The importance of water content on the conductivity of biomaterials and bioelectronic devices

Fabrication and preliminary characterization of conductive nanofillers-enhanced polymeric hydrogels for cardiac patch applications

The development of conducting polymeric nanocomposites patches for cardiac tissue engineering has opened new possibilities for restoring the health of infarcted heart tissues. Herein, we report the fabrication of biocompatible and relatively cost-effective poly(vinyl alcohol)/alginate-based hydrogels patches modified with different conducting nanofillers such as silver nanoparticles, polyaniline nanofibers, copper oxide nanoleaves, and graphene oxide nanosheets. The impact of the different nanofiller materials on the molecular structure, charge transport mechanism and mechanical characteristics of the designed nanocomposites patches was investigated. In addition, some significant parameters of the nanocomposites were characterized such as swelling ability, antioxidant activity as well as hemocompatibility. Infrared spectroscopy results demonstrated the occurrence of different interactions between the included nanofillers and the polymer matrix depending on the type of the nanofiller. Moreover, conductivity measurements revealed that only the polyaniline nanofibers-modified nanocomposites hydrogels showed the highest conductivity compared to other counterparts. Mechanical characterization, antioxidant activity, swelling and hemocompatibility proved the suitability of the developed polyaniline nanofibers-modified nanocomposites hydrogels as potential candidates for successful application in cardiac tissue engineering.

Natural biomaterials for sustainable flexible neuromorphic devices

Neuromorphic electronics use neural models in hardware to emulate brain-like behavior, and provide power-efficient, extremely compact, and massively-parallel processing, so they are ideal candidates for next-generation information-processing units. However, traditional rigid neuromorphic devices are limited by their unavoidable mechanical and geometrical mismatch with human tissues or organs. At the same time, the rapid development of these electronic devices has generated a large amount of electronic waste, thereby causing severe ecological problems. Natural biomaterials have mechanical properties compatible with biological tissues, and are environmentally benign, ultra-thin, and lightweight, so use of these materials can address these limitations and be used to create next-generation sustainable flexible neuromorphic electronics. Here, we explore the advantages of natural biomaterials in simulating synaptic behavior of sustainable neuromorphic devices. We present the flexibility, biocompatibility, and biodegradability of these neuromorphic devices, and consider the potential applicability of these properties in wearable and implantable bioelectronics. Finally, we consider the challenges of device fabrication and neuromorphic system integration by natural biomaterials, then suggest future research directions.

Proton conductivity of the protein-based velvet worm slime

The properties of complex bodily fluids are linked to their biological functions through natural selection. Velvet worms capture their prey by ensnaring them with a proteinaceous fluid (slime). We examined the electrical conductivity of slime and found that dry slime is an insulator. However, its conductivity can increase by up to 106 times in its hydrated state, which can be further increased by an order in magnitude under acidic hydration (pH ≈ 2.3). The transient current measured using ion-blocking electrodes showed a continuous decay for up to 7 h, revealing slime's nature as a proton conducting material. Slime undergoes a spontaneous fibrilization process producing high aspect ratio ≈ 105 fibers that exhibit an average conductivity ≈2.4 ± 1.1 mS cm-1. These findings enhance our understanding of slime as a natural biopolymer and provide molecular-level guidelines to rationally design biomaterials that may be employed as hygroscopic conductors.

Hydration effects on thermal transitions and molecular mobility in Xanthan gum polysaccharides

In this work, the xanthan gum (XG) polysaccharide is studied over a wide range of temperatures and water fractions 0 ≤ hw ≤ 0.70 (on a wet basis) by employing differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS). The investigation reveals that the critical water fraction for ice formation is about 0.35. Glass transition temperature (Tg) was determined through calorimetry experiments for all the samples studied. Water acts as a strong plasticizer, i.e., decreasing Tg, for water fractions up to about 0.35. A secondary (local) relaxation process is recorded in both dry and hydrated samples, which is sensitive to the presence of water molecules. This fact indicates that this process originates due to the orientation of small polar groups of the side chain, or/and due to the local main chain dynamics. Two types of long-range charge transport processes were resolved. The first is related to the conductive paths being formed via bulk-like ice structures (at high hydration levels), whereas the second can be attributed to proton mobility via the hydrogen bond (HB) network of non-freezing water existing in XG. Interestingly, this process is exactly the same in all the hydrated samples with hw > 0.25. With respect to the sample with hw = 0.27, a Vogel-Tammann-Fulcher (VTF)-like polarization process has also been recorded which seems to be related to long-range charge mobility via interconnected water clusters. As far as we are aware, this is the first time that XG is studied in terms of glass transition and molecular mobility over a wide range of hydration levels combining DSC and BDS techniques.