The surface plate is partially immerged in the up down moving liquid container. When a substrate is immersed in a liquid, three forces occur see Figure 4 : the gravity force, the upthrust buoyancy and the capillary forces. Therefore, by measuring the applied force according to the immersion depth and as we previously know the dimension of the substrate; one can calculate the wetting forces according to the equation [ 22 ]:. Moreover, the substratum weight is assumed to be nil by a direct correction fixing the pre-immersion force to the value of zero.
Therefore, the previous equation [Eq. As the surface energy of the liquid of measurement is previously known, therefore the contact angle could be deduced. It has been shown that the contact angle changes depending on the nature of the film and on its charges and thickness. The nature of liquid of measurement, the speed and temperature of measurement are also involved in this change [ 23 ]. A previous study made by Elbert et al. The liquid used for measurement can affect the surface wettability by the mean of its pH which varies from a liquid to another and controls the acid or base character as well as the liquid polarity.
This reorganization is also depending on the liquid diffusion into the polymer and on the effect of solubilization induced by the liquid to this polymer. This phenomenon represents an interesting mechanism for explaining contact angle hysteresis especially when the liquid concerned is water. Indeed, water has small molecules which allow it to diffuse easily. Therefore, after diffusion into a polymer, water will confer its hydrophilic character to this polymer which is being to have some kind of elasticity responsible for the reorganization of its polar groups as a reaction to the high surface energy level of water which is responsible for the high energy level at the interface [ 25 ].
Concerning the dynamic contact angle measurement speed, it affects the contact period between the biomaterial and the liquid and therefore it will change the period of time needed for the rearrangement of the surface polar groups during contact with the liquid. As each film has its own defined reorganization time, therefore different contact angles were found for the same surface at different measurement speeds.
Moreover, every polymer has a defined glass transition temperature T g able to induce a change on the surface wettability depending on the temperature of measurement [ 26 ]. It consists in the following equation [ 27 ]:. The different components of the solid and the liquid surface free energies as well as the contact angle are related by this equation :.
For this purpose, we used three different liquids: water, diiodomethane and formamide. Theses parameters are deduced from the shapes of the curves drawn loops. Indeed, the more the surface is rough; the more the curve is deformed non linear curve. However, the more the surface is smooth; the more the curve presents a linear shape no deformations observed. Otherwise, a roughness of about nm has been shown to induce contact angle hysteresis.
As for surface heterogeneity, it can be concluded from the different contact angle hysteresis values measured in the case of a negligible roughness. Concerning the different polyelectrolyte films used in this study, a previous investigation was made by Picart and coworkers [ 30 ]. They measured the roughness by the AFM technique, refractive index and thickness are estimated by optical waveguide light mode spectroscopy, and zeta potential is measured by streaming potential measurements.
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Indeed, these parameters give us information about the chemical heterogeneity of the polyelectrolyte used. Many studies had observed an important dependence of the contact angle hysteresis on the surface composition and topography roughness [ 31 , 32 ]. According to Morra et al. When a drop of liquid is placed on a solid surface, the liquid will either spread across the surface to form a thin, approximately uniform film or spread to a limited extent but remain as a discrete drop on the surface.
The final condition of the applied liquid to the surface is taken as an indication of the wettability of the surface by the liquid or the wetting ability of the liquid on the surface. The quantitative measure of the wetting process is taken to be the contact angle, which the drop makes with the solid as measured through the liquid in question. The wetting of a surface by a liquid and the ultimate extent of spreading of that liquid are very important aspects of practical surface chemistry.
Many of the phenomenological aspects of the wetting processes have been recognized and quantified since early in the history of observation of such processes. However, the microscopic details of what is occurring at the various interfaces and lines of contact among phases has been more a subject of conjecture and theory than of known facts until the latter part of this century when quantum electrodynamics and elegant analytical procedures began to provide a great deal of new insight into events at the molecular level. Even with all the new information of the last 20 years, however, there still remains a great deal to learn about the mechanisms of movement of a liquid across a surface.
