Blends of polyvinyl alcohol (PVA) and angico gum (AG) and/or cashew gum (CG) were used to produce films by casting method. Morphological and mechanical properties of these films were studied and compared to the properties of a commercial collagen membrane of bovine origin (MBO). The films presented thickness varying from 70 to 140
There has been an expanding search for new materials with high performance at affordable costs in recent years [
Polyvinyl alcohol (PVA) has excellent film-forming properties and has been frequently blended with synthetic and natural polymers due to its water-soluble, biodegradable, innocuous, noncarcinogenic, and biocompatible character [
In this scenario, blends of proteins or polysaccharides with polyvinyl alcohol (PVA) are promising biodegradable materials since the combination of these polymers may have beneficial effects on the characteristics of the blended material. However, the use of animal proteins in the formulation of biological membranes requires a highly purified material to avoid allergic reactions and increased inflammatory response. The laborious and time-consuming techniques of protein purification result in materials with a high cost.
On the other hand, polysaccharides have been explored as biomaterials, particularly when used as scaffolds for tissue regeneration and controlled drug releasing. Several plants produce gummous exudates mainly composed of high-molecular polysaccharides. Studies of several different gummous materials showed that they consist of complex branched polysaccharides with highly varied chemical and structural composition. Red angico (
In this research, biodegradable films were manufactured by blending cashew gum and/or angico gum with PVA. The blended films were characterized according to their morphology and mechanical properties. Additionally, in order to evaluate the potential of these blended films, their properties were compared with those presented by a commercially available biomembrane containing collagen (bovine origin).
Samples of the cashew exudates (nodules) (
The gum from cashew exudates was extracted according to the methodology described by Silva et al. [
The gums from angico exudates were milled, immersed in distilled water in a proportion of 20% (w/v), and kept at room temperature (25°C), for 24 hours. The solution was filtered to remove fragments of bark and then precipitated with absolute ethanol, in the proportion of 1 : 3 (v/v), for 24 hours. Alternatively, after filtration, the angico gum solution was acidified to pH 4.0 with acetic acid followed by precipitation with cold ethanol. The precipitated angico gum (AG or AGac) was separated by filtration, washed with ethanol, dried at room temperature (25°C), and stored at room temperature in hermetically closed vessels.
In order to obtain a film with mechanical properties similar to the commercial MBO, several formulations were tested using cashew gum (CG), angico gum (AG), or a mixture of cashew and angico gum.
The PVA/CG film was prepared by casting on the glass molds a solution containing a mixture of 7.5 mL of 3% (w/v) acidic PVA solution (pH 2.0), 7.5 mL of 3% (w/v) cashew gum aqueous solutions, 0.75 mL of 0.1 mol
The PVA/AG films were prepared by casting on the glass molds a solution containing a mixture of 7.5 mL of 3% (w/v) acidic PVA solution (pH 2.0), 7.5 mL of 3% (w/v) angico gum aqueous solutions, 0.75 mL of 0.1 mol
The PVA/CG-AG film was prepared by casting on the glass molds a solution containing a mixture of 7.5 mL of 3% (w/v) acidic PVA solution (pH 2.0), 3.25 mL of 3% (w/v) cashew gum aqueous solutions, 3.25 mL of 3% (w/v) angico gum aqueous solutions, 0.75 mL of 0.1 mol
The thickness of the blended films was determined using a manual micrometer (Mitutoyo, São Paulo, Brazil). Final thickness was determined by means of ten random determinations in all film area. The films were analyzed according to morphological overall characteristics such as color, transparency, and homogeneity.
Mechanical properties were determined in an Instron M3345 (Instron Co., Norwood, MA, USA), with a 50 N load cell equipped with tensile grips. Samples of the film were cut into strips of 10 mm wide and 30 mm long, according to the ASTM D-638M-93 standard [
Tensile strength (TS), percentage of elongation (
The modulus of elasticity (Young’s modulus) was determined according to the following equation:
All experiments were expressed as average
The PVA/CG films presented thickness values between 140 to 200
Macroscopic morphology of the films: (a) MBO; (b) PVA/CG film; (c) PVA/CG-AG film; (d) PVA/
Artificial membranes have focus of special attention owing to their potential application in the medical fields, such as drug delivery systems, artificial organs, and tissue engineering [
Mechanical properties of blended films.
Tensile strength | Elongation | Elastic modulus | |
---|---|---|---|
(kgf) | (%) | (kgf) | |
MBO | 193.61b | 2.94b | 6568.14b |
PVA/CG | 151.84b | 11.96a | 1305.25c |
PVA/CG-AG | 218.17b | 13.24a | 1800.85c |
PVA/ |
227.97b | 4.87b | 4773.82b |
PVA/AGHCl | 426.46a | 3.80b | 11590.02a |
PVA/AGac | 221.30b | 3.18b | 6972.95b |
a, b, and c: The results are the means of three determinations. Within columns, means with the same superscript letter are not significantly different (
The behavior of the films under tension test is depicted in Figure
Typical behavior of films under tension tests: (a) MBO; (b) PVA/CG film; (c) PVA/CG-AG film; (d) PVA/
Regarding PVA/AG (Figures
The films produced by blending PVA/CG-AG presented the best set of features regarding the properties of strength and flexibility (Figure
The different behavior observed for the blended films may be ascribed to the chemical structure of the polysaccharides. The property of starches to produce film is related to the relative amount of amylose and amylopectin present in the starch granule. The branching degree and the relative amount of amylopectin present in the starch granule will determine the elastic property of the produced film [
The mechanical characteristics of PVA blended films are shown in Table
The film that presented the higher TS was PVA/AGHCl with a value twofold higher than MBO. However, the value of
On the other hand, the PVA/CG film showed a remarkable percentage of elongation (
Regarding the elastic modulus (EM), three groups with distinct properties were observed: (i) PVA/AGHCl with the highest value of EM; (ii) MBO, PVA/
The results of the correlation analysis evidenced a positive relationship between TS and EM (
Graphic representation of Pearson’s correlation between (a) percentage of elongation (
Considering the macroscopic features and the mechanical properties of the blended films, the PVA/CG showed characteristics that enable this material to substitute the MBO with the advantage of higher
Although the films produced with angico gum presented inferior macroscopic characteristics, the PVA/AGHCl film showed remarkable mechanical properties such as the high values of TS and EM. In this sense, this material is also promising for biotechnological applications.
The films produced by blending PVA with AG and/or CG presented quite different macroscopic and mechanical properties. Among them, the PVA/CG film presented the macroscopic and mechanical properties similar to MBO film, with the advantage of a higher
The authors do not have any conflict of interests with the content of the paper.
F. E. F. Silva, M. C. B. Di-Medeiros, and K. A. Batista thank CAPES for the fellowship support.