US 9,932,443 B2  8  7  ferent chains 100 units long-smaller than the average  peptide in any cell. The age of the universe, by contrast, is  only 10$^{18 }$seconds old, and the total number of protons is  about 10 80 . This is sufficient proof that only a very tiny  fraction of possible sequences has been studied. All peptide  and protein research to date, therefore, though informative,  has but scratched the surface of what can be known about  peptides for materials.  Polypeptides are useful in strong, lightweight, functional  and elastic materials. Examples of natural polypeptides  include spider silk and muscle proteins. Embodiments of the  subject invention can improve on such natural polypeptides  in certain respects. Textiles, medical materials and dispos› able materials are included in areas of application for  peptide materials. These materials can provide superior  performance with regard to elasticity, energy conversion  efficiency, strength per unit mass, biodegradability and for› eign body tissue reactions. In addition, compared to syn› thetic polymers, polypeptides-especially designed pep- tides----can be made sustainably. This is a feature that can be  particularly useful in the field of advanced manufacturing.  In an embodiment, the subject invention provides manu› facturing instructions regarding amino acid composition,  degree of polymerization (DP) and solution conditions,  which determine polymer structure and interactions. In some  embodiments, the polypeptide processing is performed at  ambient temperature under mild solution conditions, and the  materials are biodegradable.  In some embodiments, peptide polymers are water soluble  and the amount of organic solvent needed in materials  manufacturing is reduced or eliminated. In further embodi› ments, the random polypeptides are soluble in water and/or  ethanol before crosslinking but insoluble in water after  crosslinking.  Additional aspects relate to the use of peptides with  random amino acid sequences for materials fabrication. The  randonmess embodied in the subject invention provides the  ability to simultaneously make the synthetic peptides less  like native globular proteins and more like the usual syn› thetic polymers in materials manufacturing and key regions  of elastomeric proteins, such as for example, ti tin and resilin.  In one aspect, the present invention provides a peptide› based material comprising cross-linked peptides with ran- dom amino acid sequences that are soluble in water or  ethanol before crosslinking but insoluble in water after  crosslinking. In one embodiment, the random amino acid  sequences are fused with one or more elastin-like peptide  (ELP). The peptide-based material may further comprise  synthetic organic polymers. In some embodiments, the  cross-linked peptides utilized in the peptide-based materials  of the invention are synthesized by ring-opening polymer› ization.  In some embodiments, the peptide-based material can be  either a one-dimensional, two-dimensional, or three-dimen› sional material. Such one-dimensional materials are fiber  materials, such as, but not limited to, anti-microbial fiber  materials. Two-dimensional materials are film materials,  such as, but not limited to, medical device coating films.  Three-dimensional materials are molded materials.  In one embodiment, the polypeptides of the subject inven› tion form entropic networks. The skilled artisan can appre› ciate that the materials of the subject invention, although  random peptides, are nevertheless at least potentially  hybrids of structure and function, not just one or the other.  In yet other embodiments, the subject invention relates to  the use of a visible-range dye to quantify the efficiency of  peptide crosslinking, wherein the decrease of dye absor› bance is a measure of the increased concentration of cross› linked polymers.  In other embodiments, the subject invention relates to the  visualization of electrospun fibers by fluorescent micros› copy.  In some embodiments, the subject invention relates to the  use of circular dichroism (CD) spectroscopy to analyze  structural properties of peptides during multilayer film  buildup.  In additional embodiments, the subject invention provides  an algorithm that relates elasticity and other aspects of  materials processing to amino acid composition, degree of  polymerization, pH, hydration and ionic strength.  In some embodiments, the subject invention provides cast  films, molded materials and foams. In further embodiments,  the cast films and molded materials are made water-in› soluble by cross-linking.  In additional embodiments, the subject invention provides  elastin-like peptides (ELPs) [(VPGVG)n] ([(SEQ ID NO:1)  n]). In further embodiments, the ELPs are spinnable from  water. The subject invention further provides peptides of a  mole fraction of glutamic acid of 0.8-1.0, which corresponds  to a maximum absolute value of average charge density for  electro spinning from aqueous solution at pH 7.  In some embodiments, the subject invention provides  electro spun fibers,  including Poly(L-omithine) (PLO),  PLEY, PLL and Poly(L-glutamic acid) (PGLA).  In other embodiments, the subject invention provides a  solution-phase approach for random peptide production. The  peptide polymers of the subject invention are polydisperse  and have a low predicted crystallinity.  In some embodiments, the subject invention provides a  blend of different recombinant random sequences useful for  material properties. In specific embodiments, the peptides  are produced at high yield in photosynthetic bacteria.  In some embodiments, the subject invention provides  control of polydispersity by reaction conditions and frac- tionation.  The subject invention is especially advantageous if  monodisperse polymers and sequence  specificity are  optional and amino acid composition, predictability of water  solubility, measurability of number-average mass and  weight-average molecular mass, and therefore polydisper- sity index, and reproducibility of polymer production mate› rials processing are desired.  In some embodiments, the subject invention provides a  method for synthesizing statistical, linear peptides in solu› tion based on ring-opening polymerization of a-amino acid  N-carboxyanhydrides, wherein growth occurs only by the  probabilistic addition of monomers to active chain ends. In  further embodiments, monomers are present throughout the  process and polymer mass and yield are functions of mecha› nism and reaction particulars. In some embodiments, the  product has a Poisson distribution of chain lengths,  (Ne/Nrexp(-N), where N is DP and N is number-average  DP, and N can range from 2 to >2,000. In some embodi› ments, short-range order is possible, long-range order is  improbable and the synthesis from a heterogeneous mono› mer population is expected to yield chains of virtually  identical amino acid composition.  In some embodiments, the subject invention provides  fusion peptides consisting of structural parts based on the  present invention and functional parts based on biochemical  research. 