Fibroblasts are spindle-shaped connective-tissue cells of mesenchymal origin that secretes proteins and especially molecular collagen from which the extracellular fibrillar matrix of connective tissue forms. They have oval or circular nucleus and a little developed cytoplasm giving rise to long prolongation forms [ 34 ]. These cells do not have a basal lamina and their surfaces are often in contact with the fibers of the collagen.
Their cytoplasm contains a rough endoplasmic reticulum, an important Golgi apparatus, few mitochondria and a little bit quantity of cytoplasmic filaments. Fibroblasts synthesize enormous quantities of the extracellular matrix constituents. Indeed, the majority part of the extracellular matrix components consists of collagen made in the intracellular space where fibroblasts sustain structural modifications. It consists in a pink connective tissue with fibrous collagen surrounded by an epithelial tissue.
Its pink color changes from one person to another, depending on pigmentation, epithelium thickness, its keratinization level and on the underlying vascularization [ 36 ]. Fibroblasts are the basic component of the gingival chorion whose intercellular matrix is essentially formed by collagen and elastin. While a cell is in contact with a biomaterial, many reactions can occur and a sensing phenomenon will launch between this cell and the biomaterial [ 37 ]. Indeed, the cell has a signal network reached as a result of the surface exploration and sensing made in order to verify whether the new environment biomaterial is in accordance with its expected physiological conditions necessary for a normal biological activity [ 38 ].
In one word, this material must be biocompatible. Indeed, biocompatibility includes the understanding of the interactive mechanisms relating the biomaterial with its biological environment. Generally, biocompatibility represents the ability of a material to be accepted by a living organism. In , Williams D. Indeed, biocompatibility is a group of networks that liaises between the biomaterial and its environment and takes into account the possible effect of this biomaterial on its environment and vice versa.
Characterizing the surface properties of a biomaterial before putting it in contact with a cell seems to be an obligation. This step allows us to know about different parameters and characters of this biomaterial topography, roughness, surface energy etc. It is well known that during the contact between a cell and a material, information will be transferred from the material surface to the cell and this contact will induce, in return, an alteration to the material. This situation may cause material remodelling [ 40 , 22 ].
Cells adhere to surfaces through adhesion proteins i. Indeed, when fibroblasts grow on a substrate, most of their cell surface is separated from the substratum by a gap of more than 50 nm; but at focal contacts, this gap is reduced to 10 to 15 nm. The main transmembrane linker proteins of focal contacts belong to the integrin family and the cytoplasmic domain of the integrin binds to the protein talin, which in turn binds to vinculin, a protein found also in other actin-containing cell junction.
Besides their role as anchors, focal contacts can also relay signals from the extracellular matrix ECM to the cytoskeleton. Several protein kinases are localized to focal contacts and seems to change their activity with the type of the substratum on which the rest. These kinases can regulate the survival, growth, morphology, movement, and differentiation of cells in response to new environment. Figure 5 shows a possible arrangement of these different proteins during a focal contact.
The formation of focal contacts occurs when the binding of matrix glycoprotein, such as fibronectin, on the outside of the cell causes the integrin molecules to cluster at the contact site. Fibronectins are associated together by proteoglycans and constitute thins fibers of the extracellular matrix ECM. The extracellular matrix ECM represents an important element in the processes of cell adhesion. Indeed, at this level, cell adhesion is under the control of a well defined zone in the cytoplasmic membrane called focal contact.
At this zone, filaments of actin are linked to fibronectin through an intracellular complex of proteins, the adherence complex. The extracellular matrix ECM is made of different proteins such as fibronectins, collagen, laminin, vitronectin [ 41 ] and represents the mediator of cell adhesion thanks to its integrins. Although the extracellular matrix generally provides mechanical support to tissues, it serves several other functions as well. Different combinations of ECM components tailor the extracellular matrix for specific purposes: strength in a tendon, tooth, or bone; cushioning in cartilage; and adhesion in most tissues.
