Silica Hydrogels as Entrapment Material for Microalgae

A novel indicator-based visualisation method to investigate diffusion behaviour of dissolved CO2 in hydrogels

Biocompatible hydrogels are versatile platforms for encapsulating living cells in biotechnology due to their unique physical, structural and mechanical properties. The diffusion of dissolved carbon dioxide (dCO2) into the hydrogel matrix is of great importance for the growth of immobilised photosynthetic cells like microalgae and cyanobacteria. However, non-invasive analysis methods for measuring the diffusion of dCO2 in hydrogels are limited. In this article, we describe an indirect method for the non-invasive measurement of diffusion rates for dCO2 in hydrogels. We visually tracked the diffusion along the axial direction of pH indicator-doped hydrogel monoliths by recording the interface position over time. We calculated the interface velocity and the pseudo diffusion coefficients (Dpseudo) over time. The obtained Dpseudo values are in a realistic range compared to literature values. Therefore, this novel analysis method for dCO2 diffusion gained valuable insights into diffusion dynamics in different hydrogels and can aid in the design of better immobilisation matrices for photosynthetic cells.•Non-invasive, rapid method for estimation of dissolved CO2 (dCO2) diffusion in hydrogels•Automatic analysis of colour interface formation due to acidification of hydrogels by diffusing dCO2•Agarose hydrogels exhibit an approximated 30x higher pseudo dCO2 diffusion coefficient than silica gel.

Silica hydrogels as a carbon-free solid media for the culture of diverse organisms

Bacteriological agar plates are commonly used to carry out experiments for the selective growth of microorganisms and the isolation of single-strain colonies. However, the presence of agar itself may be a confounding factor since it may serve as a source of carbon and energy. Moreover, there have been ongoing constraints on the production and sourcing of agar. These concerns have led to an interest in the development of agar substitutes. Silica hydrogels are entirely inorganic carbon-free polymeric materials that lack any source of micronutrients. Herein, a revised method for the preparation of silica hydrogels as a solid culture medium is reported. These gels can be formulated with a range of nutrient-rich or minimal media supplemented with various carbon sources, and can be manipulated in the same manner as agar gels. Their use for the culture and isolation of diverse microorganisms, including both Gram-positive and Gram-negative bacteria, yeast, and filamentous fungi is demonstrated. These silica hydrogels supplemented with either antibiotics or other molecules of interest can also be used for microbial selection experiments.

Processed microalgae: green gold for tissue regeneration and repair

As novel biomedical materials, microalgae have garnered significant interest because of their ability to generate photosynthetic oxygen, their antioxidant activity, and their favorable biocompatibility. Many studies have concentrated on the hypoxia-alleviating effects of microalgae within tumor microenvironments. However, recent findings indicate that microalgae can significantly increase the regeneration of various tissues and organs. To augment microalgae's therapeutic efficacy and mitigate the limitations imposed by immune clearance, it is essential to process microalgae through various processing strategies. This review examines common microalgal species in biomedical applications, such as Chlorella, Chlamydomonas reinhardtii, diatoms, and Spirulina. This review outlines diverse processing methods, including microalgae extracts, microalgae‒nanodrug composite delivery systems, surface modifications, and living microalgae‒loaded hydrogels. It also discusses the latest developments in tissue repair using processed microalgae for skin, gastrointestinal, bone, cardiovascular, lung, nerve, and oral tissues. Furthermore, future directions are presented, and research gaps for processed microalgae are identified. Collectively, these insights may inform the innovation of processed microalgae for various uses and offer guidance for ongoing research in tissue repair.

Harnessing recalcitrant lignocellulosic biomass for enhanced biohydrogen production: Recent advances, challenges, and future perspective

Biohydrogen (Bio-H2) is widely recognized as a sustainable and environmentally friendly energy source, devoid of any detrimental impact on the environment. Lignocellulosic biomass (LB) is a readily accessible and plentiful source material that can be effectively employed as a cost-effective and sustainable substrate for Bio-H2 production. Despite the numerous challenges, the ongoing progress in LB pretreatment technology, microbial fermentation, and the integration of molecular biology techniques have the potential to enhance Bio-H2 productivity and yield. Consequently, this technology exhibits efficiency and the capacity to meet the future energy demands associated with the valorization of recalcitrant biomass. To date, several pretreatment approaches have been investigated in order to improve the digestibility of feedstock. Nevertheless, there has been a lack of comprehensive systematic studies examining the effectiveness of pretreatment methods in enhancing Bio-H2 production through dark fermentation. Additionally, there is a dearth of economic feasibility evaluations pertaining to this area of research. Thus, this review has conducted comparative studies on the technological and economic viability of current pretreatment methods. It has also examined the potential of these pretreatments in terms of carbon neutrality and circular economy principles. This review paves the way for a new opportunity to enhance Bio-H2 production with technological approaches.

