**5. Chitosan and collagen films**

28 Recent Advances in Plasticizers

One of the properties of major importance of chitosan is its filmogenic capacity. The films can be prepared from moderately concentrated polymer solutions, in general at 3 % (w/w). Chitosan films possess acceptable mechanical and permeability properties, good adherence to different surfaces, are flexible, resistant to water and show excellent barrier properties against gases (O2, CO2, water vapor), that allows its application in the development of food packing

There are different methods for the productions of chitosan films, as the evaporation of solvents (Casting) -the first developed and more used at present- and the extrusion with some polyesters, olefins or carbohydrates. The last one is the most used for the industrial production of polymeric materials (Bhattacharya et al., 2005; Pelissari et al., 2009). With regard to the edible covered films, these are obtained by direct application (spraying, immersion) of chitosan solutions on the food surface or in the medicine's tablets, forming a thin layer that covers and protects the product of the environment (Janjarasskul & Krochta, 2010). Nowadays, most of the films and chitosan composites are prepared by this method, changing the solvent and the component's concentration of the blends, according to the application. Recently, it has been reported that the electrospinning technique allows the preparation of ultrathin chitosan nanofibers with unusually high porosity in their nanometer scale architecture and large surface area (Chen, Z. et al., 2009; Martínez-Camacho et al., 2011; Ohkawa et al., 2004). As particular interests have been addressed in the tissue engineering, great efforts have been made to study electrospinning of biodegradable

Due to its abundance in the nature and to its biocompatibility, chitosan is considered to be a promising polymer for the development of functional materials (Ohkawa et al., 2004; Westbroek et al., 2007). In contrast to other materials, it has been demonstrated that chitosan films possess antifungal properties (Martínez-Camacho et al., 2011; Plascencia-Jatomea et al., 2010), that make it a good alternative for food protection and food shelf life extension (Chien et al., 2007b; Chien et al., 2007a; Coma et al., 2003; El Ghaouth et al., 1992; Fornes et al., 2005; Li & Yu, 2001; No et al., 2007; Schnepf et al., 2000). In general terms, although the materials prepared with conventional synthetic polymers are functional, of easy production, and low cost, they hardly are degradable, which strongly impacts the environment (Tharanathan & Srinivasa, 2007). Nevertheless, the use of these biopolymers is limited due to problems related to its deficient mechanical properties (fragility, poor barriers against gases and

The incorporation of natural compounds has allowed the appearance of new materials with good mechanical properties, which overcome those that possess the individual materials. Most of these films are prepared mainly thinking about its use as food packing and tissue engineering materials (Tharanathan & Srinivasa, 2007). Additionally, to improve chitosan

Plasticizers are additives used to increase the flexibility or plasticity of polymers (Daniels, 1989). The most studied plasticizing agent in chitosan films has been glycerol and polyols and its efficacy in improving the properties of films has been well-documented (Table 4).

blends elasticity a biodegradable materials might be added (Butler et al., 1996).

materials (Agulló et al., 2004; Plascencia-Jatomea et al., 2010; Tharanathan et al., 2002).

**4.1 Chitosan bio-based films** 

polymers (Schauer & Schiffman, 2008).

moisture) and cost (De Azeredo, 2009).

**4.2 Chitosan films and bio-plasticizer** 

Biomaterials are increasingly being used in several fields, like packaging material (Tharanathan, 2003), tissue engineering (Nalwa, 2005), medical and pharmaceutical applications (Bures et al., 2001) due to their functional properties.

Collagen, as a natural polymer, has very weak mechanical properties, especially in aqueous media (Zhang et al., 1997). On the other hand, as it was mentioned previously, chitosan poses excellent film-forming property, antimicrobial activity, and unique coagulating ability with metal and other lipid and protein complexes due to the presence of a high density of amino groups and hydroxyl groups in the polymeric structure of chitosan (Dutta et al., 2002; Li et al., 1992; Shahidi et al., 1999). Although, mechanical properties of chitosan films are comparable to those of many medium-strength commercial polymers, it is considered that

By-Products From Jumbo Squid (*Dosidicus gigas*): A New Source of Collagen Bio-Plasticizer? 31

