Plasma lithography--thin-film patterning of polymers by RF plasma polymerization II: Study of differential binding using adsorption probes

Controlling cell behavior through the design of polymer surfaces

Polymers have gained a remarkable place in the biomedical field as materials for the fabrication of various devices and for tissue engineering applications. The initial acceptance or rejection of an implantable device is dictated by the crosstalk of the material surface with the bioentities present in the physiological environment. Advances in microfabrication and nanotechnology offer new tools to investigate the complex signaling cascade induced by the components of the extracellular matrix and consequently allow cellular responses to be tailored through the mimicking of some elements of the signaling paths. Patterning methods and selective chemical modification schemes at different length scales can provide biocompatible surfaces that control cellular interactions on the micrometer and sub-micrometer scales on which cells are organized. In this review, the potential of chemically and topographically structured micro- and nanopolymer surfaces are discussed in hopes of a better understanding of cell-biomaterial interactions, including the recent use of biomimetic approaches or stimuli-responsive macromolecules. Additionally, the focus will be on how the knowledge obtained using these surfaces can be incorporated to design biocompatible materials for various biomedical applications, such as tissue engineering, implants, cell-based biosensors, diagnostic systems, and basic cell biology. The review focusses on the research carried out during the last decade.

Novel high-resolution micropatterning for neuron culture using polylysine adsorption on a cell repellant, plasma-polymerized background

The ability to organize individual neurons and their processes in culture provides important benefits to both basic neuroscience research applications and the development of biomedical microdevices. While numerous methods have been used to produce such micropatterning of neurons and cells in general, there has yet been no method to simultaneously provide high-resolution patterns with high compliance of cells to desired patterns and good manufacturability. To develop such a process, this work used a plasma polymerized, nonfouling poly ethylene oxide (PEO)-like film to provide a cell repellant substrate on which cell adhesive micropatterns can be selectively laid down. While the use of plasma polymerized, organic films have been used for cell micropatterning, this process exploits the often-overlooked tendency for the surface of this PEO-like material to adsorb polylysine from aqueous solution while remaining nonfouling with respect to other species, such as bovine serum albumin (BSA) and immunoglobulin G (IgG). When the adsorption of polylysine was enhanced by brief plasma oxidation, which slightly alters the surface chemistry of the material, simple photolithographic liftoff could be used to micropattern stable, cell adhesive areas on an otherwise cell repellant background. We showed that the application of photolithography itself on the PEO-like material did not alter its chemical properties, nor did it result in the erosion of the micropatterned polylysine on its surface. Hippocampal neurons from embryonic mice flourished on these micropatterned substrates and exhibited viability comparable to neurons cultured on polylysine coated glass. Furthermore, the compliance of cell bodies and outgrowing neurites to the micropatterns was nearly perfect. In addition to providing cell adhesive regions, the micropatterned polylysine coating also served as a template mediating the immobilization of other bioactive species such as IgG and laminin. Using this "piggybacking" of laminin on polylysine, we were also able to culture and micropattern retinal ganglion cells (RGC).

The effect of RGD fluorosurfactant polymer modification of ePTFE on endothelial cell adhesion, growth, and function

We have synthesized and characterized a novel peptide fluorosurfactant polymer (PFSP) modification that facilitates the adhesion and growth of endothelial cells on expanded polytetrafluoroetheylene (ePTFE) vascular graft material. This PFSP consists of a poly(vinyl amine) (PVAm) backbone with integrin binding Arg-Gly-Asp (RGD) peptides and perfluorocarbon pendant branches for adsorption and stable adhesion to underlying ePTFE. Aqueous PFSP solution was used to modify the surface of fluorocarbon substrates. Following subconfluent seeding, endothelial cell (EC) adhesion and growth on PFSP was assessed by determining cell population at different time points. Spectroscopic results indicated successful synthesis of PFSP. PFSP modification of ePTFE reduced the receding water contact angle measurement from 120 degrees to 6 degrees , indicating successful surface modification. Quantification of cell population demonstrated reduced EC attachment efficiency but increased growth rate on RGD PFSP compared with fibronectin (FN). Actin staining revealed a well-developed cytoskeleton for ECs on RGD PFSP indicative of stable adhesion. Uptake of acetylated low-density lipoprotein and positive staining for VE-Cadherin confirm EC phenotype for adherent cells. Production of prostacyclin, a potent antiplatelet agent, was equivalent between ECs on FN and RGD PFSP surfaces. Our results indicate successful synthesis and surface modification with PFSP; this is a simple, quantitative, and effective approach to modifying ePTFE to encourage endothelial cell attachment, growth, and function.

Plasma lithography--thin-film patterning of polymeric biomaterials by RF plasma polymerization I: Surface preparation and analysis

Plasma lithography, combining plasma deposition with photolithography, is described as a versatile method to manufacture all-polymeric substrates with thin-film patterns for applications in biomedical engineering. Patterns of a hydrophobic fluorocarbon plasma polymer with feature sizes between 5 and 100 microm were deposited on a base substrate in a lift-off process: an intermediate tetraglyme plasma polymer layer provides non-fouling properties to the base substrate. Careful analysis of critical process parameters identified the narrow window of process conditions that led to the formation of functional surface patterns. High pattern fidelity, aspect ratios, and resolution of the patterns are demonstrated by atomic force microscopy. Electron spectroscopy for chemical analysis (ESCA) and secondary ion mass spectroscopy (SIMS) were used to characterize the surfaces, showing good retention of the original chemical structure of the pattern components throughout the process. SIMS imaging was used for specific chemical imaging of the components. Potential applications for the patterned polymer films, e.g., for studying cell behavior in vitro in dependence of shape and size of adhering cells, are discussed.