PROCESS FOR MANUFACTURING A MICROFLUIDIC DEVICE

Abstract

A process for manufacturing a microfluidic device including: a) providing a first substrate having a first surface including a first flat part and a first concavity and a second substrate having a second surface including a second flat part and an optional second concavity, b) coating at least one of the first surface and the second surface with a coating composition including i) a monomer A including one moiety represented by CH2=CR1R2 wherein R1 represents H or CH3 and R2 represents COO or CONH, and a non-ionic hydrophilic moiety; ii) a monomer B including two or more moieties represented by CH2=CR1R2 wherein R1 represents H or CH3 and R2 represents COO or CONH, and a non-ionic hydrophilic moiety; iii) optionally a photoinitiator; iv) optionally a diluent; c) evaporating the diluent if present, and forming a liquid coating; d) contacting the substrates so as to obtain an assembly in which the first flat part and the second flat part contact each other to define a microfluidic structure between the first and the second surfaces, wherein the microfluidic structure includes the first concavity and the optional second concavity; and e) at least partially irradiating the assembly with light having a wavelength between 200 and 800 nm to crosslink the liquid coating to bond the first flat part and the second flat part and obtain a crosslinked coating on at least the first concavity.

A microfluidic device having two parts bonded together with a crosslinked composition and a channel which includes at least partly the crosslinked composition as a coating.

Claims

1. A process for manufacturing a microfluidic device comprising: a) providing a first substrate having a first surface comprising a first flat part and a first concavity and a second substrate having a second surface comprising a second flat part and an optional second concavity, wherein each of the first flat part, the first concavity and the second flat part has surface groups selected from alcohol, aldehyde, carboxylic acid, ether, epoxide, alkene, alkyne, secondary or tertiary carbon atoms, arynes, azides, imines, phosphates, sulfonyl fluorides, N-sulfonylimines, vinylsilyl, quinones, phenones, and hydrazones, or a combination thereof; b) coating at least one of the first surface and the second surface with a coating composition comprising i) a monomer A comprising one moiety represented by CH2CR1R2 wherein R1 represents H or CH3 and R2 represents COO or CONH, and a non-ionic hydrophilic moiety; ii) a monomer B comprising two or more moieties represented by CH2=CR1R2 wherein R1 represents H or CH3 and R2 represents COO or CONH, and a non-ionic hydrophilic moiety; iii) optionally a photoinitiator; iv) optionally a diluent; c) evaporating the diluent if present, and forming a liquid coating; d) contacting the substrates so as to obtain an assembly in which the first flat part and the second flat part contact each other to define a microfluidic structure between the first and the second surfaces, wherein the microfluidic structure comprises the first concavity and the optional second concavity; and e) at least partially irradiating the assembly with light having a wavelength between 200 and 800 nm to crosslink the liquid coating to bond the first flat part and the second flat part and obtain a crosslinked coating on at least the first concavity, wherein at least one of the first substrate and the second substrate is transparent to said light.

2. The process according to claim 1, wherein the first flat part, the first concavity and the second flat part have surface groups selected from alcohol, aldehyde, carboxylic acid, ether, epoxide, alkene, alkyne, and secondary or tertiary carbon atoms, or a combination thereof.

3. The process according to m claim 1, wherein at least one of the substrates is made of a polymer, wherein the polymer is selected from polyolefins, polyesters, polyethers, polyamides, polycarbonates, polysulfones, polyurethanes, (meth)acrylates, (meth)acrylamides, polysaccharides, and polyalcohols.

4. The process according to claim 3, wherein the polymers are chosen from the group of cyclic olefin copolymer (COC), cyclic olefin polymer (COP), polycarbonate (PC), polystyrene (PS), poly(methyl methacrylate) (PMMA), SU-8, polyethylene and polypropylene.

5. The process according to claim 1, wherein at least one of the substrates is an inorganic material, wherein the inorganic material is selected from glass, silicon, silicon oxide, and silicon nitride.

6. The process according to claim 1, wherein monomer A is selected from acrylate, methacrylate, acrylamide or methacrylamide monomers, more preferably selected from acrylate and methacrylate monomers, most preferably selected from acrylate monomers.

7. The process according to claim 1, wherein the non-ionic hydrophilic moiety in monomer A and monomer B is made of repeating units selected from ethylene glycol, propylene glycol, or glycerol, or oligomers of (2-hydroxyethyl)acrylate, (2-hydroxyethyl)methacrylate, (2-hydroxyethyl)acrylamide, (2-hydroxyethyl)methacrylamide. (2-hydroxypropyl)acrylate, (2-hydroxypropyl)methacrylate, (2-hydroxypropyl)acrylamide, (2-hydroxypropyl)methacrylamide, N-isopropylacrylamide, 2-methyl-2-oxazoline, 2-ethyl-2-oxazoline, N-vinylpyrrolidone, N-vinyl acetamide, vinyl alcohol, vinyl acetate, vinyl butyral or amino acids, preferably ethylene glycol.

