Ultrafine Network Research Articles

Preparation of 3D Printed Polylactic Acid/Bacterial Cellulose Composite Scaffold for Tissue Engineering Applications.

Bacterial cellulose (BC) has become a universal biomaterial owing to its intrinsic properties. BC fibers are composed of microfibers with a diameter of 3-4 nm into fiber bundles with a thickness of 40-60 nm, and interweave with each other to form a well-developed ultra-fine network structure. Polylactic acid (PLA) has good mechanical properties and excellent biocompatibility and biodegradability. Therefore, PLA has been widely applied in tissue engineering. Addressed herein is a novel type of PLA/BC (PLA/BC) composite scaffold prepared by 3D printing (3D), 3D modeling of the required porous membrane material support established in the computer, and decomposition of the model into 5 layer 20 μM sheets. The range of PLA loadings assessed in this work was 1.0 wt.%, 1.5 wt.%, and 2.0 wt.%, and its physicochemical properties and biological properties were characterized and evaluated. Tensile strength of PLA/BC composite scaffolds increased to 66.49 MPa compared to that of a pure BC film (25.61 MPa). Hydrophilicity was tunable with the amount of added PLA. In this paper, the effects of 3D round hole and stripe surface topology on cell growth behavior were characterized. Schwann cells (SCs) adhered to the surface of the 3D composite membrane successfully, and their proliferation rate on the surface of the regular circular pore and stripe structure was better than that of the smooth surface. Erythrocyte fixation and platelet adhesion experiments showed that the 3D composite scaffold had excellent blood compatibility. Further degradation studies showed that loose structures appeared after 1 week, and structural defects began after 3 weeks. The in vitro degradation results showed that the degradation rate of the BC membrane in simulated body fluid after 6 weeks was 14.38%, while the degradation rate of the PLA/BC composite scaffold was 18.75%.

Designing electrospun shellac nanofibers with mupirocin using the Box-Behnken approach for topical wound care

This study attempted to develop shellac (SHL) nanofibers containing a topical antibiotic, mupirocin (MP), as an alternative wound healing material. The impacts of formulation and process parameters such as SHL concentration, MP content, and applied voltage on the morphology of fibers were examined based on a 33 Box-Behnken experimental design with triplicate center points. The results indicated that the amounts of polymeric SHL and encapsulated MP were considered factors affecting the morphology of fabricated fibers, including size and bead ratio. As the concentrations of SHL and MP increased, the large-sized fibers would be obtained. Meanwhile, the appearance of beads would be lessened with the enhanced amount of SHL. The excellent encapsulation of MP in SHL carrier was indicated by the high entrapment efficiency (88.12 ± 0.09% - 109.93 ± 3.23%) which might be possibly due to the ultrafine network and microporous structures of nanofibers and the good affinity of MP for entrapping between the polymeric SHL as referred to the results of the characterization study. According to the assay of antimicrobial activity, S. aureus, the leading cause of wound infection, was entirely killed since 5 min after exposure to the SHL nanofibers loaded with MP, and the regrowth of living S. aureus was not found throughout the next 6 h. Therefore, the SHL nanofibers containing MP seemed to be an effective wound dressing with high encapsulation efficiency and potential antimicrobial activity against S. aureus over a period of time.

Simultaneously improving the strength and ductility of the as-sintered (TiB+La2O3)/Ti composites by in-situ planting ultra-fine networks into the composite powder

This study creatively proposed a technique to effectively overcome the strength-ductility mismatch of the as-sintered titanium matrix composites by in-situ planting TiB nano-fibers and La2O3 nano-particles as ultra-fine networks into the composite powder. (TiB+La2O3)/Ti composites with excellent strength-ductility synergy were fabricated by hot pressing. The ultra-fine network eliminated the Widmanstatten microstructure and exerted a significantly fine-grain effect. Thus, the elongation of the as-sintered 1.2 vol.% (TiB+La2O3)/Ti composite was significantly improved from 2.2 to 10.8% compared with the matrix alloy, and the ultimate tensile strength was simultaneously enhanced to 1098.6 MPa. Meanwhile, the tensile strength of 2.4 vol.% (TiB+La2O3)/Ti reached 774.8 MPa at 600 °C, even superior to many wrought composites. The strength-ductility synergy effects were mainly attributed to the significant fine-grain effect and the synergistic effect between nano-reinforcements and soft matrix. This work opened up a new route for directly sintering nanoparticles reinforced titanium matrix composites components with promising comprehensive properties.