In addition, the composition of the matrix, which can vary, depending on the anatomical site and physiological status of a tissue, can let a cell know where it is and what it should do environmental cues. Changes in ECM components, which are constantly being remodeled, degraded, and resynthesized locally, can modulate the interactions of a cell with its environment. The matrix also serves as a reservoir for many extracellular signalling molecules that control cell growth and differentiation.
In addition, the matrix provides a lattice through or on which cells can move, particularly in the early stages of tissue assembly [ 42 ].
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Many functions of the matrix require transmembrane adhesion receptors that bind directly to ECM components and that also interact, through adapter proteins, with the cytoskeleton. Different proteins and their receptors are involved in fibroblast cells adhesion process. The most important and known are fibronectins and their receptors; integrins:. Fibronectins are dimers of two similar polypeptides linked at their C-termini by two disulfide bonds; each chain is about 60—70 nm long and 2—3 nm thick. The combination of different repeats composing the regions, another example of combinatorial diversity, confers on fibronectin its ability to bind multiple ligands [ 40 ].
Fibronectins help attach cells to the extracellular matrix by binding to other ECM components, particularly fibrous collagens and heparan sulfate proteoglycans, and to cell surface adhesion receptors such as integrins. Through their interactions with adhesion receptors e. Conversely, by regulating their receptor-mediated attachments to fibronectin and other ECM components, cells can sculpt the immediate ECM environment to suit their needs.
They have diverse roles in several biological processes including cell migration during development and wound healing, cell differentiation, and apoptosis. Their activities can also regulate the metastatic and invasive potential of tumor cells. They exist as heterodimers consisting of alpha and beta subunits.
Some alpha and beta subunits exhibit specificity for one another, and heterodimers often preferentially bind certain cell adhesion molecules, or constituents of the ECM. Although they themselves have no catalytic activity, integrins can be part of multimolecular signalling complexes known focal adhesions.
The two subunits, designated as alpha and beta, both participate in binding. Integrins participate in cell-cell adhesion and are of great importance in binding and interactions of cells with components of the extracellular matrix such as fibronectin.
Thermodynamic aspects of plant cell adhesion to polymer surfaces
Importantly, integrins facilitate "communication" between the cytoskeleton and extracellular matrix; allow each to influence the orientation and structure of the other. It is clear that interactions of integrins with the extracellular matrix can have profound effects on cell function, and events such as clustering of integrins activates a number of intracellular signally pathways. Biological systems exhibit electromagnetic activity in a wide frequency range from the static or quasistatic electric field to optical bands. Vibrations in biological molecules, therefore, generate an electromagnetic field [ 44 ].
Pokorny et al. Surface topography is of an important interest in cell adhesion as well as its chemical composition. Indeed, it has been shown that cells adhere and proliferate depending on the surface roughness and the more the surface is rough the more cell adhesion and proliferation is better [ 46 ]. This effect depends on the cell type. For fibroblasts, they line up along the biomaterial surface microstructures and may adapt their shape with uneven surfaces. Moreover, recent studies had shown that a weak change in the surface roughness may induce different cell reactions such as change in their shape and their way of adhesion [ 47 , 48 ].
According to Richards [ 49 ], cell adhesion to biomaterials is done thanks to focal adhesion sites which represent strict contact sites with the substrate in a so limited space. For fibroblasts, it has been shown the existence of a force called cohesion force responsible for keeping contact between cells themselves. However, this force is weaker than the adhesion force involved while a cell adheres to a biomaterial. This difference in force level depends on the cell type and on the nature of the biomaterial used for adhesion, and may explain the different ways of cell adhesion and spreading on different surface structures.