Development of a new kappa-carrageenan hydrogel system to study benthic diatom vertical movements

Benthic diatom vertical movement has been investigated mainly through indirect measurements based on chlorophyll a fluorescence and spectral reflectance signals. The presence of sediment hinders direct imaging and grazers activity renders the work under controlled conditions very difficult. This study provides a tool to study diatoms movement in a 3D hydrogel matrix. Synthetic and natural hydrogels were tested to find the best 3D transparent scaffold where diatoms could grow and freely move in all directions. Polyamidoamines (PAAm) hydrogels were no-cytocompatible and hyaluronic acid (HA) only allowed diatoms to survive for 2-days. Natural hydrogels made of gelatin/Na-alginate, Na-alginate and kappa-carrageenan (KC) were cytocompatible, with KC showing the best properties for diatom growth and movement on a long term (up to 2 months). Comparing Nitzschia spathulata, Gyrosigma limosum and Navicula phyllepta growth in liquid media vs in KC gels, we found that diatoms reached a significantly higher final biomass in the hydrogel condition. Hydrogels were also useful to isolate large size diatom species e.g., Nitzschia elongata, that did not survive in suspension. Finally, we showed three ways to study diatom species-specific movement in KC hydrogels: 1) controlled species mix; 2) natural diatom assemblages with grazers; and 3) natural diatom assemblages without grazers. With our system, single diatoms could be imaged, identified, and counted. In addition, different stimuli, e.g., light intensity and light composition can be applied and their effects on movement and physiology studied without being masked by sediment or impaired by meiofauna.

New insights into enhancement of bio-hydrogen production through encapsulated microalgae with alginate under visible light irradiation

The production of green hydrogen is a promising alternative to fossil fuels. The current study focuses on the design of microalgae as a catalyst in bioelectrochemical systems for the generation of biohydrogen. Furthermore, the abovementioned target could be achieved by optimizing different parameters, including strains of microalgae, different optical filters, and their shapes. Synechocystis sp. PAK13 (Ba9), Micractinium sp. YACCYB33 (R4), and Desmodesmus intermedius (Sh42) were used and designed as free cells and immobilized microalgae for evaluating their performance for hydrogen production. Alginate was applied for immobilization not only for protecting the immobilized microalgae from stress but also for inhibiting the agglomeration of microalgae and improving stability. The amount of studied immobilized microalgae was 0.01 g/5 ml algae-dissolved in 10 ml alginate gel at 28 °C, 12 h of light (light intensity 30.4 μmol m-2 s-1), and 12 h of darkness with continual aeration (air bump in every strain flask) at pH = 7.2 ± 0.2 in 0.05 %wuxal buffer which has 3.7 ionic strength. Different modalities, including FTIR, UV, and SEM, were performed for the description of selected microalgae. The surface morphology of Ba9 with alginate composite (immobilized Ba9) appeared as a stacked layer with high homogeneity, which facilitates hydrogen production from water. The conversion efficiencies of the immobilized microalgae were evaluated by incident photon-to-current efficiency (IPCE). Under optical filters, the optimum IPCE value was ∼ 7 % at 460 nm for immobilized Ba9. Also, its number of hydrogen moles was calculated to be 16.03 mmol h-1 cm-2 under optical filters. The electrochemical stability of immobilized Ba9 was evaluated through repetitive 100 cycles as a short-term stability test, and the curve of chrono-amperometry after 30 min in 0.05 %wuxal at a constant potential of 0.9 V for 30 min of all studied samples confirmed the high stability of all sample and the immobilized Ba9 has superior activity than others.

Biomimetic Sol-Gel Chemistry to Tailor Structure, Properties, and Functionality of Bionanocomposites by Biopolymers and Cells

Biosilica, synthesized annually only by diatoms, is almost 1000 times more abundant than industrial silica. Biosilicification occurs at a high rate, although the concentration of silicic acid in natural waters is ~100 μM. It occurs in neutral aqueous solutions, at ambient temperature, and under the control of proteins that determine the formation of hierarchically organized structures. Using diatoms as an example, the fundamental differences between biosilicification and traditional sol-gel technology, which is performed with the addition of acid/alkali, organic solvents and heating, have been identified. The conditions are harsh for the biomaterial, as they cause protein denaturation and cell death. Numerous attempts are being made to bring sol-gel technology closer to biomineralization processes. Biomimetic synthesis must be conducted at physiological pH, room temperature, and without the addition of organic solvents. To date, significant progress has been made in approaching these requirements. The review presents a critical analysis of the approaches proposed to date for the silicification of biomacromolecules and cells, the formation of bionanocomposites with controlled structure, porosity, and functionality determined by the biomaterial. They demonstrated the broad capabilities and prospects of biomimetic methods for creating optical and photonic materials, adsorbents, catalysts and biocatalysts, sensors and biosensors, and biomaterials for biomedicine.

Nanoarchitectonics to entrap living cells in silica-based systems: encapsulations with yolk-shell and sepiolite nanomaterials

In the present work, the bottom-up fabrication of biohybrid materials using a nanoarchitectonics approach has been applied to entrap living cells. Unicellular microorganisms, that is, cyanobacteria and yeast cells, have been immobilized in silica and silicate-based substrates organized as nanostructured materials. In a first attempt, matrices based on bionanocomposites of chitosan and alginate incorporating sepiolite clay mineral and shaped as films, beads, or foams have been explored for the immobilization of cyanobacteria. It has been observed that this type of biohybrid substrates leads to serious problems regarding the long-time survival of the encapsulated microorganisms. Alternative procedures using silica-based matrices with low sodium content, generated by sol-gel methods, as well as pre-synthesised yolk-shell bionanohybrids have been studied subsequently. Optical microscopy and SEM confirm that the silica shell microstructures provide a reduced contact between cells. The inorganic matrix increases the survival of the cells and maintains their bioactivity. Thus, the encapsulation efficiency is improved compared to the approach using a direct contact of cells in a silica matrix. Encapsulated yeast produced ethanol over a period of several days, pointing out the useful biocatalytic potential of the approach and suggesting further optimization of the present protocols.