Daniel Grande

Biocomposite scaffolds based on electrospun poly(3-hydroxybutyrate) nanofibers and electrosprayed hydroxyapatite nanoparticles for bone tissue engineering applications.

The electrospinning technique combined with the electrospraying process provides a straightforward and versatile approach for the fabrication of novel nanofibrous biocomposite scaffolds with structural, mechanical, and biological properties potentially suitable for bone tissue regeneration. In this comparative investigation, three types of poly(3-hydroxybutyrate) (PHB)-based scaffolds were engineered: (i) PHB mats by electrospinning of a PHB solution, (ii) mats of PHB/hydroxyapatite nanoparticle (nHA) blends by electrospinning of a mixed solution containing PHB and nHAs, and (iii) mats constituted of PHB nanofibers and nHAs by simultaneous electrospinning of a PHB solution and electrospraying of a nHA dispersion. Scaffolds based on PHB/nHA blends displayed improved mechanical properties compared to those of neat PHB mats, due to the incorporation of nHAs within the fibers. The electrospinning/electrospraying approach afforded biocomposite scaffolds with lower mechanical properties, due to their higher porosity, but they displayed slightly better biological properties. In the latter case, the bioceramic, i.e. nHAs, largely covered the fiber surface, thus allowing for a direct exposure to cells. The 21 day-monitoring through the use of MTS assays and SEM analyses demonstrated that human mesenchymal stromal cells (hMSCs) remained viable on PHB/nHA biocomposite scaffolds and proliferated continuously until reaching confluence.

Electrospinning as a powerful technique for biomedical applications: a critically selected survey

Abstract Nowadays, electrospinning has become one of the most versatile, easy, and cost-effective techniques to engineer advanced materials used for many applications, especially in the biomedical and environmental areas. Like the numerous patents around the world, the increasing number of papers witnesses the huge potential of this simple process, and many companies have been emerged during the last years to exploit its innumerable applications. This article presents a critically selected overview of polymers that can be used to produce nanofibers, along with the biomedical applications of the resulting electrospun scaffolds. We have focused on about seven natural and synthetic polymers, but many more can be found in the literature, either as their pristine state or as composites with ceramics, metals, and other polymers. The description of some strategies for nanofiber production, and the characterization used to evaluate their optimization, has been discussed. Finally, several polymers have been recognized as highlights for future work.

Feature Article: Design of Porous Polymeric Materials from Miscellaneous Macromolecular Architectures: An Overview

Porous polymeric materials offer a great versatility in most of the promising fields of applications. This article affords a critically selected overview of the recent synthetic strategies developed to design porous polymers and their potential applications in emerging areas of science and technology, such as analytical techniques, supported catalysis, controlled drug delivery, and so on. A large variety of macromolecular architectures can be employed in different template approaches: molecularly imprinted polymers, supramolecular assemblies, block copolymers, and polymer blends based on hyperbranched polymers are important precursors as specific template-oriented architectures for the creation of original porous polymers. Interpenetrating Polymer Networks represent a unique class of materials that have also been put forward for this purpose.

Porous structure of ion exchange membranes investigated by various techniques

A comparative review of various techniques is provided: mercury intrusion porosimetry, nitrogen sorption porosimetry, differential scanning calorimetry (DSC)-based thermoporosimetry, and standard contact porosimetry (SCP), which allows determining pore volume distribution versus pore radius/water binding energy in ion-exchange membranes (IEMs). IEMs in the swollen state have a labile structure involving micro-, meso- and macropores, whose size is a function of the external water vapor pressure. For such materials, the most appropriate methods for quantifying their porosity are DSC and SCP. Especially significant information is given by the SCP method allowing measuring porosimetric curves in a very large pore size range from 1 to 105nm. Experimental results of water distribution in homogeneous and heterogeneous commercial and modified IEMs are presented. The effect of various factors on water distribution is reviewed, i.e. nature of polymeric matrix and functional groups, method for membrane preparation, membrane ageing. A special attention is given to the effect of membrane modification by embedding nanoparticles in their structure. The porosimetric curves are considered along with the results of electrochemical characterization involving the measurements of membrane conductivity, as well as diffusion and electroosmotic permeability. It is shown that addition of nanoparticles may lead to either increase or decrease of water content in IEMs, different ranges of pore size being affected. Hybrid membranes modified with hydrated zirconium dioxide exhibit much higher permselectivity in comparison with the pristine membranes. The diversity of the responses of membrane properties to their modification allows for formation of membranes suitable for fuel cells, electrodialysis or other applications.

