Staff member

A major challenge in cardiac research is the limited translatability of drug screening and toxicity assays due to the use of in vitro models that poorly mimic the native cardiac environment. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) offer a promising route forward, but conventional 2D culture on rigid substrates hinders their functional maturation and predictive accuracy. This study addresses this problem by investigating the effect of hybrid fibronectin-based hydrogels with tunable stiffness on the mechanical and electrical properties of hiPSC-CMs. We engineered hydrogels with stiffness mimicking the lowest range of neonatal heart tissue stiffness (2-4 kPa) and compared hiPSC-CM behavior on these substrates to that on standard fibronectin-coated glass. Our results demonstrate that hydrogel culture promotes more uniform and stable cardiomyocyte contractions, as evidenced by increased single peak percentages and altered contraction duration. Electrophysiological analysis revealed that hydrogel stiffness influences action potential duration and signal amplitude. Furthermore, hiPSC-CMs on hydrogels exhibited enhanced cell-matrix and cell-cell adhesion, indicating improved structural and functional connectivity. Drug testing with known cardioactive compounds, including isoproterenol and nifedipine, revealed distinct differences in drug responses between hydrogel and glass cultures, suggesting that hydrogels provide a more physiologically relevant platform for assessing drug effects. This work highlights the potential of engineered hydrogel substrates to enhance the functional maturity and predictive accuracy of hiPSC-CMs for cardiac research and drug development.

JTD Keywords: Action potentials, Beat, Cell adhesion, Cell differentiation, Cells, Cells, cultured, Contraction, Fibronectins, Guinea-pig, Humans, Hydrogels, Induced pluripotent stem cells, Ipsc-cardiomyocytes, Ipsc‐cardiomyocytes, Isoproterenol, Maturation, Mechanical properties, Myocytes, cardiac, Nifedipine, Phenotype, Platform, Sensitive dye di-4-anepps

Traction force microscopy (TFM) quantifies cellular forces at the cell-extracellular matrix interface, yet elastic formulations neglect viscous dissipation and can misinterpret cellular forces on viscoelastic substrates. We introduce a semi-analytical 2D viscoelastic TFM (veTFM) that generalizes the Boussinesq framework of elastic TFM to Generalized Maxwell (GMX) substrates with one or two components. By combining Fourier and Laplace transforms, veTFM quantifies time-resolved tractions in finite-thickness substrates and resolves stress-free reference and substrate pre-stress. We derive criteria for when elastic regimes remain valid in this framework. This positions veTFM as a scalable extension of standard 2D TFM (eTFM) to viscoelastic substrates, identifying when eTFM remains sufficient, which elastic limit applies, and when full viscoelastic quantification is required. Applied to beating cardiomyocytes, epithelial cells, and dermal fibroblasts cultured on linear-polyacrylamide and alginate viscoelastic hydrogels, veTFM shows that the elastic or viscoelastic regime engaged by the cell depends on timescale matching between the loading rate and the substrate's relaxation times. Notably, for the Generalized Maxwell substrates analyzed here, viscoelastic traction magnitudes scale with the substrate's total dissipation rather than individual relaxation times, with total dissipation setting traction magnitude and timescale matching determining whether the cell engages the substrate in an elastic or viscoelastic regime.

JTD Keywords: Animals, Biomaterials, Cell, Cell-material interactions, Cell–material interactions, Elasticity, Epithelial cells, Extracellular matrix, Extracellular-matrix viscoelasticity, Fibroblasts, Focal adhesions, Guide, Humans, Hydrogels, Microscopy, atomic force, Myocytes, cardiac, Numerical inversion, Semi-analytical methods, Semi‐analytical methods, Stress relaxation, Viscoelastic hydrogels, Viscoelastic traction force microscopy, Viscosity

