COLLABORATIVE PROJECT

Transcription

1 COLLABORATIVE PROJECT Collaborative pilot project: combination of advanced laser processes for the rapid fabrication of microfluidic devices made of polymer materials Kohler/KIT

2 TABLE OF CONTENTS 1. Introduction Involved partners Experimental plan Results Conlusion... 7

3 1. Introduction The objective of Ecolaserfact Collaborative Projects is to demonstrate the capabilities of lasers for low-cost, high precision, flexible and eco-friendly micromanufacturing. Potential applications will cover a large spectrum ranging from photovoltaic to bio-medical technology, from laser additive direct fabrication to online control with 3D-laser metrology, from micro-welding to patterning and modification of thin films. The aim of the project Combination of Advanced Laser Processes for the Rapid Fabrication of Micro-Fluidic Devices made of Polymer Materials is to demonstrate the capabilities of different laser technologies in the field of manufacturing polymeric devices containing micro-fluidic structures. Polymeric microfluidic structures are a key component for Lab-on-a-Chip devices. These devices miniaturize one or several laboratory functions on a single chip. Reduced structure sizes result in small volumes which in consequence reduce the time taken to synthesize and analyse a product; the unique behaviour of liquids at the microscale allows greater control of molecular concentrations and interactions; and reagent costs and the amount of chemical waste can be much reduced. Compact devices also allow samples to be analysed at the point of need rather than a centralized laboratory. The advantages of laser-based techniques for micro-system manufacturing are numerous. Any solid can be lasermachined under the appropriate conditions and processes have been established to machine with high precision a large variety of polymers. Laser processing covers a wide range of techniques, such as macro- and microscale structuring, drilling, fine cutting, joining, and surface modification, that can be used to fabricate a device in its entirety or can be integrated in an existing processing chain with other techniques. Another situation favoring the use of laser micromachining is the use of non-planar substrates. Laser-based techniques allow a high level of flexibility in the layout because they directly use digital data generated during the design of the device; thereby allowing a design to be changed easily and rapidly and iterations with a new prototype with incremental improvements to be made in a microfluidic design.

4 2. Involved partners Cardiff University KIT (leader) SIRRIS VITO 3. Experimental plan The concept of this project is to combine different expertises of the involved partners to manufacture a joint demonstrator. An experimental plan has been set up in which the processing step each partner is responsbile for is defined. 1. Material (SIRRIS) : Selection and supply of the polymeric material. 2. Laser Cutting (KIT) : Singling of the device and manufacturing of throughholes 3. Laser Structuring (Cardiff University) : Manufacturing of the microfluidic structures 4. Laser Welding (VITO) : Hermetic sealing of the device Every partner has performed a parameter study to identify suitable process parameters (e.g. laser power, scanning speed) for their individual process. The design of the demonstrator device is shown on the right, it consists of a branching chanel structure continously decreasing in size. The white lines depict the micro-fluidic elements, while the red lines show the physical dimensions of the device as well as the through-hole via which the analyte can be injected. The dimensions of this device are 26mm x 34mm. The minimal chanel widths are 50µm.

5 4. Results SIRRIS is responsible for providing the polymeric material for the microfluidic device. The material has to be compatible for to all the following laser processing steps. After consultations with each involved partner poly methyl methacrylate (PMMA) was choosen as substrate material. PMMA has the advantage of low cost, high transparency, excellent dielectric and mechanical properties. Apart from leading this project, KIT has performed the high-precision cutting of the device. Two parts needed to be cut the top and the bottom layer. The top contained a throughhole via which a liquid can be inserted into the device. For polymer cutting a CO 2 -laser with a maximum power of 40W was used. A power of 4W with a cutting speed of 5mm/s were used. This can be easily upscalable to 50mm/s using the same laser system. The image below depicts the two laser cut pieces. Cardiff University has been responsible for the laser structuring of the micro-fluidic channel structures. A solid state (DPSS) laser from Lumera Laser GmbH (Super Rapid) operating at a wavelength of 355nm and delivering an output power 0.3W with an pulse width of 12ps was used. A high beam quality (M²<1.2) and a repetition rate up to 600kHz can be obtained. In order to creat a smooth and clean cut a series of trial cust were performed. For the actual structuring the following parameters were utilized : 10kHZ repetition rate, 40mW The model was imported into the proprietary software Waverunner.

6 The final step, the joining of the two polymeric layers, was performed by VITO. For this process laser transmission welding was used. VITO performed tests using the PMMA substrates as described in this document. For this purpose, a direct Laserline diode laser was used with a mixed wavelength 808nm and 940nm. A beam homogenizing unit yielded a rectangular laser focus of 3mm*20mm. The laser head is mounted on a ABB robot arm and is moved over the surface of the PMMA samples at speeds ranging between 1-2mm/min. The laser power ranged in an experimental set-up between 600W and 1000W. Since PMMA is basically transparent for laser wavelength in the NIR area of the spectrum, a commercially available IR absorber is used (Clearweld from Gentex) in order to guarantee a proper melting of the PMMA at the interface of the 2 components to be joined. This absorber is applied through a pen/marker, which coats the surface of the bottom part. When irradiating the parts with the laser, the IR absorber will convert the laser radiation into heat which is used to melt the PMMA. A proper contact between the two parts using a dedicated clamping device will also allow melting of the upper part which results in mixing of the 2 melted areas and yielding a transparent weld after cooling. For testing a mesh like structure is applied to the bottom part to be welding using the IR absorber marker. When irratiating this structure in a trasmission welding set-up, a proper transparent welded structure is obtained in one single step (figure).

7 Finally, the completed device is shown in the picture below. 5. Conlusion Within this project it could be demonstrated that the manufacturing of Lab-on-a- Chip devices is possible using different laser technoglogies. These micro-chanels and pockets were created using laser structuring. High precision cutting was demonstrated to manufacture through-holes and for separating of parts. Laser transmission welding was used to hermetically seal the manufactured micro-fluidic structures. The joint transnational cooperation on a single device led to the production of a demonstrator highlighting mutliple laser technologies for micromanufacturing and acting as excellent example of laser micromanufacturing for SMEs.