Optical machining of microfluidics with the IMRA μ Jewel

1. Optical machining of microfluidicswith the IMRA μJewel Sanghyun Lee / Prof. Alan Hunt / Prof. E.F. Hasselbrink

2. • • • • •Contents • Introduction • Proof-of-Principle Microfluidic Devices • Key Research Questions • The Role of Bubbles • Machining Performance • Newly observed phenomena • Conclusions and Future Work

3. $M Source:Cambridge Healthtech Institute Micro-Total Analysis Systems • Instrument Markets • Pharmaceutical (>$4B) • Massively parallel synthesis • High Throughput Screening • Inexpensive QC • Biotech/agribusiness (>$1B) • Field Instrumentation (???) • Science • Proteomics • Gene sequencing • Single-cell assays • “Better, faster, cheaper” • New capabilities by exploiting different physics • New capabilities afforded by Integration (e.g. high throughput, parallel chromatography) Agilent Technologies Optical machining with IMRA μJewel

4. 3D: A key requirement for complex microfluidics Unger, Cho, Thorsen, Scherer, and Quake, Science, Vol 288, Issue 5463, 113-116 , 7 April 2000 Thorsen, Maerkl, Quake, Science v. 298 iss. 5593, 580 - 584, 18 Oct 2002. • 3D fabrication of complex fluidic processors is possible in PDMS • PDMS (poly-dimethylsiloxane) is a silicone polymer with serious fatal flaws: • - Adsorption • - Lack of solvent resistance • - Possible catalytic activity • - Limited pressure • These problems prevent widespread adoption by the pharmaceutical industry. Optical machining with IMRA μJewel

5. 3D Femtosecond Laser Machining Machining speed is significantly improved when article is submerged underneath a layer of water. Bubbles assist in debris removal Optical machining with IMRA μJewel

6. Machining Methods for Long Channels Back-and-forth motion of stage with incremental advancing exploits bubble-driven debris removal x N dA A Us t tb Generally, Us and dA should be decreased while A andN should be increased during machining for long channel. Fluency of laser focus, transfer media, type of glass, and geometry of channel affect these factors. Increasing length requires faster-than-linear increase in machining time. Optical machining with IMRA μJewel

7. PoP Devices: Nanojumpers Out-of-plane jumpers make complex 3D microfluidic topologies possible. Optical machining with IMRA μJewel

8. PoP Devices: Long channels Up to 800 um long channels have been machined in 3D geometries Optical machining with IMRA μJewel

9. PoP Devices: 3D Mixers EK flow through nanochannels has been proven Optical machining with IMRA μJewel

10. Research Question 1: Role of Bubbles • Does bubble collapse actually assist in the machining? • How quickly will a bubble expand in a micro/nanochannel? How large will the bubble extend? • How quickly will a bubble collapse in a micro/nanochannel? • How different is the expansion/collapse behavior depending on where in the channel the bubble is originated? Optical machining with IMRA μJewel

11. Machining method: role of bubbles Although high Re bubble collapse can be a major mechanism for surface spalling, at our low Re (~10-4), bubble collapse is not a major contributor to the machining mechanism Comparison w/inviscid theory √ Bubble collapse time ~ Re-1 √ dmax5/tc2 ~ E Optical machining with IMRA μJewel

12. Machining method: role of bubbles Early on, we observed node-like regions where machining is significantly retarded Optical machining with IMRA μJewel

13. Bubbles in nanochannels However, bubble generation and collapse rate is also a strong function of: (1) gas content in the liquid, (2) location in the channel Optical machining with IMRA μJewel

14. Bubbles: Conclusions to Date • Bubbles remove debris, but do NOT do any surface damage. • Acoustics may be complicated, but the “node” behavior is surmountable. The behavior is strongest at the 1st node and becomes progressively weaker. • Degassing solutions is absolutely critical (both for effective machining, and for repeatable scientific results!) Bubbles: Ongoing work • How do bubbles and laser interact in the nanochannel? • - Bubble must collapse to allow liquid to refill into channel – better to shut off laser? (Potential big advantage for a future IMRA design) Optical machining with IMRA μJewel

15. Research Question 2: Practical Machining Performance • How long of a channel can be machined? How fast? • How does Pulse Repetition Rate (PRR) affect machining speed & quality? • How does Pulse Energy affect machining speed & quality? • What other phenomena are observed when using higher PRR? Optical machining with IMRA μJewel

16. Long channel machining • Channel Length: 300µm • Machining time: 90min • Pulse energy: 27nJ • P.R.R.: 100kHz Due to the “football” shaped focus, the cross-section of the channel is not uniform. IMRA μJewel at 100kHz shows very good performance of long channel – better than our first attempts with the 200kHz PRR. Optical machining with IMRA μJewel

