Chitosan-acetic acid solutions

Hu and coworkers [126, 127] firstly developed an in situ precipitation approach to fabrication of 3D ordered chitosan rods with a structure of concentric circles through the formation process illustrated in Fig. 11. Briefly, the chitosan/acetic acid solution is filled into a bag made of chitosan membrane, and then immersed into 5% NaOH aqueous solution. When OH ions from the outside solution permeate into... 

The multiple emulsion technique includes three steps 1) preparation of a primary oil-in-water emulsion in which the oil dispersed phase is constituted of CH2CI2 and the aqueous continuous phase is a mixture of 2% v/v acetic acid solution methanol (4/1, v/v) containing chitosan (1.6%) and Tween (1.6, w/v) 2) multiple emulsion formation with mineral oil (oily outer phase) containing Span 20 (2%, w/v) 3) evaporation of aqueous solvents under reduced pressure. Details can be found in various publications [208,209]. Chemical cross-linking is an option of this method enzymatic cross-linking can also be performed [210]. Physical cross-linking may take place to a certain extent if chitosan is exposed to high temperature. 

One of the simplest ways to prepare a chitin gel is to treat chitosan acetate salt solution with carbodiimide to restore acetamido groups. Thermally not reversible gels are obtained by AT-acylation of chitosans N-acetyl-, N-propionyl- and N-butyryl-chitosan gels are prepared using 10% aqueous acefic, propionic and bufyric acid as solvents for treatment with appropriate acyl anhydride. Both N- and 0-acylation are found, but the gelation also occurs by selective AT-acylation in the presence of organic solvents. 

Fig. 11. (A) Force normalised by radius as a function of surface separation between mica surfaces in 0.01 wt.% acetic acid solution (pH 3.8). The arrow indicates a jump from a force barrier into molecular contact. (B) Forces between mica surfaces coated with chitosan across 0.01 wt.% acetic acid solution (pH 3.8). Two sets of measurements are shown. Filled and open symbols represent the forces measured on approach and separation, respectively, after 24 h of adsorption. The crosses represent the forces measured at pH 3.8 after the cycle of exposing chitosan adsorption layers for solutions of increasing alkalinity and measuring forces at pH 4.9, 6.2 and 9.1. The solid lines represent theoretically calculated DLVO forces. Redrawn with permission from Ref. [132]. 1992, American Chemical Society.

X. Geng, 0-H. Kwon, J. Jang. 2005. Eleetrospinning of chitosan dissolved in coneentrated acetic acid solution. Biomaterials, 26. pp. 5427-5432. 

The polymer substrate consisted of low viscosity chitosan, poly(D-glucosamine), (I), which had a Brookfield viscosity of a 120-200 cps in 1% acetic acid solution. 

Chitosan is insoluble in water but soluble in acidic solvents below pH 6. Organic acids such as acetic, formic and lactic acids are used for dissolving chitosan, and the most commonly used solvent is 1% acetic acid solution. Solubility of chitosan in inorganic acid solvent is quite Umited. Chitosan is soluble in 1% hydrochloric acid but insoluble in sulfuric and phosphoric acids. Chitosan solution s stability is poor above pH 7 due to the precipitation or gelation that takes place in the alkali pH range. Chitosan solution forms a poly-ion complex with anionic hydrocolloid to produce a gel. 

Chitosan solution was prepared by dissolving chitosan (ranging between 5 and 50%, w/w) in 1% acetic acid solution the solution was stirred at 100 rpm and heated at 50 °C until homogeneous. Then, the solution was poured into steel containers with an internal diameter of 2 cm and height of 1 cm and frozen at —20 °C for 5-24 h to obtain a hydrogel that was treated in four different ways ... 

In an effort to improve the blood compatibility of chitosan in a fiber form, a metiianol-acetic acid solution of chitosan and tropocollagen was wet-spim into reasonably strong fibers. Using an ammonia solution with ammonium sulfate as a coagulation bath, acylation of these fibers was shown to increase their tenacity.i ... 

Geng X, Kwon OH, Jang J (2005) Electrospinning of chitosan dissolved in concentrated acetic acid solution. Biomaterials 26 5427-5432... 

