In vitro tobramycin elution analysis from a novel β-tricalcium phosphate-silicate-xerogel biodegradable drug-delivery system

• Published in: Journal of biomedical materials research. Part B, Applied biomaterials Vol. 70B; no. 1; pp. 1 - 20
• Main Authors: DiCicco, Michael, Goldfinger, Aaron, Guirand, Felix, Abdullah, Aquill, Jansen, Susan A.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 15.07.2004
• Subjects: Anti-Bacterial Agents - chemistry; Anti-Bacterial Agents - metabolism; Anti-Bacterial Agents - therapeutic use; Benzoates - chemistry; Biocompatible Materials - chemistry; Biocompatible Materials - metabolism; Bone Substitutes - chemistry; Bone Substitutes - metabolism; Calcium Carbonate - chemistry; Calcium Carbonate - metabolism; Calcium Phosphates - chemistry; Calcium Phosphates - metabolism; Drug Delivery Systems; drug-delivery system; fluorescence; Gels - chemistry; Gels - metabolism; Humans; Hydroxyapatites - chemistry; Hydroxyapatites - metabolism; Materials Testing; Molecular Structure; Osteomyelitis - drug therapy; Quinolines - chemistry; Reproducibility of Results; silicate xerogel; Silicates - chemistry; Silicates - metabolism; tobramycin; Tobramycin - chemistry; Tobramycin - metabolism; Tobramycin - therapeutic use; β-tricalcium phosphate
• ISSN: 1552-4973; 1552-4981
• DOI: 10.1002/jbm.b.30014

This in vitro research analyzed local tobramycin elution characteristics from a novel, biodegradable drug delivery system, consisting of a β‐TCP bone substitute, VITOSS™, encapsulated with silicate xerogel prepared by the sol‐gel process. Tobramycin elution from silicate‐xerogel‐encapsulated VITOSS was compared directly with non‐silicate‐xerogel‐encapsulated VITOSS to assess whether xerogels are effective in delivering greater tobramycin quantities in a controllable, sustained manner crucial for microbial inhibition. Tobramycin elution characteristics indicate an initial release maximum during the first 24 h that diminishes gradually several days after impregnation. The copious tobramycin quantity eluted from the VITOSS/silicate‐xerogel systems is attributed to various factors: the intrinsic ultraporosity and hydrophilicity of VITOSS, the ability of tobramycin to completely dissolve in aqueous media, tobramycin complexation with highly polar SO 42− salts that further assist dissolution, and ionic exchanges between VITOSS and the environment. Silicate‐xerogel–encapsulated VITOSS eluted 60.65 and 61.31% of impregnated tobramycin, whereas non‐silicate‐xerogel–encapsulated VITOSS eluted approximately one‐third less impregnated tobramycin, at 21.53 and 23.60%. These results suggest that silicate xerogel optimizes tobramycin elution because of its apparent biodegradability. This mechanism occurs through xerogel superficial acidic sites undergoing exchanges with various ions present in the leaching buffer. Tobramycin elution kinetics were evaluated, and demonstrate that first‐order elution rate constants are considerably less when silicate xerogels are employed, following a more uniform exponential decay‐type mechanism, thus bolstering controlled release. Overall, tobramycin elution rates adhere to linear‐type Higuchi release profiles. Elution rate constants are initially first order, and taper into zero‐order elution kinetics in the latter stages of release. Because VITOSS and silicate xerogel are completely biodegradable, essentially all impregnated tobramycin will be delivered to the surgical site after implantation. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 70B: 1–20, 2004