**2.2 Mixed chitin esters (co-esters)**

The presence of two hydroxyl groups at the C-3 and C-6 positions of chitin allows the introduction of two different acyl substituents, leading to the formation of mixed esters (co-esters) of chitin. This possibility is also due to the differential reactivity of the hydroxyl groups linked to the primary and secondary carbon atoms in chitin. Thus, under ideal conditions, it is possible to obtain mixed esters containing the same molar fraction of different acyl groups in the modified material.

**135**

*Modulating the Physicochemical Properties of Chitin and Chitosan as a Method of Obtaining…*

Different ester groups (e.g., butyric and acetic acid residues) are present in mixed esters in a single polysaccharide chain. The replacement of some large bulky butyl groups with much smaller acetate groups in one polysaccharide chain causes that in a condensed state, it becomes possible to obtain favorable conditions for the formation of intermolecular bonds of the hydrogen bridge type. This effect cannot be expected when using a mixture of two different biopolymers (e.g. chitin diacetate and chitin di-butyrate). Thus, the term mixed polymers is not the same as mixed chitin esters. In order to obtain a polymer mixture, it is necessary to use at least two chemically different polymers (**Figure 2**). In contrast mixed ester/co-ester of chitin contains only one component. It was found that the differences between chitin mixed esters (co-esters) and a mixture of two species can be observed in NMR

H and 13C) (**Figures 3** and **4**). The studies used 50:50 butyryl-acetyl-chitin

H-NMR spectra in the range of chemical shifts 2.5 ppm

co-polyester (**2**) (mixed ester), 90:10 butyryl-acetyl-chitin co-polyester (**3**) and a 1:

A comparative analysis of the 13C-NMR spectra of the 180–150 ppm range characteristic for the chemical shifts of carbon in carboxylic acid derivatives showed that the distribution in the mixed ester of chitin **2** and **3** is different from the carbon signals of the 1: 1 mixture of polymers **1** and **4** (**Figure 3**). A similar result is observed in the range of 10–40 ppm, characteristic for carbons of aliphatic ester residues introduced as a result of esterification of chitin with acetic anhydride

to 0.5 ppm also allowed to state that in the case of butyryl-acetyl chitin co-polyesters (samples **2** and **3**) the recorded signals are different than in the case of the 1: 1

The possibility of forming the intermolecular hydrogen bonds that stabilize butyryl-acetyl chitin co-polyester structure translates into fiber-forming properties, and thus the possibility of modulating the functional properties of the final materials and their use in the manufacture of new materials for medical use. In addition to stabilization by hydrogen bonds, it is also possible to create weak interactions based on hydrophobic interactions. The participation of such various weak interactions in the stabilization of materials may translate into their ability to interact with both

hydrophobic and hydrophilic structures, which affects biological activity.

Acetate-formate mixed chitin ester was obtained using formic acid, acetic anhydride and trifluoroacetic acid as a catalyst [25]. It turned out that this ester is slightly soluble in typical organic solvents. This is one of the reasons why this derivative has not found practical use, even though its biological properties are comparable to those of chitin. A similar situation was observed in the case of

Attempts to obtain a mixed butyric acetic ester of chitin by reaction using acetic and butyric anhydrides and methanesulfonic acid or trifluoroacetic acid as catalysts have been unsuccessful. The final product was a mixture of chitin acetate, chitin

The approach to synthesize mixed chitin esters using a mixture of trifluoroacetic acid and the corresponding organic acid as catalysts also led to the formation of mixtures of chitin monoesters and mixed esters (co-polyesters) of chitin. It has been shown that carrying out the reaction at the temperature of 70°C for a short time (30 min) under homogeneous conditions allows for obtaining copolyesters: acetate-butyrate, acetate-hexanoate, acetate-octanoate and acetatepalmitate of chitin. The final co-polyesters have molecular weights ranging from

1 mixture of chitin di-butyrate (**1**) and chitin diacetate (**4**).

*DOI: http://dx.doi.org/10.5772/intechopen.95815*

spectra (1

and butyric acid (**Figure 3**). Comparative studies of <sup>1</sup>

mixture of polymers **1** and **4** (**Figure 4**).

