Monolithic digital patterning of polydimethylsiloxane with successive laser pyrolysis.

The patterning of polydimethylsiloxane (PDMS) into complex two-dimensional (2D) or 3D shapes is a crucial step for diverse applications based on soft lithography. Nevertheless, mould replication that incorporates time-consuming and costly photolithography processes still remains the dominant technology in the field. Here we developed monolithic quasi-3D digital patterning of PDMS using laser pyrolysis. In contrast with conventional burning or laser ablation of transparent PDMS, which yields poor surface properties, our successive laser pyrolysis technique converts PDMS into easily removable silicon carbide via consecutive photothermal pyrolysis guided by a continuous-wave laser. We obtained high-quality 2D or 3D PDMS structures with complex patterning starting from a PDMS monolith in a remarkably low prototyping time (less than one hour). Moreover, we developed distinct microfluidic devices with elaborated channel architectures and a customizable organ-on-a-chip device using this approach, which showcases the potential of the successive laser pyrolysis technique for the fabrication of devices for several technological applications.

Rapid prototyping and facile customization of conductive hydrogel bioelectronics based on all laser process.

Proper customization in size and shape is essential in implantable bioelectronics for stable bio-signal recording. Over the past decades, many researchers have heavily relied on conventional photolithography processes to fabricate implantable bioelectronics. Therefore, they could not avoid the critical limitation of high cost and complex processing steps to optimize bioelectronic devices for target organs with various sizes and shapes. Here, we propose rapid prototyping using all laser processes to fabricate customized bioelectronics. PEDOT:PSS is selectively irradiated by an ultraviolet (UV) pulse laser to form wet-stable conductive hydrogels that can softly interact with biological tissues (50 µm line width). The encapsulation layer is selectively patterned using the same laser source by UV-curing polymer networks (110 µm line width). For high stretchability (over 100%), mesh structures are made by the selective laser cutting process. Our rapid prototyping strategy minimizes the use of high-cost equipment, using only a single UV laser source to process the electrodes, encapsulation, and substrates that constitute bioelectronics without a photomask, enabling the prototyping stretchable microelectrode array with an area of 1 cm2 less than 10 min. We fabricated an optimized stretchable microelectrode array with low impedances (∼1.1 kΩ at 1 kHz) that can effectively record rat's cardiac signals with various health states.

Controlling C2C12 Cytotoxicity on Liquid Metal Embedded Elastomer (LMEE).

Liquid metal embedded elastomers (LMEEs) are highly stretchable composites comprising microscopic droplets of eutectic gallium-indium (EGaIn) liquid metal embedded in a soft rubber matrix. They have a unique combination of mechanical, electrical, and thermal properties that make them attractive for potential applications in flexible electronics, thermal management, wearable computing, and soft robotics. However, the use of LMEEs in direct contact with human tissue or organs requires an understanding of their biocompatibility and cell cytotoxicity. In this study, the cytotoxicity of C2C12 cells in contact with LMEE composites composed of EGaIn droplets embedded with a polydimethylsiloxane (PDMS) matrix is investigated. In particular, the influence of EGaIn volume ratio and shear mixing time during synthesis on cell proliferation and viability is examined. The special case of electrically-conductive LMEE composites in which a percolating network of EGaIn droplets is created through "mechanical sintering" is also examined. This study in C2C12 cytotoxicity represents a first step in determining whether LMEE is safe for use in implantable biomedical devices and biohybrid systems.

Delivery of self-replicating messenger RNA into the brain for the treatment of ischemic stroke.

Ischemic stroke is caused by the occlusion of cerebral arteries. In the ischemic stroke, ischemia-reperfusion injury increases the damage in the brain after reperfusion. In the previous study, heme oxygenase-1 (HO1) mRNA was delivered into the ischemic brain, showing that HO1-mRNA had higher therapeutic effect and less side-effect than HO1-plasmid (pHO1). However, mRNA is degraded faster than plasmid DNA reducing the duration of gene expression. In this study, self-replicating mRNA (Rep-mRNA) was developed using a replicon system from Venezuelan Equine Encephalitis virus to compensate this disadvantage of mRNA delivery. Deoxycholic acid-conjugated polyethylenimine (DA-PEI) was used as a carrier of the mRNAs. The Rep-mRNA/DA-PEI complex had a size of around 90 nm and a zeta-potential of 33 mV. In the in vitro transfection assays, gene expression by the HO1-Rep-mRNA/DA-PEI complex persisted at least 14 days, while that by the HO1-mRNA/DA-PEI complex approached basal level at 3 days after transfection. Therapeutic effects of the HO1-Rep-mRNA/DA-PEI complexes were evaluated in the ischemic stroke animal model. The complexes were injected into the brain stereotaxically. HO1 expression by the HO1-Rep-mRNA/DA-PEI complex persisted at least 7 days after injection, but the pHO1/DA-PEI or HO1-mRNA/DA-PEI complex showed basal level of HO1-expression at 7 days after injection. Due to higher and longer expression of HO1, the apoptosis level and infarct size were decreased by the HO1-Rep-mRNA/DA-PEI complexes, compared with the pHO1/DA-PEI and HO1-mRNA/DA-PEI complex. These results suggest that HO1-Rep-mRNA/DA-PEI complex may have a potential as a long-lasting therapeutic system for the treatment of ischemic stroke.

