Programmable Droplet Microfluidics Based on Machine Learning and Acoustic Manipulation

Typical microfluidic devices are application-specific and have to be carefully designed to implement the necessary functionalities for the targeted application. Programmable microfluidic chips try to overcome this by offering reconfigurable functionalities, allowing the same chip to be used in multiple different applications. In this work, we demonstrate a programmable microfluidic chip for the two-dimensional manipulation of droplets, based on ultrasonic bulk acoustic waves and a closed-loop machine-learning-based control algorithm. The algorithm has no prior knowledge of the acoustic fields but learns to control the droplets on the fly. The manipulation is based on switching the frequency of a single ultrasonic transducer. Using this method, we demonstrate 2D transportation and merging of water droplets in oil and oil droplets in water, and we performed the chemistry that underlies the basis of a colorimetric glucose assay. We show that we can manipulate drops with volumes ranging from ∼200 pL up to ∼30 nL with our setup. We also demonstrate that our method is robust, by changing the system parameters and showing that the machine learning algorithm can still complete the manipulation tasks. In short, our method uses ultrasonics to flexibly manipulate droplets, enabling programmable droplet microfluidic devices.publishedVersionPeer reviewe

Being watched by a humanoid robot and a human: Effects on affect-related psychophysiological responses

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Capillary-driven self-assembly of microchips on oleophilic/oleophobic patterned surface using adhesive droplet in ambient air

This letter describes a capillary-driven self-assembly technique using oleophilic/oleophobic patternedsurface and adhesive in ambient air environment. We use a topographical microstructure of porous ormocer functionalized with a fluorinated trichlorosilane for the oleophobic area and goldpatterns for the oleophilic area. The resulted oleophilic/oleophobic patterns show significant wettability contrast for adhesive (Delo 18507), with a contact angle of 119° on oleophobic part and 53° on the oleophilic part. Self-alignment of SU-8 microchips on the oleophilic/oleophobic patterns has been demonstrated. The results provide a promising solution for self-alignment of microparts using commercial adhesives in ambient air environment.Peer reviewe

Biodegradable, Flexible and Transparent Tactile Pressure Sensor Based on Rubber Leaf Skeletons

Capacitive sensors have many applications in tactile sensing, human-machine interfaces, on-body sensors, and patient monitoring. Particularly in biomedical applications, it would be beneficial if the sensor is disposable and readily degradable for efficient recycling. In this study, we report a biodegradable capacitive tactile pressure sensor based on sustainable and bio resourced materials. Silver-nanowire-coated rubber tree leaf skeletons are used as transparent and flexible electrodes while a biodegradable clear tape is used as the dielectric layer. The fabricated sensor is sensitive and can respond to low pressures (7.9 mN when pressed with a probe with a surface area of 79 mm2 / 0.1 kPa) ranging to relatively high pressures (37 kPa), with a sensitivity up to ≈ 4.5×10-3 kPa-1. Owing to all bio resourced constituents, the sensor is biodegradable and does not create electronic waste.publishedVersionPeer reviewe

Performance Comparison of Fast, Transparent, and Biotic Heaters Based on Leaf Skeletons

Bioinspired, highly flexible, fast, and biodegradable heaters are fabricated based on Ag nanowires and leaf skeletons of different plant species. The leaf skeletons act as transparent substrates with a high surface-area-to-volume ratio and allow a uniform dispersion of the Ag nanowires through the surface. Ag nanowires adhered to the leaf skeletons display very good transmittance (up to ≈87%) and mechanical (flexibility) properties (curvature values >800 m−1) without any post-treatment. The flexible leaf skeleton-based heaters reach high temperatures very quickly, with very low voltages (<4 V). The performance of the bioinspired heater surface is dependent on the types of fractal structures at the microscale. The morphology of the leaf skeletons is studied in detail and is corelated with the transmittance, flexibility, and sheet resistances. Bioinspired heater surfaces based on different leaf skeletons are compared based on their multiscale morphology, and the different heating performance parameters are screened. Based on the study conducted, insights on the best-performing biotic design for the fabrication of the heaters that are useful in practical wearable, medical, or industrial heating applications are provided.publishedVersionPeer reviewe

Integrated stretchable pneumatic strain gauges for electronics-free soft robots

In soft robotics, actuators, logic and power systems can be entirely fluidic and electronics-free. However, sensors still typically rely on electric or optical principles. This adds complexity to fluidic soft robots because transducers are needed, and electrical materials have to be incorporated. Herein, we show a highly-stretchable pneumatic strain gauge based on a meandering microchannel in a soft elastomer material thus eliminating the need for an electrical signal in soft robots. Using such pneumatic sensors, we demonstrate an all-pneumatic gripper with integrated pneumatic strain gauges that is capable of autonomous closure and object recognition. The gauges can measure at least up to 300% engineering strains. The sensor exhibits a very stable signal over a 12-hour measurement period with no hysteresis. Using pneumatic sensors, all four major components of robots—actuators, logic, power, and sensors—can be pneumatic, enabling all-fluidic soft robots with proprioception and exteroception.publishedVersionPeer reviewe