*2.2.1 Chitin co-esters in dressing materials*

trifluoroacetate-formate derivatives of chitin [26].

butyrate and the expected acetate-butyrate of chitin [27, 28].

### *Modulating the Physicochemical Properties of Chitin and Chitosan as a Method of Obtaining… DOI: http://dx.doi.org/10.5772/intechopen.95815*

Different ester groups (e.g., butyric and acetic acid residues) are present in mixed esters in a single polysaccharide chain. The replacement of some large bulky butyl groups with much smaller acetate groups in one polysaccharide chain causes that in a condensed state, it becomes possible to obtain favorable conditions for the formation of intermolecular bonds of the hydrogen bridge type. This effect cannot be expected when using a mixture of two different biopolymers (e.g. chitin diacetate and chitin di-butyrate). Thus, the term mixed polymers is not the same as mixed chitin esters. In order to obtain a polymer mixture, it is necessary to use at least two chemically different polymers (**Figure 2**). In contrast mixed ester/co-ester of chitin contains only one component. It was found that the differences between chitin mixed esters (co-esters) and a mixture of two species can be observed in NMR spectra (1 H and 13C) (**Figures 3** and **4**). The studies used 50:50 butyryl-acetyl-chitin co-polyester (**2**) (mixed ester), 90:10 butyryl-acetyl-chitin co-polyester (**3**) and a 1: 1 mixture of chitin di-butyrate (**1**) and chitin diacetate (**4**).

A comparative analysis of the 13C-NMR spectra of the 180–150 ppm range characteristic for the chemical shifts of carbon in carboxylic acid derivatives showed that the distribution in the mixed ester of chitin **2** and **3** is different from the carbon signals of the 1: 1 mixture of polymers **1** and **4** (**Figure 3**). A similar result is observed in the range of 10–40 ppm, characteristic for carbons of aliphatic ester residues introduced as a result of esterification of chitin with acetic anhydride and butyric acid (**Figure 3**).

Comparative studies of <sup>1</sup> H-NMR spectra in the range of chemical shifts 2.5 ppm to 0.5 ppm also allowed to state that in the case of butyryl-acetyl chitin co-polyesters (samples **2** and **3**) the recorded signals are different than in the case of the 1: 1 mixture of polymers **1** and **4** (**Figure 4**).

The possibility of forming the intermolecular hydrogen bonds that stabilize butyryl-acetyl chitin co-polyester structure translates into fiber-forming properties, and thus the possibility of modulating the functional properties of the final materials and their use in the manufacture of new materials for medical use. In addition to stabilization by hydrogen bonds, it is also possible to create weak interactions based on hydrophobic interactions. The participation of such various weak interactions in the stabilization of materials may translate into their ability to interact with both hydrophobic and hydrophilic structures, which affects biological activity.

#### *2.2.1 Chitin co-esters in dressing materials*

Acetate-formate mixed chitin ester was obtained using formic acid, acetic anhydride and trifluoroacetic acid as a catalyst [25]. It turned out that this ester is slightly soluble in typical organic solvents. This is one of the reasons why this derivative has not found practical use, even though its biological properties are comparable to those of chitin. A similar situation was observed in the case of trifluoroacetate-formate derivatives of chitin [26].

Attempts to obtain a mixed butyric acetic ester of chitin by reaction using acetic and butyric anhydrides and methanesulfonic acid or trifluoroacetic acid as catalysts have been unsuccessful. The final product was a mixture of chitin acetate, chitin butyrate and the expected acetate-butyrate of chitin [27, 28].

The approach to synthesize mixed chitin esters using a mixture of trifluoroacetic acid and the corresponding organic acid as catalysts also led to the formation of mixtures of chitin monoesters and mixed esters (co-polyesters) of chitin. It has been shown that carrying out the reaction at the temperature of 70°C for a short time (30 min) under homogeneous conditions allows for obtaining copolyesters: acetate-butyrate, acetate-hexanoate, acetate-octanoate and acetatepalmitate of chitin. The final co-polyesters have molecular weights ranging from

