Tailoring Hydrogel Adhesion to Polydimethylsiloxane Substrates Using Polysaccharide Glue

Abstract

With the emergence of microscale biotechnology, such as biomicroelectromechanical systems ("Bio-MEMS") and microfluidic-based microchips for sensing and diagnostics, polydimethylsiloxane (PDMS)-based elastomers have become very popular materials. [1] PDMS elastomers possess several features that are well suited for these applications: mechanical stability and elasticity, chemical inertness, optical transparency, gas permeability, ease of fabrication, and biocompatibility. [1d, 2] However, the extremely hydrophobic nature of PDMS often limits its applicability (e.g. poor aqueous fluid flow and nonspecific adhesion of biomolecules). [2] Various methods have been proposed to modify the PDMS surface to impart hydrophilicity, for example, UV or plasma treatment to oxidize the surface [3] and coating the surface with hydrophilic polymers. [4] However, the treated PDMS surfaces often recover their hydrophobic traits due to the migration of unreacted PDMS oligomers to the surface and the rearrangement of PDMS polymer chains. [2b, 5] We suggest that coating PDMS with hydrophilic materials would be more effective than the molecular level modifications. Hydrogels, which are networks of cross-linked polymers taking up large amounts of water, are therefore considered promising materials. Hydrogels can also be designed to present functionalities for specific purposes, such as in vitro cell culture, cell encapsulation, and molecular capture and release. [6] Therefore, PDMS coated with hydrogels with desired properties would significantly enhance the performance of PDMS-based devices. However, it is a significant challenge to attain and sustain the adhesion between hydrogel and PDMS, due to the stark discrepancy between the bulk properties of PDMS substrates and hydrogels.To meet this challenge, we describe a unique approach to tailor hydrogel adhesion to a PDMS substrate. Alginate, a naturally derived polysaccharide, was covalently linked to the PDMS surface. This attached alginate acted as a "glue" to allow the strong, permanent adhesion of the hydrogel onto the PDMS surface by 1) imparting hydrophilicity to improve compatibility with hydrogels, and 2) providing functional groups for the stable conjugation of hydrogels. The resulting hydrogel-coated PDMS substrate was used in the following two applications: 1) it served as an in vitro cell culture platform to study cellular behavior in response to cyclic mechanical strain, and 2) it was used in a microfluidic device with hydrogel-filled channels.The PDMS surface was chemically grafted with alginate following a series of modification steps: [7] step 1: oxidation to present hydroxy groups (OH-PDMS, Figure 1 a); step 2: silanization using 3-aminopropyltriethoxysilane to present primary amino groups (NH 2 -PDMS); and step 3: conjugation of alginate by carbodiimide-mediated amide coupling between amino groups on the PDMS surface and carboxylic acid groups of alginate (alginate-PDMS). The successive modifications of PDMS were confirmed with FTIR spectroscopy ( Figure S1 and Table...

Highly Stretchable, Strain Sensing Hydrogel Optical Fibers

“…The core fiber was dipped in an Na‐alginate‐polyacrylamide precursor composed of 20 wt% AAm, 2 wt% alginate, 0.03 wt% MBAA, 0.16 wt% APS, 0.1% v/v TEMED in MES buffer (pH 6.0). EDC/Sulfo‐NHS (EDC, Sigma‐Aldrich: molar ratio of 25:1 to alginate; Sulfo‐NHS, Sigma‐Aldrich: molar ratio of 30:1 to alginate) was also added to the solution, which induces robust chemical bonding to the core matrix via EDC‐NHS chemistry . The clad‐coated core fiber hang vertically and cured by UV irradiation for 30 min.…”

“…To solve this problem, the core was first dipped in Na + ‐containing alginate‐polyacrylamide precursor and polymerized under UV light to form a layer of Na‐alginate‐polyacrylamide hydrogel that consists of covalently cross‐linked polyacrylamide chains and well‐dispersed, but not yet cross‐linked, alginate chains . To achieve robust bonding between the core and clad, we chemically anchored the alginate on the core via EDC‐NHS chemistry . Then, the fiber was immersed in an aqueous solution of CaCl 2 to complete Ca 2+ ‐mediated ionic cross‐linking of alginate in the clad.…”

Enhanced Triboelectric Performance of Modified PDMS Nanocomposite Multilayered Nanogenerators

“…These [PVA/GNP-PSS] 3 multilayers were prepared using an inexpensive and simple layer-by-layer (LbL) assembly process, which was advantageous for precise control of the thickness of the film [ 4 , 30 , 31 , 32 ]. Then, the modified PDMS negative TM layer and [PVA/GNP-PSS] 3 multilayer electrode were chemically linked by 3-aminopropylethoxysilane (APTES) as a coupling agent under mild reaction conditions without altering the desired properties of the composite films [ 33 , 34 ]. Finally, the GNP-PDMS nanocomposites, fabricated by adding 33 wt.% Na 2 CO 3 and 0.5 wt.% GNP and assembled with a [PVA/GNP-PSS] 3 electrode, achieved an open-circuit voltage and short-circuit current density of up to 270.2 V and 0.44 μA/cm 2 , respectively.…”

Stretchable Hydrogel Electronics and Devices

“…However, it is challenging to form robust adhesion between hydrogels and PDMS due to its intrinsic oxygen permeation and radical scavenging nature [38] . Although a few methods were proposed by imparting the hydrophilicity of PDMS and coating PDMS with hydrophilic materials as hydrogels, the reported adhesion between hydrogels and PDMS may be not strong enough to sustain extremely large deformation [39] . Here, we used glass slides as intermediate layers to form tough bonding between chips and hydrogel matrix.…”