Processing and Properties of Nanofibrous Bacterial Cellulose-Containing Polymer Composites: A Review of Recent Advances for Biomedical Applications

Abstract

Bacterial cellulose (BC) is an extracellular natural polymer produced by many microorganisms and its properties could be tailored via specific fabrication methods and culture conditions. There is a growing interest in BC derived materials due to the main features of BC such as porous fibrous structure, high crystallinity, impressive physico-mechanical properties, and high water content. However, pristine BC lacks some features, limiting its practical use in varied applications. Thus, fabrication of BC composites has been attempted to overcome these constraints. This review article overviews most recent advance in the development of BC composites and their potential in biomedicine including wound dressing, tissue engineering scaffolds, and drug delivery. Special emphasis is placed on the fabrication and applications of BC-containing nanofibrous composites for biomedical usage. It summarizes electrospinning of BC-based nanofibers and their surface modification with an outline on challenges and future perspective.     

Engineering quaternized chitosan in the 3D bacterial cellulose structure for antibacterial wound dressings

Balancing antibacterial properties with biocompatibility is of paramount importance for wound dressings loaded with antibacterial agents. In this work, a water soluble antibacterial agent, quaternized chitosan (hydroxypropyltrimethyl ammonium chloride chitosan, HACC) with an appropriate degree of substitution was introduced into the bacterial cellulose (BC) network by adding it into the BC culture medium. Results indicated that the addition of HACC could affect the yield of BC, porous structure, thermal stability, water absorption and antibacterial properties. HBC-1 with a low content of HACC (13.65 ± 0.30%) cannot inhibit the biofilm formation of bacteria, while HBC-3 with a high content of HACC (62.05 ± 0.90%) has a low yield of BC and confused structure. HBC-2 with an optimum concentration of HACC (37.33 ± 0.80%) possessed a typical porous structure, acceptable thermal stability, good water absorption and favorable antibacterial properties against Staphylococcus aureus (S. aureus, ATCC 25923) and methicillin-resistant S. aureus (ATCC 43300). Most importantly, none of the HACC/BC films exhibited cytotoxicity to NIH3T3 cells. We believe that obtained HACC/BC films with favorable bactericidal properties and biocompatibility could be potential candidates for wound dressings in clinical applications.     

Enhanced bacterial cellulose production from <Emphasis Type="Italic">Gluconobacter xylinus</Emphasis> using super optimal broth

The bacterial cellulose (BC) produced by Gluconobacter xylinus due to its versatile properties, is used in healthcare and industrial applications. However, its use is restricted owing to the limited yield from the existing culture protocols. In the current study, BC production is studied in the presence of Super Optimal Broth with catabolite repression (SOC) medium which is used to revive Escherichia coli cells after electroporation or chemoporation. In SOC medium, Gluconobacter xylinus produces cellulose pellicles within 5 days of incubation with an enhanced conversion of the carbon source to cellulose compared to traditional Hestrin–Schramm (HS) medium. SOC medium also maintains the pH close to 7.0 in static cultures unlike in HS medium where the pH is acidic. The physico-chemical and morphological characteristics of the BC produced in SOC are determined using powder X-ray diffraction (pXRD), thermo gravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH), and scanning electron microscopy (SEM) analyses. Our results indicate that SOC enhance the yield of bacterial cellulose and allows conversion of 50% of the carbon source to bacterial cellulose, compared to only 7% conversion in the case of traditional HS medium after 7 days of interaction. We also observe an increase in hydration capacity of BC produced using SOC as compared to HS media.     

Sustainable optically transparent composites based on epoxidized soy-bean oil (ESO) matrix and high contents of bacterial cellulose (BC)

Production of transparent composites from totally renewable resources with extraordinary potential for different applications can be made possible using cellulose. Composites of epoxidized soybean oil (ESO)/bacterial cellulose (BC) nanofibers have been prepared with high fiber content. Due to the nano-order scale network-like structure of BC nanofibers, composite films present high transparency even at high BC content. Transparency of films has been analyzed by UV–visible spectroscopy observing that only 15% of matrix transmittance is lost in the nanocomposites. ESO/BC composites show better mechanical properties with increasing BC content. Composites combine high stiffness and good ductility due to the incorporation of BC network structure in ESO matrix.     

