A micromechanical technique for monitoring cell-substrate adhesiveness: measurements of the strength of red blood cell adhesion to glass and polymer test surfaces

Extending applications of AFM to fluidic AFM in single living cell studies

In this article, a review of a series of applications of atomic force microscopy (AFM) and fluidic Atomic Force Microscopy (fluidic AFM, hereafter fluidFM) in single-cell studies is presented. AFM applications involving single-cell and extracellular vesicle (EV) studies, colloidal force spectroscopy, and single-cell adhesion measurements are discussed. FluidFM is an offshoot of AFM that combines a microfluidic cantilever with AFM and has enabled the research community to conduct biological, pathological, and pharmacological studies on cells at the single-cell level in a liquid environment. In this review, capacities of fluidFM are discussed to illustrate (1) the speed with which sequential measurements of adhesion using coated colloid beads can be done, (2) the ability to assess lateral binding forces of endothelial or epithelial cells in a confluent cell monolayer in an appropriate physiological environment, and (3) the ease of measurement of vertical binding forces of intercellular adhesion between heterogeneous cells. Furthermore, key applications of fluidFM are reviewed regarding to EV absorption, manipulation of a single living cell by intracellular injection, sampling of cellular fluid from a single living cell, patch clamping, and mass measurements of a single living cell.

Medical device-induced thrombosis: what causes it and how can we prevent it?

Blood-contacting medical devices, such as vascular grafts, stents, heart valves, and catheters, are often used to treat cardiovascular diseases. Thrombus formation is a common cause of failure of these devices. This study (i) examines the interface between devices and blood, (ii) reviews the pathogenesis of clotting on blood-contacting medical devices, (iii) describes contemporary methods to prevent thrombosis on blood-contacting medical devices, (iv) explains why some anticoagulants are better than others for prevention of thrombosis on medical devices, and (v) identifies future directions in biomaterial research for prevention of thrombosis on blood-contacting medical devices.

Cell response of anodized nanotubes on titanium and titanium alloys

Titanium and titanium alloy implants that have been demonstrated to be more biocompatible than other metallic implant materials, such as Co-Cr alloys and stainless steels, must also be accepted by bone cells, bonding with and growing on them to prevent loosening. Highly ordered nanoporous arrays of titanium dioxide that form on titanium surface by anodic oxidation are receiving increasing research interest due to their effectiveness in promoting osseointegration. The response of bone cells to implant materials depends on the topography, physicochemistry, mechanics, and electronics of the implant surface and this influences cell behavior, such as adhesion, proliferation, shape, migration, survival, and differentiation; for example the existing anions on the surface of a titanium implant make it negative and this affects the interaction with negative fibronectin (FN). Although optimal nanosize of reproducible titania nanotubes has not been reported due to different protocols used in studies, cell response was more sensitive to titania nanotubes with nanometer diameter and interspace. By annealing, amorphous TiO2 nanotubes change to a crystalline form and become more hydrophilic, resulting in an encouraging effect on cell behavior. The crystalline size and thickness of the bone-like apatite that forms on the titania nanotubes after implantation are also affected by the diameter and shape. This review describes how changes in nanotube morphologies, such as the tube diameter, the thickness of the nanotube layer, and the crystalline structure, influence the response of cells.

Quantification of carbon nanotube induced adhesion of osteoblast on hydroxyapatite using nano-scratch technique

This paper explores the nano-scratch technique for measuring the adhesion strength of a single osteoblast cell on a hydroxyapatite (HA) surface reinforced with carbon nanotubes (CNTs). This technique efficiently separates out the contribution of the environment (culture medium and substrate) from the measured adhesion force of the cell, which is a major limitation of the existing techniques. Nano-scratches were performed on plasma sprayed hydroxyapatite (HA) and HA-CNT coatings to quantify the adhesion of the osteoblast. The presence of CNTs in HA coating promotes an increase in the adhesion of osteoblasts. The adhesion force and energy of an osteoblast on a HA-CNT surface are 17 ± 2 µN/cell and 78 ± 14 pJ/cell respectively, as compared to 11 ± 2 µN/cell and 45 ± 10 pJ/cell on a HA surface after 1 day of incubation. The adhesion force and energy of the osteoblasts increase on both the surfaces with culture periods of up to 5 days. This increase is more pronounced for osteoblasts cultured on HA-CNT. Staining of actin filaments revealed a higher spreading and attachment of osteoblasts on a surface containing CNTs. The affinity of CNTs to conjugate with integrin and other proteins is responsible for the enhanced attachment of osteoblasts. Our results suggest that the addition of CNTs to surfaces used in medical applications may be beneficial when stronger adhesion of osteoblasts is desired.

