Insight into cellular response of plant cells confined within silica-based matrices

Porous silicon pillar structures/photosynthetic reaction centre protein hybrid for bioelectronic applications

Photosynthetic biomaterials have attracted considerable attention at different levels of the biological organisation, from molecules to the biosphere, due to a variety of artificial application possibilities. During photosynthesis, the first steps of the conversion of light energy into chemical energy take place in a pigment-protein complex, called reaction centre (RC). In our experiments photosynthetic reaction centre protein, purified from Rhodobacter sphaeroides R-26 purple bacteria, was bound to porous silicon pillars (PSiP) after the electropolymerisation of aniline onto the surface. This new type of biohybrid material showed remarkable photoactivity in terms of measured photocurrent under light excitation in an electrochemical cell. The photocurrent was found to increase considerably after the addition of ubiquinone (UQ-0), an e^--acceptor mediator of the RC. The photoactivity of the complex was found to decrease by the addition of terbutryn, the chemical which inhibits the e^--transport on the acceptor side of the RC. In addition to the generation of sizeable light-induced photocurrents, using the PSiP/RC photoactive hybrid nanocomposite material, the system was found to be sensitive towards RC inhibitors and herbicides. This highly ordered patterned 3D structure opens new solution for designing low-power (bio-)optoelectronic, biophotonic and biosensing devices.

Alginate@TiO2 hybrid microcapsules with high in vivo biocompatibility and stability for cell therapy

Designing new materials to encapsulate living therapeutic cells for the treatment of the diseases caused by protein or hormone deficiencies is a great challenge. The desired materials need to be biocompatible towards both entrapped cells and host organisms, have long-term in vivo stability after implantation, allow the diffusion of nutrients and metabolites, and ensure perfect immune-isolation. The current work investigates the in vivo biocompatibility and stability of alginate@TiO₂ hybrid microcapsules and the immune-isolation of entrapped HepG2 cells, to assess their potential for cell therapy. A comparison was made with alginate-silica hybrid microcapsules (ASA). These two hybrid microcapsules are implanted subcutaneously in female Wistar rats. The inflammatory responses of the rats are monitored by the histological examination of the implants and the surrounding tissues, to indicate their in vivo biocompatibility towards the hosts. The in vivo stability of the microcapsules is evaluated by the recovery rate of the intact microcapsules after implantation. The immune-isolation of the entrapped cells is assessed by their morphology, membrane integrity and intracellular enzymatic activity. The results show high viability of the entrapped cells and insignificant inflammation of the hosts, suggesting the excellent biocompatibility of alginate@TiO₂ and ASA microcapsules towards both host organisms and entrapped cells. Compared to the ASA microcapsules, more intact alginate@TiO₂ hybrid microcapsules are recovered 2-day and 2-month post-implantation and more cells remain alive, proving their better in vivo biocompability, stability, and immune-isolation. The present study demonstrates that the alginate@TiO₂ hybrid microcapsule is a highly promising implantation material for cell therapy.

Single cells in nanoshells for the functionalization of living cells

Inspired by the characteristics of cells in live organisms, new types of hybrids have been designed comprising live cells and abiotic materials having a variety of structures and functionalities. The major goal of these studies is to uncover hybridization approaches that promote cell stabilization and enable the introduction of new functions into living cells. Single-cells in nanoshells have great potential in a large number of applications including bioelectronics, cell protection, cell therapy, and biocatalysis. In this review, we discuss the results of investigations that have focused on the synthesis, structuration, functionalization, and applications of these single-cells in nanoshells. We describe synthesis methods to control the structural and functional features of single-cells in nanoshells, and further develop their applications in sustainable energy, environmental remediation, green biocatalysis, and smart cell therapy. Perceived limitations of single-cells in nanoshells have been also identified.

Detection of Singlet Oxygen Formation inside Photoactive Biohybrid Composite Material

Photosynthetic reaction center proteins (RCs) are the most efficient light energy converter systems in nature. The first steps of the primary charge separation in photosynthesis take place in these proteins. Due to their unique properties, combining RCs with nano-structures promising applications can be predicted in optoelectronic systems. In the present work RCs purified from Rhodobacter sphaeroides purple bacteria were immobilized on multiwalled carbon nanotubes (CNTs). Carboxyl—and amine-functionalised CNTs were used, so different binding procedures, physical sorption and chemical sorption as well, could be applied as immobilization techniques. Light-induced singlet oxygen production was measured in the prepared photoactive biocomposites in water-based suspension by histidine mediated chemical trapping. Carbon nanotubes were applied under different conditions in order to understand their role in the equilibration of singlet oxygen concentration in the suspension. CNTs acted as effective quenchers of ¹O₂ either by physical (resonance) energy transfer or by chemical (oxidation) reaction and their efficiency showed dependence on the diffusion distance of ¹O₂.