Simultaneously Improve the Strength and Ductility of the As-Sintered Ti Composites by Pre-Planting Ultra-Fine Network into the Composites Powder

Simultaneously Improve the Strength and Ductility of the As-Sintered Ti Composites by Pre-Planting Ultra-Fine Network into the Composites Powder

Novel strategy of planting nano-TiB fibers with ultra-fine network distribution into Ti-composite powder and its thermal transition mechanism

This work creatively planted nano-TiB fibers (10∼50 nm in width) as a novel ultra-fine network in pre-alloyed Ti-composite powder based on the rapid eutectic reaction method, constitutional supercooling would limit the ultra-fine network skeletons to micro-scale (2∼5 μm), which were thermal stabilized below 900 °C. The new configuration structure of ultra-fine network loaded the nano TiB-fibers is expected to improve the high temperature properties. However, high temperature would coarsen the nano-TiB fibers, resulting in the destruction of the ultra-fine network. The decomposition and growth of the TiB nano-fibers followed the Ostwald ripening mechanism and then coarsened following the merging mechanism, obtaining random distribution of two-scale TiB. It provided a new guidance for optimizing the nano-TiB size-scale and distribution by controlling the sintering temperature, which was useful for constructing multistage network structure enhanced Ti-composites based on pre-planted nano-TiB in alloy powders.

Effects of heat treatment on microstructure and mechanical properties of SLMed Sc-modified AlSi10Mg alloy

The influence of heat treatments on the microstructures and mechanical properties of the selective laser melting manufactured AlSi10Mg alloy modified with Sc was systematically investigated. The results showed that the addition of Sc element introduced primary Al3Sc, which increased the heterogeneous nucleation during the solidification of AlSi10Mg alloy, and then the ultrafine network eutectic structure was obtained, and hence the tensile strength was improved significantly (nearly 23 ​%). During the heat treatment process, the network eutectic structure transformed from continuous to discontinuous, and the grain refinement was weakened with an increasing heating temperature, both of which affected the mechanical properties of the Sc modified AlSi10Mg alloy. The tensile strength decreased from 438 ​± ​10 ​MPa for the Sc-modified alloy to 208 ​± ​6 ​MPa, while the fracture strain significantly increased from 6 ​± ​0.2 ​% to 30.2 ​± ​1.2 ​% when the Sc-modified alloy was heat-treated at 325 ​°C for 12 ​h. It has been found that the desirable microstructure and mechanical properties of SLM Sc-modified AlSi10Mg alloy can be realized by controlling the heat treatment process parameters.

Embedding boron into Ti powder for direct laser deposited titanium matrix composite: Microstructure evolution and the role of nano-TiB network structure

The titanium powder embedded with 2.5 vol% TiB was in-situ fabricated by gas atomization and applied for direct laser deposited (DLD) titanium matrix composites. Consistent with the network distributed boron-rich zone in composite powder, a three-dimensional (3D) in-situ ultrafine network structure, consisting of nano-TiB whiskers (TiBw), was characterized throughout the as-fabricated composite (DLDed TiB–Ti). Both the dendritic and equiaxed network, attributed to the boron-induced constitutional supercooling and subsequent nucleation and growth of primary β-Ti, existed in the composite. The addition of boron (B) had a positive effect on the equiaxial transition and grain refinement of both primary β-Ti grains and α grains. Tensile tests showed an enhancement of strength compared with conventionally fabricated homogeneous TiB–Ti composites and selective laser melted CP-Ti. Analyzing the strength mechanism of the DLDed TiB–Ti, apart from the fine-grain strengthening and load-bearing effect of TiBw, the TiB network was found to have an additional contribution to the improvement of strength. Fracture morphology and in situ tensile observation showed the role of network structure in plastic deformation limitation, crack deflection and blunting, which was mainly attributed to the ultrafine cell size and revealed the significance of network structure.

