Bacterial synthesized cellulose — artificial blood vessels for microsurgery

Cellulose-Based Bio- and Nanocomposites: A Review

Cellulose macro- and nanofibers have gained increasing attention due to the high strength and stiffness, biodegradability and renewability, and their production and application in development of composites. Application of cellulose nanofibers for the development of composites is a relatively new research area. Cellulose macro- and nanofibers can be used as reinforcement in composite materials because of enhanced mechanical, thermal, and biodegradation properties of composites. Cellulose fibers are hydrophilic in nature, so it becomes necessary to increase their surface roughness for the development of composites with enhanced properties. In the present paper, we have reviewed the surface modification of cellulose fibers by various methods. Processing methods, properties, and various applications of nanocellulose and cellulosic composites are also discussed in this paper.

Structure of bacterial cellulose synthase subunit D octamer with four inner passageways

The cellulose synthesizing terminal complex consisting of subunits A, B, C, and D in Acetobacter xylinum spans the outer and inner cell membranes to synthesize and extrude glucan chains, which are assembled into subelementary fibrils and further into a ribbon. We determined the structures of subunit D (AxCeSD/AxBcsD) with both N- and C-terminal His(6) tags, and in complex with cellopentaose. The structure of AxCeSD shows an exquisite cylinder shape (height: ∼65 Å, outer diameter: ∼90 Å, and inner diameter: ∼25 Å) with a right-hand twisted dimer interface on the cylinder wall, formed by octamer as a functional unit. All N termini of the octamer are positioned inside the AxCeSD cylinder and create four passageways. The location of cellopentaoses in the complex structure suggests that four glucan chains are extruded individually through their own passageway along the dimer interface in a twisted manner. The complex structure also shows that the N-terminal loop, especially residue Lys6, seems to be important for cellulose production, as confirmed by in vivo assay using mutant cells with axcesD gene disruption and N-terminus truncation. Taking all results together, a model of the bacterial terminal complex is discussed.

Improving bacterial cellulose for blood vessel replacement: Functionalization with a chimeric protein containing a cellulose-binding module and an adhesion peptide

Chimeric proteins containing a cellulose-binding module (CBM) and an adhesion peptide (RGD or GRGDY) were produced and used to improve the adhesion of human microvascular endothelial cells (HMEC) to bacterial cellulose (BC). The effect of these proteins on the HMEC-BC interaction was studied. The results obtained demonstrated that recombinant proteins containing adhesion sequences were able to significantly increase the attachment of HMEC to BC surfaces, especially the RGD sequence. The images obtained by scanning electron microscopy showed that the cells on the RGD-treated BC present a more elongated morphology 48h after cell seeding. The results also showed that RGD decreased the in-growth of HMEC cells through the BC and stimulated the early formation of cord-like structures by these endothelial cells. Thus, the use of recombinant proteins containing a CBM domain, with high affinity and specificity for cellulose surfaces allows control of the interaction of this material with cells. CBM may be combined with virtually any biologically active protein for the modification of cellulose-based materials, for in vitro or in vivo applications.

Development and Characteristic of Bacterial Cellulose for Antimicrobial Wound Dressing

Bacterial cellulose (BC) material was obtained through fermentation by Acetobacter xylinumis with superior functional properties. BC is an interesting material for using as a wound dressing since it provides moist environment to a wound and results in a better wound healing. With the aim of using BC as a wound dressing material, moisture content, swelling ratio, purity and antimicrobial activity were investigated. Fresh prepared BC membrane was smooth, colorless, jelly alike, and it showed translucence after NaOH treatment. The purity of the cellulosic pellicle reached 98.32%, and it had good water holding capacity (98.02%) and high swelling ratio (69.88%). Antimicrobial activity test showed that BC material had excellent sterilizing efficacy against Escherichia coli and Staphylococcus aureus. The surface of BC membranes was porous network structure observed by scanning electron microscopy (SEM). Infrared spectroscopy (IR) results showed that this membrane belong to bio-cellulose materials. BC displayed higher water content and water holding capacity, as well as higher purity and antimicrobial activity. It has an extensive usage in biomedicine areas.

