Release of sodium fluoride from poly (L-lactic acid) implants characterized by thermal history

The method of injection molding of the melt of poly(L-lactic (PLLA), M-w 11 730, containing 7.5% of particles of sodium fluoride smaller than 1 mum wa s employed to prepare cylinders of a diameter of 2 and 10 mm in length. The se matrices with an insoluble active ingredient with an amorphous structure of the carrier obtained by rapid cooling of the melt were annealed at temp eratures from 70 to 140 degreesC in the medium of a hot-air drying plant an d liquid paraffin. It has been found that crystallization of PLLA manifeste d by the rapidity of release of sodium fluoride does not take place at a te mperature of 70 degreesC; at a temperature of 75 degreesC the effect of ann ealing of polyester matrices on the decrease in the rapidity of sodium fluo ride release was already perceptible. Also in annealing of matrices at temp eratures of 120 and 140 degreesC an identical deceleration of sodium fluori de release as that at 75 degreesC took place; the rapidity of the developme nt of an effective crystalline phase was higher at higher temperatures. The method of interval cooling with the first stage of slow cooling and the se cond stage of rapid cooling of the melt of PLLA with 15% sodium fluoride fi xed the structure achieved till the moment of the change in the rapidity of cooling. This revealed the temperature range of the development of the eff ective crystalline phase from the viewpoint of sodium fluoride release lyin g between 92 and 122 degreesC. (C) 2001 Kluwer Academic Publishers.