We examined how variations in elastic modulus, surface chemistry and the height and spacing of micro-ridges interact and effect endothelial cell (EC) alignment. Specifically, we employed independent control of the surface properties in order to elucidate the relative importance of each factor. Polydimethylsiloxane elastomer (PDMSe) was fabricated with 1.5 or 5 microm tall, 5 microm spaced and 5, 10, or 20 microm wide ridge microtopographies. Elastic modulus was varied from 0.3, 1.0, 1.4, and 2.3 MPa by controlling oligomeric additives and crosslink density. Surface chemistry was left untreated, argon plasma treated, coated with fibronectin (Fn) or patterned with Fn tracks on flat PDMSe or the tops of micro-ridges. Primary porcine vascular ECs were cultured on the PDMSe substrates and nuclear form factor (NFF) was used to determine cell orientation relative to surface microtopography. Experimental results showed that microtopographical variation strongly altered EC alignment on Fn coated surfaces, but not on plasma treated surfaces. Interestingly, similar alignment was achieved with different orientation cues, either micropatterned chemistry (2D) or microtopography (3D). In total, the effect of varying one of the experimental parameters depended strongly on the state of the others, highlighting the need for multi-factor analysis of surface properties for applications where cells and tissue will contact synthetic materials.

The sol-gel synthesis of a bioactive glass (BAG) sol with the incorporation of polyvinylpyrrolidone and the subsequent spraying of short, discontinuous fibers is reported. The incorporation of the polymer into the BAG sol allowed for increased control of the rheological properties and resulted in a more homogeneous fibrous material when sprayed through an air gun. Reaction kinetics and sol viscosity were monitored and analyzed during synthesis, and fibers were characterized using scanning electron microscopy and thermal analysis. Fibers were sintered at 900 degrees C and were examined for in vitro bioactivity in a simulated body fluid solution. The presence of hydroxyapatite crystals is confirmed by examination with scanning electron microscopy, energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Both the proliferation rate and cell density of rat mesenchymal stem cells cultured on BAG fiber constructs of varying porosities were shown to be dependent upon fiber spacing.

The energetics of a polydimethylsiloxane (PDMS) elastomer biointerface were micro-engineered through topographical and chemical modification to elicit controlled cellular responses. The PDMS elastomer surfaces were engineered with micrometer scale pillars and ridges on the surface and variable mechanical properties intended to effect directed cell behavior. The topographical features were created by casting the elastomer against epoxy replicas of micropatterned silicon wafers. Using UV photolithography and a reactive ion etching process, highly controlled and repeatable surface microtextures were produced on these wafers. AFM, SEM and white light interference profilometry (WLIP) confirmed the 197 high fidelity of the pattern transfer process from wafer to elastomer. Ridges and pillars 5 μm wide and 1.5 μm or 5 μm tall separated by valleys at 5 μm, 10 μm, or 20 μm widths were examined. Mechanical properties were modulated by addition of linear and branched nonfunctional trimethylsiloxy terminated silicone oils.The modulus of the siloxane elastomer decreased from 1.43 MPa for the unmodified formulation to as low as 0.81 MPa with additives. The oils had no significant effect on the surface energy of the siloxane elastomer as measured by goniometry. Two main biological systems were studied: spores of the green alga Enteromorpha and porcine vascular endothelial cells (PVECs). The density of Enteromorpha spores that settled increased as the valley width decreased. The surface properties of the elastomer were altered by Argon plasma, radio frequency glow discharge (RFGD) treatment, to increase the hydrophilicity for PVEC culture. The endothelial cells formed a confluent layer on the RFGD treated smooth siloxane surface that was interrupted when micro-topography was introduced.

Cell movement, differentiation and metabolic function must be controlled in precise ways to produce both regenerated tissues such as bone and functional tissue equivalents such as immuno-isolated islet cells. Close examination of extracellular matrix (ECM) reveals structures on the micron and nanometer scale that are shown to influence these factors and therefore we hypothesize that cells will move based on topographical cues in the scaffold. We have engineered siloxane elastomer surfaces that mimic the ECM by combining micron and nanometer scale topographic features. Micron scale pillars and ridges ranging in height from 1.5 to 5 microns and separated by 5, 10 and 20 microns were fabricated in a silicon wafer using micro- processing techniques and replicated in polydimethylsiloxane (PDMS) elastomer. Nanometer scale pillars, ridges and more complex shapes ranging in height from 12 to 300 nanometers were superimposed on the micron scale features using nanolithography. This was achieved by using a tapping mode tip in the atomic force microscope (AFM) to plastically deform the substrate surface. The AFM enabled nano-features to be placed on sloped surfaces and added directly to the PDMS elastomer surface. Surface topography was examined using scanning electron microscopy, atomic force microscopy and white light interference profilometry to verify surface modifications and fidelity of the replication process. Results indicate that it is possible to create spatially engineered surface textures from 10-5 m to 10-8 m in size, in specified patterns, by using a combination of microprocessing and nanolithography techniques. As better understanding of ECM function and design is gained, the processing methods outlined here will assist in fabricating tissue engineering scaffolds optimized at the nanometer and micron scale.

A main limitation of biomedical devices is the inability to start, stop, and control cell growth making it crucial to develop biomaterial surfaces that induce a desired cellular response. Micropatterns of ridges and pillars were created in a siloxane elastomer (Dow Corning) by casting against epoxy replicates of a micromachined silicon wafer. Silicone oils were incorporated to determine the change in modulus and surface energy caused by these additives. SEM and white light interference profilometry verified that the micropatterning process produced high fidelity, low defect micropatterns. Mechanical analysis indicated that varying the viscosity, weight percent and functionality of the added silicone oil could change the elastic modulus by over an order of magnitude (0.1-2.3 MPa). As a self-wetting resin, silicone oils migrate to the surface, hence changing the surface properties from the bulk. Both topographical and chemical features define the surface energy, which in combination with elastic modulus, dictate biological activity. The results imply that the morphology, mechanical properties and surface energy of the siloxane elastomer can be modified to elicit a specific cell response as a function of engineered topographical and chemical functionalization.