Development of bone plates for fracture of long bones in resorbable composite with osteostimulation effect

Abstract

Bone plates for internal fracture have been used for more than 100 years. Those plates are usually made from titanium or stainless steel alloys. Metallic bone plates show inconveniences like corrosion and stress shielding. Resorbable bone plates have become of particular interest because they permit the gradual increase of stress on the bone as it progresses through healing; thus stress shielding can be reduced. Besides that, they avoid an additional surgery to remove the plate.Accordingly Gaiarsa (2012) ankle fracture is very frequent, occurring in Finland about 154 fractures per 100.000 inhabitants each year and 53% are unstable fracture and need surgical procedure. The same author stated that 30 to 40% of metallic bone plates for ankle are removed. Kukk and Nurmi (2009) reported 16% of cases in USA need removal surgery during post operative first year. At this project we will develop plates for fibula osteosynthesis by resorbable thermoplastic matrix reinforced with resorbable silicate glass fiber composite. In the first phase we intend to manufacture and characterize bone plates with elastic modulus similar to cortical bone to avoid stress shielding. They are supposed to have higher flexural strength than pure resorbable polymer plates available in the market. The evaluation of in vitro degradation of the plates by ASTM F1635-04 is part of scope of phase 1. We intend to implant those plates in animal models for second phase to check if degradation products of silicon oxide rich glass fiber have osteostimulation effect and antimicrobial properties, besides the validation of in vitro degradation results. Although the bone plate model selected to study was fibula bone plate, the know how acquired in the project will be used to develop long bones which do not have similar resorbable plates in the market.The project will start with plate design and mold and device project. The prototypes will be formed by hot compression mold, then EtO sterilization and evaluation of mechanical properties such as elastic modulus and flexural strength. After validation of strength we will begin in vitro degradation essay, where the prototypes will be immersed on thermostatic bath at 37ºC with PBS, pH=7,4 for 32 weeks. After determined time period we will check loss of weight, inherent viscosity drop and flexural strength.We expect to obtain bone plates with improved mechanical properties compared with pure resorbable polymer available at the market, enabling the development of thinner bone plates. Those plates will have elastic modulus closer to the bone, avoiding stress shielding. The use of those plates will reduce patient morbidity, preventing revision surgeries and saving the cost associated to this surgery. Thinner bone plates will give more comfort to patients and speed up patient recovering by stimulation of bone tissue growth at fracture site. (AU)