Fabrication of 3D calcium phosphates based scaffolds using bacterial cellulose as template

Bacterial cellulose – calcium phosphates composite materials were synthesized by successive immersing of bacterial cellulose membranes prepared in our laboratory in precursor solutions under ultrasonic irradiation, which provides the necessary cations for the formation of calcium phosphate phases at the surface of bacterial cellulose fibers. The subsequent thermal treatment at 700 or 1000 °C of the hybrid materials previously described allowed the obtaining of 3D porous scaffolds with different morphologies, as a function of the number of immersing cycles and calcining temperature. All samples exhibit similar phase composition, mainly based on hydroxyapatite and buchwaldite (sodium calcium phosphate). In the case of the composites thermally treated at lower temperature, the microstructure is fluffy and composed of large grains and monocrystalline nanorods, while the masses calcined at higher temperatures have a trabecular appearance, looking like a natural bone. The biological properties of the resulting architectures were also investigated.     

Tubular bacterial cellulose gel with oriented fibrils on the curved surface

On static cultivation, Acetobacter xylinum synthesizes bacterial cellulose (BC) that has a gel-like fibril network with inappropriate orientation at the air/liquid interface. This can be easily molded into desired shapes and sizes during synthesis. Here, we report a simple technique to synthesize tubular BC (BC-TS) gel with proper fibril orientation. We found that culturing BC in oxygen-permeable silicone tubes with inner diameter <8 mm yields a BC-TS gel of the desired length, inner diameter, and thickness with uniaxially oriented fibrils. The fibrils are oriented along the longitudinal axis of the silicone tube, independent of gravity, oxygen availability, and the morphology of the inner surface of the silicone tube but dependent on the curvature of the silicone tube. The degree of orientation (Δn) of the BC-TS fibrils, as revealed by their birefringence, increases with decrease in the inner diameter of the silicone tube. BC-TS with a uniaxially oriented fibril structure has excellent mechanical properties and holds promise for use as a microvessel or soft tissue material in medical and pharmaceutical applications.     

Immobilization of lecithin on bacterial cellulose nanofibers for improved biological functions

In an attempt to improve the biological behavior of pristine bacterial cellulose (BC), lecithin (LEC) has been immobilized on the surface of BC nanofibers by solution immersion and subsequent chemical crosslinking with proanthocyanidin (PA). The as-prepared LEC-immobilized BCs (denoted as BC/LECs) were characterized by SEM, FTIR, and XRD, and their dynamic mechanical properties, thermal stability, and hydrophilicity were assessed. The presence of LEC on BC surface was confirmed by SEM and FTIR analyses. It has been found that BC/LECs retain the three-dimensional (3D) porous network structure of pristine BC. The BC/LECs still demonstrate favorable mechanical properties, surface hydrophilicity, and thermal stability. More importantly, preliminary cell studies suggest that the BC/LECs show improved cell behavior over pristine BC.     

细菌纤维素膜的合成及表征

以海南椰子水为主要培养体系,实验室自行筛选的木醋杆菌(Acetobacter xylinum)为菌种,采用静态培养方法制备了细菌纤维素（BC）。对该BC和商业BC的结构和性能进行了测试对比,观察BC的微结构特点。结果表明: 制备的BC和商业BC在结构和一些性能方面是相似的,都是无色透明膜,呈三维网状结构和孔洞结构,具有良好的纳米纤维网络特征, 具有良好的吸湿性和极佳的持水能力,本实验制备的BC生产成本低,可根据需要大量制备,在生物医学领域具有良好的、广泛的应用前景。     

Characterization of water in bacterial cellulose using dielectric spectroscopy and electron microscopy

It is shown that only 10% of the 99 wt% water present in bacterial cellulose (BC) gels, produced by Acetobacter xylinum, behave like free bulk water; the majority of the water molecules in the gels is more or less tightly bound to the cellulose. The magnitude of the diffusion coefficients of ions transported in the water phase of the BC gels as well as the information contained in freeze fracture transmission electron microscopic images of the gel structures indicates that the bulk-like water is confined in “lakes” rather than forming a continuous phase throughout the gel. Water desorption isotherms suggest that these “lakes” decrease in size with increasing oxygen concentration used during the biosynthesis process of the gels.     

