Mammalian cell cultures on micropatterned surfaces of weak-acid, polyelectrolyte hyperbranched thin films on gold

Protein patterning by microcontact printing using pyramidal PDMS stamps

Micro-contact printing, μCP, is a well-established soft-lithography technique for printing biomolecules. μCP uses stamps made of Poly(dimethylsiloxane), PDMS, made by replicating a microstructured silicon master fabricated by semiconductor manufacturing processes. One of the problems of the μCP is the difficult control of the printing process, which, because of the high compressibility of PDMS, is very sensitive to minute changes in the applied pressure. This over-sensitive response leads to frequent and/or uncontrollable collapse of the stamps with high aspect ratios, thus decreasing the printing accuracy and reproducibility. Here we present a straightforward methodology of designing and fabricating PDMS structures with an architecture which uses the collapse of the stamp to reduce, rather than enlarge the variability of the printing. The PDMS stamp, organized as an array of pyramidal micro-posts, whose ceiling collapses when pressed on a flat surface, replicates the structure of the silicon master fabricated by anisotropic wet etching. Upon application of pressure, depending on the size of, and the pitch between, the PDMS pyramids, an air gap is formed surrounding either the entire array, or individual posts. The printing technology, which also exhibits a remarkably low background noise for fluorescence detection, may find applications when the clear demarcation of the shapes of protein patterns and the distance between them are critical, such as microarrays and studies of cell patterning.

Effect of composite SiO₂@AuNPs on wound healing: in vitro and vivo studies

Recently gold nanomaterials have been widely applied in the biomedical field, but their biosafety is still controversial. We immobilized small gold nanoparticles (AuNPs) on a large silica substrate to form silica-gold core-shell materials (SiO2@AuNPs) via classical seed-mediated growth. In vitro, 500 nm-SiO2@AuNPs could promote the proliferation of mouse embryonic fibroblast cells (NIH/3T3). The results of transmission electron microscope (TEM) showed that the vast majority of particles did not enter cells and that the morphology of microtubules experienced no change as observed in the confocal microscope images. The mechanism may be that the large silica substrate kept AuNPs outside the cells and the nano-size concavo-convex gold shell facilitated to cell adhesion, resulting in the proliferation. In vivo, a cutaneous full-thickness excisional wound rat model was applied to assess the healing efficiency of 500 nm-SiO2@AuNPs. The results indicated that SiO2@AuNPs could promote wound healing, which was potentially related to the anti-inflammatory and antioxidation of AuNPs. The pathological finding showed that the healing levels of SiO2@AuNPs were significantly better than those of the control groups. Our study may provide insight into the application of silica-gold core-shell materials in the treatment of cutaneous wounds.

PDMS substrate stiffness affects the morphology and growth profiles of cancerous prostate and melanoma cells

A deep understanding of the interaction between cancerous cells and surfaces is particularly important for the design of lab-on-chip devices involving the use of polydimethylsiloxane (PDMS). In our studies, the effect of PDMS substrate stiffness on mechanical properties of cancerous cells was investigated in conditions where the PDMS substrate is not covered with any of extracellular matrix proteins. Two human prostate cancer (Du145 and PC-3) and two melanoma (WM115 and WM266-4) cell lines were cultured on two groups of PDMS substrates that were characterized by distinct stiffness, i.e. 0.75 ± 0.06 MPa and 2.92 ± 0.12 MPa. The results showed the strong effect on cellular behavior and morphology. The detailed analysis of chemical and physical properties of substrates revealed that cellular behavior occurs only due to substrate elasticity.

Patterning of hyperbranched polymer films

This Review describes new methods for patterning functional hyperbranched poly(acrylic acid) thin polymer films. "Hyperbranched polymer" is a generic term used to describe a wide variety of polymeric materials that contain a high percentage of functional groups, that are highly branched, and that are irregular in structure. Hyperbranched polymer films (HPFs) are prepared by an iterative three-step process: activation of an acid functionalized surface, surface grafting of amine-terminated poly(tert-butyl acrylate), and hydrolysis to regenerate the acid surface. The resulting materials have a high density of acid groups, which can be functionalized with moieties that introduce interesting optical, electrochemical, biological, and mechanical properties to the films. HPFs can be patterned with micron-scale resolution using either a template-based approach or photolithography. Templates consist of self-assembled monolayers prepared by microcontact printing, whereas photolithographic patterning relies on selective hydrolysis using photoacids. Biocompatibility can be introduced by grafting a conformal layer of poly(ethylene glycol) atop the HPFs. Such patterns serve as templates for spatially segregating viable mammalian and bacterial cells. In addition to the PAA HPFs, another family of patternable HPFs consisting of dendrimers and an active anhydride copolymer is described.

