Effects of Surface Oxidation Treatment of Carbon Fibers on Biotribological Properties of CF/PEEK Materials

Carbon Fiber (CF) reinforced polyetheretherketone (PEEK) composite is one of the most promising implant biomaterials used in orthopedics.In this article,unfilled PEEK and CF/PEEK specimens were prepared by vacuum hot pressing method,and their tribological properties were evaluated by sliding against a cobalt-chromium-molybdenum (Co-Cr-Mo) alloy block.The influences of mass fraction of carbon fibers in CF/PEEK and the surface oxidation treatment of carbon fibers were explored.The results showed that the water contact angles on the surfaces of CF/PEEK specimens decreased,indicating that their surface wettability was improved.The hardness value of CF/PEEK was significantly improved,the friction coefficients of CF/PEEK were effectively reduced and its wear resistance was enhanced compared with unfilled PEEK.The leading effect on CF/PEEK tribological properties was the mass fraction of CF,followed by surface oxidation of CF,and the calf serum solution had better lubricity than that of saline and deionized water.     

Flexural and Dynamic Mechanical Properties of Alkali-Treated Coir/Pineapple Leaf Fibres Reinforced Polylactic Acid Hybrid Biocomposites

Polylactic acid(PLA)possesses good mechanical and biodegradability properties which make it a suitable material for polymer composites whereas brittleness and high costs limit its utilization in various applications.The reinforcement of natural fibres with biopolymers has been formed to be an efficient technique to develop composites having the ability to be fully biodegradable.This study concerns with the incorporation of various percentages of untreated and alkali-treated Coir Fibres(CF)and pineapple leaf fibres(PALF)in PLA biocomposites and characterizations of flexural,morphological and dynamic mechanical properties.Flexural properties showed that the treated C1P1 hybrid composites(C1P1A)displayed highest flexural strength(35.81 MPa)and modulus(5.28 GPa)among all hybrid biocomposites.Scanning Electron Micros-copy(SEM)revealed a behaviour of fibre-matrix adhesion in untreated treated biocomposites.SEM observation revealed good dispersion of the fillers in PLA.Dynamic mechanical analysis revealed that C1P1A showed highest glass transition temperature(Tg)and storage modulus(E')while untreated C3P7 displayed the least Tg and E'.Overall findings showed that alkali-treated hybrid biocomposites(CF/PALF/PLA)especially C1P1A have improved flexural properties,dynamic and morphological properties over untreated biocomposites.Success of these findings will provide attracting consideration of these hybrid biocomposites for various lightweight uses in a broad selection of industrial applications such as biomedical sectors,automobile,construction,electronics equipment,and hardware tools.     

植物乳杆菌粘附性与其表面特征关系的探究

本文通过16s rDNA鉴定获得4株植物乳杆菌,并以HT29细胞为体外黏附筛选模型,进一步探讨了这些菌株粘附能力与表面疏水性、自聚共聚能力等表型特征的相关性。结果表明,植物乳杆菌AR326菌株对HT29细胞的粘附性最强,并显示高度的自聚性(25%)和共聚性(25%),但其表面疏水性偏低(15%);通过相关性分析发现,植物乳杆菌的自聚性和共聚性与HT29细胞粘附性呈显著相关性(r=1.0和0.8,p0.05),但表面疏水性、自凝聚性和共聚性两两之间并无显著相关性(p0.05)。本研究结果为建立快速筛选高粘附性植物乳杆菌的方法及其菌株在体内定植和分布研究提供一定参考依据。     

材料表面特征对生物膜形成的影响及其应用

生物膜是微生物细胞粘附于材料表面的群体性生长方式。在实践应用中,有目的地调控微生物在材料表面的成膜进程具有重要意义。本文概述了生物膜在材料表面的形成机制及其影响因素,综述了材料表面的电荷特征、亲疏水性、形貌模式和功能性化学修饰等物化特性对细胞粘附和生物膜形成的影响,并介绍了目前在不同实际应用场景中抑制成膜和促进成膜材料的研发现状。     