Assessment of techniques used in calculating cell-material interactions

A review of the techniques used in measuring the forces of deadhesion of cells that have been adhering on substrate surfaces is presented. Two categories of techniques are described, those that utilize fluid flowing against the adhered cells and counting the percentage of cells that detach (global tests) and the manipulation of single cells in various configurations which lend themselves to more specific force application and provide the basis for theoretical analysis of the receptor-ligand mechanics.

In vitro evaluation of the biofunctionality of osteoblasts cultured on DegraPol-foam

The biofunctionality of osteoblasts cultured on DegraPol-foam, a biodegradable, elastic, and highly porous polyesterurethane-foam, was determined here to examine the possible use of this structure as bone repair material. Osteoblasts from rat tibia and from the cell line (MC3T3-E1) exhibited relatively high attachment and low doubling time that result in a confluent cell multilayer on the surface of the foam. They produced high concentrations of collagen type I and osteocalcin, and expressed increasing alkaline phosphatase activity. Exposure to 1,25-dihydroxy vitamin D (Vit. D) increased dose- and time-dependent alkaline phosphatase activity and osteocalcin concentration, and decreased the level of collagen type I and cell density. Maximal effects of Vit. D on alkaline phosphatase activity (2.2 fold), osteocalcin (1.5 fold), collagen type I (50% reduction), and on cell density (35% reduction) were found at 100 ng Vit. D ml(-1). Osteoblasts cultured on DegraPol-foam in the presence of Vit. D exhibited more spreading and less spindle-like morphology than cells cultured in the absence of Vit. D. Cell ingrowth into the pores of the foam was not affected by Vit. D treatment. Taken collectively, the osteoblasts, capability of responding to Vit. D confirms the osteoblast compatibility of DegraPol-foam and the possible use of this scaffold in the bone healing process.

Osteoblast adhesion on biomaterials

The development of tissue engineering in the field of orthopaedic surgery is now booming. Two fields of research in particular are emerging: the association of osteo-inductive factors with implantable materials; and the association of osteogenic stem cells with these materials (hybrid materials). In both cases, an understanding of the phenomena of cell adhesion and, in particular, understanding of the proteins involved in osteoblast adhesion on contact with the materials is of crucial importance. The proteins involved in osteoblast adhesion are described in this review (extracellular matrix proteins, cytoskeletal proteins, integrins, cadherins, etc.). During osteoblast/material interactions, their expression is modified according to the surface characteristics of materials. Their involvement in osteoblastic response to mechanical stimulation highlights the significance of taking them into consideration during development of future biomaterials. Finally, an understanding of the proteins involved in osteoblast adhesion opens up new possibilities for the grafting of these proteins (or synthesized peptide) onto vector materials, to increase their in vivo bioactivity or to promote cell integration within the vector material during the development of hybrid materials.

Soft tissue and epithelial models

The applicability of a biomaterial for the manufacturing of oral implants is determined by its physicochemical and geometric surface properties. Research, therefore, is concerned with the cellular reactions that occur when an implant material comes into contact with body tissues. For permucosal oral implants, this involves both the reaction of bone and gingival cells. In vitro cell culturing--including the use of various analytical techniques like light microscopy, scanning and transmission electron microscopy, confocal laser scanning microscopy, and digital image analysis--is a good tool whereby investigators can obtain more insight into the relevant components of implant-tissue adhesion. In the current overview, the role of cell models in oral implant research is discussed, specifically with reference to responses of epithelial cells and fibroblasts.

Cellular and cytoskeleton morphology and strength of adhesion of cells on self-assembled monolayers of organosilanes