By-products of the cider production: an alternative source of nutrients to produce bacterial cellulose

In the present work a culture process to produce bacterial cellulose (BC) using by-products of the cider production from the Basque Country was investigated. The apple pomace was mixed with sugar cane (AR/SC medium) and the mixture was found to be a potential carbon source for Gluconacetobacter medellinensis strain ID13488 since higher cellulose production was observed with respect to the commercial Hestrin and Shramm medium (H–S). The culture media were characterized in terms of pH, oxygen and sugars consumption. The expression level of the operon bcs (genes involved in BC biosynthesis) in apple residue containing medium respect to standard H–S medium was determined. It was found that in AR/SC medium the expression levels of bcsA gene, wich is the first gene of the bcs operon, was increased in 1.5-fold respect to the H–S media which correlates with the fact that BC production in AR/SC media is higher than in H–S media. The physico-chemical and mechanical properties, microstructure, crystallinity and water holding capacity of the biosynthesized BC membranes were analyzed and it was found that, in general, the BC obtained from AR/SC medium presented superior properties than that obtained from H–S medium. In this study an economic method for BC production is proposed with suitable properties for many applications.     

Enhanced Production of Bacterial Cellulose by Using Gluconacetobacter hansenii NCIM 2529 Strain Under Shaking Conditions

Bacterial cellulose (BC), a biopolymer, due to its unique properties is valuable for production of vital products in food, textile, medicine, and agriculture. In the present study, the optimal fermentation conditions for enhanced BC production by Gluconacetobacter hansenii NCIM 2529 were investigated under shaking conditions. The investigation on media components and culture parameters revealed that 2 % (w/v) sucrose as carbon source, 0.5 % (w/v) potassium nitrate as nitrogen source, 0.4 % (w/v) disodium phosphate as phosphate source, 0.04 % (w/v) magnesium sulfate, and 0.8 % (w/v) calcium chloride as trace elements, pH?5.0, temperature 25 °C, and agitation speed 170 rpm with 6 days of fermentation period are optimal for maximum BC production. Production of BC using optimized media components and culture parameters was 1.66 times higher (5.0 g/l) than initial non optimized media (3.0 g/l). Fourier transform infrared spectroscopy spectrum and comparison with the available literature suggests that the produced component by G. hansenii in the present study is pure bacterial cellulose. The specific action of cellulase out of the investigated hydrolytic enzymes (cellulase, amylase, and protease) further confirmed purity of the produced BC. These findings give insight into conditions necessary for enhanced production of bacterial cellulose, which can be used for a variety of applications.     

Improved Cell Viability and Biocompatibility of Bacterial Cellulose through in Situ Carboxymethylation

Bacterial cellulose (BC) is a natural product with multiple properties, which has been utilized in tissue engineering. However, cell adhesion and proliferation are reported to be weaker on native BC, providing less support compared to other types of biomaterials, like collagen. To increase the biocompatibility and the medical performance of BC, in situ modification is used to add carboxymethyl group to BC. By partially changing the structure and physical properties of BC, carboxymethylation significantly increases cell affinity and viability, especially on the initial cell adhesion. Furthermore, in the in vivo implantation, the tissue reaction shows that carboxymethylation significantly increases the biocompatibility of BC, exhibiting better tissue condition and a lower inflammatory reaction which are proved through HE staining and immunohistochemistry. The data prove that in situ carboxymethylation is a simple and direct way of improving the performance of BC in medical applications.     

Inelastic behaviour of bacterial cellulose hydrogel: In aqua cyclic tests

Hydrogels are finding increasingly broad use, especially in biomedical applications. Their complex structure – a low-density network of microfibrils – defines their non-trivial mechanical behaviour. The focus of this work is on test-based quantification of mechanical behaviour of a bacterial cellulose (BC) hydrogel exposed to cyclic loading. Specimens for the tests were produced using Gluconacetobacter xylinus ATCC 53582 and tested in aqua under uniaxial cyclic loading conditions in a displacement-controlled regime. Substantial microstructural changes were observed in the process of deformation. A combination of qualitative microstructural observations with quantitative force-displacement relations allowed identification of main deformation mechanisms, confirming inelastic behaviour of the BC hydrogel under a loading-unloading-reloading regime. Elastic deformation was accompanied by non-elastic (viscoplastic) deformation in both tension and compression. This study also aims to establish a background for micromechanical modelling of overall properties of BC hydrogels.     

