Three-dimensional Gel Research Articles

Multifunctional graphene incorporated conducting gel electrolytes in enhancing photovoltaic performances of quasi-solid-state dye-sensitized solar cells

Three-dimensional (3D) gel electrolytes are versatile in elevating encapsulation of liquid electrolyte in dye-sensitized solar cells (DSSCs), however, the poor contact at gel electrolyte/Pt counter electrode interface is unfavorable in electrocatalyzing triiodide ions. In the current work, we report the multifunctions of graphene, graphene oxide, or nanographite incorporated microporous poly(acrylic acid)-cetyltrimethylammonium bromide (PAA-CTAB) conducting gel electrolytes in both sealing liquid electrolyte and conducting refluxed electrons (electrons from external circuit to Pt counter electrode) into 3D framework of the conducting gel electrolyte, aiming at elevating liquid electrolyte content in per unit volume of gel electrolyte, increasing electrocatalytic area toward triiodide ions and diminishing charge-transfer resistance. The electrical and electrochemical performances of the resultant conducting gel electrolytes are thoroughly characterized. Light-to-electric power conversion efficiencies of 7.06%, 6.35%, and 6.17% are determined from DSSCs using graphene, graphene oxide, and nanographite incorporated PAA-CTAB conducting gel electrolytes in comparison with 6.07% from pure PAA-CTAB based DSSC.

Photocatalysis degradation of Azo dye using nanoTiO 2 ‐coated porous cellulose gel: enhancement by adsorption and its self‐clean characteristic

Three-dimensional cellulose gel was prepared by a crosslinking of the cellulose chains using epichlorohydrin in the presence of the NH 4 OH, and the TiO 2 nanoparticles which were fixed on the surface of cellulose gel to form microcrystalline cellulose gel/nanoTiO 2 composites (MCC-TiO 2 ). The composites were characterised by means of X-ray diffraction, thermogravimetric analysis and scanning electron microscopy, respectively. The composites showed an efficient removal of methyl orange (MO) from their aqueous solution, and a two-step mechanism is involved. At first, the MO molecules were enriched on the surface of the MCC-TiO 2 by absorption, and then they were degraded there via photocatalysis, and the degradation of the adsorbed MO promoted the further adsorption of MO from the solution. After 30 min, 94% of MO was removed, and the MCC-TiO 2 can be cleaned by itself and reused without additional treatments.

The multiple faces of leukocyte interstitial migration

Spatiotemporal control of leukocyte dynamics within tissues is critical for successful innate and adaptive immune responses. Homeostatic trafficking and coordinated infiltration into and within sites of inflammation and infection rely on signaling in response to extracellular cues that in turn controls a variety of intracellular protein networks regulating leukocyte motility, migration, chemotaxis, positioning, and cell-cell interaction. In contrast to mesenchymal cells, leukocytes migrate in an amoeboid fashion by rapid cycles of actin polymerization and actomyosin contraction, and their migration in tissues is generally referred to as low adhesive and nonproteolytic. The interplay of actin network expansion, contraction, and adhesion shapes the exact mode of amoeboid migration, and in this review, we explore how leukocyte subsets potentially harness the same basic biomechanical mechanisms in a cell-type-specific manner. Most of our detailed understanding of these processes derives from in vitro migration studies in three-dimensional gels and confined spaces that mimic geometrical aspects of physiological tissues. We summarize these in vitro results and then critically compare them to data from intravital imaging of leukocyte interstitial migration in mouse tissues. We outline the technical challenges of obtaining conclusive mechanistic results from intravital studies, discuss leukocyte migration strategies in vivo, and present examples of mode switching during physiological interstitial migration. These findings are also placed in the context of leukocyte migration defects in primary immunodeficiencies. This overview of both in vitro and in vivo studies highlights recent progress in understanding the molecular and biophysical mechanisms that shape robust leukocyte migration responses in physiologically complex and heterogeneous environments.

Protocol and cell responses in three-dimensional conductive collagen gel scaffolds with conductive polymer nanofibres for tissue regeneration.