The objective of this study was to explore the potential use of self-assembled monolayers (SAMs) of alkylamine and arylalkyamine as well-defined, homogeneous, tailored in vitro model surfaces for exploring the effect of hydrodynamic flow on morphology and strength of adhesion of human umbilical vein endothelial cells. The cell surface area, shape, f-actin distribution, and adhesion strength of human umbilical vein endothelial cells cultured on self-assembled monolayers of organosilanes were found to be dependent on the chemical composition of the organosilane film and the magnitude of wall shear stress. The direct effects of the differences in chemistry between the two silanes, in modulating cellular response, are probably only secondary to the modulation of cellular functions mediated by differential protein adsorption and conformation on the two silanes. For short seeding times (30 min), prior to application of flow, both substrate chemistry and shear stress modulated the cellular morphology and cytoskeletal organization. For longer seeding times (24 h), prior to application of flow, the chemistry of the underlying surface was the dominant variable in modulating cellular morphology, while the hydrodynamic shear stress modulated the cytoskeleton organization. Cells on N-(2-aminoethyl)-3-aminopropyl trimethoxysilane (EDA) were pleomorphic, while cells on ((((aminoethyl)amino)methyl)phenylethyl)trimethoxysilane (PEDA) expressed a rounded morphology. Application of an incrementally loaded flow regime (0.07-1.25 ml/s) resulted in a time- and shear stress-dependent (10-180 dyn/cm2) detachment of cells, with the cells on EDA depicting higher resistance to wall shear stress. Cellular morphology correlated with the strength of adhesion; cells with rounded morphology on a hydrophobic silane, PEDA, were less tightly bound to the silane, while spread cells on a hydrophilic silane, EDA, were more tightly bound. The higher surface free energy of EDA is speculated to influence the increased cell spreading and strength of adhesion observed in these studies. The presence of the phenyl group in PEDA reduces the surface free energy and may account for the reduced spreading and lower strength of adhesion. The use of well-defined systems, such as monolayer organosilanes, with tunable surface physicochemical properties may serve to deconstruct the complex interaction of cells with extracellular matrix components: surface charge, surface hydrophobicity, and other short- and long-range forces can be individually controlled and correlated with cellular functions. The organosilane monolayers could serve as the building blocks for sequential addition of proteins or cell adhesive/cell repulsive cues to stepwise engineering and construction of more complex systems resembling ECM matrices.

Degradable and highly porous polyesterurethane foam as biomaterial: effects and phagocytosis of degradation products in osteoblasts

Recently, a new class of biodegradable PHB-based polyesterurethane (DegraPol/btc) has been prepared and found to exhibit favorable cell and tissue compatibility. The present study has been designed to evaluate the response of primary isolated rat tibia osteoblasts to small crystalline particles of short-chain poly[(R)-3-hydroxybutyric acid] (PHB-P diameter: 2-20 microm), of fluorescent-labeled analogs (DPHP-P), and of lysine methyl ester as possible degradation products of DegraPol/btc. Observations made using confocal microscopy clearly indicate that osteoblasts have the capability of taking up PHB-P particles. Although in single-cell analysis the number of DPHB-P-positive osteoblasts gradually increased up to 16 days, the fluorescence intensity per osteoblast increased only during the first 4 h after DPHB-P incubation, and then it retained the 4 h level up to 16 days. No significant change in the production levels of collagen type I and osteocalcin was detectable after treatment with low concentrations of PHB-P for up to 32 days. In contrast, a time- and dose-dependent alteration of the alkaline phosphatase (ALP) activity was found. Maximal activity was measured after 4 days of treatment with 2 microg of PHB-P/mL (170% of control cells). Rat peritoneal macrophages co-cultured with osteoblasts in a transwell culture system mimicked the observed PHB-P induced ALP elevation. Therefore, the PHB-P-induced ALP increase could be the result of direct or indirect stimulation of osteoblasts, possibly via soluble factors produced by contaminating osteoclasts. Taken collectively, the data demonstrate that osteoblasts are capable of phagocytosing PHB-P and that this process is accompanied at low PHB-P concentrations by dose- and time-dependent alteration of alkaline phosphatase activity but not of collagen type I or osteocalcin.

Red blood cell adhesion on a solid/liquid interface

Red blood cells (RBCs), previously fixed with glutaraldehyde, adhere to glass slides coated with fibrinogen. The RBC deposition process on the horizontal glass surface is investigated by analyzing the relative surface covered by the RBCs, as well as the variance of this surface coverage, as a function of the concentration of particles. This study is performed by optical microscopy and image analysis. A model, derived from the classical random sequential adsorption model, has been developed to account for the experimental results. This model highlights the strong influence of the hydrodynamic interactions during the deposition process.