Rapid Synthesis of Multifunctional Apatite via the Laser-Induced Hydrothermal Process.

Synthetic biomaterials are used to overcome the limited quantity of human-derived biomaterials and to impart additional biofunctionality. Although numerous synthetic processes have been developed using various phases and methods, currently commonly used processes have some issues, such as a long process time and difficulties with extensive size control and high-concentration metal ion substitution to achieve additional functionality. Herein, we introduce a rapid synthesis method using a laser-induced hydrothermal process. Based on the thermal interaction between the laser pulses and titanium, which was used as a thermal reservoir, hydroxyapatite particles ranging from nanometer to micrometer scale could be synthesized in seconds. Further, this method enabled selective metal ion substitution into the apatite matrix with a controllable concentration. We calculated the maximum temperature achieved by laser irradiation at the surface of the thermal reservoir based on the validation of three simplification assumptions. Subsequent linear regression analysis showed that laser-induced hydrothermal synthesis follows an Arrhenius chemical reaction. Hydroxyapatite and Mg2+-, Sr2+-, and Zn2+-substituted apatite powders promoted bone cell attachment and proliferation ability due to ion release from the hydroxyapatite and the selective ion-substituted apatite powders, which had a low crystallinity and relatively high solubility. Laser-induced hydrothermal synthesis is expected to become a powerful ceramic material synthesis technology.

Messenger RNA/polymeric carrier nanoparticles for delivery of heme oxygenase-1 gene in the post-ischemic brain.

Ischemic stroke is a cerebrovascular disease caused by narrowed cerebral arteries. Thrombolytic agents such as tissue-plasminogen activators have been used for recanalization of the blood supply into the ischemic region. However, ischemia-reperfusion damage continues to increase the infarction volume. In this study, heme oxygenase-1 (HO1)-mRNA was delivered into the brain, using a non-viral carrier. Various non-viral carriers such as polyethylenimine (25 kDa, PEI25k), lipofectamine, dexamethasone-conjugated PEI2k (Dexa-PEI2k), deoxycholic acid-conjugated PEI2k (DA-PEI2k), and R3V6 peptides were evaluated as carriers of mRNA into the brain. Gene delivery assays showed that DA-PEI2k and lipofectamine had a higher mRNA delivery efficiency than the other carriers in Neuro2A cells in vitro and a rat brain in vivo. Cytotoxicity assays showed that lipofectamine had higher toxicity than DA-PEI2k. Therefore, DA-PEI2k was used for delivery of HO1-mRNA. Unlike plasmid DNA (pDNA), mRNA is expressed in the cytosol without nuclear translocation. This suggests that mRNA may have higher gene expression than pDNA, since the nuclear location of pDNA is an inefficient step. Indeed, in in vitro transfection assays, HO1-mRNA/DA-PEI2k had higher gene expression than HO1-pDNA/DA-PEI2k without induction of a pro-inflammatory cytokine. The therapeutic effects of HO1-mRNA delivery using DA-PEI2k were evaluated in the middle cerebral artery occlusion animal model after local injection. HO1-mRNA delivery had higher gene expression than HO1-pDNA delivery 24 h after the local injection. In addition, HO1-mRNA delivery reduced the infarct size more efficiently than HO1-pDNA delivery. The results suggest that the delivery of mRNA using DA-PEI2k may be useful for gene therapy of ischemic stroke.

Next generation non-vacuum, maskless, low temperature nanoparticle ink laser digital direct metal patterning for a large area flexible electronics.

Flexible electronics opened a new class of future electronics. The foldable, light and durable nature of flexible electronics allows vast flexibility in applications such as display, energy devices and mobile electronics. Even though conventional electronics fabrication methods are well developed for rigid substrates, direct application or slight modification of conventional processes for flexible electronics fabrication cannot work. The future flexible electronics fabrication requires totally new low-temperature process development optimized for flexible substrate and it should be based on new material too. Here we present a simple approach to developing a flexible electronics fabrication without using conventional vacuum deposition and photolithography. We found that direct metal patterning based on laser-induced local melting of metal nanoparticle ink is a promising low-temperature alternative to vacuum deposition- and photolithography-based conventional metal patterning processes. The "digital" nature of the proposed direct metal patterning process removes the need for expensive photomask and allows easy design modification and short turnaround time. This new process can be extremely useful for current small-volume, large-variety manufacturing paradigms. Besides, simple, scalable, fast and low-temperature processes can lead to cost-effective fabrication methods on a large-area polymer substrate. The developed process was successfully applied to demonstrate high-quality Ag patterning (2.1 µΩ·cm) and high-performance flexible organic field effect transistor arrays.