Flexible Material Formulations for 3D Printing of Porous Beds with Applications in Bioprocess Engineering

Background: 3D printing is revolutionizing many industrial sectors and has the potential to enhance also the biotechnology and bioprocessing fields. Here, we propose a new flexible material formulation to 3D print support matrices with complex, perfectly ordered morphology and with tuneable properties to suit a range of applications in bioprocess engineering. Findings: Supports for packed-bed operations were fabricated using functional monomers as the key ingredients, enabling matrices with bespoke chemistry such as charged groups, chemical moieties for further functionalization, and hydrophobic/hydrophilic groups. Other ingredients, e.g. crosslinkers and porogens, provide the opportunity to further tune the mechanical properties of the supports and the morphology of their porous network. Through this approach, we fabricated and demonstrated the operation of Schoen gyroid columns with I) positive and negative charges for ion-exchange chromatography, II) enzyme bioreactors with immobilized trypsin to catalyse hydrolysis, and III) bacterial biofilms bioreactors for fuel desulfurization. Conclusions: This study demonstrates a simple, cost-effective and flexible fabrication of customized 3D printed supports for different biotechnology and bioengineering applications.

Pore Network Modelling of Porous Media for Carbon Dioxide Sequestration: A Case Study of Pakistan

Carbon dioxide (CO2) storage in natural rocks is an important strategy for reducing and capturing greenhouse gas emissions in the atmosphere. The amount of CO2 stored in a natural reservoir such as natural rocks is the major challenge for any economically viable CO2 storage. The intricate nature of the porous media and the estimates of the replacement of residing aqueous media with the invading CO2 is the challenge. The current study uses MATLAB to construct a similar porous network model for simulation of complex porous storage. The model is designed to mimic the overall properties of the natural porous media in terms of permeability, porosity and inter-pore connectivity. Here a dynamic pore network is simulated and validated, firstly in the case of a porous network with one fluid invading empty network. Subsequently, the simulations for an invading fluid (CO2) capturing the porous media with filled aqueous brine solution are also carried out in a dynamic fashion. This resembles the actual storage process of CO2 sequestration in natural rocks. While the sensitivity analysis suggests that the differential pressure and porosity have a direct effect on saturation, increasing differential pressure or porosity increases the saturation of CO2 storage. The results for typically occurring rocks in Pakistan are also studies and related with the findings of the study.

Self-Healing Behavior of Polymer/Protein Hybrid Hydrogels

The paper presents the viscoelastic properties of new hybrid hydrogels containing poly(vinyl alcohol) (PVA), hydroxypropylcellulose (HPC), bovine serum albumin (BSA) and reduced glutathione (GSH). After heating the mixture at 55 °C, in the presence of GSH, a weak network is formed due to partial BSA unfolding. By applying three successive freezing/thawing cycles, a stable porous network structure with elastic properties is designed, as evidenced by SEM and rheology. The hydrogels exhibit self-healing properties when the samples are cut into two pieces; the intermolecular interactions are reestablished in time and therefore the fragments repair themselves. The effects of the BSA content, loaded deformation and temperature on the self-healing ability of hydrogels are presented and discussed through rheological data. Due to their versatile viscoelastic behavior, the properties of PVA/HPC/BSA hydrogels can be tuned during their preparation in order to achieve suitable biomaterials for targeted applications.

Photocatalytic Hydrogen Evolution from Water Splitting Using Core-Shell Structured Cu/ZnS/COF Composites

Hydrogen is considered to be a very efficient and clean fuel since it is a renewable and non-polluting gas with a high energy density; thus, it has drawn much attention as an alternative fuel, in order to alleviate the issue of global warming caused by the excess use of fossil fuels. In this work, a novel Cu/ZnS/COF composite photocatalyst with a core-shell structure was synthesized for photocatalytic hydrogen production via water splitting. The Cu/ZnS/COF microspheres formed by Cu/ZnS crystal aggregation were covered by a microporous thin-film COF with a porous network structure, where COF was also modified by the dual-effective redox sites of C=O and N=N. The photocatalytic hydrogen production results showed that the hydrogen production rate reached 278.4 µmol g−1 h−1, which may be attributed to its special structure, which has a large number of active sites, a more negative conduction band than the reduction of H+ to H2, and the ability to inhibit the recombination of electron-hole pairs. Finally, a possible mechanism was proposed to effectively explain the improved photocatalytic performance of the photocatalytic system. The present work provides a new concept, in order to construct a highly efficient hydrogen production catalyst and broaden the applications of ZnS-based materials.