Tissue-engineered conduit using urine-derived stem cells seeded bacterial cellulose polymer in urinary reconstruction and diversion

The objective of this study was to generate bacterial cellulose (BC) scaffolds seeded with human urine-derived stem cells (USC) to form a tissue-engineered conduit for use in urinary diversion. Microporous BC scaffolds were synthesized and USC were induced to differentiate into urothelial and smooth muscle cells (SMC). Induced USC (10(6) cells/cm(2)) were seeded onto BC under static and 3D dynamic (10 or 40 RPM) conditions and cultured for 2 weeks. The urothelial cells and SMC derived from USC formed multilayers on the BC scaffold surface, and some cells infiltrated into the scaffold. The urothelium derived from USC differentiation expressed urothelial markers (uroplakin Ia and AE1/AE3) and the SMC expressed SMC markers (α-smooth muscle actin and desmin). In addition, USC/BC scaffold constructs were implanted into athymic mice, and the cells were tracked using immunohistochemical staining for human nuclear antigen. In vivo, the cells appeared to differentiate and express urothelial and SMC markers. In conclusion, porous BC scaffolds allow 3 dimensional growth of USC, leading to formation of a multilayered urothelium and cell-matrix infiltration. Thus, cell-seeded BC scaffolds hold promise for use in tissue-engineered urinary conduits for urinary reconstruction.

Novel in vivo-degradable cellulose-chitin copolymer from metabolically engineered Gluconacetobacter xylinus

Despite excellent biocompatibility and mechanical properties, the poor in vitro and in vivo degradability of cellulose has limited its biomedical and biomass conversion applications. To address this issue, we report a metabolic engineering-based approach to the rational redesign of cellular metabolites to introduce N-acetylglucosamine (GlcNAc) residues into cellulosic biopolymers during de novo synthesis from Gluconacetobacter xylinus. The cellulose produced from these engineered cells (modified bacterial cellulose [MBC]) was evaluated and compared with cellulose produced from normal cells (bacterial cellulose [BC]). High GlcNAc content and lower crystallinity in MBC compared to BC make this a multifunctional bioengineered polymer susceptible to lysozyme, an enzyme widespread in the human body, and to rapid hydrolysis by cellulase, an enzyme commonly used in biomass conversion. Degradability in vivo was demonstrated in subcutaneous implants in mice, where modified cellulose was completely degraded within 20 days. We provide a new route toward the production of a family of tailorable modified cellulosic biopolymers that overcome the longstanding limitation associated with the poor degradability of cellulose for a wide range of potential applications.

Preparation and Characterization of Novel Bacterial Cellulose/Gelatin Scaffold for Tissue Regeneration Using Bacterial Cellulose Hydrogel

Bacterial cellulose (BC) and gelatin are well-known biomaterials. The novel bacterial cellulose/gelatin composite scaffolds were prepared using aqueous gelatin solution and bacterial cellulose excreted by Acetobacter xylinum. The prepared bacterial cellulose/gelatin scaffolds were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, mechanical test, swelling, and thermal studies. The morphology of these bacterial cellulose/gelatin scaffolds indicated that the gelatin molecules could penetrate well between the individual nanofibers of the bacterial cellulose. With the incorporation of gelatin in the bacterial cellulose, the crystallinity index tended to decrease while the thermal stability was improved. After the incorporation of gelatin in the bacterial cellulose, Young’s modulus of the composite was increased from 3.7 GPa to 3.9 GPa, while the tensile strength and strain at break point were decreased from 170 MPa (7.5%) to 114 MPa (4%), respectively. The swelling behavior test indicated that the water uptake capacity of the composite was only half of the pure bacterial cellulose. Cell adhesion studies were carried out using 3T3 fibroblast cells. The cells incubated with BC/gelatin scaffolds for 48 h were capable of forming cell adhesion and proliferation. It showed much better biocompatibility than pure bacterial cellulose. So, the prepared BC/gelatin scaffolds are bioactive and may be suitable for cell adhesion/attachment, suggesting that these scaffolds can be used for wound dressing or tissue engineering scaffolds. Therefore, these novel BC/gelatin scaffolds are useful for biomedical applications.

