Nanoporous Scaffolds Research Articles

Nanomaterials, inflammation, and tissue engineering.

Nanomaterials exhibit unique properties that are absent in the bulk material because decreasing material size leads to an exponential increase in surface area, surface area to volume ratio, and effective stiffness, resulting in altered physiochemical properties. Diverse categories of nanomaterials such as nanoparticles, nanoporous scaffolds, nanopatterned surfaces, nanofibers, and carbon nanotubes can be generated using advanced fabrication and processing techniques. These materials are being increasingly incorporated in tissue engineering scaffolds to facilitate the development of biomimetic substitutes to replace damaged tissues and organs. Long-term success of nanomaterials in tissue engineering is contingent upon the inflammatory responses they elicit in vivo. This review seeks to summarize the recent developments in our understanding of biochemical and biophysical attributes of nanomaterials and the inflammatory responses they elicit, with a focus on strategies for nanomaterial design in tissue engineering applications.

In situ immobilization of tin dioxide nanoparticles by nanoporous polymers scaffold toward monolithic humidity sensing devices

Reported here is in situ immobilization of tin dioxide (SnO2) nanoparticles (NPs) within nanoporous polymer scaffolds for the development of monolithic humidity sensing devices. Through solvothermal polymerization of divinylbenzene (DVB) monomers in the interspaces of SnO2 fine powders, SnO2 NPs could be homogeneously immobilized in polymer matrices, forming a novel composite material. Immobilization of SnO2 NPs in nanoporous polymer matrices not only simplifies the fabrication process of NPs-based sensing devices, but also improves their adsorptive properties. The resultant nanoporous polymer/SnO2 NPs composites with adjustable SnO2 contents possess high BET surface areas, large pore sizes and pore volumes, thus they exhibit high adsorptive capacities for H2O vapor. As a general approach to NPs/nanoporous polymer composites, this work may open up a new way to nanomaterial-based sensing devices that features enhanced adsorptive property.

Characterization of the Dehydrogenation Process of LiBH4 Confined in Nanoporous Carbon

Annealing in the transmission electron microscope allows direct comparison of the same nanoporous carbon scaffold particles following dehydrogenation of the confined LiBH4. At a nominal temperature of 200 °C, a granular crust of cubic and cuboidal LiH nanocrystals ∼8–15 nm wide grew on the outer surface of the scaffold. Furthermore, these crystals migrated on the carbon support film away from the scaffold. Ejection of material from the scaffold also occurred upon dehydrogenation in a differential scanning calorimeter. The form of the ejected material was different, being bristles instead of cubes or cuboids. This ejection of LiH and thus preferential segregation of lithium from boron is proposed to explain the observed continual decrease in hydrogen storage capacity with the number of cycles.

Poly(hydroxybutyrate‐co‐hydroxyvalerate) Bilayer Skin Tissue Engineering Constructs with Improved Epidermal Rearrangement

Bilayer skin substitutes constitute an attractive strategy towards improved skin wound healing. Therefore, solvent casting and freeze-drying methodologies are used to produce polyhydroxybutyrate-co-hydroxyvalerate (PHBV) thin nanoporous membranes and 3D porous scaffolds that are combined in bilayer structures to recreate the epidermal and dermal layers, respectively. The combination of these methodologies allow attaining a bilayer structure with a high water retention capability and adequate mechanical properties, susceptible to enzymes degradative action. Cultures established with human keratinocytes (hKC) and dermal fibroblasts (hDFb) confirm the suitability of the PHBV structures to support cell adhesion and proliferation. Nonetheless, when co-cultured under defined conditions, hKC are able to grow and rearrange in a multilayer structure with proliferative cells in the basal layer, and cells expressing a terminal differentiation marker in the upper layer. Therefore, PHBV bilayer structures demonstrate properties that favor skin cells performance, thus representing a promising strategy to improve wound healing.

