Control of Bioprecipitated Ceramic Morphology and Thickness Through Nucleating Sequence Repetition

Metal oxide-based ceramics have a multitude of applications in material engineering, from military vehicle coatings and textile finishes to nonstick cookware. Over the past decades, specialized bioceramic peptides have been used to adhere nano surface ceramics to textile and material substrates as an alternative to traditional adhesive/binder and microparticle systems. These bioceramic peptides bind to the material substrate on one terminal end and precipitate metal oxides with the other, creating a ceramic that is tethered to the base material surface with a single process. Typically, the engineering and production of ceramics for functional coatings uses hazardous materials, resulting in high costs, and requires adhesive for application of pre-formed particles that may change the physical properties of materials - especially textile hand, breathability, and flexibility. By using biosynthesis to fabricate bioceramic peptides, we are able to provide a new system that both binds and precipitates ceramic finishes using techniques that are cheap, fast, effective, and environmentally friendly.<br/>Bioceramic peptides contain a material binding region made up of 7 to15 amino acids that can be tailored to a variety of materials and metals. Binding sequences for chitin, cellulose, polyethylene, and nylon were fabricated, with ceramic nucleating sequences including alumina, zinc, titania, silver, and zirconia. Pichia pastoris is a popular choice to use in biological production systems for its robust protein processing, folding, and modification abilities. One advantage of using P. pastoris as a biosynthesizer is that it allows bioceramic peptides to be produced with multiple nucleating sequences that cannot be made synthetically. Using the P. pastoris system, bioceramic peptide with up to 32 ceramic nucleating sites were synthesized. These peptides would allow for a thicker and more durable ceramic layer to precipitate compared to a single nucleating site produced through traditional synthesis.<br/>To produce the bioceramic peptides, amino acid sequences were translated to a DNA sequence and inserted into a P. pastoris plasmid. Plasmids were transformed using heat shock methods into cultured, competent Escherichia coli and P. pastoris cells. E. coli was used as a vector to replicate more plasmids while P. pastoris produced the peptide. SEM, XPS, and microscopy were used to analyze ceramic layers precipitated after binding the material substrates. After adjusting for concentration and purity, the bioceramic peptides were able to precipitate a uniform ceramic on multiple surfaces with thickness controlled by number of nucleating sites, with peptide length confirmed through gel electrophoresis.<br/>The successful fabrication and application of these bioceramic peptides provides a new technique for precipitating surface transition metals onto materials, with potential to be a universal platform system that tailors peptides for a library of substrate materials and metal oxide ceramics. Applications such as water repellency, fire retardation, and cut/slash protection that use ceramic coatings or finishes will benefit from the lower cost, material flexibility, and environmentally friendly practices. Additionally, the combination of centralized peptide production and surface metal precipitation results in a streamlined<br/>process that can be completed in a single lab or easily transition to an industrial production line.