Topographical and physicochemical modification of material surface to enable patterning of living cells

Cellular alignment by grafted adhesion peptide surface density gradients

The extracellular matrix and extracellular matrix-associated proteins play a major role in growth and differentiation of tissues and organs. To date, few methods have been developed that allow researchers to examine the affect of surface density gradients of adhesion molecules in a controlled manner. Fibroblasts cultured on surfaces with a surface density gradient of RGD peptide aligned parallel to the gradient while fibroblasts on constant density RGD surfaces spread but did not align as has been shown in numerous earlier studies. Not only did fibroblasts align on the gradient surfaces, but they also showed significantly greater elongation than on constant density peptide surfaces or on control surfaces. This type of method is easy to replicate and can be used by laboratories interested in investigating alignment of various cell types without mechanical force or other stimulation, and without cell-cell interaction or for investigation of affects of surface density gradients of molecules on cellular biochemistry and biophysics. This method also has potential applications for developing scaffolds for tissue engineering applications where cellular alignment is necessary.

Surface chemistry modulates focal adhesion composition and signaling through changes in integrin binding

Biomaterial surface properties influence protein adsorption and elicit diverse cellular responses in biomedical and biotechnological applications. However, the molecular mechanisms directing cellular activities remain poorly understood. Using a model system with well-defined chemistries (CH3, OH, COOH, NH2) and a fixed density of the single adhesive ligand fibronectin, we investigated the effects of surface chemistry on focal adhesion assembly and signaling. Surface chemistry strongly modulated integrin binding and specificity--alpha5beta1 integrin binding affinity followed the pattern OH>NH2=COOH>CH3, while integrin alphaVbeta3 displayed the relationship COOH>NH2>>OH=CH3. Immunostaining and biochemical analyses revealed that surface chemistry modulates the structure and molecular composition of cell-matrix adhesions as well as focal adhesion kinase (FAK) signaling. The neutral hydrophilic OH functionality supported the highest levels of recruitment of talin, alpha-actinin, paxillin, and tyrosine-phosphorylated proteins to adhesive structures. The positively charged NH2 and negatively charged COOH surfaces exhibited intermediate levels of recruitment of focal adhesion components, while the hydrophobic CH3 substrate displayed the lowest levels. These patterns in focal adhesion assembly correlated well with integrin alpha5beta1 binding. Phosphorylation of specific tyrosine residues in FAK also showed differential sensitivity to surface chemistry. Finally, surface chemistry-dependent differences in adhesive interactions modulated osteoblastic differentiation. These differences in focal adhesion assembly and signaling provide a potential mechanism for the diverse cellular responses elicited by different material properties.

Guiding neuronal development with in situ microfabrication

We report the ability to modify microscopic 3D topographies within dissociated cultures, providing a means to alter the development of neurons as they extend neurites and establish interconnections. In this approach, multiphoton excitation is used to focally excite noncytotoxic photosensitizers that promote protein crosslinking, such as BSA, into matrices having feature sizes >/=250 nm. Barriers, growth lanes, and pinning structures comprised of crosslinked proteins are fabricated under conditions that do not compromise the viability of neurons both on short time scales and over periods of days. In addition, the ability to fabricate functional microstructures from crosslinked avidin enables submicrometer localization of controllable quantities of biotinylated ligands, such as indicators and biological effectors. Feasibility is demonstrated for using in situ microfabrication to guide the contact position of cortical neurons with micrometer accuracy, opening the possibility for engineering well defined sets of synaptic interactions.

