Interfacial Electrofabrication of Freestanding Biopolymer Membranes with Distal Electrodes (original) (raw)
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Membranes
Microfluidic-integrated freestanding membranes with suitable biocompatibility and tunable physicochemical properties are in high demand for a wide range of life science and biological studies. However, there is a lack of facile and rapid methods to integrate such versatile membranes into microfluidics. A recently invented interfacial electrofabrication of chitosan membranes offers an in-situ membrane integration strategy that is flexible, controllable, simple, and biologically friendly. In this follow-up study, we explored the ability to program the physical properties of these chitosan membranes by varying the electrofabrication conditions (e.g., applied voltage and pH of alginate). We found a strong association between membrane growth rate, properties, and fabrication parameters: high electrical stimuli and pH of alginate resulted in high optical retardance and low permeability, and vice versa. This suggests that the molecular alignment and density of electrofabricated chitosan me...
Characterization of electrodeposited chitosan: An interfacial layer for bio-assembly and sensing
2009
on-a-Chip devices have revolutionized the field of analytical biology. To fully optimize the potential of the microfluidic environment it is critical to be able to isolate reactions in specific locations within a channel. One solution is found using chitosan, an amine-rich biopolymer with pH responsive solubility. Induction of hydrolysis at patterned electrodes within the fluidic channel provides a means to spatially control the pH, thus enabling biochemical functionalization that is both spatially and temporally programmable.
2010
We report the first in situ quantitative visualization and characterization of electro-induced chitosan hydrogel growth in an aqueous environment. This was enabled with a pair of sidewall electrodes within a transparent fluidic system, which allowed us to resolve the electrogelling mechanism and interpret the dominant causes responsible for the formation and density distribution of the deposited hydrogel. The pH and the time-dependent growth profiles of the chitosan hydrogel were directly visualized, analyzed, and characterized. The results indicate that the gelation and immobilization of chitosan onto the cathode at a pH above its pK a value ($6.3) are due to the electrochemically generated concentration gradient of reactant OH À ions, and their subsequent neutralization of the NH 3 + groups of chitosan chains in solution near the cathode. The increased gel density around the fringes of the electrodes was demonstrated and correlated with the electrophoretic migration of chitosan cations during deposition. Simulation of the electric potential/field distribution, together with the corresponding dry film topography confirmed the non-uniform, electric field-dependent density distribution of deposited hydrogel. This report provides fundamental understanding towards the mechanism and the kinetics of the electro-induced chitosan gel formation. It also provides important guidelines for pursuing its application in bio-components integrated microsystems. The method in use exemplifies a simple, effective and non-destructive approach for in situ characterization of electro-responsive biopolymers in an aqueous environment.
Voltage-Dependent Assembly of the Polysaccharide Chitosan onto an Electrode Surface
Langmuir, 2002
We examined the assembly of the amine-rich polysaccharide chitosan from solution onto electrode surfaces as a result of voltage bias on the electrode. Chitosan is positively charged and water soluble under mildly acidic conditions and is uncharged and insoluble under basic conditions. We observed that chitosan is deposited from acidic solution onto the surface of a negative electrode and the thickness of the deposited layer is on the order of a micron. The thickness of the deposited layer was observed to be dependent upon the deposition time, the applied voltage, and the chitosan concentration. No deposition was observed on the positive electrode or on an "electrode" that had no applied voltage. Once deposited and neutralized, the chitosan layer can be retained on the electrode surface without the need for an applied voltage. Infrared (FT-IR) and electrospray mass spectrometry confirmed that the deposited material was chitosan. These results demonstrate that chitosan can be deposited and retained on electrode surfaces, and the potential advantages for applications in microfabricated devices are discussed.
Lab Chip, 2010
We report the in situ generation of pH gradients in microfluidic devices for biofabrication of freestanding, semi-permeable chitosan membranes. The pH-stimuli-responsive polysaccharide chitosan was enlisted to form a freestanding hydrophilic membrane structure in microfluidic networks where pH gradients are generated at the converging interface between a slightly acidic chitosan solution and a slightly basic buffer solution. A simple and effective pumping strategy was devised to realize a stable flow interface thereby generating a stable, well-controlled and localized pH gradient. Chitosan molecules were deprotonated at the flow interface, causing gelation and solidification of a freestanding chitosan membrane from a nucleation point at the junction of two converging flow streams to an anchoring point where the two flow streams diverge to two output channels. The fabricated chitosan membranes were about 30-60 mm thick and uniform throughout the flow interface inside the microchannels. A T-shaped membrane formed by sequentially fabricating orthogonal membranes demonstrates flexibility of the assembly process. The membranes are permeable to aqueous solutions and are removed by mildly acidic solutions. Permeability tests suggested that the membrane pore size was a few nanometres, i.e., the size range of antibodies. Building on the widely reported use of chitosan as a soft interconnect for biological components and microfabricated devices and the broad applications of membrane functionalities in microsystems, we believe that the facile, rapid biofabrication of freestanding chitosan membranes can be applied to many biochemical, bioanalytical, biosensing applications and cellular studies.