Breathable, Flexible, Transparent, Hydrophobic, and Biotic Sustainable Electrodes for Heating and Biopotential Signal Measurement Applications

Pressure to reduce the global amount of e-waste has increased in recent years. The optimal use of natural resources is a demanding area especially due to the overabundance of the use of resources and challenges with after-life disposal. Herein, an easy method is developed to fabricate an improved version of leaf skeleton-based biodegradable, transparent, flexible, and hydrophobic electrodes. A fractal-like rubber leaf skeleton is used as the substrate, physical vapor deposited Au interlayer to promote adhesion, and uniform deposition of overlayer silver nanowires. The fabricated surfaces present a high level of electrical stability, optical transparency, hydrophobicity, and robust mechanical properties. The prepared electrodes demonstrate a comparable level of optical transmittance to the virgin leaf skeleton. The mechanical sturdiness of the electrodes is verified by 1k bending cycles. To demonstrate the functionality of these hybrid biotic conductive network (HBCN) electrodes, their performance is evaluated as flexible transparent heating elements and as biosignal measurement electrodes. The heater can reach a temperature of 140 °C with only 2.5 V in ≈5 s and Ag nanowire loading of ≈160 μg cm−2. Likewise, electrocardiogram (ECG) and electromyogram (EMG) signals are successfully obtained from the electrodes without using any electrode gel or other electrolytes.publishedVersionPeer reviewe

Pisaran itsekohdistus: Tarkkuusmikrokokoonpano hyödyntäen robotiikkaa ja itsekokoonpanoa

Droplet self-alignment is a microassembly process where the surface tension of liquid aligns microparts to a substrate. Traditionally, solder has been used, but using unconventional liquids, such as water or adhesives in air, has several attractive properties. Water is compatible with most materials and processes, it is easy to achieve good droplet confinement and it evaporates quickly. Adhesives have the ability to make irreversible bonding. Nevertheless, achieving adhesive droplet self-alignment is difficult, because adhesives generally have a small surface tension. Both liquids can be adapted to low temperature processes. This thesis describes water droplet self-alignment in high detail, by measuring yield, accuracy, capabilities to build complex structures, and speed of the process. Experiments have been done using an environment-controlled microassembly station and recorded using high-speed microscopy. The results show that droplet self-alignment can achieve industrially relevant performance, and the results may be used as a basis of future process design rules. A new, microfabricated silicon capillary gripper has been developed, which picks microparts using the surface tension of water. Pick-and-place experiments showed that microparts are self-aligned to the tool by droplet self-alignment. The developed gripper enables handling microparts accurately and delicately. Finally, new patterned oleophilic / oleophobic surfaces have been developed that enable self-alignment using oil-like liquids, including low-temperature curable adhesives. Self-alignment using an industrial adhesive on the patterns was demonstrated. While this surface was used for droplet self-alignment, a micropatterned oleophilic / oleophobic surface may well have other applications outside droplet self-alignment.Pisaran itsekohdistus on mikrokokoonpanoprosessi, jossa nesteen pintajännitys kohdistaa mikrokokoisia kappaleita alustalle. Perinteisesti nesteenä on käytetty juotetta. Epätavanomaisten nesteiden, kuten veden tai liiman, käyttö ilmassa on useilla tavoilla houkuttelevaa. Vesi on yhteensopiva useimpien materiaalien ja prosessien kanssa. On helppo valmistaa pintoja, jotka rajaavat veden kostumista. Lisäksi vesi haihtuu nopeasti. Liimat taas pystyvät muodostamaan pysyvän liitoksen. Liimapisaraan perustuva itsekohdistus on kuitenkin hankalaa, koska liimoilla on pieni pintajännitys. Molempia nesteitä voidaan käyttää matalissa lämpötiloissa. Tässä väitöskirjatyössä tutkittiin vesipisaraan perustuvaa itsekohdistusta mittaamalla sen saantoa, tarkkuutta, kykyä rakentaa monimutkaisia rakenteita ja nopeutta. Kokeita on tehty mikrokokoonpanoasemalla, joka sijaitsee olosuhteiltaan säädellyssä kammiossa. Kokeet nauhoitettiin suurnopeusmikroskoopilla. Tulokset näyttävät, että pisaraan perustuvalla itsekohdistuksella voidaan saavuttaa teollisesti merkittävä tehokkuus, ja tuloksia voidaan hyödyntää tulevaisuuden prosessisuunnittelun pohjana. Lisäksi väitöskirjatyössä on kehitetty uudentyyppinen, piipohjainen kapillaaritarttuja, joka poimii mikrokappaleita veden pintajännitystä käyttäen. Poimintakokeissa osoitettiin, että kappaleet itsekohdistuvat työkaluun pisaran avulla. Tarttuja mahdollistaa mikrokappaleiden käsittelyn tarkasti ja niitä vahingoittamatta. Väitöskirjassa näytetään myös, että kuvioituja oleofobisia / oleofiilisiä pintoja voidaan käyttää liimapisaraan perustuvassa itsekohdistuksessa. Itsekohdistus näytettiin kokeellisesti käyttäen kaupallista liimaa ja kehitettyä pintaa. Vaikka kyseistä pintaa käytettiin itsekohdistukseen, kuvioidulla oleofobisella / oleofiilisellä pinnalla voi hyvin olla muitakin sovelluksia

