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Sequential Photoactivation of Self-Assembled Monolayers to Direct Cell Adhesion and Migration.

ABSTRACT: Dynamic substrates for cell culture control the spatial and temporal presentation of extracellular matrix ligands that interact with adherent cells. This paper reports a photoactive surface chemistry that can repeatedly activate regions of the substrate for cell adhesion, spreading, and migration. The approach uses self-assembled monolayers presenting the integrin ligand RGD that is caged with a nitrophenyl-based photoprotecting group. The group is also modified with a maltoheptaose oligosaccharide to prevent nonspecific protein adsorption and cell attachment. The peptide is uncaged when irradiated with a laser source at 405 nm on a microscope to reveal micron-size regions for single cell attachment. This method is applied to studies of gap junction-mediated communication between two neighboring cells and requires the patterning of an initial receiver cell population and then the patterning of a second sender population to give a culture wherein each pair of cells are separated by 30 μm. Finally, activation of the region between the cells permits cell-cell contact and gap junction assembly between the sender and receiver cells. This example demonstrates the broad relevance of this method to studying complex phenotypes in cell culture.

SUBMITTER: Bugga P

PROVIDER: S-EPMC8262134 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Reversible Self-Assembled Monolayers with Tunable Surface Dynamics for Controlling Cell Adhesion Behavior.

Project description:Cells adhering onto surfaces sense and respond to chemical and physical surface features. The control over cell adhesion behavior influences cell migration, proliferation, and differentiation, which are important considerations in biomaterial design for cell culture, tissue engineering, and regenerative medicine. Here, we report on a supramolecular-based approach to prepare reversible self-assembled monolayers (rSAMs) with tunable lateral mobility and dynamic control over surface composition to regulate cell adhesion behavior. These layers were prepared by incubating oxoacid-terminated thiol SAMs on gold in a pH 8 HEPES buffer solution containing different mole fractions of ω-(ethylene glycol)2-4- and ω-(GRGDS)-, α-benzamidino bolaamphiphiles. Cell shape and morphology were influenced by the strength of the interactions between the amidine-functionalized amphiphiles and the oxoacid of the underlying SAMs. Dynamic control over surface composition, achieved by the addition of inert filler amphiphiles to the RGD-functionalized rSAMs, reversed the cell adhesion process. In summary, rSAMs featuring mobile bioactive ligands offer unique capabilities to influence and control cell adhesion behavior, suggesting a broad use in biomaterial design, tissue engineering, and regenerative medicine.

| S-EPMC9501787 | biostudies-literature

Using self-assembled monolayers to understand α8β1-mediated cell adhesion to RGD and FEI motifs in nephronectin.

Project description:Nephronectin is an extracellular matrix protein that interacts with the α8β1 integrin receptor and plays a role in tissue and organ development, though the motifs that mediate adhesion to the receptor remain unclear. This paper describes the use of self-assembled monolayers to study the adhesion of α8β1-presenting cells to the RGD and DLFEIFEIER ligands in nephronectin and found that both ligands can independently mediate cell adhesion through nonoverlapping binding sites on the integrin. Peptide truncation experiments showed FEI to be the minimal binding sequence within the DLFEIFEIER sequence, and adhesion experiments with peptides that include both the RGD and FEI sequences demonstrate that the two peptides bind synergistically to the receptor. Finally, a peptide array was used to establish a strict requirement for the glutamate residue of FEI and tolerance of other aromatic and hydrophobic residues in the first and third positions, respectively. This work provides an enhanced understanding of the binding of nephronectin with α8β1 and identifies a peptide ligand that can be used for targeting the α8β1 integrin.

| S-EPMC3200005 | biostudies-literature

Using self-assembled monolayers to model cell adhesion to the 9th and 10th type III domains of fibronectin.

