Bioinspired Oil-Infused Slippery Surfaces with Water and Ion Barrier Properties

Liquid-based encapsulation for implantable bioelectronics across broad pH environments

Wearable and implantable bioelectronics that can interface for extended periods with highly mobile organs and tissues across a broad pH range would be useful for various applications in basic biomedical research and clinical medicine. The encapsulation of these systems, however, presents a major challenge, as such devices require superior barrier performance against water and ion penetration in challenging pH environments while also maintaining flexibility and stretchability to match the physical properties of the surrounding tissue. Current encapsulation materials are often limited to near-neutral pH conditions, restricting their application range. In this work, we report a liquid-based encapsulation approach for bioelectronics under extreme pH environments. This approach achieves high optical transparency, stretchability, and mechanical durability. When applied to implantable wireless optoelectronic devices, our encapsulation method demonstrates outstanding water resistance in vitro, ranging from extremely acidic environments (pH = 1.5 and 4.5) to alkaline conditions (pH = 9). We also demonstrate the in vivo biocompatibility of our encapsulation approach and show that encapsulated wireless optoelectronics maintain robust operation throughout 3 months of implantation in freely moving mice. These results indicate that our encapsulation strategy has the potential to protect implantable bioelectronic devices in a wide range of research and clinical applications.

Covalently Attached Slippery Surface Coatings to Reduce Protein Adsorptions on Poly(dimethylsiloxane) Planar Surfaces and 3D Microfluidic Channels

Silicone elastomers, such as poly(dimethylsiloxane) (PDMS), have a broad range of applications in basic biomedical research and clinical medicine, ranging from the preparation of microfluidic devices for organs-on-chips and ventriculoperitoneal shunts for the treatment of hydrocephalus to implantable neural probes for neuropharmacology. Despite the importance, the protein adsorptions on silicone elastomers in these application environments represent a significant challenge. Surface coatings with slippery lubricants, inspired by the Nepenthes pitcher plants, have recently received much attention for reducing protein adsorptions. Nevertheless, the depletion of the physically infused lubricants limits their broad applications. In this study, we report a covalently attached slippery surface coating to reduce protein adsorptions on PDMS surfaces. As demonstrations, we show that the adsorption of serum proteins, human fibrinogen and albumin, can be significantly reduced by the slippery surface coating in both planar PDMS surfaces and 3D microfluidic channels. The preparation of slippery surface coatings relies on the acid-catalyzed polycondensation reaction of dimethyldimethoxysilane, which utilizes a low-cost and scalable dip-coating method. Furthermore, cell metabolic activity and viability studies demonstrate the biocompatibility of the surface coating. These results suggest the potential applications of slippery surface coatings to reduce protein adsorptions for implantable medical devices, organs-on-chips, and many others.

Engineered small extracellular vesicles as a versatile platform to efficiently load ferulic acid via an “esterase-responsive active loading” strategy

As nano-drug carriers, small extracellular vesicles (sEVs) have shown unique advantages, but their drug loading and encapsulation efficiency are far from being satisfied, especially for the loading of hydrophilic small-molecule drugs. Inspired by the strategies of active loading of liposomal nanomedicines, pre-drug design and immobilization enzyme, here we developed a new platform, named “Esterase-responsive Active Loading” (EAL), for the efficient and stable drug encapsulation of sEVs. Widely used ferulic acid ester derivatives were chosen as prodrugs based on the EAL of engineered sEVs to establish a continuous transmembrane ion gradient for achieving efficient loading of active molecule ferulic acid into sEVs. The EAL showed that the drug loading and encapsulation efficiency were around 6-fold and 5-fold higher than passive loading, respectively. Moreover, characterization by nano-flow cytometry and Malvern particle size analyzer showed that differential ultracentrifugation combined with multiple types of membrane filtration methods can achieve large-scale and high-quality production of sEVs. Finally, extracellular and intracellular assessments further confirmed the superior performance of the EAL-prepared sEVs-loaded ferulic acid preparation in terms of slow release and low toxicity. Taken together, these findings will provide an instructive insight into the development of sEV-based delivery systems.