Microorganism mediated biosynthesis of metal chalcogenides; a powerful tool to transform toxic effluents into functional nanomaterials

Cadmium contained in soil and water can be taken up by certain crops and aquatic organisms and accumulate in the food-chain, thus removal of Cd from mining or industrial effluents - i.e. Ni-Cd batteries, electroplating, pigments, fertilizers - becomes mandatory for human health. In parallel, there is an increased interest in the production of luminescent Q-dots for applications in bioimaging, sensors and electronic devices, even the present synthesis methods are economic and environmentally costly. An alternative green pathway for producing Metal chalcogenides (MC: CdS, CdSe, CdTe) nanocrystals is based on the metabolic activity of living organisms. Intracellular and extracellular biosynthesis of can be achieved within a biomimetic approach feeding living organisms with Cd precursors providing new routes for combining bioremediation with green routes for producing MC nanoparticles. In this mini-review we present the state-of-the-art of biosynthesis of MC nanoparticles with a critical discussion of parameters involved and protocols. Few existing examples of scaling-up are also discussed. A modular reactor based on microorganisms entrapped in biocompatible mineral matrices - already proven for bioremediation of dissolved dyes - is proposed for combining both Cd-depletion and MC nanoparticle's production.

A multiscale study of bacterial proliferation modes within novel E. coli@Si(HIPE) hybrid macrocellular living foams

This multiscale study depicts the fundamentals of bacterial proliferation modes within hybrid E. coli@Si(HIPE) macrocellular living foams.

A stable, reusable, and highly active photosynthetic bioreactor by bio-interfacing an individual cyanobacterium with a mesoporous bilayer nanoshell

An individual cyanobacterium cell is interfaced with a nanoporous biohybrid layer within a mesoporous silica layer. The bio-interface acts as an egg membrane for cell protection and growth of outer shell. The resulting bilayer shell provides efficient functions to create a single cell photosynthetic bioreactor with high stability, reusability, and activity.

Photosynthetic machineries in nano-systems

Photosynthetic reaction centres are membrane-spanning proteins, found in several classes of autotroph organisms, where a photoinduced charge separation and stabilization takes place with a quantum efficiency close to unity. The protein remains stable and fully functional also when extracted and purified in detergents thereby biotechnological applications are possible, for example, assembling it in nano-structures or in optoelectronic systems. Several types of bionanocomposite materials have been assembled by using reaction centres and different carrier matrices for different purposes in the field of light energy conversion (e.g., photovoltaics) or biosensing (e.g., for specific detection of pesticides). In this review we will summarize the current status of knowledge, the kinds of applications available and the difficulties to be overcome in the different applications. We will also show possible research directions for the close future in this specific field.

A simple and effective method to encapsulate tobacco mesophyll protoplasts to maintain cell viability

Protoplasts have been widely used for genetic transformation, cell fusion, and somatic mutation due to the absence of a cell wall. However, without the protection of a cell wall, protoplasts are easy to rupture and aggregate during washing, collecting, and gene transfection. In this work, we propose a simple and effective silica/alginate two-step method to immobilize protoplasts with advantages in experimental manipulation and microscopic imaging, as well as in potentially studying cell biological processes such as secretion and metabolism. The proposed two-step immobilization method adopts Transwell with clear tissue culture-treated membrane to support protoplasts in the form of uniform thin layer, which has three unique properties.

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The tissue culture-treated membrane has a good affinity for the plant cell; thus, protoplasts can spread evenly and form a very thin layer.

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There are more choices for membrane pore size, depending on the application.

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It is very convenient to change or collect the solution without mechanically disturbing the protoplasts. This simple and effective silica sol–gel/alginate two-step immobilization of protoplasts in Transwell has great potential for applications in genetic transformation, metabolite production, and migration assays.

Specific localization and measurement of hydrogen peroxide in Arabidopsis thaliana cell suspensions and protoplasts elicited by COS-OGA

H2O2 acts as an important signaling molecule during plant/pathogen interactions but its study remains a challenge due to the current shortcomings in H2O2-responsive probes. In this work, ContPY1, a new molecular probe developed to specifically detect H2O2 was used to study the elicitation of Arabidopsis thaliana cells by a complex of chitosan oligomers (COS) and oligogalacturonides (OGA). The comparison of cell suspensions, protoplasts of cell suspensions and leaf protoplasts treated with different inhibitors gave indications on the potential sources of hydrogen peroxide in plant cells. The relative contribution of the cell wall, of membrane dehydrogenases and of peroxidases depended on cell type and treatment and proved to be variable. Our present protocol can be used to study hydrogen peroxide production in a large variety of plant species by simple protocol adaptation.