Effect of different Bacillus subtilis lipopeptides on surface hydrophobicity and adhesion of Bacillus cereus 98/4 spores to stainless steel and Teflon

Various lipopeptides produced by Bacillus subtilis were examined for their ability to modify the surface hydrophobicity of two substrata, stainless steel (SS) and Teflon. These modifications were evaluated by water contact angle measurements. The effects depended on the lipopeptide, its concentration, and the tested substratum. Treatment of SS with different concentrations of surfactin S1 showed an increase of the hydrophobicity between 1 and 100 mg l^?1. On the same substratum, fengycin increased hydrophobicity up to its critical micelle concentration (6.25 mg l^?1). With higher concentrations of fengycin, hydrophobicity decreased. Surfactin, mycosubtilin, and iturin A decreased hydrophobicity on Teflon. The different effects of these three families of lipopeptides were related to their structural differences. A good correlation was shown between hydrophobicity modifications of surfaces and the attachment of B. cereus 98/4 spores. Enhancement in the hydrophobicity of the surfaces increased the number of adhering spores.     

Biomimetic Hydrophobic Surfaces with Low or High Adhesion Based on Poly(vinyl alcohol) and SiO2 Nanoparticles

Superhydrophobic surfaces are often found in nature,such as plant leaves and insect wings.Inspired by superhydrophobic phenomenon of the rose petals and the lotus leaves,biomimetic hydrophobic surfaces with high or low adhesion were prepared with a facile drop-coating approach in this paper.Poly(vinyl alcohol) (PVA) was used as adhesive and SiO2 nanoparticles were used to fabricate surface micro-structure.Stearic acid or dodecafluoroheptyl-propyl-trimethoxysilane (DFTMS) were used as low surface energy materials to modify the prepared PVA/SiO2 coating surfaces.The effects of size of SiO2 nanoparticles,concentration of SiO2 nanoparticle suspensions and the modifications on the wettability of the surface were investigated.The morphology of the PVA/SiO2 coating surfaces was observed by using scanning electron microscope.Water contact angle of the obtained superhydrophilic surface could reach to 3°.Stearic acid modified PVA/SiO2 coating surfaces showed hydrophobicity with high adhesion.By mixing the SiO2 nanoparticles with sizes of 40 nm and 200 nm and modifying with DFTMS,water contact angle of the obtained coating surface could be up to 155° and slide angle was only 5°.This work provides a facile and useful method to control surface wettability through changing the roughness and chemical composition of a surface.     

Mechanical and Frictional Properties of the Elytra of Five Species of Beetles

The mechanical and frictional properties of different parts of the elytra of five species of beetle were measured using a nano-indenter and a micro-tribometer. The surface microstructures of the elytra were observed by optical microscopy and scanning white light interferometry. The surface microstructures of the elytra of all five species are characterized as non-smooth concavo-convex although specific morphological differences demonstrate the diversity of beetle elytra. Young's modulus and the hardness of the elytral materials vary with the species of beetle and the sampling locations, ranging from 1.80 GPa to 12.44 GPa, and from 0.24 GPa to 0.75 GPa, respectively. In general, both the Young's modulus and the hardness are lower in samples taken from the center of the elytra than those taken from other regions, which reflects the functional heterogeneity of biological material in the process of biological evolution. The elytra have very low friction coefficient, ranging from 0.037 to 0.079, which is related to their composition and morphology. Our measurements indicate that the surface texture and its microstructural size of beetle elytra contribute to anti-friction effects.     

