Optical Monitoring of Water Side Permeation in Thin Film Encapsulation.

The stability of long-term microfabricated implants is hindered by the presence of multiple water diffusion paths within artificially patterned thin-film encapsulations. Side permeation, defined as infiltration of molecules through the lateral surface of the thin structure, becomes increasingly critical with the trend of developing high-density and miniaturized neural electrodes. However, current permeability measurement methods do not account for side permeation accurately nor quantitatively. Here, a novel optical, magnesium (Mg)-based method is proposed to quantify the side water transmission rate (SWTR) through thin film encapsulation and validate the approach using micrometric polyimide (PI) and polyimide-silicon carbide (PI-SiC) multilayers. Through computed digital grayscale images collected with corroding Mg film microcells coated with the thin encapsulation, side and surface WTRs are quantified. A 4.5-fold ratio between side and surface permeation is observed, highlighting the crucial role of the PI-PI interface in lateral diffusion. Universal guidelines for the design of flexible, hermetic neural interfaces are proposed. Increasing encapsulation's width (interelectrode spacing), creating stronger interfacial interactions, and integrating high-barrier interlayers such as SiC significantly enhance the lateral hermeticity.

Eco-Friendly Production of Polyvinyl Alcohol/Carboxymethyl Cellulose Wound Healing Dressing Containing Sericin.

Wound dressing production represents an important segment in the biomedical healthcare field, but finding a simple and eco-friendly method that combines a natural compound and a biocompatible dressing production for biomedical application is still a challenge. Therefore, the aim of this study is to develop wound healing dressings that are environmentally friendly, low cost, and easily produced, using natural agents and a physical crosslinking technique. Hydrogel wound healing dressings were prepared from polyvinyl alcohol/carboxymethyl cellulose and sericin using the freeze-thawing method as a crosslinking method. The morphological characterization was carried out by scanning electron microscopy (SEM), whereas the mechanical analysis was carried out by dynamic mechanical analysis (DMA) to test the tensile strength and compression properties. Then, the healing property of the wound dressing material was tested by in vitro and ex vivo tests. The results show a three-dimensional microporous structure with no cytotoxicity, excellent stretchability with compressive properties similar to those of human skin, and excellent healing properties. The proposed hydrogel dressing was tested in vitro with HaCaT keratinocytes and ex vivo with epidermal tissues, demonstrating an effective advantage on wound healing acceleration. Accordingly, this study was successful in developing wound healing dressings using natural agents and a simple and green crosslinking method.

Soft and Flexible Bioelectronic Micro-Systems for Electronically Controlled Drug Delivery.

The concept of targeted and controlled drug delivery, which directs treatment to precise anatomical sites, offers benefits such as fewer side effects, reduced toxicity, optimized dosages, and quicker responses. However, challenges remain to engineer dependable systems and materials that can modulate host tissue interactions and overcome biological barriers. To stay aligned with advancements in healthcare and precision medicine, novel approaches and materials are imperative to improve effectiveness, biocompatibility, and tissue compliance. Electronically controlled drug delivery (ECDD) has recently emerged as a promising approach to calibrated drug delivery with spatial and temporal precision. This article covers recent breakthroughs in soft, flexible, and adaptable bioelectronic micro-systems designed for ECDD. It overviews the most widely reported operational modes, materials engineering strategies, electronic interfaces, and characterization techniques associated with ECDD systems. Further, it delves into the pivotal applications of ECDD in wearable, ingestible, and implantable medical devices. Finally, the discourse extends to future prospects and challenges for ECDD.

Recent Advances in Encapsulation of Flexible Bioelectronic Implants: Materials, Technologies, and Characterization Methods.

Bioelectronic implantable systems (BIS) targeting biomedical and clinical research should combine long-term performance and biointegration in vivo. Here, recent advances in novel encapsulations to protect flexible versions of such systems from the surrounding biological environment are reviewed, focusing on material strategies and synthesis techniques. Considerable effort is put on thin-film encapsulation (TFE), and specifically organic-inorganic multilayer architectures as a flexible and conformal alternative to conventional rigid cans. TFE is in direct contact with the biological medium and thus must exhibit not only biocompatibility, inertness, and hermeticity but also mechanical robustness, conformability, and compatibility with the manufacturing of microfabricated devices. Quantitative characterization methods of the barrier and mechanical performance of the TFE are reviewed with a particular emphasis on water-vapor transmission rate through electrical, optical, or electrochemical principles. The integrability and functionalization of TFE into functional bioelectronic interfaces are also discussed. TFE represents a must-have component for the next-generation bioelectronic implants with diagnostic or therapeutic functions in human healthcare and precision medicine.

