by Keyword: Collagen
Lehmann, J., Praktiknjo, M., Nielsen, M. J., Schierwagen, R., Meyer, C., Thomas, D., Violi, F., Strassburg, C. P., Bendtsen, F., Moller, S., Krag, A., Karsdal, M. A., Leeming, D. J., Trebicka, J., (2019). Collagen type IV remodelling gender-specifically predicts mortality in decompensated cirrhosis Liver International 39, (5), 885-893
Background & Aims: Remodelling of extracellular matrix is crucial in progressive liver fibrosis. Collagen type III desposition has been shown in acute decompensation. Extratracellular matrix is compiled of deposition of various components. The role of basement membrane collagen type IV in advanced cirrhosis and acute decompensation is unclear and investigated in this study. Methods: Patients with decompensated cirrhosis from the prospective NEPTUN cohort (ClinicalTrials.gov Identifier: NCT03628807), who underwent transjugular intrahepatic portosystemic shunt procedure were included. Clinical and laboratory parameters, PRO-C4 and C4M levels were measured in blood samples from portal and hepatic veins just before transjugular intrahepatic portosystemic shunt placement. Results: Levels of C4M and PRO-C4 are significantly lower in patients with massive ascites and impaired renal sodium excretion. C4M and PRO-C4 show gender-specific profiles with significantly lower levels in females compared to males. Females with higher C4M levels show higher mortality. By contrast, males with higher C4M levels show lower mortality. In multivariate Cox regression analysis, C4M is an independent predictor of survival in female patients. Conclusion: This study shows that markers of collagen type IV remodelling do not accumulate in severe renal dysfunction. Although collagen type IV degradation markers derive from the liver, portal venous C4M levels are relevant for survival. Moreover, it demonstrates that circulating C4M shows gender-specific profiles, which can independently predict survival in female patients with decompensated cirrhosis.
Keywords: ACLF, Acute decompensation, Acute-on-chronic liver failure, Cirrhosis, Collagen type IV, Extracellular matrix remodelling, Gender, Liver, Portal hypertension, Transjugular intrahepatic portosystemic shunt
Malandrino, Andrea, Trepat, Xavier, Kamm, Roger D., Mak, Michael, (2019). Dynamic filopodial forces induce accumulation, damage, and plastic remodeling of 3D extracellular matrices PLoS Computational Biology PLOS Computational Biology , 15, (4), e1006684
The mechanical properties of the extracellular matrix (ECM)–a complex, 3D, fibrillar scaffold of cells in physiological environments–modulate cell behavior and can drive tissue morphogenesis, regeneration, and disease progression. For simplicity, it is often convenient to assume these properties to be time-invariant. In living systems, however, cells dynamically remodel the ECM and create time-dependent local microenvironments. Here, we show how cell-generated contractile forces produce substantial irreversible changes to the density and architecture of physiologically relevant ECMs–collagen I and fibrin–in a matter of minutes. We measure the 3D deformation profiles of the ECM surrounding cancer and endothelial cells during stages when force generation is active or inactive. We further correlate these ECM measurements to both discrete fiber simulations that incorporate fiber crosslink unbinding kinetics and continuum-scale simulations that account for viscoplastic and damage features. Our findings further confirm that plasticity, as a mechanical law to capture remodeling in these networks, is fundamentally tied to material damage via force-driven unbinding of fiber crosslinks. These results characterize in a multiscale manner the dynamic nature of the mechanical environment of physiologically mimicking cell-in-gel systems.