Microfabricated Cell-based Biosensor Arrays

Here, we described the fabrication using photolithography of poly(ethylene glycol) (PEG)-based hydrogel microstructures encapsulating viable mammalian cells on glass and silicon substrates. Substrates were treated with 3-(trichlorosilyl) propyl methacrylate to form pendant acrylate group to covalent link the hydrogel microstructure. Cells were encapsulated in arrays of cylindrical hydrogel microstructures 600 and 50 μm in diameter and viability assays demonstrated that encapsulated cells remained viable after photoencapsulation. These microstructures had clearly defined, three-dimensional structure without any residual cells remaining surface and no delamination of hydrogel elements from functionalized substrate occurred in aqueous environment for over a week. By changing spin-coating rates and feature sizes of photomasks, we could create cell-containing microstructures with aspect ratios ranging from 0.12 to 1.4. In case of 50 μm hydrogel microstructure, number of cells could be limited to 1 or 2 cells per element and array consisting of 400 elements could be fabricated in a square of 2 mm². These cell-containinghydrogel microstructures were also successfully fabricated in poly(dimethylsiloxane) microchannels to create optical biosensor arrays of individually addressable single or multiple cell- containing hydrogel microstructures with potential applications in drug screening or pathogen detection.

Endothelial cell micropatterning: methods, effects, and applications

The effects of flow on endothelial cells (ECs) have been widely examined for the ability of fluid shear stress to alter cell morphology and function; however, the effects of EC morphology without flow have only recently been observed. An increase in lithographic techniques in cell culture spurred a corresponding increase in research aiming to confine cell morphology. These studies lead to a better understanding of how morphology and cytoskeletal configuration affect the structure and function of the cells. This review examines EC micropatterning research by exploring both the many alternative methods used to alter EC morphology and the resulting changes in cellular shape and phenotype. Micropatterning induced changes in EC proliferation, apoptosis, cytoskeletal organization, mechanical properties, and cell functionality. Finally, the ways these cellular manipulation techniques have been applied to biomedical engineering research, including angiogenesis, cell migration, and tissue engineering, are discussed.

Dopamine-assisted immobilization of poly(ethylene imine) based polymers for control of cell-surface interactions

Non-fouling coatings play a critical role in many biomedical applications, such as diagnostic assay materials, biosensors, blood contacting devices and other implants. In the present work we have developed a facile, one step deposition method based on dopamine polymerization for preparation of non-fouling and biotinylated surfaces for biomedical applications. Poly(ethylene imine)-graft-poly(ethylene glycol) co-polymer (PEI-g-PEG) was mixed with an alkaline dopamine solution and then deposited onto different substrates. The dopamine coatings formed by this method were characterized by X-ray photoelectron spectroscopy (XPS), and the results indicated successful deposition of PEG. The resultant dopamine coatings formed on tissue culture polystyrene by this method revealed successful deposition of PEG, as shown by XPS. PEI-g-PEG/dopamine deposition for 2h inhibited the adsorption of serum proteins and the attachment of fibroblasts, suggesting that PEG molecules were immobilized in a sufficient density on the surface of the coating. Furthermore, co-deposition of PEI-g-PEG and PEI-g-biotin in alkaline dopamine solutions provided a cell-resisting background surface, at the same time providing accessible biotin molecules. We have demonstrated that the surface can be used for the selective binding of avidin, followed by the binding of Arg-Gly-Asp-Ser-biotin and enhanced cell attachment by specific cell-ligand interactions. In conclusion, our one step immobilization method provides a simple tool to fabricate surfaces with controllable cell affinity.