Novel Organic Solvent Free Micro-/Nano-fibrillar, Nanoporous Scaffolds for Tissue Engineering

Novel organic solvent free micro-/nano-fibrillar composite scaffolds have been manufactured using poly(L-lactide) and glycol-modified poly(ethylene terephthalate) to evaluate cell growth potential on the nanoporous networks. The authors describe a method for producing nanoporous scaffolds from polymer blends and highlights some limitations and inaccuracies when measuring mechanical properties of fibrillar porous structures. It illustrates the importance of determining the actual cross-sectional surface area of the load resisting fibers rather than using the simple geometrical area if properties are to be determined accurately. Cellular-biocompatible testing with a mouse pre-osteoblastic (early bone-forming cells) cell line shows promise, with a live monolayer of cells present on the biomaterial after 7–10 days of culture. In addition, scaffolds have also been manufactured by using the traditional electrospinning method and their cyto-biocompatibility compared to the micro-/nano-fibrillar composite scaffolds, employing cell attachment and morphology studies. Some scaffold manufacturing issues have also been identified and discussed in relation to improved cell growth.

Nanoconfined NaAlH4: prolific effects from increased surface area and pore volume

Nanoconfinement is a promising technique to improve the properties of nanomaterials such as the kinetics for hydrogen release and uptake and the stability during cycling. Here we present a systematic study of nanoconfined NaAlH4 in nanoporous scaffolds with increasing surface area and pore volume and almost constant pore sizes in the range of 8 to 11 nm. A resorcinol formaldehyde carbon aerogel was CO2-activated under different conditions and provided aerogels with BET surface areas of 704, 1267 and 2246 m(2) g(-1) and total pore volumes of 0.91, 1.30 and 2.21 mL g(-1), respectively. Nanoconfinement of NaAlH4 was achieved by melt infiltration and (27)Al MAS NMR reveals that the respective scaffolds incorporate 68, 82 and 91 wt% NaAlH4, for the above-mentioned samples, while the remaining fraction decomposes to metallic Al indicating that increasing CO2-activation tends to facilitate the infiltration process. The frequencies for the (23)Na and (27)Al MAS NMR centerband resonances from NaAlH4 vary systematically for the infiltrated samples and are shifted towards higher frequency and become more narrow with increasing degree of CO2 activation of the scaffolds. This new effect is attributed to increasing interactions with conduction electrons from increasingly graphite-/graphene-like scaffolds. The bulk versus nanoconfined ratio of NaAlH4 was investigated using Rietveld refinement, revealing that the majority of added NaAlH4 is confined inside the nanopores. The hydrogen desorption kinetics decreased with increasing surface area and the hydrogen storage capacity is more stable and decreases less during continuous hydrogen release and uptake cycles. In fact, the available amount of hydrogen (2.7 wt% H2) was more than doubled compared to the nanoconfinement in the non-activated carbon aerogel (1.3 wt% H2). Furthermore, it was demonstrated that Ti-functionalization of the CO2-activated aerogels combines the high storage capacity with fast hydrogen release kinetics from NaAlH4 which fully decomposes into Na3AlH6 at T ≤ 100 °C.

A Novel Microfibrillar Composite Approach towards Manufacturing Nanoporous Tissue Scaffolds

Nanofibrous interconnected networks have been fabricated from PLA and PET using two different techniques, namely, electrospinning and the concept of microfibrillar composite (MFC), to compare the morphology, production methods, costs, and, to an extent, their potential as scaffolds. Both methods of production create a three-dimensional network, with the electrospun scaffolds being comprised of a fibrillar, cross-plyed structure compared to the extruded scaffolds that consist of an interconnected porous network. The average diameter of the fibers ranged from 125–145 nm and 70–75 nm for the electrospun and extruded scaffolds, respectively. Mouse osteoblastic MC3T3-E1 cells have been used to test the biocompatibility of the electrospun scaffolds. A live/dead stain indicated that cells could attach and grow on the PLA and PET scaffolds. A preliminary cost analysis demonstrates that electrospinning is substantially more time and cost effective for larger quantities produced; however, the MFC technique can potentially produce totally solvent-free scaffolds.

