(10f) Biocompatible Detachable Polyelectrolyte Multilayer Films for Applications in Tissue Engineering

We report the design and assembly of novel, detachable, free-standing polyelectrolyte multilayer (PEM) films. PEMs have been used to design anti-bacterial coatings, non-cytotoxic surfaces, and to assemble three dimensional cellular architectures. The majority of reports in the literature are studies on PEMs deposited and adherent on a solid substrate. By modulating the deposition properties of the PE and through deposition on an inert, hydrophobic substrate, we have assembled detachable PEMs for applications in tissue engineering and drug delivery. The sequential adsorption of alternately charged polyelectrolytes (PEs) using layer by layer deposition provides a unique approach to tailor the properties of PEMs. The properties of the PEM can be varied by changing variables such as pH, ionic strength and deposition conditions. Hyaluronic acid (HA) and chitosan are biocompatible polyelectrolytes. Chitosan an anionic PE and HA a cationic PE were used to assemble the PEM.

We have assembled PEMs on inert hydrophobic substrates such as polypropylene or polytetrafluoroethylene substrates with water contact angles of 102.31 ± 2.81° and 109.64 ± 1.59°, respectively. A typical PEM consists of 30-50 bilayers of HA and chitosan. To achieve detachability, PE deposition time and concentration were varied. After PEM assembly, the films were detached from the solid substrate and subsequently cross-linked to enhance stability. Crosslinked films placed in a phosphate buffered solution at 37°C, exhibited 6-8% weight loss over a 7-day period.

The optical properties of the films were investigated using a spectrophotometer. Dry PEMs were translucent and transmitted 50 to 60% of light in the visible light range (400 to 900 nm). Hydrated films transmitted 90 to 97% of light, making these films good candidates for applications requiring optical microscopy. Surface topography was investigated using atomic force microscopy (AFM) and our results indicate that the films are smooth and exhibit surface features ranging from 10-30nm. The Young's modulus of the uncrosslinked and crosslinked PEMs was measured for crosslinked and unmodified films using an nanoindentation method.

Our current studies are focused upon conducting cell-based studies and using x-ray photoelectron spectroscopy to measure the surface chemical composition of the PEMs. In the future, the detachable PEMs will be used as scaffolds in liver tissue engineering.