Keywords: Collagens, Fibrin, Extracellular matrix, Cross-linking, Cell physiology, Deformation, Fluorescence imaging, Cell biology
de la Mata, Ana, Mateos-Timoneda, Miguel A., Nieto-Miguel, Teresa, Galindo, Sara, López-Paniagua, Marina, Planell, Josep A., Engel, Elisabeth, Calonge, Margarita, (2019). Poly-l/dl-lactic acid films functionalized with collagen IV as carrier substrata for corneal epithelial stem cells Colloids and Surfaces B: Biointerfaces 177, 121-129
Limbal epithelial stem cells (LESCs) are responsible for the renewal of corneal epithelium. Cultivated limbal epithelial transplantation is the current treatment of choice for restoring the loss or dysfunction of LESCs. To perform this procedure, a substratum is necessary for in vitro culturing of limbal epithelial cells and their subsequent transplantation onto the ocular surface. In this work, we evaluated poly-L/DL-lactic acid 70:30 (PLA) films functionalized with type IV collagen (col IV) as potential in vitro carrier substrata for LESCs. We first demonstrated that PLA-col IV films were biocompatible and suitable for the proliferation of human corneal epithelial cells. Subsequently, limbal epithelial cell suspensions, isolated from human limbal rings, were cultivated using culture medium that did not contain animal components. The cells adhered significantly faster to PLA-col IV films than to tissue culture plastic (TCP). The mRNA expression levels for the LESC specific markers, K15, P63α and ABCG2 were similar or greater (significantly in the case of K15) in limbal epithelial cells cultured on PLA-col IV films than limbal epithelial cells cultured on TCP. The percentage of cells expressing the corneal (K3, K12) and the LESC (P63α, ABCG2) specific markers was similar for both substrata. These results suggest that the PLA-col IV films promoted LESC attachment and helped to maintain their undifferentiated stem cell phenotype. Consequently, these substrata offer an alternative for the transplantation of limbal cells onto the ocular surface.
Keywords: Corneal epithelium, Collagen IV, Limbal stem cells, Polylactic acid, Tissue engineering
Hristova-Panusheva, K., Keremidarska-Markova, M., Altankov, G., Krasteva, N., (2017). Age-related changes in adhesive phenotype of bone marrow-derived mesenchymal stem cells on extracellular matrix proteins Journal of New Results in Science , 6, (1), 11-19
Mesenchymal stem cells (MSCs) are a promising cell source for cell-based therapies because of their self-renewal and multi-lineage differentiation potential. Unlike embryonic stem cells adult stem cells are subject of aging processes and the concomitant decline in their function. Age-related changes in MSCs have to be well understood in order to develop clinical techniques and therapeutics based on these cells. In this work we have studied the effect of aging on adhesive behaviour of bone marrow-derived MSC and MG- 63 osteoblastic cells onto three extracellular matrix proteins: fibronectin (FN), vitronectin (VN) and collagen I (Coll I). The results revealed substantial differences in adhesive behaviour of both cell types during 21 days in culture. Bone-marrow derived MSCs decreased significantly their adhesive affinity to all studied proteins after 7th day in culture with further incubation. In contrast, MG-63 cells, demonstrated a stable cell adhesive phenotype with high affinity to FN and Coll I and low affinity to vitronectin over the whole culture period. These data suggest that adhesive behaviour of MSCs to matrix proteins is affected by aging processes unlike MG-63 cells and the age-related changes have to be considered when expanding adult stem cells for clinical applications.
Keywords: Cell morphology, Cell attachment and spreading, Fibronectin, Vitronectin, Collagen I
Li, Haiyue, Xu, Bin, Zhou, Enhua H., Sunyer, Raimon, Zhang, Yanhang, (2017). Multiscale measurements of the mechanical properties of collagen matrix ACS Biomaterials Science & Engineering 3, (11), 2815-2824
The underlying mechanisms by which extracellular matrix (ECM) mechanics influences cell and tissue function remain to be elucidated because the events associated with this process span size scales from tissue to molecular level. Furthermore, ECM has an extremely complex hierarchical 3D structure and the load distribution is highly dependent on the architecture and mechanical properties of ECM. In the present study, the macro- and microscale mechanical properties of collagen gel were studied. Dynamic rheological testing was performed to study the macroscale mechanical properties of collagen gel. The microscale mechanical properties of collagen gel were measured using optical magnetic twisting cytometry (OMTC). Ferromagnetic beads embedded in the matrix were used as mechanical probes. Our study on the multiscale mechanical properties of collage matrix suggests several interesting differences between macro and microscale mechanical properties originated from the scales of measurements. At the macroscopic scale, storage and loss modulus increase with collagen concentrations. Nonaffine collagen fibril structural network deformation plays an important role in determining the macroscopic mechanical properties of the collagen matrix. At the microscopic scale, however, the local mechanical properties are less sensitive to changes in collagen concentration because of the more immediate/direct deformation of collagen fibrils in the OMTC measurements through forces exerted by locally attached ferromagnetic beads. The loss modulus is more affected by the local interstitial fluid environment, leading to a rather dramatic increase in viscosity with frequency, especially at higher frequencies (>10 Hz). A finite element model was developed to study the geometric factors in the OMTC measurements when the collagen matrix was considered to be hyperelastic. Our results show that the geometric factors are dependent on collagen concentration, or the stiffness of matrix, when nonlinear material properties of the matrix are considered, and thus interpretation of the apparent modulus from OMTC measurements should be conducted carefully.
