The treatment of bone traumas and fractures concerns a yearly market of about one million patients in the EU and the US. Bone is the most often transplanted tissue, with up to one million grafts realized each year in Europe only. Autografts (tissue that is taken from one part of a person's body and transplanted to a different part of the same person) are ideally suited to repair bones from an immunology standpoint; however, they require to harvest bone in the patient, which needs to perform a second operation with possible associated complications; in addition, large reconstructions remain difficult. Allografts (a tissue graft from a donor genetically unrelated to the recipient) are essentially obtained from decellularized bone scaffolds taken from human cadavers; although quite efficient regarding the scaffold structure itself, they may cause possible adverse immunologic reactions. In addition, their osteoinductive properties are limited.

In native bone, osteoblasts (bone cells), osteogenic precursors and endothelial cells (cells that lines the interior surface of blood vessels) interact in a synergetic way towards the coordinated development of vasculature and mineralized tissue; therefore, close spatial relationships are established between the two tissues in the forming bone: the vascular network acts as a ‘template’ for the deposition of bone mineral (Figure 1).

Figure 1

The study of Mesenchymal Stem Cells (MSC, stem cells able to generate osteoblast and then bone) has raised the hope of a cell-based therapy for tissue engineering due to their high availability based on self-renewal and their high capability of differentiation into different kind of cells. Identification of factors that maintain their stemness properties, monitor and control MSC differentiation is crucial. In vivo, cells evolve following nanoscale physical and chemical signals they receive from ExtraCellular Matrix (ECM) surrounding cells. The challenge lies in synthesizing materials able to reproduce these processes. Such materials could be used for implantation, but also as physiologically relevant models in basic and translational studies of bone development, disease and drug discovery.

The objective of our project is to create new bioactive nano-, micro-structured surfaces able to maintain MSC in their stem state or to allow their selective differentiation.

This thesis, co-supervised between Universities Bordeaux and Luxembourg, will focus on surface patterning that would be easily transposable to 3D scaffolds, and the study of the behavior of MSC's on these surfaces with the aim to favor differentiation towards osteoblast cells or, conversely, to preserve stemness. The thesis will be a joint PhD between ULuxembourg/LIST research center and UBordeaux, with Dr. S. Krishnamoorthy as recognized expert for the controlled nanoscale patterning of surfaces using combination of self-assembly and lithography techniques and Dr. D. Lenoble for nanoscale materials engineering and physics, and Dr. MC. Durrieu and Dr L. Plawinski specialized in the behavior of MSC's on micro- and nano-patterned surfaces.

This thesis will be performed in close collaboration with SCREVO industry. SCREVO is involved as industrial partner due to its expertise in implantable 3D macroarray systems that can be used to investigate cell interactions with environment, and cell-functions. SCREVO’s devices have already been tested as 3D screening of optimal cartilage regeneration condition in mice models, using co-cultures of MSCs and primary bovine chondrocytes [1]. The bidirectional feedback of mutual benefit between the LIST-UBordeaux collaboration and SCREVO is envisaged - The consortium benefits from access to relevant technology expertise from SCREVO, providing insights for applied aspects of this thesis; SCREVO would stand to benefit from the consortium’s feedback in enhancing/developing its existing product line and towards development of new products.

The thesis work will investigate means of producing nanoscale morphologies at the sub-micron to nanoscale using techniques of nanoimprint lithography [2] and block copolymer self-assembly. The latter is particularly interesting, since it could be transposed to more complex geometries. The processing conditions for fabrication of the nanoscale morphologies will be controlled in a manner that allows a systematic variation in each of the geometric variable of interest in steps of a few nanometers [3].  The variation in size, distribution (periodic/aperiodic), edge-edge separations, and aspect ratios of titanium or Ti- 6Al -4V nanostructures are envisaged (Figure 2). This task will be performed by the Nano-enabled medicine and cosmetics group (NEMC) at LIST.

Figure 2: Si nanopillar arrays as an example of structured surface with controlled geometries to be investigated in this work

The titanium surfaces will be functionalized by grafting surface peptides (BMP growth factors mimetic peptides with or without cell adhesion peptides) [4] or incubated with osteoblast microvesicles and the impact of these surfaces on hMSCs adhesion and differentiation will be studied. This task will be performed by UBordeaux.

To be exposed to the environment in SCREVO, and in specific to the aspects of implants and cell-screening macroarrays of interest for the thesis. The student would also be exposed to the study of cell-functions using implants employed by SCREVO; Additional important outcomes include scientific exchanges directed at identifying potential barriers in exploitation of nanoarrays developed during the thesis into SCREVO’s implants.

At the end of the thesis, we will have clearly identified the underlying correlation between nanostructure geometry, bioactivity and MSC response, and the morphologies that dictate a desired cell response, such as preserving stemness or to determine cell differentiation pathway.

The goals of the present PhD project may be summarized as follows:
-    correlate surface nano-morphology and chemical patterning with differentiation and stemness preservation.
-    control the presence of chemical and physical cues with the possibility to tune signal localization in the vertical and lateral directions in the 100 nanometer-range, while remaining compatible with deposition on 3D porous scaffolds.

[1]  Wu L. et al., Tissue Eng Part A (2011). 17, (9-10):1425
[2]  (a) Krishnamoorthy, S. et al., ACS Applied Materials & Interfaces, 2011, 3(4), 1033 (b) Suresh, V.  et al., J. Phys. Chem. C, 2012, 116 (44), 23729-23734 (c) Krishnamoorthy, S. et al., ACS Applied Materials & Interfaces, 2011, 3(4), 1033 (d) Yap, F. L. et al., Journal of Materials Chemistry, 2010, 20, 10211
[3] (a) Krishnamoorthy, S. et al, Advanced Functional Materials, 2011, 21(6), 1102 (b) Suresh, V. et al., ACS Nano, 2013, 7(9), 7513 (c) Yap, F. L. et al., ACS Nano, 2012, 6 (3), 2056-2070
[4] (a) Durrieu MC, Biomaterials 2004, 25(19) 4837 ; (b) Durrieu MC, Biomaterials 2010 ; (c) Durrieu MC., Biomaterials 2009, 30(5) 711 ; (d) Durrieu MC, Journal of Cell Science 2012 125(5) 1217 ; (e) Durrieu MC, Biology OPEN 2013, 2(9) 872 ; (f) Durrieu MC, Biomaterials 2013, 34(9) 2157 ; (g) Durrieu MC, Nanoletters 2013, 13 3923 ; (h) Durrieu MC, ACS Nano 2013 7(4) 3351


Project Partners

Institute of Chemistry & Biology of Membranes & Nanoobjects, University Bordeaux, France

Nano-enabled medicine and cosmetics group (NEMC), Luxembourg Institute for Science and Technology

Industry Partner: SCREVO, Netherlands

Host Country (employment): France

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