Effect of antibiotic-induced morphological changes on surface properties, motility and adhesion of nosocomial Pseudomonas aeruginosa strains under different physiological states

AIM: To investigate the influence of antibiotic-induced morphological changes on adhesion and motility abilities and surface properties of nosocomial Pseudomonas aeruginosa under different physiological states. METHODS AND RESULTS: The effects of subinhibitory concentration (sub-MIC) of Piperacillin/Tazobactam (P/T) and Imipenem (IMP) were studied on P. aeruginosa adhesion (1 h) using a modified microtitre-plate assay, on their ability to swim and to twitch, on surface hydrophobicity and on acid-base interactions of P. aeruginosa strains by measuring their ability to adhere to n-hexadecane, chloroform and ethyl acetate, respectively. Our results show that antibiotic-induced morphological changes and bacterial physiological state can affect differently surface properties, motility and adhesion abilities of P. aeruginosa. CONCLUSIONS: Under different physiological states P/T induced morphological changes, reduced motility abilities, decreased adhesion to polystyrene and cell surface hydrophobicity (CSH). Moreover, P/T and IMP led to similar changes in exponential population adhesion to chloroform and ethyl acetate. Additionally, IMP induced morphological changes and showed no differences on CSH, adhesion and motility abilities in both growth phases. SIGNIFICANCE AND IMPACT OF THE STUDY: Adhesion is an attractive target for new antibacterial strategies, namely by using sub-MIC antibiotics that induce morphological, motility and surface properties changes, which are dependent of P. aeruginosa phenotype and physiological state.     

Thermodynamic aspects of cell spreading on solid substrata

To verify the validity of thermodynamic approaches to the prediction of cellular behavior, cell spreading of three different cell types on solid substrata was determined in vitro. Solid substrata as well as cell types were selected on the basis of their surface free energies, calculated from contact angle measurements. The surface free energies of the solid substrata ranged from 18–116 erg cm⁻². To measure contact angles on cells, a technique was developed in which a multilayer of cells was deposited on a filter and air dried. Cell surface free energies ranged from 60 erg cm⁻² for fibroblasts, and 57 for smooth muscle cells, to 91 for HeLa epithelial cells. After adsorption of serum proteins, cell surface free energies of all three cell types converged to approx 74 erg cm⁻². The spreading of these cell types from RPMI 1640 medium on the various solid substrata showed that both in the presence and in the absence of serum proteins in the medium, cells spread poorly on low energy substrata (Y _s <50 erg cm⁻²), whereas good cell spreading was observed on the higher energy substrata. Calculations of the interfacial free energy of adhesion (ΔF _adh) show that ΔF _adh decreases with increasingY _s , and equals zero around 45 erg cm⁻² for all three cell types in the presence of serum proteins and for HeLa epithelium cells in the absence of serum proteins. This explains the spreading of these cells on the various substrata upon a thermodynamic basis. The results clearly show that substratum surface free energy has a predictive value with respect to cell spreading in vitro, both in the presence and absence of serum proteins. It is noted, however, that interfacial thermodynamics fail to explain the behavior of fibroblasts and smooth muscle cells in the absence of serum proteins, most likely because of the relatively high surface charges of these two cell types.     

Effect of growth time on the surface and adhesion properties of Lactobacillus rhamnosus GG

Aims:  To investigate the changes in the surface properties of Lactobacillus rhamnosus GG during growth, and relate them with the ability of the Lactobacillus cells to adhere to Caco-2 cells.
Methods and Results:  Lactobacillus rhamnosus GG was grown in complex medium, and cell samples taken at four time points and freeze dried. Untreated and trypsin treated freeze dried samples were analysed for their composition using SDS-PAGE analysis and Fourier transform infrared spectroscopy (FTIR), hydrophobicity and zeta potential, and for their ability to adhere to Caco-2 cells. The results suggested that in the case of early exponential phase samples (4 and 8 h), the net surface properties, i.e. hydrophobicity and charge, were determined to a large extent by anionic hydrophilic components, whereas in the case of stationary phase samples (13 and 26 h), hydrophobic proteins seemed to play the biggest role. Considerable differences were also observed between the ability of the different samples to adhere to Caco-2 cells; maximum adhesion was observed for the early stationary phase sample (13 h). The results suggested that the adhesion to Caco-2 cells was influenced by both proteins and non-proteinaceous compounds present on the surface of the Lactobacillus cells.
Conclusion:  The surface properties of Lact. rhamnosus GG changed during growth, which in return affected the ability of the Lactobacillus cells to adhere to Caco-2 cells.
Significance and Impact of the Study:  The levels of adhesion of Lactobacillus cells to Caco-2 cells were influenced by the growth time and reflected changes on the bacterial surface. This study provides critical information on the physicochemical factors that influence bacterial adhesion to intestinal cells.     

