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Technical Article


MULTIFUNCTIONAL BIO-HYBRID NANOCOMPOSITES USING GENETICALLY ENGINEERED SILK/ELASTIN COPOLYMERS

The development of genetically engineered protein-based polymers, or recombinant protein-based polymers (rPBPs), is an emerging field of research that have been the focus of great interest due to the absolute control over chain length and composition, which are key attributes for the design of advanced polymeric materials. As a protein is defined by a DNA sequence, recombinant technology allows the design and biosynthesis of complex molecules with a precise control over its composition, and a production not dependent on natural or oil based resources (achieved using microbial cell factories). This clearly highlights the potential of recombinant protein polymers as central players to revolutionize the use of polymers in materials science.

 

Silk-elastin-like proteins (SELPs) are a class of genetically engineered protein polymers tailored to combine in the same molecule the structural components of silk fibroin and mammalian elastin (Machado, 2013). Due to its versatility of processing, biodegradability and biocompatibility, SELPs have been fabricated into different structures such as fibres and films, demonstrating unique properties (Machado, 2015). The formulation of composites comprising active nanofillers and recombinant protein-based polymers further expands the potential range of applications, opening new perspectives and paving the way for a new generation of multifunctional biocomposites. Here, physically active bio-hybrid nanobiocomposites displaying magnetic and piezoresistive properties were obtained through incorporation of cobalt ferrite nanoparticles (Fernandes, 2018) and carbon nanotubes into the SELP matrix (Correia, 2019). For nanocomposite formulation, pure lyophilized SELP was dissolved in formic acid followed by addition of cobalt ferrite nanoparticles (CFO NPs) or carbon nanotubes (CNTs) at different concentrations. Free standing films were obtained by solvent casting and stabilized by exposure to methanol.

 

Analysis by scanning electron microscopy demonstrates an overall homogenous distribution of nanofiller into the polymer matrix (Figure 1). The produced SELP/CFO composites demonstrated a magnetic response proportional to the filler content (Figure. 2A), demonstrating a high yield of NP incorporation into the films and the possibility of using these nanocomposites as magnetically responsive materials suitable for a wide range of applications, from sensors to tissue engineering. The incorporation of CNTs (1 wt.%) demonstrated to greatly improve the mechanical properties of the SELP matrix leading to a 6-fold increase in strain-to-failure and to increase the ultimate tensile strength with minor differences in modulus of elasticity (Fig. 2B). The samples were characterized by a linear piezoelectric behavior indicating that the electrical resistance follows a direct correlation with the mechanical deformation, increasing linearly upon tensile loading and decreasing linearly upon unloading (Fig. 2C). These results pave the way for the development of a new generation of multifunctional bioinspired materials, opening new perspectives in the future engineering of advanced functional biocomposites.

 

ACKNOWLEDGMENTS

This work was supported by the strategic programme UID/BIA/04050/2019 funded by national funds through FCT I.P. (Fundação para a Ciência e Tecnologia, Portugal) and EcoAgriFood [NORTE-01-0145-FEDER-000009], supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (ERDF). The present work was also supported by FCT I.P. within the ERA-NET IB-2 project FunBioPlas (ERA-IB-2-6/0004/2014). The authors acknowledge funding from FCT I.P. under grants SFRH/BPD/121526/2016, SFRH/BD/111478/2015, and SFRH/BPD/90870/2012.

 

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