Ice-segregation-induced Self-assembly Research Articles

A natural polymer-based porous sponge with capillary-mimicking microchannels for rapid hemostasis

Natural polymer materials have attracted great attention in the field of hemostasis because of their wide range of source, nontoxicity, hydrophilicity, and air permeability. In the present study, two natural polymers composed of carboxymethyl chitosan (CMCS) and sodium carboxymethylcellulose (CMCNa) plus γ-(2,3-epoxypropoxy) propytrimethoxysilane (KH560) that serves as a crosslinking agent were selected to synthesize a capillary-mimicking composite hemostatic (CCK) sponge with a low density, interconnected microchannel architecture, suitable mechanical strength, high resilience, and ultrastrong liquid absorption capacity. The introduction of a large number of hydrophilic carboxymethyl functional groups and the design of capillary-mimicking structures formed by the ice segregation-induced self-assembly (ISISA) process endowed the CCK sponges with an ultrastrong liquid absorption capacity, which significantly enhanced the hemostatic ability of the materials. Both in vivo and in vitro hemostatic experiments confirmed the potential of the CCK sponges to achieve rapid hemostasis. Additionally, cytotoxicity and hemolysis assays showed that the CCK sponges exhibited good biocompatibility and hemocompatibility. The possible hemostatic mechanism was also discussed in this study. In conclusion, the capillary-mimicking hemostatic sponge exhibits a high potential to induce rapid hemostasis in prehospital emergency and clinical settings. STATEMENT OF SIGNIFICANCE: In the present study, an oriented composite hemostatic (CCK) sponge with a capillary-mimicking structure formed by the ice segregation-induced self-assembly (ISISA) process was designed and used to achieve rapid hemostasis. The unique aligned microchannel structure of the sponge exhibited an ultrastrong capillary-mimicking action and endowed the prepared CCK hemostatic sponge with a strong liquid absorption capacity. By changing the proportion of raw materials, we could modify the unique capillary-mimicking structure with aligned microchannels. Two natural polymer-based materials with abundant hydrophilic groups were chosen to prepare the CCK sponge to fully utilize the characteristics of this structure. The oriented natural polymer-based porous sponge with capillary-mimicking microchannels exhibited a strong hemostatic ability in both in vivo and in vitro tests. The results showed that the CCK sponge with the capillary-mimicking structure has a high potential to achieve rapid hemostasis.

Highly Efficient and Recyclable Carbon-Nanofiber-Based Aerogels for Ionic Liquid-Water Separation and Ionic Liquid Dehydration in Flow-Through Conditions.

Ionic liquids (ILs) are being widely used in many diverse areas of social interest, including catalysis, electrochemistry, etc. However, issues related to hygroscopicity of many ILs and the toxic and/or nonbiodegradable features of some of them limit their practical use. Developing materials capable of IL recovery from aqueous media and dehydration, thus allowing their recycling and subsequent reutilization, in a single and efficient process still poses a major challenge. Herein, electrically conductive aerogels composed of carbon nanofibers (CNFs) with remarkable superhydrophobic features are prepared. CNF-based 3D aerogels are prepared through a cryogenic process, so called ice-segregation-induced self-assembly (ISISA) consisting of the unidirectional immersion of an aqueous chitosan (CHI) solution also containing CNFs in suspension into a liquid nitrogen bath, and subsequent freeze-drying. The CNF-based 3D aerogels prove effective for absorption of ILs from aqueous biphasic systems and recovery with quite low water contents just through a single process of filtration. Moreover, the electrical conductivity of CNF-based 3D aerogels is particularly interesting to treat highly viscous ILs because the Joule effect allows not only shortening of the absorption process but also enhancement of the flux rate when operating in flow-through conditions.