Interfacial instability and the agglutination of erythrocytes by polylysine

Human erythrocytes have been exposed to poylysine of molecular weight range 4 to 220 kDa and concentration range 0.5 to 2,000 /ml at 37°C. Threshold concentrations for cell agglutination by the polycation have been determined for the samples of different molecular weight. Light and electron micrographs show that, in the erythrocyte agglutinates, cell-cell contact is generally made only at discrete, spatially periodic, regions which are distributed over a significant part of the cell surface. The average spacing between contact regions is 0.83 m. The cell membrane has a wavy profile between contact regions. Agglutination occurs only in cell samples whose electrophoretic mobility is significantly altered by polylysine and, in agreement with a previous report, occurs even when the electrophoretic mobility reaches high positive values. The electrophoretic mobility data implies that agglutination requires some protrusion of polylysine from the cell glycocalyx. We discuss how a resulting net attractive intercellular force could act to destabilize the aqueous layer between two cells, allowing surface wave growth which results in spatially periodic contact regions. Examples of situations where cell and membrane contact might be explained by the general concept of interfacial instability are discussed.     

Adhesion and aggregation ability of probiotic strain Lactobacillus acidophilus M92

AIMS: To investigate aggregation and adhesiveness of Lactobacillus acidophilus M92 to porcine ileal epithelial cells in vitro, and the influence of cell surface proteins on autoaggregation and adhesiveness of this strain. METHODS AND RESULTS: Lactobacillus acidophilus M92 exhibits a strong autoaggregating phenotype and manifests a high degree of hydrophobicity determined by microbial adhesion to xylene. Aggregation and hydrophobicity were abolished upon exposure of the cells to pronase and pepsin. Sodium dodecyl sulphate polyacrylamide gel electrophoresis of cell surface proteins revealed the presence of potential surface layer (S-layer) proteins, approximated at 45 kDa, in L. acidophilus M92. The relationship between autoaggregation and adhesiveness to intestinal tissue was investigated by observing the adhesiveness of L. acidophilus M92 to porcine ileal epithelial cells. Removal of the S-layer proteins by extraction with 5 mol l-1 LiCl reduced autoaggregation and in vitro adhesion of this strain. CONCLUSIONS: These results demonstrate that there is relationship between autoaggregation and adhesiveness ability of L. acidophilus M92, mediated by proteinaceous components on the cell surface. SIGNIFICANCE AND IMPACT OF THE STUDY: This investigation has shown that L. acidophilus M92 has the ability to establish in the human gastrointestinal tract, which is an important determinant in the choice of probiotic strains.     

Effect of Microscale Contact State of Polyurethane Surface on Adhesion and Friction

The effect of microscale contact of rough surfaces on the adhesion and friction under negative normal forces was experimentally investigated. The adhesive force of single point contact - sapphire ball to flat polyurethane did not vary with the normal force. With rough surface contact, which was assumed to be a great number of point contacts, the adhesive force increased logarithmically with the normal force. Under negative normal force adhesive state, the tangential force （more than hundred mN） were much larger than the negative normal force （several mN） and increased with the linear decrease of negative normal force. The results reveal why the gecko＇s toe must slide slightly on the target surface when it makes contact on a surface and suggest how a biomimetic gecko foot might be designed.     

Tangent Resistance of Soil on Moldboard and the Mechanism of Resistance Reduction of Bionic Moldboard

The tangent resistance on the interface of the soil-moldboard is an important component of the resistance to moving soil . We developed simplified mechanical models to analyze this resistance. We found that it is composed of two components, the frictional and adhesive resistances. These two components originate from the soil pore, which induced a capillary suction effect, and the soil-moldboard contact area produced tangent adhesive resistance. These two components varied differently with soil moisture. Thus we predicted that resistance reduction against soil exerted on the non-smooth bionic moldboard is mainly due to the elimination of capillary suction and the reduction of physical-chemical adsorption of soil.     