Synthesis of regenerated bacterial cellulose-zinc oxide nanocomposite films for biomedical applications

Regenerated bacterial cellulose (RBC) composites with zinc-oxide nanoparticles (ZnO) were prepared using a new strategy for enhanced biomedical applications of BC. Powdered BC was dissolved in N-methylmorpholine-N-oxide, and different concentrations of ZnO nanoparticles were mixed into the BC solution. RBC, RBC-ZnO1 (1 % ZnO) and ZnO-RBC2 (2 % ZnO) nanocomposite films were prepared by casting the solutions through an applicator. FE-SEM images confirmed the structural features and impregnation of the RBC films by nanoparticles. XRD analysis indicated the presence of specific peaks for RBC and ZnO in the composites. The RBC nanocomposites were found to have greatly enhanced thermal, mechanical and biological properties. Specifically, the degradation temperatures were improved from 334 °C for RBC to 339 and 344 °C for RBC-ZnO1 and RBC-ZnO2, respectively. The mechanical strength and Young’s modulus of the composites were also higher than those of pure RBC. The greatly improved antibacterial properties of the RBC-ZnO nanocomposites are the most striking feature of the present study. The bacterial growth inhibition measured for the RBC was zero, but reached up to 34 and 41 mm for RBC-ZnO1 and RBC-ZnO2, respectively. In addition to their antibacterial properties, the RBC-ZnO nanocomposites were found to be nontoxic and biocompatible with impressive cell adhesion capabilities. These RBC-ZnO nanocomposites can be used for different biomedical applications and have the potential for use in bioelectroanalysis.     

Wet and Dry Forms of Bacterial Cellulose Synthetized by Different Strains of <Emphasis Type="Italic">Gluconacetobacter xylinus</Emphasis> as Carriers for Yeast Immobilization

The present study aimed to explore and describe the properties of bacterial cellulose (BC) membranes obtained from three different strains of Gluconacetobacter xylinus for 72, 120, and 168 h, used as a carrier support for the immobilization of Saccharomyces cerevisiae. The experiments also included the analysis of glucose consumption and alcohol production during the fermentation process displayed by yeasts immobilized on the BC surface. The results of the present study demonstrate that the number of immobilized yeast cells is dependent on the type of cellulose-synthesizing strain, cellulose form, and duration of its synthesis. The BC in the form of wet membranes obtained after 3 days of synthesis displayed the most favorable properties as a carrier for yeast immobilization. The immobilization of yeast cells on BC, regardless of its form, increased the amount of the produced alcohol as compared to free cells. The yeast cells immobilized in BC were able to multiply on its surface during the fermentation process.     

Use of bacterial cellulose in the textile industry and the wettability challenge—a review

Bacterial cellulose (BC) has been studied as an alternative material in several segments of the food, pharmaceutical, materials and textile industries. The importance of BC is linked to sustainability goals, since it is an easily degradable biomaterial of low toxicity to the environment and is a renewable raw material. For use in the textile area, bacterial cellulose has attracted great interest from researchers, but it presents some challenges notably to its hydrophilic structure. This integrative review article brings together studies and methods related to minimizing the hydrophilicity of bacterial cellulose, in order to expand its applicability in the textile industry in its dry state. The databases consulted were Scopus, ScienceDirect, ProQuest and Web of Science, the documents investigated were scientific articles and the time period investigated was between 2015 and 2021. The results showed that although there are methods to make the BC membrane more hydrophobic, future studies in this regard and on other properties must continue so that bacterial cellulose can be commercially introduced in the textile sector.

     

Effect of cellulose crystallinity on bacterial cellulose assembly

Bacterial cellulose (BC) is a promising biomaterial as well as a model system useful for investigating cellulose biosynthesis. BC produced under static cultivation condition is a hydrous pellicle consisting of an interconnected network of fibrils assembled in numerous dense layers. The mechanisms responsible for this layered BC assembly remain unknown. This study used calcofluor as a fluorescent marker to examine BC layer formation at the air/liquid interface. Layers are found to move downward into the media after formation while new layers continue to form at the air/liquid interface. Calcoflour is also known to reduce the crystallinity of cellulose, changing the mechanical properties of the formed BC microfibrils. Consecutive addition and accumulation of calcofluor in the culture medium is found to disrupt the layered assembly of BC. BC crystalllinity decreased by 22 % in the presence of 12 % calcofluor (v/v) in the medium as compared to BC produced without calcofluor. This result suggests that cellulose crystallinity and the mechanical properties which crystallinity provides to cellulose are major factors influencing the layered BC structure formed during biosynthesis.     