Influence of 1-methylcyclopropene (1-MCP) on the production of bacterial cellulose biosynthesized by Acetobacter xylinum under the agitated culture

AIMS

Bacterial cellulose is an extracellular polysaccharide secreted by Acetobacter xylinum, which has become a novel material increasingly used in food and medical industries. However, its broad application is limited by its low yield and high cost. 1-Methylcyclopropene (1-MCP) is a potent inhibitor to either exogenous or endogenous ethylene during the biological senescence of plants, which has been broadly applied in commercial preservation of fruits and vegetables. The purpose of this study was to investigate the effects of 1-MCP on both the growth of Acet. xylinum and its cellulose production to demonstrate the potential enhancement of bacterial cellulose yield.

METHODS AND RESULTS

Three groups of samples were fermented under agitated culture with 125 rev min(-1) rotational speed. To the culture media, 0.14 mg of 1-MCP contained in 100 mg dextrose powder was added on assigned days or on the first culture day only. Results from the measurement of bacterial cell concentration and bacterial cellulose yield at the end of a 12-day culture demonstrated that cultures excluding 1-MCP displayed a higher cell concentration and a lower cellulose production, while cultures containing 1-MCP produced 15.6% more cellulose (1-MCP added on day 1) and 25.4% (1-MCP added on each assigned day) with less biomass.

CONCLUSIONS

1-MCP was able to affect the growth of Acet. xylinum cells and resulted in increasing bacterial cellulose yield up to 25.4% over controls, which did not contain 1-MCP.

SIGNIFICANCE AND IMPACT OF THE STUDY

This was the first study to use the growth inhibitor of plants to investigate its effects on bacterial growth and production. It also demonstrated a significant enhancement of bacterial cellulose yield by the addition of 1-MCP during the common agitated culture of Acet. xylinum.

White biotechnology for cellulose manufacturing--the HoLiR concept

A variety of approaches are available for generation of bacteria-produced nanocellulose (BNC) in different forms. BNC production under static cultivation conditions usually results in fleeces or foils, characterized by a homogeneous, three-dimensional network of nanofibers and a uniform surface. However, under static cultivation conditions in batch vessels, the widths and the lengths of the BNC sheets cultured are determined by the dimensions of the culture vessel. In this contribution, a novel, efficient process for a (semi-)continuous cultivation of planar BNC fleeces and foils with a freely selectable length and an adjustable height is presented. By means of comprehensive investigations, the comparability of the BNC harvested to that gained from static cultivation under batch conditions is demonstrated. A first estimation of the production costs further shows that this type of processing allows for significant cost reductions compared to static cultivation of BNC in Erlenmeyer flasks.

Improving the affinity of fibroblasts for bacterial cellulose using carbohydrate-binding modules fused to RGD

The attachment of cells to biomedical materials can be improved by using adhesion sequences, such as Arg-Gly-Asp (RGD), found in several extracellular matrix proteins. In this work, bifunctional recombinant proteins, with a Cellulose-Binding Module (CBM), from the cellulosome of Clostridium thermocellum and cell binding sequences-RGD, GRGDY-were cloned and expressed in E.coli. These RGD-containing cellulose binding proteins were purified and used to coat bacterial cellulose fibres. Its effect on the cell adhesion/biocompatibility properties was tested using a mouse embryo fibroblasts culture. Bacterial cellulose (BC) secreted by Gluconacetobacter xylinus (=Acetobacter xylinum) is a material with unique properties and promising biomedical applications. CBMs adsorbs specifically and tightly on cellulose. Thus, they are a useful tool to address the fused RGD sequence (or other bioactive peptides) to the cellulose surface, in a specific and simple way. Indeed, fibroblasts exhibit improved ability to interact with bacterial cellulose sheets coated with RGD-CBM proteins, as compared with cellulose treated with the CBM, that is, without the adhesion peptide. The effect of the several fusion proteins produced was analyzed.

