title: Silk macromolecules with amino acid-poly(ethylene glycol) grafts for controlling layer-by-layer encapsulation and aggregation of recombinant bacterial cells.
abstract: This study introduces double-brush designs of functionalized silk polyelectrolytes based upon regenerated silk fibroin (SF), which is modified with poly-L-lysine (SF-PLL), poly-L-glutamic acid (SF-PGA), and poly(ethylene glycol) (PEG) side chains with different grafting architecture and variable amino acid-PEG graft composition for cell encapsulation. The molecular weight of poly amino acids (length of side chains), molecular weight and degree of PEG grafting (D) were varied in order to assess the formation of cytocompatible and robust layer-by-layer (LbL) shells on two types of bacterial cells (Gram-negative and Gram-positive bacteria). We observed that shells assembled with charged polycationic amino acids adversely effected the properties of microbial cells while promoting the formation of large cell aggregates. In contrast, hydrogen-bonded shells with high PEG grafting density were the most cytocompatible, while promoting formation of stable colloidal suspensions of individual cell encapsulates. The stability to degradation of silk shells (under standard cell incubation procedure) was related to the intrinsic properties of thermodynamic bonding forces, with shells based on electrostatic interactions having stronger resistance to deterioration compared to pure hydrogen-bonded silk shells. By optimizing the charge density of silk polyelectrolytes brushes, as well as the length and the degree of PEG side grafts, robust and cytocompatible cell coatings were engineered that can control aggregation of cells for biosensor devices and other potential biomedical applications.
authors.affiliation: School of Materials Science and Engineering, Georgia Institute of Technology , Atlanta, Georgia 30332, United States.
authors.forename: Irina
authors.initials: I
authors.lastname: Drachuk
authors.forename: Rossella
authors.initials: R
authors.lastname: Calabrese
authors.forename: Svetlana
authors.initials: S
authors.lastname: Harbaugh
authors.forename: Nancy
authors.initials: N
authors.lastname: Kelley-Loughnane
authors.forename: David L
authors.initials: DL
authors.lastname: Kaplan
authors.forename: Morley
authors.initials: M
authors.lastname: Stone
authors.forename: Vladimir V
authors.initials: VV
authors.lastname: Tsukruk
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D001412:Bacillus subtilis / Q000166:cytology* / Q000187:drug effects / Q000235:genetics; D015374:Biosensing Techniques; D002214:Capsules; D004274:DNA, Recombinant / Q000235:genetics*; D004926:Escherichia coli / Q000166:cytology* / Q000187:drug effects / Q000235:genetics; D005349:Fibroins / Q000737:chemistry* / Q000494:pharmacology*; D011092:Polyethylene Glycols / Q000737:chemistry*; D058928:Riboswitch / Q000235:genetics
chemical_list: D000596:Amino Acids; D002214:Capsules; D004274:DNA, Recombinant; D058928:Riboswitch; D011092:Polyethylene Glycols; D005349:Fibroins
keywords: bacterial cells; brush silk polyelectrolytes; hydrogen bonded shells; layer-by-layer (LbL) assembly