*Chitin and Chitosan - Physicochemical Properties and Industrial Applications*

to the low reaction yields and possibly incomplete esterification of the chitin hydroxyl groups, resulting in the formation of a significant amount of insoluble gel fractions when dissolved in acetone prior to precipitation with water. For DHCH, it is preferable to use low synthesis temperatures (0°C and 8°C). The yield of DHCH synthesis was relatively high (above 70%), with the highest efficiency observed at 21°C (84 to 95%). Unfortunately, carrying out the synthesis of DHCH at 21°C resulted in a low molecular weight product. A trend analogous to that of chitin di-pentanoate was observed, indicating that the longer the reaction time, the higher the reaction performance and the lower the molecular weight of the obtained biopolymers. Although in DHCH the hydroxyl groups of chitin are substituted with longer alkyl chains than in DVCH or DBC, it has been found that DHCH retains good solubility in solvents such as ethanol, acetone, dichloromethane, 1,2-dichloroethane, N,N-dimethylformamide, N,N-dimethylacetamide and ethyl acetate and no solubility in water. Good solubility, filmogenic and fiber-forming properties of DHCH give greater possibilities of its processing (film casting, washing method, electrospinning method) compared to chitin alone. The mechanical properties of DHCH and DBC in the form of thin solid layers poured from solution were investi-

gated in relation to their molecular weights. DHCH and DBC showed semicontinuous properties and cracked rapidly upon exceeding the plasticity point, similar to that observed for DVCH. The elongation at break was small and did not exceed 4%. For both biopolymers, their tensile properties correlate with the

pores of various sizes (pore size in the range 78–421 μm, average pore size 253 μm ± 93 μm) [21–24]. Due to its physic-chemical properties, DHCH can successfully replace or support materials based on di-butyrylchitin (e.g. in the form of mixtures of both biopolymers) and thus it can be used as a material for medical and pharmaceutical applications, especially in tissue engineering scaffolds and in healing wounds. The described procedure of chitin esterification to obtain products of high purity. Moreover, this method is universal (the possibility of preparation various chitin diesters) and is easy to produce and is not time-consuming [21]. Another method of chemical modification of chitin is esterification leading to carboxymethylchitin (CMCht, CM-chitin) [22, 23] or dicarboxymethylchitin using monochloroacetic or mono-chloropropionic acid followed by substitution of halogen with a hydroxyl group. This modification leads to the loss of the supramolecular structure of chitin and the formation of water-soluble derivatives [24].

The presence of two hydroxyl groups at the C-3 and C-6 positions of chitin allows the introduction of two different acyl substituents, leading to the formation of mixed esters (co-esters) of chitin. This possibility is also due to the differential reactivity of the hydroxyl groups linked to the primary and secondary carbon atoms in chitin. Thus, under ideal conditions, it is possible to obtain mixed esters containing the same molar fraction of different acyl groups in the modified material.

molecular weight. Parameters such as modulus of elasticity, stress at yield, as well as stress and strain at break, were found to increase with increasing DHCH and DBC molecular weight. Comparing the mechanical properties of DHCH, DBC and DVCH, it can be concluded that Young's modulus decreases with increasing chain length of the acyl group of chitin diesters (a similar relationship is observed for chitin monoesters, where only one hydroxyl group is acylated). Due to the good solubility of hydrophobic chitin diesters in organic solvents and their insolubility in water, it is possible to obtain porous structures based on DHCH and DBC by using the salt leaching method. The prepared porous materials are characterized by a united network of interconnected channels and a high degree of open porosity with

**134**

**2.2 Mixed chitin esters (co-esters)**

### *Chitin and Chitosan - Physicochemical Properties and Industrial Applications*

**Figure 2.**

*Chemical structure of chitin di-acetate, chitin di-butyrate, butyryl-acetyl chitin co-polyester (mixture ester, co-ester).*

**137**

**Figure 4.** *Fragments of 1*

*Modulating the Physicochemical Properties of Chitin and Chitosan as a Method of Obtaining…*

30 to 150 kDa and the degree of esterification ranging from 1.0 to 2.0, depending

Another approach to obtain mixed butyryl-acetyl esters of chitin [29] is based on the use of butyric and acetic acid anhydrides and methanesulfonic acid as a catalyst. However, this method is not very friendly from the point of view of industrial stoppage. Thinking about the industrial synthesis of the butyryl-acetyl chitin derivative, it was necessary to establish reaction conditions that would eliminate the need to

