Coatings from Polyelectrolytes: Fundamentals of Buildup and Control over Mechanical Properties for Bioapplications

• Other Authors: Lehaf, Ali (authoraut)
• Format: Others
• Language: English; English
• Published: Florida State University
• Subjects: Chemistry; Biochemistry
• Online Access: http://purl.flvc.org/fsu/fd/FSU_migr_etd-6954

Controlling cell fate via mechanical properties of the culture substrates provides an important tool for biomedical applications. Thin films of polyelectrolyte multilayers (PEMUs) have been used as substrates for cell culture due to their biocompatibility. Photocrosslinkable polyelectrolyte multilayers were prepared from poly(acrylic acid) grafted with photosensitive benzophenone (PAABp) as the polyanion and poly(allylamine hydrochloride) (PAH) as the polycation. Young's modulus measured by force spectroscopy using nano-indentation showed smooth controlled increase after irradiation with UV light. The permeability of PEMUs for iodide ions, measured with a rotating disc electrode, decreased significantly. The surface wettability and charge density were not affected by irradiation, suggesting that surface chemistry and charge remained essentially unaltered. This provides substrate material for cell culture applications where the only variable is the mechanical stiffness. Since photocrosslinking provided control over the region of crosslinking, photomasks were used to prepare substrates with gradient elasticity. The behavior of rat aortic smooth muscle cells (A7r5) and osteosarcoma (U2OS) was followed on uniform substrates of increasing stiffness and on substrates with gradient elasticity. A7r5 cells detected the elasticity gradient and those that were on the soft side could polarize and orient towards the stiff side, where they showed better adhesion. U2OS cells also showed preference to the stiff side; however U2OS cells that were on the soft side did not adhere and underwent apoptosis. Nano-indentation was used to study some important fundamental properties of polyelectrolyte multilayer from poly(diallyldimethylammounium chloride) PDADMAC as the polycation and sodium poly(styrene sulfonate) (NaPSS) as the polyanion, which allowed proposing mechanism for PEMU build-up. The degree of swelling varied depending on the type of polyelectrolyte on the surface, with PDADMA-ending films more swollen than PSS ending films. This observation correlated well with the change in modulus. This suggested that PDADMA-ending films are extrinsically compensated while PSS-ending films are more intrinsically compensated. Also using nano-indentation, we demonstrated that the surface features and roughness of polyelectrolyte multilayers were not due to phase separation. Using nano-indentation, we demonstrated the role of water in controlling the mechanical properties of PEMUs. Previously, it was shown that salt plasticizes PEMUs and they were termed "saloplastics". A complimentary study was done to investigate the plasticizing effect of water. We used osmotic stress to control the amount of water in the films without affecting the degree of ionic crosslinks. Poly(ethylene glycol) (PEG) was used as the osmotic stressor. We showed that water increases free volume between the polyelectrolyte chains and acted as lubricant and the elastic modulus increases with decreasing water content. Water was also found to contribute to the viscoelastic properties of the polyelectrolyte multilayer, suggesting that water acts in plasticizing polyelectrolyte multilayers. === A Dissertation submitted to the Department of Chemistry and Biochemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy. === Fall Semester, 2012. === October 31, 2012. === cell adhesion, modulus, multilayer, nanoindentations, plasticizer, polyelecrolytes === Includes bibliographical references. === Joseph B. Schlenoff, Professor Directing Dissertation; Teng Ma, University Representative; Igor Alabugin, Committee Member; Mike Roper, Committee Member; Alan Marshall, Committee Member.