Microfabricating high-aspect-ratio structures in polyurethane-methacrylate (PUMA) disposable microfluidic devices

Abstract

We recently reported a new UV-curable polyurethane-methacrylate (PUMA) resin that has excellent qualities as a disposable microfluidic substrate for clinical diagnostic applications. This article discusses strategies to improve the production yield of PUMA chips that contain dense and high-aspect-ratio features, which presents unique challenges in demolding and bonding steps. These fabrication improvements were deployed to produce a microfiltration device that contained closely spaced and high-aspect-ratio columns, suitable for retaining and concentrating cells or beads from a highly diluted suspension.

Thiolene and SIFEL-based microfluidic platforms for liquid–liquid extraction

“…Previously, silicon- and glass-based microfluidic configurations have been reported for parallel flow extraction that use microstructures, including posts, micro pillars, or partitions at the interface to stabilize the liquid-liquid interface [17, 32]. Although these strategies were effective in stabilizing the liquid-liquid interface, these structures effectively reduced the extraction length, and these platforms contain features with smaller than 5 µm dimensions, which generally are more challenging to fabricate than the ~100 µm channels used in the split-length design studied here, especially in certain materials such as flexible polymers [70]. …”

Materials and methods for the microfabrication of microfluidic biomedical devices

“…However, these fabrication techniques are not suitable for replicating the intricate and detailed microscale features present in microfl uidics devices. PU-based microfabrication typically involves injection molding (Folch et al ., 2000;Kuo et al ., 2009), hot embossing (Shen et al ., 2006), imprinting (Xu et al ., 2000), plasma etching (Rossier et al ., 2002), sacrifi cial material (Haraldsson et al ., 2006), and reaction polymerization (Thorsen et al ., 2001;Kim et al ., 2003;Haraldsson et al ., 2006;Piccin et al ., 2007;Kuo et al ., 2009). These methods are not suited for rapid prototyping as they use high cost intermediate molds and expensive fabrication equipment.…”

“…To achieve irreversible bonding, semi-cured parts of PU have been placed in contact and heated above the glass transition temperature, causing fusion of the two parts (Piccin et al ., 2007;Kuo et al ., 2009). However, this method is not suitable for retaining the fi ne structural features needed in microchannels.…”

“…Due to its excellent hardness, high-aspect-ratio (~3.5) microstructure made from PU can be easily fabricated and bonded, whereas microstructures made from PDMS are too soft to stand their own weight. These microstructures were then used as microfl uidic fi lters to separate or concentrate the targeted particles or cells (Kuo et al ., 2009). The other main advantage of PU over other polymers is in its feasibility to be chemically tailored for specifi c applications; thus, it has been widely used in applications such as cell culture and tissue scaffolds (Folch et al ., 2000;Vermette et al ., 2001;Shen et al ., 2006;Moraes et al ., 2009).…”

Ageing properties of polyurethane methacrylate and off‐stoichiometry thiol‐ene polymers after nitrogen and argon plasma treatment

“…Another variant of PUMA, Polydiam SF‐45 Photopolymer (UK), also possessed other suitable properties such as high chemical and thermal stability, high optical transparency, and strong interfacial bonding strength to form the microfluidic device . The properties of PUMA attracted several process and design innovations to produce lab‐on‐chip for various applications such as blood cell or cancer cell separation …”