In the works on the development of a method for the production of the butyrylacetyl chitin co-polyester on an industrial scale, it was necessary to develop, in the first stage, the conditions for the synthesis on a laboratory scale, which would later be transferred to an industrial scale. The esterification in laboratory conditions is carried out under heterogeneous conditions at 20-25°C, using chloric (VI) acid as a catalyst and a mixture of butyric and acetic acid anhydrides, used in a molar ratio of 90:10 [22, 23]. The product was obtained with a yield of 82 to 89% is soluble in DMF, DMSO and NMP, has a high molar mass (intrinsic viscosity of these products determined in DMF at the level of 2.0–2.05 dL/g) and a full degree of esterification. In the research on the development of a method of producing butyryl-acetyl chitin co-polyester in industrial conditions it was crucial to eliminate the possibility of formation an explosive mixture which may arise as a result of direct contact of acetic anhydride with perchloric acid. It turned out that the priority was to use an efficient cooling system so that the process temperature did not exceed 20°C. In laboratory conditions, it was sufficient to use an ice-water bath with NaCl (brine bath) and intensive mixing of the suspension. In laboratory conditions, diethyl ether is added to the slurry to remove excess unreacted anhydrides and formed carboxylic acids and the crude product is filtered off. The crude acetylation product is washed with water and dilute ammonia water, dried and finally dissolved in ethanol. The transfer of the conditions from the laboratory scale to the macro scale

*H-NMR spectra of* **1***,* **2***,* **3** *and* **4** *derivatives in the range 2.5–0.5 ppm.*

*DOI: http://dx.doi.org/10.5772/intechopen.95815*

on the raw materials used.

use methanesulfonic acid.

**Figure 3.** *Fragments of 13C-NMR spectra of* **1***,* **2***,* **3** *and* **4** *derivatives.* *Modulating the Physicochemical Properties of Chitin and Chitosan as a Method of Obtaining… DOI: http://dx.doi.org/10.5772/intechopen.95815*

30 to 150 kDa and the degree of esterification ranging from 1.0 to 2.0, depending on the raw materials used.

Another approach to obtain mixed butyryl-acetyl esters of chitin [29] is based on the use of butyric and acetic acid anhydrides and methanesulfonic acid as a catalyst. However, this method is not very friendly from the point of view of industrial stoppage. Thinking about the industrial synthesis of the butyryl-acetyl chitin derivative, it was necessary to establish reaction conditions that would eliminate the need to use methanesulfonic acid.

In the works on the development of a method for the production of the butyrylacetyl chitin co-polyester on an industrial scale, it was necessary to develop, in the first stage, the conditions for the synthesis on a laboratory scale, which would later be transferred to an industrial scale. The esterification in laboratory conditions is carried out under heterogeneous conditions at 20-25°C, using chloric (VI) acid as a catalyst and a mixture of butyric and acetic acid anhydrides, used in a molar ratio of 90:10 [22, 23]. The product was obtained with a yield of 82 to 89% is soluble in DMF, DMSO and NMP, has a high molar mass (intrinsic viscosity of these products determined in DMF at the level of 2.0–2.05 dL/g) and a full degree of esterification. In the research on the development of a method of producing butyryl-acetyl chitin co-polyester in industrial conditions it was crucial to eliminate the possibility of formation an explosive mixture which may arise as a result of direct contact of acetic anhydride with perchloric acid. It turned out that the priority was to use an efficient cooling system so that the process temperature did not exceed 20°C. In laboratory conditions, it was sufficient to use an ice-water bath with NaCl (brine bath) and intensive mixing of the suspension. In laboratory conditions, diethyl ether is added to the slurry to remove excess unreacted anhydrides and formed carboxylic acids and the crude product is filtered off. The crude acetylation product is washed with water and dilute ammonia water, dried and finally dissolved in ethanol. The transfer of the conditions from the laboratory scale to the macro scale

**Figure 4.** *Fragments of 1 H-NMR spectra of* **1***,* **2***,* **3** *and* **4** *derivatives in the range 2.5–0.5 ppm.*

*Chitin and Chitosan - Physicochemical Properties and Industrial Applications*

*Chemical structure of chitin di-acetate, chitin di-butyrate, butyryl-acetyl chitin co-polyester (mixture ester,* 