Biopolymeric pellets of polyvinyl alcohol and alginate for the encapsulation of Ib-M6 peptide and its antimicrobial activity against E. coli

The encapsulation of Ib-M6 antibacterial peptide in pellets of polyvinyl alcohol (PVA) and polyvinyl alcohol-alginate (PVA-Alg) matrices was carried out in order to explore its controlled release and activity against Escherichia coli K-12. The pellets were obtained by combined ice segregation induced self-assembly (ISISA) and freezing-thawing methods and their microstructure was studied by scanning electron microscopy. Bromothymol blue was used as a model compound to study the transport mechanisms and release from pellets. The results show that there is a significant effect of the total concentration of PVA precursor solutions, the mass ratio of PVA of different molecular weights and the addition of alginate on the microstructure and transport properties of pellets. The antibacterial activity of Ib-M6 against Escherichia coli K-12 was not affected by the encapsulation in PVA pellets. However, the release of Ib-M6 from PVA-Alg pellets was not possible, probably due to the electrostatic interaction of positively charged Ib-M6 and negatively alginate structure. Nonetheless, the controlled release of Ib-M6 from polymeric matrices can be fitting by modifying parameters such as the concentration and type of polymer precursors.

Synthesis and characterization of simple and binary drug delivery systems for sustainable release of ciprofloxacin

Biopolymers are widely used for design sustained drug delivery systems (SDDS) and biomaterials for tissue engineering. Reducing wound infections still constitutes one of the major challenges facing the wound care. The aim of this study was to synthetize, characterize and evaluate a single (polymeric spheres) and a binary polymeric biomaterial (polymeric spheres imbedded in a poly(vinyl alcohol) (PVA) scaffold) as a SDDS. Polymeric spheres were prepared by complex coacervation and the binary system of the chitosan (CH) -PVA beads embedded in a PVA scaffold prepared by Ice Segregation Induced Self-Assembly (ISISA) process. Both systems were physicochemically characterized using Fourier Transform Infrared spectroscopy (FTIR), X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). In vitro ciprofloxacin (CFX) release kinetics were evaluated simulating physiological conditions under sink conditions. Physicochemical characterization showed interactions between all components forming beads; in contrast, beads-scaffold interactions were not detected making evident the presence of two different phases in the binary system. The CFX release kinetics revealed that both systems were SDDS, simple system release 97.0 ± 6.9% in 7 days, while the binary was 68.56 ± 6.6% during 14 days of evaluation. Binary system emerges as a potential tool for evaluate the long-lasting infection control in the treatment of skin wounds.

Macroporous Calcium Phosphate/Chitosan Composites Prepared via Unidirectional Ice Segregation and Subsequent Freeze-Drying.

Calcium phosphate chitosan-based composites have gained much interest in recent years for biomedical purposes. In this paper, three-dimensional calcium phosphate chitosan-based composites with different mineral contents were produced using a green method called ice segregation induced self-assembly (ISISA). In this methodology, ice crystals were used as a template to produce porous structures from an aqueous solution of chitosan (CS) and hydroxyapatite (Hap) also containing acetic acid (pH = 4.5). For better characterization of the nature of the inorganic matter entrapped within the resulting composite, we performed either oxygen plasma or calcination processes to remove the organic matter. The nature of the phosphate salts was studied by XRD and NMR studies. Amorphous calcium phosphate (ACP) was identified as the mineral phase in the composites submitted to oxygen plasma, whereas crystalline Hap was obtained after calcination. SEM microscopy revealed the formation of porous structures (porosity around 80–85%) in the original composites, as well as in the inorganic matrices obtained after calcination, with porous channels of up to 50 µm in diameter in the former case and of up to 20 µm in the latter. The biocompatibility of the composites was assessed using two different cell lines: C2C12GFP premyoblastic cells and MC3T3 preosteoblastic cells.

Ice as a Green-Structure-Directing Agent in the Synthesis of Macroporous MWCNTs and Chondroitin Sulphate Composites.

