NANO LETTERS
Receptor−Ligand-Based Specific Cell Adhesion on Solid Surfaces: Hippocampal Neuronal Cells on Bilinker Functionalized Glass
2006 Vol. 6, No. 9 1977-1981
Siyuan Lu,† Anubhuti Bansal,‡ Walid Soussou,§ Theodore W. Berger,§ and Anupam Madhukar*,†,‡,§ Departments of Physics, Chemical Engineering & Material Science, and Biomedical Engineering, UniVersity of Southern California, Los Angeles, California 90089-0241 Received May 18, 2006; Revised Manuscript Received July 6, 2006
ABSTRACT Cell adhesion through binding between specific cell membrane receptors and corresponding cell-adhesion-molecule (CAM)-coated solid surfaces is examined. The morphology of surfaces at various modification steps leading to functionalization with cell-binding CAMs is characterized. In one week neuron cultures, enhanced growth on surfaces modified with neuron-binding versus astrocyte-binding CAMs is observed. However, nonspecific adhesion on a poly-D-lysine-coated positive control surface is found to be even higher. Potential reasons and further studies needed are discussed.
Introduction. Interaction between abiotic surfaces and cells and tissue is inherent in the use of medical prosthetic implants. For neural prostheses, stable external electrical stimulation of neuronal cells is a central objective for both basic studies and clinical therapies. Studies of this sort constitute a large part of neuroscience literature in areas such as brain1,2 and vision.1,3 In recent years, the introduction of multielectrode arrays that conform to the spatial architecture of the particular region of interest has allowed more effective stimulation and recording.1,4 A particular long-term objective of ours is to mimic the normal function provided by the CA3 (CA ) comu ammonis) subregion of the hippocampal slice in an appropriately designed biomimetic electronic chip whose purpose is to replace the brain function lost due to damage to the CA3. Although such an electronic chip is to reside on the skull, it is to receive input from and provide output to the undamaged regions adjacent to the damaged CA3 region through the use of deep penetrating metallic electrodes placed according to the local cortical architecture. In typical stimulation and recording studies, the involved abiotic surfaces, the metallic electrodes and the substrate, are coated with nonspecifically binding proteins to promote cell adhesion, growth, proliferation, and motility.5 Suppressing unwanted adsorption of proteins in the cell environment * Corresponding author. E-mail:
[email protected]. Phone: 1-213740-4323. Fax: 1-213-740-4333. † Department of Physics. ‡ Department of Chemical Engineering & Material Science. § Department of Biomedical Engineering. 10.1021/nl061139w CCC: $33.50 Published on Web 07/27/2006
© 2006 American Chemical Society
(culture medium or in vivo) and controlling electrode distance from the targeted cells are of central importance to efficient stimulation. There have, thus, been studies that examine specific binding of cells by coating the abiotic surface with a cell-adhesion molecule (CAM) specific to the surface receptor type of the neuronal cell, neuron or glia, of interest.6-9 We report here some initial results of studies motivated by our interest in understanding and controlling such specific and spatially selective binding of hippocampal neurons and astrocytes to, respectively, the electrode (metal) and ceramic surfaces presented to the neuronal tissue by the deep penetrating cortical implants such as in the hippocampus. The conducting electrode and nonconducting substrate regions in stimulating prostheses are shown schematically in Figure 1. For the deep penetrating cortical prostheses, the nonconducting region is made of a hard ceramic such as alumina and the electrodes are long stripes. For applications such as retinal prostheses, the substrate is a soft polymer with a two-dimensional array of electrodes.3 As noted above, a particular approach to tailoring and controlling such abiotic-biotic interfaces for specific and spatially selective adhesion of the neuronal cells is by functionalizing the surfaces with appropriate small peptide molecules6-9 called cell-adhesion molecules (CAMs), as shown schematically in Figure 2. The CAMs represent a small (∼1 nm) region of the extracellular matrix proteins, thought to be the minimal set of amino acid sequences effective in creating adhesion
Figure 1. Schematic of conducting electrodes on nonconducting substrates employed in prosthesis for electrical stimulation of cells and tissue.
Figure 2. (a) Schematic of cell binding to the substrate via specific membrane receptor interaction with corresponding cell-adhesion molecules (CAMs) coated on the substrate. Note that the undulation in the substrate surface is to depict a lateral scale (∼200 nm) of typical variation in the extracellular matrix topology and is on a length scale several orders of magnitude smaller than the size of the cell (b) Magnified view of a laterally nanoscale (
