A bacteriorhodopsin-based biohybrid solar cell using carbon-based electrolyte and cathode components.

There is currently a high demand for energy production worldwide, mainly producing renewable and sustainable energy. Bio-sensitized solar cells (BSCs) are an excellent option in this field due to their optical and photoelectrical properties developed in recent years. One of the biosensitizers that shows promise in simplicity, stability and quantum efficiency is bacteriorhodopsin (bR), a photoactive, retinal-containing membrane protein. In the present work, we have utilized a mutant of bR, D96N, in a photoanode-sensitized TiO2 solar cell, integrating low-cost, carbon-based components, including a cathode composed of PEDOT (poly(3,4-ethylenedioxythiophene) functionalized with multi-walled carbon nanotubes (CNT) and a hydroquinone/benzoquinone (HQ/BQ) redox electrolyte. The photoanode and cathode were characterized morphologically and chemically (SEM, TEM, and Raman). The electrochemical performance of the bR-BSCs was investigated using linear sweep voltammetry (LSV), open circuit potential decay (VOC), and impedance spectroscopic analysis (EIS). The champion device yielded a current density (JSC) of 1.0 mA/cm2, VOC of -669 mV, a fill factor of ~24 %, and a power conversion efficiency (PCE) of 0.16 %. This bR device is one of the first bio-based solar cells utilizing carbon-based alternatives for the photoanode, cathode, and electrolyte. This may decrease the cost and significantly improve the device's sustainability.

PEDOT-Carbon Nanotube Counter Electrodes and Bipyridine Cobalt (II/III) Mediators as Universally Compatible Components in Bio-Sensitized Solar Cells Using Photosystem I and Bacteriorhodopsin.

In nature, solar energy is captured by different types of light harvesting protein-pigment complexes. Two of these photoactivatable proteins are bacteriorhodopsin (bR), which utilizes a retinal moiety to function as a proton pump, and photosystem I (PSI), which uses a chlorophyll antenna to catalyze unidirectional electron transfer. Both PSI and bR are well characterized biochemically and have been integrated into solar photovoltaic (PV) devices built from sustainable materials. Both PSI and bR are some of the best performing photosensitizers in the bio-sensitized PV field, yet relatively little attention has been devoted to the development of more sustainable, biocompatible alternative counter electrodes and electrolytes for bio-sensitized solar cells. Careful selection of the electrolyte and counter electrode components is critical to designing bio-sensitized solar cells with more sustainable materials and improved device performance. This work explores the use of poly (3,4-ethylenedioxythiophene) (PEDOT) modified with multi-walled carbon nanotubes (PEDOT/CNT) as counter electrodes and aqueous-soluble bipyridine cobaltII/III complexes as direct redox mediators for both PSI and bR devices. We report a unique counter electrode and redox mediator system that can perform remarkably well for both bio-photosensitizers that have independently evolved over millions of years. The compatibility of disparate proteins with common mediators and counter electrodes may further the improvement of bio-sensitized PV design in a way that is more universally biocompatible for device outputs and longevity.

Supercritical CO2 technology for one-pot foaming and sterilization of polymeric scaffolds for bone regeneration.

Sterilization is a quite challenging step in the development of novel polymeric scaffolds for regenerative medicine since conventional sterilization techniques may significantly alter their morphological and physicochemical properties. Supercritical (sc) sterilization, i.e. the use of scCO2 as a sterilizing agent, emerges as a promising sterilization method due to the mild operational conditions and excellent penetration capability. In this work, a scCO2 protocol was implemented for the one-pot preparation and sterilization of poly(ε-caprolactone) (PCL)/poly(lactic-co-glycolic acid) (PLGA) scaffolds. The sterilization conditions were established after screening against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) vegetative bacteria and spores of Bacillus stearothermophilus, Bacillus pumilus and Bacillus atrophaeus. The transition from the sterilization conditions (140 bar, 39 °C) to the compressed foaming (60 bar, 26 °C) was performed through controlled depressurization (3.2 bar/min) and CO2 liquid flow. Controlled depressurization/pressurization cycles were subsequently applied. Using this scCO2 technology toolbox, sterile scaffolds of well-controlled pore architecture were obtained. This sterilization procedure successfully achieved not only SAL-6 against well-known resistant bacteria endospores but also improved the scaffold morphologies compared to standard gamma radiation sterilization procedures.

Conductive nanostructured materials based on poly-(3,4-ethylenedioxythiophene) (PEDOT) and starch/κ-carrageenan for biomedical applications.

Smart electroactive biomaterials are sought to allow the direct delivery of electrical, electrochemical and electromechanical signals to biological tissues. Specifically, poly-(3,4-ethylenedioxythiophene) (PEDOT) is a polymer of special interest attending to its biocompatibility, tuneable electrical conductivity and processing versatility. In this work, nanostructured PEDOT was synthesized using starch/κ-carrageenan aerogels as templates. κ-carrageenan biopolymer acted as doping agent of the conductive polymer to enhance the biocompatibility and the electrical response. The physicochemical, morphological, mechanical and electrical properties of the nanostructured PEDOT and templates were characterized. The incorporation of κ-carrageenan to the nanostructured materials resulted in an increase in the compressive strength of ca. 40% and a decrease in the electrical impedance of one order-of-magnitude. The synergistic combination of the inherent electrical properties of the PEDOT, the advantageous features of κ-carrageenan as doping agent and the porous morphology of the aerogel template resulted in electroactive PEDOT nanostructures with relevant properties for biomedical applications.

Synthesis of an organic conductive porous material using starch aerogels as template for chronic invasive electrodes.

We report the development of an organic conducting mesoporous material, as coat for invasive electrodes, by a novel methodology based on the use of starch aerogel as template. The poly(3,4-ethylenedioxythiophene) (PEDOT) aerogel was synthesized by polymerization of 3,4-ethylenedioxythiophene within a saturated starch aerogel with iron (III) p-toluenesulfonate (oxidizing agent) and subsequent removal of the polysaccharide template, followed by supercritical CO2 drying. The chemical structure and oxidation state of the resulting material were studied by Raman spectroscopy. The morphology and surface properties of the obtained nanoporous material were investigated by scanning electron microscopy (SEM), micro computed tomography (µCT) and nitrogen adsorption-desorption techniques. The composition and thermal behaviour were evaluated by energy dispersive spectroscopy (EDS) and thermogravimetric analysis (TGA) respectively. A preliminary biocompatibility test verified the non-cytotoxic effects of the PEDOT aerogel. The large surface area and wide pore size distribution of the PEDOT conductive aerogel, along with its electrical properties, enable it to be used as extracellular matrix scaffold for biomedical applications.