Publications (33)56.2 Total impact
- [Show abstract] [Hide abstract] ABSTRACT: A polymer MEMS sensor was developed for measuring the mechanical forces generated by single adherent cells. Mechanical forces are known to play a role in cell regulation, and measuring these forces is an important step in understanding cellular mechanotransduction. The sensor consisted of four polystyrene microcantilever beams with cell adhesion pads at the end of each beam. Finite element analysis was used to guide the design of a compound cantilever to allow measurement of forces in any direction in the plane of the sensor. The device was used to measure the forces generated by WS1 human skin fibroblasts under a microscope. Single cells were placed on the sensor using a custom micromanipulator. Forces were calculated by optically measuring the deflection of each probe during cell attachment and spreading. Measurements were performed on normal WS1 fibroblast cells and those treated with cytochalasin D to disrupt the actin cytoskeleton. Cytochalasin D treated cells showed a significant decrease in force, with time information about the rate of force change obtained from the sensor. This device can be used to evaluate the mechanical response of cells to a variety of chemical, mechanical, and other environmental stimuli.
- [Show abstract] [Hide abstract] ABSTRACT: In this work, the use of patterned proteins and peptides for the deposition of gold nanoparticles on several substrates with different surface chemistries is presented. The patterned biomolecule on the surface acts as a catalyst to precipitate gold nanoparticles from a precursor solution of HAuCl4 onto the substrate. The peptide patterning on the surfaces was accomplished by physical adsorption or covalent attachment. It was shown that by using covalent attachment with a linker molecule, the influence of the surface properties from the different substrates on the biomolecule adsorption and subsequent nanoparticle deposition could be avoided. By adjusting the reaction conditions such as pH or HAuCl4 concentration, the sizes and morphologies of deposited gold nanoparticle agglomerates could be controlled. Two biomolecules were used for this experiment, 3XFLAG peptide and bovine serum albumin (BSA). A micro-transfer molding technique was used to pattern the peptides on the substrates, in which a pre-patterned poly(dimethylsiloxane) (PDMS) mold was used to deposit a lift-off pattern of polypropylmethacrylate (PPMA) on the various substrates. The proteins were either physically adsorbed or covalently attached to the substrates, and an aqueous HAuCl4 solution was applied on the substrates with the protein micropatterns, causing the precipitation of gold nanoparticles onto the patterns. SEM, AFM, and Electron Beam Induced Current (EBIC) were used for characterization.
- [Show abstract] [Hide abstract] ABSTRACT: The process of spin dewetting was used to fabricate polymer micro and nanostructures from poly(methyl methacrylate) (PMMA), poly (propyl methacrylate) (PPMA), and polystyrene (PS). Polymer structures were formed on poly(dimethylsiloxane) (PDMS) molds by dewetting of a polymer solution during spin coating. Features were removed from the mold using heat and pressure to transfer the polymer to silicon or glass substrates. By varying the coating conditions, a variety of different polymer feature morphologies were obtained for a given PDMS mold geometry. In this study, the ability to fabrication polymer micro and nanostructures using spin dewetting was demonstrated on a variety of PDMS mold geometries. The effects of polymer solution concentration and mold feature size on the resulting polymer structures were examined. In addition, microfabricated PMMA structures were used as etch masks for anisotropic etching of silicon in an aqueous solution of tetramethylammonium hydroxide (TMAH).
- [Show abstract] [Hide abstract] ABSTRACT: We describe the combination of soft-lithographic patterning and biomolecule-induced deposition to create microscale patterns of silica on a diverse array of substrates. A soft lithographic technique was used to create a sacrificial layer of the polymer poly(n-propyl methacrylate) (PPMA) on the desired substrate. Subsequently, poly-L-lysine was deposited on the substrate, after which removal of the PPMA yielded a pattern of PLL on the substrate. Exposure of the PLL template to a silicic acid solution resulted in silica deposition in the pattern spatially and geometrically controlled by the PLL. With this procedure, we have created both continuous and discontinuous silica patterns on metallic, ceramic, and polymer substrates. While morphology of the deposited silica varied between substrates, the ability to pattern silica through this templated growth was demonstrated on all investigated substrates. EDS, optical micrography, and SEM analysis verified the controlled deposition of silica on the PLL template patterns. This PLL template-mediated induction of silica formation may facilitate the incorporation of silica in new microdevices and serve as a prototype process for controlled deposition with other biomolecule-material systems.
- [Show abstract] [Hide abstract] ABSTRACT: P-protein bodies (forisomes), in phloem cells of legumes, transform the chemical free energy of their reaction with alkaline earth metal ions into mechanical energy. In addition to using the bending of glass fibers, micromechanical forces generated by the switching of forisomes in aqueous solutions were measured by monitoring the bending of microscale polymer cantilever beams. The forisomes were fixed by chemisorption to the tips of four orthogonal beams of a BioMEMS microsystem designed and manufactured using the process of sacrificial layer micromolding. The sensor layout allows force measurements in the longitudinal and radial direction of the forisomes. For different forisomes a longitudinal force in the range from 84-136 nN and a radial force of 22-61 nN were measured.
