Synthesis and characterization of thermosensitive and pH-sensitive block copolymers based on polyetheramine and pullulan with different length

Carbohydr Polym Special Issue Invited contribution: Click chemistry for block polysaccharides with dihydrazide and dioxyamine linkers - A review

Engineered block polysaccharides is a relatively new class of biomacromolecules consisting of chemical assembly of separate block structures at the chain termini. In contrast to conventional, laterally substituted polysaccharide derivatives, the block arrangement allows for much higher preservation of inherent chain properties such as biodegradability and stimuli-responsive self-assembly, while at the same time inducing new macromolecular properties. Abundant, carbon neutral, and even recalcitrant biomass is an excellent source of blocks, opening for numerous new uses of biomass for a wide range of novel biomaterials. Among a limited range of methodologies available for block conjugation, bifunctional linkers allowing for oxyamine and hydrazide 'click' reactions have recently proven useful additions to the repertoire. This article focuses the chemistry and kinetics of these reactions. It also presents some new data with the aim to provide useful protocols and methods for general use towards new block polysaccharides.

Photopolymerizable pullulan: Synthesis, self-assembly and inkjet printing

HYPOTHESIS

Pullulan, an exopolysaccharide consisting of maltotriose repeating units, has recently found many applications in different fields, such as food, packaging, cosmetics and pharmaceuticals. The introduction of photo-crosslinkable methacrylic units potentially allows to use pullulan derivative in inkjet 3D printing.

EXPERIMENTS

Pullulan was functionalized with methacrylic groups and the derivative was characterized by NMR, FT-IR and Raman spectroscopy. Water dispersions were thoroughly investigated by optical microscopy, SAXS and rheology to evaluate the self-assembly properties and they were used as photo-crosslinkable inks in a 3D printer, also in comparison with pristine pullulan. The structural and mechanical properties of the obtained films were studied by Atomic Force Microscopy and tensile strength tests.

FINDINGS

The introduction of methacrylic groups moderately affects the self-assembly of the polymer in water, resulting in a slight increase of the gyration radius of the polymer coils and in a small decrease of the viscosity, retaining the typical shear-thinning behavior of concentrated polysaccharides in water. The structural and mechanical properties of the 3D printed films are much more affected, showing the presence of sub-micrometric phase segregated domains which are further separated by the cross-linking. As a result, the deformability of the materials is improved, with a lower tensile strength.

Examining the Use of Nanocellulose Composites for the Sorption of Contaminants of Emerging Concern: An Experimental and Computational Study

The occurrence of contaminants of emerging concern (CECs) in water is an environmental issue that must be addressed to avoid damage to ecosystems and human health. Inspired by this current issue, in this work, we fabricated nanocellulose (NC) particles grafted with the block copolymer Jeffamine ED 600 (NC-Jeffamine) capable of adsorbing acetaminophen, sulfamethoxazole, and N,N-diethyl-meta-toluamide (DEET) from aqueous solution by electrostatic interactions. NC-Jeffamine composites were prepared by carboxylation of the NC surface via 2,2,6,6-tetramethyl-1-piperidinyloxy oxidation followed by the covalent attachment of Jeffamine using the N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide/N-hydroxysulfosuccinimide sodium salt reaction. The reaction was followed and confirmed by Fourier transform infrared and conductometric titration. The physical characterization was performed by thermogravimetric analysis, Brunauer-Emmett-Teller analysis, scanning electron microscopy, dynamic light scattering, and Z-potential analysis. This material was used to study the adsorption profile of three CECs in deionized water, namely, acetaminophen, sulfamethoxazole, and DEET. The adsorption isotherms were obtained at pH 3, 7, and 9, where the best adsorption results corresponded to pH 9 because of the uniform dispersion of the adsorbate in solution. A computational study based on the density functional theory determined that the possible interactions of the CECs with the adsorbent material were related to hydrogen bonds and/or van der Waals forces. The calculated binding energies were used as a descriptor to characterize the optimum adsorption site of CECs onto NC-Jeffamine.