Optimization of the mechanical performance of bacterial cellulose/poly(L-lactic) acid composites

Understanding the nature of the interface between nanofibers and polymer resins in composite materials is challenging because of the complexity of interactions that may occur between fibers and between the matrix and the fibers. The ability to select the most efficient amount of reinforcement for stress transfer, making a saving on both cost and weight, is also a key part of composite design. The use of Raman spectroscopy to investigate micromechanical properties of laminated bacterial cellulose (BC)/poly(l-lactic) acid (PLLA) resin composites is reported for the first time as a means for understanding the fundamental stress-transfer processes in these composites, but also as a tool to select appropriate processing and volume fraction of the reinforcing fibers. Two forms of BC networks are investigated, namely, one cultured for 3 days and another for 6 days. The mechanical properties of the latter were found to be higher than the former in terms of Young's modulus, stress at failure, and work of fracture. However, their specific Young's moduli (divided by density) were found to be similar. Young's modulus and stress at failure of transparent predominantly amorphous PLLA films were found to increase by 100 and 315%, respectively, for an 18% volume fraction of BC fibers. BC networks cultured for 3 days were shown to exhibit enhanced interaction with PLLA because of their higher total surface area compared, as measured by nitrogen adsorption, to the material cultured for 6 days. This enhanced interaction is confirmed by using the Raman spectroscopic approach, whereby larger band shift rates, of a peak initially located at 1095 cm(-1), with respect to both strain and stress, are observed, which is a quantitative measure of enhanced stress transfer. Thermal analysis (differential scanning calorimetry) and electron microscopy imaging (scanning electron microscopy) of the samples also confirms the enhanced coupling between the resin and the BC networks cultured for 3 days, compared to those cultured for 6 days. These results are shown to have implications for the use of BC networks for composite reinforcement, whereby less material can be used for the same specific mechanical properties. The technique also gives opportunities to study the interfaces in these composite materials in detail.

Biossíntese e recentes avanços na produção de celulose bacteriana

O presente trabalho discute os recentes avanços na biossíntese e na produção de celulose bacteriana (CB) pela gram-negativa, aeróbia e aceto-ácida Gluconacetobacter. xylinus. A CB se difere de seu par vegetal, principalmente devido ao seu caráter de fibras nanométricas, contra o caráter micrométrico da vegetal, são extruídas através da parede celular de G. xylinus, com isso sua estrutura macroscópica é mecanicamente e fisicamente mais resistente, abrindo grandes oportunidades de aplicações tecnológicas e biológicas, muito além das obtidas pela celulose vegetal. O desafio atual está no aumento da produção de CB, que se debruça num maior entendimento de sua biossíntese para que seja possível uma posterior manipulação genético-bioquímica oriundas do recente avanço na biologia molecular e nos bioprocessos. São relacionados trabalhos utilizando a CB como base para produção de compósitos como também o que a está sendo feito de mais atual com este material biológico.

Biocompatible Bacterial Cellulose Composites for Biomedical Application

This paper reports bacterial cellulose composites made by blending chitosan, poly(ethylene glycol) (PEG), and gelatin for potential biomedical application of tissue-engineering scaffold and wound-dressing material. The bacterial cellulose composites were successfully prepared by immersing a wet bacterial cellulose pellicle into chitosan, PEG, or gelatin solutions followed by freeze-drying. The products look like a foam structure. Scanning electron microscopy images show that chitosan molecules penetrated into bacterial cellulose forming a multilayer and a well interconnected porous network structure with a large aspect surface. The morphology of the bacterial cellulose/gelatin scaffold indicates that the gelatin molecules could penetrate well between the individual nanofibers of the bacterial cellulose. Cell adhesion studies for these composites were carried out using 3T3 fibroblast cells. They showed much better biocompatibility than pure bacterial cellulose. Preparation and material characterization of these composites are explained.

