Grafting of proteins onto polymeric surfaces: A synthesis and characterization challenge.

This review aims at answering the following question: how can a researcher be sure to succeed in grafting a protein onto a polymer surface? Even if protein immobilization on solid supports has been used industrially for a long time, hence enabling natural enzymes to serve as a powerful tool, emergence of new supports such as polymeric surfaces for the development of so-called intelligent materials requires new approaches. In this review, we introduce the challenges in grafting protein on synthetic polymers, mainly because compared to hard surfaces, polymers may be sensitive to various aqueous media, depending on the pH or reductive molecules, or may exhibit state transitions with temperature. Then, the specificity of grafting on synthetic polymers due to difference of chemical functions availability or difference of physical properties are summarized. We present next the various available routes to covalently bond the protein onto the polymeric substrates considering the functional groups coming from the monomers used during polymerization reaction or post-modification of the surfaces. We also focus our review on a major concern of grafting protein, which is avoiding the potential loss of function of the immobilized protein. Meanwhile, this review considers the different methods of characterization used to determine the grafting efficiency but also the behavior of enzymes once grafted. We finally dedicate the last part of this review to industrial application and future prospective, considering the sustainable processes based on green chemistry.

Mechanistic insights into the formation of polyion complex aggregates from cationic thermoresponsive diblock copolymers.

HYPOTHESIS: The formation of polyion complexes (PICs) comprising thermoresponsive polymers is intended to result in the formation of aggregates that undergo significant structural changes with temperature. Moreover the observed modifications might be critically affected by polymer structure and PICs composition. EXPERIMENTS: Different block copolymers based on cationic poly(3-acrylamidopropyltrimethylammonium chloride) and thermoresponsive poly(N-isopropylacrylamide) were synthesized by aqueous RAFT/MADIX polymerization at room temperature. Addition of poly(acrylic acid) in a controlled fashion led to the formation of PICs aggregates. The structural changes induced by temperature were characterized by differential scanning calorimetry, Nuclear Magnetic Resonance spectroscopy and scattering methods. FINDINGS: Thermoresponsive PICs undergo significant structural changes when increasing temperature above the cloud point of the thermoresponsive block. The reversibility of these phenomena depends strongly on the structural parameters of the block copolymers and on PICs composition.

Extended photo-induced endosome-like structures in giant vesicles promoted by block-copolymer nanocarriers.

Upon irradiation, the photosensitizer pheophorbide-a causes dramatic morphological transitions in giant unilamellar lipid vesicles. This endocytosis-like process occurs only when the photoactive species are encapsulated in a copolymer nanocarrier and strictly depends on the chemical nature of the copolymer. Altogether, these results open up new perspectives in the field of photo-chemical internalization mediated by nanoassemblies.

Transport of nano-objects in narrow channels: influence of Brownian diffusion, confinement and particle nature.

This paper presents experimental results about transport of dilute suspensions of nano-objects in silicon-glass micrometric and sub-micrometric channels. Two kinds of objects are used: solid, rigid latex beads and spherical capsule-shaped, soft polymersomes. They are tracked using fluorescence microscopy. Three aspects are studied: confinement (ratio between particle diameter and channel depth), Brownian diffusion and particle nature. The aim of this work is to understand how these different aspects affect the transport of suspensions in narrow channels and to understand the different mechanisms at play. Concerning the solid beads we observe the appearance of two regimes, one where the experimental mean velocity is close to the expected one and another where this velocity is lower. This is directly related to a competition between confinement, Brownian diffusion and advection. These two regimes are shown to be linked to the inhomogeneity of particles distribution in the channel depth, which we experimentally deduce from velocity distributions. This inhomogeneity appears during the entrance process into the sub-micrometric channels, as for hydrodynamic separation or deterministic lateral displacement. Concerning the nature of the particles we observed a shift of transition towards the second regime likely due to the relationships between shear stress and polymersomes mechanical properties which could reduce the inhomogeneity imposed by the geometry of our device.

Hybrid vesicles from lipids and block copolymers: Phase behavior from the micro- to the nano-scale.