- [Show abstract] [Hide abstract] ABSTRACT: Polyvinylidene fluoride (PVDF) microstructures are of interest for a number of BioMEMS applications both for their piezoelectric and biocompatible properties. In this work, simple soft lithography-based techniques were developed to fabricate PVDF microstructures with diverse geometries, including microarrays of pillars, lines, and wells. Four different microstructure configurations were created: freestanding, stamped discontinuous, stamped continuous and imprinted patterns. Features with lateral dimensions down to 1 μm were consistently reproduced on 2.5 cm diameter areas. Atomic force microscopy (AFM) measurements of poled PVDF microstructures confirmed a marked inverse piezoelectric behavior. The techniques presented here have a number of advantages over previously demonstrated PVDF micropatterning approaches.
- [Show abstract] [Hide abstract] ABSTRACT: A combination of soft lithography and lift-off processing is presented for the fabrication of sulfonated polyaniline (SPAN) microstructures. A soft lithography based micromolding process was used to pattern sacrificial layers using a thermoplastic polymer. SPAN was then polymerized in situ to coat the patterned substrate. The sacrificial layer was removed by lift-off in an organic solvent, leaving the patterned SPAN on the substrate. This process was performed on several rigid and flexible substrates including glass, silicon, and polyimide. The film thickness and roughness were measured as a function of reaction time using atomic force microscopy. Patterns were also imaged using scanning electron microscopy. This process provides a cost effective and versatile method of patterning SPAN and has potential applications in a number of conducting polymer devices.
- [Show abstract] [Hide abstract] ABSTRACT: While there has been rapid development of microfabrication techniques to produce high-resolution surface modifications on a variety of materials in the last decade, there is still a strong need to produce novel alternatives to induce guided tissue regeneration on dental implants. High-resolution microscopy provides qualitative and quantitative techniques to study cellular guidance in the first stages of cell-material interactions. The purposes of this work were (1) to produce and characterize the surface topography of isotropic and anisotropic microfabricated silica thin films obtained by sol-gel processing, and (2) to compare the in vitro biological behavior of human bone marrow stem cells on these surfaces at early stages of adhesion and propagation. The results confirmed that a microstamping technique can be used to produce isotropic and anisotropic micropatterned silica coatings. Atomic force microscopy analysis was an adequate methodology to study in the same specimen the sintering derived contraction of the microfabricated coatings, using images obtained before and after thermal cycle. Hard micropatterned coatings induced a modulation in the early and late adhesion stages of cell-material and cell-cell interactions in a geometry-dependent manner (i.e., isotropic versus anisotropic), as it was clearly determined, using scanning electron and fluorescence microscopies.
- [Show abstract] [Hide abstract] ABSTRACT: We present a simple method to actively pattern individual cells and groups of cells in a polymer-based microdevice using vacuum-assisted cell seeding. Soft lithography is used to mold polymer microwells with various geometries on top of commercially available porous membranes. Cell suspensions are placed in a vacuum filtration setup to pull culture medium through the microdevice, trapping the cells in the microwells. The process is evaluated by determining the number of cells per microwell for a given cell seeding density and microwell geometry. This method is tested with adherent and nonadherent cells (NIH 3T3 fibroblasts, PANC-1 pancreatic ductal epithelial-like cells, and THP-1 monocytic leukemia cells). These devices could find applications in high-throughput cell screening, cell transport studies, guided formation of cell clusters, and tissue engineering.
Conference Paper: Polymer MEMS for Measuring Single Cell Forces[Show abstract] [Hide abstract] ABSTRACT: We have developed a polymer MEMS sensor for measuring mechanical forces generated by single adherent cells. Mechanical forces are known to play a role in cell regulation, and measuring these forces is an important step in understanding cellular mechanotransduction. The sensor consists of four polystyrene microcantilever beams with cell adhesion pads at each end. Finite element analysis was used to guide the design of a compound cantilever to allow measurement of forces in multiple directions. The device was evaluated by measuring forces generated by WS-1 human skin fibroblasts. A single cell was placed on the sensor using a custom micromanipulator. Forces were calculated by optically measuring the deflection of each probe during cell attachment and spreading. Measurements were performed on normal cells and those treated with cytochalasin D to disrupt the actin cytoskeleton. Cytochalasin D treated cells showed a significant decrease in force. This device can be used to evaluate the mechanical response of cells to a variety of chemical, mechanical, and other environmental stimuli.