Validation of the boronate sensor ContPY1 as a specific probe for fluorescent detection of hydrogen peroxide in plants

Studying the implication of hydrogen peroxide in biological processes in plants remains a challenge due to the current shortcomings of H2O2-responsive probes. The use of ContPY1, a new fluorescent probe, which is highly selective and sensitive for H2O2, was investigated. To validate the use of ContPY1 on plants, we have generated protocols employing cells suspensions and leaves, and measured specifically H2O2 production by plants using spectrofluorometry and microscopy.

A hybrid assembly by encapsulation of human cells within mineralised beads for cell therapy

BACKGROUND

The design of new technologies for treatment of human disorders such as protein deficiencies is a complex and difficult task. Particularly, the construction of artificial organs, based on the immunoisolation of protein-secreting cells, requires the use of suitable materials which have to be biocompatible with the immunoisolated cells and avoid any inappropriate host response.

METHODOLOGY/PRINCIPAL FINDINGS

This work investigates the in vivo behavior of mechanically resistant hybrid beads which can be considered as a model for artificial organ for cell therapy. This hybrid system was designed and fabricated via the encapsulation of living cells (HepG2) within alginate-silica composites. Two types of beads (alginate-silica hybrid (AS) or alginate/silica hybrid subsequently covered by an external layer of pure alginate (ASA)), with or without HepG2 cells, were implanted into several female Wistar rats. After four weeks, the potential inflammatory local response that might be due to the presence of materials was studied by histochemistry. The results showed that the performance of ASA beads was quite promising compared to AS beads, where less abnormal rat behaviour and less inflammatory cells in histological sections were observed in the case of ASA beads.

CONCLUSIONS/SIGNIFICANCE

The current study highlights that alginate-silica composite materials coated with an extra-alginate shell offer much promise in the development of robust implantation devices and artificial organs.

Porous silicon/photosynthetic reaction center hybrid nanostructure

The purified photosynthetic reaction center protein (RC) from Rhodobacter sphaeroides R-26 purple bacteria was bound to porous silicon microcavities (PSiMc) either through silane-glutaraldehyde (GTA) chemistry or via a noncovalent peptide cross-linker. The characteristic resonance mode in the microcavity reflectivity spectrum red shifted by several nanometers upon RC binding, indicating the protein infiltration into the porous silicon (PSi) photonic structure. Flash photolysis experiments confirmed the photochemical activity of RC after its binding to the solid substrate. The kinetic components of the intraprotein charge recombination were considerably faster (τ(fast) = 14 (±9) ms, τ(slow) = 230 (±28) ms with the RC bound through the GTA cross-linker and only τ(fast) = 27 (±3) ms through peptide coating) than in solution (τ(fast) = 120 (±3) ms, τ(slow) = 1387 (±2) ms), indicating the effect of the PSi surface on the light-induced electron transfer in the protein. The PSi/RC complex was found to oxidize the externally added electron donor, mammalian cytochrome c, and the cytochrome oxidation was blocked by the competitive RC inhibitor, terbutryne. This fact indicates that the specific surface binding sites on the PSi-bound RC are still accessible to external cofactors and an electronic interaction with redox components in the aqueous environment is possible. This new type of biophotonic material is considered to be an excellent model for new generation applications at the interface of silicon-based electronics and biological redox systems designed by nature.

Light-harvesting bio-nanomaterial using porous silicon and photosynthetic reaction center

Porous silicon microcavity (PSiMc) structures were used to immobilize the photosynthetic reaction center (RC) purified from the purple bacterium Rhodobacter sphaeroides R-26. Two different binding methods were compared by specular reflectance measurements. Structural characterization of PSiMc was performed by scanning electron microscopy and atomic force microscopy. The activity of the immobilized RC was checked by measuring the visible absorption spectra of the externally added electron donor, mammalian cytochrome c. PSi/RC complex was found to oxidize the cytochrome c after every saturating Xe flash, indicating the accessibility of specific surface binding sites on the immobilized RC, for the external electron donor. This new type of bio-nanomaterial is considered as an excellent model for new generation applications of silicon-based electronics and biological redox systems.