Evaluation of Different Methods for Cultivating Gluconacetobacter hansenii for Bacterial Cellulose and Montmorillonite Biocomposite Production: Wound-Dressing Applications.

Bacterial cellulose (BC) has received considerable attention due to its unique properties, including an ultrafine network structure with high purity, mechanical strength, inherent biodegradability, biocompatibility, high water-holding capacity and high crystallinity. These properties allow BC to be used in biomedical and industrial applications, such as medical product. This research investigated the production of BC by Gluconacetobacter hansenii ATCC 23769 using different carbon sources (glucose, mannitol, sucrose and xylose) at two different concentrations (25 and 50 g∙L−1). The BC produced was used to develop a biocomposite with montmorillonite (MMT), a clay mineral that possesses interesting characteristics for enhancing BC physical-chemical properties, at 0.5, 1, 2 and 3% concentrations. The resulting biocomposites were characterized in terms of their physical and barrier properties, morphologies, water-uptake capacities, and thermal stabilities. Our results show that bacteria presented higher BC yields in media with higher glucose concentrations (50 g∙L−1) after a 14-day incubation period. Additionally, the incorporation of MMT significantly improved the mechanical and thermal properties of the BC membranes. The degradation temperature of the composites was extended, and a decrease in the water holding capacity (WHC) and an improvement in the water release rate (WRR) were noted. Determining a cost-effective medium for the production of BC and the characterization of the produced composites are extremely important for the biomedical applications of BC, such as in wound dressing materials.

Optimization of Anion Exchange Membranes Derived from Bacterial Cellulose for Solid-State Supercapacitors

At present, supercapacitors have received increasing attention, due to its low cost, light-weight, high-performance environmentally-friendly and flexible. Electrolyte has been identified as one of the most influential components in the performance of electrochemical supercapacitors. However, mostly conventional supercapacitors used liquid electrolyte, such as (KOH solution). These liquid electrolytes limit the development of supercapacitors owing to their corrosivity and easy leak. Solid electrolytes not only eliminate leakage problems, but also act as membranes to prevent internal short circuits. Bacterial cellulose (BC) membrane attracted extensive attention, due to the high crystallinity, ultra-fine network structure, high mechanical strength, low cost and good degradability. In this work, Alkaline anion exchange membrane (AAEM) have been developed by using modified BC membrane. The membranes are characterized and tested in detail by fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), Differential scanning calorimetry (DSC), thermal gravity analysis (TG), mechanical property, ion transport number, AC impedance technique, water uptake, ion exchange capacity (IEC) and swelling ratio to evaluate their applicability in solid-state supercapacitors. The membrane shows a high OH- conductivity of 0.031 S cm-1, excellent stability, and has potential in the application of supercapacitors.

Design and characterisation of electrospun shellac-polyvinylpyrrolidone blended micro/nanofibres loaded with monolaurin for application in wound healing

Due to their ultrafine network structures, electrospun nanofibres have been potentially used for wound application. In order to develop a desired wound dressing material, shellac (SHL) was blended with polyvinyl pyrrolidone (PVP). Monolaurin (ML), which is a natural antimicrobial lipid, was incorporated into the SHL-PVP blended fibres to prevent delayed wound healing resulting from microbial infection. A full factorial design with three replicated centre points was employed in order to determine the main and interaction effects of various factors including SHL ratio in SHL-PVP blended solution, ML content and applied voltage on the multiple responses such as morphology, surface wettability, absorbency and mechanical properties. According to the results, an increase in the PVP content could lead to a significant increase in tensile strength and elongation. In addition, the presence of PVP contributed to an improvement in the drug loading capacity and dissolution rate. The fabricated fibres loaded with ML exhibited an excellent activity against Staphylococcus aureus and Candida albicans, and also provided an enhanced ability in the cell adhesion. Therefore, SHL-PVP blended fibres loaded with ML might be effectively used for application in wound healing.

