Rapid prototyping of chitosan-coated alginate scaffolds through the use of a 3D fiber deposition technique.

Three dimensional, periodic scaffolds of chitosan-coated alginate are fabricated in a layer-by-layer fashion by rapid prototyping. A novel dispensing system based on two coaxial needles delivers simultaneously alginate and calcium chloride solutions permitting the direct deposition of alginate fibers according to any designed pattern. Coating of the alginate fiber with chitosan and subsequent cross-linking with EDC and genipin assured the endurance of the scaffold in the culture environment for a prolonged period of time. The cross-linking protocol adopted imparted to the scaffold a hierarchical chemical structure as evidenced by Confocal Laser Microscopy and FTIR spectroscopy. The core of the fibers making up the scaffold is represented by alginate chains cross-linked by ester bonds only, the periphery of the fiber is constituted by an inter-polyelectrolyte complex of alginate and chitosan cross-linked in all pair combinations. Fibers belonging to adjacent layers are glued together by the chitosan coating. Mechanical behavior of the scaffolds characterized by different layouts of deposition was determined revealing anisotropic properties. The biocompatibility and capability of the scaffolds to sustain hepatocyte (HepaRG) cultures were demonstrated. Typical hepatic functions such as albumin and urea secretion and induction of CYP3A4 enzyme activity following drug administration were excellent, thus proving the potential of these constructs in monitoring the liver specific function.

Chitosan nanogels by template chemical cross-linking in polyion complex micelle nanoreactors.

Chitosan covalent nanogels cross-linked with genipin were prepared by template chemical cross-linking of chitosan in polyion complex micelle (PIC) nanoreactors. By using this method, we were able to prepare chitosan nanogels using only biocompatible materials without organic solvents. PIC were prepared by interaction between chitosan (X(n) = 23, 44, and 130) and block copolymer poly(ethylene oxide)-block-poly[sodium 2-(acrylamido)-2-methylpropanesulfonate] (PEO-b-PAMPS) synthesized by single-electron transfer-living radical polymerization (SET-LRP). PIC with small size (diameter about 50 nm) and low polydispersity were obtained up to 5 mg/mL. After cross-linking of chitosan with genipin, the nanoreactors were dissociated by adding NaCl. The dissociation of the nanoreactors and the formation of the nanogels were confirmed by (1)H NMR, DLS, and TEM. The size of the smallest nanogels was about 50 nm in the swollen state and 20 nm in the dry state. The amount of genipin used during reticulation was an important parameter to modulate the size of the nanogels in solution.