Thermoresponsive graphene oxide - starch micro/nanohydrogel composite as biocompatible drug delivery system

Introduction: Stimuli-responsive hydrogels, which indicate a significant response to the environmental change (e.g., pH, temperature, light, …), have potential applications for tissue engineering, drug delivery systems, cell therapy, artificial muscles, biosensors, etc. Among the temperature-responsive materials, poly (N-isopropylacrylamide) (PNIPAAm) based hydrogels have been widely developed and their properties can be easily tailored by manipulating the properties of the hydrogel and the composite material. Graphene oxide (GO), as a multifunctional and biocompatible nanosheet, can efficiently improve the mechanical strength and response rate of PNIPAAm-based hydrogels. Here, hydrogel composites (HCs) of PNIPAAm with GO was developed using the modified starch as a biodegradable cross-linker. Methods: Micro/nanohydrogel composites were synthesized by free radical polymerization of NIPAAm in the suspension of different feed ratio of GO using maleate-modified starch (St-MA) as cross-linker and Tetrakis (hydroxymethyl) phosphonium chloride (THPC) as a strong oxygen scavenger. The HCs were characterized by FT-IR, DSC, TGA, SEM, and DLS. Also, the phase transition, swelling/deswelling behavior, hemocompatibility and biocompatibility of the synthesized HCs were investigated. Results: The thermal stability, phase transition temperature and internal network crosslinking of HCs increases with increasing of the GO feed ratio. Also, the swelling/deswelling, hemolysis, and MTT assays studies confirmed that the HCs are a fast response, hemocompatible and biocompatible materials. Conclusion: The employed facile approach for the synthesis of HCs yields an intelligent material with great potential for biomedical applications.

Microfluidics-assisted generation of stimuli-responsive hydrogels based on alginates incorporated with thermo-responsive and amphiphilic polymers as novel biomaterials

We used a droplet-based microfluidics technique to produce monodisperse responsive alginate-block-polyetheramine copolymer microgels. The polyetheramine group (PEA), corresponding to a propylene oxide /ethylene oxide ratio (PO/EO) of 29/6 (Jeffamine(®) M2005), was condensed, via the amine link, to alginates with various mannuronic/guluronic acids ratios and using two alginate:jeffamine mass ratios. The size of the grafted-alginate microgels varied from 60 to 80 μm depending on the type of alginate used and the degree of substitution. The droplet-based microfluidics technique offered exquisite control of both the dimension and physical chemical properties of the grafted-alginate microgels. These microgels were therefore comparable to isolated grafted-alginate chains in retaining both their amphiphilic and thermo-sensitive properties. Amphiphilicity was demonstrated at the oil-water interface where grafted-alginate microgels were found to decrease interfacial tension by ∼ 50%. The thermo-sensitivity of microgels was clearly demonstrated and a 10 to 20% reduction in size between was evidenced on increasing the temperature above the lower critical solution temperature (TLCST) of Jeffamine. In addition, the reversibility of thermo-sensitivity was demonstrated by studying the oil-water affinity of microgels with temperature after Congo red labeling. Finally, droplet-based microfluidics was found to be a good and promising tool for generating responsive biobased hydrogels for drug delivery applications and potential new colloidal stabilizers for dispersed systems such as Pickering emulsions.

Nano-thermometers with thermo-sensitive polymer grafted USPIOs behaving as positive contrast agents in low-field MRI

Two commercial statistical copolymers of ethylene oxide and propylene oxide, Jeffamine® M-2005 (PEO5-st-PPO37) and M-2070 (PEO46-st-PPO13), exhibiting lower critical solution temperature (LCST) in water, were grafted onto the surface of ultra-small superparamagnetic iron oxide nanoparticles (USPIOs) using silanization and amide-bond coupling reactions. The LCSTs of the polymers in solution were measured by dynamic light scattering (DLS) and nuclear magnetic resonance (NMR). In accordance with the compositions of EO vs. PO, the transition temperature was measured to be 22 ± 2 °C for M-2005 by both DLS and NMR, while the LCST was much higher, 52 ± 2 °C, for M-2070 (a second transition was also detected above 80 °C by NMR in that case, ascribed to the full dehydration of chains at the molecular level). The resulting polymer-grafted USPIOs exhibit a temperature-responsive colloidal behaviour, their surface reversibly changing from hydrophilic below LCST to hydrophobic above it. This phenomenon was utilised to design thermo-sensitive contrast agents for MRI. Transverse relaxivities (r2) of the USPIO@PEO5-st-PPO37 core-shell nanoparticles were measured at 8.25, 20, 60, and 300 MHz. Nuclear magnetic resonance dispersion (NMRD) profiles, giving longitudinal relaxivities (r1) between 0.01 and 60 MHz, were acquired at temperatures ranging from 15 to 50 °C. For all tested frequencies except 300 MHz, both r1 and r2 decrease with temperature and show an inflection point at 25 °C, near the LCST. To illustrate the interest of such polymer-coated USPIOs for MRI thermometry, sample tubes were imaged on both low-field (8.25 MHz/0.194 Tesla) and high-field (300 MHz/7.05 Tesla) MRI scanners with either T1- or T2*-weighted spin echo sequences. The positive contrast on low-field MR images and the perfect linearity of the signal with a T2*-weighted sequence over the entire temperature range 15-50 °C render these LCST polymer coated USPIOs interesting positive contrast agents, also working as "nano-thermometers".

