versão On-line ISSN 0717-9707
J. Chil. Chem. Soc. v.51 n.4 Concepción dez. 2006
J. Chil. Chi. Soc., 51, N°.4 (2006), p.1022-1024
PREPARATION AND CHARACTERIZATION OFCHITOSAN GELS
MARCOS FERNÁNDEZ1, CARLOS VON PLESSING1 and GALO CÁRDENAS2*
1 Departamento de Farrmacia, Facultad de Farmacia, Universidad de Concepción, Casilla 237,Concepción, Chile.
The main goal of this work is the preparation and characterization of gelsusingchitosan for further formulation and topic applications. To achieve this goal several gels from pharmaceutical quality chitosan of low( Mw= 72.180 g/mol ) andmedium.( Mw= 103.000 g/mol) molecular weight with a 4% w/w were employed.The prepared gels were characterized by infrared spectroscopy, scanning electron microscopy andreological analyses.The spectroscopic study shows no great difference between both gels and most of chitosan bands are exhibited.The reological studies shows that both gels exhibit a non newtonian flow independent of the time, with seudoplastic for low molecular weight chitosan and plastic behavior for the medium molecular weight.
Key Words:gels, chitosan, chitin, seudoplastic,reologic.
The chitosan is a copolymer of b-(1->4) linked to 2-acetamide-2-deoxy-glucopyranose and 2-amino-2-deoxy-D-glucopyranose.There are several commercial chitosan degrees which difference depends on the deacetylation degree and molecular weight (1,2,3).
Chitosan is currently receiving a great deal of interest for medical and pharmaceutical applications. Chitosan is known for its biocompatibility allowing its use in various medical applications such as topical ocular applications (4), implantation (5) or injection (6).Furthermore, chitosan is metabolized by certain human enzymes, e.g. lysozyme, and can be considered as biodegradable (7,8).Besides,
Chitosan acts as a pentration enhancer by openingepithelial tight-junctins (9,10). Due to its positive charges at physiological pH, chitosan is also bioadhesive, which increases retention at the site of application (11,12).Chitosan also promotes wound healing (13,14) and has bacteriostatic effects (15,16).Chitosan is of low cost and is ecologically interesting (17).The chitosanis a biopolymer, biocompatible and biodegradable with antifungic andbiobacterizide, properties :(Candida albicans, Trichophyton mentagrophytes y Microsporum canis) and antibacterial (Escherichia coli, Staphilococcus aureus, Pseudomona aeruginosa y Salmonella paratyphi B),besides this improves the effect in the wound dressing injuries.Inmedical and pharmaceutical applications, chitosan is used as a component in hydrogels.
There are several possible definitions of a hydrogel, Peppes (18) defined hydrogels as macromolecular networks in water or biological fluids.Based on the definition, hydrogels are often divided into three classes depending on the nature of their network, namely entrangled networks and networks formed by physical interactions.
Chemical hydrogels are formed by irreversible covalent links, as in covalently crosslinked chitosan hydrogels.Formation ofchitosan hydrogels by polyelectrolyte complexation is an alternative to covalently crosslinked hydrogels. On the other hand, chitosan shows the ability to form biocompatible gels that can be applied directly on the injuries and for that reason this polymer becomes with enormous potential in the biomedical field.
In this study chitosan gels of low molecular weight (Mw=72.180 g/mol) with 92% degree of deacetylation and medium molecular weight (Mw=103.200 g/mol)with 97% degree of deacetylation, both with a 4% w/w concentration and characterized by several methods .
The information obtained from the gels characterization will be fundamental for the formulation of this semisolids of topic use in the treatment of cutaneous injuries of different ethiologies.
Synthesis of chitosan pharmaceutical degree.
The chitosan pharmaceutical degree was obtained from the shrimp shells from usinga chemical method in a pilot plant fromQuitoquimica Ltda. (19,20).
Preparation of Chitosan Gels.