Nature-Inspired High Temperature Scale-Resistant Slippery Lubricant-Induced Porous Surfaces (HTS-SLIPS)

Scale formation is a longstanding and unresolved problem in a number of fields, including power production, petroleum exploration, thermal desalination, and construction. Herein, a high-temperature scale-resistant slippery lubricant-induced surface (HTS-SLIPS) is developed by one-step electrodeposition and lubricant infusion. The fractal cauliflower-like morphology with lubricant oil is conducive to forming an ultralow contact angle hysteresis of ≈1°. The 10-d real-world boiling trial indicates that by replacing the uncoated surface with HTS-SLIPS, the reduction in scale mass is greater than 200% because of the low surface free energy (4.3 mJ m^-2 ) and outstanding smoothness (R_a  = 41 ± 8 nm) of HTS-SLIPS. Thanks to the scale retardation, the bubble departure frequency of HTS-SLIPS is eightfold higher than that of uncoated surfaces, signifying superior heat transfer efficiency. In these demonstrations, HTS-SLIPS coated spiral tube exhibits better flowability and lower pressure drop than the uncoated one. In addition, favorable compatibility between HTS-SLIPS and mechanical vibration is experimentally verified to strengthen the descaling of SLIPS synergistically. It is anticipated that the simple and scalable coating fabrication approach will be applicable in numerous industrial high-temperature processes where scale formation is encountered.

Mucosa-interfacing electronics

The surface mucosa that lines many of our organs houses myriad biometric signals and, therefore, has great potential as a sensor-tissue interface for high-fidelity and long-term biosensing. However, progress is still nascent for mucosa-interfacing electronics owing to challenges with establishing robust sensor-tissue interfaces; device localization, retention and removal; and power and data transfer. This is in sharp contrast to the rapidly advancing field of skin-interfacing electronics, which are replacing traditional hospital visits with minimally invasive, real-time, continuous and untethered biosensing. This Review aims to bridge the gap between skin-interfacing electronics and mucosa-interfacing electronics systems through a comparison of the properties and functions of the skin and internal mucosal surfaces. The major physiological signals accessible through mucosa-lined organs are surveyed and design considerations for the next generation of mucosa-interfacing electronics are outlined based on state-of-the-art developments in bio-integrated electronics. With this Review, we aim to inspire hardware solutions that can serve as a foundation for developing personalized biosensing from the mucosa, a relatively uncharted field with great scientific and clinical potential.

Soft, Pressure-Tolerant, Flexible Electronic Sensors for Sensing under Harsh Environments

Energy-efficient, miniaturized electronic ocean sensors for monitoring and recording various environmental parameters remain a challenge because conventional ocean sensors require high-pressure chambers and seals to survive the large hydrostatic pressure and harsh ocean environment, which usually entail a high-power supply and large size of the sensor system. Herein, we introduce soft, pressure-tolerant, flexible electronic sensors that can operate under large hydrostatic pressure and salinity environments, thereby eliminating the need for pressure chambers and reducing the power consumption and sensor size. Using resistive temperature and conductivity (salinity) sensors as an example for demonstration, the soft sensors are made of lithographically patterned metal thin films (100 nm) encapsulated with soft oil-infused elastomers and tested in a customized pressure vessel with well-controlled pressure and temperature conditions. The resistance of the temperature and pressure sensors increases linearly with a temperature range of 5-38 °C and salinity levels of 30-40 Practical Salinity Unit (PSU), respectively, relevant for this application. Pressure (up to 15 MPa) has shown a negligible effect on the performance of the temperature and salinity sensors, demonstrating their large pressure-tolerance capability. In addition, both temperature and salinity sensors have exhibited excellent cyclic loading behaviors with negligible hysteresis. Encapsulated with our developed soft oil-infused elastomer (PDMS, poly(dimethylsiloxane)), the sensor has shown excellent performance under a 35 PSU salinity water environment for more than 7 months. The soft, pressure-tolerant and noninvasive electronic sensors reported here are suitable for integration with many platforms including animal tags, profiling floats, diving equipment, and physiological monitoring.