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European Joint Doctorate in Functional Materials Research

Periodic Reporting for period 2 - EJD-FunMat (European Joint Doctorate in Functional Materials Research)

Reporting period: 2017-06-01 to 2019-05-31

Materials science is recognized as one of the key drivers for development of technology and knowledge-based economies. In this context, the project EJD-FunMat aimed at addressing key issues in six main materials research domains located at the interface between physics, chemistry, cell biology, biotechnology and engineering. The research fields, each addressed by a cluster of PhD projects, were: 1) efficient photocatalysts for hydrogen production and water cleaning; 2) new transparent conductors for energy, lighting and electronic displays; 3) lead-free piezoelectrics for biomedical devices, sensors and sonars; 4) composite materials for energy-efficient optical communication; 5) cellulose-based polymers for green chemistry; 6) functionalised scaffolds and templates for bone tissue engineering.
14 PhD candidates were trained not only through research training in one of the fields listed above, but also in joint training schools and workshops, covering materials science but also transversal skills, such as technology intelligence, entrepreneurship, scientific communication, and life cycle analysis of materials.
Each PhD candidate had two co-supervisors from different countries, and received a double or joint PhD degree. Three bilateral joint doctoral degrees in materials science were created as part of the project.
In photocatalysis, on one hand NiO clusters were deposited by magnetron sputtering over well-defined vertically-aligned ZnO nanorods and, on the other hand, selective deposition of co-catalyst (Ag, RuOx, Ni(B) and CoOx) on faceted BiVO4 particles have been achieved. Both approaches provide Janus type inhomogeneous films and particles showing enhanced photocatalytic properties for dye decomposition which were rationalized on the basis of band alignment determination.
In the second topic, improvement of the electrical conductivity of transparent conducting oxide (TCO) films was achieved by deposition of an oxide layer (as Al2O3) onto TCOs (as ITO) by different methods (Atomic Layer Deposition or magnetron sputtering). Similarly drastic enhancement of both thermal and electrical stabilities of silver nanowire networks was achieved by coating them with a thin layer of ZnO or Al2O3. Finally, an optimal NiO layer thickness over silicon-SiO2 wafers has been determined to reach a suitable electrochemical response for Oxygen Evolution Reaction.
For lead-free piezoelectrics BaZrO3, CaTiO3 and BCTZ single crystals were grown by the Czochralski method or a self-flux method. The BCTZ (“BaCaTiZr”) single crystals show good piezoelectric properties. In parallel a systematic theoretical study of BCTZ provided key information on the competition between ferroelectric and antiferrodistorsive instabilities and on the conditions of the emergence of a ferroelectric instability in this system. Appropriate feedback between experimental and theoretical advances should allow the development of lead-free piezoelectric materials.
In the fourth topic, lanthanide-doped sesquioxides nanoparticles have been prepared to be dispersed in organic-inorganic hybrid matrices to obtain films showing optical amplification. Furthermore, a model has been built to predict the dielectric function and the refractive index which led to a better understanding of the ingredients required for the design of optical devices. These approaches allowed selecting promising materials for energy-efficient communication technology.
In the field of green chemistry, functionalization of bacterial cellulose (BC) was first achieved by surface modification of BC with aminopropyltrimethoxysilane in order to induce antibacterial properties and to further anchor an active peptide, which is expected to confer antimicrobial activity to bacterial cellulose, notably required for applications in wound dressing. Due to the lack of stability in humid environments, BC has been then functionalized with various methoxysilanes and promising results were obtained regarding bacterial growth inhibition. Furthermore, direct functionalization of cellulose using the Ugi-5 component was realized in CO2-based switchable solvents leading to new processable functionalized celluloses, thus opening the field of cellulose-based materials. Finally, different copolymers (EVA, poly(ethylene)-b-poly(vinyl acetate) (PVAc-b-PE), and homo-telechelic poly(ethylene) (PE-X)) were prepared and used as compatibilizers to disperse, at the nanoscale, cellulose in various polymer matrices.
The classic bone tissue engineering paradigm highlights 4 key players: (1) a biocompatible scaffold that mimics the bone extracellular matrix niche, (2) osteogenic cells, (3) morphogenic signals that help to direct the cells to the phenotypically desirable type, and (4) sufficient vascularization to meet the growing tissue nutrient supply. A novel solvent-free process to prepare synthetic biodegradable and bioactive microcarriers with controllable size and porosity was developed. Such a technology is of great interest to scale up the microcarrier production to industrial level due its simplicity and environmental safety. The microporous structure of the microcarriers was shown to be very similar to demineralized bone matrix currently used. Moreover, bioactive nanostructured surfaces able to modulate human mesenchymal stem cells (hMSC) response were developed. These surfaces were prepared by nanolithography starting from self-assembled block copolymer reverse micelles templates followed by pattern-transfer using atomic layer deposition, reactive ion etching with gas plasmas, nanoimprint lithography and sputtering. The impact of these nanostructured surfaces on the differentiation of MSC is currently under investigation. In parallel, functionalized microchannels were developed using polycarbonate for the stimulation of tubulogenesis of endothelial cells.
All these systems provide very promising advances in the field of functional materials. Thus, Janus-type heterojunction films and particles favor efficient charge separation and some of the systems developed showed significant photocatalytic activities under solar light illumination. This will lead to improvements in two real-world applications – namely hydrogen production and water cleaning. Furthermore, the new films based on coated silver nanowires appeared to be suitable alternatives to existing TCOs, which include scarce elements or are limited by their brittleness. This opens new avenues in the field of electronics and smart devices. Besides the promising piezoelectric properties of “BaCaTiZr” single crystals opens new avenues to substitute lead-based piezolelectric materials in various sensors and actuators. In the field of bio-sourced polymers, different new systems based on cellulose or biocellulose gave rise to new functional polymers that can replace advantageously conventional polymers synthesized from non renewable resources. Finally although much progress has been made, many crucial hurdles remain to be cleared on the way to bone tissue engineering becoming a true clinical reality. Careful attention is thus devoted to the synthesis of smart materials with micro- and nano-structural properties, with the incorporation of biomimetic properties and/or growth factors able to favour the differentiation of stem cells in osteoblastic lineage. The impact of these smart materials on human mesenchymal stem cells (MSCs) is carefully examined.