17. nCE channel machining • Channel Length: 850µm • Machining time: 250min • Pulse energy: 27nJ • P.R.R.: 100kHz Black spots are dirt mixed with debris in surrounding water. IMRA μJewel also showed very good performance of nCE device machining. Optical machining with IMRA μJewel

18. Machining with laser chopping 100Hz 200Hz 400Hz 800Hz Optical machining with IMRA μJewel

19. Machining with laser chopping • Machining performance is affected by the laser chopping and the feed rate. • 800Hz chopping shows best performance. The advantage of chopping is bigger at the slow feed rate region. In high feed rate region, only 800Hz chopping shows clear difference. Optical machining with IMRA μJewel

20. Machining with laser chopping • Although laser chopping decreases the average power input to an half, the machining performance increased up to double. • The chopping may increase the water supply to the focus area • Pressure field inside channel will also be affected by the chopping frequency. Optical machining with IMRA μJewel

21. Machining with various feed rate Slow feed rate can make longer channel in single scanning of laser. However, slow feed rate means longer machining time. Feed rate is also related to the surface roughness. Optimal feed rate can be decided by these two factors. Optical machining with IMRA μJewel

22. Intralase expts (lower PRR): effect of feed rate, multiple passes Optical machining with IMRA μJewel

23. Intralase (lower PRR) expts: effect of pulse energy Optical machining with IMRA μJewel

24. Intralase (lower PRR) expts: effects of PRR Optical machining with IMRA μJewel

25. Other observed phenomena Induced bubbles on/above the surface * Pulse energy: 27nJ, PRR: 100kHz Bubbles are induced on/above the glass surface during the machining with 27nJ pulse energy. It is not because of the penetration holes. Surface vibration, or secondary focus? Optical machining with IMRA μJewel

26. Newly observed phenomena Bubble entrapment at the focus Surprisingly bubbles extruded from the central hole are strongly attracted to the focus, being trapped at the focus. And it is released, when the bubble has enough buoyancy force. * Pulse energy: 23nJ, PRR: 100kHz The reason of strong attraction and entrapment is not clear. a. The surface vibration by the laser pulsation can explain the attracting and trapping of bubbles b. The circulation of water due to the local heating by laser focus can explain the attraction. Optical machining with IMRA μJewel

27. Machining with different glass substrate Machining with different cover slips having different geometry (different natural frequency) were tested to see the resonance effect. Normal glass substrate 25x25mm, 170um thickness cover slip Modified glass substrate Normal cover slip glued with cylindrical reservoir containing water Optical machining with IMRA μJewel

28. Machining with different substrate resonance frequency (presumed) The modified cover slip shows a little bit better performance (6.78 μm) than the normal cover slip (5.88 μm). The surface vibration may affect machining; thus entrapment of bubbles on the surface (as observed with the mJewel) is likely to have a modest effect on machining rate. Optical machining with IMRA μJewel

29. Conclusions: Machining Performance • PRR is a major factor we would like to be able to vary. Owing to the complexity of the interplay between bubbles, material, and the laser, ideally we could potentially observe big improvements in machining speed with complete “pulse picking” capability (or a least a fast gate). • Pulse energy is also a major factor deciding the material removal rate. The ability to remove large volumes and small volumes in a single laser would be an extraordinary capability. Optical machining with IMRA μJewel

30. Future Work • Continued investigation of PRR, feed rate, and Energy for complex 3D networks. • Performance of laser-machined microfluidic devices • Serial-machining is limited. Should we consider aiming for 3D nanomold-making? • Coupling with devices that require 3D machining. Optical machining with IMRA μJewel

31. 3D: A key requirement for complex microfluidics Unger, Cho, Thorsen, Scherer, and Quake, Science, Vol 288, Issue 5463, 113-116 , 7 April 2000 Thorsen, Maerkl, Quake, Science v. 298 iss. 5593, 580 - 584, 18 Oct 2002. • 3D fabrication of complex fluidic processors is possible in PDMS • PDMS (poly-dimethylsiloxane) is a silicone polymer with serious fatal flaws: • - Adsorption • - Lack of solvent resistance • - Possible catalytic activity • - Limited pressure • These problems prevent widespread adoption by the pharmaceutical industry. Optical machining with IMRA μJewel

32. Future Work Optical machining with IMRA μJewel

33. Future Work Optical machining with IMRA μJewel

34. Future Work Optical machining with IMRA μJewel