- [Show abstract] [Hide abstract] ABSTRACT: From a biomaterials perspective, it is now understood that success in the osseointegration of a dental implant is conditioned by its “macro”, “micro” and “nano” scale features. Macro-scale roughness is necessary to improve primary stabilization in the post-surgical phase inducing a peri-implant thin fibrous layer. However, the more complex process in the true cell-material interaction is dependent on micro and nano scale phenomena. There is clear evidence that cell adhesion, proliferation, organization and phenotype are modulated at the micro-scale and that protein absorption is fundamentally a process conditioned at nano-scale.
- [Show abstract] [Hide abstract] ABSTRACT: Cell behaviour such as adhesion, morphology, proliferation and functional activity are highly influenced by surface properties including hydrophobicity, roughness, texture and morphology. These surface properties may be controlled using a mixture of additive coating techniques to produce glass coatings by sol-gel process and soft lithography on dental ceramics. The purpose of this work was to compare cell adhesion and early orientation of Human Bone Marrow (HBM) cells cultured on micro-patterned (micro-PGC) and on flat glass coatings (FGC) produced by sol-gel processing. Spin coating was used to apply SiO 2 flat coatings on glass substrates as model surfaces. Photolithography was applied to produce master patterns with microscale dimensions. A moulding technique was used to print micropatterned SiO 2 glass coatings produced by a sol-gel process. The coatings were then sintered, sterilized and cultured with HBM cells derived from primary cultures, using a standardized protocol, for 1 and 7 days. Cell morphology and orientation were observed using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Flat and MPGC with line shaped features were produced. Cells presented a typical osteoblastic morphology on flat surfaces while slimmer, preferentially oriented and more elongated morphologies could be seen on line micro-patterned surfaces. HBM cells cultured on flat glass coatings showed increased tendency to spread and to assume more randomized proliferation when compared to the cells on the micro-patterned glass coatings. Micro-patterned glass coatings showed higher orientation control and smaller delay in the rate of proliferation, in early stages of in vitro culture as compared to flat coatings. These preliminary studies revealed that Micro-PGC induce significant morphological changes and controlled orientation of HBM cells during early stages of cell proliferation.
- [Show abstract] [Hide abstract] ABSTRACT: Mechanical forces generated by forisomes were measured using a microfabricated polymer cantilever sensor. The forces were simultaneously measured in both the longitudinal and radial directions. Sensors were fabricated from polystyrene using the sacrificial layer micromolding process. The sensor response was simulated using finite element analysis. Forces in the longitudinal direction ranged from 84 to 136 nN and forces in the radial direction were 22-61 nN. This device offers a new approach to measuring small magnitude biological forces. In addition, the ability to accurately measure forces generated by forisomes is an important step toward their implementation as functional structures in microdevices.
- [Show abstract] [Hide abstract] ABSTRACT: We report a method for depositing bioactive coatings onto cement materials for bone tissue engineering applications. White Portland cement substrates were hydrated under a 20% CO2 atmosphere, allowing the formation of CaCO3. The substrates were incubated in a calcium phosphate solution for 1, 3, and 6 days (CPI, CPII, and CPIII respectively) at 37 °C to induce the formation of carbonated apatite. Cement controls were prepared and hydrated with and without CO2 atmosphere (C+ and C− respectively). The presence of apatite-like crystals was verified by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The substrate cytocompatibility was evaluated via SEM after 24 hour cell cultures. SEM revealed the presence Ca(OH)2 on C−, and CaCO3 on C+. Apatite-like crystals were detected only on CPIII, confirmed by phosphorus EDS peaks only for CPIII. Cells attached and proliferated similarly well on all the substrates except C−. These results prove the feasibility of obtaining biocompatible and bioactive coatings on Portland cement for bone tissue engineering applications.
- [Show abstract] [Hide abstract] ABSTRACT: Precise surface geometrical morphologies have been shown to improve cellular proliferation, adhesion, and functionality. It has been found that cells respond strongly to feature dimensions a fraction of their size. In this paper, soft lithography techniques were applied to microfabricate polydimethylsiloxane molds with precisely controlled micro-scale patterns. Three-dimensional polycaprolactone (PCL) scaffolds were fabricated using a multilayer micromolding (MMM) method. Proper heating and stamping parameters were developed for micromolding PCL. This process allowed control of the size, shape, and spacing of support structures within the scaffold. The micromolding of multiple layers with independent features allowed for alignment between layers. The high porosity, abundant interconnections, and sharp features were inherent advantages of the scaffolds. Human osteosarcoma cells were seeded in the 3-D scaffolds for cell growth testing. Fluorescent microscopy and scanning electron micrographs showed that cells responded well to the 3-D scaffolds and the scaffolds regulated cell morphology and adhesion.