**136**

**Figure 3.**

**Figure 2.**

*co-ester).*

*Fragments of 13C-NMR spectra of* **1***,* **2***,* **3** *and* **4** *derivatives.*

did not involve only increasing the amount of reagents and the size of the synthesizer. The key was to optimize the process conditions and the use of reagents that can be used in industrial conditions from the point of view of safety, environmental impact and economics. A reactor with a capacity of 60 dm3 with an effective cooling system was used. A 3 kg chitin input was used for the synthesis. The remaining reagents (2 dm3 of perchloric acid, 15 dm3 of butyric anhydride and 1 dm3 of acetic anhydride) were added in portions. The time required for all reagents to be introduced and for complete conversion was about 24 h. In place of diethyl ether, under industrial conditions, ethyl acetate was used to remove excess unreacted butyric and acetic anhydrides. In industrial conditions it was also necessary to replace the ammonia water to neutralize the acetic and butyric acid residues. It turned out that it is possible to use sodium carbonate for this purpose. Also, the step of separation of raw product required changes in the industrial process. In the synthesis under laboratory conditions, G4 Schott funnels were used for filtration. However, the use of this method on a large scale was ineffective. So suction filtration was used, the efficiency of which was 100 dm3 per hour. The process efficiency on an industrial scale was comparable to that of a laboratory scale synthesis. The physical and chemical properties of the final products were also comparable. The conducted research guaranteed the reproducible and required parameters of the raw material for the production of new medical materials [22, 23]. **Figure 5** shows a set for the synthesis of butyryl-acetyl chitin co-polyester on an industrial scale.

The development of an efficient synthesis of the butyryl-acetyl chitin co-polyester (BAC 90/10) made it possible to demonstrate that the obtained chitin derivative has the ability to form fibers from a wet solution with a strength slightly above 20 cN/tex with high porosity. Fibers with a strength at this level can be the basis for the production of 3D polymer-fiber composites. BAC 90/10 fibers show a stronger predisposition to apatite crystallization; strong sorption tendencies of fibers allowing the possibility of local supersaturation favoring the nucleation of apatite. It has been also found that BAC 90/10 fibers degrade fast under *in vitro* conditions.

One application of the butyryl-acetyl chitin co-polyester (BAC 90/10) is its use to produce highly porous film materials [30].

The research work began with laboratory tests during which two methods of formation of porous materials were tested: (a) pouring a 5% ethanol BAC 90/10 solution on a layer of solid inorganic salt (porophor agent), which, after solidification, was exposed to water to wash out the porophor agent, and (b) the use of porophor

**139**

**Figure 6.**

*Modulating the Physicochemical Properties of Chitin and Chitosan as a Method of Obtaining…*

agent suspensions in BAC 90/10 solution, which was a mixture of solvents with a density close to the bulk density of the porophor agent. Various organic and inorganic salts (K2CO3, KHCO3, KHSO4, KNO2, (NH4)2CO3, (NH4)HCO3, (NH4)2HPO4, (NH4)2SO4, Na2CO3, NaHCO3, Na2HPO4, Na2S2O3 x 5H2O, NaCl, di-ammonium citrate, di-ammonium oxalate were tested. It was found that all tested salts can be used as porophors. However, the most optimal porophor agent, in terms of porosity

Based on laboratory work, it was possible to start work on optimizing the production of porous dressing materials (Medisorb R, Medisorb R Ag). In the industrial method, solid NaCl as porophor agents and a 3% solution of BAC 90/10 in ethanol were used. The membrane was formed by pouring a 3% solution of BAC 90/10 onto a layer of porophor agent to produce a spongy structure. After drying, the membrane is rinsed in distilled water at 40°C until the porophor agent is washed off. The product is then dried at 80°C. After packing, the obtained membrane dressings are subjected to a process of radiation sterilization (in the case of the variant without the addition of an antibacterial substance). To obtain a silver-coated membrane, the membrane is sprayed with a suspension of metallic silver dispersed in water by means of a spray nozzle. The silver particles are evenly distributed in the suspension using an ultrasonic device. After drying and then packing, the product is subjected to radiation sterilization. The powder dressing is obtained by grinding the byturyl-acetyl chitin co-polyester, which is then sterilized by radiation [23, 31]. **Figure 6** shows a scheme for the preparation of porous

