Microdroplet-based On-Demand Drawing of High Aspect-Ratio Elastomeric Micropillar and Its Contact Sensing Application

Biomimetic Soft Polymer Microstructures and Piezoresistive Graphene MEMS Sensors Using Sacrificial Metal 3D Printing

Recent advances in 3D printing technology have enabled unprecedented design freedom across an ever-expanding portfolio of materials. However, direct 3D printing of soft polymeric materials such as polydimethylsiloxane (PDMS) is challenging, especially for structural complexities such as high-aspect ratio (>20) structures, 3D microfluidic channels (∼150 μm diameter), and biomimetic microstructures. This work presents a novel processing method entailing 3D printing of a thin-walled sacrificial metallic mold, soft polymer casting, and acidic etching of the mold. The proposed workflow enables the facile fabrication of various complex, bioinspired PDMS structures (e.g., 3D double helical microfluidic channels embedded inside high-aspect ratio pillars) that are difficult or impossible to fabricate using currently available techniques. The microfluidic channels are further infused with conductive graphene nanoplatelet ink to realize two flexible piezoresistive microelectromechanical (MEMS) sensors (a bioinspired flow/tactile sensor and a dome-like force sensor) with embedded sensing elements. The MEMS force sensor is integrated into a Philips 9000 series electric shaver to demonstrate its application in "smart" consumer products in the future. Aided by current trends in industrialization and miniaturization in metal 3D printing, the proposed workflow shows promise as a low-temperature, scalable, and cleanroom-free technique of fabricating complex, soft polymeric, biomimetic structures, and embedded MEMS sensors.

Technological Challenges in the Development of Optogenetic Closed-Loop Therapy Approaches in Epilepsy and Related Network Disorders of the Brain

Epilepsy is a chronic, neurological disorder affecting millions of people every year. The current available pharmacological and surgical treatments are lacking in overall efficacy and cause side-effects like cognitive impairment, depression, tremor, abnormal liver and kidney function. In recent years, the application of optogenetic implants have shown promise to target aberrant neuronal circuits in epilepsy with the advantage of both high spatial and temporal resolution and high cell-specificity, a feature that could tackle both the efficacy and side-effect problems in epilepsy treatment. Optrodes consist of electrodes to record local field potentials and an optical component to modulate neurons via activation of opsin expressed by these neurons. The goal of optogenetics in epilepsy is to interrupt seizure activity in its earliest state, providing a so-called closed-loop therapeutic intervention. The chronic implantation in vivo poses specific demands for the engineering of therapeutic optrodes. Enzymatic degradation and glial encapsulation of implants may compromise long-term recording and sufficient illumination of the opsin-expressing neural tissue. Engineering efforts for optimal optrode design have to be directed towards limitation of the foreign body reaction by reducing the implant's elastic modulus and overall size, while still providing stable long-term recording and large-area illumination, and guaranteeing successful intracerebral implantation. This paper presents an overview of the challenges and recent advances in the field of electrode design, neural-tissue illumination, and neural-probe implantation, with the goal of identifying a suitable candidate to be incorporated in a therapeutic approach for long-term treatment of epilepsy patients.

Rapid Design and Analysis of Microtube Pneumatic Actuators Using Line-Segment and Multi-Segment Euler-Bernoulli Beam Models

Soft material-based pneumatic microtube actuators are attracting intense interest, since their bending motion is potentially useful for the safe manipulation of delicate biological objects. To increase their utility in biomedicine, researchers have begun to apply shape-engineering to the microtubes to diversify their bending patterns. However, design and analysis of such microtube actuators are challenging in general, due to their continuum natures and small dimensions. In this paper, we establish two methods for rapid design, analysis, and optimization of such complex, shape-engineered microtube actuators that are based on the line-segment model and the multi-segment Euler–Bernoulli’s beam model, respectively, and are less computation-intensive than the more conventional method based on finite element analysis. To validate the models, we first realized multi-segment microtube actuators physically, then compared their experimentally observed motions against those obtained from the models. We obtained good agreements between the three sets of results with their maximum bending-angle errors falling within ±11%. In terms of computational efficiency, our models decreased the simulation time significantly, down to a few seconds, in contrast with the finite element analysis that sometimes can take hours. The models reported in this paper exhibit great potential for rapid and facile design and optimization of shape-engineered soft actuators.