Protein-based materials polymers

Kiick KL (2007) Biosynthetic methods for the production of advanced protein-based materials. Polym Rev 47 1-7... 

To extend the application area of silk proteins-based materials, blending the fibroin with other natural macromolecules and synthetic polymers, or even manufacturing composites with silk fibers are a few of the possible strategies. 

Finally, for medical applications, the extraordinary biocompatibility of these elastic protein-based materials, we believe, arises from the specific means whereby these elastic protein-based polymers exhibit their motion. Being composed of repeating peptide sequences that order into regular, nonrandom, dynamic structures, these elastic protein-based polymers exhibit mechanical resonances that present barriers to the approach of antibodies as required to be identified as foreign. In addition, we also believe that these mechanical resonances result in extraordinary absorption properties in the acoustic frequency range. 

Protein-based polymers have the potential to surpass the polyesters and other polymers because they can be directly produced in microorganisms and plants by recombinant DNA technology resulting in the capacity for diverse and precisely controlled composition and sequence. This is not possible with any other polymer, and it increases range of properties and the numbers of applications. Remarkably, with the proper design of composition, protein-based materials can be thermoplastics, melting at temperatures as much as 100°C below their decomposition temperatures. Therefore, they can be molded, extruded, or drawn into shapes as desired. Aspects of protein-based materials as plastics is also considered below. 

There is analogy in the development of protein-based materials. Bioelastics, Inc., the general partner to Bioelastics Research Ltd. (BRL), has been working for about 15 years to arrive at a killer app that could launch the protein-based material industry. More specifically, BRL has been developing the scientific and intellectual property foundation that would pave the way for the extraordinary materials capacity of protein-based polymers to result in successful commercial applications. 

The initial preparation of protein-based polymers utilized solution and solid phase peptide chemistry. This made possible the preparation of more than 1,000 polymer compositions. As discussed in Chapter 5, these compositions were studied for determination of their basic properties, for the development of the set of phenomenological axioms for protein engineering and function, and for the demonstration of the basic mechanism that underlies function. In short, it is the chemical synthesis that has allowed development of much of the basic science and the demonstration of the potential of protein-based materials in a timely manner. Mostly because of the historical relevance, but also because of the unique contributions of chemical synthesis to arriving at satisfactory purification of microbially prepared protein-based polymers, a brief description of the chemical synthesis of protein-based polymers is given below. 

As stated in Chapter 9, The consilient approach to tissue engineering utilizes biology s own materials and mechanisms, concerned with tissue structure and function, to achieve tissue restoration. The key materials elements are three the capacity of the elastic protein-based material to match the elastic modulus of the tissue to be restored, a remarkable biocompatibility of the pure elastic protein-based material, and the facility to design into the protein-based polymer sequence any desired biologically active sequence, which, by virtue of the innocuousness of the elastic protein-based material, allows proper expression of the incorporated biologically active sequence. This provides the opportunity for the proper functional relationship of protein-based material to the cells and the extracellular matrix of the tissue to be restored. 

Ferrari, F.A. and Cappello, J. (1997) Biosynthesis of Protein Polymers in Protein-Based Materials, Biorkauser, Boston. 

ProLastin polymers are a family of protein-based materials w hose resorption rate in vivo can be controlled by adjusting the sequence and not just the composition of the polymer (Cappello et al, 1995). These adjustments can be made so as to cause little change in the formulation characteristics of the materials, their physical forms, or their mechanical properties. They have good mechanical integrity with no need for chemical crosslinking. They degrade by enzymatic proteolysis and are presumed to resorb by surface erosion. Their breakdowm products are peptides or amino acids w hich are electroneutral at physiological pH and cause no undue inflammation or tissue response. 

In recent years, soy products such as soy whole flour (SF), soy protein concentrate (SPC), and soy protein isolate (SPI) have been considered as alternatives to petroleum polymers because of their abundance, low cost, perfect adhesion, and good biodegradability (Maruthi et al. 2014). SF contains about 40-60 % protein, combined with fats and carbohydrates. Soy protein concentrate contains about 60-70 % protein. SPI contains more than 90 % of protein and is the most widely used soybean product for film processing (Ciannamea et al. 2014). Moreover, SPI-based films are clearer, smoother, and more flexible compared to other plant protein-based films, and they have impressive gas barrier properties compared to those prepared from lipids and polysaccharides. When SPI films are not moist, their O2 permeability was 500, 260, 540, and 670 times lower than that of films based on low-density polyethylene, methylceUulose, starch, and pectin, respectively (Song et al. 2011). Thus, in addition to their large availability, soy protein-based materials have interesting barrier and release properties ideal for packaging applications. 

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