Christophe Meunier

Encapsulation of cells within silica matrixes: Towards a new advance in the conception of living hybrid materials

Living cells can be considered as a highly efficient molecular engines spatially enclosed, remaining however fragile. By combining cells with silica materials in an appropriate way, novel living hybrid material technologies can be designed. After showing the real interplay between silica species and living organisms in nature, this featuring article summarizes the considerable progress in cell encapsulation into silica matrixes. Generally speaking, bioencapsulation allows protecting cells from harsh environment and controlling their surrounding as well as their concentration. This combination produces ultimately a device that can be oriented to drive the desired biochemical reactions. Particularly, this article highlights that functional living matters are very promising in the development of new eco-friendly processes. Compared to conventional chemical process, these hybrid systems would be enabled to use greater and in more efficient way renewable resources (i.e. solar energy) to produce a vast array of chemicals. Additionally, encapsulated cell technology has opened the possibility to design various other kinds of bioactive materials such as cleaning systems, biosensors and artificial organs. Through different examples, including the immobilization of microorganisms, photosynthetic organelles, plant cells and animal cells, the interests and the preparation methods of these living hybrid materials are discussed.

Whole-cell based hybrid materials for green energy production, environmental remediation and smart cell-therapy

This critical review highlights the advances that have been made over recent years in the domain of whole-cell immobilisation and encapsulation for applications relating to the environment and human health, particularly focusing on examples of photosynthetic plant cells, bacteria and algae as well as animal cells. Evidence that encapsulated photosynthetic cells remain active in terms of CO(2) sequestration and biotransformation (solar driven conversion of CO(2) into biofuels, drugs, fine chemicals etc.), coupled with the most recent advances made in the field of cell therapy, reveals the need to develop novel devices based on the preservation of living cells within abiotic porous frameworks. This review shall corroborate this statement by selecting precise examples that unambiguously demonstrate the necessity and the benefits of such smart materials. As will be described, the handling and exploitation of photosynthetic cells are enhanced by entrapment or encapsulation since the cells are physically separated from the liquid medium, thereby facilitating the recovery of the metabolites produced. In the case of animal cells, their encapsulation within a matrix is essential in order to create a physical barrier that can protect the cells auto-immune defenders upon implantation into a living body. For these two research axes, the key parameters that have to be kept in mind when designing hybrid materials will be identified, concentrating on essential aspects such as biocompatibility, mechanical strength and controlled porosity (264 references).

Energy from photobioreactors: Bioencapsulation of photosynthetically active molecules, organelles, and whole cells within biologically inert matrices

Photosynthesis is a highly efficient solar energy transformation process. Exploiting this natural phenomenon is one way to overcome the shortage in the Earth’s fuel resources. This review summarizes the work carried out in the field of photobioreactor design via the immobilization of photosynthetically active matter within biologically inert matrices and the potential biotechnological applications of the obtained hybrid materials within the domain of solar energy to chemical energy transformation. The first part deals with the design of artificial photosynthetic reaction centers (RCs) by the encapsulation of pigments, proteins, and complexes. The action of thylakoids, chloroplasts, and whole plant cells, immobilized in biocompatible supports, in the conversion of CO2 into chemical energy, is also addressed. Finally, the latest advances in the exploitation of the bioactivity of photosynthetically active micro-organisms are explored in terms of the production of secondary metabolites and hydrogen.

Biofuel cells Based on the Immobilization of Photosynthetically Active Bioentities

Natural photosynthesis is a highly efficient process that uses sunlight irradiation to convert carbon dioxide into value‐added biomass. This review summarizes the recent advances in the transformation of solar energy into electrical power through the exploitation of photosynthetically active proteins, organelles, and living cells. During the past decade, the considerable progress made in bioentities immobilization offers the possibility to integrate biological systems into electronic devices. Even though solar energy technologies are gaining increasing attention, photosynthetic biofuel cells are still in their infancy. Advances in materials science are necessary to protect, stabilize, and even increase the catalytic performance of bioentities. Moreover, host materials could guarantee higher loading and better electrical charge transport, which would be crucial in the commercial success of biofuel cells. In the future, such semi‐artificial hybrid assemblies could hold promise as sustainable sources of energy.

Novel photosynthetic CO2 bioconvertor based on green algae entrapped in low-sodium silica gels

A photosynthetic bioreactor for CO2 assimilation has been designed using silica sol–gel immobilisation technologies with the chlorophyta Botryococcus braunii (Kutzing) and Chlorella vulgaris (Beijerinck). The living hybrid gels formed revealed a mesoporosity that enabled diffusion of nutrients and gases, promoting the light and dark photosynthetic reactions from within the bulk of the material. To determine the efficiency of the photosynthetic bioreactor in terms of CO2 remediation, the activity and viability of the encapsulated cells have been monitored through oximetry, 14C assimilation, pulse amplitude modulation fluorimetry and confocal microscopy, revealing a long term productivity of living hybrid materials capable of photosynthetic processes for at least 80 days. Structural and textural properties of the gels were established through 29Si MASNMR and N2 physisorption respectively.

Design of photochemical materials for carbohydrate production via the immobilisation of whole plant cells into a porous silica matrix

Photochemical materials that act as bioreactors by exploiting the photosynthesis mechanism have been fabricated by entrapping whole plant cells within a porous silica matrix. The immobilisation step has been achieved via the in situ co-polymerisation of an aqueous silica precursor and a biocompatible trifunctional silane directly around cells. The cells remain undivided whilst the photochemical activity of the cells is well preserved over time. The design of a photochemical material that can act like a leaf, converting water into O2 and produce valuable organic compounds from CO2 under light irradiation is described. In particular, the increased excretion of polysaccharides by this photochemical material has been highlighted. The organic compounds formed have been extracted and analysed. The success of this work could open the door to new exciting photochemical materials with long-term photosynthetic activity and stability and to new green chemical processes for the conversion of solar energy into chemical energy with a concomitant reduction in CO2.

Selective and reusable iron(II)-based molecular sensor for the vapor-phase detection of alcohols

A mononuclear iron(II) neutral complex (1) is screened for sensing abilities for a wide spectrum of chemicals and to evaluate the response function toward physical perturbation like temperature and mechanical stress. Interestingly, 1 precisely detects methanol among an alcohol series. The sensing process is visually detectable, fatigue-resistant, highly selective, and reusable. The sensing ability is attributed to molecular sieving and subsequent spin-state change of iron centers, after a crystal-to-crystal transformation.

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.

Hybrid photosynthetic materials derived from microalgae Cyanidium caldarium encapsulated within silica gel.

Cyanidium caldarium (Tilden) Geitler SAG 16.91 has been encapsulated within a porous silica host structure to target novel photosynthetic hybrid materials suitable for use in solar cells or CO(2) fixation. C. caldarium cells are both thermophilic and acidophilic; on account of these tolerances the hybrid materials could be employed in more extreme heat conditions. TEM highlights that the external cell membrane can remain intact after encapsulation. The images reveal an alignment of silica gel around the external membrane of the cell, providing evidence that the cell wall acts as both a nucleation and polymerisation site for silica species and that the silica scaffold formed by the aggregation of colloidal particles, generates a porosity that can facilitate the transport of nutrients towards the cell. Epifluorescence microscopy and UV-visible spectroscopy have revealed the preservation of photosynthetic apparatus post-immobilisation. Productivity studies showed how the presence of silica nanoparticles within the matrix can adversely interact with the exterior cellular structures preventing the production of oxygen through photosynthesis.

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 todays society because it leads to global warming. Photosynthesis is Natures 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.