It has been established that nerves and skeletal muscles respond and communicate via electrical signals. In regenerative medicine, there is current emphasis on using conductive nanomaterials to enhance electrical conduction through tissue-engineered scaffolds to increase cell differentiation and tissue regeneration. We investigated the role of chemically synthesized polyaniline (PANI) and poly(3,4-ethylenedioxythiophene) (PEDOT) conductive polymer nanofibres for conductive gels. To mimic a naturally derived extracellular matrix for cell growth, type I collagen gels were reconstituted with conductive polymer nanofibres and cells. Cell viability and proliferation of PC-12 cells and human skeletal muscle cells on these three-dimensional conductive collagen gels were evaluated in vitro. PANI and PEDOT nanofibres were found to be cytocompatible with both cell types and the best results (i.e. cell growth and gel electrical conductivity) were obtained with a low concentration (0.5 wt%) of PANI. After 7 days of culture in the conductive gels, the densities of both cell types were similar and comparable to collagen positive controls. Moreover, PC-12 cells were found to differentiate in the conductive hydrogels without the addition of nerve growth factor or electrical stimulation better than collagen control. Importantly, electrical conductivity of the three-dimensional gel scaffolds increased by more than 400% compared with control. The increased conductivity and injectability of the cell-laden collagen gels to injury sites in order to create an electrically conductive extracellular matrix makes these biomaterials very conducive for the regeneration of tissues.

Diagnostic and clinical value of 3D gel installation sonohysterography in addition to 2D gel installation sonohysterography in the assessment of intrauterine abnormalities

ObjectiveTo study the diagnostic value of three-dimensional gel instillation sonography (3D GIS) in addition to two-dimensional (2D) GIS in the assessment of intrauterine abnormalities. Secondly, the clinical value of 3D GIS in the planning for hysteroscopic procedures was evaluated. Study designA prospective cohort study was performed from 2008 till 2010. All women with a suspected intrauterine abnormality on 2D GIS suitable for hysteroscopic resection or with recurrent postmenstrual bleeding were planned for a hysteroscopic procedure. Diagnostic accuracy tests were calculated for the detection of fibroids and polyps with both histology and hysteroscopy as the reference standard. For the assessment of type and size of fibroids hysteroscopy was used as the reference standard. We compared the planning for type of hysteroscopy based on 2D GIS findings with the combined 2D–3D GIS findings. ResultsIn total 110 patients were analysed. In comparison to histology, addition of 3D GIS did not change sensitivity or specificity substantially in the discrimination between fibroids and polyps. In comparison to hysteroscopy, sensitivity increased for detecting fibroids and polyps, without major interference with the specificity. Despite an improved accuracy after the addition of 3D GIS, the planning for hysteroscopic procedures did not improve substantially. ConclusionIn daily practice, the addition of 3D GIS to 2D GIS improved the accuracy for the detection of polyps and fibroids compared to hysteroscopy, but only marginally improved the planning of hysteroscopic procedures, and therefore the clinical relevance seems to be limited.

Differentiation of adipose-derived stem cells toward nucleus pulposus-like cells induced by hypoxia and a three-dimensional chitosan-alginate gel scaffold in vitro

Background Injectable three-dimensional (3D) scaffolds have the advantages of fluidity and moldability to fill irregular-shaped defects, simple incorporation of bioactive factors, and limited surgical invasiveness. Adipose-derived stem cells (ADSCs) are multipotent and can be differentiated toward nucleus pulposus (NP)-like cells. A hypoxic environment may be important for differentiation to NP-like cells because the intervertebral disc is an avascular tissue. Hence, we investigated the induction effects of hypoxia and an injectable 3D chitosan-alginate (C/A) gel scaffold on ADSCs. Methods The C/A gel scaffold consisted of medical-grade chitosan and alginate. Gel porosity was calculated by liquid displacement method. Pore microstructure was analyzed by light and scanning electron microscopy. ADSCs were isolated and cultured by conventional methods. Passage 2 BrdU-labeled ADSCs were co-cultured with the C/A gel. ADSCs were divided into three groups (control, normoxia-induced, and hypoxia-induced groups). In the control group, cells were cultured in 10% FBS/DMEM. Hypoxia-induced and normoxia-induced groups were induced by adding transforming growth factor-β1, dexamethasone, vitamin C, sodium pyruvate, proline, bone morphogenetic protein-7, and 1% ITS-plus to the culture medium and maintaining in 2% and 20% O2, respectively. Histological and morphological changes were observed by light and electron microscopy. ADSCs were characterized by flow cytometry. Cell viability was investigated by BrdU incorporation. Proteoglycan and type II collagen were measured by safranin O staining and the Sircol method, respectively. mRNA expression of hypoxia-inducing factor-1α (HIF-1α), aggrecan, and Type II collagen was determined by reverse transcription-polymerase chain reaction. Results C/A gels had porous exterior surfaces with 80.57% porosity and 50-200 μm pore size. Flow cytometric analysis of passage 2 rabbit ADSCs showed high CD90 expression, while CD45 expression was very low. The morphology of induced ADSCs resembled that of NP cells. BrdU immunofluorescence showed that most ADSCs survived and proliferated in the C/A gel scaffold. Scanning electron microscopy showed that ADSCs grew well in the C/A gel scaffold. ADSCs in the C/A gel scaffold were positive for safranin O staining. Hypoxia-induced and normoxia-induced groups produced more proteoglycan and Type II collagen than the control group (P <0.05). Proteoglycan and Type II collagen levels in the hypoxia-induced group were higher than those in the normoxia-induced group (P <0.05). Compared with the control group, higher mRNA expression of HIF-1α, aggrecan, and Type II collagen was detected in hypoxia-induced and normoxia-induced groups (P <0.05). Expression of these genes in the hypoxia-induced group was significantly higher than that in the normoxia-induced group (P <0.05). Conclusion ADSCs grow well in C/A gel scaffolds and differentiate toward NP-like cells that produce the same extracellular matrix as that of NP cells under certain induction con ditions, which is promoted in a hypoxic state.