In situ electrochemical imaging of membrane glycan expression on micropatterned adherent single cells

A scanning electrochemical microscopic (SECM) method for in situ imaging of four types of membrane glycan motifs on single adherent cells was proposed using BGC-823 human gastric carcinoma (BGC) cells as the model. These adherent cells were first micropatterned in the microwell of poly(dimethylsiloxane) membrane for precisely controlling the localized surface interaction, and the membrane glycans were then specifically recognized with corresponding lectins labeled with horseradish peroxidase (HRP). On the basis of the enzymatic oxidization of ferrocenylmethanol (FMA) by H(2)O(2) to yield FMA(+), the glycan expression level was detected by the reduction current of FMA(+) at the SECM tip. The cell-surface glycans could, thus, be in situ imaged by SECM at a single-cell level without peeling the cells from culture dish. Under the optimized conditions, four types of membrane glycan motifs showed statistically distinguishable expression levels. The SECM results for different glycan motifs on adherent single cells were consistent with those estimated by flow cytometric assay. This work provides a reliable approach for in situ evaluation of the characteristic glycopattern of single living cells and can be applied in cell biologic study based on cell surface carbohydrate expression.

Synthesis of gelatin-stabilized gold nanoparticles and assembly of carboxylic single-walled carbon nanotubes/Au composites for cytosensing and drug uptake

Gelatin-stabilized gold nanoparticles (AuNPs-gelatin) with hydrophilic and biocompatible were prepared with a simple and "green" route by reducing in situ tetrachloroauric acid in gelatin. The nanoparticles showed the excellent colloidal stability. UV-vis spectra, transmission electron microscopy (TEM), and atomic force microscopy revealed the formation of well-dispersed AuNPs with different sizes. By combination of the biocompatibility of AuNPs and excellent conductivity of carboxylic single-walled carbon nanotubes (c-SWNTs), a novel nanocomposite was designed for the immobilization and cytosensing of HL-60 cells at electrodes. The immobilized cells showed sensitive voltammetric response, good activity, and increased electron-transfer resistance. It can be used as a highly sensitive impedance sensor for HL-60 cells ranging from 1 x 10(4) to 1 x 10(7) cell mL(-1) with a limit of detection of 5 x 10(3) cell mL(-1). Moreover, the nanocomposite could effectively facilitate the interaction of adriamycin (ADR) with HL-60 cells and remarkably enhance the permeation and drug uptake of anticancer agents in the cancer cells, which could readily lead to the induction of the cell death of leukemia cells.

Patterned Au/poly(dimethylsiloxane) substrate fabricated by chemical plating coupled with electrochemical etching for cell patterning

In this paper, we present a novel approach for preparing patterned Au/poly(dimethylsiloxane) (PDMS) substrate. Chemical gold plating instead of conventional metal evaporation or sputtering was introduced to achieve a homogeneous gold layer on native PDMS for the first time, which possesses low-cost and simple operation. An electrochemical oxidation reaction accompanied by the coordination of gold and chloride anion was then exploited to etch gold across the region covered by electrolyte. On the basis of such an electrochemical etching, heterogeneous Au/PDMS substrate which has a gold "island" pattern or PDMS dots pattern was fabricated. Hydrogen bubbles which were generated in the etching process due to water electrolysis were used to produce a safe region under the Pt auxiliary electrode. The safe region would protect gold film from etching and lead to the formation of the gold "island" pattern. In virtue of a PDMS stencil with holes array, gold could be etched from the exposed region and take on the PDMS dots pattern which was selected to for protein and cell patterning. This patterned Au/PDMS substrate is very convenient to construct cytophobic and cytophilic regions. Self-assembled surface modification of (1-mercaptoundec-11-yl)hexa(ethylene glycol) on gold and adsorption of fibronectin on PDMS are suitable for effective protein and cell patterning. This patterned Au/PDMS substrate would be a potentially versatile platform for fabricating biosensing arrays.

Microfabricated implants for applications in therapeutic delivery, tissue engineering, and biosensing

By adapting microfabrication techniques originally developed in the microelectronics industry novel devices for drug delivery, tissue engineering and biosensing have been engineered for in vivo use. Implant microfabrication uses a broad range of techniques including photolithography, and micromachining to create devices with features ranging from 0.1 to hundreds of microns with high aspect ratios and precise features. Microfabrication offers device feature scale that is relevant to the tissues and cells to which they are applied, as well as offering ease of en masse fabrication, small device size, and facile incorporation of integrated circuit technology. Utilizing these methods, drug delivery applications have been developed for in vivo use through many delivery routes including intravenous, oral, and transdermal. Additionally, novel microfabricated tissue engineering approaches propose therapies for the cardiovascular, orthopedic, and ocular systems, among others. Biosensing devices have been designed to detect a variety of analytes and conditions in vivo through both enzymatic-electrochemical reactions and sensor displacement through mechanical loading. Overall, the impact of microfabricated devices has had an impact over a broad range of therapies and tissues. This review addresses many of these devices and highlights their fabrication as well as discusses materials relevant to microfabrication techniques.