Biodegradable oligo (poly-l-lysine) as a high-performance hydration inhibitor for shale

Oligo (poly-l-lysine) (OPLL), utilized as a high-performance inhibitor for the hydration of shale, was synthesized with l-lysine as a monomer by the thermal copolymerization method.

Two methods for one-point anchoring of a linear polysaccharide on a gold surface

Two strategies to achieve a one-point anchoring of a hydrolyzed pullulan (P9000) on a gold surface are compared. The first strategy consists of forming a self-assembled monolayer of a 6-amino-1-hexanethiol (AHT) and then achieving reductive amination on the surface between the aminated surface and the aldehyde of the polysaccharide reductive end sugar. The second consists of incorporating a thiol function at the extremity of the pullulan (via the same reductive amination), leading to P9000-AHT and then immobilizing it on gold by a spontaneous reaction between solid gold and thiol. The modified pullulan was characterized by NMR and size-exclusion chromatography coupled to a light-scattering detector. P9000-AHT appears to be in a disulfide dimer form in solution but recovers its unimer form with dithiothreitol (DTT) treatment. The comparison of the two strategies by contact angle and XPS revealed that the second strategy is more efficient for the pullulan one-point anchoring. P9000-AHT even in its dimer form is easily grafted onto the surface. The grafted polymer seems to be more in a coil conformation than in a rigid brush. Furthermore, QCM measurements highlighted that the second strategy leads to a grafting density of around 3.5 × 10(13) molecules·cm(-2) corresponding to a high surface coverage. The elaboration of a dense and oriented layer of polysaccharides covalently linked to a gold surface might enhance the use of such modified polysaccharides in various fields.

Sulfated glycosaminoglycan-based block copolymer: preparation of biocompatible chondroitin sulfate-b-poly(lactic acid) micelles

Despite a growing interest in amphiphilic polysaccharide-based diblock copolymers as functional polymeric drug delivery nanosystems, biologically relevant sulfated glycosaminoglycan systems were not yet investigated. Here, we report the synthesis and the self-assembly properties in water of chondroitin sulfate-b-poly(lactic acid) (CS-b-PLA(n)). The CS-b-PLA(n) were synthesized using click-grafting onto method implying reducing-end alkynation of low-molecular weight depolymerized CS (M(w) = 5000 g·mol(-1)) and azide-terminated functionalization of PLAn (M(w) = 6500 g·mol(-1) (n = 46) and M(w) = 1700 g·mol(-1) (n = 20)). The diblock copolymer self-assembled in water giving rise to spherical micelles that were characterized in solution using dynamic/static light scattering and at dry state by TEM technique. In vitro assays on healthy cells showed that at high concentrations, up to 10 μg·mL(-1), CS-b-PLA(n) were noncytotoxic. Those preliminary studies are promising in the perspective to use them as biocompatible nanovehicles for anticancer drug delivery.

Self-assembly of maltoheptaose-block-polystyrene into micellar nanoparticles and encapsulation of gold nanoparticles

The present paper discusses the controlled self-assembly of sugar-containing block copolymer, maltoheptaose-block-polystyrene (MH(1.2k)-b-PS(4.5k)), into micellar nanoparticles of ca. 30 nm radius in aqueous media and their possibility of gold encapsulation. Micellar association of MH(1.2k)-b-PS(4.5k) into nanoparticles was demonstrated by mixing a large amount of water (MH-selective solvent) with a solution of MH(1.2k)-b-PS(4.5k) in a mixture of tetrahydrofuran (THF) (PS-selective solvent) and water with a certain weight fraction [4:1 (w/w) THF/water], where MH(1.2k)-b-PS(4.5k) exists as well-swollen single chains, followed by evaporation of THF. The mean hydrodynamic radii (Rh) of the nanoparticles were determined by dynamic light scattering (DLS) to be ca. 30 and 80 nm depending upon the method of preparation. The resulting nanoparticles were clearly visualized by transmission electron microscopy (TEM), atomic force microscopy (AFM), and field emission gun-scanning electron microscopy (FEG-SEM) imaging and complemented by nanoparticle tracking analysis (NTA) using a NanoSight instrument. The preliminary study of the self-assembly of MH(1.2k)-b-PS(4.5k) in the presence of gold nanoparticles functionalized with PS chains grafted on their surface indicated potential possibilities of encapsulation of gold nanoparticles into the block copolymer nanoparticles in aqueous media.