The incorporation of multi-walled carbon nanotubes (MWCNTs) into chondroitin sulphate-based scaffolds and the effect on the structural, mechanical, conductive, and thermal properties of the resulting scaffolds is investigated. Three-dimensional hierarchical materials are prepared upon the application of the ice segregation-induced self-assembly (ISISA) process. The use of ice as structure-directing agents avoids chemicals typically used for this purpose (e.g., surfactants, block copolymers, etc.), hence, emphasising the green features of this soft-templating approach. We determine the critical parameters that control the morphology of the scaffolds formed upon ice-templating (i.e., MWCNTs type, freezing conditions, polymer and MWCNT concentration). MWCNTs are surface functionalized by acidic treatment. MWCNT functionalization is characterized by Raman, Fourier transfer infrared (FTIR) and X-ray Photoelectron (XPS) spectroscopies. Scanning electron microscopy (SEM) analysis and porosity studies reveal that MWCNT content modifies the morphology of the macroporous structure, which decreases by increasing MWCNT concentration. Differences in scaffold morphology should be translated into their conductivity and mechanical properties. As a general trend, the Young’s modulus and the electrical conductivity of the scaffolds increase with the MWCNT content. Preliminary biocompatibility tests with human osteoblast-like cells also reveal the capability of these structures to support cell growth.

Anisotropic compressive properties of porous CNT/SiC composites produced by direct matrix infiltration of CNT aerogel

AbstractCarbon nanotube‐reinforced silicon carbide composites (CNT/SiC) produced by direct infiltration of matrix into a porous CNT arrays have been demonstrated to possess a unique microstructure and excellent micro‐mechanical properties. However, the thickness of the array preforms is usually very small, typically less than 2 mm. Therefore, fabrication of macroscopic CNT/SiC composites by chemical vapor infiltration (CVI) process requires that the nanoscale fillers could form macroscopic architectures with an open pore network. Here, this study reports an experimental strategy for the fabrication of SiC matrix composites reinforced by CNT based on an ice‐segregation‐induced self‐assembly (ISISA) technique. Macroscopic CNT aerogel with well‐defined macroporous network was produced by ISISA technique and was subsequently infiltrated by SiC in a CVI reactor. After five CVI cycles, the porosity of as‐fabricated composites was 11.6±0.3% and the machined specimens exhibited lamellar structure with parallel lamellaes intersected at discrete angles. By observed, there are in fact five different representative anisotropic macrostructures, the compressive strengths of these five different loading modes with respect to lamella orientation were 933±55, 619±34, 200±45, 199±21, and 297±41 MPa, respectively, and the failure mechanisms were attributed to the anisotropic nature of the macrostructures. Energy dissipation toughening mechanism at the nanoscale such as CNT pull‐out was observed and the phase composition of the fabricated materials included β‐SiC, CNT, and SiO2.

Green Synthesis of Hierarchically Structured Silver-Polymer Nanocomposites with Antibacterial Activity.

The in situ formation of silver nanoparticles (AgNPs) aided by chondroitin sulfate and the preparation of a hierarchically structured silver-polymer nanocomposite with antimicrobial activity is shown. Green synthesis of AgNPs is carried out by thermal treatment (80 and 90 °C) or UV irradiation of a chondroitin sulfate solution containing AgNO3 without using any further reducing agents or stabilizers. Best control of the AgNPs size and polydispersity was achieved by UV irradiation. The ice-segregation-induced self-assembly (ISISA) process, in which the polymer solution containing the AgNPs is frozen unidirectionally, and successively freeze-drying were employed to produce the chondroitin sulfate 3D scaffolds. The scaffolds were further crosslinked with hexamethylene diisocyanate vapors to avoid water solubility of the 3D structures in aqueous environments. The antimicrobial activity of the scaffolds was tested against Escherichia coli. The minimum inhibitory concentration (MIC) found for AgNPs-CS (chondroitin sulfate) scaffolds was ca. 6 ppm.

Novel cellulose aerogel coated on polypropylene separators as gel polymer electrolyte with high ionic conductivity for lithium-ion batteries

The low ionic conductivity of polypropylene (PP) separators has stymied their use as polymer electrolytes in high-power lithium-ion batteries. To improve the ionic conductivity, we coated PP separators with cellulose aerogel based on hydroxyethyl cellulose (HEC), via ice segregation induced self-assembly (ISISA). The coating was characterized via scanning electron microscopy (SEM), attenuated total reflection–infrared spectra (ATR-IR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). In addition, the electrochemical performances of the separator were evaluated by using a cell consisting of the coated separator, lithium foil as the counter and reference electrodes, and LiFePO4 as the cathode. The porous cellulose aerogel-coated separator exhibited superior dimensional stability, electrolyte uptake, and hence a higher ionic conductivity and better cycling performance, than its non-coated counterpart. Furthermore, the separator was coated without the use of toxic solvents, thereby rendering the preparation process cost effective and highly efficient.