Facile synthesis of nickel network supported three-dimensional graphene gel as a lightweight and binder-free electrode for high rate performance supercapacitor application

Here we report a simple strategy to prepare three-dimensional graphene gel coated on nickel foam for supercapacitor applications by a simple 'dipping and drying' process. The supercapacitors based on three-dimensional graphene gel (G-gel@NF-1) exhibited high rate capability of 152 F g(-1) at 0.36 A g(-1) and 107 F g(-1) at 90.9 A g(-1), good cycle stability with capacitance retention of 89% after 2000 cycles and low internal resistance (0.58 Ω). Furthermore, a flexible electrode (G-gel@NF-2) was obtained by etching most of the nickel foam but maintains the conductive backbone of the nickel foam, which greatly reduces the total mass of the electrode (can be reduced from 30 mg cm(-2) to less than 5 mg cm(-2)), and can be compressed from a thickness of 1 mm to ∼30 μm. With the aid of a conductive network composed of a small amount of nickel, G-gel@NF-2 still has good performance in high rate capability and displays excellent flexible properties. The specific capacitance when the mass density of the electrode was only 5.4 mg cm(-2) still reached ∼115 F g(-1). This strategy can improve the rate capability performance, greatly reduce the mass of the electrode, and lower the fabrication cost of supercapacitors.

<I>In Vitro</I> Angiogenesis Assay for the Guidance of Microvessel Containing Multi-Cellular Lumen Formation

Angiogenesis is a development process of new capillaries from the pre-existing blood microvessel. It involves multiple steps, including proliferation of endothelial cells (ECs), migration, alignment, sprouting, cell-to-cell connection, tube-like structure and lumen formation. One of the major problems faced by the angiogenesis researchers has been the difficulty of finding suitable in vitro assay to follow the morphological events during angiogenesis development. Morphological events of EC undergoing angiogenesis is of important knowledge for tissue engineering and biomedical societies. In this work we describe step-by-step angiogenesis process and morphological development of human umbilical vein endothelial cells (HUVECs) in the in vitro three-dimensional fibrin gel assays. Endothelial cell was firstly used to cover polymer fiber surface. When the fiber covered with cells was sandwiched between two fibrin gel containing cells, endothelial cell-covered fiber recruits cells inside the gel to form cell-to-cell connection and tube-like structure. Afterwards cells were degraded their fibrin matrix in order to form complex networks of microvessel containing multi-cellular lumen in between two adjacent fibers.

Generation of Cell-Instructive Collagen Gels through Thermodynamic Control.

Recent studies have demonstrated the usefulness of three-dimensional hydrogel scaffolds for cell instruction. However, the control of gel architectures in cell-friendly conditions remains a challenge. Here, we report a novel method to generate unique three-dimensional collagen gel structures for the modulation of cell phenotypes. This was achieved by directing collagen self-assembly with unreactive hydrophilic polyethylene glycol (PEG) chains. Our approach allowed the fiber sizes and mechanics of three-dimensional collagen gels to be readily controlled. It also enabled the recapitulation of distinctive structures such as large perimysial collagen cables. Through different experiments, we elucidated the underlying mechanism for this PEG-mediated thermodynamic regulation of gel structure. We further used these cell-instructive three-dimensional gels to bring about pronounced morphological changes in encapsulated fibroblasts and their activation to form contractile bundles. Overall, our platform fills a gap in the existing array of collagen scaffolds and can potentially be adapted to a variety of self-assembling systems.