Stable cycling and excess capacity of a nanostructured Sn electrode based on Sn(CH3COO)2 confined within a nanoporous carbon scaffold

A high capacity, electrochemically stable, nanostructured Sn electrode for Li ion battery anodes is described. This electrode utilizes a rigid, electrically conductive, nanoporous carbon aerogel scaffold by incorporating tin acetate, Sn(CH3COO)2, into the scaffold pore volume through melt infusion. Incorporation of the Sn(CH3COO)2 by melt infusion ensures a chemically stable contact with the scaffold. The mechanical rigidity of the pore volume confines the Sn to nanometer dimensions without sintering, leading to stable cycling. Separation of the synthesis of the scaffold from the loading with Sn(CH3COO)2 permits optimized division of the scaffold pore volume for expansion and electrolyte access during reaction with Li. Using this design, an electrode based on an aerogel with a 5 nm mode pore size was cycled over 300 times without degradation. In addition, after subtracting the contribution from the carbon scaffold, the capacity exceeded the theoretical capacity for Sn, due to an oxidation reaction occurring at 1.2 V. This excess capacity may be related to the solid–solid or solid–electrolyte interfaces in the electrode, possibly representing a new reversible Li ion reaction.

Nanoconfined NaAlH4: Determination of Distinct Prolific Effects from Pore Size, Crystallite Size, and Surface Interactions

Nanoconfinement is a new method to improve the hydrogen storage properties for metal hydrides. A systematic study of melt-infiltrated NaAlH4 in resorcinol formaldehyde carbon aerogels with pore sizes of Dmax = 4, 7, 10, 13, 19, 22, 26, 39 and >100 nm is presented. A linear correlation between pore size and crystalline domain size is observed using PXD. The distinct effects from pore size, crystallite size, and interfacial contact between NaAlH4 and carbon aerogel on hydrogen release and uptake properties are investigated. In situ synchrotron powder X-ray diffraction shows that formation of crystalline NaAlH4 nanoparticles only occurs in the nanoporous scaffolds (4 100 nm) as compared to bulk NaAlH4, i.e., reduction of the temperature for maximum hydrogen release rate of ΔTmax = −90 °C. Additional improvement is induced by reducing the pore sizes in the range 7 ≤ Dmax ≤ 39 nm and...

Hydrogen-storage materials dispersed into nanoporous substrates studied through incoherent inelastic neutron scattering

Incoherent inelastic neutron scattering measurements on four impregnated/infiltrated composites of hydrides (namely, NaAlH4, NH3BH3, LiBH4+Mg(BH4)2, and MgH2) plus nanoporous scaffolds (active carbon fibers or silica-based MCM41) have been performed at low temperature. After a careful data analysis, the present experimental results have been compared to the corresponding spectroscopic data of bulk hydrides. Evident signatures induced by infiltration process on the NaAlH4 phonon bands have been detected, showing up as a strong peak broadening and smoothing together with, in some cases, an energy shift. Less pronounced phonon spectrum modifications have been found in MgH2 and NH3BH3, mainly concentrated in the low-energy acoustic region. Finally, no relevant effect has been observed for LiBH4+Mg(BH4)2.

Gas anti-solvent precipitation assisted salt leaching for generation of micro- and nano-porous wall in bio-polymeric 3D scaffolds

The mass transport through biocompatible and biodegradable polymeric 3D porous scaffolds may be depleted by non-porous impermeable internal walls. As consequence the concentration of metabolites and growth factors within the scaffold may be heterogeneous leading to different cell fate depending on spatial cell location, and in some cases it may compromise cell survival.In this work, we fabricated polymeric scaffolds with micro- and nano-scale porosity by developing a new technique that couples two conventional scaffold production methods: solvent casting-salt leaching and gas antisolvent precipitation. 10–15w/w solutions of a hyaluronic benzyl esters (HYAFF11) and poly-(lactic acid) (PLA) were used to fill packed beds of 0.177–0.425mm NaCl crystals. The polymer precipitation in micro and nano-porous structures between the salt crystals was induced by high-pressure gas, then its flushing extracted the residual solvent. The salt was removed by water-wash. Morphological analysis by scanning electron microscopy showed a uniform porosity (~70%) and a high interconnectivity between porous. The polymeric walls were porous themselves counting for 30% of the total porosity. This wall porosity did not lead to a remarkable change in compressive modulus, deformation, and rupture pressure. Scaffold biocompatibility was tested with murine muscle cell line C2C12 for 4 and 7days. Viability analysis and histology showed that micro- and nano-porous scaffolds are biocompatible and suitable for 3D cell culture promoting cell adhesion on the polymeric wall and allowing their proliferation in layers. Micro- and nano-scale porosities enhance cell migration and growth in the inner part of the scaffold.