Protein adsorption and cell adhesion on nanoscale bioactive coatings formed from poly(ethylene glycol) and albumin microgels

Late-term thrombosis on drug-eluting stents is an emerging problem that might be addressed using extremely thin, biologically active hydrogel coatings. We report a dip-coating strategy to covalently link poly(ethylene glycol) (PEG) to substrates, producing coatings with approximately <100 nm thickness. Gelation of PEG-octavinylsulfone with amines in either bovine serum albumin (BSA) or PEG-octaamine was monitored by dynamic light scattering (DLS), revealing the presence of microgels before macrogelation. NMR also revealed extremely high end-group conversions prior to macrogelation, consistent with the formation of highly crosslinked microgels and deviation from Flory-Stockmayer theory. Before macrogelation, the reacting solutions were diluted and incubated with nucleophile-functionalized surfaces. Using optical waveguide lightmode spectroscopy (OWLS) and quartz crystal microbalance with dissipation (QCM-D), we identified a highly hydrated, protein-resistant layer with a thickness of approximately 75 nm. Atomic force microscopy in buffered water revealed the presence of coalesced spheres of various sizes but with diameters less than about 100 nm. Microgel-coated glass or poly(ethylene terephthalate) exhibited reduced protein adsorption and cell adhesion. Cellular interactions with the surface could be controlled by using different proteins to cap unreacted vinylsulfone groups within the coating.

Micro- and nanometer-scale patterned surface in a microchannel for cell culture in microfluidic devices

A novel microdevice which had a micro- and nanometer-scale patterned surface for cell adhesion in a microchip was developed. The surface had a metal pattern fabricated by electron-beam lithography and metal sputtering and a chemical pattern consisting of a self-assembled monolayer of alkanethiol. The metal patterned surface had a gold stripe pattern which was as small as 300 nm wide and 150 nm high and both topography and chemical properties could be controlled. Mouse fibroblast NIH/3T3 cells were cultured on the patterned surface and elongated along the gold stripes. These cells recognized the size of the pattern and the chemical properties on the pattern though it was much smaller than they were. There was satisfactory cell growth under fresh medium flow in the microchip. The combination of the patterned surface and the microchip provides cells with a novel environment for their growth and will facilitate many cellular experiments.

Micropatterned surfaces of PDMS as growth templates for HEK 293 cells

In this paper the easy and reliable preparation of precise micropatterns on PDMS surfaces is described and the growth of HEK 293 cells on those patterns during culture over several days is examined. The first patterning approach described is based on soft-lithography and polyelectrolyte multilayer deposition. Two different soft-lithographic techniques are employed for creating surface patterns of PAH, PSS, untreated and oxidized PDMS. The growth behavior of HEK 293 cells is investigated on all the dual combinations of the four surfaces, and decreasing preference of the cells for the surfaces in the order PAH (-NH2)>ox-PDMS (-OH)>>PSS (-SO3-)>PDMS (-CH3) is revealed. As the second patterning approach a method is introduced, which allows the deposition of gel droplets in a microarray format utilizing differences in the surface wettability. This concept is new and expected to be very useful for various applications. Finally, a speculative explanation for the different cell spreading behavior is provided considering the interplay between individual cell-surface interactions and a permanent cell tractional force.

Anisotropic three-dimensional peptide channels guide neurite outgrowth within a biodegradable hydrogel matrix

The objective of this study was to investigate the neurite guidance potential of concentration gradients of glycine-arginine-glycine-aspartic acid-serine (GRGDS) oligopeptides immobilized within three-dimensional patterned cylindrical volumes created in a biodegradable nerve guidance matrix. This was achieved using ultraviolet (UV) laser micropatterning of a hyaluronan (HA) hydrogel matrix modified with S-2-nitrobenzyl cysteine. Upon exposure to focused laser light, the 2-nitrobenzyl group was cleaved, exposing thiol groups which reacted with maleimide-terminated GRGDS exclusively within these laser-defined volumes. We show that the UV laser micropatterning technique can be used to create GRGDS peptide concentration gradients within the oligopeptide channels and that these channels guide neurite outgrowth from primary neural cells.