Zinc sulfide nanoparticles template by bacterial cellulose and their optical properties

Spherical zinc sulfide (ZnS) nanoparticles dispersed on bacterial cellulose (BC) nanofibers homogeneously were successfully fabricated through in situ precipitation method using BC as template and explored the formation mechanism. The structure and properties were characterized by Fourier transform infrared, X‐ray diffractometer, FESEM, and so on. The results demonstrated that the nanoparticles were sphalerite structure ZnS and the size increased with the increase of the zinc precursor concentrations. Moreover, a high photocatalytic activity (92%) for degradation of methyl orange was observed and the photoluminescence spectra of the nanocomposites exhibited a blue emission band centered at 468 nm. The flexible BC membrane carried of ZnS nanoparticles might be a promising candidate in the application fields of fluorescence and photo‐catalysis. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40874.     

Biotemplated synthesis of Ag-ZnO nanoparticles/bacterial cellulose nanocomposites for photocatalysis application

ABSTRACT

Bacterial cellulose (BC) was used as a biotemplate for facile fabrication of silver-zinc oxide nanoparticles/bacteria cellulose (Ag-ZnO/BC) nanocomposite having high potential application in photocatalysis via a one-step method. Scanning electron microscopy images confirmed that BC nanofibers were uniformly coated with Ag-ZnO in aqueous suspension using co-precipitation method. The size of Ag-ZnO nanoparticle in BC and its photodegradability were increased with the increasing concentration of AgNO₃ added. The greatest efficiency is demonstrated by the ability of this material to degrade methylene blue (MB) by up to 76% after a 180 min ultraviolet irradiation period, indicated that the Ag-ZnO/BC nanocomposite is a promising candidate as robust ultraviolet responsive photocatalyst.     

Aligned unidirectional PLA/bacterial cellulose nanocomposite fibre reinforced PDLLA composites

In an effort to enhance the properties of polylactide (PLA), we have developed melt-spinning techniques to produce both PLA/nanocellulose composite fibres, and a method akin to layered filament winding followed by compression moulding to produce self-reinforced PLA/nanocellulose composites. Poly(L-lactide) (PLLA) fibres were filled with 2 wt.% neat and modified bacterial cellulose (BC) in an effort to improve the tensile properties over neat PLA fibres. BC increased the viscosity of the polymer melt and reduced the draw-ratio of the fibres, resulting in increased fibre diameters. Nonetheless, strain induced chain orientation due to melt spinning led to PLLA fibres with enhanced tensile modulus (6 GPa) and strength (127 MPa), over monolithic PLLA, previously measured at 1.3 GPa and 61 MPa, respectively. The presence of BC also enhanced the nucleation and growth of crystals in PLA. We further produced PLA fibres with 7 wt.% cellulose nanocrystals (CNCs), which is higher than the percolation threshold (equivalent to 6 vol.%). These fibres were spun in multiple, alternating controlled layers onto spools, and subsequently compression moulded to produce unidirectional self-reinforced PLA composites consisting of 60 vol.% PLLA fibres reinforced with 7 wt.% CNC in a matrix of amorphous PDLLA, which itself contained 7 wt.% of CNC. We observed improvements in viscoelastic properties of up to 175% in terms of storage moduli in bending. Furthermore, strains to failure for PLLA fibre reinforced PDLLA were recorded at 17%.     

