María L. Ferrer

Biocompatible MWCNT scaffolds for immobilization and proliferation of E. coli

Ultralightweight (specific gravity 8.0 × 10–2) and highly conductive (1.4 S cm–1) MWCNT scaffolds exhibited remarkable biocompatibility for E. coli which allows for bacteria immobilization and proliferation within its microchanneled structure. The above-mentioned features make these scaffolds potentially useful as electrodes in microbial fuel cells (MFCs).

PPO15-PEO22-PPO15block copolymer assisted synthesis of monolithic macro- and microporous carbon aerogels exhibiting high conductivity and remarkable capacitance

Ultralightweight (specific gravity 5 × 10−2) and highly conductive (2.5 S/cm) monolithic carbon aerogels exhibiting a three-dimensionally continuous micro- and macroporous structure have been prepared through a PPO-PEO-PPO block copolymer assisted route. The resulting carbon aerogels were highly suitable as electrodes of electric double layer capacitors, with remarkable values of capacitance of up to 225 F/g (normalized by mass) and 31 µF/cm2 (normalized by BET surface area).

3D free-standing porous scaffolds made of graphene oxide as substrates for neural cell growth

The absence of efficient therapies for the treatment of lesions affecting the central nervous system encourages scientists to explore new materials in an attempt to enhance neural tissue regeneration while preventing inhibitory fibroglial scars. In recent years, the superlative properties of graphene-based materials have provided a strong incentive for their application in biomedicine. Nonetheless, a few attempts to date have envisioned the use of graphene for the fabrication of three-dimensional (3D) substrates for neural repair, but none of these involve graphene oxide (GOx) despite some attractive features such as higher hydrophilicity and versatility of functionalization. In this paper, we report novel, free-standing, porous and flexible 3D GOx-based scaffolds, produced by the biocompatible freeze-casting procedure named ISISA, with potential utility in neural tissue regeneration. The resulting materials were thoroughly characterized by Fourier-transform infrared, Raman, and X-ray photoelectron spectroscopies and scanning electron microscopy, as well as flexibility testing. Embryonic neural progenitor cells were then used to investigate adhesion, morphology, viability, and neuronal/glial differentiation. Highly viable and interconnected neural networks were formed on these 3D scaffolds, containing both neurons and glial cells and rich in dendrites, axons and synaptic connections, and the results are in agreement with those obtained in initial studies performed with two-dimensional GOx films. These results encourage further investigation in vivo on the use of these scaffolds as guide substrates to promote the repair of neural injuries.

Self-assembled titania–silica–sepiolite based nanocomposites for water decontamination

This work describes the preparation of microchannel structured monolithic pieces by the “ice-segregation induced self-assembly” (ISISA) process. The monoliths exhibit a hierarchical structure composed of homogeneously mixed colloidal silica resulting from hydrolysis and condensation of an alkoxysilane precursor (e.g., TEOS) and TiO2 polycrystalline nanoparticles adsorbed onto sepiolite fibres. The combination of such a different species into a single macroporous structure provides a multifunctional material capable of water decontamination by pollutant removal from aqueous media (via adsorption on sepiolite) and subsequent elimination by UV irradiation (via photocatalytic oxidation on TiO2nanoparticles). The performance of the resulting materials has been studied using two organic compounds often present in wastewater such as p-nitrophenol (PNP) and methylene blue (MB).

Urea assisted hydroxyapatite mineralization on MWCNT/CHI scaffolds

Urea assisted hydroxyapatite (HAp) mineralization was performed on scaffolds composed of a major fraction of multiwall carbon nanotubes (MWCNT, 85 wt.%) and a minor one of chitosan (CHI, 15 wt.%). The MWCNT/CHI scaffolds were synthesized through a cryogenic process (so called ISISA, ice segregation induced self-assembly) that allowed the achievement of macroporous monoliths whose structure resembled a chamber-like architecture in the form of interconnected MWCNT/CHI sheets arranged in parallel layers crossed by pillars. The mineralized architectures were composed of flower like hydroxyapatite (HAp) crystalline clusters of ca. 1 µm, homogeneously distributed throughout the internal surface of the scaffold macrostructure. HAp mineralized MWCNT/CHI scaffolds were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR) and scanning and transmission electron microscopy (SEM and TEM, respectively). Calibrated energy dispersion X-ray spectroscopy (EDS) and selected-area electron diffraction (SAED) were also performed in the transmission electron microscope to further HAp characterization. Preliminary in vitro experiments demonstrated the suitability of HAp mineralized MWCNT/CHI scaffolds for bone tissue growth.

DES assisted synthesis of hierarchical nitrogen-doped carbon molecular sieves for selective CO2versus N2 adsorption

Deep eutectic solvents (DESs) composed of resorcinol, 3-hydroxypyridine and tetraethylammonium bromide were used for the synthesis of hierarchical nitrogen-doped carbon molecular sieves. DESs played multiple roles in the synthetic process, as the liquid medium that ensures reagent homogenization, the structure-directing agent responsible for the achievement of the hierarchical structure, and the source of carbon and nitrogen for the solid sorbent obtained after carbonization. Thus, the synthesis offers an economy of reagents that emphasizes the green nature and low cost of conventional polycondensation. Interestingly, while macropores facilitated mass transport and access to the surface area, the combination of the molecular sieve structure and nitrogen functionalization provided, respectively, excellent CO2 adsorption capacities of up to 3.7 mmol g−1, and outstanding CO2–N2 selectivities of up to 14.4 from single component gas data. Nonetheless, the CO2–N2 selectivity in the Henry law regime – representative of post-combustion flue-gas streams – of some of our carbons was particularly remarkable (e.g. 96), comparable to or even higher than those described for most recent carbons, and only surpassed by those of certain zeolites.