Chitosan dissolved acetic acid solution can be employed for the fabrication of solid-state proton conducting batteries. The... 

Figure 4.5 Storage modulus (G in Pa.) for chitosan-g-methylcellulose in 0.3 M acetic acid solution as a function of temperature. Comparison with initial chitosan. Filled symbols for temperature increase and open symbols for temperature decrease.

It has been established that the process of enzymatic destmction of chitosan (CHT) film specimens obtained from acetic acid solution experiences the influence of the prehistory of film formation, including the concentration of acetic acid used for films preparation and the thermal film modification. 

Figures 1 show the SEM photomicrographs of the silver containing chitosan fibers. It can be seen that although the silver containing chitosan fiber generally has a smooth surface structure, the AlphaSan RC5000 particles are visible and can be seen embedded into the chitosan structure. When the fiber is wet with 0.1% aqueous acetic acid solution, it can be seen under optical microscope that the silver containing AlphaSan RC5000 particles are fairly uniformly distributed inside the fiber structure, acting as the reservoir for releasing the antimicrobial silver ions.

Chitosan solntion was prepared in acetic acid solution (chitosan acetic acid = 5 4). Starch powder was mixed with glycerol homogenously with the above prepared chitosan solution to form 15% starch and chitosan s isoUd gel-like mixtures by heating at lOO C for 2h. The gel-like mixtures in hot state were cold pressed to prepare wet starch/chitosan films. 

Chitosan (1%, w/v) was mixed in acetic acid solution (1%, v/v) at 40°C. Tween 80 at 0.1% (v/v) was added to improve wettability. The solution was stirred for 8h and then oleic acid added to chitosan solution to reach a final concentration of 0%, 1%, 2%, and 4% (v/v). These mixtures were emulsified at 13,500rpm for 4min. In order to guarantee the stability of the emulsions, pH was adjusted to 5 with 1N NaOH (Jumaa et al. 2002). 

Chitosan solution (1.5%, w/v) was prepared in 1.0% (v/v) acetic acid solution. The solution was allowed to stand overnight to remove air bubbles. Then the solution was poured into a glass disk in a dust-free environment and dried in air. The dried film was neutralized by 1N NaOH solution and washed with phosphate-buffered saline (PBS). Aqueous aGSA solution was prepared. After that, chitosan film was immersed in aGSA solution for cross-linking. After 6h, it was washed with deionized water to remove excess aGSA and dried in air. 

Chitosan solutions (2%, w/v) prepared in 1% acetic acid solution and stirred overnight. After that, solutions were filtered with cheesecloth. Aqueous starch solutions (1%, w/v) were prepared by... 

Chitosan film was prepared by dissolving 1 g of shrimp chitosan in lOOmL of 1% acetic acid solution. The solution was filtered through a silk screen. The three antimicrobial agents—garlic oil, potassium sorbate, and nisin— were incorporated into chitosan film forming solution at various levels. The solutions were cast in polyacrylic plates and dried. The dry films obtained were peeled off and stored in a chamber at 50% RH and 25°C until evaluation. 

FIGURE 8.2 The dependence of characteristic viscosity changes from the time of chitosan exposure in the solution of CHT-1 separated from the 1 % acetic acid solution in the absence of enzyme agents (4) and with enzyme agents Tripsin (1), Liraza (2), and CoUagenase (3). 

On the contrary, chitosan holding in an acetic acid solution in the presence of the enzymes leads to considerate reduction in the sedimentation constant and increase of the diffusion coefficient (see Table 8.1). Thus, it results in significant reduction of the chitosan molecular weight taking place during the biodegradation process. 

The observed changes in the values of characteristic and intrinsic viscosity in the absence of enzyme agents are probably coimected with structural transformations such as destruction of chitosan associates in the acetic acid solution. As a XRD analysis shows, the source chitosan and the one dissolved in the acetic acid have different supramolecular organization (Fig. 8.3). 

BoUo et al [53] reported an interesting comparison of the electrochemical behavior of GCE modified with l.Omgml of chemically oxidized MWCNT dispersed in water, dimethylformamide (DMF), chitosan (CHI) (in 1.0%v/v acetic acid solution) and Nafion (Naf) in ethanol (Figure 3.7). 

---