Functionalized tricalcium phosphate and poly(3-hydroxyoctanoate) derived composite scaffolds as platforms for the controlled release of diclofenac

Novel bone substitutes such as highly porous ceramic scaffolds can serve as platforms for delivering active molecules. A common problem is to control the release of the drug, therefore, it is beneficial to use a drug-functionalized polymer coating. In this study, β-tricalcium phosphate-based porous scaffolds were obtained and coated with diclofenac-functionalized biopolymer – poly(3-hydroxyoctanoate) – P(3HO). To the best of our knowledge, studies using P(3HO) as a component in ceramic-polymer based drug delivery system for bone tissue regeneration have not yet been reported. Presented materials were comprehensively investigated by various techniques such as powder X-ray diffraction, scanning electron microscopy with energy dispersive spectroscopy, hydrostatic weighing and compression tests, pH and ionic conductivity measurements, high-performance liquid chromatography and in vitro cytotoxicity studies. The obtained diclofenac-loaded composite was not only characterised by controlled and sustained drug release, but also possessed improved mechanical properties. Moreover, the precipitation of apatite-like forms on its surface was observed after incubation in simulated body fluid, which indicates its bioactive potential. After 24 hours no cytotoxic effect on MC3T3-E1 mouse preosteoblastic cells was confirmed using indirect cytotoxicity studies. Thus, this promising multifunctional composite scaffold can be a promising candidate as an anti-inflammatory drug-delivery system in bone tissue engineering.     

Composite scaffolds for cartilage tissue engineering based on natural polymers of bacterial origin,thermoplastic poly(3‐hydroxybutyrate) and micro‐fibrillated bacterial cellulose

Cartilage tissue engineering is an emerging therapeutic strategy that aims to regenerate damaged cartilage caused by disease, trauma, ageing or developmental disorder. Since cartilage lacks regenerative capabilities, it is essential to develop approaches that deliver the appropriate cells, biomaterials and signalling factors to the defect site. Materials and fabrication technologies are therefore critically important for cartilage tissue engineering in designing temporary, artificial extracellular matrices (scaffolds), which support 3D cartilage formation. Hence, this work aimed to investigate the use of poly(3‐hydroxybutyrate)/microfibrillated bacterial cellulose (P(3HB)/MFC) composites as 3D‐scaffolds for potential application in cartilage tissue engineering. The compression moulding/particulate leaching technique employed in the study resulted in good dispersion and a strong adhesion between the MFC and the P(3HB) matrix. Furthermore, the composite scaffold produced displayed better mechanical properties than the neat P(3HB) scaffold. On addition of 10, 20, 30 and 40 wt% MFC to the P(3HB) matrix, the compressive modulus was found to have increased by 35%, 37%, 64% and 124%, while the compression yield strength increased by 95%, 97%, 98% and 102% respectively with respect to neat P(3HB). Both cell attachment and proliferation were found to be optimal on the polymer‐based 3D composite scaffolds produced, indicating a non‐toxic and highly compatible surface for the adhesion and proliferation of mouse chondrogenic ATDC5 cells. The large pores sizes (60 ‐ 83 µm) in the 3D scaffold allowed infiltration and migration of ATDC5 cells deep into the porous network of the scaffold material. Overall this work confirmed the potential of P(3HB)/MFC composites as novel materials in cartilage tissue engineering. © 2016 Society of Chemical Industry     

pH-triggered phase inversion and separation of hydrophobised bacterial cellulose stabilised Pickering emulsions

The pH-triggered transitional phase behaviour of Pickering emulsions stabilised by hydrophobised bacterial cellulose (BC) is reported in this work. Neat BC was esterified with acetic (C₂–), hexanoic (C₆–) and dodecanoic (C₁₂–) acids, respectively. We observed that C₆– and C₁₂–BC stabilised emulsions exhibited a pH-triggered reversible transitional phase separation. Water-in-toluene emulsions containing of 60 vol.% dispersed phase stabilised by C₆– and C₁₂–BC were produced at pH 5. Lowering the pH of the aqueous phase to 1 did not affect the emulsion type. Increasing the pH to 14, however, caused the emulsions to phase separate. This phase separation was caused by electrostatic repulsion between modified BC due to dissociable acidic surface groups at high pH, which lowered the surface coverage of the water droplets by modified BC. When the pH was re-adjusted to 1 again, w/o emulsions re-formed for C₆– and C₁₂–BC stabilised emulsions. C₂–BC stabilised emulsions, on the other hand, underwent an irreversible pH-triggered transitional phase separation and inversion. This difference in phase behaviour between C₂–BC and C₆–/C₁₂–BC was attributed to the hydrolysis of the ester bonds of C₂–BC at high pH. This hypothesis is in good agreement with the measured degree of surface substitution (DSS) of modified BC after the pH-triggered experiments. The DSS of C₂–BC decreased by 20% whilst the DSS remained constant for C₆– and C₁₂–BC.     