8. The process according to claim 1, wherein monomer A is a monofunctional acrylate monomer containing a moiety made of repeating units of ethylene glycol.

9. The process according to claim 1, wherein the coating composition comprises a crosslinking monomer B comprising two or more moieties represented by CH2=CR1R2 wherein R1 represents H or CH3 and R2 represents COO or CONH, and one or more non-ionic hydrophilic moieties, and wherein the number of moieties represented by CH2=CR1R2 in the monomer B is between 2 and 8, preferably between 2 and 4.

10. The process according to claim 1, wherein the monomer B is selected from acrylate, methacrylate, acrylamide or methacrylamide monomers, more preferably selected from acrylate and methacrylate monomers, most preferably selected from acrylate monomers, preferably wherein the monomer B is a bifunctional acrylic monomer, i.e. it comprises 2 acrylic groups.

11. The process according to claim 1, wherein the monomer B is a diacrylate monomer containing a moiety made of repeating units of ethylene glycol.

12. The process according to claim 1, wherein the number of the repeating units in the non-ionic hydrophilic moiety in the monomer A or the monomer B is selected between 1 and 20, preferably between 2 and 10.

13. The process according to claim 1, wherein the monomer A has 6-10 ethylene glycol units, more preferably 7-9 ethylene glycol units, most preferably 9 ethylene glycol units and the monomer B has 1-5 ethylene glycol units, more preferably 2-4 ethylene glycol units, most preferably 3 ethylene glycol units.

14. The process according to am claim 1, wherein the monomers A and B are both liquid at room temperature, with a viscosity <1000 mPa s, preferably <500 mPa s, more preferably <200 mPa s, and more preferably <100 mPa s.

15. The process according to claim 1, wherein the amount of monomer A ranges between 5 and 90 vol %, preferably 10 to 50 vol %, more preferably 20 to 40 vol %, for example 25 to 35 vol %, relative to the total volume of the monomers A and B.

16. The process according to claim 1, wherein, the amount of monomer B ranges between 10 and 95 vol % relative to the total volume of the monomers A and B.

17. The process according to claim 1, wherein the coating composition comprises 0.1 to 10 wt. % of a photo-initiator, relative to the total weight of the monomers A and B and the photo-initiator.

18. The process according to claim 21, wherein the photoinitiators is chosen from of Norrish type I (for example, acetophenones or phosphine oxides) and of Norrish type II (for example, benzophenones), preferably, the photoinitiator is chosen from 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, 2,2-Dimethoxy-2-phenylacetophenone, benzophenone, and perfluorobenzophenone.

19. The process according to claim 1, wherein the coating composition comprises a diluent, wherein the amount of diluent ranges between 0.1 and 20 vol % for application by spin coating, and ranges between 50 and 99 vol % for application by spray coating, wherein the amount of the diluent is relative to the total volume of the coating composition.

20. The process according to claim 1, wherein the diluent is chosen from the group of tetrahydrofuran, diethyl ether, methanol and ethanol, diethylene glycol diethyl ether, diethylene glycol dimethyl ether, dioxane, 2-butanone, dimethoxyethane, ethyl acetate, methoxyacetone, propylene glycol monomethyl ether acetate, methyl isobutyl ketone, ethyl butyrate, methoxy propyl acetate, propyl acetate, 2-butoxyethyl acetate, and wherein the diluent is chosen from tetrahydrofuran (THF) or diethyl ether when using COC as a substrate.

21. The process according to claim 1, wherein the thickness of the liquid coating is between 100 nm and 20 m, preferably between 200 nm and 10 m, more preferably between 500 nm and 5 m.

22. The process according to claim 1, wherein the amount of the diluent in the liquid coating on the substrate is less than 5 vol %, preferably less than 2 vol %, more preferably less than 1 vol %, or less than 0.1 vol %, relative to the liquid coating.

23. The process according to claim 1, wherein during steps d) and/or e) an external pressure is applied below 0.8 MPa.

24. The process according to claim 1, wherein the liquid coating composition is cured in step e) with an energy of at least 10 mJ/cm2, by irradiation of light having a wavelength between 250-400 nm.

25. The process according to claim 1, wherein the liquid coating composition is not pre-cured prior to step e).

26. A microfluidic device, comprising: a bottom part, a top part and a channel having a bottom wall, sidewalls and a top wall, wherein the bottom part and top part are bonded together with a crosslinked composition, wherein at least one of the bottom wall, sidewalls and top wall is coated with the crosslinked composition, wherein the crosslinked composition comprises i) Between 2.5-90 mol % monomeric units A comprising one moiety [CH2-CR1R2]- wherein R1 represents H or CH3 and R2 represents COO or CONH, and a non-ionic hydrophilic moiety; ii) Between 97.5-10 mol % monomeric units B comprising two or more moieties represented by [CH2-CR1R2]-, wherein R1 represents H or CH3 and R2 represents COO or CONH, and a non-ionic hydrophilic moiety.