Proliferation and osteoblastic differentiation of human bone marrow stromal cells on hydroxyapatite/bacterial cellulose nanocomposite scaffolds

In this study, we prepared hydroxyapatite/bacterial cellulose (HAp/BC) nanocomposite scaffolds utilizing the biomimetic technique, and investigated the proliferation and osteoblastic differentiation of stromal cells derived from human bone marrow (hBMSC) on them. Scanning electron microscopy proved that cells could adhere and spread on scaffolds. The hBMSC seeded on the nanocomposites exhibited better adhesion and activity than those seeded upon the pure BC. After 6 days of culture on scaffolds, the cells proliferated faster on the nanocomposites than on the pure BC, as assessed by Alamar Blue assay. Real-time reverse transcription PCR results showed that the alkaline phosphatase (ALP) activity of hBMSC and the expression of osteopontin, osteocalcin, bone sialoprotein, and ALP mRNA were all higher for up to 7 days for hBMSC cultured on the nanocomposites than for those cultured upon the pure BC with and without the presence of osteogenic supplements (L-ascorbic acid, glycerophosphate, and dexamethasone, p<0.05). These results suggest that the attachment, proliferation, and differentiation in cultured hBMSC can be modulated by the HAp/BC nanocomposite scaffold properties. In summary, we have developed a scaffold that displays in vitro biocompatibility, which may have potential use for bone tissue engineering.

Bacterial extracellular polysaccharides involved in biofilm formation

Extracellular polymeric substances (EPS) produced by microorganisms are a complex mixture of biopolymers primarily consisting of polysaccharides, as well as proteins, nucleic acids, lipids and humic substances. EPS make up the intercellular space of microbial aggregates and form the structure and architecture of the biofilm matrix. The key functions of EPS comprise the mediation of the initial attachment of cells to different substrata and protection against environmental stress and dehydration. The aim of this review is to present a summary of the current status of the research into the role of EPS in bacterial attachment followed by biofilm formation. The latter has a profound impact on an array of biomedical, biotechnology and industrial fields including pharmaceutical and surgical applications, food engineering, bioremediation and biohydrometallurgy. The diverse structural variations of EPS produced by bacteria of different taxonomic lineages, together with examples of biotechnological applications, are discussed. Finally, a range of novel techniques that can be used in studies involving biofilm-specific polysaccharides is discussed.

Nanocomposites of bacterial cellulose/hydroxyapatite for biomedical applications

In the present work, a nanocomposite material formed by bacterial cellulose (BC) networks and calcium-deficient hydroxyapatite (HAp) powders was synthesized and characterized. The HAp nanoparticles were previously prepared by a wet chemical precipitation method, starting from aqueous solutions of calcium nitrate and di-ammonium phosphate salts. Energy-dispersive spectroscopy reveals that the prepared HAp corresponds to calcium-deficient hydroxyapatite. BC-HAp nanocomposites were prepared by introducing carboxymethylcellulose (CMC) into the bacteria culture media. HAp nanoparticles were then introduced and remained suspended in the culture medium during the formation of cellulose nanofibrils. The maximum gel thickness was obtained after 21 days of bacteria cultivation. X-ray diffractograms showed the difference of crystallinity among the materials involved in the formation of nanocomposites. The inorganic and organic bonds that corresponded to hydroxyapatite and bacterial cellulose respectively, were depicted by attenuated total reflectance Fourier transform infrared spectra. Scanning electron microscopy and atomic force microscopy measurements confirmed the formation of networks and fibres with smaller diameter corresponding to BC synthesized in the presence of CMC. Image analysis was also used to assess the orientation distributions and Feret diameters for networks of BC and BC-CMC. Thermogravimetric analysis showed that the amount of the mineral phase is 23.7% of the total weight of the nanocomposite. Moreover, HEK cells were cultivated and the biocompatibility of the materials and the cell viability was demonstrated.