Project description:Most mammalian cells must adhere to the extracellular matrix (ECM) to maintain proper growth and development. Fibronectin is a predominant ECM protein that engages integrin cell receptors through its Arg-Gly-Asp (RGD) and Pro-His-Ser-Arg-Asn (PHSRN) peptide binding sites. To study the roles these motifs play in cell adhesion, proteins derived from the 9th (containing PHSRN) and 10th (containing RGD) type III fibronectin domains were engineered to be in frame with cutinase, a serine esterase that forms a site-specific, covalent adduct with phosphonate ligands. Self-assembled monolayers (SAMs) that present phosphonate ligands against an inert background of tri(ethylene glycol) groups were used as model substrates to immobilize the cutinase-fibronectin fusion proteins. Baby hamster kidney cells attached efficiently to all protein surfaces, but only spread efficiently on protein monolayers containing the RGD peptide. Cells on RGD-containing protein surfaces also displayed defined focal adhesions and organized cytoskeletal structures compared to cells on PHSRN-presenting surfaces. Cell attachment and spreading were shown to be unaffected by the presence of PHSRN when compared to RGD alone on SAMs presenting higher densities of protein, but PHSRN supported an increased efficiency in cell attachment when presented at low protein densities with RGD. Treatment of suspended cells with soluble RGD or PHSRN peptides revealed that both peptides were able to inhibit the attachment of FN10 surfaces. These results support a model wherein PHSRN and RGD bind competitively to integrins--rather than a two-point synergistic interaction--and the presence of PHSRN serves to increase the density of ligand on the substrate and therefore enhance the sticking probability of cells during attachment.

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DNA orientation-specific adhesion and patterning of living mammalian cells on self-assembled DNA monolayers.

Project description:To better understand cell behaviors on substrates, the precise control of density and orientation of cell-specific ligands remains a great challenge. In this study, we established an easy-to-use approach to manipulate the adhesion and patterning of mammalian cells on gold substrates. We prepared DNA self-assembled monolayers (DNA-SAMs) on gold substrates and found that the sequence-specific orientation of DNA-SAMs played an important role in modulating cell adhesion. We also found that the DNA-SAMs on gold substrates could be used as a potentially universal cell culture substrate, which showed properties similar to cationic polymers (e.g. poly-l lysine, PLL) substrates. Furthermore, we could manipulate cell adhesion by tuning the length of poly adenine (polyA) in the DNA sequence. We also prepared a DNA aptamer-based SAM to regulate cell adhesion by exploiting stimuli-responsive conformational change of the aptamer. By using the well-established DNA spotting technology, we patterned cells on DNA-SAMs to form a spot matrix and four English letters "CELL". Our findings suggest that DNA-SAMs on gold substrates are potentially useful for making smart surfaces for cell studies, thus introducing a new platform for cell/tissue engineering research.

| S-EPMC5477012 | biostudies-literature

Organic chemistry on surfaces: Direct cyclopropanation by dihalocarbene addition to vinyl terminated self-assembled monolayers (SAMs).

Project description:C11-Vinyl-terminated self-assembled monolayers (SAMs) on silica surfaces are successfully modified in C-C bond forming reactions with dihalocarbenes to generate SAMs, terminated with dihalo- (fluoro, chloro, bromo) cyclopropane motifs with about 30% surface coverage.

| S-EPMC4273226 | biostudies-literature

Mobility of charge carriers in self-assembled monolayers.

Project description:We present a new approach to study charge transport within 2D layers of organic semi-conductors (OSCs) using atomic force microscopy (AFM)-based lithography applied to self-assembled monolayers (SAMs), fabricated from appropriate organothiols. The extent of lateral charge transport was investigated by insulating pre-defined patches within OSC-based SAMs with regions of insulating SAM made from large band gap alkanethiolates. The new method is demonstrated using a phenyl-linked anthracenethiolate (PAT), 4-(anthracene-2-ylethynyl)benzyl thiolate. I-V characteristics of differently shaped PAT-islands were measured using the AFM tip as a top electrode. We were able to determine a relationship between island size and electrical conductivity, and from this dependence, we could obtain information on the lateral charge transport and charge carrier mobility within the thin OSC layers. Our study demonstrates that AFM nanografting of appropriately functionalized OSC molecules provides a suitable method to determine intrinsic mobilities of charge carriers in OSC thin films. In particular, this method is rather insensitive with regard to influence of grain boundaries and other defects, which hamper the application of conventional methods for the determination of mobilities in macroscopic samples.

| S-EPMC6941449 | biostudies-literature

Simple direct formation of self-assembled N-heterocyclic carbene monolayers on gold and their application in biosensing.

