A doubly cross-linked nano-adhesive for the reliable sealing of flexible microfluidic devices

Abstract

Along with the expansion of microfluidics into many areas of applications such as sensors, microreactors and analytical tools, many other materials besides poly(dimethylsiloxane) (PDMS) have been suggested such as poly(imide) (PI) or poly(ethylene terephthalate) (PET). However, the sealing methods for these materials are not reliable in that many of the methods are specific to the substrate materials. Here, we report a novel robust doubly cross-linked nano-adhesive (DCNA) for bonding of various heterogeneous substrates. By depositing 200 nm of epoxy-containing polymer, poly(glycidyl methacrylate), via initiated chemical vapour deposition (iCVD) onto various substrates and cross-linking them with ethylenediamine, a strong adhesion was obtained between the substrates. This adhesive system was not only able to bond various difficult-to-bond substrates, such as PET or PI, but it could also preserve the complicated morphology of the surfaces owing to the thin nature of the DCNA system. The DCNA allowed fabrication of microfluidic devices using both rigid substrates, such as silicon wafer and glass, and flexible substrates, such as PDMS, PET and PI. The burst pressure of the devices sealed with DCNA exceeded 2.5 MPa, with a maximum burst pressure of 11.7 MPa. Furthermore, the adhesive system demonstrated an exceptional chemical and thermal resistance. The adhesion strength of the adhesive sandwiched between glass substrates remained the same even after a 10 day exposure to strong organic solvents such as toluene, acetone, and tetrahydrofuran (THF). Also, exposure to 200 °C for 15 h was not able to damage the adhesion strength. Using the high adhesive strength and flexibility of DCNA, flexible microfluidic devices that can be completely folded or rolled without any delamination during the operation were fabricated. The DCNA bonding is highly versatile in the sealing of microfluidic systems, and is compatible with a wide selection of materials, including flexible and foldable substrates, even upon sealing few-μm-sized channels.

Micro Total Analysis Systems: Fundamental Advances and Biological Applications

“…In addition to the photoresist 25 bonding described above in the materials section, a doubly cross-linked nano-adhesive was demonstrated to improve the bonding between any combination of PDMS, glass, silicon, polyimide and poly(ethylene) terephthalate (PET). 26 This promising coating was vapor deposited in a 200nm layer and the bond strength was at least 2.5 MPa in all cases. PDMS was also bonded to a biologically friendly photoresist poly(2,2-dimethoxy nitrobenzyl methacrylate-r-methyl methacrylate-r-poly(ethylene glycol) methacrylate) (PDMP) using a mussel inspired poly(dopamine) adhesion layer.…”

Lab-on-a-chip devices: How to close and plug the lab?

“…They reported compatibility with working pressures up to 10 MPa for chips sealed at 60°C. Very recently, a doubly crosslinked nano-adhesive was introduced by You et al, wherein they deposited 200 nm of epoxy-containing polymer on various substrates via chemical vapor deposition and reported a maximum burst pressure of 11.7 MPa after curing the film at 70°C for 5 h [118].…”

Wafer Scale Solventless Adhesive Bonding with iCVD Polyglycidylmethacrylate: Effects of Bonding Parameters on Adhesion Energies

“…We noted that You et al, [ 25 ] which investigated cross-linking of PGMA interfaces using ethylene diamine, commented that some of the adhesive characteristics might stem from reaction directly between the epoxy groups (they annealed samples at 70 °C for 5 h). Considering that we, in our thermal degradation data, see no evident crosslinking in PGMA samples annealed under similar conditions ( Figure S7, Supporting Information), the amine-epoxy interface reaction is likely the main contributing factor for their observed results.…”

“…Previous efforts using iCVD polymer fi lms as adhesives have either involved a reaction at the interface between complementary functional groups on PGMA and polyaminostyrene (PAS) fi lms respectively, or by introducing small cross-linker molecules to create a bond. [ 23,25 ] However, numerous studies have shown that the adhesion between poorly miscible polymers, such as PGMA-PAS, or use of short linkers (ethylene diamine) are generally weak due to poor chain diffusion and localized stress concentration. [ 29,[42][43][44] The symmetric PGMA-PGMA interface employed in our studies enables diffusion and chain entanglement of polymer chains between the fi lms, which are important factors to realize higher adhesion energies.…”

“…[ 27 ] Our bonding approach as shown in Scheme 1 employs a "symmetric" polymer interface where iCVD PGMA fi lms were deposited on each respective substrate. Previous demonstrations of iCVD polymers for adhesion applications have relied on fi lms with complimentary functional groups [ 23 ] or linker molecules [ 25 ] for covalent bonding at the interface. However, these present some potential practical challenges such as: (i) limited opportunity to manipulate bond energies, (ii) stress accumulation due to an interface-confi ned adhesion reaction, [ 28,29 ] and (iii) increased processing costs as deposition of different polymers is needed.…”