Nanofibrous PEDOT-Carbon Composite on Flexible Probes for Soft Neural Interfacing

In this study, we report a flexible implantable 4-channel microelectrode probe coated with highly porous and robust nanocomposite of poly (3,4-ethylenedioxythiophene) (PEDOT) and carbon nanofiber (CNF) as a solid doping template for high-performance in vivo neuronal recording and stimulation. A simple yet well-controlled deposition strategy was developed via in situ electrochemical polymerization technique to create a porous network of PEDOT and CNFs on a flexible 4-channel gold microelectrode probe. Different morphological and electrochemical characterizations showed that they exhibit remarkable and superior electrochemical properties, yielding microelectrodes combining high surface area, low impedance (16.8 ± 2 MΩ µm2 at 1 kHz) and elevated charge injection capabilities (7.6 ± 1.3 mC/cm2) that exceed those of pure and composite PEDOT layers. In addition, the PEDOT-CNF composite electrode exhibited extended biphasic charge cycle endurance and excellent performance under accelerated lifetime testing, resulting in a negligible physical delamination and/or degradation for long periods of electrical stimulation. In vitro testing on mouse brain slices showed that they can record spontaneous oscillatory field potentials as well as single-unit action potentials and allow to safely deliver electrical stimulation for evoking field potentials. The combined superior electrical properties, durability and 3D microstructure topology of the PEDOT-CNF composite electrodes demonstrate outstanding potential for developing future neural surface interfacing applications.

Hierarchically 3-D Porous Structure of Silk Fibroin-Based Biocomposite Adsorbent for Water Pollutant Removal

This study explored the tunability of a 3-D porous network in a freeze-dried silk fibroin/soursop seed (SF:SS) polymer composite bioadsorbent. Morphological, physical, electronic, and thermal properties were assessed using scanning electron microscopy, the BET N2 adsorption-desorption test, Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). A control mechanism of pore opening–closing by tuning the SS fraction in SF:SS composite was found. The porous formation is apparently due to the amount of phytic acid as a natural cross-linker in SS. The result reveals that a large pore radius is formed using only 20% wt of SS in the composite, i.e., SF:SS (4:1), and the fibrous network closes the pore when the SS fraction increases up to 50%, i.e., SF:SS (1:1). The SF:SS (4:1) with the best physical and thermal properties shows an average pore diameter of 39.19 nm, specific surface area of 19.47 m2·g−1, and thermal stability up to ~450 °C. The removal of the organic molecule and the heavy metal was assessed using crystal violet (CV) dye and the Cu2+ adsorption test, respectively. The adsorption isotherm of both CV and Cu2+ on SF:SS (4:1) follows the Freundlich model, and the adsorption kinetic of CV follows the pseudo-first-order model. The adsorption test indicates that physisorption dominates the adsorption of either CV or Cu2+ on the SF:SS composites.

Ionic Porous Aromatic Framework as a Self-Degraded Template for the Synthesis of a Magnetic γ-Fe2O3/WO3·0.5H2O Hybrid Nanostructure with Enhanced Photocatalytic Property

An ionic porous aromatic framework is developed as a self-degraded template to synthesize the magnetic heterostructure of γ-Fe2O3/WO3·0.5H2O. The Fe3O4 polyhedron was obtained with the two-phase method first and then reacted with sodium tungstate to form the γ-Fe2O3/WO3·0.5H2O hybrid nanostructure. Under the induction effect of the ionic porous network, the Fe3O4 phase transformed to the γ-Fe2O3 state and complexed with WO3·0.5H2O to form the n-n heterostructure with the n-type WO3·0.5H2O on the surface of n-type γ-Fe2O3. Based on a UV-Visible analysis, the magnetic photocatalyst was shown to have a suitable band gap for the catalytic degradation of organic pollutants. Under irradiation, the resulting γ-Fe2O3/WO3·0.5H2O sample exhibited a removal efficiency of 95% for RhB in 100 min. The charge transfer mechanism was also studied. After the degradation process, the dispersed powder can be easily separated from the suspension by applying an external magnetic field. The catalytic activity displayed no significant decrease after five recycles. The results present new insights for preparing a hybrid nanostructure photocatalyst and its potential application in harmful pollutant degradation.