27. The microfluidic device according to claim 26, wherein the monomeric units A are obtained from polymerization of a monofunctional acrylate monomer containing a moiety made of repeating units of ethylene glycol and wherein monomeric units B are obtained from polymerization of a diacrylate monomer containing a moiety made of repeating units of ethylene glycol.

28. The microfluidic device according to claim 27, wherein the monomeric unit A contains between 5-10 ethylene glycol units and wherein the monomeric unit B contains between 2 and 4 repeating units of ethylene glycol.

29. The microfluidic device according to claim 26, wherein at least 80 mol % of all monomeric units of the crosslinked coating consist of monomeric units A and B.

30. The microfluidic device according to claim 26, wherein at least bottom wall and sidewalls are coated with the crosslinked composition.

31. The microfluidic device according to claim 26, wherein bottom wall, sidewalls and optionally and top wall are coated with the crosslinked composition.

32. The microfluidic device according to claim 26, wherein the bottom part and top part are bonded together with a lap shear strength higher than 0.1 MPa.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0144] FIG. 1 shows a comparison between a coated and uncoated COC channel: left) water in an untreated COC channel (hydrophobic, indicated by the WCA of approximately 90), (right) water in a PEG-coated channel (hydrophilic, indicated by the WCA of <40).

[0145] FIG. 2 shows Avidin, Fibrinogen, and BSA fouling behavior in COC microfluidic devices that are bonded and coated with PEG (left), untreated (middle, COC), and activated with oxidizing air plasma (right, COCOx).

[0146] FIG. 3 shows the Visualization by SEM of a PEG-coated channel. The crosslinked coating is visible as a thin, uniform, conformal layer on the channel walls.

[0147] FIG. 4 shows an Optical transmission spectrum of crosslinked coatings according to experiments 5, CE7, and CE8

[0148] FIG. 5 shows Partial irradiation by masking a part of the substrate (left) results in bonded devices with channels with a partial hydrophilic coating. The uncoated part remains hydrophobic and does not allow the capillary flow of water to continue (right).

[0149] FIG. 6 shows Capillary flow of an aqueous dye solution (a droplet of which is visible on the left) through a COC with one concavity on top of a silicon oxide photonic sensor and bonded thereto by a process according to the invention. A microchannel is formed between the COC substrate and the silicon oxide photonic sensor as the second substrate. An inlet to the channel is present on the left hand side and an outlet (visible as a small hole) on the right hand side of the flow cell). It can be seen that the solution is present in the channel, which, together with the shape of the meniscus of the solution confirms that the channel is hydrophylic as a result of the coating. No leaking was observed.

[0150] FIG. 7 shows the fabrication of a microfluidic device having a liquid coating on both the bottom part (10) and top part (20) to prepare a device having a crosslinked coating on all sides of the channel.

[0151] FIG. 8 shows the fabrication of a microfluidic device having a liquid coating on the bottom part (10) to prepare a device having a crosslinked coating on the bottom wall (31) and sidewalls (32) of the channel.

[0152] FIG. 9 shows the fabrication of a microfluidic device having a liquid coating on the top part (20) to prepare a device having a crosslinked coating on top wall (33) of the channel.

[0153] FIG. 10 shows the fabrication of a microfluidic device having a liquid coating on both the bottom part (10) and top part (20) to prepare a device having a crosslinked coating on all sides of the channel, including side walls (32) and (34).

[0154] FIG. 11 shows the fabrication of a microfluidic device having a liquid coating on the bottom part (10) to prepare a device having a crosslinked coating on the bottom wall (31) and sidewalls (32) of the channel.

DETAILED DESCRIPTION OF THE INVENTION

[0155] The invention also relates to a microfluidic device, having a bottom part (10), a top part (20) and a channel (30). The channel is defined by a bottom wall (31), sidewalls (32) and optionally (34) and top wall (33). Bottom part (10) and top part (20) are bonded together with a crosslinked composition, and at least one of the walls of the channel is coated with the crosslinked composition.

[0156] In an embodiment bottom wall (31) and sidewalls (32) are coated with the crosslinked composition (see FIGS. 8, 11).

[0157] In an embodiment bottom wall (31), sidewalls (32) and top wall (33) are coated with the crosslinked composition (see FIG. 7).

[0158] In an embodiment only top wall (33) is coated with the crosslinked composition (see FIG. 9).

[0159] In an embodiment bottom wall (31), top wall (33) and sidewalls (32) and (34) are coated with the crosslinked composition (see FIG. 10).

[0160] The bottom part (10) and top part (20) of the device are bonded together with a strong bond: the bottom part (10) and top part (20) are bonded together with a lap shear strength higher than 0.1 MPa.

