technology. In order to improve the adhesion strength, ultrasonic agitation method is applied during the micro electroforming process in this paper. To explore the effect of the ultrasonic agitation, micro electroforming experiments were carried out under ultrasonic and ultrasonic-free conditions. The effects of the ultrasonic agitation on the micro electroforming process were investigated by polarization and alternating current (a.c.) impedance methods. The real surface area of the electroforming layer was measured by cyclic voltammetry method. The compressive stress and the crystallite size of the electroforming layer were measured by X-ray Diffraction (XRD) method. The adhesion strength of the electroforming layer was measured by scratch test. The experimental results show that the imposition of the ultrasonic agitation decreases the polarization overpotential and increases the charge transfer process at the electrode-electrolyte interface during the electroforming process. The ultrasonic agitation increases the crystallite size and the real surface area, and reduces the compressive stress. Then the adhesion strength is improved about 47% by the ultrasonic agitation in average. In addition, mechanisms of the ultrasonic agitation improving the adhesion strength are originally explored in this paper. The mechanisms are that the ultrasonic agitation increases the crystallite size, which reduces the compressive stress. The lower the compressive stress is, the larger the adhesion strength is. Furthermore, the ultrasonic agitation increases the real surface area, enhances the mechanical interlocking strength and consequently increases the adhesion strength. This work contributes to fabricating the electroforming layer with large adhesion strength.

Dual pipette aspiration: a unique tool for studying intercellular adhesion

The dual pipette aspiration (DPA) assay is a highly versatile tool that enables the micromanipulation of cells and the precise measurement of a range of biophysical parameters in combination with concurrent high-resolution imaging. DPA permits the juxtaposition of cells, their manipulation using pressure and the controlled formation or separation of cell-cell contacts. The DPA set-up can thus readily be used to probe the dynamics and mechanics of cell-cell adhesion, notably adhesion strength and adhesion energy. In particular, the DPA set-up has been used to measure a wide range of separation forces between pairs of cells. Here, we describe how to build and use the DPA set-up in order to measure the separation force of cell doublets. We first describe how to prepare adequate pipettes, then how to assemble and calibrate the pipettes and pressure control devices, followed by how to manipulate cells in order to calculate separation forces. Finally, we give recommendations on how to use the DPA set-up and compare it to other methods used to study cell-cell contacts and adhesion strength in particular.