Chondroitin sulphate-based 3D scaffolds containing MWCNTs for nervous tissue repair

Nervous tissue lesions are an important social concern due to their increasing prevalence and their high sanitary costs. Their treatment still remains a challenge because of the reduced ability of nervous tissue to regenerate, its intrinsic structural and functional complexity and the rapid formation of fibroglial scars inhibiting neural repair. Herein, we show that 3D porous scaffolds made of chondroitin sulphate (CS), a major regulatory component of the nervous tissue, and multi-walled carbon nanotubes (MWCNTs) are selective substrates for the formation of a viable and neuron-enriched network with a transitory low glial content. Scaffolds have been fabricated by using the ice segregation-induced self-assembly technique and cultured with embryonic neural progenitor cells. Cell adhesion, morphology, viability, neuron/glial differentiation, calcium signaling dynamics, and mitochondrial activity have been studied over time on the scaffolds and compared to appropriate 2D control substrates. Our results indicate the formation of viable cultures enriched in neuron cells for up to 20 days, with ability to display calcium transients and active mitochondria, even in the absence of poly-D-lysine coating. A synergistic neural-permissive signaling from both the scaffold structure and its components (i.e., MWCNTs and CS) is suggested as the major responsible factor for these findings. We anticipate that these scaffolds may serve nerve regeneration if implanted in the acute phase after injury, as it is during the first stages of graft implantation when the most critical sequence of phenomena takes place to drive either nervous regeneration or fibroglial scar formation. The temporary glial inhibition found may be, indeed, beneficial for promoting the formation of neuron-enriched circuits at early phases while guaranteeing posterior glial integration to support longer-term neuron survival and activity.

Chitosan Scaffolds Containing Calcium Phosphate Salts and rhBMP-2: In Vitro and In Vivo Testing for Bone Tissue Regeneration

Numerous strategies that are currently used to regenerate bone depend on employing biocompatible materials exhibiting a scaffold structure. These scaffolds can be manufactured containing particular active compounds, such as hydroxyapatite precursors and/or different growth factors to enhance bone regeneration process. Herein, we have immobilized calcium phosphate salts (CPS) and bone morphogenetic protein 2 (BMP-2) – combined or alone – into chitosan scaffolds using ISISA process. We have analyzed whether the immobilized bone morphogenetic protein preserved its osteoinductive capability after manufacturing process as well as BMP-2 in vitro release kinetic. We have also studied both the in vitro and in vivo biocompatibility of the resulting scaffolds using a rabbit model. Results indicated that rhBMP-2 remained active in the scaffolds after the manufacturing process and that its release kinetic was different depending on the presence of CPS. In vitro and in vivo findings showed that cells grew more in scaffolds with both CPS and rhBMP-2 and that these scaffolds induced more bone formation in rabbit tibia. Thus chitosan scaffolds containing both CPS and rhBMP-2 were more osteoinductive than their counterparts alone indicating that could be useful for bone regeneration purposes, such as some applications in dentistry.

Subacute Tissue Response to 3D Graphene Oxide Scaffolds Implanted in the Injured Rat Spinal Cord

The increasing prevalence and high sanitary costs of lesions affecting the central nervous system (CNS) at the spinal cord are encouraging experts in different fields to explore new avenues for neural repair. In this context, graphene and its derivatives are attracting significant attention, although their toxicity and performance in the CNS in vivo remains unclear. Here, the subacute tissue response to 3D flexible and porous scaffolds composed of partially reduced graphene oxide is investigated when implanted in the injured rat spinal cord. The interest of these structures as potentially useful platforms for CNS regeneration mainly relies on their mechanical compliance with neural tissues, adequate biocompatibility with neural cells in vitro and versatility to carry topographical and biological guidance cues. Early tissue responses are thoroughly investigated locally (spinal cord at C6 level) and in the major organs (i.e., kidney, liver, lung, and spleen). The absence of local and systemic toxic responses, along with the positive signs found at the lesion site (e.g., filler effect, soft interface for no additional scaring, preservation of cell populations at the perilesional area, presence of M2 macrophages), encourages further investigation of these materials as promising components of more efficient material-based platforms for CNS repair.

Modulating the cytocompatibility of tridimensional carbon nanotube-based scaffolds†

Carbon nanotubes (CNTs) have lately attracted significant attention in the field of biomedicine. Although a wide repertoire of CNT-based composites has been explored as substrates for cell growth, the fabrication of 3D scaffolds has been more rarely accomplished. Additionally, concerns referred to CNT biocompatibility make their use in biomaterials still controversial. Herein we explore the interaction of three types of CNT-based 3D scaffolds - prepared with multi-walled CNTs and processed to show different architectural and morphological features at the microscale by using three different polymers (i.e., chitosan, chondroitin sulphate and gelatin) - with three types of mammalian cells displaying different sizes and adhesion patterns. Cell-material interaction has been assessed by studying cell viability, adhesion, morphology, and apoptosis. By means of time-lapse confocal laser scanning microscopy, we investigate, for the first time in CNT-based scaffolds, cell migration processes in real time. Scaffolds displaying both a pore size in range with that of cells and lower surface roughness reveal the highest viability values. In contrast, those with a smaller pore size and higher surface roughness account for the lowest cytocompatibility. Results from these studies benefit the fabrication of optimized biomaterials by varying scaffold-dependent parameters in accordance with those of target cells. Furthermore, they may serve to anticipate the response of other cell types sharing similar characteristics to those described herein when in contact with CNT-based scaffolds.