[0161] The crosslinked composition comprises [0162] i. between 2.5-90 mol % or between 10-90 mol % monomeric units A comprising one moiety [CH2-CR1R2]-, wherein R1 represents H or CH3 and R2 represents COO or CONH, and a non-ionic hydrophilic moiety, and [0163] ii. between 97.5-10 mol %, or between 90-10 mol % monomeric units B comprising two or more moieties represented by [CH2-CR1R2]-, wherein R1 represents H or CH3 and R2 represents COO or CONH, and a non-ionic hydrophilic moiety.

[0164] Preferably the crosslinked composition comprises between 3-80 or 20-80 mol % monomeric units A and 97-20 mol % or 80-20 mol % monomeric units B. More preferably the crosslinked composition comprises 4-75 mol % or 25-75 mol % monomeric units A and 25-96 mol % or 75-25 mol % monomeric units B.

[0165] Preferably the crosslinked composition comprises mainly monomeric units A and monomeric units B: preferably at least 80 mol % of all monomeric units of the crosslinked coating consist of monomeric units A and B.

[0166] The mol % of monomeric moieties can be determined with 13C-NMR and/or 1H-NMR.

[0167] Preferably, the crosslinked composition comprises monomeric units A, which are obtained from polymerization of a monofunctional acrylate monomer containing a moiety made of repeating units of ethylene glycol, and monomeric units B, which are obtained from polymerization of a diacrylate monomer containing a moiety made of repeating units of ethylene glycol.

[0168] Preferably the monomeric unit A contains between 5-10 repeating units of ethylene glycol and the monomeric unit B contains between 2 and 4 repeating units of ethylene glycol.

[0169] The invention also relates to a microfluidic device comprising a bottom part (10), a top part (20) and a channel (30) having a bottom wall (31), sidewalls (32) and a top wall (33), wherein the bottom part (10) and top part (20) are bonded together with a crosslinked composition, wherein at least one of the bottom wall (31), sidewalls (32) and top wall (33) is coated with the crosslinked composition, wherein the crosslinked composition is obtained by crosslinking a composition comprising: [0170] i) between 5-90 vol % monomeric units A comprising one moiety [CH2-CR1R2]- wherein R1 represents H or CH3 and R2 represents COO or CONH, and a non-ionic hydrophilic moiety; relative to the total volume of monomeric units A and monomeric units B [0171] ii) between 10-95 vol % monomeric units B comprising two or more moieties represented by [CH2-CR1R2]-, wherein R1 represents H or CH3 and R2 represents COO or CONH, and a non-ionic hydrophilic moiety, relative to the total volume of monomeric units A and monomeric units B.

[0172] It is noted that the invention relates to the subject-matter defined in the independent claims alone or in combination with any possible combinations of features described herein, preferred in particular are those combinations of features that are present in the claims. It will therefore be appreciated that all combinations of features relating to the composition according to the invention; all combinations of features relating to the process according to the invention and all combinations of features relating to the composition according to the invention and features relating to the process according to the invention are described herein.

[0173] It is further noted that the term comprising does not exclude the presence of other elements. However, it is also to be understood that a description on a product/composition comprising certain components also discloses a product/composition consisting of these components. The product/composition consisting of these components may be advantageous in that it offers a simpler, more economical process for the preparation of the product/composition. Similarly, it is also to be understood that a description on a process comprising certain steps also discloses a process consisting of these steps. The process consisting of these steps may be advantageous in that it offers a simpler, more economical process.

[0174] When values are mentioned for a lower limit and an upper limit for a parameter, ranges made by the combinations of the values of the lower limit and the values of the upper limit are also understood to be disclosed.

[0175] The invention is now elucidated by way of the following experiments, without however being limited thereto.

TABLE-US-00001 Experiments Chemical CAS # Abbreviation provider Methoxy poly(ethylene glycol) 32171-39-4 PEG9-Ac Sigma-Aldrich monoacrylate Poly(ethylene glycol) diacrylate 26570-48-9 PEG3-diAc Sigma-Aldrich 4-Arm PEG-Acrylate, MW 2k N/A PEG-tetraAc Creative PEGWorks (PSB 420) Ethylene glycol dimethacrylate 97-90-5 PEG1-diMAc Sigma-Aldrich Acrylate-PEG-Acrylate, MW 20k N/A PEG20k-diAc Creative PEGWorks (PSB-349) Methacrylate-PEG-Methacrylate, N/A PEG20k-diMAc Creative PEGWorks MW 20k (PSB-3478) Methoxy PEG methacrylate 26915-72-0 PEG9-MAC Tetrahydrofuran 109-99-9 THF Sigma-Aldrich Perfluorobenzophenone 853-39-4 F10-BP Sigma-Aldrich Benzophenone 119-61-9 BP Sigma-Aldrich diphenyl(2,4,6- 75980-60-8 TPO Sigma-Aldrich trimethylbenzoyl)phosphine oxide 2-hydroxy-4-(2-hydroxyethoxy)-2- 106797-53-9 Irgacure 2959 Sigma-Aldrich methylpropiophenone

Experiment 1

[0176] Cyclic Olefin Copolymer (COC) microscope slides (2575 mm2) with 4 parallel straight channels were used as substrates. The channels were 58 mm long, 1 mm wide and 100 m deep. The substrates were activated by exposure to a low-pressure air plasma for 30 s. A coating composition was prepared consisting of PEG9-Ac (45 vol %) as monomer A, PEG3-diAc (45 vol %) as monomer B and THF (10 vol %) as a diluent. The coating composition was applied on both substrates by spin coating. The diluent evaporates during the spin coating. Thus, spin coating results in the presence of a liquid coating on the substrates without taking special measures for evaporating the diluent.