Analytical Expressions for Spring Constants of Capillary Bridges and Snap-in Forces of Hydrophobic Surfaces

When a force probe with a small liquid drop adhered to its tip makes contact with a substrate of interest, the normal force right after contact is called the snap-in force. This snap-in force is related to the advancing contact angle or the contact radius at the substrate. Measuring snap-in forces has been proposed as an alternative to measure the advancing contact angles of surfaces. The snap-in occurs when the distance between the probe surface and the substrate is hS, which is amenable to geometry, assuming the drop was a spherical cap before snap-in. Equilibrium is reached at a distance hE < hS. At equilibrium, the normal force F = 0, and the capillary bridge is a spherical segment, amenable again to geometry. For a small normal displacement Δh = h - hE, the normal force can be approximated with F ≈ -k1Δh or F ≈ -k1Δh - k2Δh2, where k1 = -∂F/∂h and k2 = -1/2·∂2F/∂h2 are the effective linear and quadratic spring constants of the bridge, respectively. Analytical expressions for k1,2 are found using Kenmotsu's parameterization. Fixed contact angle and fixed contact radius conditions give different forms of k1,2. The expressions for k1 found here are simpler, yet equivalent to the earlier derivation by Kusumaatmaja and Lipowsky (2010). Approximate snap-in forces are obtained by setting Δh = hS - hE. These approximate analytical snap-in forces agree with the experimental data from Liimatainen et al. (2017) and a numerical method based on solving the shape of the interface. In particular, the approximations are most accurate for super liquid-repellent surfaces. For such surfaces, readers may find this new analytical method more convenient than solving the shape of the interface numerically.publishedVersionPeer reviewe

Ruuansulatusjärjestelmän etämittalaitteen anturimittausten analysointi

Tässä diplomityössä esitellään ruuansulatusjärjestelmän etämittalaitteen prototyyppi ja matemaattiset menetelmät prototyypin anturimittausten analysoimiseksi. Tutkimuksen tavoitteena on kehittää automaattisia menetelmiä ärtyneen suolen syndrooman diagnosoimiseksi. Tämä diplomityö on tehty osana TEKES-rahoitteista MIRRI-projektia. Tutkimustyö tehtiin Teknillisen korkeakoulun systeemitekniikan laboratoriossa. Projektin toisena tutkimusosapuolena on Helsingin yliopiston biomateriaalien ja kudosteknologian tutkimusryhmä. Työn selvitysosuudessa esitellään ruuansulatusjärjestelmä ja ärtyneen suolen syndrooma. Osuudessa luodaan myös katsaus huipputasoa edustaviin kaupallisiin ja prototyyppiasteella oleviin ruuansulatusjärjestelmän etämittalaitteisiin. Työn seuraavassa osuudessa esitellään kehitetyt menetelmät anturimittauksiin pohjautuvaan automaattiseen diagnoosiin. Analyysi alkaa suodatuksella, johon käytetään aaltosmuunnokseen perustuvaa stationääri-epästationäärisuodatinta. Suodatuksen jälkeen signaaleista lasketaan ominaispiirremuuttujia. Tärkeä muuttuja syndrooman havaitsemiseksi on suoliäänien keskimääräinen aikaväli. Lopullinen diagnoosi tehdään ominaispiirremuuttujista monikerroksisella myötäkytkentäneuroverkolla. Työn kokeellisessa osuudessa kehitettyjen menetelmien soveltuvuutta arvioidaan käytännössä. Kokeet osoittavat, että kehitetyt menetelmät ovat soveltuvia automaattiseen diagnoosiin