Interactions of osteoblasts and macrophages with biodegradable and highly porous polyesterurethane foam and its degradation products

The macrophage cell line J774, primary rat osteoblasts, and the osteoblast cell line MC3T3-E1 were used to examine the biocompatibility of a newly developed polyesterurethane foam and the possible use of this structure as bone-repair materials. The newly developed, biodegradable, and highly porous (pore size 100-150 microns) DegraPol/btc polyesterurethane foam was found to exhibit good cell compatibility; the cell-to-substrate interactions induced neither cytotoxic effects nor activation of macrophages. Osteoblasts and macrophages exhibited normal cell morphology. No signs of cell damage were detected using scanning electron microscopy (SEM). No significant increase in the production of tumor necrosis factor-alpha (TNF-alpha) or nitric oxide (NO) was detected in macrophages. Compared with cells cultured on tissue culture polystyrene (TCPS), macrophages exhibited relatively high cell attachment (150% of TCPS) but significantly high doubling time (about 8 days) compared with TCPS (4.6 days). Primary rat osteoblasts and the osteoblast cell line exhibited relatively high attachment (140% and 180% of TCPS, respectively) and a doubling time of about 5 days, compared with TCPS (6 days and 8.8 days, respectively). Eight days after cell seeding, osteoblasts exhibited a confluent cell multilayer and migrated into the pores of the polymer. In addition they produced high concentrations of collagen type I, the main protein of the bone, and expressed increasing alkaline phosphatase activity and osteocalcin production throughout the 12 days of the experiment. During degradation of these polymers, small crystalline particles of short-chain poly[(R)-3-hydroxybutyric acid] (M(n) approximately 2300) (PHB-P) are released. Therefore PHB-P (diameter, 2-20 microns), as possible degradation products of the polymer, are investigated here for their effects on macrophages and osteoblasts. Results obtained in the present study clearly indicate that macrophages and, to a lesser degree, osteoblasts have the ability to take up (phagocytose) PHB-P. At low concentrations particles of PHB failed to induce cytotoxic effects or to activate macrophages. Osteoblasts showed only limited PHB-P phagocytosis and no signs of cellular damage. At high concentrations of PHB-P, this process was accompanied by cytotoxic effects in macrophages (> 200 pg PHB-P/cell) and to a lesser extent in osteoblasts (> 400 pg PHB-P/cell).

Fibroblast growth on polymer surfaces and biosynthesis of collagen

The growth and morphology of rat fibroblasts cultured on various polymer substrates, as well as their collagen biosynthesis, were studied. A clear difference in cell growth and cell morphology was observed among the substrates. The dependence of cell growth on the water contact angle of substrate was similar to that of the adhesion. Fibroblasts could proliferate at the highest rate and showed the highest-ordered morphology when cultured on the substrate with a contact angle around 70 degrees, which was also the most favorable for cell adhesion. The amount of collagen synthesized by total cells and of adsorption of the synthesized collagen to substrates were in good correlation with the cell growth dependence on the contact angle of substrate, whereas the collagen synthesis per cell was more active on the surfaces poor for cell growth than on the good ones. Cells on surfaces promoting active collagen synthesis had a round shape and clustered upon each other. The collagen-immobilized surface had nearly the highest cell adhesion, high cell proliferation, and high collagen adsorption among the substrates studied. In addition, the highest-ordered morphology and no lag time for proliferation were observed for the collagen-immobilized surface. These results indicate that the collagen-immobilized substrate provides the most favorable surface for cell growth at the initial stage.

The effect of ion implantation on cellular adhesion

As there are only a finite number of materials suitable for orthopaedic reconstruction, considerable effort has been devoted recently to investigating ways of altering the surface chemistry of prosthetic materials without altering their bulk properties. Ion beam implantation is one such technique which is appropriate for orthopaedic reconstructive materials. This paper investigates the early effect of ion beam modification on cellular attachment of bone derived cells using a prototype device which measures the strength of attachment of individual cells to a silicon substratum. The results point to several conclusions. (1) There is no evidence that ion beam implantation with nitrogen, phosphorus, manganese or magnesium produces increased adhesion of human bone derived cells. (2) Surface etching with hydrofluoric acid, electron bombardment and thermal oxidation increases the strength of attachment between cells and substrata. (3) There is a correlation between wettability and rate of cellular attachment to oxygen implanted substrata during the first 2 h after cellular seeding. However, the increase in cellular attachment cannot be entirely explained by the change in critical surface tension or via increased fibronectin attachment to the substrata.