[0177] The substrates were then contacted with each other to form an assembly in which a microfluidic structure is defined by the concavity. The slides were contacted with an overlap area of 5025 mm2. Subsequently the assembly was irradiated with UV light (Hg/Xe lamp with a 280 nm high-pass cutoff filter) for 1 hour using a collimated light beam. During irradiation, an external pressure of 0.32 MPa was continuously applied. To ensure the channels are not clogged, a flow of nitrogen was applied through the channel during irradiation. After irradiation, the assemblies were characterized without further treatment.

Bond strength characterization

[0178] The assemblies obtained above were subjected to lap shear tests using a Zwick Z010 materials tester. The substrates are pulled apart at a fixed speed of 0.5 mm/s and the shear stress (expressed in MPa, force per unit bond area) is recorded as a function of the applied strain. The stress at which the substrates in the assemblies are pulled apart s taken as the lap shear strength and is a measure for the bond strength. In some instances the assembly itself broke but the substrates did not come apart, indicating a lap shear strength higher than the applied stress. The values are mentioned in tables below. The values are the average and standard deviation of the measurement results of 5 samples. A lap shear strength of at least 0.1 MPa is considered sufficiently strong. Preferably, a lap shear strength higher than 0.2 MPa is obtained. More preferably, the lap shear strength is higher than 0.3 MPa.

Coating Characterization

[0179] To demonstrate the formation of a hydrophilic PEG coating on the channel wall, the wettability of coated and (commercially available) uncoated channels was compared. The meniscus of a water droplet in the channel shows that the coated channel is very hydrophilic (see FIG. 1), with a water contact angle (WCA) of <40. The uncoated channel on the other hand, shows a contact angle of approximately 90, as expected for the untreated hydrophobic COC.

[0180] To demonstrate the antifouling properties of the hydrophilic PEG coating, solutions of fluorescently labelled proteins were flushed through the channels, followed by rinsing with buffer solutions with and without added surfactant, and water. Then, the fluorescence intensity inside the channels was measured using a fluorescence microscope. The results of these experiments (average fluorescence intensity and standard deviation of 12 spots in 4 channels) are shown in FIG. 2. Uncoated COC channels show a measurable fluorescence, indicating adsorption of the proteins to the channel wall. The PEG-coated channels, on the other hand, show a greatly reduced fluorescence intensity, which is in fact similar to the background signal. This result clearly indicates that the PEG coating prevents protein adsorption. As a control, bonded chips which were activated by exposure to oxidizing air plasma but not coated with PEG were also measured. These oxidized samples have a very high surface energy, leading to strong protein adsorption and a very high fluorescence intensity.

Scanning Electron Microscopy

[0181] Selected samples were visualized by Scanning Electron Microscopy (SEM) to confirm that all walls of the channel are coated uniformly and conformally. FIG. 3 shows a cross section of a coated channel with nominal dimensions of 200200 m2 (height width at top). The cross section was prepared by freezing the sample in liquid nitrogen followed by application of pressure on the normal axis of the top surface while half of the bottom surface was made immobile by means of a support surface, which resulted in cracking of the device along the longitudinal plane and subsequent delamination of the bonded top substrate. In the SEM micrograph of this longitudinal cross-section, the presence of the PEG coating on the side and bottom walls of the channel can be observed. The coating layer has a uniform thickness of a few micrometers on all walls and is also present conformally in the corners between the side walls and the bottom wall of the channel.

[0182] In subsequent experiments, several parameters were varied to demonstrate different embodiments of the invention. Unless stated otherwise, the first and the second substrates were COC substrates as described above; the coating composition used consists of PEG9-Ac (45 vol %), PEG3-diAc (45 vol %) and THF (10 vol %); the UV irradiation was for 1 hour at an external pressure of 0.32 MPa.

Externally Applied Pressure (Experiments 1-6)

[0183] The assembly was irradiated while applying a varying external pressure on the substrates that are being bonded.

TABLE-US-00002 TABLE 1 Experiment # External pressure (MPa) lap shear strength (MPa) 1 0.32 0.7 0.2 2 0.00 0.67 0.09 3 0.08 0.57 0.06 4 0.16 0.8 0.2 5 0.24 0.7 0.1 6 0.40 0.6 0.1

[0184] Pressures between 0 and 0.4 MPa were applied (experiments 1-6). Strong bonding is observed at all applied pressures. A strong bond (average lap shear strength 0.67 MPa) was formed even when the substrates are contacted without applying any external pressure (experiment 2).