Leukaemias, driven by mutations in haematopoietic stem cells (HSCs), rely on interactions with the bone marrow (BM) niche and other cell populations such as mesenchymal stromal cells (MSCs) for growth and survival. While chimeric antigen receptor (CAR) T-cell therapy shows promise for other haematological malignancies, its application to acute myeloid leukaemia (AML) is hindered by tumour heterogeneity and off-target toxicity. Combining CRISPR-Cas9 gene editing with CAR T-cell therapy has potential for selectively targeting AML cells while sparing healthy tissue. However, validating the efficacy of these treatments prior to clinical trial is hampered by the differences between humans and animal models typically used for pre-clinical testing. Furthermore, traditional in vitro models fail to replicate the complexity of the BM niche and often overestimate treatments' efficacy. Here, we present a bioengineered human-cell containing endosteal BM niche model combining a fibronectin-presenting polymeric surface and a synthetic peptide hydrogel (PeptiGel) that mimics native BM tissue's mechanical properties. This platform supports niche phenotypes in MSCs and HSCs and enables the evaluation of combined CRISPR-CAR T-cell therapy, demonstrating potential as a preclinical human model for testing novel therapies.

JTD Keywords: Cd33, Extracellular-matrix, Hematopoietic stem-cells, Immunotherapy, Insights, Maintenance, Vivo

Growth factor mimetics offer great potential for osteogenic biomaterials; yet, their use remains limited, likely due to an incomplete understanding of the effects of the microenvironment on their activity. The extracellular matrices (ECMs) where growth factors are presented in vivo are viscoelastic environments, where dynamic receptor-ligand interactions drive cellular responses. Here, supported lipid bilayers of varying viscosity are used as 2D dynamic ECM models, where the bone morphogenetic 2 (BMP-2) mimetic DWIVA is presented to mesenchymal stem cells alongside the adhesive peptide RGD. DWIVA is demonstrated to have no impact on mechanotransductive processes, including actin organisation, focal adhesion formation and YAP localisation, which are exclusively controlled by viscosity via RGD. Interestingly, DWIVA promotes osteogenic markers' expression only on a viscous bilayer, through a process that involves non-canonical BMP-2 pathways; on a mobile bilayer or on a static control, it lacks osteogenic activity. Crucially, osteogenesis is accompanied by a translocation of BMP receptor 1a to the cell edge, where it colocalises with focal adhesions. Our ECM models hence reveal that both a viscosity-enabled threshold of cell-generated forces and a dynamic environment are necessary to harness the osteogenic potential of DWIVA, uncovering key microenvironment properties for the design of DWIVA-based biomaterials.

JTD Keywords: Activated protein-kinase, Adsorption, Bmp-2, Bone, Cells, Differentiation, Dwiva, Dynamics, Lipid-bilayers, Mesenchymal stem cell, Microscopy, Osteogenesis, Receptor, Viscosity

The growing demand for safer, more targeted therapeutics requires the development of advanced biomaterials. Among these, Engineered Living Materials (ELMs)-which integrate synthetic biology with material science-are emerging as promising platforms for biomedical applications. This review focuses on a subclass of ELMs based on genetically engineered probiotics combined with matrices, that are termed Probiotic Living Materials (PLMs) to differentiate them from Living Biotherapeutic Products (LBPs). Recent studies highlight PLM's potential in addressing different health conditions, offering targeted and dynamic therapies. However, PLMs face multiple challenges to be implemented in clinics, including a lack of robust genetic toolkits for probiotic engineering, concerns about biosafety (e.g., horizontal gene transfer or non-desirable biological activity), difficulties in translating preclinical results to humans, and the absence of clear regulatory guidance for clinical use. This review first explores the fundamental features of ELMs, then provides an overview of probiotics, followed by recent advances in the design of engineered PLMs for biomedical applications, particularly in biosensing development, infection treatment, bone repair, wound healing, vaginal imbalances, gut-related conditions, and cancer therapy. Finally, biosafety issues and current gaps in regulatory frameworks to ensure safe and effective use of PLMs, with a particular focus on vulnerable populations, are discussed.

