Development of new lab-on-a-chip (LoC) devices requires an optimization phase in which it could be necessary to continuously modify the architecture and geometry. However, this is only possible if easy, controllable fabrication methods and low-cost materials are available. For this reason, rapid prototyping approaches for the fabrication of polymeric LoC are on the rise, as they allow high degrees of precision and flexibility. Here, we describe the fabrication platform of polymeric microfluidic devices, from the design (CAD) to the proof-ofconcept application as LoC for biological applications. The fabrication procedure is mainly based on fs-laser micromachining techniques. The ability of femtosecond (fs)-laser pulses to produce localized modification of the materials, thereby avoiding either debris, recast layers or unsought thermal affected zones, without restriction of the substrate materials, makes this technology particularly suitable for microfluidic device fabrication. In our work, fs-laser has been also possibly combined with other techniques, without the need for the expensive masks and facilities required by the lithographic process. The LoC devices have been realized in polymethyl methacrylate (PMMA), a low cost and biocompatible material. The fs-based smart fabrication platform has been exploited in the fabrication of disposable LoC devices for particles manipulation. In particular, a serpentine microchannel able to distinguish cancer from non-cancer cells without labeling and a fully inertial sorting 3D device have been fabricated and tested.
Utilization of parts made by combining dissimilar materials, such as different polymers, metals, or semiconductor to polymers, are nowadays highly demanded for the fabrication of electronic, electromechanical, medical micro-devices, and analytical systems (e.g., lab-on-chip). Techniques for joining such hybrid micro-devices, generally based on gluing or thermal processes, remain a challenging task presenting some drawbacks, such as deterioration and contamination of the substrates. Ultrashort laser welding is a non-contact and flexible technique to precisely weld similar and dissimilar materials. In this case, the only constrain is that the upper substrate is transparent to the laser wavelength. This technique has been demonstrated both for welding polymers and polymers to metallic substrates, but never for joining polymers to silicon. In this work, we report on direct femtosecond laser welding of Poly(methyl methacrylate) (PMMA) and silicon. The laser welding was performed in ambient air by focusing ultrashort laser pulses at high repetition rate at the interface between the two, being PMMA transparent to the laser wavelength. A mechanical homogenous pressure was applied on the sandwiched substrates during all the laser process. The Si-PMMA weld strength was evaluated as a function of the laser and processing parameters, e.g., repetition rate, scan speed, and the overlap between adjacent scan lines.
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