Dressing materials obtained by leaching salt from butyryl-acetyl chitin copolyester (BAC 90/10) and sodium chloride with a diameter of 0.16–0.40 nm and/ or microsilver were characterized by a high degree of porosity, pore size in the range of 275–305 nm and a degree of crystallinity in the range of 27.2–27.4%. SEM

*A scheme for the preparation of porous dressings based on butyryl-acetyl chitin co-polyester.*

*DOI: http://dx.doi.org/10.5772/intechopen.95815*

(95–99%) and tensile strength of 5 cN, was NaCl.

dressings based on butyryl-acetyl chitin co-polyester.

**Figure 5.** *Set for the synthesis of butyryl-acetyl chitin co-polyester on an industrial scale.*

*Modulating the Physicochemical Properties of Chitin and Chitosan as a Method of Obtaining… DOI: http://dx.doi.org/10.5772/intechopen.95815*

agent suspensions in BAC 90/10 solution, which was a mixture of solvents with a density close to the bulk density of the porophor agent. Various organic and inorganic salts (K2CO3, KHCO3, KHSO4, KNO2, (NH4)2CO3, (NH4)HCO3, (NH4)2HPO4, (NH4)2SO4, Na2CO3, NaHCO3, Na2HPO4, Na2S2O3 x 5H2O, NaCl, di-ammonium citrate, di-ammonium oxalate were tested. It was found that all tested salts can be used as porophors. However, the most optimal porophor agent, in terms of porosity (95–99%) and tensile strength of 5 cN, was NaCl.

Based on laboratory work, it was possible to start work on optimizing the production of porous dressing materials (Medisorb R, Medisorb R Ag). In the industrial method, solid NaCl as porophor agents and a 3% solution of BAC 90/10 in ethanol were used. The membrane was formed by pouring a 3% solution of BAC 90/10 onto a layer of porophor agent to produce a spongy structure. After drying, the membrane is rinsed in distilled water at 40°C until the porophor agent is washed off. The product is then dried at 80°C. After packing, the obtained membrane dressings are subjected to a process of radiation sterilization (in the case of the variant without the addition of an antibacterial substance). To obtain a silver-coated membrane, the membrane is sprayed with a suspension of metallic silver dispersed in water by means of a spray nozzle. The silver particles are evenly distributed in the suspension using an ultrasonic device. After drying and then packing, the product is subjected to radiation sterilization. The powder dressing is obtained by grinding the byturyl-acetyl chitin co-polyester, which is then sterilized by radiation [23, 31]. **Figure 6** shows a scheme for the preparation of porous dressings based on butyryl-acetyl chitin co-polyester.

Dressing materials obtained by leaching salt from butyryl-acetyl chitin copolyester (BAC 90/10) and sodium chloride with a diameter of 0.16–0.40 nm and/ or microsilver were characterized by a high degree of porosity, pore size in the range of 275–305 nm and a degree of crystallinity in the range of 27.2–27.4%. SEM

**Figure 6.** *A scheme for the preparation of porous dressings based on butyryl-acetyl chitin co-polyester.*

*Chitin and Chitosan - Physicochemical Properties and Industrial Applications*

impact and economics. A reactor with a capacity of 60 dm3

of perchloric acid, 15 dm3

reagents (2 dm3

efficiency of which was 100 dm3

to produce highly porous film materials [30].

*Set for the synthesis of butyryl-acetyl chitin co-polyester on an industrial scale.*

did not involve only increasing the amount of reagents and the size of the synthesizer. The key was to optimize the process conditions and the use of reagents that can be used in industrial conditions from the point of view of safety, environmental

system was used. A 3 kg chitin input was used for the synthesis. The remaining

anhydride) were added in portions. The time required for all reagents to be introduced and for complete conversion was about 24 h. In place of diethyl ether, under industrial conditions, ethyl acetate was used to remove excess unreacted butyric and acetic anhydrides. In industrial conditions it was also necessary to replace the ammonia water to neutralize the acetic and butyric acid residues. It turned out that it is possible to use sodium carbonate for this purpose. Also, the step of separation of raw product required changes in the industrial process. In the synthesis under laboratory conditions, G4 Schott funnels were used for filtration. However, the use of this method on a large scale was ineffective. So suction filtration was used, the

scale was comparable to that of a laboratory scale synthesis. The physical and chemical properties of the final products were also comparable. The conducted research guaranteed the reproducible and required parameters of the raw material for the production of new medical materials [22, 23]. **Figure 5** shows a set for the

