Next generation on‐skin electrodes will require soft, flexible, and gentle materials to provide both high‐fidelity sensing and wearer comfort. However, many commercially available on‐skin electrodes lack these key properties due to their use of rigid hardware, harsh adhesives, uncomfortable support structures, and poor breathability. To address these challenges, this work presents a new device paradigm by joining biocompatible electrospun spider silk with printable liquid metal to yield an incredibly soft and scalable on‐skin electrode that is strain‐tolerant, conformable, and gentle on‐skin. These electrodes, termed silky liquid metal (SLiM) electrodes, are found to be over five times more breathable than commercial wet electrodes, while the silk's intrinsic adhesion mechanism allows SLiM electrodes to avoid the use of harsh artificial adhesives, potentially decreasing skin irritation and inflammation over long‐term use. Finally, the SLiM electrodes provide comparable impedances to traditional wet and other liquid metal electrodes, offering a high‐fidelity sensing alternative with increased wearer comfort. Human subject testing confirmed the SLiM electrodes ability to sense electrophysiological signals with high fidelity and minimal irritation to the skin. The unique properties of the reported SLiM electrodes offer a comfortable electrophysiological sensing solution especially for patients with pre‐existing skin conditions or surface wounds.

Background: Depolymerizing polyethylene terephthalate (PET) plastics using enzymes, such as PETase, offers a sustainable chemical recycling route. To enhance degradation, many groups have sought to engineer PETase for faster catalysis on PET and elevated stability. Considerably less effort has been focused toward expressing large quantities of the enzyme, which is necessary for large-scale application and widespread use. In this work, we evaluated several E. coli strains for their potential to produce soluble, folded, and active IsPETase, and moved the production to a benchtop bioreactor. As PETase is known to require disulfide bonds to be functional, we screened several disulfide-bond promoting strains of E. coli to produce IsPETase, FAST-PETase and Hot-PETase. Results: We found expression in SHuffle T7 Express results in higher active expression of IsPETase compared to standard E. coli production strains such as BL21(DE3), reaching a purified titer of 20 mg enzyme per L of culture from shake flasks using 2xLB medium. We characterized purified IsPETase on 4-nitrophenyl acetate and PET microplastics, showing the enzyme produced in the disulfide-bond promoting host has high activity. Using a complex medium with glycerol and a controlled bioreactor, IsPETase titer reached 104 mg per L for a 46-h culture. FAST-PETase was found to be produced at similar levels in BL21(DE3) or SHuffle T7 Express, with purified production reaching 65 mg per L culture when made in BL21(DE3). Hot-PETase titers were greatest in BL21(DE3) reaching 77 mg per L culture. Conclusions: We provide protein expression methods to produce three important PETase variants. Importantly, for IsPETase, changing expression host, medium optimization and movement to a bioreactor resulted in a 50-fold improvement in production amount with a per cell dry weight productivity of 0.45 mg_PETase g_CDW⁻¹ h⁻¹, which is tenfold greater than that for K. pastoris. We show that the benefit of using SHuffle T7 Express for expression only extends to IsPETase, with FAST-PETase and Hot-PETase better produced and purified from BL21(DE3), which is unexpected given the number of cysteines present. This work represents a systematic evaluation of protein expression and purification conditions for PETase variants to permit further study of these important enzymes.

Enzymatic depolymerization of polyethylene terephthalate (PET) is a promising alternative to traditional recycling showing promise in addressing issues with high energy demands and challenges associated with mixed-waste streams. While engineered, thermostable PETase variants exist, achieving high yields under industrially relevant process conditions remains a significant hurdle. Poor thermostability and PET crystallinity are often blamed for low conversions, but these factors do not fully account for the low productivity observed in all cases. This suggests that other poorly understood phenomena may be limiting the catalytic efficiency of PETase warranting further investigation. This work systematically explores the impact of mixing, and in particular, the presence of the air–water and the solid–liquid interfaces, on PETase stability. We found that PET degradation plateaus while soluble PETase activity is lost at increasing mixing rates when an air–water interface is present. It is hypothesized that the enzyme adsorbs to the air–water interface leading to denaturation, aggregation and precipitation. Additional studies demonstrate that the hydrophobic PET film negatively impacts enzyme stability and the rate of enzyme inactivation is also proportional to the PET surface area. Traditional approaches to mitigate enzyme inactivation at interfaces, such as using blocking agents, were effective in preserving enzyme activity, but resulted in significantly reduced PET degradation rates. In contrast, PEGylation of PETase yielded improved stability and enhanced PET degradation during mixing. These findings help explain the significant conversion discrepancies reported in previous studies and demonstrate a robust strategy for improving PETase performance under industrially relevant conditions.