Keywords: Keywords: collagen, Extracellular matrix, Geometric factor, Nonaffine deformation, Optical magnetic twisting cytometry
Zhao, M., Altankov, G., Grabiec, U., Bennett, M., Salmeron-Sanchez, M., Dehghani, F., Groth, T., (2016). Molecular composition of GAG-collagen I multilayers affects remodeling of terminal layers and osteogenic differentiation of adipose-derived stem cells Acta Biomaterialia 41, 86-99
The effect of molecular composition of multilayers, by pairing type I collagen (Col I) with either hyaluronic acid (HA) or chondroitin sulfate (CS) was studied regarding the osteogenic differentiation of adhering human adipose-derived stem cells (hADSCs). Polyelectrolyte multilayer (PEM) formation was based primarily on ion pairing and on additional intrinsic cross-linking through imine bond formation with Col I replacing native by oxidized HA (oHA) or CS (oCS). Significant amounts of Col I fibrils were found on both native and oxidized CS-based PEMs, resulting in higher water contact angles and surface potential under physiological condition, while much less organized Col I was detected in either HA-based multilayers, which were more hydrophilic and negatively charged. An important finding was that hADSCs remodeled Col I at the terminal layers of PEMs by mechanical reorganization and pericellular proteolytic degradation, being more pronounced on CS-based PEMs. This was in accordance with the higher quantity of Col I deposition in this system, accompanied by more cell spreading, focal adhesions (FA) formation and significant Î±2Î²1 integrin recruitment compared to HA-based PEMs. Both CS-based PEMs caused also an increased fibronectin (FN) secretion and cell growth. Furthermore, significant calcium phosphate deposition, enhanced ALP, Col I and Runx2 expression were observed in hADSCs on CS-based PEMs, particularly on oCS-containing one. Overall, multilayer composition can be used to direct cell-matrix interactions, and hence stem cell fates showing for the first time that PEMs made of biogenic polyelectrolytes undergo significant remodeling of terminal protein layers, which seems to enable cells to form a more adequate extracellular matrix-like environment. Statement of Significance: Natural polymer derived polyelectrolyte multilayers (PEMs) have been recently applied to adjust biomaterials to meet specific tissue demands. However, the effect of molecular composition of multilayers on both surface properties and cellular response, especially the fate of human adipose derived stem cells (hADSCs) upon osteogenic differentiation has not been studied extensively, yet. In addition, no studies exist that investigate a potential cell-dependent remodeling of PEMs made of extracellular matrix (ECM) components like collagens and glycosaminoglycans (GAGs). Furthermore, there is no knowledge whether the ability of cells to remodel PEM components may provide an added value regarding cell growth and differentiation. Finally, it has not been explored yet, how intrinsic cross-linking of ECM derived polyelectrolytes that improve the stability of PEMs will affect the differentiation potential of hADSCs. The current work aims to address these questions and found that the type of GAG has a strong effect on properties of multilayers and osteogenic differentiation of hADSCs. Additionally, we also show for the first time that PEMs made of biogenic polyelectrolytes undergo significant remodeling of terminal layers as completely new finding, which allows cells to form an ECM-like environment supporting differentiation upon osteogenic lineage. The finding of this work may open new avenues of application of PEM systems made by layer by layer (LbL) technique in tissue engineering and regenerative medicine.