Fabrication of cell-containing hydrogel microstructures inside microfluidic devices that can be used as cell-based biosensors

This paper describes microfluidic systems containing immobilized hydrogel-encapsulated mammalian cells that can be used as cell-based biosensors. Mammalian cells were encapsulated in three-dimensional poly(ethylene glycol)(PEG) hydrogel microstructures which were photolithographically polymerized in microfluidic devices and grown under static culture conditions. The encapsulated cells remained viable for a week and were able to carry out enzymatic reactions inside the microfluidic devices. Cytotoxicity assays proved that small molecular weight toxins such as sodium azide could easily diffuse into the hydrogel microstructures and kill the encapsulated cells, which resulted in decreased viability. Furthermore, heterogeneous hydrogel microstructures encapsulating two different phenotypes in discrete spatial locations were also successfully fabricated inside microchannels.

Patterning of a Random Copolymer of Poly[lactide-co-glycotide-co-(ɛ-caprolactone)] by UV Embossing for Tissue Engineering

The random copolymer, poly[lactide-co-glycotide-co-(epsilon-caprolactone)] (PLGACL) diacrylate was prepared by ring-opening polymerization of L-lactide, glycolide, and epsilon-caprolactone initiated with tetra(ethylene glycol). The diacrylated polymers were extensively characterized. With a UV embossing method, these copolymers were successfully fabricated into microchannels separated by microwalls with a high aspect (height/width) ratio. The PLGACL network films showed good cytocompatibility. Varieties of microstructures were fabricated, such as 10 x 40 x 60, 10 x 80 x 60, 25 x 40 x 60, or 25 x 80 x 60 microm(3) structures (microwall width x microchannel width x microwall height). The results demonstrated that smooth muscle cells (SMCs) can grow not only on the microchannel surfaces but also on the surfaces of the microwall and sidewall. The SMCs aligned along the 25 microm wide microwall with an elongated morphology and proliferated very slowly in comparison to those on the smooth surface with a longer cell-culture term. Few cells could attach and spread on the surface of the 40 microm wide microchannel, while the cells flourished on the 80 microm, or more than 80 microm, wide microchannel with a spindle morphology. The biophysical mechanism mediated by the micropattern geometry is discussed. Overall, the present micropattern, consisting of biodegradable and cytocompatible PLGACL, provides a promising scaffold for tissue engineering.

The bioartificial pancreas: progress and challenges

Diabetes remains a devastating disease, with tremendous cost in terms of human suffering and healthcare expenditures. A bioartificial pancreas has the potential as a promising approach to preventing or reversing complications associated with this disease. Bioartificial pancreatic constructs are based on encapsulation of islet cells with a semipermeable membrane so that cells can be protected from the host's immune system. Encapsulation of islet cells eliminates the requirement of immunosuppressive drugs, and offers a possible solution to the shortage of donors as it may allow the use of animal islets or insulin-producing cells engineered from stem cells. During the past 2 decades, several major approaches for immunoprotection of islets have been studied. The microencapsulation approach is quite promising because of its improved diffusion capacity, and technical ease of transplantation. It has the potential for providing an effective long-term treatment or cure of Type 1 diabetes.

Interaction of polyelectrolytes and their composites with living cells

Since the layer-wise polyelectrolyte deposition offers the opportunity to modify surfaces for biomedical applications, interactions and toxicity between polyelectrolytes and living cells become interesting. The aim of the present work is to determine the different factors such as contact area, charge, and transplantation site that influence the cell reaction to a specific polymer. We found that toxicity is influenced by all these factors and cannot be tested easily in a model.

A novel single-step fabrication technique to create heterogeneous poly(ethylene glycol) hydrogel microstructures containing multiple phenotypes of mammalian cells

In this study, a novel method for the one-step fabrication of stacked hydrogel microstructures using a microfluidic mold is presented. The fabrication of these structures takes advantage of the laminar flow regime in microfluidic devices, limiting the mixing of polymer precursor solutions. To create multilayered hydrogel structures, microfluidic devices were rotated 90 degrees from the traditional xy axes and sealed with a cover slip. Two discreet fluidic regions form in the channels, resulting in the multilayered hydrogel upon UV polymerization. Multilayered patterned poly(ethylene glycol) hydrogel arrays (60 mum tall, 250 mum wide) containing fluorescent dyes, fluorescein isothiocyanate, and tetramethylrhodamine isothiocyanate were created for imaging purposes. Additionally, this method was used to generate hydrogel layers containing murine fibroblasts and macrophages. The cell adhesion promoter, RGD, was added to hydrogel precursor solution to enhance fibroblast cell spreading within the hydrogel matrix in one layer, but not the other. We were able to successfully generate patterns of hydrogels containing multiple phenotypes by using this technique.