The development of an efficient synthesis of the butyryl-acetyl chitin co-polyester (BAC 90/10) made it possible to demonstrate that the obtained chitin derivative has the ability to form fibers from a wet solution with a strength slightly above 20 cN/tex with high porosity. Fibers with a strength at this level can be the basis for the production of 3D polymer-fiber composites. BAC 90/10 fibers show a stronger predisposition to apatite crystallization; strong sorption tendencies of fibers allowing the possibility of local supersaturation favoring the nucleation of apatite. It has been also found that BAC 90/10 fibers degrade fast under *in vitro* conditions.

One application of the butyryl-acetyl chitin co-polyester (BAC 90/10) is its use

The research work began with laboratory tests during which two methods of formation of porous materials were tested: (a) pouring a 5% ethanol BAC 90/10 solution on a layer of solid inorganic salt (porophor agent), which, after solidification, was exposed to water to wash out the porophor agent, and (b) the use of porophor

synthesis of butyryl-acetyl chitin co-polyester on an industrial scale.

with an effective cooling

of acetic

of butyric anhydride and 1 dm3

per hour. The process efficiency on an industrial

**138**

**Figure 5.**

tests confirmed the porous structure of pores, which are negative for the crystals of the inorganic porophor agent used. In addition, the pores are open pores, which increases the effectiveness of water adsorption. **Figure 7** shows microscopic picture of porous structures obtained by the porophor agent washout method.

Dressings made of butyryl-acetyl chitin co-polyester (**Figure 8**) are intended for wounds of various etiologies, including chronic wounds, where the healing process is disturbed by comorbidities. In order to accelerate the healing of deep wounds, a dressing in the form of a backfill has been designed. Wounds are often accompanied by a bacterial infection, therefore, apart from the dressing in the form of a membrane made of chitin co-polyester only, there is also a variant containing the addition of silver, showing a bactericidal effect in the wound environment. Silver may appear in various forms, however, it has been assumed that only the ionic form of silver has a bactericidal effect. Any other form of silver must be converted to its ionic form. Hence, metallic silver with a small particle size after oxidation and hydrolysis is characterized by the highest antibacterial activity. Silver in ionic form also has the ability to interact with proteins. It has been found that the ionic form of silver has a higher protein binding capacity compared to nanoparticles [32–36].

The presence of pores and microcapillaries in the structure of membrane dressings allows drainage of wound exudate. Dressings made on the basis of chitin co-polyesters are characterized by high biocompatibility. Biological tests confirmed the lack of cytotoxic, irritating and allergenic effects. These dressings are degraded

### **Figure 7.**

*Microscopic picture of porous structures obtained by the porophor agent washout method.*

**141**

equation:

*Modulating the Physicochemical Properties of Chitin and Chitosan as a Method of Obtaining…*

in the subcutaneous tissue and gradually become smaller. The dressing shortens and weakens the exudative phase, drains the wound and accelerates the productive phase. The epithelialization process under the butyryl-acetyl chitin co-polyester

FTIR ATR analysis was made for samples of untreated Medisorb R dressings and material treated with fresh human plasma in order to test the dressing surface degradation and protein absorption on the dressing surface. Comparing spectra of samples treated with fresh human plasma and pure material, the decreasing of intensity of the vibration band of C=O at 1733 cm−1 in relation to the amide I signal at 1659 cm−1 was observed. It confirmed the sample surface degradation, which was connected to the hydrolysis of ester BAC 90/10 groups. In the *in vivo* tests, the dressings under macroscopic examination, in full thickness defects of subcutaneous tissue and skin caused wound healing with no inflammation, undergoing the most gradual biodegradation between weeks 4 and 8, and the observed differences were