Bridging the bio-electronic interface with biofabrication
2012
Advancements in lab-on-a-chip technology promise to revolutionize both research and medicine through lower costs, better sensitivity, portability, and higher throughput. The incorporation of biological components onto biological microelectromechanical systems (bioMEMS) has shown great potential for achieving these goals. Microfabricated electronic chips allow for micrometer-scale features as well as an electrical connection for sensing and actuation. Functional biological components give the system the capacity for specific detection of analytes, enzymatic functions, and whole-cell capabilities. Standard microfabrication processes and bio-analytical techniques have been successfully utilized for decades in the computer and biological industries, respectively. Their combination and interfacing in a lab-on-a-chip environment, however, brings forth new challenges. There is a call for techniques that can build an interface between the electrode and biological component that is mild and is easy to fabricate and pattern.
Individually, advances in microelectronics and biology transformed the way we live our lives. However, there remain few examples in which biology and electronics have been interfaced to create synergistic capabilities. We believe there are two major challenges to the integration of biological components into microelectronic systems: (i) assembly of the biological components at an electrode address, and (ii) communication between the assembled biological components and the underlying electrode. Chitosan possesses a unique combination of properties to meet these challenges and serve as an effective bio-device interface material. For assembly, chitosan’s pH-responsive film-forming properties allow it to “recognize” electrode-imposed signals and respond by self-assembling as a stable hydrogel film through a cathodic electrodeposition mechanism. A separate anodic electrodeposition mechanism was recently reported and this also allows chitosan hydrogel films to be assembled at an electrode address. Protein-based biofunctionality can be conferred to electrodeposited films through a variety of physical, chemical and biological methods. For communication, we are investigating redox-active catechol-modified chitosan films as an interface to bridge redox-based communication between biology and an electrode. Despite significant progress over the last decade, many questions still remain which warrants even deeper study of chitosan’s structure, properties, and functions.
Electrochemically Induced Deposition of a Polysaccharide Hydrogel onto a Patterned Surface
Langmuir, 2003
Hydrogels are increasingly considered for creating three-dimensional structures in miniaturized devices, yet few techniques exist for creating such hydrogel structures. We report a new approach for creating hydrogels using the amine-containing polysaccharide chitosan. Specifically, electrodes are immersed into a slightly acidic chitosan solution and a voltage is applied to promote the proton-consuming hydrogen evolution reaction at the cathode surface. This reaction leads to a high localized pH in the vicinity of the cathode surface, and if this localized pH exceeds about 6.3, then chitosan becomes insoluble and deposits at the cathode surface. As the current density is increased, the region of high pH is expected to extend further from the cathode surface into the bulk solution. Using moderately high current densities (50 A/m 2 ), we observed that chitosan deposited as a thick hydrogel. Measurements of the water content confirmed that the deposited chitosan was a hydrogel. To suggest the potential utility, we deposited a chitosan hydrogel on a patterned surface to create a channel. Because of chitosan's pH-dependent solubility, this channel could be "disassembled" by mild acid treatment. We envision that electrochemically-induced deposition of chitosan-based hydrogels may offer interesting opportunities for the integration of biological systems into miniaturized devices.
Electrodeposition of a Biopolymeric Hydrogel: Potential for One-Step Protein Electroaddressing
Biomacromolecules, 2012
The electrodeposition of hydrogels provides a programmable means to assemble soft matter for various technological applications. We report an anodic method to deposit hydrogel films of the aminopolysaccharide chitosan. Evidence suggests the deposition mechanism involves the electrolysis of chloride to generate reactive chlorine species (e.g., HOCl) that partially oxidize chitosan to generate aldehydes that can couple covalently with amines (presumably through Schiff base linkages). Chitosan's anodic deposition is controllable spatially and temporally. Consistent with a covalent cross-linking mechanism, the deposited chitosan undergoes repeated swelling/deswelling in response to pH changes. Consistent with a covalent conjugation mechanism, proteins could be codeposited and retained within the chitosan film even after detergent washing. As a proof-of-concept, we electroaddressed glucose oxidase to a side-wall electrode of a microfabricated fluidic channel and demonstrated this enzyme could perform electrochemical biosensing functions. Thus, anodic chitosan deposition provides a reagentless, single-step method to electroaddress a stimuli-responsive and biofunctionalized hydrogel film.
2003
The amino-polysaccharide chitosan has distinct properties that make it an attractive interface material for the assembly of biomolecules onto microfabricated surfaces. Chitosan has pH-responsive electrostatic and solubility properties that allow it to be deposited and retained on cathode surfaces. Deposition is shown to be spatially controllable at µm levels by "templating" the chitosan onto micropatterned gold cathodes. Temporal control of deposition can be achieved depending on when the micropatterned electrodes are polarized. Chitosan also has nucleophilic amine groups that can be easily reacted using standard, amine-specific chemistries. Studies show that the sequence of chitosan deposition and chemical modification is repeatable. Finally, standard chemistries can be exploited to couple biomolecules onto chitosan films that have been "templated" onto the micropatterened gold cathodes. Specifically, we used glutaraldehyde activation to assemble the model protein, green fluorescent protein (GFP) onto a chitosan deposit. These studies demonstrate that chitosan has unique properties that allow it to serve as an interface material for the assembly of biomolecules onto microfabricated surfaces.