Biotemplated materials for sustainable energy and environment: current status and challenges

Materials science will play a key role in the further development of emerging solutions for the increasing problems of energy and environment. Materials found in nature have many inspiring structures, such as hierarchical organizations, periodic architectures, or nanostructures, that endow them with amazing functions, such as energy harvesting and conversion, antireflection, structural coloration, superhydrophobicity, and biological self-assembly. Biotemplating is an effective strategy to obtain morphology-controllable materials with structural specificity, complexity, and related unique functions. Herein, we highlight the synthesis and application of biotemplated materials for six key areas of energy and environment technologies, namely, photocatalytic hydrogen evolution, CO(2) reduction, solar cells, lithium-ion batteries, photocatalytic degradation, and gas/vapor sensing. Although the applications differ from each other, a common fundamental challenge is to realize optimum structures for improved performances. We highlight the role of four typical structures derived from biological systems exploited to optimize properties: hierarchical (porous) structures, periodic (porous) structures, hollow structures, and nanostructures. We also provide examples of using biogenic elements (e.g., C, Si, N, I, P, S) for the creation of active materials. Finally, we disscuss the challenges of achieving the desired performance for large-scale commercial applications and provide some useful prototypes from nature for the biomimetic design of new materials or systems. The emphasis is mainly focused on the structural effects and compositional utilization of biotemplated materials.

Designing photobioreactors based on living cells immobilized in silica gel for carbon dioxide mitigation

Atmospheric carbon dioxide levels have been rising since the industrial revolution, with the most dramatic increase occurring since the end of World War II. Carbon dioxide is widely regarded as one of the major factors contributing to the greenhouse effect, which is of major concern in today's society because it leads to global warming. Photosynthesis is Nature's tool for combating elevated carbon dioxide levels. In essence, photosynthesis allows a cell to harvest solar energy and convert it into chemical energy through the assimilation of carbon dioxide and water. Therefore photosynthesis is regarded as an ideal way to harness the abundance of solar energy that reaches Earth and convert anthropologically generated carbon dioxide into useful carbohydrates, providing a much more sustainable energy source. This Minireview aims to tackle the idea of immobilizing photosynthetic unicellular organisms within inert silica frameworks, providing protection both to the fragile cells and to the external ecosystem, and to use this resultant living hybrid material in a photobioreactor. The viability and activity of various unicellular organisms are summarized alongside design issues of a photobioreactor based on living hybrid materials.

Hybrid shell engineering of animal cells for immune protections and regulation of drug delivery: towards the design of "artificial organs"

Background

With the progress in medicine, the average human life expectancy is continuously increasing. At the same time, the number of patients who require full organ transplantations is augmenting. Consequently, new strategies for cell transplantation are the subject of great interest.

Methodology/Principal Findings

This work reports the design, the synthesis and the characterisation of robust and biocompatible mineralised beads composed of two layers: an alginate-silica composite core and a Ca-alginate layer. The adequate choice of materials was achieved through cytotoxicity LDH release measurement and in vitro inflammatory assay (IL-8) to meet the biocompatibility requirements for medical purpose. The results obtained following this strategy provide a direct proof of the total innocuity of silica and alginate networks for human cells as underscored by the non-activation of immune defenders (THP-1 monocytes). The accessible pore size diameter of the mineralised beads synthesized was estimated between 22 and 30 nm, as required for efficient immuno-isolation without preventing the diffusion of nutrients and metabolites. The model human cells, HepG2, entrapped within these hybrid beads display a high survival rate over more than six weeks according to the measurements of intracellular enzymatic activity, respiration rate, as well as the “de novo” biosynthesis and secretion of albumin out of the beads.

Conclusions/Significance

The current study shows that active mammalian cells can be protected by a silica-alginate hybrid shell-like system. The functionality of the cell strain can be maintained. Consequently, cells coated with an artificial and a biocompatible mineral shell could respond physiologically within the human body in order to deliver therapeutic agents in a controlled fashion (i.e. insulin), substituting the declining organ functions of the patient.

How to design cell-based biosensors using the sol-gel process

Inorganic gels formed using the sol-gel process are promising hosts for the encapsulation of living organisms and the design of cell-based biosensors. However, the possibility to use the biological activity of entrapped cells as a biological signal requires a good understanding and careful control of the chemical and physical conditions in which the organisms are placed before, during, and after gel formation, and their impact on cell viability. Moreover, it is important to examine the possible transduction methods that are compatible with sol-gel encapsulated cells. Through an updated presentation of the current knowledge in this field and based on selected examples, this review shows how it has been possible to convert a chemical technology initially developed for the glass industry into a biotechnological tool, with current limitations and promising specificities.