Chemokine receptor CX3CR1 contributes to macrophage survival in tumor metastasis

BackgroundMacrophages, the key component of the tumor microenvironment, are differentiated mononuclear phagocyte lineage cells that are characterized by specific phenotypic characteristics that have been implicated in tumor growth, angiogenesis, and invasion. CX3CR1, the chemoattractant cytokine CX3CL1 receptor, plays an important role in modulating inflammatory responses, including monocyte homeostasis and macrophage phenotype and function. However, the role of CX3CR1 in the regulation of the tumor inflammatory microenvironment is not fully understood.MethodsUsing in vivo hepatic metastasis model, human colon carcinoma specimens, immunohistochemical staining, TUNEL staining, flow cytometry analysis, Western blotting assay and co-culture in three-dimensional peptide gel, we determined the effects of CX3CR1 on angiogenic macrophage survival and tumor metastasis.ResultsIn this study, we found that CX3CR1 was expressed in human colon carcinomas in a histologic grade- and stage-dependent manner, and CX3CR1 upregulation in TAMs was correlated with poor prognosis. Furthermore, we showed that in a microenvironment lacking CX3CR1, the liver metastasis of colon cancer cells was significantly inhibited. The underlying mechanism is associated with decrease accumulation of angiogenic macrophages that can be partly attributed to increased apoptosis in the tumor microenvironment, thus leading to impaired tumor angiogenesis in the liver and suppressed tumor metastasis.ConclusionsOur results suggest a role of CX3CR1 in angiogenic macrophage survival in the tumor microenvironment contributing to tumor metastasis.

Change, Challenge, and Opportunity: Psychiatry Through the Looking Glass of Research

Change, Challenge, and Opportunity: Psychiatry Through the Looking Glass of Research

Hyaluronic acid colloidal gels as self‐assembling elastic biomaterials

Hyaluronic acid (HA) is a naturally occurring biodegradable polymer with a variety of applications in medicine. The use of HA as a filler or scaffold for regenerating tissues often requires improving the elastic properties of HA. This is conventionally accomplished via chemical crosslinking, which might require the generation of toxic free radicals. Although the mechanical properties of the resulting gel material can be tuned, these types of materials are static and susceptible to mechanical failure. The aim of this study was to develop a colloidal system for scaffold fabrication that is held together by physical interactions between HA nanoparticles. HA nanoparticles composed of 17 kDa HA suspended in water at different concentrations (15%, 30%, and 45% w/v, respectively) formed a stable three-dimensional (3D) colloidal gel as a result of physical entanglement of free polymer chains on the surfaces of nanoparticles. The swelling ratio, shear moduli (G), compressive failure properties, and viscosity of colloidal gels were concentration dependent. The colloidal gels also were found to exhibit dynamic and recoverable properties, thus suggesting that these "self-associating colloids" offer characteristics distinct arising from crosslinked polymers or high concentration colloids.

Deformation Gradients Imprint the Direction and Speed of En Masse Fibroblast Migration for Fast Healing

En masse cell migration is more relevant than single cell migration in physiological processes of tissue formation, such as embryogenesis, morphogenesis and wound healing. In these situations, cells are influenced by the proximity of other cells including interactions facilitated by substrate mechanics. Here we found that when fibroblasts migrated en masse over a hydrogel, they established a well-defined deformation field by traction forces and migrated along a trajectory defined by field gradients. The mechanics of the hydrogel determined the magnitude of the gradient. For materials stiff enough to withstand deformation related to cellular traction forces, such patterns did not form. Furthermore, migration patterns functioned poorly on very soft matrices where only a minimal traction gradient could be established. The largest degree of alignment and migration velocity occurred on the gels with the largest gradients. Granulation tissue formation in punch wounds of juvenile pigs was correlated strongly with the modulus of the implanted gel in agreement with in vitro en masse cell migration studies. These findings provide basic insight into the biomechanical influences on fibroblast movement in early wounds and relevant design criteria for development of tissue-engineered constructs that aim to stimulate en masse cell recruitment for rapid wound healing.