Surface free energy is a thermodynamic measurement which contributes to the interpretation of the phenomena occurring in interfaces. It has an important effect on cell adhesion in the way that every change in its value induces the modification of the surface wettability, and therefore cell behaviour will be affected too [ 50 , 51 , 52 ].
Cell-biomaterial interface depends on the physico-chemical properties of the biomaterial and every change in the chemical composition or in the electric charge of the surface will affect its surface free energy. Surface roughness has been the subject of many studies as a deciding factor in the process of cell adhesion to biomaterials. Ponsonnet et al. Indeed, these cells presented a flattened shape spreading practically over the substrate surface after adhesion to smooth surfaces.
However, on rough surfaces, cell morphology was affected by the surface grooves and they were reoriented by the surface structure.
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According to Richards [ 48 ], smooth titanium surfaces always increase fibroblasts adhesion and proliferation better than rough surfaces. They suggested that this kind of surfaces should be a better candidate for biological implant thanks to their ability to resist to bacterial infections. Indeed, their weak roughness is unfavourable to the adhesion of bacteria.
In the majority of the studies carried out about biomaterials made from polyelectrolyte film, as in our case, the electric charge effect is in proportion with the thickness of the film built and depends on the charged functional group of the polyelectrolyte used [ 54 ].
However, it has been shown that a better adhesion of cells was observed on negatively charged polyelectrolyte [ 55 ]. In reality, most of the existed cells and their corresponding adhesion proteins are negatively charged. Nevertheless, this charge can be without any effect in the case when functional groups become able to control cell adhesion mechanism by their hydrophilic or hydrophobic character as it will be shown later in this text.
Dubois [ 56 ] presumed that an electric charge trapped within an insulating biomaterial, none associated to a particular chemical group, is able to affect its biological environment. Moreover, Maroudas [ 57 ] revealed the dependence of cell adhesion and spreading on a solid surface on the surface charge of the substrate. The different chemical components of a biomaterial must be studied and known before to start investigating cell adhesion to that biomaterial.
Therefore, this step is fundamental for concluding about the biocompatibility of a given biomaterial and its effect on cell adhesion [ 58 ].
The wettability of a surface depends on the chemical composition of the material and each change than can occur at this level will disturb cell adhesion process [ 59 ]. Besides the effect of the biomaterial, the adhered cell type plays an important role in adhesion. Indeed, for the same biomaterial surface, different cell reactions were observed for two types of cells [ 60 ]; this kind of biomaterial seems to be biocompatible with one cell type but not tolerated by the other cell type.
According to Marmur [ 61 ], most of the materials in the nature are rough and heterogeneous and contact angle may change along the contact line with a value depending on the roughness and heterogeneity level. Contact angle measurement allows us to calculate surface free energy [ 62 ]. Moreover, one can deduce from it the hydrophilic or the hydrophobic character of a surface [ 63 ]. A study about polyelectrolyte films found that hydrophobic interactions on a surface induce the adsorption of proteins and stabilise the complex formed [ 64 ].
Indeed, it has been proved that myoglobin or lysozymes are able to adhere to polystyrene sulfonate PSS and form many layers. However, this adhesion was not possible when using another surface having the same electric charge as PSS but with a hydrophilic character. The electrostatic interactions between the protein complex and this hydrophilic surface were easily destructed after water rinsing. Thus, surface hydrophilicity and hydrophobicity are a determinant parameter for substrate wettability on account of the rearrangement of the functional groups at the surface of a biomaterial in contact with a cell [ 65 , 66 , 67 ].
Indeed, it has been shown that fibroblast cells adhere and proliferate better on biomaterials with a moderate hydrophilicity [ 68 , 69 ]. Andrade [ 66 ] presumed that, in the case of deformable materials, an elasticity model of 3. A roughness below 0. The same author estimated that the majority of polymers have a changeable volume which can be the reason for contact angle change: this change is depending on the duration of the contact with water, on the nature of the liquid and on the temperature of measurement. Non existent contact angle hysteresis may be due to the duration of contact between the material and the liquid which is shorter or longer than the measurement time needed for recording contact angle change.
