Fabrication of Sodium Trimetaphosphate-Based PEDOT:PSS Conductive Hydrogels.

Conductive hydrogels are highly attractive for biomedical applications due to their ability to mimic the electrophysiological environment of biological tissues. Although conducting polymer polythiophene-poly-(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonate (PSS) alone exhibit high conductivity, the addition of other chemical compositions could further improve the electrical and mechanical properties of PEDOT:PSS, providing a more promising interface with biological tissues. Here we study the effects of incorporating crosslinking additives, such as glycerol and sodium trimetaphosphate (STMP), in developing interpenetrating PEDOT:PSS-based conductive hydrogels. The addition of glycerol at a low concentration maintained the PEDOT:PSS conductivity with enhanced wettability but decreased the mechanical stiffness. Increasing the concentration of STMP allowed sufficient physical crosslinking with PEDOT:PSS, resulting in improved hydrogel conductivity, wettability, and rheological properties without glycerol. The STMP-based PEDOT:PSS conductive hydrogels also exhibited shear-thinning behaviors, which are potentially favorable for extrusion-based 3D bioprinting applications. We demonstrate an interpenetrating conducting polymer hydrogel with tunable electrical and mechanical properties for cellular interactions and future tissue engineering applications.

Conductive gradient hydrogels allow spatial control of adult stem cell fate.

Electrical gradients are fundamental to physiological processes including cell migration, tissue formation, organ development, and response to injury and regeneration. Current electrical modulation of cells is primarily studied under a uniform electrical field. Here we demonstrate the fabrication of conductive gradient hydrogels (CGGs) that display mechanical properties and varying local electrical gradients mimicking physiological conditions. The electrically-stimulated CGGs enhanced human mesenchymal stem cell (hMSC) viability and attachment. Cells on CGGs under electrical stimulation showed a high expression of neural progenitor markers such as Nestin, GFAP, and Sox2. More importantly, CGGs showed cell differentiation toward oligodendrocyte lineage (Oligo2) in the center of the scaffold where the electric field was uniform with a greater intensity, while cells preferred neuronal lineage (NeuN) on the edge of the scaffold on a varying electric field at lower magnitude. Our data suggest that CGGs can serve as a useful platform to study the effects of electrical gradients on stem cells and potentially provide insights on developing new neural engineering applications.

Optimum concentration of fly ash nanoparticles to stabilize CO2 foams for aquifer and soil remediation.

Contamination caused by non-aqueous phase liquids (NAPLs) in aquifers and soil is an important challenge that requires effective remediation techniques. One potential approach is through the use of CO2 foams to displace NAPLs from permeable media. CO2 foams generated only by surfactants are not stable enough for the efficient removal of NAPLs contamination. This shortcoming may be alleviated via the use of nanoparticles (NPs)-surfactant mixtures as a stabilizing agent. This work focuses on the evaluation of the optimum concentration of fly ash nanoparticles for stabilizing CO2 foam with the combined action of the surfactant. The performance of this foam is evaluated in remediating a contaminated 41 mm × 36 mm surrogate permeable medium in a microfluidic device. Mixtures of fly ash, a by-product of coal-burning power plants, and alpha-olefin sulfonate (AOS) and lauramidopropyl betaine (LAPB) surfactants are used to generate stable foams. The results show that a 1000 mg/L AOS-LAPB surfactant solution along with 1000 mg/L of fly ash NPs produces the best performance. Formation of deposits in the matrix is observed. These deposits, which are more prominent at higher NP concentrations, appear to adversely affect displacement, displacement efficiency and remediation of the medium. This study demonstrates that using fly ash nanoparticles and optimizing their concentration can effectively stabilize CO2 foams and improve the displacement efficiency for aquifer and soil remediation.

[Enzyme ancestral sequence reconstruction and directed evolution].

The amino acid sequence of ancestral enzymes from extinct organisms can be deduced through in silico approach termed ancestral sequence reconstruction (ASR). ASR usually has six steps, which are the collection of nucleic acid/amino acid sequences of modern enzymes, multiple sequence alignment, phylogenetic tree construction, computational deduction of ancestral enzyme sequence, gene cloning, and characterization of enzyme properties. This method is widely used to study the adaptation and evolution mechanism of molecules to the changing environmental conditions on planetary time scale. As enzymes play key roles in biocatalysis, this method has become a powerful method for studying the relationship among the sequence, structure, and function of enzymes. Notably, most of the ancestral enzymes show better temperature stability and mutation stability, making them ideal protein scaffolds for further directed evolution. This article summarizes the computer algorithms, applications, and commonly used computer software of ASR, and discusses the potential application in directed evolution of enzymes.