“Clickable” thiol-functionalized nanoporous polymers: from their synthesis to further adsorption of gold nanoparticles and subsequent use as efficient catalytic supports

A straightforward and versatile approach towards thiol-functionalized nanoporous polystyrene frameworks is reported through the selective cleavage of a disulfide bridge at the junction between both blocks of newly synthesized polystyrene-block-poly(D,L-lactide) (PS-b-PLA) diblock copolymer precursors. This methodology requires the synthesis of a disulfide-bearing heterodifunctional initiator that allows for the production of well-defined diblock copolymers by combining atom transfer radical polymerization (ATRP) of styrene and ring-opening polymerization (ROP) of D,L-lactide. After macroscopic orientation of the copolymer precursors through channel die processing and subsequent quantitative degradation of the disulfide bridge via triphenylphosphine-mediated reduction, thiol-functionalized porous polymers are obtained. Further, “click” thiol–ene-mediated functionalization of thiol-coated pore walls within nanoporous frameworks is implemented. More interestingly, adsorption of in situ generated gold nanoparticles and subsequent and unprecedented supported catalytic reduction of a model nitroaromatic compound, i.e. para-nitrophenol, are successfully achieved. Reusability of the hybrid catalyst is also proved over a 5 run-cycle with conversion of nearly 70% within only two hours.

Simultaneous Au(III) extraction and in-situ formation of polymeric membrane-supported gold nanoparticles: a sustainable process with application in catalysis

A polymeric membrane-supported catalyst with immobilized gold nanoparticles (AuNPs) was prepared through the extraction and in situ reduction of AuIII salts in a one-step strategy. Polymeric inclusion membranes (PIMs) and polymeric nanoporous membranes (PNMs) were tested as different membrane-support systems. Transport experiments indicated that PIMs composed of cellulose triacetate, 2-nitrophenyloctyl ether, and an aliphatic tertiary amine (Adogen 364 or Alamine 336) were the most efficient supports for AuIII extraction. The simultaneous extraction and reduction processes were proven to be the result of a synergic phenomenon in which all the membrane components were involved. Scanning electron microscopy characterization of cross-sectional samples suggested a distribution of AuNPs throughout the membrane. Transmission electron microscopy characterization of the AuNPs indicated average particle sizes of 36.7 and 2.9 nm for the PIMs and PNMs, respectively. AuNPs supported on PIMs allowed for >95.4 % reduction of a 0.05 mmol L-1 4-nitrophenol aqueous solution with 10 mmol L-1 NaBH4 solution within 25 min.

Design of functionalized biodegradable PHA-based electrospun scaffolds meant for tissue engineering applications

Modification of electrospun nanofibrous poly(3-hydroxyalkanoate) (PHA)-based mats was implemented through two routes to obtain biomimetic scaffolds meant for tissue engineering applications. The first strategy relied on a physical functionalization of scaffolds thanks to an original route which combined both electrospinning and electrospraying, while the second approach implied the chemical modification of fiber surface via the introduction of reactive functional groups to further conjugate bioactive molecules. The degree of glycidyl methacrylate grafting on PHA reached 20% after 300s under photoactivation. Epoxy groups were modified via the attachment of a peptide sequence, such as Arg-Gly-Asp (RGD), to obtain biofunctionalized scaffolds. SEM and TEM analysis of mats showed uniform and well-oriented beadless fibers. The electrospinning/electrospraying tandem process afforded highly porous scaffolds characterized by a porosity ratio up to 83% and fibers with a surface largely covered by the electrosprayed bioceramic, i.e. hydroxyapatite. Gelatin was added to the latter PHA-based scaffolds to improve the hydrophilicity of the scaffolds (water contact angle about 0°) as well as their biological properties, in particular cell adhesion, proliferation, and osteogenic differentiation after 5days of human mesenchymal stromal culture. Human mesenchymal stromal cells exhibited a better adhesion and proliferation on the biofunctionalized scaffolds than that on non-functionalized PHA mats.