Project description:The formation of organic films on gold employing N-heterocyclic carbenes (NHCs) has been previously shown to be a useful strategy for generating stable organic films. However, NHCs or NHC precursors typically require inert atmosphere and harsh conditions for their generation and use. Herein we describe the use of benzimidazolium hydrogen carbonates as bench stable solid precursors for the preparation of NHC films in solution or by vapour-phase deposition from the solid state. The ability to prepare these films by vapour-phase deposition permitted the analysis of the films by a variety of surface science techniques, resulting in the first measurement of NHC desorption energy (158±10 kJ mol(-1)) and confirmation that the NHC sits upright on the surface. The use of these films in surface plasmon resonance-type biosensing is described, where they provide specific advantages versus traditional thiol-based films.

| S-EPMC5025784 | biostudies-literature

Human mesenchymal stem cell differentiation on self-assembled monolayers presenting different surface chemistries.

Project description:Human mesenchymal stem cells (hMSCs) have tremendous potential as a cell source for regenerative medicine due to their capacity for differentiation into a wide range of connective tissue cell types. Although significant progress has been made in the identification of defined growth factor conditions to induce lineage commitment, the effect of underlying biomaterial properties on functional differentiation is far less understood. Here we conduct a systematic assessment of the role for surface chemistry on cell growth, morphology, gene expression and function during hMSC commitment along osteogenic, chondrogenic and adipogenic lineages. Using self-assembled monolayers of omega-functionalized alkanethiols on gold as model substrates, we demonstrate that biomaterial surface chemistry differentially modulates hMSC differentiation in a lineage-dependent manner. These results highlight the importance of initial biomaterial surface chemistry on long-term functional differentiation of adult stem cells, and suggest that surface properties are a critical parameter that must be considered in the design of biomaterials for stem cell-based regenerative medicine strategies.

| S-EPMC2787851 | biostudies-literature

The electronic structure of mixed self-assembled monolayers.

Project description:The electronic structure of mixed self-assembled monolayers (SAMs) on Au(111) surfaces is modeled using slab-type density-functional theory calculations. The studied molecules have a dipolar character induced by polar and electron donating or accepting tail-group substituents. The resulting electronic structure of mixed layers is found to differ qualitatively from a simple superposition of those of the respective pure layers. Specifically, the positions of the frontier electronic states are shifted relative to the metal Fermi level, with the sign and magnitude of that shift depending on the dipole moment of the molecules and the mixing ratio in the film. This appears counterintuitive considering previous investigations, in which it has been shown that, for densely packed layers, tail-group substituents have no impact on the interfacial energy-level alignment. The seeming contradiction can be lifted by considering the local electrostatic interactions within the films in both mixed and homogeneous monolayers. Beyond that, we show that mixed SAMs provide an efficient tool for continuously tuning substrate work functions over a range that far exceeds that accessible by merely changing the coverage of homogeneous layers, with the net effect depending linearly on the mixing ratio in agreement with recent experimental findings.

| S-EPMC3011841 | biostudies-other

Photocatalytic nanolithography of self-assembled monolayers and proteins.

Project description:Self-assembled monolayers of alkylthiolates on gold and alkylsilanes on silicon dioxide have been patterned photocatalytically on sub-100 nm length-scales using both apertured near-field and apertureless methods. Apertured lithography was carried out by means of an argon ion laser (364 nm) coupled to cantilever-type near-field probes with a thin film of titania deposited over the aperture. Apertureless lithography was carried out with a helium-cadmium laser (325 nm) to excite titanium-coated, contact-mode atomic force microscope (AFM) probes. This latter approach is readily implementable on any commercial AFM system. Photodegradation occurred in both cases through the localized photocatalytic degradation of the monolayer. For alkanethiols, degradation of one thiol exposed the bare substrate, enabling refunctionalization of the bare gold by a second, contrasting thiol. For alkylsilanes, degradation of the adsorbate molecule provided a facile means for protein patterning. Lines were written in a protein-resistant film formed by the adsorption of oligo(ethylene glycol)-functionalized trichlorosilanes on glass, leading to the formation of sub-100 nm adhesive, aldehyde-functionalized regions. These were derivatized with aminobutylnitrilotriacetic acid, and complexed with Ni(2+), enabling the binding of histidine-labeled green fluorescent protein, which yielded bright fluorescence from 70-nm-wide lines that could be imaged clearly in a confocal microscope.

| S-EPMC4327559 | biostudies-other

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