Therefore, surface hydrophilicity and hydrophobicity depends on the volume blowing of the material, on the diffusion phenomenon and on the mobility and reorientation of the molecules on the material surface. Some materials are able to go out of shape in contact with a liquid depending on their mechanical properties and on their relaxation time and temperature. So, what characterizes a polymer is its chemical composition, roughness, mobility, wettability, surface free energy and its electric charge [ 70 ]. Contact angle hysteresis is the result of contact angle change between the surface we are characterizing and another ideal surface physico-chemically homogeneous.
According to Rupp et al. Immersion and emersion loops showing the two types of hysteresis: A : thermodynamic hysteresis and B : kinetic hysteresis. The sample is repeatedly immersed in the liquid leading to typical hysteresis loops. From each loop, wettability parameters advancing and receding contact angle or wetting tension can be calculated.
Thermodynamic hysteresis is due to the surface roughness and heterogeneity. Contact angle hysteresis is often assigned to the surface roughness and heterogeneity. Actually, a study made by Lam et al. Liquid resorption and retention are the direct causes of hysteresis. Indeed, liquids having smaller molecular chains or smaller molecular weight diffuse faster into the polymer surface leading to an important decrease in contact angle.
According to Shananan et al. In the other hand, when the polymer is contact with a non polar liquid, its functional groups conserve their state and will not reorient. These authors assumed the existence of two parameters behind hysteresis: the intrinsic polarity of the material and the mobility of its polar groups on the surface.
Nishioka et al. This reorientation represents the polymer reaction to every environmental change air, liquid. Each material has its own glass transition temperature T g allowing a defined molecular mobility sufficient for an important rearrangement [ 74 ]. The concepts of solid surfaces assumed that the surfaces in question were effectively rigid and immobile. Such assumptions allow one to develop certain models and mathematical relationships useful for estimating and understanding surface energies, surface stresses, and specific interactions, such as adsorption, wetting, and contact angles.
It is assumed that the surfaces themselves do not change or respond in any specific way to the presence of a contacting liquid phase, thereby altering their specific surface energy [ 75 ]. Although such assumptions are or may be valid for truly rigid crystalline or amorphous solids, they more often than not do not apply strictly to polymeric surfaces.
In contact with condensed phases, especially liquids, surface relaxations and transitions can become quite important leading to a possible dramatically change in the interfacial characteristics of a polymer with possibly important consequences in a particular application. And since the processes are time-dependent, the changes may not be evident over the short span of a normal experiment. For critical applications in which a polymer surface will be in contact with a liquid phase, such as implant device for biomedical application, it is not only important to know the surface characteristics e.
A surface chemistry approach to studying cell adhesion - Chemical Society Reviews (RSC Publishing)
It is therefore important for biomedical as well as many other applications that the surface characteristics of a material of interest be determined under conditions that mimic as closely as possible the conditions of use and over extended periods of exposure to those conditions, in addition to the usual characterizations. Before use, glass slides were cleaned in 0. Polyelectrolyte solutions were prepared by dissolution of the polyelectrolyte powders in 0. Cleaning was made before film characterization. The films were all prepared at the same pH before being in contact with culture medium.
The measurements were performed with a Wilhelmy balance for the characterization of solids using the 3S tensiometer and the corresponding software GBX, France. For these experiments, the glass slides were coated with polyelectrolyte multilayer films on both sides. Before beginning the measurements, the films were washed in Solid and liquid SFE components and contact angle are related according to the equation below:.
Microscope focus and stage were motorized and software controlled. The cell viability was determined with the MTT colorimetric assay. Amazon Global Store US International products have separate terms, are sold from abroad and may differ from local products, including fit, age ratings, and language of product, labeling or instructions. Manufacturer warranty may not apply Learn more about Amazon Global Store.
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