Keywords: Collagen reorganization, Glycosaminoglycans, Layer-by-layer technique, Mesenchymal stem cells, Osteogenic differentiation
Forget, J., Awaja, F., Gugutkov, D., Gustavsson, J., Gallego Ferrer, G., Coelho-Sampaio, T., Hochman-Mendez, C., Salmeron-Sánchez, M., Altankov, G., (2016). Differentiation of human mesenchymal stem cells toward quality cartilage using fibrinogen-based nanofibers Macromolecular Bioscience 16, (9), 1348-1359
Mimicking the complex intricacies of the extra cellular matrix including 3D configurations and aligned fibrous structures were traditionally perused for producing cartilage tissue from stem cells. This study shows that human adipose derived mesenchymal stem cells (hADMSCs) establishes significant chondrogenic differentiation and may generate quality cartilage when cultured on 2D and randomly oriented fibrinogen/poly-lactic acid nanofibers compared to 3D sandwich-like environments. The adhering cells show well-developed focal adhesion complexes and actin cytoskeleton arrangements confirming the proper cellular interaction with either random or aligned nanofibers. However, quantitative reverse transcription-polymerase chain reaction analysis for Collagen 2 and Collagen 10 genes expression confirms favorable chondrogenic response of hADMSCs on random nanofibers and shows substantially higher efficacy of their differentiation in 2D configuration versus 3D constructs. These findings introduce a new direction for cartilage tissue engineering through providing a simple platform for the routine generation of transplantable stem cells derived articular cartilage replacement that might improve joint function.
Keywords: Cartilage, Chondrogenic response, Collagen, FBG/PLA nanofibers, Mesenchymal stem cells
Coelho, N. M., Llopis-Hernández, V., Salmerón-Sánchez, M., Altankov, G., (2016). Dynamic reorganization and enzymatic remodeling of type IV collagen at cell–biomaterial interface Advances in Protein Chemistry and Structural Biology (ed. Christo, Z. Christov), Academic Press (San Diego, USA) 105, 81-104
Abstract Vascular basement membrane remodeling involves assembly and degradation of its main constituents, type IV collagen (Col IV) and laminin, which is critical during development, angiogenesis, and tissue repair. Remodeling can also occur at cellâ€“biomaterials interface altering significantly the biocompatibility of implants. Here we describe the fate of adsorbed Col IV in contact with endothelial cells adhering on positively charged NH2 or hydrophobic CH3 substrata, both based on self-assembly monolayers (SAMs) and studied alone or mixed in different proportions. AFM studies revealed distinct pattern of adsorbed Col IV, varying from single molecular deposition on pure NH2 to network-like assembly on mixed SAMs, turning to big globular aggregates on bare CH3. Human umbilical endothelial cells (HUVECs) interact better with Col IV adsorbed as single molecules on NH2 surface and readily rearrange it in fibril-like pattern that coincide with secreted fibronectin fibrils. The cells show flattened morphology and well-developed focal adhesion complexes that are rich on phosphorylated FAK while expressing markedly low pericellular proteolytic activity. Conversely, on hydrophobic CH3 substrata HUVECs showed abrogated spreading and FAK phosphorylation, combined with less reorganization of the aggregated Col IV and significantly increased proteolytic activity. The later involves both MMP-2 and MMP-9, as measured by zymography and FITC-Col IV release. The mixed SAMs support intermediate remodeling activity. Taken together these results show that chemical functionalization combined with Col IV preadsorption provides a tool for guiding the endothelial cells behavior and pericellular proteolytic activity, events that strongly affect the fate of cardiovascular implants.
Keywords: Type IV collagen, Adsorption, Remodeling, Pericellular proteolysis, Reorganization, Substratum chemistry, CH3 and NH2 groups, Self-assembly monolayers
Perez, R. A., Altankov, G., Jorge-Herrero, E., Ginebra, M. P., (2013). Micro- and nanostructured hydroxyapatite-collagen microcarriers for bone tissue-engineering applications Journal of Tissue Engineering and Regenerative Medicine 7, (5), 353-361
Novel hydroxyapatite (HA)-collagen microcarriers (MCs) with different micro/nanostructures were developed for bone tissue-engineering applications. The MCs were fabricated via calcium phosphate cement (CPC) emulsion in oil. Collagen incorporation in the liquid phase of the CPC resulted in higher MC sphericity. The MCs consisted of a porous network of entangled hydroxyapatite crystals, formed as a result of the CPC setting reaction. The addition of collagen to the MCs, even in an amount as small as 0.8wt%, resulted in an improved interaction with osteoblast-like Saos-2 cells. The micro/nanostructure and the surface texture of the MCs were further tailored by modifying the initial particle size of the CPC. A synergistic effect between the presence of collagen and the nanosized HA crystals was found, resulting in significantly enhanced alkaline phosphatase activity on the collagen-containing nanosized HA MCs.