DNA detection and cell adhesion on plasma‐polymerized pyrrole

This study investigates the application of Plasma‐polymerized pyrrole (ppPY) as bioactive platform for DNA immobilization and cell adhesion based on the fundamental properties of ppPY, such as chemical structure, electrochemical property, and protein adsorption. Variations in electrochemical properties of the ppPY film deposited under different plasma conditions before and after DNA immobilization were measured using electrochemical impedance spectroscopy (EIS). The equilibrium concentration of the probe DNA immobilized on the ppPY surface was deduced by detecting the variations in the surface charge transfer resistance (R_ct) of the ppPY films after DNA immobilization with different concentrations. In addition, the detection limit of the target DNA hybridization with probe DNA, the association constant, K_a, and the dissociation constant were deduced from Langmuir isotherm equations simulated using the experimental data collected by EIS. Moreover, inverted microscope was used to observe the cell adhesions onto the surface of the ppPY films prepared under different plasma conditions. Different adhesive behaviors of cells were observed, demonstrating that ppPY films could be an alternative biomaterial used as the sensitive layer for DNA sensor or cell adhesion. © 2013 Wiley Periodicals, Inc. Biopolymers 101: 496–503, 2014.     

Microtubular Protofilament Analysis Based on Molecular Level Tubulin Interaction

Nonlinear microstructure of the microtubules (MTs) plays an important role in their mechanical properties. Despite the extensive efforts into the development of continuum models for microtubules, a mesoscale finite element model that can link the molecular level information to the overall performance of microtubules is still missing. The aim of this study is to develop a molecular dynamics model (MDM), finite element model (FEM) and structural mechanics beam model (SMBM) for tubulins of protofilament (PF). In MDM, the backbone atoms of α-tubulin were fixed while the backbone atoms of β-tubulin were attached to a molecular dynamics (MD) atom through a virtual spring. In FEM, both α and β tubulins are modeled as spherical shells and adjacent tubulins are connected by linear springs. The spherical shells were framed as beams in SMBM. Corresponding parameters such as the elasticity of tubulin-tubulin interaction (TTI) and the stiffness of springs and beam are derived from MD simulation. Marginal differences in the force-deflection curve among the FEM, the MDM and SMBM indicate the good accuracy in describing the mechanical properties of microtubules. Simulation results show that the protofilament behaves non-linearly under tension and torsion but linearly under bending. Deformation pattern of a PF from the SMBM frame bending can be well captured by the classical Euler-Bernouli beam theory and the flexural rigidity derived from FEM is in good agreement with SMBM. These findings lend compelling credence in our developed models of PF to deepen our understanding of the underlying mechanism of statics and dynamics of MTs. In perspective our approach provides a tool for the analysis of MTs mechanical behavior under different conditions.     

Role of organic solvents on Pa-hydroxynitrile lyase interfacial activity and stability

Catalytic activity and adsorption of Pa-hydroxynitrile lyase (Pa-Hnl) was investigated at various organic solvent/water interfaces. We focused on the role of solvent polarity in promoting activity and stability in two-phase systems, specifically for the solvents heptane, dibutyl ether (DBE), diisopropyl ether (DIPE), butylmethyl ether (BME), and methyl tert-butyl ether (MTBE). Enzyme activity towards mandelonitrile cleavage was determined in a recycle reactor with a well-defined interfacial area as described by Hickel, et al. 1999. Here the recycle reactor was modified to permit exchange of the aqueous phase. With this modification, irreversibility of enzyme adsorption was determined as a function of the adsorption time at the interface. Irreversibility of enzyme adsorption was also investigated by measuring the surface pressure of a sessile-drop upon washout. We find that Pa-Hnl exhibits the highest stability but the lowest initial catalytic activity at the aqueous/organic solvent interface with the most polar organic solvents. Thus, DIPE and MTBE display no loss in enzyme activity over a period of several hours. However, the more apolar the solvent is the higher the initial Pa-Hnl activity, but the faster the loss of activity. Dynamic tensiometry reveals that Pa-Hnl adsorbs more strongly at the interface of the more apolar solvents. Surprisingly, Pa-Hnl develops some irreversible adsorption after 30 min at the DIPE/water interface, but does not lose catalytic activity.     

