Alexandre Léonard

Mechanical testing of electrospun PCL fibers

Poly(ε-caprolactone) (PCL) fibers ranging from 250 to 700 nm in diameter were produced by electrospinning a polymer tetrahydrofuran/N,N-dimethylformamide solution. The mechanical properties of the fibrous scaffolds and individual fibers were measured by different methods. The Youngs moduli of the scaffolds were determined using macro-tensile testing equipment, whereas single fibers were mechanically tested using a nanoscale three-point bending method, based on atomic force microscopy and force spectroscopy analyses. The modulus obtained by tensile-testing eight different fiber scaffolds was 3.8±0.8 MPa. Assuming that PCL fibers can be described by the bending model of isotropic materials, a Youngs modulus of 3.7±0.7 GPa was determined for single fibers. The difference of three orders of magnitude observed in the moduli of fiber scaffolds vs. single fibers can be explained by the lacunar and random structure of the scaffolds.

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).

Surfactant-assisted synthesis of unprecedented hierarchical meso-macrostructured zirconia

A surfactant-assisted one-step synthesis route was developed, leading to the formation of a very high surface area (600 m2 g−1) of zirconia and unprecedented hierarchical meso-macroporous structure with wormhole-like mesoporous walls and a novel, uniform assembly of macropores ranging in size from 300 to 500 nm.

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.

One-pot surfactant assisted synthesis of aluminosilicate macrochannels with tunable micro- or mesoporous wall structure

A one-step surfactant assisted synthesis pathway was developed leading to novel hierarchical macro-meso- (or micro-)porous aluminosilicates made of an assembly of macrochannels with openings between 0.5 and 2.0 microm and wormhole-like amorphous walls with tunable pore sizes.

A novel and template-free method for the spontaneous formation of aluminosilicate macro-channels with mesoporous walls

A simple and template-free synthesis pathway was developed leading to hierarchical meso-macroporous aluminosilicates made of an assembly of macro-channels with openings between 0.5 and 2.0 microm and mesoporous walls.

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.

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

The encapsulation of living plant cells into materials could offer the possibility to develop new green biochemical technologies. With the view to designing new functional materials, the physiological activity and cellular response of entrapped cells within different silica-based matrices have been assessed. A fine-tuning of the surface chemistry of the matrix has been achieved by the in situ copolymerization of an aqueous silica precursor and a biocompatible trifunctional silane bearing covalently bound neutral sugars. This method allows a facile control of chemical and physical interactions between the entrapped plant cells and the scaffold. The results show that the cell-matrix interaction has to be carefully controlled in order to avoid the mineralization of the cell wall which typically reduces the bioavailability of nutrients. Under appropriate conditions, the introduction of a trifunctional silane (ca. 10%) during the preparation of hybrid gels has shown to prolong the biological activity as well as the cellular viability of plant cells. The relations of cell behavior with some other key factors such as the porosity and the contraction of the matrix are also discussed.

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.