Bacterial Cellulose/Alginate Nanocomposite for Antimicrobial Wound Dressing

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Synthesis of bacterial cellulose and bacterial cellulose nanocrystals for their applications in the stabilization of olive oil pickering emulsion

Although bacterial cellulose (BC) and bacterial cellulose nanocrystals (BCNs) have considered to be edible, non-toxic, biocompatible and biodegradable, there is still the dearth of reports of BC and BCNs as the emulsifiers of Pickering emulsions with respect to the applications in foods, cosmetics and medicines. In this work, BC with ultrafine network architecture and 8–40 nm crystalline microfibrils in diameter was produced by Acetobacter xylinum, and then it was hydrolyzed by sulfuric acid followed by the oxidation of hydrogen peroxide to prepare BCNs. The physicochemical properties of BC and BCNs were contrastively evaluated by FT-IR, XRD, TGA and dynamic light scattering (DLS). The emulsifying performances of BC and BCNs in the stabilization of olive oil Pickering emulsion were further evaluated by optical microscope (OM) and fluorescent microscope (FM). Experimental results showed that the sulfuric acid hydrolysis of BC induced the removal of the amorphous components and the cleavage of the crystalline microfibrils, making BCNs possess the initiating decomposition temperature of 350 °C, the crystallinity index (CrI) of 89.6%, average size of 259.6 nm with PDI of 0.26 and zeta potential at about −34.8 mV, which exhibited high thermal stability and good emulsifying performance in comparison with BC. Furthermore, the effects of pH and ionic strength on emulsion stability were also investigated. In comparison to BC, BCNs were more sensitive in response to the change of pH and ionic strength.

Oxygen‐Deficient Bismuth Oxide/Graphene of Ultrahigh Capacitance as Advanced Flexible Anode for Asymmetric Supercapacitors

Oxygen‐deficient bismuth oxide (r‐Bi2O3)/graphene (GN) is designed, fabricated, and demonstrated via a facile solvothermal and subsequent solution reduction method. The ultrafine network bacterial cellulose (BC) as substrate for r‐Bi2O3/GN exhibits high flexibility, remarkable tensile strength (55.1 MPa), and large mass loading of 9.8 mg cm−2. The flexible r‐Bi2O3/GN/BC anode delivers appreciable areal capacitance (6675 mF cm−2 at 1 mA cm−2) coupled with good rate capability (3750 mF cm−2 at 50 mA cm−2). In addition, oxygen vacancies have great influence on the capacitive performance of Bi2O3, delivering significantly improved capacitive values than the untreated Bi2O3 flexible electrode, and ultrahigh gravimetric capacitance of 1137 F g−1 (based on the mass of r‐Bi2O3) can be obtained, achieving 83% of the theoretical value (1370 F g−1). Flexible asymmetric supercapacitor is fabricated with r‐Bi2O3/GN/BC and Co3O4/GN/BC paper as the negative and positive electrodes, respectively. The operation voltage is expanded to 1.6 V, revealing a maximum areal energy density of 0.449 mWh cm−2 (7.74 mWh cm−3) and an areal power density of 40 mW cm−2 (690 mW cm−3). Therefore, this flexible anode with excellent electrochemical performance and high mechanical properties shows great potential in the field of flexible energy storage devices.