[0185] The lack of necessity for application of high external pressure ensures that there is minimal deformation of any microstructures within the microfluidic device. This is in contrast to common methods of solvent bonding and thermal bonding, which typically require the application of external pressure to achieve a sufficiently high bond strength. These methods therefore often yield significant deformation of microfluidic structures which may affect the performance of the bonded device.

Monomer Ratio (Experiments 5, 7-11)

[0186] The weight ratio of the mono-functional monomer and the multi-functional monomer was varied.

TABLE-US-00003 TABLE 2 lap shear Experiment Monomer monomer THF strength Optical # A vol % B vol % vol % (MPa) transparency CE7* 90 0 10 0.21 0.04 bad CE8* 0 90 10 0.9 0.1 bad 9 60 30 10 0.7 0.2 good 10 30 60 10 0.91 0.02 good 11 22.5 67.5 10 0.67 0.09 good 5 45 45 10 0.7 0.2 good Note: experiments marked with * are comparative experiments and are not processes according to the invention.

[0187] It was found that using only a monofunctional acrylic monomer containing PEG moieties (experiment CE7) results in an average lap shear strength 0.21 MPa. This bond strength is weak compared to experiments with mixtures of mono- and multifunctional monomers. Also, the crosslinked coating blocks a significant amount of light (>20% in comparison to an uncoated COC-substrate) at wavelengths below 370 nm (FIG. 4), which is undesirable.

[0188] When using only a multifunctional acrylic monomer containing PEG moieties (experiment CE8), strong bonding was observed (average lap shear strength 0.9 MPa), but the optical transparency of the crosslinked coating was seriously compromised due to the high level of crosslinking. This is shown in FIG. 4, which shows a transmission of <60% for all wavelengths between 300 and 800 nm.

[0189] When mixtures of varying ratios of mono- and multifunctional acrylic monomers with PEG moieties were used (experiments 5, 9-11), strong bonding was achieved without reducing the optical transparency of the crosslinked coating. FIG. 4 shows that the transmission is >80% for all wavelengths between 320 and 800 nm.

Irradiation

Irradiation without Photoinitiator, Varied Irradiation Time (Experiments 10, 12, 13)

[0190] The irradiation time was varied.

TABLE-US-00004 TABLE 3 lap shear Monomer monomer THF UV strength Experiment # A vol % B vol % vol % Time (s) (MPa) 12 30 60 10 600 0.2 0.1 13 1800 0.35 0.09 10 3600 0.91 0.02

[0191] For industrial application, it is preferable to have a short irradiation time. It was found that compared to experiment 10 the irradiation time can be significantly reduced without making any further changes to the process and still achieve sufficiently strong bonding (experiments 12, 13).

[0192] Irradiation with photoinitiator, varied irradiation time (experiments 14-28) A photoinitiator was added to the liquid composition and the irradiation time was varied.

TABLE-US-00005 TABLE 4 lap shear Experiment Monomer A monomer B THF Photo- UV strength # vol % vol % vol % initiator wt % time(s) (MPa) 14 30 60 10 F10-BP 2 5 0.16 0.06 15 30 0.3 0.1 16 60 0.37 0.02 17 600 0.72 0.05 18 1800 0.7 0.2 19 3600 0.70 0.2

[0193] It was found that perfluorobenzophonene (F10-BP) is a suitable photoinitiator. When 2 wt. % of F10-BP is added to the liquid composition, the irradiation time can be greatly reduced while maintaining a sufficiently high bond strength (experiments 14-19).

Irradiation with Photoinitiator, Varied Amount (Experiments 22-26)

[0194] The amount of F10-BP was varied at a fixed irradiation time of 300 s (experiments 20-24).

TABLE-US-00006 TABLE 5 lap shear Experiment monomer A monomer B THF Photo- UV strength # vol % vol % vol % initiator wt % Time(s) (MPa) 20 30 60 10 F10-BP 0.1 300 0.46 0.06 21 1 0.6 0.1 22 2 0.57 0.08 23 5 0.53 0.08 24 10 0.53 0.07

[0195] It was found that at this irradiation time, sufficiently strong bonding can be achieved at photoinitiator concentrations between 0.1 and 10 wt. %.

[0196] Irradiation with photoinitiator, varied type of photoinitiator (experiments 27-30) The type of the photoinitiator was varied (Experiments 25-28).

TABLE-US-00007 TABLE 6 lap shear Experiment Monomer A Monomer B THF Photo- UV strength # vol % vol % vol % initiator wt. % Time(s) (MPa) 25 22.5 67.5 10 TPO 2 60 0.41 0.06 26 Irgacure 2 60 0.49 0.04 2959

[0197] It was found that the addition of 2 wt. % of diphenyl(2,4,6-trimethyl benzoyl)phosphine oxide (TPO) and 2-hydroxy-4-(2-hydroxyethoxy)-2-methyl prop iophenone (Irgacure 2959) results in strong bonding at an irradiation time of only 1 minute (experiments 25, 26).

