Influence of sterilization on injectable bone biomaterials

Injectable biomaterials used in bone surgery include acrylic bone cements, calcium phosphate cements, and new composite-type biomaterials with a miner al content and an organic phase dispersed or dissolved in water. Cellulose derivatives, chitosan solutions, alginates, and other polymers are studied as useful modifiers and binding agents in calcium phosphate cements. We hav e developed proprietary polyester copolymers including lactic acid moieties and present here results concerning the effect of sterilization on the phy sico-chemical properties of derived bone biomaterials, Chitosan solutions s how a dramatic decrease in viscosity after 25-kGy gamma sterilization, Aque ous copolylactic solutions also show, by capillary electrophoresis, that hy drolysis occurs to liberate monomers after 25-kGy gamma sterilization, Heat sterilization also degrades chitosan solutions, and ultrafiltration is dif ficult because of high viscosity. However, apatite-copolylactic solids can he steam sterilized without deterioration. Gelatin has been used as a natur al polymer to bind apatite particles. Gel exclusion chromatography reveals crosslinking of the chains by irradiation. Standard acrylic cements contain monomers sterilized by ultrafiltration because they do not tolerate irradi ation. We have used ultrafiltration to prepare aqueous copolylactic solutio ns without polymer hydrolysis, Implantation of calcium phosphate cement mod ified by; copolylactic acid in a rabbit metaphyseal model defect shows prog ressive substitution of the biomaterial by new bone tissue. At 3 months, a mild inflammatory reaction still remains associated with the continuing res orption of the biomaterial. These results show that interesting biological properties can be obtained with products not sterilized by irradiation. Und oubtedly, many biopolymers are fragile and, like reactive monomers, need to be sterilized by special methods if they are to he used in injectable, liq uid form, (Bone 25:63S-65S; 1999) (C) 1999 by Elsevier Science Inc, All rig hts reserved.