Foldable micropatterned hydrogel film made from biocompatible PCL-b-PEG-b-PCL diacrylate by UV embossing

Foldable hydrogel films with micropatterns measuring 480 microm by 45 microm by 54 microm by 2 cm (width of microchannel by width of microwall by height of wall by length of pattern) were made by UV embossing of a block copolymer of polycaprolactone (PCL) and poly(ethylene glycol) (PEG), specifically PCL-b-PEG-b-PCL-diacrylate (DA), with a polydimethylsiloxane mold. The mold was treated with Ar/CF(4) plasma to simultaneously promote microchannel filling and demolding, and the glass substrate was modified with 3-(trimethoxysilyl) propyl acrylate to promote hydrogel adhesion to avoid delamination of the gel during demolding. The micropatterned hydrogel film was detached from the glass substrate by freeze-drying. As the films were demolded, the microstructured pattern was well replicated in the hydrogel. The gel pattern dimensions shrank with freeze-drying and increased with water swelling, but under both conditions, the gel micropattern morphology was perfectly preserved. PCL-b-PEG-b-PCL-DA hydrogel was found to have good biocompatibility compared with PEGDA hydrogel. A micropattern with a smaller microchannel width of 50 microm was also made. Micropatterned foldable and biocompatible hydrogel films have potential applications in the construction of tissue-engineering scaffolds.

The immobilization of hepatocytes on 24 nm-sized gold colloid for enhanced hepatocytes proliferation

Bioartificial liver and hepatocyte transplantation is anticipated to supply a temporary metabolic support for candidates of liver transplantation or for patients with fulminant liver failure. An essential restriction of this form is the inability to acquire an enough amount of hepatocytes. Enhancement of the proliferation and differentiated function of hepatocytes is becoming a pursued target. Here, porcine hepatocytes were successfully immobilized on nano-sized gold colloid particles to construct a "hepatocyte/gold colloid" interface at which hepatocytes can be quickly proliferated. The properties of this resulting interface were characterized and confirmed by scanning electron microscopy and atomic force microscopy. The proliferative mechanism of hepatocytes was also discussed. The proliferated hepatocytes could be applied to the clinic based on their excellent functions for the synthesis of protein, glucose and urea as well as lower lactate dehydrogenase release.

Multilayer assembly and patterning of poly(p-phenylenevinylene)s via covalent coupling reactions

Poly(p-phenylenevinylene)s with amines and pentafluorophenyl esters on side chains were synthesized and assembled on solid substrates by sequential layer-by-layer (LBL) deposition. This approach enables the creation of robust multilayer thin films via in-situ covalent coupling reactions between successive layers. The buildup of the multilayers was followed by UV/vis absorption spectroscopy and ellipsometry. The observed complex assembly behavior suggests that both covalent and hydrogen-bonding interactions are involved in the formation of multilayer films. The organized structure and surface morphology of resultant multilayers were investigated by reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. This covalent LBL method was further applied to generate conjugated polymer micropatterns using microstamped self-assembled monolayers as templates.

Polyelectrolyte multilayer films with pegylated polypeptides as a new type of anti-microbial protection for biomaterials

Adhesion of bacteria at the surface of implanted materials is the first step in microbial infection, leading to post-surgical complications. In order to reduce this adhesion, we show that poly(L-lysine)/poly(L-glutamic acid) (PLL/PGA) multilayers ending by several PLL/PGA-g-PEG bilayers can be used, PGA-g-PEG corresponding to PGA grafted by poly(ethylene glycol). Streaming potential and quartz crystal microbalance-dissipation measurements were used to characterize the buildup of these films. The multilayer films terminated by PGA and PGA-g-PEG were found to adsorb an extremely small amount of serum proteins as compared to a bare silica surface but the PGA ending films do not reduce bacterial adhesion. On the other hand, the adhesion of Escherichia coli bacteria is reduced by 72% on films ending by one (PLL/PGA-g-PEG) bilayer and by 92% for films ending by three (PLL/PGA-g-PEG) bilayers compared to bare substrate. Thus, our results show the ability of PGA-g-PEG to be inserted into multilayer films and to drastically reduce both protein adsorption and bacterial adhesion. This kind of anti-adhesive films represents a new and very simple method to coat any type of biomaterials for protection against bacterial adhesion and therefore limiting its pathological consequences.

