Shin-Hee Jun

A bioactive coating of a silica xerogel/chitosan hybrid on titanium by a room temperature sol-gel process

A bioactive coating consisting of a silica xerogel/chitosan hybrid was applied to Ti at room temperature as a novel surface treatment for metallic implants. A crack-free thin layer (<2 microm) was coated on Ti with a chitosan content of >30 vol.% through a sol-gel process. The coating layer became more hydrophilic with increasing silica xerogel content, as assessed by contact angle measurement. The hybrid coatings afforded excellent bone bioactivity by inducing the rapid precipitation of apatite on their surface when immersed in a simulated body fluid (SBF). Osteoblastic cells cultured on the hybrid coatings were more viable than those on a pure chitosan coating. Furthermore, the alkaline phosphate activity of the cells was significantly higher on the hybrid coatings than on a pure chitosan coating, with the highest level being achieved on the hybrid coating containing 30% chitosan. These results indicate that silica xerogel/chitosan hybrids are potentially useful as room temperature bioactive coating materials on titanium-based medical implants.

Silica xerogel-chitosan nano-hybrids for use as drug eluting bone replacement.

Silica xerogel-chitosan hybrids containing vancomycin were fabricated by the sol–gel process at room temperature and their potential as a drug eluting bone replacement was evaluated in terms of their mechanical properties and drug release behaviors. Regardless of the content of chitosan, all of the prepared hybrids had a uniform mesoporous structure, which would allow the effectual loading of vancomycin. As the content of chitosan was increased, the strength, strain to failure, and work of fracture of the hybrids were significantly enhanced, while the elastic modulus was decreased. These changes in the mechanical properties were mainly attributed to the mitigation of the brittleness of the silica xerogel through its hybridization with the flexible chitosan phase. In addition, the initial burst-effect was remarkably reduced by increasing the content of chitosan. The hybrids with more than 30% chitosan could release the vancomycin for an extended period of time in a controlled manner.

Functionally gradient chitosan/hydroxyapatite composite scaffolds for controlled drug release

This study explored the potential of chitosan/hydroxyapatite (HA) composites to act as a controlled drug delivery system by developing functional scaffolds with a gradient of structure and drug concentration. Firstly, a porous composite scaffold was prepared and tetracycline hydrochloride (TCH) was impregnated in the scaffold as a model drug. The pore size of the scaffold was negatively dependent on the HA content and ranged about 40-250 microm. Subsequently, a porous chitosan/HA composite layer without drug was coated on the scaffold to create a gradient drug concentration in the specimen. The in vitro drug-release test demonstrated that the porous layer without drug on the outer surface of the scaffold significantly reduced the initial burst of drug release and extended the release period. Finally, a successive and dense chitosan/HA composite layer endowed the scaffold with a sustained, drug-release pattern without any initial drug burst. These findings confirmed the high effectiveness of the hybrid scaffolds in regulating the release of drugs, and hence their capability to serve as a temporary drug carrier in tissue regeneration. These functional scaffolds also have potential application to the delivery of some bioactive molecules such as growth factors.