Bacterial cellulose/hyaluronic acid composite hydrogels with improved viscoelastic properties and good thermodynamic stability

Improved viscoelastic composite hydrogels were successfully prepared from bacterial cellulose and hyaluronic acid by physical gelling. The composite hydrogels were characterised by Scanning electron microscope, Fourier transform infrared spectroscope, and X-ray diffraction. The thermodynamic and rheological properties of the gels were tested, and their thermodynamic stability and viscoelasticity were evaluated. The viscoelasticity of the composite hydrogels was improved because of the integration of BC nanofibrils. The material was able to be dried to avoid contamination and facilitate transportation. The rehydrated composite hydrogels maintained a high transmittance. The high porosity and high transmittance make these gels potential corneal tissue engineering scaffolds.     

Calcium Phosphate Crystallization on Electrospun Cellulose Non‐Woven Fabrics Containing Synthetic Phosphorylated Polypeptides

The preparation of electrospun non‐woven fabrics composed of cellulose and synthetic phosphorylated polypeptides, copoly[Ser(PO₃H₂)^XAsp^Y]s (X:Y = 100:0, 75:25, 50:50, 25:75), is described. The non‐wovens were subjected to an alternate immersion in CaCl₂ and Na₂HPO₄ solutions to induce crystallization of calcium phosphate. The deposited calcium phosphate crystals were analyzed by means of EDX analysis and WXRD. The amounts of calcium phosphate deposition are greater for the cellulose non‐woven fabrics containing copoly[Ser(PO₃H₂)^XAsp^Y] than those of cellulose‐only non‐woven fabrics. These results indicate that copoly[Ser(PO₃H₂)^XAsp^Y] can entrap Ca²⁺ ions around the fine fiber matrix to accelerate crystallization of the calcium phosphate.

     

Cellulose phosphates as biomaterials. II. Surface chemical modification of regenerated cellulose hydrogels

Cellulose regenerated by the viscose process was previously investigated as an implantable material in orthopedic surgery. It was envisaged to take advantage not only of its good matching with mechanical properties of bone but also of its hydroexpansivity, therefore allowing a satisfactory fixation to hard tissue. Both the osteoconduction and the lack of osteoinduction of this material were demonstrated. Grafting of phosphate groups was then envisaged as the means to render cellulose more suitable for orthopedic applications by enhancing its bioactivity. In the present work, the previously optimized phosphorylation reaction was successfully adapted to the surface modification of regenerated cellulose. Modified materials were characterized by XPS, FTIR, and ³¹P MAS NMR spectroscopic studies, and contact angle measurements, revealing the chemical bond between phosphate groups and cellulose, as well as the hydrophilic nature of phosphorylated materials, which increases with increasing phosphate contents. Water swelling and resistance to gamma sterilization were assessed as well, showing that phosphorylated materials swell considerably in water and were not affected when sterilization was carried out under a nitrogen atmosphere. The increase in surface roughness attributed to chemical modification was demonstrated through laser rugosimetry measurements. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3354–3365, 2001     

细菌纤维素/热塑性聚氨酯复合气凝胶纤维制备及性能

使用绿色有机材料细菌纤维素(BC),并掺杂增强材料热塑性聚氨酯弹性体(TPU)经过湿法纺丝制备复合气凝胶纤维,通过傅里叶变换红外光谱(FTIR)、X射线衍射光谱(XRD)、热重分析(TG)、扫描电子显微镜(SEM)、全自动比表面孔隙度分析仪和单丝强力仪对制备的气凝胶纤维进行结构分析和性能表征,结果表明复合气凝胶纤维具有多孔结构,良好的力学性能和隔热性能,断裂强度达到24.69Mpa,断裂伸长为38.54%。     

