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Conductive biocomposite with potential for medical applications


The main objective of tissue engineering is to obtain materials similar to those found in the human body, and to use them to improve health and extend quality of life. In the case of cardiac applications, a material with similar properties to myocardial tissue, like elasticity, tenacity and conductivity, could be an aid in medical intervention to remedy heart conditions. It can help to regenerate tissues by providing a site for cell growth and also offer protection to injured muscle tissue. Many biomaterials have been developed in the last decades, including poly (glycerol sebacate) (PGS). This biodegradable polyester is prepared by polycondensation of sebacic acid and glycerol, both obtained from castor oil. PGS exhibits good cell and tissue compatibility, and can be used in many biomedical applications, like heart patches, nerve guides, retinal transplantation, and cartilages. In the same way, PPy is a biocompatible and electrically conductive polymer, even in small amounts. Medical applications of PPy have been studied with success over the years.

Objetivos - Metodologia - Resultados - Discussão dos Resultados/Objectives - Methodology - Results - Discussion of Results/Objetivos - Metodología - Resultados - Discusión de los resultados

We hypothesized that PGS and PPy polymers, together in a conductive polymer biocomposite, can achieve similar mechanical and electrical properties to the myocardial tissue, with the goal of developing a material which could be used as a heart patch.
An electrically conductive composite of poly(glycerol sebacate) (PGS) and polypyrrole (PPy) was prepared by solvent free synthesis. The PGS matrix was obtained with a 1:1 proportion of sebacic acid and glycerol. The PPy was prepared by chemical synthesis, using iron chloride as oxidant, and purified in water. Films containing 1, 3 and 5% PPy were prepared by adding the conductive polymer, as a finely dispersed powder, into the PGS pre-polymer matrix. The composites were crosslinked in a vacuum oven, for 48 h at 130 °C. The films were characterized by dynamic mechanical analysis and electrical conductivity tests.
In order to be used as a cardiac patch, a candidate material must present similar mechanical properties to those of myocardial tissue, in terms of elongation and stiffness. The Young’s modulus of a human heart muscle ranges between 0.02 – 0.5MPa. Under normal conditions, the maximum strain of dynamic loading required by soft tissue such as cardiac muscle is typically around 15%.
Tensile tests are performed in PGS and PGS/PPy composites, indicating that the matrix behaved as an elastomer at room temperature. The PGS control had a Young’s modulus of 0.15 MPa and elongation at break of 126%. With 3% of PPy in the composite, the Young’s modulus was 0.26 MPa and elongation at break was 25%. With 5% the Young’s modulus was three times that of the PGS control, but the elongation at break decrease to 13%. The PPy acted as a filler in the composite, thereby increasing the Young’s modulus, achieving mechanical characteristics similar of heart muscle.
The electrical conductivity of the composite films was 5x10-5 S/cm. That value is in the range of the electrical conductivity of myocardial tissue, of 1.6x10-3 S/cm (longitudinally) and 5x10-5 S/cm (transversally), indicating that the conductivity of the composites is similar to that of myocardial tissue.

Considerações Finais/Final considerations/Consideraciones finales

As both PGS and PPy are good candidates for biomedical applications, and the findings are in agreement with the mechanical and electrical characteristics of myocardial tissue, this novel biocomposite could potentially be used in heart reparation treatment.

Palavras-chave/Key words/Palabras clave

biocomposite; electrical conductivity, cardiac patch