Chitosan gels at 4% w/w of low molecular weight (Mw=72.180 g/mol)with a 92% degree of deacetylation and medium molecular weight (Mw=103.200 g/mol) with a 97% degree of deacetylation (2). The chitosan powderwas solution dispersed in lactic acidsolutionat 3.2%, and heatedat 85ºC with stirring for 24 h until complete solution. The gels was neutralizedwith NaOH 1Mup to pH= 5 and later on filtered .
The gel chitosan composition were obtained by FT-IRNicoletMagna550. The gels werespreadbetween twoKBr windows.Thespectra was recorded with 64 accumulations.
Scanning Electron Microscopy.
The morphology of the gels was studiedby SEM using a JEOL Model JSM 6380. The samples were treated with gold sputteringto obtain a thickness of 150 A°.
The reological behavior of the chitosan gels was measuredin a rotation viscometer Haake Rotovisco a 500 head and the rotors MV-I and MV-II for both gels of different molecular weight, respectively. The temperature was keep constant at25±1°C.
RESULTS AND DISCUSSION.
In the FT-IR,some characteristic bandsof chitosan gels are shown1 in figure 1. The IR spectrum of both gels are quite similar (21,22).A nC-C band at 850-853 cm-1 is shown. The nC-H band at 2790-2881 cm-1 and the nC-H(CH2) at 2931-2933 cm-1. The amide band at 1316-1410 cm-1 is shown due to the low amount of chitin present. On the other hand, the bands corresponding to lactic acid are present in both formulations.The nC-H of the acid appears at 3564-3514 cm-1. The nC-O exhibit different absorptions at 1043 and 1021 cm-1 for low and medium molecular weight. The nC=O of the lactic acid at 1654 cm-1 with medium molecular weight gels is more intense.The nCH2 of the lactic acid appears at 1453 and 1449 cm-1, respectively.
The morphological study of the due shows the formation of a homogeneouschitosan films ( fig. 3 and 4) once the water has been evaporated from the gelsat 30°C. The surface are smooth and they look like a film on the surface, no difference between both.This characteristics is favored if the further application is for the cutaneous injuries protecting from contaminant agent and avoiding the loss of body fluids.
As we can see in figures 5 and 6, both gels show a non newtonian behaviour, independent of the time,in fact, their viscosity thus not remain constant but changes with the speed velocity applied.The chitosan gel of low MW show a seudoplastic flow which is characteristicof dispersed system of polymeric type.When a force is applied over the system, which is characteristic of dispersedpolymeric systems.When a force is applied over the system, the chitosan chains are forming an structure in the aqueous media can separate and aligned in the flow direction, decreasing their viscosity with the increase of displacement.On the other hand, the chitosan gel of medium MW exhibit a plastic flow with a yield value of 20 equivalent to 710 dyn/cm2.
The gel formulation of semisolid of topic application will be necessary to incorporate inthe formulation some additive to increase the viscosity and produces some degree of tixotropy to the mixture.In practical terms that means to obtain an easy extraction of the flask when decreases the viscosity of the preparation, besides remains in the same place of application without flow because increases their viscosity when the product remains quite?.
1. The gels of medium and low molecular weight chitosan do not exhibit a great show difference in their IR spectrum, only the intensity and shift of some bands was observed. This indicate no difference in their composition.
2. The capacity of the gels to formadhesive and flexible films after their application at 37°C will be very useful for topic preparations.
3.In order to formulate this gels as semisolid systems for topic application would be recommendable to incorporate some agent that increase the viscosity in the formulation and give tixotropy to the preparation.When the viscosity of the preparation decreases by stirring and in that way facilitates the extraction of the pot andbesides remains stable with the increase of the viscosity when remains quite.
This work was supported by Research Project DIUC 204.074.036-1.0 (Marcos Fernández), Universidad de Concepción, Chile, and Project INNOVA BIO-BIO 03-B1-212-L1 (Galo Cárdenas). It is also part of the Master Thesis on Pharmaceutical Sciences of Marcos Fernández E.
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