Preparation and characterization of crosslinked chitosan/gelatin scaffolds by ice segregation induced self-assembly

Chitosan and gelatin are biodegradable and biocompatible polymers which may be used in the preparation of 3D scaffolds with applications in biomedicine. Chitosan/gelatin scaffolds crosslinked with glutaraldehyde were prepared by ice segregation induced self-assembly (ISISA); a unidirectional freezing at −196°C followed freeze-drying to produce macroporous materials with a well-patterned structure. This process may be included within the green chemistry by the preparation of the porous structures without using organic solvents, moreover is a versatile, non-difficult and cheap process.The scaffolds prepared by ISISA were characterized by scanning electron microscopy, attenuated total reflectance Fourier transform infrared spectroscopy, thermal gravimetric analysis, differential scanning calorimetry, and their stability was evaluated by degree swelling and degradation tests. The scaffolds present properties as high porosity, high degree swelling and good stability which make them suitable of applications as biomaterials.

Effect of doping in carbon nanotubes on the viability of biomimetic chitosan‐carbon nanotubes‐hydroxyapatite scaffolds

This work describes the preparation and characterization of biomimetic chitosan/multiwall carbon nanotubes/nano-hydroxyapatite (CTS/MWCNT/nHAp) scaffolds and their viability for bone tissue engineering applications. The cryogenic process ice segregation-induced self-assembly (ISISA) was used to fabricate 3D biomimetic CTS scaffolds. Proper combination of cryogenics, freeze-drying, nature and molecular ratio of solutes give rise to 3D porous interconnected scaffolds with clusters of nHAp distributed along the scaffold surface. The effect of doping in CNT (e.g. with oxygen and nitrogen atoms) on cell viability was tested. Under the same processing conditions, pore size was in the range of 20-150 μm and irrespective on the type of CNT. Studies on cell viability with scaffolds were carried out using human cells from periosteum biopsy. Prior to cell seeding, the immunophenotype of mesenchymal periosteum or periosteum-derived stem cells (MSCs-PCs) was characterized by flow cytometric analysis using fluorescence-activated and characteristic cell surface markers for MSCs-PCs. The characterized MSCs-PCs maintained their periosteal potential in cell cultures until the 2nd passage from primary cell culture. Thus, the biomimetic CTS/MWCNT/nHAp scaffolds demonstrated good biocompatibility and cell viability in all cases such that it can be considered as promising biomaterials for bone tissue engineering.

Cryogenic Process to Elaborate Poly(ethylene glycol) Scaffolds. Experimental and Simulation Studies

Porous materials are of great importance because of their multiple applications in pharmacy, catalysis, and biomedicine among others. Ice segregation induced self-assembly (ISISA) is a cryogenic technique that uses the ice as a template that forms upon immersion of a polymer solution into liquid nitrogen to obtain highly porous materials. Some highlights of this technique are its versatility, simplicity, and control over the final structure of the produced material; besides, no organic solvents are used during the process, and the material can be used without the need of further cleaning. In this contribution, the elaboration of scaffolds using a poly(ethylene glycol) aqueous solutions by an ice-template process has been studied from experimental and theoretical viewpoints. The experimental study of the process parameters, such as immersion velocity and a prescribed freezing front on the morphology, was carried out. Simulations were performed to understand the ISISA process by calculating temperature profiles and pore size as a function of time. The most important result of this study was the effect of freezing rate on pore size. The technique was optimized such that a recipe is proposed to form materials with 1–100 μm pore sizes.

