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Spectroscopic ellipsometry is increasingly used for investigation of biofilms and biological materials because of its non-invasive manner. In case of biofilms, the investigated material might be present on the surface only in small amounts forming an island-like coating. In this work we investigate the applicability of different ellipsometric models for such discontinuous biofilms. We used various types of peptides for which adhesion differences in the case of deposition to n- and p-type silicon were theoretically determined in [1]. Since the adhesion of these types of peptides to differently doped silicon significantly differs, resulting in selective deposition of peptides from liquid solutions, the applicability of the ellipsometric models can be tested sufficiently. [1] S. K. Ramakrishnan, M. Martin, T. Cloitre, L. Firlej, C. Gergely, Molecular Mechanism of Selective Binding of Peptides to Silicon Surface. J. Chem. Inf. Model. 54, 2117 (2014).

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Casein micelles (CMs) are colloidal protein-mineral complexes in equilibrium in the milk serum. Their enzymatic cross-linking by transglutaminase (TGase) allow a modification of their characteristics. The aim of this work is to determine the impact of this modification on their characteristics (size and elastic properties) in a native liquid environment by atomic force microscopy (AFM). The challenge is to immobilize the particles on a surface in their natural state in order to investigate the effect of covalent cross-linking in a simulated milk ultrafiltrate (SMUF).

Commentaires: le titre est différent sur site de la conférence Elsevier "Investigation of properties of casein micelles depleted in beta casein by atomic force microscopy performed in liquid environment"

Ref HAL: hal-01212814_v1
DOI: 10.1021/acs.langmuir.5b02857
WoS: 000364354800015
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7 Citations
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Engineering peptides that present selective recognition and high affinity towards a material is a major challenge for assembly-driven elaboration of complex systems with wide applications in the field of biomaterials, hard-tissue regeneration and functional materials for therapeutics. Peptide–material interactions are of vital importance in natural processes, but less exploited for the design of novel systems for practical applications due to poor understanding of mechanisms underlying these interactions. Here, we present an approach based on the synthesis of several truncated peptides issued from a silicon-specific peptide recovered via phage display technology. We use the photonic response provided by porous silicon microcavities to evaluate the binding efficiency of fourteen different peptide derivatives. We identify and engineer a short peptide sequence (SLVSHMQT) revealing the highest affinity towards p+ -Si. The molecular recognition behavior of the obtained peptide fragment can be revealed through mutations enabling identification of the preferential affinity of certain amino acids towards silicon. These results constitute an advance in both the engineering of peptides that reveal recognition properties for silicon and the understanding of biomolecule-material interactions.

Ref HAL: hal-01179792_v1
DOI: 10.1007/s00705-015-2515-y
WoS: 000361817600004
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5 Citations
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Several variants of the major ‘‘a’’ determinant of the HBsAg, the main target of HBV neutralization by antibodies, have been described. However, mutations out- side this region have not been as thoroughly investigated. During the genotyping of HBV from Tunisian patients with chronic hepatitis B, we identified a variant with a C69R substitution in the cytosolic loop of the S protein, resulting in a change in the hydrophobicity profile compared to the wild-type HBsAg. Wild-type and mutant HBsAgs were produced in Saccharomyces cerevisiae and recombinant proteins were tested for their ability to correctly self- assemble into virus-like particles (VLPs), and their ability to bind to HBs antibodies. The C69R substitution resulted in a decrease in binding to commercial anti-HBs antibod- ies, and although the variant appeared to assemble properly into VLPs, the average size of the particles was larger than that of the wild-type HBsAg. Prediction of the tertiary structure of the C69R mutant revealed a change in the first (aa 60-70) and the second loop (aa 110 to 120) compared to the wild-type protein. Furthermore, we showed by an isothermal titration calorimetry assay that the interaction between the wild-type HBsAg and the anti-HBs antibody was exothermic, whereas that with the mutant C69R was endothermic, indicating an effect on the binding affinity.

Ref HAL: hal-01743361_v1
DOI: 10.1021/am4046316
WoS: 000331493200052
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49 Citations
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In regenerative medicine, stem cell-based therapy often requires a scaffold to deliver cells and/or growth factors to the injured site. Porous silicon (pSi) is a promising biomaterial for tissue engineering as it is both non-toxic and bioresorbable. Moreover, surface modification can offer control over the degradation rate of pSi and can also promote cell adhesion. Dental pulp stem cells (DPSC) are pluripotent mesenchymal stem cells found within the teeth and constitute a readily source of stem cells. Thus, coupling the good proliferation and differentiation capacities of DPSC with the textural and chemical properties of the pSi substrates provides an interesting approach for therapeutic use. In this study, the behavior of human DPSC is analyzed on pSi substrates presenting pore of various sizes, 10 ± 2 nm, 36 ± 4 nm and 1.0 ± 0.1 μm, and undergoing different chemical treatments: thermal oxidation, silanization with aminopropyltriethoxysilane (APTES), and hydrosilylation with undecenoic acid or semicarbazide. DPSC adhesion and proliferation were followed for up to 72 h by fluorescence microscopy, scanning electron microscopy (SEM), enzymatic activity assay, and BrdU assay for mitotic activity. Porous Silicon with 36 nm pore size was found to offer the best adhesion and the fastest growth rate for DPSC compared to pSi comporting smaller pore size (10 nm) or larger pore size (1 μm), especially after silanization with APTES. Hydrosilylation with semicarbazide favored cell adhesion and proliferation, especially mitosis after cell adhesion, but such chemical modification has been found to led to a scaffold that is stable for only 24 to 48 h in culture medium. Thus, semicarbazide-treated pSi appeared to be an appropriate scaffold for stem cell adhesion and immediate in vivo transplantation, while APTES-treated pSi was found to be more suitable for long term in vitro culture, for stem cells proliferation and differentiation.

Ref HAL: hal-01114990_v1
DOI: 10.1039/c4cp05112b
WoS: 000349005900028
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14 Citations
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Understanding the mechanism of biomolecules’ interaction with inorganic surfaces might pave the way for the design of material interfaces with controlled and highly predictable properties. Here we have focused on the adsorption mechanism of facet-specific amino acids in the sequence of peptides selected for programmed synthesis of Pt(111) and Pt(100) nanocrystals. Using the first principles calculations we have demonstrated that the specific surface recognition of amino acid side chains occurs due to the combination of multiple processes: electron exchange, partial charge transfer and/or dispersive effects providing a high binding affinity to both polar and non-polar residues against both Pt facets. Our approach points towards promising novel routes for controlled design of material-specific linkers for future materials engineering.