In recent years, there has been a growing interest in the formation of copolymers-lipids hybrid self-assemblies, which allow combining and improving the main features of pure lipids-based and copolymer-based systems known for their potential applications in the biomedical field. In this contribution we investigate the self-assembly behavior of dipalmitoylphosphatidylcholine (DPPC) mixed with poly(butadiene-b-ethyleneoxide) (PBD-PEO), both at the micro- and at the nano-length scale. Epifluorescence microscopy and Laser Scanning Confocal microscopy are employed to characterize the morphology of micron-sized hybrid vesicles. The presence of fluid-like inhomogeneities in their membrane has been evidenced in all the investigated range of compositions. Furthermore, a microfluidic set-up characterizes the mechanical properties of the prepared assemblies by measuring their deformation upon flow: hybrids with low lipid content behave like pure polymer vesicles, whereas objects mainly composed of lipids show more variability from one vesicle to the other. Finally, the structure of the nanosized assemblies is characterized through a combination of Dynamic Light Scattering, Small Angle Neutron Scattering and Transmission Electron Microscopy. A vesicles-to-wormlike transition has been evidenced due to the intimate mixing of DPPC and PBD-PEO at the nanoscale. Combining experimental results at the micron and at the nanoscale improves the fundamental understanding on the phase behavior of copolymer-lipid hybrid assemblies, which is a necessary prerequisite to tailor efficient copolymer-lipid hybrid devices.

Comparison of methods for the fabrication and the characterization of polymer self-assemblies: what are the important parameters?

The ability to self-assemble was evaluated for a large variety of amphiphilic block copolymers, including poly(ethyleneoxide-b-ε-caprolactone), poly(ethyleneoxide-b-d,l-lactide), poly(ethyleneoxide-b-styrene), poly(ethyleneoxide-b-butadiene) and poly(ethyleneoxide-b-methylmethacrylate). Different methods of formation are discussed, such as cosolvent addition, film hydration or electroformation. The influence of experimental parameters and macromolecular structures on the size and morphology of the final self-assembled structures is investigated and critically compared with the literature. The same process is carried out regarding the characterization of these structures. This analysis demonstrates the great care that should be taken when dealing with such polymeric assemblies. If the morphology of such assemblies can be predicted to some extent by macromolecular parameters like the hydrophilic/hydrophobic balance, those parameters cannot be considered as universal. In addition, external experimental parameters (methods of preparation, use of co-solvent, …) appeared as critical key parameters to obtain a good control over the final structure of such objects, which are very often not at thermodynamic equilibrium but kinetically frozen. A principal component analysis is also proposed, in order to examine the important parameters for forming the self-assemblies. Here again, the hydrophilic/hydrophobic fraction is identified as an important parameter.

Sorption properties of functionalized liquid crystalline networks.

Functionalized polydomain chiral elastomers were obtained by cross-linking side-chain liquid crystalline polysiloxanes bearing acid functions. Sorption experiments were performed by the use of an electronic microbalance, in the presence of one enantiomer of a chiral amine molecule, able to interact with the acid groups. The results showed that Fick's diffusion law is not valid anymore as soon as an interaction between the material and the molecule is present. Moreover, it was demonstrated that the grafting of interacting groups on a chiral elastomer enhanced both the capacity and selectivity toward one enantiomer.

Analysis of commercial plastination agents.

S3, S6 and S10 are the most commonly used agents for tissue plastination. Surprisingly, their chemical structures are not known. We therefore decided to fully characterize these products by standard analytical methods: multinucleus magnetic resonance, infrared spectroscopy and size exclusion chromatography. These experiments have shown that Biodur S10 is a polydimethylsiloxane with a molecular weight of 27,200 and silanol functionalities, Biodur S6 is tetraethoxysilane, and Biodur S3 is a mixture the main component of which is dibutyltindilaurate.

Study of a (trimethylenecarbonate-co-epsilon-caprolactone) polymer part 1: preparation of a new nerve guide through controlled random copolymerization using rare earth catalysts.

Random copolymers of trimethylene carbonate and epsilon-caprolactone have been synthesized through ring-opening polymerization using rare earth alkoxides as initiator. The structure of the copolymers has been characterized by 1H and 13C NMR. Their thermal behaviour, their permeability to liquid and their mechanical properties have also been evaluated. These copolymers have been used to process a new nerve guide.