Micro/Nanostructured Hyaluronic Acid Matrices with Tuned Swelling and Drug Release Properties

Hyaluronic acid (HA) hydrogels were structured in the form of porous monoliths by means of the ice-segregation-induced self-assembly (ISISA) method coupled with freeze-drying. Physical and chemical parameters were explored in order to fine-tune the microstructure and the incidence on both swelling and dissolution behavior in aqueous media. Gentamicin-loaded HA matrices with tuned drug release properties were also prepared; their inherent properties and behavior in solution are discussed in the framework of thermal analysis and scanning electron microscopy inspection.

Aligned/Unaligned Conducting Polymer Cryogels with Three-Dimensional Macroporous Architectures from Ice-Segregation-Induced Self-Assembly of PEDOT-PSS

Porous conducting polymers are of great interest because of the huge potential to combine high surface areas in the dry state with physical properties relevant to organic electronics. Aligned or unaligned conducting polymer cryogels with 3D macroporous architectures have been prepared using the ice-segregation-induced self-assembly (ISISA) of different poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) freezing precursors as a dispersion or a formed hydrogel. The chemical composition and molecular structure of the resulting conducting polymer cryogels have been investigated by X-ray photoelectron spectroscopy and Raman spectroscopy, respectively. The morphologies of the PEDOT-PSS cryogels, together with their textural structures, have been revealed by scanning electron microscopy, mercury porosimetry, and nitrogen sorption tests. Processing PEDOT-PSS via ISISA endows the conducting polymers with novel properties, as demonstrated by a series of X-ray diffraction, differential scanning calorimetry, and electrical conductivity tests. These conducting polymer cryogels with aligned/unaligned macroporous architectures suggest the potential in the development of electronic components, tissue engineering, and next-generation catalytic and separation supports.

Chitosan Gelation Induced by the in Situ Formation of Gold Nanoparticles and Its Processing into Macroporous Scaffolds

This work describes a simple synthetic route to induce chitosan (CHI) gelation by the in situ formation of gold nanoparticles (AuNPs). AuNPs were obtained by thermal treatment (e.g., 40 and 80 °C) of CHI aqueous solutions containing HAuCl(4) and in the absence of further reducing agents. The CHI hydrogels resulting after AuNP formation were submitted to unidirectional freezing and subsequent freeze-drying via ISISA (ice-segregation-induced self-assembly) process for the preparation of CHI scaffolds. The study of AuNP-CHI scaffolds by SEM and confocal fluorescence microscopy revealed a morphological structure characteristic of the hydrogel nature of the samples subjected to the ISISA process. Interestingly, not only the morphology but also the dissolution and swelling degree of the resulting CHI scaffolds were strongly influenced by the strength of the hydrogels obtained by the in situ formation of AuNP. We have also studied the catalytic activity AuNP-CHI scaffolds in the reduction of p-nitrophenol. The negligible dissolution and low swelling degree obtained in certain AuNP-CHI scaffolds allowed them to be used for more than four cycles with full preservation of the reaction kinetics.

Enzyme-induced graft polymerization for preparation of hydrogels: synergetic effect of laccase-immobilized-cryogels for pollutants adsorption

The use of polyethylene oxide-polypropylene oxide-polyethylene oxide block-copolymers as a mediator in the laccase-induced graft polymerization of diacrylic derivate of polyethylene glycols resulted in the formation of PEG-g-F68 hydrogels. The proper oxygen content in the reaction medium to obtain reasonable polymerization conversions (i.e., on one hand, laccase needs oxygen as substrate whereas, on the other, oxygen is a strong inhibitor of radical polymerizations) was achieved by the use of an enzymatic scavenging system consisting of glucose oxidase and glucose. Eventually, laccase was immobilized within the resulting PEG-g-F68 hydrogel with full preservation of enzyme activity. Laccases have been used for bioremediation purposes because of their ability to degrade phenolic compounds. Thus, laccase-immobilized PEG-g-F68 hydrogels were submitted to the ISISA (ice segregation induced self-assembly) process for preparation of laccase-immobilized PEG-g-F68 cryogels which exhibited a macroporous structure where immobilized laccase preserved almost total activity (ca. 90%) for a period exceeding three months after preparation. Synergy between macroporous structure (deriving from the ISISA process), amphiphilic domains (deriving from graft copolymer) and activity of the immobilized enzyme provided outstanding adsorption capabilities to the cryogels (up to 235 mg g−1).