JTD Keywords: Animals, Artificial-intelligence, Biocompatible materials, Clinical-trials, Commensal bacterium, Engineered lactococcus-lactis, Engineered living materials, Escherichia-coli, Gene-expression, Humans, Probiotics, Protein, Saccharomyces-cerevisiae, System, Therapeutics, Yeast

Cells are sensitive to the physical properties of their microenvironment and transduce them into biochemical cues that trigger gene expression and alter cell behavior. Numerous proteins, including integrins, are involved in these mechanotransductive events. Here, a novel role for the boron transporter NaBC1 is identified as a mechanotransducer. It is demonstrated that soluble boron ions activate NaBC1 to enhance cell adhesion and intracellular tension in C2C12 myoblasts seeded on fibronectin-functionalized polyacrylamide (PAAm) hydrogels. Retrograde actin flow and traction forces exerted by these cells are significantly increased in vitro in response to both increased boron concentration and hydrogel stiffness. These effects are fibronectin and NaBC1-mediated as they are abrogated in hydrogels coated with laminin-111 in place of fibronectin and in esiRNA NaBC1-silenced cells. These findings thus demonstrate that NaBC1 controls boron homeostasis and also functions as a mechanosensor.

JTD Keywords: Activation, Animals, Beta-1-integrin, Biomaterials, Boron, Cell adhesion, Cell line, Cell-matrix, Differentiation, Fibronectins, Focal adhesion kinase, Growth, Hydrogels, Integrins, Mechanobiology, Mechanotransduction, Mechanotransduction, cellular, Mediated adhesion, Mice, Muscle cells, Myoblasts, Nabc1, Skeletal-muscle, Stiffnes, Tissue engineerin, Tissue engineering

Extracellular matrix (ECM) viscoelasticity has emerged as a potent regulator of physiological and pathological processes, including cancer progression. Spatial confinement within the ECM is also known to influence cell behavior in these contexts. However, the interplay between matrix viscoelasticity and spatial confinement in driving epithelial cell mechanotransduction is not well understood, as it relies on experiments employing purely elastic hydrogels. This work presents an innovative approach to fabricate and micropattern viscoelastic polyacrylamide hydrogels with independently tuneable Young's modulus and stress relaxation, specifically designed to mimic the mechanical properties observed during breast tumor progression, transitioning from a soft dissipative tissue to a stiff elastic one. Using this platform, this work demonstrates that matrix viscoelasticity differentially modulates breast epithelial cell spreading, adhesion, YAP nuclear import and cell migration, depending on the initial stiffness of the matrix. Furthermore, by imposing spatial confinement through micropatterning, this work demonstrates that confinement alters cellular responses to viscoelasticity, including cell spreading, mechanotransduction and migration. These findings establish ECM viscoelasticity as a key regulator of epithelial cell mechanoresponse and highlight the critical role of spatial confinement in soft, dissipative ECMs, which was a previously unexplored aspect.

JTD Keywords: Cell adhesion, Cell movement, Confinement, Dynamics, Elastic modulus, Elasticity, Epithelial cells, Extracellular matrix, Extracellular-matrix, Force transmission, Humans, Hydrogels, Mechanics, Mechanotransduction, cellular, Micropatterning, Migration, Morphology, Motilit, Polyacrylamide hydrogels, Stiffness, Substrate, Viscoelasticit, Viscoelasticity, Viscosity