Stimuli pH‐responsive (N‐vinyl imidazole‐co‐acryloylmorpholine) Hydrogels; Mesoporous and Nanoporous Scaffolds

Tunable mesoporosity and nanoporosity of stimuli pH-responsive (N-vinyl imidazole-ran-acryloylmorpholine) hydrogels studied in terms of %swelling at various ionic strength, pH, temperature, and crosslinker concentration values were investigated. Hydrogel properties including diffusional exponent, number of links between two crosslinks, rms end-to-end distance and mesh size of gels were evaluated. The structural sequence of the scaffolds was tested and verified using Kelen-Tudos technique, and Alfrey-Price relationship. Hydrogels were characterized using FTIR, thermogravimetric analysis, differential scanning calorimetry, and freeze-dried Scanning electron micrographs techniques. The reversible pH responsiveness and possible mesoporous and nanoporous (i.e., 0.88-4.03 nm) structures suggest their suitable candidate in membrane technology and/or is an adequate drug delivery vehicle in drug delivery systems.

Gyroid nanoporous scaffold for conductive polymers

Conductive nanoporous polymers with interconnected large surface area have been prepared by depositing polypyrrole onto nanocavity walls of nanoporous 1,2-polybutadiene films with gyroid morphology. Vapor phase polymerization of pyrrole was used to generate ultrathin films and prevent pore blocking. The resulting nanoporous polymers exhibited a promising electroactivity.

Enzyme entrapped nanoporous scaffolds formed through flow-induced gelation in a microfluidic filter device for sensitive biosensing of organophosphorus compounds

A novel and versatile processing method was developed for the formation of gel scaffolds with in situ AChE-AuNPs immobilization for biosensing of organophosphorus compounds. The biosensor designed by our new approach shows high sensitivity, selectivity and reactivation efficiency. This flow-induced immobilization technique opens up new pathways for designing a simple, fast, biocompatible, and cost-effective process for enhanced sensor performance and on-site monitoring of a variety of toxic organophosphorus compounds.

Dye-Sensitized Solar Cells Fabricated from Atomic Layer Deposited Photoanodes on Aerogel Scaffolds

Dye-sensitized solar cells (DSSCs) based on mesoporous, high surface area nanocrystalline titania (TiO2) exhibiting up to 11% solar energy-conversion efficiencies are promising materials for cost-effective devices. Our objective here is to realize a cost-effective fabrication technique coupled with suitable device architecture of nanostructured DSSCs to achieve high photoconversion efficiencies. Atomic layer deposition (ALD) offers an attractive synthetic route for fabricating conformal photoanode coating materials on a nanoporous scaffold. Here, we used silica aerogels processed by doctor blading as structural scaffolds on transparent conducting oxide substrates, to promote subsequent conformal growth of thin films of TiO2 and aluminum-doped zinc oxide (AZO) by ALD. The resulting interdigitated architecture of the photoanodes can facilitate fast electron transfer. Dye sensitization of the photoanodes was accomplished using di-tetrabutylammonium cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II) ("N719", Dyesol, B2 dye) and assembled into photocells using liquid electrolytes. Co-sensitization with a second dye was found to increase the photon absorption and cell efficiency.

