Mechanical moduli of common organic electronic materials are measured by the buckling method. The organic layers were prepared on the elastomer polydimethylsiloxane (PDMS) substrate by transfer, direct spin-coating, or thermal evaporation. When a small (∼2%) compressive strain is applied to organic/PDMS film samples, the layer becomes buckled with a characteristic wavelength. Fitting the experimentally measured data of buckling wavelength as a function of layer thickness with a model equation yields the mechanical modulus of the organic layer. The measured values compare well with those from theoretical predictions for materials such as poly(3-hexylthiophene) (P3HT) and its blend with [6,6]-phenyl C61-butyric acid methyl ether (PCBM). The modulus of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is similar to that of pure PSS, which is contrary to the common expectation that the ionic interaction between PEDOT and PSS chains may lead to a modulus value 2−3 times larger than that of the constituent polymers. The similarity is likely due to a very small amount of PEDOT added and the oligomeric nature of PEDOT. Thermally evaporated pentacene film has a modulus value of ∼15 GPa, which is an order of magnitude larger than those of other polymeric materials investigated here, and reveals delamination bukling behavior when the magnitude of compression is relatively large. The residual solvent in polyaniline (PANI) plays the role of plasticizer and leads to a very small modulus. The measured mechanical moduli of common organic electronic materials would be valuable for designing and implementing flexible and/or stretchable organic electronics.

A novel three dimensional blood brain barrier (BBB) platform was developed by independently supplying different types of media to separate cell types within a single device. One channel (vascular channel, VC) is connected to the inner lumen of the vascular network while the other supplies media to the neural cells (neural channel, NC). Compared to co-cultures supplied with only one type of medium (or 1:1 mixture), best barrier properties and viability were obtained with culturing HUVECs with endothelial growth medium (EGM) and neural cells with neurobasal medium supplemented with fetal bovine serum (NBMFBS) independently. The measured vascular network permeability were comparable to reported in vivo values (20 kDa FITC-dextran, 0.45 ± 0.11 × 10−6 cm/s; 70 kDa FITC-dextran, 0.36 ± 0.05 × 10−6 cm/s) and a higher degree of neurovascular interfacing (astrocytic contact with the vascular network, GFAP-CD31 stain overlap) and presence of synapses (stained with synaptophysin). The BBB platform can dependably imitate the perivascular network morphology and synaptic structures characteristic of the NVU. This microfluidic BBB model can find applications in screening pharmaceuticals that target the brain for in neurodegenerative diseases.

Recently, a mechanical crack-based strain sensor with high sensitivity was proposed by producing free cracks via bending metal coated film with a known curvature. To further enhance sensitivity and controllability, a guided crack formation is needed. Herein, we demonstrate such a ultra-sensitive sensor based on the guided formation of straight mechanical cracks. The sensor has patterned holes on the surface of the device, which concentrate the stress near patterned holes leading to generate uniform cracks connecting the holes throughout the surface. We found that such a guided straight crack formation resulted in an exponential dependence of the resistance against the strain, overriding known linear or power law dependences. Consequently, the sensors are highly sensitive to pressure (with a sensitivity of over 1 × 105 at pressures of 8–9.5 kPa range) as well as strain (with a gauge factor of over 2 × 106 at strains of 0–10% range). A new theoretical model for the guided crack system has been suggested to be in a good agreement with experiments. Durability and reproducibility have been also confirmed.

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We introduce a novel microfluidic device to co-culture a blood vessel network and cell tissues in an in vivo-like niche. Our "open-top" microfluidic device is composed of microchannels with micropores in the ceiling, which provides direct fluid access from reservoir to microchannel. Fluid connections through micropores afford novel advantages, including: i) the long-term culture of large-scale microvessel network, ii) access of different fluids to inner and exterior sides of the microvessel, and iii) co-culturing of the microvessel network and small cell tissue. In this study, we have successfully assembled microvessels with 5 mm channel widths. We were also able to mimic capillary bed conditions by co-culturing microvessels with cancer spheroids. Intimate contact between the cancer spheroid and microvessel caused vessel recruitment and an increase in vessel formation, and affected vessel morphology. We expect this device to be used as a novel platform for vascularized tissue models.