Microgels show advantages over bulk hydrogels due to convenient control over microgel size and composition, and the ability to use microgels to modularly construct larger hierarchical scaffold hydrogel materials. Here, supramolecular chemistry is used to formulate supramolecular polymer, dynamic microgels solely held together by non-covalent interactions. Four-fold hydrogen bonding ureido-pyrimidinone (UPy) monomers with different functionalities are applied to precisely tune microgel properties in a modular way, via variations in monomer concentration, bifunctional crosslinker ratio, and the incorporation of supramolecular dyes and peptides. Functionalization with a bioactive supramolecular cell-adhesive peptide induced selectivity of cells toward the bioactive microgels over non-active, non-functionalized versions. Importantly, the supramolecular microgels can also be applied as microscale building blocks into supramolecular bulk macrogels with tunable dynamic behavior: a robust and weak macrogel, where the micro- and macrogels are composed of similar molecular building blocks. In a robust macrogel, microgels act as modular micro-building blocks, introducing multi-compartmentalization, while in a weak macrogel, microgels reinforce and enhance mechanical properties. This work demonstrates the potential to modularly engineer higher-length-scale structures using small molecule supramolecular monomers, wherein microgels serve as versatile and modular micro-building units.

JTD Keywords: Biomaterials, Cell culture, Droplet-based microfluidics, Droplet‐based microfluidics, Fabrication, Hydrogel, Hydrogels, Microgel, Multiscale modularity, Scaffolds, Siz, Supramolecular biomaterial, Synthetic extracellular matri, Synthetic extracellular matrix

Mesenchymal stem cells (MSCs) interact with their surroundings via integrins, which link to the actin cytoskeleton and translate physical cues into biochemical signals through mechanotransduction. N-cadherins enable cell-cell communication and are also linked to the cytoskeleton. This crosstalk between integrins and cadherins modulates MSC mechanotransduction and fate. Here we show the role of this crosstalk in the mechanosensing of viscosity using supported lipid bilayers as substrates of varying viscosity. We functionalize these lipid bilayers with adhesion peptides for integrins (RGD) and N-cadherins (HAVDI), to demonstrate that integrins and cadherins compete for the actin cytoskeleton, leading to an altered MSC mechanosensing response. This response is characterised by a weaker integrin adhesion to the environment when cadherin ligation occurs. We model this competition via a modified molecular clutch model, which drives the integrin/cadherin crosstalk in response to surface viscosity, ultimately controlling MSC lineage commitment. The crosstalk between cell-cell and cell-matrix adhesions regulates stem cell fate. Here, the authors reveal a critical role for matrix viscosity in controlling this crosstalk, which they explain via a modified molecular clutch model.

JTD Keywords: Actin cytoskeleton, Adhesion, Animals, Arginyl-glycyl-aspartic acid, Cadherins, Cell adhesion, Cell communication, Fibronectin, Force transmission, Humans, Hydrogel, Integrins, Lipid bilayers, Matrix, Mechanotransduction, Mechanotransduction, cellular, Mesenchymal stem cells, Mobility, Oligopeptides, Osteogenic differentiation, Substrate stiffness, Vinculin, Viscosity

The blood-brain barrier (BBB) tightly regulates substance transport between the bloodstream and the brain. Models for the study of the physiological processes affecting the BBB, as well as predicting the permeability of therapeutic substances for neurological and neurovascular pathologies, are highly desirable. Existing models, such as Transwell utilizing-models, do not mimic the extracellular environment of the BBB with their stiff, semipermeable, non-biodegradable membranes. To help overcome this, we engineered electrospun membranes from poly L-lactic acid in combination with a nanometric coating of poly(ethyl acrylate) (PEA) that drives fibrillogenesis of fibronectin, facilitating the synergistic presentation of both growth factors and integrin binding sites. Compared to commercial semi-porous membranes, these membranes significantly improve the expression of BBB-related proteins in brain endothelial cells. PEA-coated membranes in combination with different growth factors and extracellular protein coatings reveal nerve growth factor (NGF) and fibroblast growth factor (FGF-2) caused formation of better barriers in vitro. This BBB model offers a robust platform for studying key biochemical factors influencing barrier formation that marries the simplicity of the Transwell model with the highly tunable electrospun PEA-fibronectin membranes. This enables the generation of high-throughput drug permeability models without the need of complicated co-culture conditions. The blood-brain barrier (BBB) tightly regulates substance transport between the bloodstream and the brain. Here a simple model of the BBB that allows culture of endothelial cells on growth-factor functionalised membranes is introduced. This novel in vitro model of the BBB offers a robust platform for studying key barriergenic biochemical factors influencing barrier formation without the use of the complicated co-culture conditions. image