Nanoporous Scaffold with Immobilized Enzymes during Flow‐Induced Gelation for Sensitive H2O2 Biosensing

A novel and versatile processing method is developed for the formation of nanoporous scaffolds with in-situ enzyme immobilization for highly sensitive biosensor applications. The nanoporous scaffold-based biosensor shows high sensitivity, stability, selectivity, and good precision. This flow-induced immobilziation technique opens up new pathways for designing simple, fast, biocompatible, and cost-effective processes for enhanced sensor performance.

A Reversible Nanoconfined Chemical Reaction

Hydrogen is recognized as a potential, extremely interesting energy carrier system, which can facilitate efficient utilization of unevenly distributed renewable energy. A major challenge in a future "hydrogen economy" is the development of a safe, compact, robust, and efficient means of hydrogen storage, in particular, for mobile applications. Here we report on a new concept for hydrogen storage using nanoconfined reversible chemical reactions. LiBH4 and MgH2 nanoparticles are embedded in a nanoporous carbon aerogel scaffold with pore size Dmax approximately 21 nm and react during release of hydrogen and form MgB2. The hydrogen desorption kinetics is significantly improved compared to bulk conditions, and the nanoconfined system has a high degree of reversibility and stability and possibly also improved thermodynamic properties. This new scheme of nanoconfined chemistry may have a wide range of interesting applications in the future, for example, within the merging area of chemical storage of renewable energy.

Tracer Diffusion in Silica Inverse Opals

We employed fluorescence correlation spectroscopy (FCS) to study the diffusion of small fluorescence tracers in liquid filled silica inverse opals. The inverse opals consisted of a nanoporous silica scaffold spanning a hexagonal crystal of spherical voids of 360 nm diameter connected by circular pores of 70 nm diameter. The diffusion of Alexa Fluor 488 in water and of perylene-3,4,9,10-tetracarboxylic diimide (PDI) in toluene was studied. Three diffusion modes could be distinguished: (1) Free diffusion limited by the geometric constraints given by the inverse opal, where, as compared to the free solution, this diffusion is slowed down by a factor of 3-4, (2) slow diffusion inside the nanoporous matrix of the silica scaffold, and (3) diffusion limited by adsorption. On the length scale of the focus of a confocal microscope of roughly 400 nm diffusion was non-Fickian in all cases.

Reversibility of the hydrogen desorption from LiBH4: a synergetic effect of nanoconfinement and Ni addition

The reversible hydrogen capacity of LiBH(4) was improved by a combination of Ni addition, nanosizing and confinement of the active phase in a nanoporous carbon scaffold.

Polynuclear Photocatalysts in Nanoporous Silica for Artificial Photosynthesis

In this article, recent progress towards robust photocatalysts for the visible light-driven reduction of CO2 by H2O is presented. All-inorganic polynuclear photocatalysts consisting of an oxo-bridged binuclear charge-transfer chromophore (metal-to-metal charge-transfer) coupled to a multi-electron transfer catalyst anchored in a nanoporous silica scaffold have been developed. Mild synthetic methods afford assembly, on silica nanopore surfaces, of heterobinuclear units with donor and acceptor metal centers selected for optimum solar coverage and photon to chemical energy conversion efficiency. A photocatalyst featuring a TiOCrIII group coupled to an IrO2 nanocluster on MCM-41 silica support is shown to function as an efficient visible light water oxidation unit. Nanostructured Co3O4 clusters in mesoporous silica SBA-15 constitute the first example of a nanometer-sized multi-electron catalyst made of an earth-abundant metal oxide that evolves oxygen from water efficiently. For carbon dioxide reduction, a binuclear unit consisting of a Zr acceptor and a CuI donor (ZrOCuI) acts as light absorber as well as redox site, splitting CO2 to CO and H2O upon excitation of the charge-transfer transition. Structural and mechanistic insights of the photocatalytic units based on static and time-resolved optical, FT-infrared, FT-Raman, EPR, X-ray absorption spectroscopy and transmission electron microscopy are critical for improving designs. The photocatalytic units presented here form the basis for developing robust and efficient artificial photosynthetic systems for the conversion of carbon dioxide and water to a liquid fuel.