Evaluation of radiochromic gel dosimetry and polymer gel dosimetry in a clinical dose verification

A quantitative comparison of two full three-dimensional (3D) gel dosimetry techniques was assessed in a clinical setting: radiochromic gel dosimetry with an in-house developed optical laser CT scanner and polymer gel dosimetry with magnetic resonance imaging (MRI). To benchmark both gel dosimeters, they were exposed to a 6 MV photon beam and the depth dose was compared against a diamond detector measurement that served as golden standard. Both gel dosimeters were found accurate within 4% accuracy. In the 3D dose matrix of the radiochromic gel, hotspot dose deviations up to 8% were observed which are attributed to the fabrication procedure. The polymer gel readout was shown to be sensitive to B0 field and B1 field non-uniformities as well as temperature variations during scanning. The performance of the two gel dosimeters was also evaluated for a brain tumour IMRT treatment. Both gel measured dose distributions were compared against treatment planning system predicted dose maps which were validated independently with ion chamber measurements and portal dosimetry. In the radiochromic gel measurement, two sources of deviations could be identified. Firstly, the dose in a cluster of voxels near the edge of the phantom deviated from the planned dose. Secondly, the presence of dose hotspots in the order of 10% related to inhomogeneities in the gel limit the clinical acceptance of this dosimetry technique. Based on the results of the micelle gel dosimeter prototype presented here, chemical optimization will be subject of future work. Polymer gel dosimetry is capable of measuring the absolute dose in the whole 3D volume within 5% accuracy. A temperature stabilization technique is incorporated to increase the accuracy during short measurements, however keeping the temperature stable during long measurement times in both calibration phantoms and the volumetric phantom is more challenging. The sensitivity of MRI readout to minimal temperature fluctuations is demonstrated which proves the need for adequate compensation strategies.

A Safe and Efficient Method to Retrieve Mesenchymal Stem Cells from Three-Dimensional Fibrin Gels

Mesenchymal stem cells (MSCs) display multipotent characteristics that make them ideal for potential therapeutic applications. MSCs are typically cultured as monolayers on tissue culture plastic, but there is increasing evidence suggesting that they may lose their multipotency over time in vitro and eventually cease to retain any resemblance to in vivo resident MSCs. Three-dimensional (3D) culture systems that more closely recapitulate the physiological environment of MSCs and other cell types are increasingly explored for their capacity to support and maintain the cell phenotypes. In much of our own work, we have utilized fibrin, a natural protein-based material that serves as the provisional extracellular matrix during wound healing. Fibrin has proven to be useful in numerous tissue engineering applications and has been used clinically as a hemostatic material. Its rapid self-assembly driven by thrombin-mediated alteration of fibrinogen makes fibrin an attractive 3D substrate, in which cells can adhere, spread, proliferate, and undergo complex morphogenetic programs. However, there is a significant need for simple cost-effective methods to safely retrieve cells encapsulated within fibrin hydrogels to perform additional analyses or use the cells for therapy. Here, we present a safe and efficient protocol for the isolation of MSCs from 3D fibrin gels. The key ingredient of our successful extraction method is nattokinase, a serine protease of the subtilisin family that has a strong fibrinolytic activity. Our data show that MSCs recovered from 3D fibrin gels using nattokinase are not only viable but also retain their proliferative and multilineage potentials. Demonstrated for MSCs, this method can be readily adapted to retrieve any other cell type from 3D fibrin gel constructs for various applications, including expansion, bioassays, and in vivo implantation.

Effects of formulation properties on sol–gel behavior of chitosan/glycerolphosphate hydrogel

Chitosan solution containing glycerolphosphate disodium salt (Gp) is an injectable thermosensitive in situ gel-forming system which undergoes sol–gel transition under certain physiological pH and temperature conditions. When a drug-incorporated chitosan/Gp solution is injected into the body, it forms a three-dimensional gel at 37 °C, which allows the drug to be released in a sustained manner. This hydrogel can be used as a drug delivery system for prolonged release of peptides and glycopeptides. The objective of this work was to investigate the effect of different excipients on the sol–gel behavior of this thermosensitive hydrogel. Chitosan polymeric solutions (2 % w/v) containing Gp and different excipients, such as hydroxypropyl methyl cellulose (HPMC), polyethylene glycol (PEG) with two different molecular weights (PEG200 and PEG1000), and poloxamer (F127) in various concentrations, were prepared, and the pH, sol–gel transition time, and syringeability of the final solutions were evaluated. The obtained results point to HPMC as the best additive for chitosan/Gp solutions in developing an in situ gel-forming drug delivery system with optimum gelling time. A significant decrease was noted in the sol-to-gel transition time (from 90 to 60 s) when HPMC was added to the system. This may have been due to the HPMC structure which acted as a viscosity-enhancing and gel-promoting agent. The in vitro release of vancomycin hydrochloride from chitosan/Gp/HPMC hydrogel was also studied. Vancomycin release studies showed a sustained release profile for over 20 days. It can be concluded that combining chitosan/Gp and HPMC is a promising strategy for preparing a thermally reversible in situ gel-forming delivery system with an optimized gelation time.