Development and use of a parallel-plate flow chamber for studying cellular adhesion to solid surfaces

A parallel-plate flow chamber is developed in order to study cellular adhesion phenomena. An image analysis system is used to observe individual cells exposed to flow in situ and to determine area, perimeter, and shape of these cells as a function of time and shear stress. With this flow system the behavior of human fibroblasts spread on glass is studied when exposed to an increasing laminar flow. The flow system appears to be well-suited for following individual cells during detachment. After 75 to 90 min, at a shear stress of 350 dynes/cm2, more than 50% of the spread cells are detached from the surface. Cells with higher spreading areas stay longer at the glass surface. Cells round up before detaching. Sometimes the cell body is attached to the substratum through a thin filament during detachment. At the scanning electron microscopy level numerous filopodial extensions are observed. Cell material could only rarely be observed at the light or scanning electron microscopic level on the substratum once a cell was detached.

Influence of glutaraldehyde fixation of cells adherent to solid substrata on their detachment during exposure to shear stress

In order to determine the response of fixed and nonfixed cells adherent to a solid substratum to shear stress, human fibroblasts were allowed to adhere and spread on either hydrophilic glass or hydrophobic Fluoroethylene-propylene (FEP-Teflon) and fixed with glutaraldehyde. Then, the cells were exposed to an incrementally loaded shear stress in a parallel plate flow chamber up to shear stresses of about 500 dynes/cm2, followed by exposure to a liquid-air interface passage. The cellular detachment was compared with the one of nonfixed cells. In case of fixed cells, 50% of the adhering cells detached from FEP-Teflon at a shear stress of 350 dynes/cm2, whereas 50% of the adhering, nonfixed cells detached already at a shear stress of 20 dynes/cm2. No fixed cells detached from glass for shear stresses up to at least 500 dynes/cm2. More than 50% of the nonfixed cells were detached from glass at a shear stress of 350 dynes/cm2. Furthermore, the shape and morphology of fixed cells did not change during the incrementally loaded flow, in contrast to the ones of nonfixed cells, which clearly rounded up prior to detachment.

Influence of substratum wettability on the strength of adhesion of human fibroblasts

To determine the strength of adhesion and the detachment mechanisms of fibroblasts from substrata with different wettability, the behaviour of adhered cells was studied in a parallel-plate flow chamber during exposure to shear. Adhered cells were observed in situ, i.e. in the flow chamber, by phase-contrast microscope and images were analysed semiautomatically. Detachment was found to be dependent both on shear stress and time, although a critical shear stress can be found below which no detachment occurs. On all substrata, cells round up before detachment and are approximately spherical immediately before detachment. The strength of adhesion calculated ranged from 0.6-3.5 x 10(-10) N per cell on FEP-Teflon (the least wettable material included) to 9.4 x 10(-9) N per cell for glass (the most wettable). Ease of detachment seemed to decrease with increasing wettability. However, cells reacted more strongly with tissue culture polystyrene (TCPS) than expected on the basis of its wettability, probably due to surface chemistry.

On the shape of human red blood cells interacting with flat artificial surfaces--the 'glass effect'

The morphology of the human red blood cell (RBC) contained between two flat artificial surfaces has been investigated. Shape transformation from the discocytic into various crenated (echinocytic) states was not caused solely by glass ('glass effect'). Various organic polymers, and mica, were effective, provided the distance (0.1 mm) between the two surfaces was carefully controlled. The discocytic state could only be preserved using moderately hydrophobic glass, extensive dimethylsilylation induced stomatocytes. With washed blood samples crenation occurred in a potassium chloride medium and in the presence of EDTA. Temperature-dependent transformation in the shape of human erythrocytes occurred between two glass surfaces 0.1 mm apart, e.g., in a hemacytometer. With cells in blood diluted directly 200-times with isotonic saline crenation appeared at 32-36 degrees C. A sphero-echinocytic state prevailed at 34 degrees C and outside the temperature range of 32-36 degrees C the RBCs retained the shape of a biconcave disk. Cells responding to the 'glass effect' even at temperatures below the transition region did not respond further at elevated temperatures. The 'glass effect' was found to be dependent on the RBC concentration (hematocrit). Raising this concentration reversibly decreased the degree of crenation. The amount of endogenous albumin present was estimated to be insufficient to cover the exposed glass surfaces with a protein monolayer. With washed cells over a wide concentration range, approximately the same total amount of albumin (serum) had to be present to avoid crenation, as long as observation was performed at a fixed low cell concentration. The effect of albumin was not abolished by gamma-globulin or anti-human albumin IgG. The discocyte-stabilizing influence of albumin is discussed.