Glass formation and chemical durability of dysprosium lithium borate glasses intended for in vivo radiation synovectomy

The glass formation and structure/property relationships for Dy₂O₃-Li₂O-B₂O₃ glasses were investigated. Such glasses are currently being considered for in vivo radiation delivery vehicles. Chemical dissolution tests were conducted in simulated synovial fluid (pH 7.4, at 37°C, for 11 d) to evaluate the release of dysprosium from selected glasses. The chemical durability, T_g, n_D and density increased as either the Li₂O or Dy₂O₃ content in a glass was increased. Such property trends are attributed to increased crosslinking within the glass structure as BO₃ triangles are converted to BO₄ tetrahedra. A proposed structural model assumes dysprosium is incorporated into the glass with a coordination number of eight and is surrounded by four BO₄ tetrahedra. Glasses containing ≥ 1.0 mol% Dy₂O₃ released less than 0.1% of their initial dysprosium content after being immersed in simulated synovial fluid for 11 d at 37°C. These glasses are considered safe for in vivo radiation delivery from the standpoint of radiation release, since dysprosium will be the only radioisotope in the glass during treatment.