细菌纤维素的研究进展

细菌纤维素是由细菌如胶膜醋酸菌和致癌农杆菌等在一定条件下产生的。由于它的物理、化学性质与天然纤维素极其相似,因而通过对其生物合成机制的研究将有利于人们更深入地了解天然纤维素的合成机制,从而可更好地利用纤维素资源,而且细菌纤维素因它的可控制性和结构均一性而在越来越多的工业领域得到重视和应用。     

Cerium-doped calcium phosphates precipitated on bacterial cellulose platform by mineralization

Bacterial cellulose (BC) membranes biosynthesized by Komagataeibacter rhaeticus AF1 strain were used as a platform for precipitating cerium-doped calcium phosphates (Ce:CaP), which were synthetized by successive soaking of BC membranes in solutions containing Ca²⁺, PO₄³⁻ and Ce³⁺ precursor ions. After obtaining the as-prepared composites, BC-Ce:CaP was submitted to a thermal treatment at 600 °C for 3 h, and Ce:CaP was characterized by scanning electronic microscopy (SEM), energy dispersive X-ray spectrometry (EDX), thermogravimetric analysis (TG), derivative thermogravimetric analysis (DTG) and X-ray diffraction (XRD). Ce:CaP presented hydroxyapatite, chlorapatite and buchwaldite (sodium calcium phosphate) phases and revealed a trabecular structure composed per nanowires with interconnected pores. Furthermore, BC-Ce:CaP and Ce:CaP show cell viability and has been suggested for use as a mineral scaffold.     

Carbon fiber-embedded bacterial cellulose/polyaniline nanocomposite with tailored for microbial fuel cells electrode

Microbial fuel cells (MFC) are of great interest for new sources of renewable energies from the waste of biomass and debris. This work aimed was to develop an anode electrode of the carbon fiber-embedded of bacterial cellulose/polyaniline (CF/BC/PANI) nanocomposite for MFC applications. For this purpose, carbon fiber was wrapped onto bacterial cellulose (BC) fibers network during the BC synthesis. The CF/BC/PANI was obtained by polyaniline polymerization on the BC nanofibers as a scaffold. To characterize the electrode, scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis analysis were carried out. The electrical conductivity was determined by measuring the resistivity. MFC using the CF/BC/PANI electrode was monitored and the maximum current density generated was 0.009 mA/cm². The results obtained from the CF/BC/PANI demonstrate great potential for the use as an MFC electrode, as well as a microenvironment favorable to a microbial biofilm formation.     

Inorganic calcium filled bacterial cellulose based hydrogel scaffold: novel biomaterial for bone tissue regeneration

Abstract

This work emphasizes the structural, physio-chemical characterization and cell biological efficiency analysis of novel inorganic calcium (only calcium phosphate and in combination of calcium phosphate & CaCO₃) filled bacterial cellulose (BC) based hydrogel scaffolds. FTIR and TG analysis indicates the presence of BC and inorganic calcium within the hydrogel scaffolds. SEM establishes the porous structures (50–200 µm). Swelling study indicates significant swelling ability in both calcium phosphate filled and calcium phosphate & CaCO₃ filled hydrogel scaffolds. Compressive strength (0.24–0.60?MPa) of the calcium filled hydrogel scaffolds are similar like trabecular bone. Significant cell viability (Lep-3) was further noticed until 72,120 and 168?h.     

Enhanced conductivity of bacterial cellulose films reinforced with NH4I-doped graphene oxide

ABSTRACT

Bacterial cellulose (BC) films reinforced with reduced graphene oxide (RGO) platelets were investigated to assess their potential application as solid polymeric electrolytes. BC-RGO composites were further doped with NH₄I at different concentrations to evaluate the effect of NH₄I doping on the conductivity. Scanning electron microscopy images confirmed that GO addition did not alter BC coherent three-dimensional morphology. Electrochemical impedance spectroscopy studies revealed that the ionic conductivity increased with the ammonium iodide salt concentration. The highest conductivity found was 1.32 × 10^?4 S/cm for the samples doped with 5% NH₄I, suggesting that BC-RGO can be a promising candidate for electrochemical applications.