Structure and Properties of Bacterial Cellulose Produced Using a Trickling Bed Reactor

Structure and properties of bacterial cellulose (BC) produced by trickling fermentation were studied. The following indexes, such as extrinsic shapes, microstructure, chemical structure, purity, water holding capacity, porosity, and thermogravimetric characteristics, are recommended for assessing the structure and properties of bacterial cellulose. With the comparison to bacterial cellulose produced by static fermentation and shaking fermentation, the results showed that for different BC cultivation methods, the extrinsic shapes, synthetic mode, and microstructure were different. The basic consistency of the infrared spectrogram from three kinds of bacterial cellulose reflected that the chemical structures were very similar. But the –OH associating degree of trickling fermentation BC was higher, and the polymerization degree, purity, water holding capacity, porosity, and thermal stability of trickling fermentation BC were also higher than those of static fermentation BC and shaking fermentation BC. But the crystallinity and crystal grain size of trickling fermentation BC were less than those of static fermentation BC and greater than those of shaking fermentation BC and plant fiber. These above structure and properties of trickling fermentation BC could reference bacterial cellulose’s application in food and material field.     

A resorbable calcium-deficient hydroxyapatite hydrogel composite for osseous regeneration

It was previously discovered that the unique structure and chemistry of bacterial cellulose (BC) permits the formation of calcium-deficient hydroxyapatite (CdHAP) nanocrystallites under aqueous conditions at ambient pH and temperature. In this study, BC was chemically modified via a limited periodate oxidation reaction to render the composite degradable and thus more suitable for bone regeneration. While native BC does not degrade in mammalian systems, periodate oxidation yields dialdehyde cellulose which breaks down at physiological pH. The composite was characterized by tensile testing, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. X-ray diffraction showed that oxidized BC retains its structure and could biomimetically form CdHAP. Degradation behavior was analyzed by incubating the samples in simulated physiological fluid (pH 7.4) at 37 °C under static and dynamic conditions. The oxidized BC and oxidized BC-CdHAP composites both lost significant mass after exposure to the simulated physiological environment. Examination of the incubation solutions by UV–Vis spectrophotometric analysis demonstrated that, while native BC released only small amounts of soluble cellulose fragments, oxidized cellulose releases carbonyl containing degradation products as well as soluble cellulose fragments. By entrapping CdHAP in a degradable hydrogel carrier, this composite should elicit bone regeneration then resorb over time to be replaced by new osseous tissue.     

Bacterial Nanocellulose in Dentistry: Perspectives and Challenges

Bacterial cellulose (BC) is a natural polymer that has fascinating attributes, such as biocompatibility, low cost, and ease of processing, being considered a very interesting biomaterial due to its options for moldability and combination. Thus, BC-based compounds (for example, BC/collagen, BC/gelatin, BC/fibroin, BC/chitosan, etc.) have improved properties and/or functionality, allowing for various biomedical applications, such as artificial blood vessels and microvessels, artificial skin, and wounds dressing among others. Despite the wide applicability in biomedicine and tissue engineering, there is a lack of updated scientific reports on applications related to dentistry, since BC has great potential for this. It has been used mainly in the regeneration of periodontal tissue, surgical dressings, intraoral wounds, and also in the regeneration of pulp tissue. This review describes the properties and advantages of some BC studies focused on dental and oral applications, including the design of implants, scaffolds, and wound-dressing materials, as well as carriers for drug delivery in dentistry. Aligned to the current trends and biotechnology evolutions, BC-based nanocomposites offer a great field to be explored and other novel features can be expected in relation to oral and bone tissue repair in the near future.     

Alteration of bacterial nanocellulose structure by in situ modification using polyethylene glycol and carbohydrate additives

Bacterial nanocellulose (BC) is characterized by an exciting interconnection of the important and well-known cellulose properties with the outstanding features of nano-scale materials. As a remarkable benefit of BC the property-controlling fiber network and pore system formed by self-assembly of the cellulose molecules can be modified in situ using additives during biosynthesis. The addition of polyethylene glycol (PEG) 4000 causes a pore size decrease. In presence of β-cyclodextrin or PEG 400 remarkably increased pores can be achieved. Surprisingly, these co-substrates act as removable auxiliaries not incorporated in the BC samples. In contrast, carboxymethyl cellulose and methyl cellulose as additives lead to structural modified composite materials. Using cationic starch (2-hydroxy-3-trimethylammoniumpropyl starch chloride, TMAP starch) double-network BC composites by incorporation of the starch derivative in the BC prepolymer were obtained.     

