Without a doubt, polydimethylsiloxane (PDMS) is taking centre stage in vast areas of bio, material, and mechanical researches. Naturally, shaping PDMS into a sophisticated structure has become one of the highest interest of relevant researchers. Although the replication moulding (REM) has taken root as a standard protocol of various PDMS-associated researches, for the researchers in the field, the multi-step procedures of REM was a tedious, time-consuming legacy of suffering. Especially when it comes to researches demanding frequent design change, which is essential to increase the completeness of the study, the repetition of the complex process of REM was like an uphill battle.

 Under this background, several researchers explored an alternative pathway aiming far efficient PDMS patterning with the aid of direct laser patterning. However, the transparent nature of PDMS frustrated the challenges so far; the laser passes through the PDMS without doing anything. Alternatively, the attempts of laser ablation utilising pulsed laser could circumvent the transparency, while facing burrs, debris, and cleavages, making the result impractical.

 In the recent paper of Nature Materials, our research team present a possible solution for such inveterate conundrum between laser and PDMS. Our study started from observation of darkish residue of laser-pyrolysed PDMS. Focusing on the principle of a chain reaction that the result of prior event leads to the initiation of the same event, we could predict the possibility of ‘laser-guided chain reaction’ of PDMS pyrolysis; the opaque by-product of the pyrolysis, which can far more efficiently absorb the laser, could induce the second pyrolysis. If this idea works, we would directly form PDMS structures starting from a PDMS monolith without any treatment to change PDMS properties based on a one-touching drawing fashion. And the paper is reporting the experimental proof of this idea.

Featured images of SLP. Left: Digital image of SLP process forming vertical microchannels inside PDMS. Right: Digital image of ‘Skin-on-a-chip’ device fabricated from a PDMS monolith through SLP process.

 Consequently, the successive laser pyrolysis (SLP), our naming for this new technique, realises the high-quality direct machining of PDMS for the first time. The continuous progression of pyrolysis phenomena, not the ablation or burning, along a laser scanning contour, realises a smooth machining surface. At the same time, the digital manoeuver of the laser enables on-demand maskless patterning of various 2D and even some 3D PDMS structures with a remarkably reduced lead time (< 1 h). Compared to the conventional process that takes at least one day, this reduction in fabrication time would bring enormous benefits to researchers.

 When we imagine the future this new technology will bring, the rapid and agile PDMS machining through SLP could pave a shortcut to bridge a researcher’s bare idea to a real device in a surprisingly fast and inexpensive way. So we hope this new technology could boost researchers in the relevant fields to go further, faster, and easier. And importantly, in order for this hope to happen, active cooperation with professionals from diverse background is essential. This is why we are waiting for voices from many researchers.

Realtime SLP process. Original full version of video can be found at the following journal link. 

The paper

Shin, J., Ko, J., Jeong, S., Won, P., Lee, Y., Kim, J., Hong, S.J., Jeon, N.L., Ko, S.H., “Monolithic digital patterning of polydimethylsiloxane with successive laser pyrolysis”, Nat. Mater., doi:10.1038/s41563-020-0769-6 (2020).

Lab website: http://ants.snu.ac.kr/

Twitter handle: @SeungHwanKo1