JTD Keywords: Animals, Bbb, Blood-brain barrier, Densit, Differentiation, Ecm, Electrospinning, Endothelial cells, Endothelial-cell lines, Expression, Fiber diameter, Fibroblast-growth-factor, Growth factors, Humans, In vitro mode, In vitro model, Membranes, artificial, Models, biological, Morphology, Permeability, Poly(l-lactic acid), Poly(lactide), Polyesters, Proteins

Conventional osteogenic platforms utilize active growth factors to repair bone defects that are extensive in size, but they can adversely affect patient health. Here, an unconventional osteogenic platform is reported that functions by promoting capture of inactive osteogenic growth factor molecules to the site of cell growth for subsequent integrin-mediated activation, using a recombinant fragment of latent transforming growth factor beta-binding protein-1 (rLTBP1). It is shown that rLTBP1 binds to the growth-factor- and integrin-binding domains of fibronectin on poly(ethyl acrylate) surfaces, which immobilizes rLTBP1 and promotes the binding of latency associated peptide (LAP), within which inactive transforming growth factor beta 1 (TGF-beta 1) is bound. rLTBP1 facilitates the interaction of LAP with integrin beta 1 and the subsequent mechanically driven release of TGF-beta 1 to stimulate canonical TGF-beta 1 signaling, activating osteogenic marker expression in vitro and complete regeneration of a critical-sized bone defect in vivo. An osteogenic platform that functions by capturing inactive growth factor molecules is engineered to overcome conventional challenges associated with the use of active growth factors. The platform triggers capture of inactive transforming growth factor beta-1 for its subsequent integrin-mediated activation which activates osteogenic downstream signaling in vitro and fully repairs critical-sized bone defect in vivo. image

JTD Keywords: Animals, Bone, Bone defect, Bone regeneration, Cell proliferation, Cells, Chemical activation, Defects, Differentiation, Fibronectin, Fibronectins, Growth factor, Growth factors, Humans, Integrin beta1, Integrins, Latency associated peptides, Latent tgf-beta binding proteins, Ltbp1, Osteogenesis, Osteogenic, Protein binding, Recombinant proteins, Release, Repair, Signal transduction, Surface properties, Tgf-beta, Tgf-β1, Transforming growth factor beta1, Transforming growth factors

Mimicking bone extracellular matrix (ECM) is paramount to develop novel biomaterials for bone tissue engineering. In this regard, the combination of integrin-binding ligands together with osteogenic peptides represents a powerful approach to recapitulate the healing microenvironment of bone. In the present work, we designed polyethylene glycol (PEG)-based hydrogels functionalized with cell instructive multifunctional biomimetic peptides (either with cyclic RGD-DWIVA or cyclic RGD-cyclic DWIVA) and cross-linked with matrix metalloproteinases (MMPs)-degradable sequences to enable dynamic enzymatic biodegradation and cell spreading and differentiation. The analysis of the intrinsic properties of the hydrogel revealed relevant mechanical properties, porosity, swelling and degradability to engineer hydrogels for bone tissue engineering. Moreover, the engineered hydrogels were able to promote human mesenchymal stem cells (MSCs) spreading and significantly improve their osteogenic differentiation. Thus, these novel hydrogels could be a promising candidate for applications in bone tissue engineering, such as acellular systems to be implanted and regenerate bone or in stem cells therapy.Copyright © 2023 Oliver-Cervelló, Martin-Gómez, Gonzalez-Garcia, Salmeron-Sanchez, Ginebra and Mas-Moruno.