The developed biodegradable dressings based on butyryl-acetyl chitin co-polyester were subjected to clinical evaluation using a wide range of patients. The use of dressings significantly accelerated the wound healing process caused by venous insufficiency and diabetes, also in patients whose healing process was disturbed by comorbidities. The improvement of the clinical condition of the wound depends on the individual patient and is most often observed after 30–60 days. The obtained results indicate that the tested dressings significantly reduce the time of wound healing. Medisorb R Ag is more effective than Medisorb R Membrane in the treatment of infected wounds. The powder form (Medisorb R Powder) allows the application of the dressing to deeper wounds. Thanks to their unique structure, dressings drain wound exudates beyond its environment, thus restoring the proper course of the cell reconstruction process. The ability to biodegrade in contact with the wound secretion eliminates the need to replace dressings, so the newly formed granulation

tissue is not disturbed - cell reconstruction processes run smoothly [38].

Chitosan is obtained as a result of the hydrolysis of chitin N-acetylamide groups (partial deacetylation of chitin). The main advantage of chitosan is its much better solubility in aqueous acid solutions, especially organic acids. Chitin deacetylation by chemical or enzymatic methods allows for obtaining materials with various degrees of hydrolysis (**Figure 9**). However, it is assumed that at least 50% chitin deacetylation is necessary for the material to be classified as chitosan. The degree of deacetylation (DD) is defined as the ratio of the number of free NH2 groups to the initial number of NHCOCH3 groups present in chitin and is presented in the

> 2 2 3

*NH NHCOCH*

*N N* <sup>=</sup> <sup>⋅</sup> <sup>+</sup>

*N*

where N - the number of specific units (structural units) in the polymer. The value of DD affects the biological and physicochemical properties of the

Chitosan obtained by chemical (concentrated NaOH) or enzymatic (chitin deacetylase) deacetylation of chitin. The first step of preparation of chitosan

polymer, such as solubility, swelling and stability, as well as reactivity.

100% *NH*

**3. Chitosan- raw materials obtained from chitin**

*DD*

*DOI: http://dx.doi.org/10.5772/intechopen.95815*

statistically significant [37].

was completed faster compared to the control sample [37].

**Figure 8.** *Picture of porous structures obtained by the porophor agent washout method.*

#### *Modulating the Physicochemical Properties of Chitin and Chitosan as a Method of Obtaining… DOI: http://dx.doi.org/10.5772/intechopen.95815*

in the subcutaneous tissue and gradually become smaller. The dressing shortens and weakens the exudative phase, drains the wound and accelerates the productive phase. The epithelialization process under the butyryl-acetyl chitin co-polyester was completed faster compared to the control sample [37].

FTIR ATR analysis was made for samples of untreated Medisorb R dressings and material treated with fresh human plasma in order to test the dressing surface degradation and protein absorption on the dressing surface. Comparing spectra of samples treated with fresh human plasma and pure material, the decreasing of intensity of the vibration band of C=O at 1733 cm−1 in relation to the amide I signal at 1659 cm−1 was observed. It confirmed the sample surface degradation, which was connected to the hydrolysis of ester BAC 90/10 groups. In the *in vivo* tests, the dressings under macroscopic examination, in full thickness defects of subcutaneous tissue and skin caused wound healing with no inflammation, undergoing the most gradual biodegradation between weeks 4 and 8, and the observed differences were statistically significant [37].

The developed biodegradable dressings based on butyryl-acetyl chitin co-polyester were subjected to clinical evaluation using a wide range of patients. The use of dressings significantly accelerated the wound healing process caused by venous insufficiency and diabetes, also in patients whose healing process was disturbed by comorbidities. The improvement of the clinical condition of the wound depends on the individual patient and is most often observed after 30–60 days. The obtained results indicate that the tested dressings significantly reduce the time of wound healing. Medisorb R Ag is more effective than Medisorb R Membrane in the treatment of infected wounds. The powder form (Medisorb R Powder) allows the application of the dressing to deeper wounds. Thanks to their unique structure, dressings drain wound exudates beyond its environment, thus restoring the proper course of the cell reconstruction process. The ability to biodegrade in contact with the wound secretion eliminates the need to replace dressings, so the newly formed granulation tissue is not disturbed - cell reconstruction processes run smoothly [38].