不同食性哺乳动物及人的牙釉质微结构对比研究

根据动物食性将搜集于西藏、新疆、江苏和吉林4省和自治区16种哺乳动物的581颗牙齿分为食草、杂食和食肉3类,设计了录像-截图-测量-定标4步微米量级牙釉质结构测量方法,测量得到牙釉质的颊面厚度和舌面厚度比、臼齿外轮廓平均牙釉质厚度比等牙釉质分布规律,观测到不同哺乳动物釉柱的组装直径均在100 μm 左右,但柱间晶体的宽度不同,发现3类哺乳动物牙釉柱与釉牙本质界夹角的规律:人和食肉动物狗的釉柱角度最大,接近90°,杂食动物猪釉柱角度约为70°,而食草动物釉柱角度在54°～68°之间.研究表明,不同食性哺乳动物牙齿外在和内在结构都和其生物力学功能密切相关,牙釉质的异型结构是使得釉质具有优异的力学性能的优化结构模式.     

Alginate-chitosan complex coacervation for cell encapsulation: effect on mechanical properties and on long-term viability

The use of chitosan in complexation with alginate appears to be a promising strategy for cell microencapsulation, due to the biocompatibility of both polymers and the high mechanical properties attributed by the use of chitosan. The present work focuses on the optimization and characterization of the alginate-chitosan system to achieve long-term cell encapsulation. Microcapsules were prepared from four types of chitosan using one- and two-stage encapsulation procedures. The effect of reaction time and pH on long-term cell viability and mechanical properties of the microcapsules was evaluated. Using the single-stage encapsulation procedure led to increase of at least fourfold in viability compared with the two-stage procedure. Among the four types of chitosan, the use of high molecular weight (MW) chitosan glutamate and low MW chitosan chloride provided high viability levels as well as good mechanical properties, i.e., more than 93% intact capsules. The high viability levels were found to be independent of the reaction conditions when using high MW chitosan. However, when using low MW chitosan, better viability levels (195%) were obtained when using a pH of 6 and a reaction time of 30 min. An alginate-chitosan cell encapsulation system was devised to achieve high cell viability levels as well as to improve mechanical properties, thus holding great potential for future clinical application.     

Influence of Dimensions of UHMW-PE Protuberances on Sliding Resistance and Normal Adhesion of Bangkok Clay Soil to Biomimetic Plates

A number of investigations into application of polymers for macro-morphological modification of tool surface have been carried out. These researches, with extensive stress on convex or domed protuberations as one of the widely used construction units, have tried to harness benefits from using polymers in agriculture. Ultra high molecular weight polyethylene （UHMW-PE） has proved an emerging polymer in its application to reduce soil adhesion. This research was conducted to study the effect of shape （flat, semi-spherical, semi-oblate, semi short-prolate and semi long-prolate） and dimensions （base diameter and dome height） on sliding resistance and normal adhesion of biomimetic plates. To incorporate both shape and size, a dimensionless ratio of height to diameter （HDR） was introduced to characterize the effect of construction unit＇s physique. Experiments were conducted in Bangkok clay soil with dry （ 19.8% d.b.）, sticky （36.9% d.b.） and flooded （60.1% d.b.） soil conditions respectively. Soil at sticky limit exhibited the highest sliding resistance （77.8 N） and normal adhesion （3 kPa to 7 kPa）, whereas these values were 61.7 N and 〈0.2 kPa in dry, and 53.7 N and 0.5 kPa to 1.5 kPa in flooded soil conditions. Protuberances with HDR ≤ 0.5 lowered sliding resistance by 10% - 30% and the same reduced normal adhesion by 10% - 60%. The amount of reduction in both sliding resistance and normal adhesion was higher in flooded soil. Lighter normal loads obviously produced lesser resistance and adhesion.