A photochemical method for patterning the immobilization of ligands and cells to self-assembled monolayers

This work describes a chemically well defined method for patterning ligands to self-assembled monolayers (SAMs) of alkanethiolates on gold. This method begins with monolayers presenting a nitroveratryloxycarbonyl (NVOC)-protected hydroquinone which is photochemically irradiated to reveal a hydroquinone group. The resulting hydroquinone is then oxidized to the corresponding benzoquinone, providing a site for the Diels-Alder mediated immobilization of ligands. The rate constant for the photochemical deprotection is 0.032 s(-1) (with an intensity of approximately 100 mW/cm(2) between 355 and 375 nm), corresponding to a half-life of 21 s. The hydroquinone is oxidized to the benzoquinone using either electrochemical or chemical oxidation and then functionalized by reaction with a cyclopentadiene-tagged ligand. Two methods for patterning the immobilization of ligands are described. In the first, the substrate is illuminated through a mask to generate a pattern of hydroquinone groups, which are elaborated with ligands. In the second method, an optical microscope fit with a programmable translational stage is used to write patterns of deprotection which are then again elaborated with ligands. This technique is characterized by the use of well-defined chemical reactions to control the regions and densities of ligand immobilization and will be important for a range of applications that require patterned ligands for biospecific interactions.

Engineering the morphology and electrophysiological parameters of cultured neurons by microfluidic surface patterning

The ability to control the orientation, morphology, and electrophysiological characteristics of neurons in culture allows the construction of neural circuits with defined physiological properties. Using microfluidic protein deposition onto chemically modified glass, we achieve the controlled growth of Aplysia neurons on geometrical patterns of poly-L-lysine and collagen IV, surrounded by nonadhesive regions of bovine albumin. We investigate the parameters essential for forming functional neuronal networks, the morphology, biochemistry, and electrophysiology under engineered cell culture conditions. We demonstrate that not only the orientation of neurite extension but also the number of primary neurites originating from the cell soma, their length, and branching pattern depend on the spatial constraints presented by the size and shape of the adhesion region on the patterned substrate. In addition, the physicochemical properties of the support layer influence the electrical activity of the cultured neurons. Substrate-dependent changes in the amplitude and in the dynamic parameters of the action potential cause decreased spike broadening in patterned neurons, which reflects changes in the number or functioning of active membrane ion channels. In contrast to morphology and electrophysiology, the neuropeptide content, as determined by mass spectrometry of individual patterned neurons, is not affected by the growth on patterned surfaces. Our results suggest that the morphological and electrophysiological parameters of neurons can be predictably altered/engineered by modulation of the chemical, physical, and topographical features of culture substrates. We also demonstrate that a full suite of techniques is required for functional characterization of neurons on engineered substrates.

A biochip platform for cell transfection assays

In this paper, we describe the development and characterization of a biochip platform for cell transfection assays. Silicon wafers were surface modified by plasma polymerization of allylamine plasma polymer (ALAPP) and grafting of a protein-resistant layer of poly(ethylene oxide) (PEO) on the plasma polymer surface. Excimer laser ablation was then used to pattern ALAPP-PEO coated samples for spatially controlled protein adsorption and subsequent cell attachment. X-ray photoelectron spectroscopy (XPS) was used to characterize the surface modifications before and after excimer laser ablation. Experiments confirmed the creation of a two-dimensionally controlled surface chemistry on the biochip. Cell culture experiments using human embryonic kidney (HEK 293) cells showed that cells attached exclusively to laser ablated areas. In addition, cells confined to ablated areas were successfully transfected with plasmid DNA containing the gene for green fluorescent protein (GFP). The cell transfection efficiencies of cells growing in a culture flask and cells confined on the biochip were determined to be 21 and 13%, respectively.

Quantification of substratum contact required for initiation of Colletotrichum graminicola appressoria

Colletotrichum graminicola, like many plant pathogenic fungi develop appressoria on germling apices, to facilitate penetration of their host. Induction of these structures occurs after contact with the host surface has been established by the germling. Surface contact and subsequent development of appressoria by germlings of C. graminicola was assessed using interference-reflection microscopy (IRM) and microfabricated pillared silicon substrata. Observations with IRM revealed that under low nutrient conditions, 90% of the germlings developed appressoria once they established 4.5 microm of continuous contact with the substratum. Substrata bearing pillars < or =5 microm in width supported < or =10% appressoria; however, as pillar width was increased the percentage of appressoria formed increased in a sigmoid fashion to a maximum of 80%. The percentage of appressoria produced experimentally on these surfaces was compared to data sets generated from a model designed to calculate the probability of appressorium development on similar pillar arrays at various germ tube contact lengths. These results indicate that germ tubes of C. graminicola require more than 4microm of continuous contact with a hydrophobic substratum for induction of appressoria.