Keywords: Bone regeneration, Calcium phosphate cement, Cell response, Collagen, Hydroxyapatite, Microcarrier
Miranda Coelho, Nuno, Gonzalez-Garcia, Cristina, Salmeron-Sanchez, Manuel, Altankov, George, (2011). Arrangement of type IV collagen on NH(2) and COOH functionalized surfaces Biotechnology and Bioengineering , 108, (12), 3009-3018
Apart from the paradigm that cell-biomaterials interaction depends on the adsorption of soluble adhesive proteins we anticipate that upon distinct conditions also other, less soluble ECM proteins such as collagens, associate with the biomaterials interface with consequences for cellular response that might be of significant bioengineering interest. Using atomic force microscopy (AFM) we seek to follow the nanoscale behavior of adsorbed type IV collagen (Col IV)-a unique multifunctional matrix protein involved in the organization of basement membranes (BMs) including vascular ones. We have previously shown that substratum wettability significantly affects Col IV adsorption pattern, and in turn alters endothelial cells interaction. Here we introduce two new model surfaces based on self-assembled monolayers (SAMs), a positively charged - NH(2), and negatively charged -COOH surface, to learn more about their particular effect on Col IV behavior. AFM studies revealed distinct pattern of Col IV assembly onto the two SAMs resembling different aspects of network-like structure or aggregates (suggesting altered protein conformation). Moreover, the amount of adsorbed FITC-labeled Col IV was quantified and showed about twice more protein on NH(2) substrata. Human umbilical vein endothelial cells attached less efficiently to Col IV adsorbed on negatively charged COOH surface judged by altered cell spreading, focal adhesions formation, and actin cytoskeleton development. Immunofluorescence studies also revealed better Col IV recognition by both alpha(1) and alpha(2) integrins on positively charged NH(2) substrata resulting in higher phosphorylated focal adhesion kinase recruitment in the focal adhesion complexes. On COOH surface, no integrin clustering was observed. Taken altogether these results, point to the possibility that combined NH(2) and Col IV functionalization may support endothelization of cardiovascular implants.
Keywords: Collagen type IV, SAMs, AFM, Surface-induced protein assembly, Endothelial cells, Vascular grafts
Coelho, N. M., Gonzalez-Garcia, C., Planell, J. A., Salmeron-Sanchez, M., Altankov, G., (2010). Different assembly of type iv collagen on hydrophilic and hydrophobic substrata alters endothelial cells interaction European Cells & Materials , 19, 262-272
Considering the structural role of type IV collagen (Col IV) in the assembly of the basement membrane (BM) and the perspective of mimicking its organization for vascular tissue engineering purposes, we studied the adsorption pattern of this protein on model hydrophilic (clean glass) and hydrophobic trichloro(octadecyl) silane (ODS) surfaces known to strongly affect the behavior of other matrix proteins. The amount of fluorescently labeled Col IV was quantified showing saturation of the surface for concentration of the adsorbing solution of about 50 mu g/ml, but with approximately twice more adsorbed protein on ODS. AFM studies revealed a fine-nearly single molecular size-network arrangement of Col IV on hydrophilic glass, which turns into a prominent and growing polygonal network consisting of molecular aggregates on hydrophobic ODS. The protein layer forms within minutes in a concentration-dependent manner. We further found that human umbilical vein endothelial cells (HUVEC) attach less efficiently to the aggregated Col IV (on ODS), as judged by the significantly altered cell spreading, focal adhesions formation and the development of actin cytoskeleton. Conversely, the immunofluorescence studies for integrins revealed that the fine Col IV network formed on hydrophilic substrata is better recognized by the cells via both alpha 1 and alpha 2 heterodimers which support cellular interaction, apart from these on hydrophobic ODS where almost no clustering of integrins was observed.