Molding of hydrogel microstructures to create multiphenotype cell microarrays

The fabrication of mammalian cell-containing poly(ethylene glycol) (PEG) hydrogel microstructures on glass and silicon substrates is described. Using photoreaction injection molding in poly(dimethylsiloxane) microfluidic channels, three-dimensional hydrogel microstructures encapsulating cells (fibroblasts, hepatocytes, macrophage) were fabricated with cells uniformly distributed to each hydrogel microstructure, and the number of cells in each hydrogel microstructure was controlled by changing the cell density of the precursor solution. PEG hydrogels were modified using an Arg-Gly-Asp (RGD) peptide sequence, with the incorporation of RGD into the hydrogel matrix promoting the spreading of encapsulated fibroblasts over a 24-h period in culture. Cells remained viable encapsulated in these hydrogel microstructures for a period in excess of 1 week in culture. Arrays of hydrogel microstructures encapsulating two or more phenotypes on a single substrate were successfully fabricated using multimicrofluidic channels, creating the potential for multiphenotype cell-based biosensors.

Properties of crosslinked protein matrices for tissue engineering applications synthesized by multiphoton excitation

We demonstrate the fabrication of model scaffolds and extracellular matrices using multiphoton excited photochemistry. This method is three-dimensional in nature and has excellent biocompatibility. Crosslinked matrices were fabricated from the proteins fibrinogen, fibronectin, and concanavalin A using two-photon rose bengal photoactivation and the relatives rates were determined. Immunofluorescence labeling of fibrinogen and fibronectin indicated retention of bioactivity following the multiphoton crosslinking process. Using the fluorescence recovery after photobleaching method, we measured the lateral mobility of fluorescent dyes of different mass and chemistry in order to model the behavior of therapeutic agents and bioactive molecules and found diffusion coefficients within these fabricated structures to be on the order of 10(-9)-10(-10) cm(2)/s, or approximately three to four orders of magnitude slower than in free solution. The precise diffusion coefficients can be smoothly tuned by varying the laser exposure during the fabrication of the matrix, which results in both an increase in crosslink density as well as protein concentration in the matrix. Terminal crosslink density is achieved at integrated high exposure dose and the relative fabrication rates were determined for these proteins. For all the proteins, the range of diffusion coefficients between the threshold for fabrication and the terminal limit is correlated with the change in matrix mesh size as determined by Flory-Rehner swelling analysis. Both normal Fickian as well as hindered anomalous diffusion is observed depending on specific molecular interactions of the tracer dyes and protein host. (c) 2004 Wiley Periodicals, Inc. J Biomed Mater Res 71A: 359-368, 2004.

Automated Gain Control and Internal Calibration with External Ion Accumulation Capillary Liquid Chromatography-Electrospray Ionization-Fourier Transform Ion Cyclotron Resonance

When combined with capillary LC separations, electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR MS) has demonstrated capabilities for advanced characterization of proteomes based upon analyses of proteolytic digests. Incorporation of external (to the ICR cell) multipole devices with FTICR for ion selection and ion accumulation has enhanced the dynamic range, sensitivity, and duty cycle of measurements. However, the highly variable ion production rate from an LC separation can result in "overfilling" of the external trap during the elution of major peaks and result in m/z discrimination and fragmentation of peptide ions. Excessive space charge trapped in the ICR cell also causes significant shifts in the detected ion cyclotron frequencies, reducing the achievable mass measurement accuracy (MMA) and making protein identification less effective. To eliminate m/z discrimination in the external ion trap, further increase duty cycle, and improve MMA, we have developed the capability for data-dependent adjustment of ion accumulation times in the course of an LC separation, referred to as automated gain control (AGC). This development has been implemented in combination with low kinetic energy gated ion trapping and internal calibration using a dual-channel electrodynamic ion funnel. The overall system was initially evaluated in the analysis of a tryptic digest of bovine serum albumin. In conjunction with internal calibration, the capillary LC-ESI-AGC-FTICR instrumentation provided a approximately 10-fold increase in the number of identified tryptic peptides compared to that obtained using a fixed ion accumulation time and external calibration methods.

