Microfluidics Manufacturing: Micromilling
Micromilling in Microfluidics:Using small cutting tools to create microfluidic architectures.
It is a mechanical method, in which we use small cutting tools to remove the materials from a specific part of the microfluidic architecture.
All thermoplastics can be subjected to micromilling and can be used only on hardened materials. The structure resolution depends on the tool dimension; it can go down to 25μm.
PDMS structure cannot be obtained directly by this method. The replica of the design can be machined and the mould(are reusable) can be casted in order to get PDMS devices.
Technique: A computer is used to control the position of the tool and the cutting of the structures.The milling time,depends on the milling structure, and can vary from minutes to hours .
The advantage of this technique is that it does not affect the polymeric material by UV radiation or heating, but it creates stress near the cut structures that can be avoided by heating and slow cooling.
Microfluidics: Liquid handling
The aim of this document is to scratch the surface of microfluidics, trying to describe the most significant phenomena at this scale.
The first goal of microfluidics is to take advantage of the benefits of scaling down: better control, lower cost, faster results and more. These benefits are especially relevant for biological reactions.
The effects that become dominant in microfluidics include laminar flow, diffusion, fluidic resistance, surface area to volume ratio, and surface tension. As the magnitude of these physical effects is different to the ones experienced at the macroscopic scale, fluid integrated microdevices must be designed from first principles and not simply by miniaturizing macroscopic devices.
Liquid flow in the microdomain belongs to the regime of viscous dominated flow. There is a fundamental change in hydrodynamics that occurs here, which significantly affects microfluidic operations like mixing. This barrier occurs when the Reynolds number is of the order of unity. At these scales, viscous forces dominate over inertial forces, turbulence is nonexistent, surface tension can be a powerful force, diffusion becomes the basic method for mixing, and evaporation acts quickly on exposed liquid surfaces. At low Reynolds numbers, fluid dynamics is dominated by viscous drag rather than by inertia and this is why devices that rely on inertial effects for their operation will no longer work.
One consequence of laminar flow is that two or more streams flowing in contact with each other will not mix except by diffusion. Diffusion is the process, by which a concentrated group of particles in a volume will, by Brownian motion, spread out over time so that the average concentration of particles throughout the volume is constant.
As diffusion times can be short at the microscale, microchannels can be used to create concentration gradients having complex profiles. Mixing schemes at the microscale must find ways to maximize the interfaces between solutions to allow diffusion to act quickly.
Surface area to volume ratio is another factor that becomes important at the microscale. The inverse characteristic length scaling of the surface-area-to-volume ratio implies that heat and mass transfer into or out of a chip can be enhanced as the dimensions of the device are reduced.
When working at the micro scale, another element as the surface tension forces become significant. Surface tension is the result of cohesion between liquid molecules at the interfaces. The surface free energy of a liquid is a measure of how much tension its surface contains. The path a fluid will travel through a capillary is directly related to the water’s surface free energy and inversely related to the radius of the capillary.
When microchannels with dimensions on the order of microns are used, the lengths liquids travel based only on capillary forces are significant. Surface energies have been widely exploited in microfluidics as pumping systems.
Microfluidic Prototyping: Molds for PDMS Microfluidic Chips
In microLIQUID, we manufacture SU8 molds. The moulds are used as tools for soft casting polymers such as PDMS or polymers Hot Embossing.
Microfluidic Prototyping systems
In microLIQUID, we fabricate the microfluidic structures according to the customer specific requirements.
With no minimum quantities requirements, we start the fabrication from 1 unit at affordable prices.
Our in-house facilities allows us to use different fabrication methods and/or materials.
Techniques: Photolithography, Hot Embossing, Etching (Wet and dry), stereolithography, inject moulding, micromachining, sputtering and vaporization
Materials: Plastics, glass and silicon
The microfluidic channel geometries may vary with high aspect ratio, curved channels, high precision height or length and no depth-width constraints.
Heaters and sensors: We integrate the electrodes inside the microfluidic structures. Made in: Gold, Platinum. Titanium, Chromium or Aluminium or other materials.
Experience:We’ve been developing our microfluidic expertise in the last years through several projects as: Microprobe flexible-semiflexible, Combining delivery and electrical signalling, qPCR Lab on a Chip, Electrolysis pump, Embedded microcantilevers, SU8 free standing structures embedded in microchannels for microfluidic control