The use of biocompatible and biodegradable materials as implants is a promising approach to temporarily replace endogenous functions and replace tissue during a healing process. Electrospun fiber mats can be used in the field of tissue engineering (TE) and to engineer tendon/ligament-to-bone interfaces, showing high surface to volume ratio and a good roughness, which is promising for initial cell attachment and growth. Using Polycaprolactone (PCL) as a basic material for implants is favorable because of its good mechanical properties and its slow degradation. However, due to its hydrophobic characteristics PCL is an unfavorable material for cell attachment and growth. Multiple approaches have been made to improve the cellular behavior such as plasma treatment or chemical modification. Another approach uses a “shish-kebab” coating of the electrospun fibers. Chitosan (CS)-PCL graft copolymers (CS-g-PCL) can spontaneously crystallize as kebabs on PCL nanofibers which act as shishes.
The graft-polymerization to synthesize CS-g-PCL copolymer is easy to perform and can be nicely controlled. Specific graft lengths and ratios for the PCL side-arms are accessible. The “shish-kebab” coating of CS-g-PCL onto electrospun PCL fibers is a fast and scalable approach to create fibermats more attractive for human cells. Additionally using CS-g-PCL for PCL surface modification creates surface charges on the fibers due to the presence of amino groups. This allows the attachment of nanoparticle drug-release systems using electrostatic interactions in an easy and scalable process.
The organic nanoparticles (chitosan-tripolyphosphate-, alginate-poly-L-lysin) do not form stable and clearly distinguishable particles when adsorbed onto the fiber surface, however, they seem to form a film as it already has been described previously. This makes it difficult to proof the coating via REM. However, using fluorescently labeled nanoparticles and CLSM hollow structures can be established indicting, that only the surface of the modified PCL nanofibers is coated with the labeled drug-release systems. The inorganic nanoparticles (silica-system) can be clearly identified using REM and CLSM. They are well distributed among the whole sample surface and show minor aggregation.