The Long-term Biological Performance Of Poly-L-lactide/Poly-L-lactide Grafted Nano-hydroxyapatite (PLLA/PLLA-gHA) Bone Plates

ObjectiveThis paper aims to study the long-term (2 years'period) chronic toxicity of poly-L-lactide/poly-L-lactide grafted nano-hydroxyapatite bone plates during degradation. MethodsAdult Beagle dogs weighed 13-15kg, female and male alternatively, without trauma history in the head and neck. Fracture modeling was conducted artificially on the mandible between molar teeth and premolar teeth in each dog, undergoing fixation with poly-L-lactide/poly-L-lactide (PLLA/PLLA-gHA) plates, and PLLA/PLLA-gHA bone plates were implanted into the erector spinae. Postoperative dietary, movement and wound healing was observed. On the predetermined time point, the blood was collected by vein for blood biochemical assays. And then, the weigh loss and degradation of bone plates, as well as the histopathology around bone plates, were detected.ResultsEvection was observed on the mandible after surgery. Dietary and movement were normal. Three days after operation, mandible had little swelling but healed without hyperaemia and secretion in one week. Each dog had normal information.After 24 months, PLLA/PLLA-gHA bone plates implanted into the back muscles and mandibles swelled in volume, maintained certain shapes, and displayed hollowed white fragile. The bioadsorption of bone plates by dog was 38.76% corresponding to the mandible-implanting plates. The degradation (molecular weight loss) was 92.31%, less than PLLA plates (94.77%). Electronic scanning microscopy showed the section of materials had many splits and holes, indicating the substantial degradation.After 24 months, organs were normal, fibrous membranous capsule around the plates turned to be very thin without inflammation or lymph infiltration, the bone fracture healed completely by implanting PLLA/PLLA-gHA plates, the blood biochemistry was observed normal including total protein, total bilirubin, triglyeride, glucose, ALT and globulin. As the implanting PLLA/PLLA-gHA plate was increasingly absorbed in vivo, the concentration of LDH also increased.ConclusionsThis paper implanted new bone plates, tested the implanting reaction, conducted the histopathology assay and the biochemical assay, tested the adsorption and degradation of bone plates, and studied the correlation of adsorption with enzyme contents (LDH). Thereupon, this paper evaluated the locally implanting reaction and the 2-year long-term chronic toxicity in animals.This trial found that the PLLA/PLLA-gHA bone plate had weigh loss up to 38.76% in 2 years; the degradation (molecular weight loss) to 92.31%; maintained certain forms, did not fuse to tissues around; white fragile; did not induce any local tissue deforming or uncomforting, either not caused the delayed inflammation or other malefactions.This copyrighted PLLA/PLLA-gHA bone plate did not cause any malefactions but fibrous capsule encapsulating plates during the 2-year period of degradation in vivo dogs. Therefore, it has not the delayed long-term systemic chronic toxicity to animals and can serve as the auxiliary materials of internal fixation to repairing the impaired bones.This study supplementary evaluated the biological risks of PLLA/PLLA-gHA bone plates, and confirmed that PLLA/PLLA-gHA has the satisfactory biological safety and could be applied to clinical surgery and other fundamental research.