Applications of bacterial cellulose in food, cosmetics and drug delivery

Bacterial cellulose (BC) is a versatile biopolymer with better material properties, such as purity, high degree of porosity, relative high permeability to liquid and gases, high water-uptake capacity, tensile strength and ultrafine network. This review explores the applications of BC and its hydrogels in the fields of food, cosmetics and drug delivery. Applications of BC in foods are ranging from traditional dessert, low cholesterol diet, vegetarian meat, and as food additive and dietary aid to novel applications, such as immobilization of enzymes and cells. Applications in cosmetics include facial mask, facial scrub, personal cleansing formulations and contact lenses. BC for controlled drug delivery, transdermal drug delivery, dental drug delivery, protein delivery, tissue engineering drug delivery, macromolecular prodrug delivery and molecularly imprinted polymer based enantioselective drug delivery are also discussed in this review. The applications of BC in food and cosmetics provide the basis for BC-based functional foods, nutraceuticals, cosmeceuticals and medicated cosmetics. On the basis of current studies, the BC-based drug delivery could be further fine-tuned to get more sophisticated control on stimuli-responsive drug release. Along with the currently available literature, further experiments are required to obtain a blueprint of drug in vivo performance, bioavailability and in vitro–in vivo correlation.

Bacterial cellulose production from the litchi extract by Gluconacetobacter xylinus

ABSTRACTAlthough litchi has both nutrient and edible value, the extremely short preservation time limited its further market promotion. To explore processed litchi products with longer preservation time, litchi extract was selected as an alternative feedstock for production of bacterial cellulose (BC). After 2 weeks of static fermentation, 2.53 g/L of the BC membrane was obtained. The trace elements including magnesium (Mg) and sodium (Na) in the litchi extract were partly absorbed in the BC membrane, but no potassium (K) element was detected in it, curiously. Scanning electron microscope (SEM) photographs exhibited an ultrafine network nanostructure for the BC produced in the litchi extract. Analysis of the fourier-transform infrared spectroscopy (FTIR) confirmed the pellicles to be a cellulosic material. Interestingly, X-ray diffraction (XRD) results showed the BC membrane obtained from litchi extract had higher crystallinity of 94.0% than that from HS medium. Overall, the work showed the potential of producing high value-added polymer from litchi resources.

Novel Antimicrobial Peptides Bacterial Cellulose Obtained by Symbioses Culture Between Polyhexanide Biguanide (PHMB) and Green Tea

Bacterial cellulose is a highly hydrated pellicle made up of a random assembly of ribbon shaped fibers less than 5 nm wide. The unique properties provided by the nanometric structure have led to a number of diagnostic biological probes, display devices due to their unique size-dependent medical applications. Bacterial cellulose matrix extracellular is a novel biotechnology and unique medicine indicated for ultimate chronic wound treatment management, drug delivery, tissue engineering, skin cancer and offers an actual and effective solution to a serious medical and social problem and to promote rapid healing in lesions caused by Diabetic burns, ulcers of the lower limbs or any other circumstance in which there's epidermal or dermal loss. In this work, it is reported novel antimicrobial peptides (AMPs) bacterial cellulose/polyhexanide biguanide (PHMB) which are produced by symbioses culture between polyhexanide biguanide and green tea culture medium resulting in the pure 3-D structure consisting of an ultra-fine network of novel biocellulose/PHMB nanofibres matrix (2-8 nm), highly hydrated (99% in weight), and with higher molecular weight, full biocompatibility.

Recent advances in bacterial cellulose

Bacterial cellulose (BC) produced by some microorganisms has been widely accepted as a multifunctional nano-biomaterial. It is composed of linear glucan molecules attached with hydrogen bonds, which appears similar to plant cellulose. However, when compared with other conventional natural or synthesized counterparts, BC performs better in areas such as biomedicine, functional devices, water treatment, nanofillers, etc. for its distinct superior chemical purity, crystallinity, biocompatibility, and ultrafine network architecture. When BC is incorporated in a material or used as a scaffold, novel features result that are related to BC’s intrinsic characteristics mentioned above. This review mainly summarizes the recent developments of the functional products fabricated with BC. Besides, the controllable cultivation conditions should also be discussed for expecting to make a breakthrough in its productivity. We highlight the literatures mainly in last 5 years, exerting ourselves to provide the state-of-the-art opinions in areas wherever are focused on for BC researching.