Hydrogel system stable Capable of encapsulating T4

Water resistant Deformable Increase in breaking strength Rubbery semi-crystalline materials Antimicrobial activity Biodegradable films

Electrostatic interactions Intereconnected porous structure Excellent mechanical properties Collagen-chitosan scaffolds with superior characteristics

Fibrous membrane softer, flexible and

Fibrous membrane inflexible, less

Polyelectrolytic interaction Low thermal stability Small porous size Promising feature to be processed into porous structures Application in cell transplantation and tissue regeneration

products

It accelerates of cellular proliferation; It reduces the biodegradation rate. Materials for tissue engineering.

> Thermally stable Less mechanical stable

Low thermal stability

Effective for the controlled release of transforming growth factor beta 1 Satisfy specifications for cartilage tissue engineering

Porous composite matrix Good tensile strength Biocompatible and biodegradable May be used as a chondrocyte carrier for cartilage tissue engineering

Material suitable for tissue-engineered

Chitosan/Gelatin copolymer Very suitable for coating meat

(Chiu & Radisic, 2011)

(Gómez-Estaca et al., 2011)

(Wang & Stegemann, 2011)

(Horn et al., 2009)

(Shane & Champa, 2009)

(Tangsadthakun et al., 2007)

(Sionkowska et al., 2006)

(Lee et al., 2006)

(Shi et al., 2005)

elastics (Chen, Z. et al., 2009)

compact (Chen et al., 2009)

Low mechanical stability (Sionkowska, 2006)

cornea (Chen et al., 2005)

Composition Main characteristics Reference

Collagen/Chitosan composite

Gelatin -Chitosan films

Collagen/Chitosan scaffolds fabricated via thermally triggered cofibrillogenesis

Electrospun 80 % Collagen/20

Electrospun 20 % Collagen/80

Anionic collagen /Chitosan

Collagen/Chitosan Scaffold

70% Collagen-30% Chitosan

Collagen/chitosan composite

Collagen /Chitosan Scaffold

Table 5. Properties of collagen/gelatin-chitosan blends.

Complex membranes of collagen/chitosan.sodium

hydrogel

approach

% Chitosan fibers

% Chitosan fibers

sponges by freeze lyophilization

Films

50% Collagen-50% Chitosan Films

microgranules

hyaluronate

this properties could be improved, mainly its elasticity (Suyatma et al., 2005). One strategy to increase chitosan elasticity is to associate it with biodegradable materials. However, the interactions that may occur between biopolymers are very important when the characteristics of any material are considered to be transformed. These interactions depend on the miscibility of its components.

Miscibility in polymer blends is attributed to specific interactions between polymeric components, which usually give rise to a negative free energy of mixing in spite of the high molecular weight of polymers (Shanmugasundaram et al., 2001). On the other hand, the interactions between natural polymers of different chemical structures, whether they are hydrogen bonding or electrostatic in nature, considerably improve the mechanical properties of the material obtained from such mixtures (Zhang et al., 1997). Although, most of polymers blends are immiscible with each other due to the absence of specific interactions, TEM micrographs of collagen–chitosan composites have shown that chitosan network can interpenetrate into the collagen network; the chitosan phase is wrapped in the collagen phase and is denser; besides, the amount of chitosan phase grows with the content of chitosan increasing (Zhang et al., 1997).

The main kinds of interactions that can give rise between the two polymers when they are in contact with water are: an electrostatic complex and an hydrogen bonding type of complex, in the presence of a great excess of chitosan (Taravel & Domard, 1993; Taravel & Domard, 1995). Hydrogen bonds between collagen and chitosan can be formed as follows: between either a carbonyl, hydroxyl, or an amino group from collagen, and either hydroxyl, amino, or a carbonyl group from chitosan. The formation of hydrogen bonds between two different macromolecules competes with the formation of hydrogen bonds between molecules of the same polymer (Mo et al., 2008). Apparently, interactions between collagen and chitosan depend on the structural organization of collagen and the amount and distribution of charges along the polymer chains. These properties are directly related to the pH of the medium, which is of fundamental importance for the study of interactions present between the biopolymers (Tohni, 2002).
