Characterization of Thin Polymer Layer Prepared from Liposomes and Polyelectrolytes for TGF-β Release in Tissue Engineering.

Implant-integrated drug delivery systems that enable the release of biologically active factors can be part of an in situ tissue engineering approach to restore biological function. Implants can be functionalized with drug-loaded nanoparticles through a layer-by-layer assembly. Such coatings can release biologically active levels of growth factors. Sustained release is desired for many in vivo applications. The layer-by-layer technique also allows for the addition of extra layers, which can serve as "barriers" to delay the release. Electrospun Polycaprolactone (PCL) fiber mats are modified with a Chitosan (CS) grafted with PCL sidechains (CS-g-PCL) and coated with transforming growth factor beta 3 (TGF-β) loaded Chitosan/tripolyphosphate nanoparticles as a drug delivery system. Additional layers including polystyrene sulfonate, alginate, carboxymethyl cellulose, and liposomes (phosphatidylcholine) are applied. Streaming potential and X-ray photoelectron spectroscopy (XPS) measurements indicated a strong interpenetration of the chitosan and polyanion layers, while liposomes formed separate layers, which are more promising for sustained release. All samples release TGF-β at different cumulative levels without altering release kinetics. Variations in layer structure, interpenetration, and stability depending on the chitosan used are observed, which ultimately has minimal impact on the release kinetics. Polyelectrolyte layers strongly interpenetrated the active layers and therefore do not act as effective diffusion barriers, while the liposome layer, though separated, lacked sufficient stability.