Computation of permeability with Fast Fourier Transform from 3-D digital images of porous microstructures

Purpose – The purpose of this paper is to present a fully automated numerical tool for computing the effective permeability of porous media from digital images which come from the modern imagery technique. Design/methodology/approach – The permeability is obtained by the homogenization process applied to a periodic rigid solid in which the fluid flow is described by the Stokes equations. The unit cell problem is solved by using the Fast Fourier Transform (FFT) algorithm, well adapted for the microstructures defined by voxels. Findings – Various 3-D examples are considered to show the capacity of the method. First, the case of flow through regular arrays of aligned cylinders or spheres are considered as benchmark problems. Next, the method is applied to some more complex and realistic porous solids obtained with assemblies of overlapping spherical pores having identical or different radii, regularly or randomly distributed within the unit cell. Originality/value – The use of FFT allows the resolution of hi...

Synergistic actions of mixed small and large pores for capillary absorption through biporous polymeric materials

Water absorption in porous media is an important process involved in numerous materials for various applications, such as in the building industry, food processing and bioengineering. Designing new materials with appropriate absorption properties requires an understanding of how absorption behavior depends on both the materials morphology and the properties of the solid matrix, i.e. hydrophilic/hydrophobic nature and swelling/deformation properties. Although the basic principles of imbibition are well-known for simple porous systems, much less is known about absorption in complex porous systems, in particular those containing several coexisting porous phases, such as wood for example. Here, water absorption is studied for model porous organic materials exhibiting several degrees of hydrophobicity and two pore size levels, either as monoporous materials (large or small pores) or as biporous materials (mixed large and small pores). The interconnected biporous structure is designed via a double porogen templating approach using cubic sodium chloride particles as templates for the generation of the larger pore size (250-400 μm) and i-PrOH as a porogenic solvent for the smaller pore size (2-5 μm). While absorption for the small pore material is well described by the classical Washburn theory, the large pore material shows a drastic reduction in the imbibition rate. This behavior is attributed to the slow breakthrough mechanism for the water interface at sharp edge connections between pores. Remarkably, this slow regime is suppressed for the biporous material and the imbibition rate is even higher than the sum of rates obtained for its monoporous counterparts, which highlights the synergistic action of mixed small and large pores.

From the functionalization of polyelectrolytes to the development of a versatile approach to the synthesis of polyelectrolyte multilayer films with enhanced stability

A general approach to side-chain allyl-functionalization of three different polyelectrolytes (PEs), namely poly(allylamine hydrochloride) (PAH·HCl), branched polyethyleneimine (PEI) and poly(sodium 4-styrenesulfonate) (PSS), is reported for the first time. This functionalization does not affect the electrolytic properties of the newly functionalized PEs (named PEs-ene), as confirmed by the effective formation of PE-ene multilayer (PEM) films. The stepwise construction of these films is monitored using different techniques, including QCM, SEM, XPS, and WCA measurements. The incorporation of allyl functional groups into the PE side-chains allows for the stabilization of the resulting PEM films via thiol–ene UV photo-crosslinking in the presence of a water-soluble dithiol crosslinker. To overcome the problem of film delamination, the covalent crosslinking occurs not only between different layers of PEM films but also with the substrates preliminarily functionalized with allyl functional groups either via sulfur–gold chemistry or via chemical reduction of aryldiazonium salts using two newly synthesized anilinium derivatives. The stability of the resulting crosslinked PEM films in a strongly alkaline solution (pH = 14) is validated on gold substrates under QCM conditions (from 30 min to 3 h), while XPS and WCA measurements are used for evidencing such a stability under strongly acidic conditions (pH = 1) or at high salt concentration (saturated NaCl solution) on a modified anion-exchange membrane during a longer study time, i.e. 10 days. Finally, this stability study also gives evidence for a greater crosslinking efficiency of PEG-diSH, namely a macromolecular crosslinker, over dithiothreitol (DTT), a small molecule. The versatility and effectiveness of the approach presented here are expected to find widespread interest in different fields of emerging applications.