BC-PVA

Characteristics Biosynthesis Synthesis methods Impregnation Blending 

Chemical structure -Strong hydrogen — bonds of intramolecule and intermolecule [84] 

Crystallinity -Improvement of crystallinity with adding BC (a reference material PVA) [83] -Reduction of — crystallinity after cross-linking reaction [85] 

Application -Cardiovascular application (Hemocompat-ibility] [88] -Cardiovascular application (similarity of mechanical properties to those of porcine aorta and aortic heart valve] [89] 

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Table 14.5 Comparative characteristics of BC-PVA composites prepared from various methods.

The strong hydrogen bonds of intra-molecule and inter-molecular type formed in the BC-PVA structure, resulting in the detection of the hydroxyl (0-H] stretching vibration [3200-3500 cm ] [84],... 

In the comparison of BC and the BC-PVA composite, the crystallinity of BC in the composite was decreased by 50%. By immersing wet BC pellicles in polyvinyl alcohol [PVA] solution, PVA could penetrate the BC network structure and filled the pores. Acetal linkages were formed in the BC-PVA composites by a cross-linking reaction, which made PVA insoluble in water. However, the crystal destruction was observed after the cross-linking [84]. 

By using biosynthesis technique to synthesize BC-PVA composite [83], PVA powders and glyoxal aqueous solution [as a cross-linking agent] were added into the culture medium. The homogeneous distribution of the composite ribbons was noticed throughout the matrix, which could be implied that BC, PVA and also glyoxal were compatible with each other. 

PVA could penetrate into the BC structure and enwrapped the BC fibrils. From the SEM images, it could be observed that the diameter of the composite fibrils was larger than that of unmodified BC [84]. However, the overall structure of BC and BC-PVA composite, fiber thickness, fiber distribution and three-dimensional orientations were quite similar [85]. The SEM examination of BC and BC-PVA revealed that interpenetrated networks could be formed by integrating PVA fiber into the original BC pellicle [85]. The drying method and conditions also have significant effects on the composite structure. The BC-PVA composites dehydrated by freeze-drying process [84] had a structure that was different from those dried in an incubator oven [85]. When PVA fibers are heated, they contract [86]. 

To synthesize the BC-PVA composite by blending method, the homogenized BC was mixed with PVA solution. Then the films were prepared by casting the mixture on Teflon coated tray [87]. It was found that PVA coated the BC fibrils, leading to a denser structure and more transparency with increasing PVA content. 

Using PVA as a reference, it was shown that the tensile strength and Young s modulus of the BC-PVA composites synthesized by using biosynthesis were improved with increasing BC content [83]. 

Although the fracture strain of PVA was very high, the fracture strain of the BC-PVA composite prepared hy immersing BC pellicle in PVA was much lower than that of PVA and close to that of BC. It was suggested that bonding between BC and PVA in the composite was extremely tight, resulting in a brittle composite [84]. 

Wang JH, Gao C, Zhang YS, Wan YZ (2010) Preparation and in vitro characterization of BC/PVA hydrogel composite for its potential use as artificial cornea biomaterial. Mater Sci Eng C Mater Biol Appl 30 214—218... 

Abbreviations. PEG, polyethylene glycol PVP, polyvinylpyrrolidone PVA, polyvinylalcohol HPMC, hydroxypropylmethylcellulose CMEC, carboxymethylethylcellulose, BCS, biopharmaceutical classification system Y, Yes. 

Dubey et al. [74] improved the BC membrane by the impregnation of chitosan [Mw 100-300 kDa]. The composite membrane was dried under vacuum. The potential of the composite membrane for the pervaporative separation of the ethanol/water azeotrope was comparable to that of a polyvinyl alcohol [PVA] membrane [74]. The normalized flux, selectivity, and PSI of the composite membrane were 42.8 kg pm m h , 9.2 and 350 kg pm m h , respectively. Compared with the PVA membrane, BC membrane impregnated with chitosan had excellent dimensional stability, better mechanical strength, and improved thermal stability. 

BC suspension obtained from an agitation culture system was mixed with PVA powder to fabricate PVA-BC composite by considering PVA as a matrix and BC as a reinforcement material. The composite was proposed for cardiovascular soft tissue replacement application [78], The composite could be adjusted its mechanical properties to get close to those of specific tissue [aorta and heart valve] by changing the composition of the composite and the processing parameters. 

PVA-BC Poly(vinyl alcohol) bacterial cellulose composite... 

The PVA-BC nanocomposite is able to provide a wide range of mechanical properties, depending on the processing parameters chosen for the material s application. As discussed in Sect. 3.1.2, the addition of an initial strain following the first FTC can produce a cryogel with anisotropic mechanical properties. Cardiovascular tissue is composed of the structural proteins collagen and elastin, and is... 

Fig. 10 Effect of addition of bacterial cellulose (BC) on the compression elastic modulus of the PVA-BC nanocomposite as a function of the number of ETCs at 45 % strain and 100 %/s strain rate. Reprinted from [45] with permission. Copyright 2009 Wiley Periodicals...

A study conducted by Wang et al. employed the use of PVA-BC produced by freeze-thawing as a composite material for use as an artificial cornea replacement. 

Future research efforts in IVD arthroplasty should focus on either partial or full disc functional restoration. This may include NP implants and/or reinforcement or total disc replacement. PVA-C, as a hydrogel, has many interesting properties, such as its long-term biocompatibility and nontoxicity. It is also strongly hydrophilic and viscoelastic with nonlinear stress-strain characteristics similar to the IVD. It has a very low coefficient of friction and has good wear resistance [23]. However, its strength is still too low to serve as a practical functional replacement of the annulus fibrosus. PVA-BC may further increase the strength of the PVA-C to make it a viable candidate material for IVD fabrication. 

Another composite material, PVA-BC (described in Sect. 4.1), was studied by Millon et al. as a potential material for cartilage tissue replacement. Bacterial cellulose added to PVA to form a nanocomposite cryogel showed improved strain-rate dependence and good viscoelastic properties for mimicking natural cartilage tissue [45]. 

Figure 4.10 PVA/BC composites degraded over time by a single fungal strain. Reproduced from [207] with permission from Springer.

Furthermore, the addition of a small amount of bacterial cellulose nanofibrUs to anisotropic polyvinyl alcohol produces the nanocomposite material PVA-BC. This material possesses a broad range of mechanical properties, including anisotropy by controlling material and processing parameters. A PVA-BC nanocomposite with a controlled degree of anisotropy that matches the mechanical properties of soft tissue can be created. 

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