- [Show abstract] [Hide abstract] ABSTRACT: We present a method for the fabrication of electroactive polyvinylidene fluoride (PVDF) microstructures via soft lithography for BioMEMS applications. Previously patterned PDMS stamps were used to produce arrays of PVDF microstructures with different geometries, dimensions, and configurations. The microstructures were electrically poled and the inverse piezoelectric effect was studied using a stimulating voltage between 0 and ± 8 V. Non-poled specimens served as controls. Scanning electron microscopy (SEM) was used for morphological characterization. Preliminary cytocompatibility studies were conducted using a bone marrow stem cell line and the direct contact assay. SEM observations revealed that PVDF structures presented highly defined geometry at the microscale. Feature dimensions ranged between ~ 3 and 20 μm. Poled microstructures were effectively deformed in response to the stimulating voltage. Control samples did not exhibit piezoelectric behavior. Cell culture experiments confirmed the cytocompatibility of PVDF (both flat and micropatterned). The cells exhibited strong interactions with tips and corners of the microfeatures. Piezoelectric PVDF microstructures could potentially be used in a number of BioMEMS applications, including the development of electroactive tissue engineering scaffolds, cell and tissue force sensing microdevices, microactuators, acoustic microtransducers, and energy harvesting microcomponents among others.
Conference Paper: Measurement of Cell Forces Using a Polymer MEMS Sensor.[Show abstract] [Hide abstract] ABSTRACT: Cellular mechanics are responsible for execution and regulation of a number of cell functions. Mechanical forces generated within the cytoskeleton are transmitted via transmembrane linkages to the underlying substrate. Measurement of these forces could lead to a wealth of additional information about the role of cell mechanics in regulating cell function and signal transduction. Here we describe the design, fabrication, and testing of a polystyrene cantilever beam array for measuring forces generated by WS1 human skin fibroblasts. Finite element analysis was used to guide the design of a compound cantilever beam. Sensors were fabricated from polystyrene to provide a well-studied and biocompatible surface for cell attachment. Soft lithography based techniques were used for microfabrication of the sensors. Cells were placed on four and eight probe cantilever sensors and deflection of the probes was measured optically during attachment and spreading of the cells. The device was successfully used to measure time varying mechanical forces generated by fibroblast cells.
- [Show abstract] [Hide abstract] ABSTRACT: Two soft lithography based fabrication techniques are employed for fabricating mechanically independent, freely suspended polymer microstructure from poly(n-propyl methacrylate) (PPMA), poly(methyl methacrylate) (PMMA), and polystyrene. Both methods involve a micromolding process followed by thermal bonding to the substrate. The first method, sacrificial layer micromolding, uses a water soluble sacrificial layer, allowing functional structures to be released by immersion in water. The second method, patterned substrate micromolding, uses a permanent substrate patterned via photolithography. Functional regions of the polymer MEMS are suspended over the voids in the photoresist pattern. The processes have been applied to the fabrication of polymer microstructures with a variety of geometries for specific applications. Devices have included microcantilevers, beams, and other more complicated microstructures. The thermal molding process is conceivably applicable to the fabrication of microstructures from a wide variety of thermoplastic polymers, allowing material selection to be tailored based on application.
- [Show abstract] [Hide abstract] ABSTRACT: Large and well-defined arrays of both nanowires and micro/nanoparticles or only micro/nanoparticles are fabricated from aqueous solutions through a one-step dewetting process on an array of polydimethylsiloxane (PDMS) micropillars.
- [Show abstract] [Hide abstract] ABSTRACT: Polymers are used in biological micro-nanoelectromechanical systems (BioMEMS/NEMS) applications due to their desirable mechanical properties, biocompatibility, and reduced cost relative to silicon microfabrication processes. Understanding the interfacial properties of the films that are used in BioMEMS/NEMS serves as a useful tool in obtaining higher device yield and greater mechanical reliability. In this study, polystyrene (PS) and glycidyl-ether-bisphenol-A novolac polymer (SU8) on silicon substrates were investigated. SU8 is a commonly used material in MEMS/NEMS fabrication, while PS is evaluated for its potential use in BioMEMS/NEMS for interaction with biological cells. The aim is to examine the delamination of the interfaces. Nanoindentation was employed on the PS/Si and SU8/Si film systems coated with a thin metallic layer of Cr to facilitate delamination. The interfacial adhesion energy was determined from measuring the size of the resulting delamination and the contact radius. Scale effects were investigated by comparing the behavior of thin and thick PS and SU8 films, where a thickness dependence on the interfacial adhesion energy was observed. In addition to room temperature testing, film delamination experiments were conducted at 50 and 70 ° C by fitting the nanoindenter with a heating stage in order to study temperature effects. Nanoindentation-induced delamination is demonstrated for microstrips of PS and SU8 and the measured interfacial adhesion energy is compared to those obtained from films.
The Ohio State University
Columbus, OH, United States
- Department of Biomedical Engineering