Cationic polyelectrolyte hydrogel fosters fibroblast spreading, proliferation, and extracellular matrix production: Implications for tissue engineering

Fibrous encapsulation is known to occur to many prosthetic implants and is thought to be due to the cells not adhering adequately to the surface. For developing new materials able to enhance cellular adhesion by mimicking extracellular matrix components, polyelectrolyte polymers, characterized by tunable surface charges, have been proposed. Here we demonstrate that panoply of cell functions over a two-dimensional substratum is influenced by surface charge. We have at first generated structurally related polyelectrolyte substrata varying in their positive surface charge amount and subsequently evaluated a variety of behaviors of human primary fibroblasts seeded on these polymers. The proportion of adherent, spreading, and proliferating cells was increased significantly on cationic hydrophilic surfaces when compared with the neutral base surface. The extent of cell spreading correlated with cytoskeleton organization as assessed using immunofluorescence techniques. In the key experiment, the presence of cationic charges on cell adhesion-resistant neutral surface increased the synthesis of collagen I and III, the release of their metabolites, and the expression of their mRNA by fibroblasts. Interestingly, the scarce collagen deposits on neutral polymer consisted, for the most part, of collagen I while collagen III was present only in traces probably due to the secretion of metalloproteinase-2 by non-adherent fibroblasts. Taken together, these results show that polyelectrolyte films may promote the attachment of fibroblast cells as well as their normal secretory phenotype. Both effects could be potentially useful in integrating soft connective tissue to the implant, decreasing the chance of its fibrous encapsulation.

A microfluidic bioreactor based on hydrogel-entrapped E. coli: cell viability, lysis, and intracellular enzyme reactions

Viable E. coli cells were entrapped in hydrogel micropatches photopolymerized within microfluidic systems. The microfluidic channels and the micropatches have sizes on the order of 100-500 microm. Small molecules, such as dyes and surfactants, present in the solution surrounding the hydrogel, are able to diffuse into the gel and encounter the cells, but the cells are sufficiently large to be retained. For example, sodium dodecyl sulfate is a lysis agent that is able to penetrate the hydrogel and disrupt the cellular membrane. Entrapment of viable cells within hydrogels, followed by lysis, could provide a convenient means for preparing biocatalysts without the need for enzyme extraction and purification. Hydrogel-immobilized cells are able to carry out chemical reactions within microfluidic channels. Specifically, a nonfluorescent dye, BCECF-AM, is able to penetrate both the hydrogel and the bacterial membrane and be converted into a fluorescent form (BCECF) by the interior cellular machinery. These results suggest that cells immobilized within microfluidic channels can act as sensors for small molecules and as bioreactors for carrying out reactions.

Cell interactions with polyelectrolyte multilayer films

The short-term interactions of chondrosarcoma cells with polyelectrolyte multilayer films built up by the alternate adsorption of poly(L-lysine) (PLL) and poly(L-glutamic acid) (PGA) was studied in the presence and in the absence of serum. The films and their interaction with serum proteins were first characterized by means of optical waveguide lightmode spectroscopy, quartz crystal microbalance, and zeta potential measurements. In a serum-containing medium, the detachment forces measured by the micropipet technique were about eight times smaller on PGA-ending than on PLL-ending films. For these latter ones, the adhesion force decreased when the film thickness increased. In a serum-free medium, the differences between the negative- and positive-ending films were enhanced: adhesion forces on PLL-ending films were 40-100% higher, whereas no cellular adherence was found on PGA-terminating films. PGA-ending films were found to prevent the adsorption of serum proteins, whereas important protein adsorption was always observed on PLL-ending films. These results show how cell interactions with polyelectrolyte films can be tuned by the type of the outermost layer, the presence of proteins, and the number of layers in the film.

Poly(ethylene glycol) hydrogel microstructures encapsulating living cells

We present an easy and effective method for the encapsulation of cells inside PEG-based hydrogel microstructures fabricated using photolithography. High-density arrays of three-dimensional microstructures were created on substrates using this method. Mammalian cells were encapsulated in cylindrical hydrogel microstructures of 600 and 50 micrometers in diameter or in cubic hydrogel structures in microfluidic channels. Reducing lateral dimension of the individual hydrogel microstructure to 50 micrometers allowed us to isolate 1-3 cells per microstructure. Viability assays demonstrated that cells remained viable inside these hydrogels after encapsulation for up to 7 days.