Fabrication of ice-templated macroporous TiO2–chitosan scaffolds for photocatalytic applications

Higher-ordered 3D macroporous TiO2-functionalized chitosan scaffolds were prepared by ice segregation induced self-assembly (ISISA), in which homogenous dispersions of 6, 27 or 200 nm sized TiO2nanoparticles and chitosan cross-linked with glycidoxypropyltrimethoxysilane were unidirectionally frozen at −196 °C. Scanning electron microscopy showed that under established optimum conditions the monoliths comprised well-aligned 30–50 µm sized micro-channels running parallel to the direction of ice growth. The surface morphology of the internal wall structure was influenced by the size of the titania nanoparticles. Scaffolds prepared in the presence of 6 nm sized anatase particles showed featureless walls with concealed/embedded nanoparticles, whereas larger TiO2 particles remained exposed at the surface of the channel walls. Mechanical properties of the composite scaffolds were studied under compressive loads and stress–strain measurements obtained, and the effect of particle size on the elastic properties of the macroporous constructs determined. The hybrid scaffolds were shown to be reusable substrates for the photocatalytic degradation of methylene blue and Orange II dye molecules.

Ice-Templated Materials: Sophisticated Structures Exhibiting Enhanced Functionalities Obtained after Unidirectional Freezing and Ice-Segregation-Induced Self-Assembly

This review aims to demonstrate the capability of the ice-segregation-induced self-assembly (ISISA) process for the preparation of materials with highly sophisticated structures (e.g., hierarchical materials exhibiting organization at different scale levels). Cryogenic processes (consisting of the freezing, storage in the frozen state for a definite time, and defrosting of low - or high-molecular-weight precursors, as well as colloid systems, as either a water solution or suspension, or forming a hydrogel) have been widely used for the scaffolds preparation. However, the recent success in the control of the morphology (e.g., by unidirectional freezing in nitrogen liquid) and the possibility to extend the compositional nature of the resulting materials has recently attracted much attention to the ISISA process. Besides, this review aims to exemplify how the aqueous nature of the ISISA process allows for the in-situ incorporation of biological entities which provides not only hierarchy but also functionalit...

Macroporous 3D Architectures of Self-Assembled MWCNT Surface Decorated with Pt Nanoparticles as Anodes for a Direct Methanol Fuel Cell

Microchannelled 3D architectures composed of multiwall carbon nanotubes (MWCNTs) surface decorated with Pt nanoparticles and chitosan (CHI) are prepared by an ice segregation induced self-assembly (ISISA) process. The microchannelled structures are highly porous (specific gravity ∼10-2) and exhibit excellent electron conductivity (2.5 S·cm-1) thanks to both the high content of MWCNTs (up to 89 wt %) and their interconnection. The Pt/MWCNT/CHI 3D architectures provide remarkable performance as anodes for a direct methanol fuel cell (DMFC).

Freezing of Binary Colloidal Systems for the Formation of Hierarchy Assemblies

Cryo-etch scanning electron microscopy (cryo-etch SEM) of aqueous gels composed of colloidal silica nanoparticles in the 1−40 nm range and liposomes of ∼200 nm gave unique morphologies. The aqueous gels are frozen at subcooled liquid nitrogen and fractured to obtain a fresh surface. High-vacuum sublimation of ice from the freshly exposed surface (etching) results in the formation of a hierarchy assembly, characterized by granular fences composed of colloidal silica and liposomes surrounded by empty areas in which amorphous ice originally resided. The biocompatible character of this ice segregation induced self-assembly (ISISA) process that allows for the preservation of the structural integrity of liposomes within the assembly is demonstrated by fluorescence anisotropy performed at the binary colloidal aqueous gels and differential scanning calorimetry and electron microscopy at the hierarchy assembly. The resulting assembly shows an interesting dual character, with one colloidal entity supporting the structure (e.g., silica) and the other providing functionality (e.g., liposomes).