Partial Irradiation

[0198] In another experiment, a photomask was used to partially block the UV light, leaving part of the channels uncoated (see FIG. 5). For this experiment, the coating composition and process parameters of experiment 22 were used. The coated part of the channels is hydrophilic and can thus be filled by capillary force by simply applying a droplet of water on the inlet. Since uncoated COC is hydrophobic, this also serves as a barrier, effectively stopping the flow of water when it reaches the end of the coated area. As expected, fully irradiated and thus fully coated channels are completely filled.

[0199] This result shows that the process according to the invention can be used to achieve patterned coating and bonding of a microfluidic device in a single step.

Substrate Material (Experiments 27-33)

[0200] The substrate material was varied (experiments 27-33). PEG9-Ac (22.5 vol %) was used as monomer A. The coating composition further comprised 67.5 vol % of different monomers B, 10 vol % of THF, and 1 wt. % of F10-BP. UV irradiation was applied for 60 seconds while applying an external pressure of 0.32 MPa.

TABLE-US-00008 TABLE 7 lap shear strength Experiment # substrate 1 substrate 2 Monomer B (MPa) 27 COP COP PEG3-diAc 0.33 0.07 28 PMMA PMMA 0.63 0.03 29 COC PMMA 0.58 0.02 CE30* Glass Glass 0.06 0.06 31 Glass-PEG Glass-PEG PEG-tetraAc 0.11 0.01 32 Glass-PEG COC 0.19 0.03 33 Glass-PEG COC PEG3-diAc 014 0.03

[0201] Beside COC, also other substrate materials may be used in the process according to the invention. Examples of suitable substrate materials include Cyclic Olefin Polymer (COP, experiment 27), and poly(methyl methacrylate) (PMMA, experiment 28). In this experiment, the substrates were not activated before applying the liquid composition, thus demonstrating that activation of the surface is not required for successful bonding of substrates. The process according to the invention may also be used to coat and bond dissimilar materials, for example COC and PMMA (experiment 29).

[0202] The process according to the invention may also be used to coat and bond inorganic materials, such as glass. However, the average lap shear strength for glass-glass bonding (0.06 MPa, experiment CE30) is much lower than for the polymer substrates and does not yield sufficiently strong bonding. The bond strength for glass and other inorganic substrates can be increased by preparing an organic surface modification layer on the glass surface before application of the liquid composition. For example, processes for creating alkoxy- or chlorosilane layers on hydroxylated glass (SiOH) and other oxide surfaces are well known in the art and may be used for this purpose. In experiments 31-33, a layer of PEG-triethoxysilane was created on the surface of the glass substrates, thus providing glycol (H2CH2CO) groups on the surface. The PEG layer provides a better anchoring point for grafting of the acrylic monomers than the silanol groups on the bare glass surface. In these experiments, sufficiently high lap shear strengths above 0.1 MPa are obtained.

Monomer Type (Experiments 34-37)

[0203] The type of monomer was varied (experiments 34-37). COC substrates were used for these experiments. UV irradiation was applied for 60 seconds while applying an external pressure of 0.32 MPa.

TABLE-US-00009 TABLE 8 Mono- Multi- lap shear Experiment functional functional Photo- strength # monomer vol % monomer vol % additive vol % initiator wt % (MPa) 34 PEG9-Ac 22.5 PEG-tetraA c 67.5 THF 10 F10-BP 2 0.19 0.03 35 PEG9- 22.5 PEG1- diMAC 67.5 THF 10 F10-BP 2 0.5 0.2 MAc CE36* PEG2 0k- diAc 100 no bond CE37* PEG2 0k- diMAc 100 no bond

[0204] A variety of monomers A and B can be used in the process according to the invention. For example, the bifunctional monomer PEG3-diAc that is used in most experiments may be replaced by multifunctional monomers with a different number of acrylic groups, for example the tetrafunctional monomer PEG-tetraAc (experiment 34). Experiment 35 shows that methacrylate monomers may also be used instead of acrylate monomers in the process according to the invention.

[0205] The number of glycol (H2CH2CO) units per monomer may also be varied, as long as the composition remains liquid after evaporation of the diluent. When very long PEG monomers are used that are solid at room temperature (for example monomers having a molecular weight of approximately 20 kDa), no bond is formed between the substrates (experiments CE36, CE37).

Presence of Diluent (Experiments 38-41)

[0206] The type and amount of diluent was varied (Experiments 38-41). COC substrates were used for these experiments. UV irradiation was applied for 60 seconds while applying an external pressure of 0.32 MPa.