In vitro enzymatic conversion of γ-aminobutyric acid immobilization of glutamate decarboxylase with bacterial cellulose membrane (BCM) and non-linear model establishment

The work investigated the properties and feasibility of using bacterial cellulose membrane (BCM) as a new and environmental friendly support carrier to immobilize glutamate decarboxylase (GAD) (a unique enzyme in the conversion of γ-aminobutyric acid (GABA) production). During cultivation, the porosities of BCM decreased successively with more extended fibrils piling above one another in a criss-crossing manner thus forming condensed and spatial structure. The BCM with this ultrafine network structure was found to immobilize GAD best via covalent binding because of the highest efficiency of immobilization (87.56% of the enzyme was bonded) and a good operational stability. And the covalent binding efficiency (amount of enzyme immobilized versus lost) was closely related to the porosity or the inner network of the BCM, not to the surface area. The capacity per surface area (mg/cm2) increased from 1.267mg/cm2 to 3.683mg/cm2 when the porosity of BCM ranged from 49% to 73.80%, while a declining trend of the loss of GAD specific activity (from 29.30%/cm2 to 7.38%/cm2) was observed when the porosity increased from 49.9% to 72.30%. Two non-linear regression relationships, between the porosity and loading capacity and between porosity and enzyme activity loss, were empirically modeled with the determination of coefficient R2 of 0.980 and 0.977, respectively. Finally, the established in vitro enzymatic conversion process demonstrated 6.03g/L of GABA at 0.10mol/L Glu, 60min of retention time and 160mL of suspension volume after the 1st run and a loss of 4.15% after the 4th run. The productivity of GABA was 6.03gL−1h−1, higher than that from other reported processes.

Antimicrobial porous hybrids consisting of bacterial nanocellulose and silver nanoparticles

The increasing resistance of pathogens and bacteria is a serious problem in the medical treatment of wounds and injuries. Therefore, new therapeutic agents are not solely based on antibiotics, but also on the use of antimicrobial metal nanoparticles. In this paper we present an innovative method to prepare porous hybrids consisting of bacterial nanocellulose (BNC) and silver nanoparticles (AgNPs). The stepwise modification is based on fairly simple chemical reactions already described for two-dimensional cellulose films. We transferred this method to the three-dimensional, porous network of BNC leading to an antimicrobial activation of its surface. Compared to former approaches, the ultrafine network structure of BNC is less damaged by using mild chemicals. The amount and distribution of the AgNPs on the modified BNC was investigated using scanning electron microscopy. The AgNPs are firmly immobilized on the top and bottom surface of the BNC by chemical interactions. Their size and quantity increase with an increasing concentration of AgNO3 and extended reaction time in the AgNO3 solution. A strong antimicrobial activity of the BNC-AgNP hybrids against Escherichia coli was detected. Furthermore, agar diffusion tests confirmed that this activity is restricted to the modified dressing itself, avoiding a release of NPs into the wound. Therefore, the produced hybrids could be potentially suited as novel antimicrobial wound dressings.

Ductile and High Strength White Cast Iron of Ultrafine Interconnected Network Morphology

Fe100–x C x melts (x = 18 to 24) can be cast under B2O3 flux into solids of interconnected network morphology, with a wavelength in the submicron range. There are two major constituent subnetworks, which are a brittle Fe3C subnetwork and a ductile αFe subnetwork. The Fe100–x C x network alloys, therefore, are white cast iron of novel microstructure. Fe100–x C x specimens of x = 18 to 21 are ductile and the yield strength can be as large as ~3200 MPa. Fe100–x C x specimens of x = 22 to 24 are in the regime of a ductile-to-brittle transition. The compressive strength is high, at ~2700 MPa. Microstructural analysis indicates that the ultrafine network morphology and the ductile αFe subnetwork are responsible for the ductility exhibited in Fe100–x C x network alloys of x = 17 to 21. They are also responsible for the high compressive strength in Fe100–x C x network alloys of x = 22 to 24.