Keywords: Collagen type IV, Adsorption, Assembly, Hydrophilic, Hydrophobic, Surfaces
Merolli, A., Rocchi, L., Catalano, F., Planell, J., Engel, E., Martinez, E., Sbernardori, M. C., Marceddu, S., Leali, P. T., (2009). In vivo regeneration of rat sciatic nerve in a double-halved stitch-less guide: a pilot-study Microsurgery , 29, (4), 310-318
It is about 20 years that tubular nerve guides have been introduced into clinical practice as a reliable alternative to autograft, in gaps not-longer-than 20 mm, bringing the advantage of avoiding donor site sacrifice and morbidity. There are limitations in the application of tubular guides. First, tubular structure in itself makes surgical implantation difficult; second, stitch sutures required to secure the guide may represent a site of unfavorable fibroblastic reaction; third, maximum length and diameter of the guide correlate with the occurrence of a poorer central vascularization of regenerated nerve. We report on the in vivo testing of a new concept of nerve-guide (named NeuroBox) which is double-halved, not-degradable, rigid, and does not require any stitch to be held in place, employing acrylate glue instead. Five male Wistar rats had the new guide implanted in a 4-mm sciatic nerve defect; two guides incorporated a surface constituted of microtrenches aligned longitudinally. Further five rats had the 4-mm gap left without repair. Contralateral intact nerves were used as controls. After 2 months, nerve regeneration occurred in all animals treated by the NeuroBox; fine blood vessels were well represented. There was no regeneration in the un-treated animals. Even if the limited number of animals does not allow to draw definitive conclusions, some result can be highlighted: an easy surgical technique was associated with the box-shaped guide and acrylate glue was easily applied; an adequate intraneural vascularization was found concurrently with the regeneration of the nerve and no adverse fibroblastic proliferation was present.
Keywords: Peripheral-nerve, Polyglycolic acid, Guidance cues, Collagen tube, Median nerve, Repair, Growth, Cyanoacrylate, Complications, Anastomosis
Maneva-Radicheva, L., Ebert, U., Dimoudis, N., Altankov, G., (2008). Fibroblast remodeling of adsorbed collagen type IV is altered in contact with cancer cells Histology and Histopathology , 23, (7), 833-842
A series of co-culture experiments between fibroblasts and H-460 human lung carcinoma cells were performed to learn more about the fate of adsorbed type IV collagen (Coll IV). Fibroblasts were able to spatially rearrange Coll IV in a specific linear pattern, similar but not identical to the fibronectin (FN) fibrils. Coll IV partly co-aligns with fibroblast actin cytoskeleton and transiently co-localize with FN, as well as with beta 1 and a 2 integrin clusters, suggesting a cell-dependent process. We further found that this Coll IV reorganization is suppressed in contact with H460 cells. Zymography revealed strongly elevated MMP-2 activity in supernatants of co-cultures, but no activity when fibroblasts or cancer cells were cultured alone. Thus, we provide evidence that reorganization of substrate associated Coll IV is a useful morphological approach for in vitro studies on matrix remodeling activity during tumorigenesis.
Keywords: Adsorbed collagen IV reorganization, Fibroblasts and cancer cells co-culture, MMP-2
Manara, S., Paolucci, F., Palazzo, B., Marcaccio, M., Foresti, E., Tosi, G., Sabbatini, S., Sabatino, P., Altankov, G., Roveri, N., (2008). Electrochemically-assisted deposition of biomimetic hydroxyapatite-collagen coatings on titanium plate Inorganica Chimica Acta 361, (6), 1634-1645
A biomimetic bone-like composite, made of self-assembled collagen fibrils and carbonate hydroxyapatite nanocrystals, has been performed by an electrochemically-assisted deposition on titanium plate. The electrolytic processes have been carried out using a single type I collagen molecules suspension in a diluted Ca(NO3)(2) and NH4H2PO4 solution at room temperature and applying a constant current for different periods of time. Using the same electrochemical conditions, carbonate hydroxyapatite nanocrystals or reconstituted collagen. brils coatings were obtained. The reconstituted collagen. brils, hydroxyapatite nanocrystals and collagen fibrils/apatite nanocrystals coatings have been characterized chemically, structurally and morphologically, as well as for their ability to bind fibronectin (FN). Fourier Transform Infrared microscopy has been used to map the topographic distribution of the coating components at different times of electrochemical deposition, allowing to single out the individual deposition steps. Moreover, roughness of Ti plate has been found to affect appreciably the nucleation region of the inorganic nanocrystals. Laser scanning confocal microscopy has been used to characterize the FN adsorption pattern on a synthetic biomimetic apatitic phase, which exhibits a higher affinity when it is inter-grown with the collagen fibrils. The results offer auspicious applications in the preparation of medical devices such as biomimetic bone-like composite-coated metallic implants.
Keywords: Hydroxyapatite-collagen coating, Electrochemically-assisted deposition, Micro-imaging FTIR spectroscopy, Laser scanning confocal microscopy, Biomimetic crystal growth, Fibronectin binding