TABLE-US-00010 TABLE 9 Mono- Multi- lap shear Experiment functional functional Photo- strength # monomer vol % monomer vol % additive vol % initiator wt % (MPa) 38 PEG9-Ac 22.5 PEG3- diAc 67.5 none N/A 10-BP 2 0.52 0.09 CE39* PEG9-Ac 22.5 PEG3- diAc 67.5 water 10 Irgacure 2 opaque 2959 hydrogel CE40* PEG9-MAc 10 PEG1- 10 water 80 Irgacure 2 0.08 0.02 diMAc 2959 CE41* PEG9-Ac 10 PEG3- diAc 10 water 80 Irgacure 2 0.03 0.01 2959

[0207] The presence of a diluent in the liquid composition is optional. THF has been used as a diluent in most experiments, but experiment 38 demonstrates that the process also works without the presence of THF. In most experiments, 10 vol % of THF was used, but this amount may be adjusted.

[0208] The role of the diluent may be to facilitate application of the liquid composition and/or spreading of the liquid composition on the substrate surface by reducing the viscosity.

[0209] However, it should not interfere with the process during the steps of contacting the substrates and irradiation of the assembly. In the case of THF and other volatile organic compounds, the diluent will disappear from the liquid composition by evaporation before the substrates are contacted and the assembly is irradiated. Therefore, THF and other suitable volatile organic compounds may be used as a component of the liquid composition.

[0210] For comparison, water was used instead of THF (experiments CE39-CE41). Water is much less volatile than THF and will not evaporate from the liquid composition during the process (at room temperature). Therefore, water is still present in the liquid composition during contacting of the substrates and irradiation of the assembly, and interferes with the coating and bonding process. Instead of forming a strong bond between the substrates, a hydrogel is formed which results in weak bonding (lap shear strength <0.1 MPa) and/or a loss of transparency.

[0211] Coating and bonding of a microfluidic flow cell onto a photonic biochip (experiment 42) The process according to the invention was used to coat and bond a microfluidic flow channel made from COC to a photonic biosensor chip (experiment 44). The biosensor chip comprises a silicon substrate with silicon nitride waveguides embedded in a silicon oxide cladding. The silicon oxide surface of the biosensor chip was modified using a PEG-silane (2-[Methoxy(polyethyleneoxy)propyl]dimethylsilane, 6-9 ethyleneoxy units) to create a PEG layer on the surface. The liquid composition was applied to the surface of the flow cell by spin coating. The coating composition comprised PEG9-Ac (22.5 vol %) as monomer A, PEG3-diAC (67.5 vol %) as monomer B, THF (10 vol %) as a diluent, and 2 wt. % of F10-BP as photo-initiator. The flow cell and the biosensor chip were contacted without applying any external pressure and irradiated for 10 minutes.

[0212] No lap shear strength testing can be performed on this sample. Therefore, a different characterization method was employed to demonstrate the simultaneous bonding and coating of the device. An aqueous dye solution was introduced by pipetting a droplet of the dye solution on the inlet of the flow cell. As shown in FIG. 6, the flow channel is readily filled by capillary action without applying any external pressure, thus demonstrating the presence of the hydrophilic PEG coating on the channel walls. The hydrophilicity of the flow channel walls can also be deduced from the contact angle of the dye solution with the side walls of the channel.

[0213] No leakage of the bonded flow cell was observed when flowing liquids through the channel, even when applying external pressure up to 1000 mbar. Thus, it is clearly demonstrated that the bond between the sensor chip and the flow cell is strong enough for common microfluidic applications, which typically require pressures well below 1 bar.

Application of Liquid Composition by Spray Coating (Example 43)

[0214] A COC substrate (2575 mm2) with 4 parallel straight channels was used as the bottom part, and COC foil (125 m thickness) as the top part. On the bottom part the channels were 58.5 mm long, 1 mm wide, and 200 m deep. The substrates were cleaned by ultrasonication in acetone and dried by a nitrogen flow. The substrates were activated by exposure to a low-pressure air plasma for 60 s. A coating composition was prepared containing PEG9-Ac (6 vol %) as monomer A, PEG3-diAc (64 vol %) as monomer B, THF (30 vol %) as a diluent, and 0.8 w/v % of benzophenone (BP) as photo-initiator.

[0215] The coating composition was applied on the substrates by spray coating, during which the diluent evaporates. This results in the formation of a liquid coating on flat parts of the substrates and the walls of the channels without completely filling the channels. No additional steps were taken for evaporating the diluent or avoiding channel clogging. The substrates were then contacted with each other to form an assembly, and the assembly was irradiated with UV light (365 nm, 40 W) through a quartz mask for 5 min under an argon flow. Bonded channels were then characterized without further rinsing, washing or other treatments.

[0216] To demonstrate the formation of a hydrophilic PEG coating on the channel walls, the wettability of coated and uncoated COC channels (commercially available) was compared. A droplet of water or an aqueous dye solution was deposited on the inlet of the coated and uncoated channels. The coated channels are readily filled by capillary action without applying any external pressure, thus demonstrating the presence of the hydrophilic PEG coating on the channel walls. The contact angle of water with the side walls of the coated channels is <40. In contrast, the uncoated COC channels are hydrophobic, and are not filled by capillary action when a water droplet is deposited on the inlet.