Shrinking the biologic world--nanobiotechnologies for toxicology

Although toxicologic effects need to be considered at the organismal level, the adverse events originate from interactions and alterations at the molecular level. Cellular structures and functions can be disrupted by modifications of the nanometer structure of critical molecules; therefore, devices used to assess biologic and toxicologic processes at the nanoscale will allow important new research pursuits. In order to properly assess alterations at these dimensions, nanofabricated tools are needed to detect, separate, analyze, and manipulate cells or biologic molecules of interest. The emergence of laser tweezers, surface plasmon resonance (SPR), laser capture microdissection (LCM), atomic force microscopy (AFM), and multi-photon microscopes have allowed for these assessments. Micro- and nanobiotechnologies will further advance biologic, clinical, and toxicologic endeavors with the aid of miniaturized, more sensitive devices. Miniaturized table-top laboratory equipment incorporating additional innovative technologies can lead to new advances, including micro total analysis systems (microTAS) or "lab-on-a-chip" and "sentinel sensor" devices. This review will highlight several devices, which have been made possible by techniques originating in the microelectronics industry. These devices can be used for toxicologic assessment of cellular structures and functions, such as cellular adhesion, signal transduction, motility, deformability, metabolism, and secretion.

Chemically patterned, metal oxide based surfaces produced by photolithographic techniques for studying protein- and cell-surface interactions I: Microfabrication and surface characterization

Chemical patterns on smooth wafer substrates comprising areas with two different metals have been produced by vacuum metal deposition and photolithographic techniques. The combination of metals has been chosen from the series titanium (Ti), aluminium (Al), vanadium (V) and niobium (Nb), producing patterns (dots and stripes with dimensions of 50, 100 and 150 micrometer) with one of the metals as the background and with the second metal (foreground pattern) deposited on the background metal. The structure and chemical composition of the patterned surfaces were evaluated by scanning electron microscopy, X-ray photoelectron spectroscopy and imaging time-of-flight secondary-ion mass spectrometry. The surfaces proved to be geometrically well defined with the expected surface-chemical composition, i.e. a surface oxide (passive) film essentially composed of TiO(2),Al(2)O(3),V(2)O(5), or Nb(2)O(5). Ti/Ti patterned surfaces were produced as controls and found to show no chemical composition contrast. The surface roughness of the pattern was greater than that of the background by a factor of 2-3, but was still extremely smooth with Ra<2nm. The patterns serve as model surfaces for studying in vitro the behaviour of cells as well as the adsorption of serum proteins on different metal oxides, which will be reported in a companion paper. These surfaces can be used to compare and contrast the response of osteoblasts to Ti and other alloy components, such as Al, V, or Nb, which are used in load-bearing medical implants.

What can surface chemistry do for cell biology?

Recent research has enhanced the development of substrates that serve as models of extracellular matrix and their use in studies of cell adhesion and migration. Advances include the development of methods to prepare substrates having ligands immobilized in controlled densities and patterns, and recent work that is developing dynamic substrates which can modulate, in real-time, the activities of ligands. These technologies are providing new opportunities for studies of cell-extracellular-matrix interactions.

Cell interactions with three-dimensional matrices

Signaling and other cellular functions differ in three-dimensional compared with two-dimensional systems. Cell adhesion structures can evolve in vitro towards in-vivo-like adhesions with distinct biological activities. In this review, we examine recent advances in studies of interactions of fibroblasts with collagen gels and fibronectin-containing matrices that mimic in vivo three-dimensional microenvironments. These three-dimensional systems are illuminating mechanisms of cell-matrix interactions in living organisms.