Roles of xyloglucan and pectin on the mechanical properties of bacterial cellulose composite films

Xyloglucan and pectin are major non-cellulosic components of most primary plant cell walls. It is believed that xyloglucan and perhaps pectin are functioning as tethers between cellulose microfibrils in the cell walls. In order to understand the role of xyloglucan and pectin in cell wall mechanical properties, model cell wall composites created using Gluconacetobacter xylinus cellulose or cellulose nanowhiskers (CNWs) derived there from with different amounts of xyloglucan and/or pectin have been prepared and measured under extension conditions. Compared with pure CNW films, CNW composites with lower amounts of xyloglucan or pectin did not show significant differences in mechanical behavior. Only when the additives were as high as 60 %, the films exhibited a slightly lower Young’s modulus. However, when cultured with xyloglucan or pectin, the bacterial cellulose (BC) composites produced by G. xylinus showed much lower modulus compared with that of the pure BC films. Xyloglucan was able to further reduce the modulus and extensibility of the film compared to that of pectin. It is proposed that surface coating or tethering of xyloglucan or pectin of cellulose microfibrils does not alone affect the mechanical properties of cell wall materials. The implication from this work is that xyloglucan or pectin alters the mechanical properties of cellulose networks during rather than after the cellulose biosynthesis process, which impacts the nature of the connection between these compounds.     

Homogeneous and porous modified bacterial cellulose achieved by in situ modification with low amounts of carboxymethyl cellulose

To improve the rehydration ability of bacterial cellulose (BC), many macromolecules have been used as modifiers in previous reports. However, the aggregation of additives in the BC matrix appears to be inevitable. We investigated different parts of a BC pellicle, which was achieved by in situ modification with carboxymethyl cellulose (CMC) in culture with Gluconacetobacter xylinus ATCC53582 or Enterobacter sp. FY-07. We observed a concentration gradient of CMC in the BC pellicle from G. xylinus ATCC53582, but not with Enterobacter sp. FY-07. Low concentrations of CMC (0.01 %, m/v) are sufficient to modify BC in situ in culture with Enterobacter sp. FY-07, in which CMC could sufficiently contact with the newly formed BC. The crystallinity of the modified BC decreased by more than 39.8 %, and its rehydration ability and water holding capacity increased by 43.3 and 31.0 %, respectively. Unlike the pellicle of modified BC achieved from obligate aerobes, such as G. xylinus ATCC53582, that produced by Enterobacter sp. FY-07 exhibited better homogeneity and porosity.     

高力学强度细菌纤维素气凝胶纤维的连续化制备

气凝胶纤维因其高外表面积和高柔韧性在能量管理系统中具有潜在应用而引起了广泛关注.但是,目前制备的气凝胶纤维力学强度较低,限制了其实际应用.为提高气凝胶纤维力学性能,在始终保持细菌纤维素(BC)纳米纤维处于湿态下,利用NaOH/尿素/硫脲复合溶剂直接低温溶解原生BC,获得透明的BC纺丝原液;通过湿法纺丝制备了BC水凝胶纤维,经过水洗和冷冻干燥后处理,制得BC气凝胶纤维.采用偏光显微镜(POM)、13C核磁共振(13C-NMR)和高级旋转流变仪研究BC在复合溶剂中的溶解过程与状态;利用全反射傅里叶变换红外吸收光谱(ATR-FTIR)、X射线衍射(XRD)和热失重(TG)研究BC溶解前后结构与性能变化;利用场发射扫描电镜(FESEM)、全自动比表面积和孔径分布分析仪、单丝强力仪对获得的BC气凝胶纤维结构与性能进行表征.结果表明,复合溶剂在?15℃条件下可以直接溶解原生湿态BC,最高溶解浓度为3 wt%;采用湿法纺丝制得高度多孔的连续BC气凝胶纤维,比表面积高达192 m^2/g且具有优异的力学性能,断裂强度和杨氏模量高达(9.36±1.68)MPa和(176±17.55)MPa,如0.4 mg BC气凝胶纤维可以支撑高于其本身质量5×10^4倍的重物.     

Thermal behavior of cellulose acetate produced from homogeneous acetylation of bacterial cellulose

Cellulose acetate (CA) is one of the most important cellulose derivatives and its main applications are its use in membranes, films, fibers, plastics and filters. CAs are produced from cellulose sources such as: cotton, sugar cane bagasse, wood and others. One promissory source of cellulose is bacterial cellulose (BC). In this work, CA was produced from the homogeneous acetylation reaction of bacterial cellulose. Degree of substitution (DS) values can be controlled by the acetylation time. The characterization of CA samples showed the formation of a heterogeneous structure for CA samples submitted to a short acetylation time. A more homogeneous structure was produced for samples prepared with a long acetylation time. This fact changes the thermal behavior of the CA samples. Thermal characterization revealed that samples submitted to longer acetylation times display higher crystallinity and thermal stability than samples submitted to a short acetylation time. The observation of these characteristics is important for the production of cellulose acetate from this alternative source.