Metal-Free Multilayer Hybrid PENG Based on Soft Electrospun/-Sprayed Membranes with Cardanol Additive for Harvesting Energy from Surgical Face Masks.

Disposable surgical face masks are usually used by medical/nurse staff but the current Covid-19 pandemic has caused their massive use by many people. Being worn closely attached to the people's face, they are continuously subjected to routine movements, i.e., facial expressions, breathing, and talking. These motional forces represent an unusual source of wasted mechanical energy that can be rather harvested by electromechanical transducers and exploited to power mask-integrated sensors. Typically, piezoelectric and triboelectric nanogenerators are exploited to this aim; however, most of the current devices are too thick or wide, not really conformable, and affected by humidity, which make them hardly embeddable in a mask, in contact with skin. Different from recent attempts to fabricate smart energy-harvesting cloth masks, in this work, a wearable energy harvester is rather enclosed in the mask and can be reused and not disposed. The device is a metal-free hybrid piezoelectric nanogenerator (hPENG) based on soft biocompatible materials. In particular, poly(vinylidene fluoride) (PVDF) membranes in the pure form and with a biobased plasticizer (cardanol oil, CA) are electrospun onto a laser-ablated polyimide flexible substrate attached on a skin-conformable elastomeric blend of poly(dimethylsiloxane) (PDMS) and Ecoflex. The multilayer structure of the device harnesses the piezoelectricity of the PVDF nanofibers and the friction triboelectric effects. The ultrasensitive mechanoelectrical transduction properties of the composite device are determined by the strong electrostatic behavior of the membranes and the plasticization effect of cardanol. In addition, encapsulation based on PVDF, PDMS, CA, and parylene C is used, allowing the hPENG to exhibit optimal reliability and resistance against the wet and warm atmosphere around the face mask. The proposed device reveals potential applications for the future development of smart masks with coupled energy-harvesting devices, allowing to use them not only for anti-infective protection but also to supply sensors or active antibacterial/viral devices.

Flexible SAW Microfluidic Devices as Wearable pH Sensors Based on ZnO Nanoparticles.

In this work, a new flexible and biocompatible microfluidic pH sensor based on surface acoustic waves (SAWs) is presented. The device consists of polyethylene naphthalate (PEN) as a flexible substrate on which aluminum nitride (AlN) has been deposited as a piezoelectric material. The fabrication of suitable interdigitated transducers (IDTs) generates Lamb waves (L-SAW) with a center frequency ≈500 MHz traveling in the active region. A SU-8 microfluidics employing ZnO nanoparticles (NPs) functionalization as a pH-sensitive layer is fabricated between the IDTs, causing a shift in the L-SAW resonance frequency as a function of the change in pH values. The obtained sensitivity of ≈30 kHz/pH from pH 7 to pH 2 demonstrates the high potential of flexible SAW devices to be used in the measurement of pH in fluids and biosensing.

Reliability of Protective Coatings for Flexible Piezoelectric Transducers in Aqueous Environments.

Electronic devices used for marine applications suffer from several issues that can compromise their performance. In particular, water absorption and permeation can lead to the corrosion of metal parts or short-circuits. The added mass due to the absorbed water affects the inertia and durability of the devices, especially for flexible and very thin micro-systems. Furthermore, the employment of such delicate devices underwater is unavoidably subjected to the adhesion of microorganisms and formation of biofilms that limit their reliability. Thus, the demand of waterproofing solutions has increased in recent years, focusing on more conformal, flexible and insulating coatings. This work introduces an evaluation of different polymeric coatings (parylene-C, poly-dimethyl siloxane (PDMS), poly-methyl methacrylate (PMMA), and poly-(vinylidene fluoride) (PVDF)) aimed at increasing the reliability of piezoelectric flexible microdevices used for sensing water motions or for scavenging wave energy. Absorption and corrosion tests showed that Parylene-C, while susceptible to micro-cracking during prolonged oscillating cycles, exhibits the best anti-corrosive behavior. Parylene-C was then treated with oxygen plasma and UV/ozone for modifying the surface morphology in order to evaluate the biofilm formation with different surface conditions. A preliminary characterization through a laser Doppler vibrometer allowed us to detect a reduction in the biofilm mass surface density after 35 days of exposure to seawater.