JTD Keywords: biomaterials, cross-linking, dwiva, functionalization, hydrogel, integrin, kinetics, marrow stromal cells, matrices, multifunctionality, myogenic differentiation, osteogenic differentiation, regeneration, stem-cells, Biomimetic peptides, Dwiva, Functionalization, Hydrogel, Multifunctionality, Osteogenic differentiation, Poly(ethylene glycol) hydrogels

The microenvironment where cells reside provides them with arange of cues that collectively affect their fate. These include bio-chemical cues, mediated by interactions with the extracellular matrix(via integrins) and between cells (via cadherins), and physicalproperties, such as stiffness and viscosity. While the effect of stiff-ness on cell fate has been widely studied, the role of viscosity hasbeen only recently addressed (1). In our group, we demonstrated thatcells sense viscosity using the same mechanotransductive mecha-nisms that they use for stiffness (2). Here, we investigate the role ofviscous interactions in controlling stem cell fate. We designed mo-bile surfaces based on supported lipid bilayers of controlled viscos-ity, which target the adhesive crosstalk between integrins (RGDreceptors) and cadherins (HAVDI-containing proteins) (3).Using human mesenchymal stem cells, we observed an increase incell adhesion and a decrease in actin flow when the viscosity of thesurface and the concentration of RGD increased. When HAVDI wasadded to the surface, cell adhesion was reduced, while the actin flowincreased. These changes provoked alterations in the activation ofmechanotransductive pathways: the nuclear translocation of me-chanosensitive YAP increased with viscosity and decreased withHAVDI ligation. Finally, early differentiation markers were differ-entially expressed, revealing an effect of viscosity on cell fate: whilemore mobile surfaces favored adipogenesis and HAVDI ligation onthem triggered chondrogenesis, more viscous substrates promotedosteogenesis. Further investigations on the signaling pathways in-volved will allow to establish a paradigm to collectively understandand exploit cell response to viscous interactions

JTD

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 α2β1 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.

JTD Keywords: Collagen reorganization, Glycosaminoglycans, Layer-by-layer technique, Mesenchymal stem cells, Osteogenic differentiation

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.

JTD Keywords: Collagen type IV, Adsorption, Assembly, Hydrophilic, Hydrophobic, Surfaces

The initial cellular events that take place at the biomaterials interface mimic to a certain extent the natural adhesive interaction of cells with the extracellular matrix (ECM) (Spie, 2002; Griffin & Naughton, 2002; Grinnell, 1986). In fact, the living cells cannot interact directly with foreign materials, but they readily attach to the adsorbed layer of proteins (upon contact with physiological fluids in vivo or culture medium in vitro) such as fibronectin (FN), vitronectin (VN), fibrinogen (FG), representing the so-called soluble matrix proteins in the biological fluids (Grinnell 1986).

JTD Keywords: Tissue Engineering, Protein-material interaction, ECM, Biomaterials

The influence of surface chemistry -substrates with controlled surface density of -OH groups- on fibronectin conformation and distribution is directly observed by Atomic Force Microscopy (AFM). FN fibrillogenesis, which is known to be a process triggered by interaction with integrins, is shown in our case to be induced by the substrate (in absence of cells), which is able to enhance FN-FN interactions leading to the formation of a protein network on the material surface. This phenomenon depends both on surface chemistry and protein concentration. The level of the FN fibrillogenesis was quantified by calculating the fractal dimension of the adsorbed protein from image analysis of the AFM results. The total amount of adsorbed FN is obtained by making use of a methodology which employs western-blotting combined with image analysis of the corresponding protein bands, with the lowest sensitivity threshold equal to 15 ng of adsorbed protein. Furthermore, FN adsorption is correlated to human osteoblast adhesion through morphology and actin cytoskeleton formation. Actin polymerization is in need of the formation of the protein network on the substrate's surface. Cell morphology is more rounded (as quantified by calculating the circularity of the cells by image analysis) the lower the degree of FN fibrillogenesis on the substrate.

JTD Keywords: Cell-adhesion, Conformational-changes, Electron-microscopy, Protein adsorption, Fractal dimension, Integrin binding, Biocompatibility, Monolayers, Matrix, Fibrillogenesis