Purification and characterization of transcription factors

Transcription factors (TFs) are essential for the expression of all proteins, including those involved in human health and disease. However, TFs are resistant to proteomic characterization because they are frequently masked by more abundant proteins due to the limited dynamic range of capillary liquid chromatography-tandem mass spectrometry and protein database searching. Purification methods, particularly strategies that exploit the high affinity of TFs for DNA response elements (REs) on gene promoters, can enrich TFs prior to proteomic analysis to improve dynamic range and penetrance of the TF proteome. For example, trapping of TF complexes specific for particular REs has been achieved by recovering the element DNA-protein complex on solid supports. Additional methods for improving dynamic range include two- and three-dimensional gel electrophoresis incorporating electrophoretic mobility shift assays and Southwestern blotting for detection. Here we review methods for TF purification and characterization. We fully expect that future investigations will apply these and other methods to illuminate this important but challenging proteome.

The Effectiveness of Cryoprotectants in Inhibiting Multiple Freeze-Thaw-Induced Functional and Rheological Changes in the Myofibrillar Proteins of Common Carp (Cyprinus carpio) Surimi

The purpose of the present study was to investigate the effects of cryoprotectants (4 % sucrose + 4 % sorbitol) on functional and rheological changes, including thermal stability, dynamic rheological and emulsifying properties, gel texture profile, gel whiteness, gel water-binding capacity, and gel microstructure, in the myofibrillar proteins (MP) of common carp (Cyprinus carpio) surimi subjected to multiple freeze-thaw cycles (FT, 0, 1, 3 and 5 times). Increased numbers of FT cycles were accompanied by reduced thermal transition temperature (Tmax), reduced enthalpy of denaturation (ΔH) (P < 0.05), and enhanced susceptibility to thermal aggregation. The observation of the gel microstructure indicated that the FT processes produced empty spaces and changed the aggregate gel structure into a coarser-stranded network. The addition of cryoprotectants significantly prevented the reduction of MP thermal stability (P < 0.05). The protective effect on protein functionality was demonstrated by the cryoprotectant’s efficacy in maintaining the three-dimensional gel network by small-strain oscillatory rheological testing and increasing the emulsifying capacity and emulsion stability of the MP. The FT process caused a decrease (P < 0.05) in whiteness, water-binding capacity, and texture (hardness, springiness, and gumminess) of the MP gels, which were reduced by the addition of cryoprotectants. Overall, the FT-induced loss of the abovementioned functional and rheological properties was significantly reduced by the presence of cryoprotectants.

Evaluation of three-dimensional gel electrophoresis to improve quantitative profiling of complex proteomes

Two-dimensional remains one of the main experimental approaches in proteome analysis. However, comigration of protein leads to several limitations: lack of accuracy in protein identification, impaired comparative quantification, and PTM detection. We have optimized a third additional step of in-gel separation to alleviate comigration associated drawbacks. Spot resolution is strikingly improved following this simple and rapid method and the positive impact on protein and peptide identification from MS/MS data, on the analysis of relative changes in protein abundance, and on the detection of PTM is described.

Investigation of cellulose acetate viscoelastic properties in different solvents and microstructure

This paper deals with the effect of solvent on the viscoelastic properties and microstructure of cellulose acetate (CA) by means of rheological measurements, dynamic-mechanical analysis and scanning electron microscopy. Acetone, acetic acid, dimethylacetamide (DMAc) and dimethylformamide (DMF) were used as good solvents and water as a non-solvent. The addition of water in the cellulose acetate/solvent mixture led to the development of an intense shear thinning behavior, as it caused the formation of CA agglomerates which were disrupted in a steady shearing condition. Apart from this, a three-dimensional elastic gel behavior in the CA/DMF/water and CA/DMAc/water solutions was observed during dynamical rheological analysis. The formation of CA agglomerates was controlled by the solvent type and resulted in microstructure changes, going from a dense structure to a porous one, and also influenced the CA chain rigidity and consequently the glass transition temperatures of the CA films.