Effect of annealing temperature on the degradation of reinforcing fibers for absorbable implants

Abstract

Calcium phosphate fibers designed for reinforcement of bioabsorbable fracture fixation devices were evaluated for their properties upon annealing. The composition of these fibers were 54% PO4, 27% Ca, 12% ZnO, 2.5% NaPO3, and 4.5% Fe2O3, and they were either not annealed, annealed at 250 degrees C, or annealed at 420 degrees C. Chemical degradation, mass loss, and morphology upon degradation were studied. Chemical degradation was performed in Tris-buffered HCl, while mass loss and morphologic studies were performed in both physiologic and nonphysiologic solutions. The results showed that degradation rates for fibers were inversely proportional to the annealing temperature. Mass loss analysis of fibers immersed in the two physiologic solutions (calf serum and simulated body fluid) revealed little change in fiber diameter up to 60 days. Morphologic examination revealed little change in fibers immersed in the two physiologic solutions until 60 days, after which thin shells were found to be peeling off the outer coating of the fiber. Samples in tris-buffered HCl revealed a dramatic difference in mode of degradation among the three fibers. Fibers not annealed and those annealed at lower temperatures underwent a delaminating type of degradation that appeared to destroy the overall integrity of the fiber, whereas fibers annealed at 420 degrees C underwent crater-like deterioration in which the overall alignment of the fiber remained intact. It is therefore concluded that annealing fibers at higher temperatures also undergo a mode of degradation that allows them to maintain their structural integrity. Although annealing fibers close to glass transition temperature may produce an initially weaker fiber, chemical and physical degradation occur much slower, making these fibers most suitable for reinforcement of biodegradable implants.

Phosphate glass fibres and their role in neuronal polarization and axonal growth direction

“…Other authors in the literature investigated the influence of a heat treatment on the dissolution of phosphate glass fibres, and found similar results [38][39][40]. Choueka et al [38] studied the influence of heat treatments on the dissolution of phosphate glass fibres containing zinc and iron. The authors observed that the degradation rates for the fibres were inversely proportional to the annealing temperature.…”

“…Numerous studies in the literature describe a loss of structural integrity of the phosphate glass fibres during dissolution [7,[38][39][40]42,43]. Cozien-Cazuc et al [39,40] observed the formation of an outer hydrated layer and delamination during dissolution on both as-drawn and annealed glass fibres with composition 40P 2 O 5 -20Na 2 O-16CaO-24MgO (mol.%).…”

“…Cozien-Cazuc et al [39,40] observed the formation of an outer hydrated layer and delamination during dissolution on both as-drawn and annealed glass fibres with composition 40P 2 O 5 -20Na 2 O-16CaO-24MgO (mol.%). Choueka et al [38] ob-served thin shells peeling off the outer coating of phosphate glass fibres containing zinc and iron after 2 months in physiological solutions. Abou Neel et al [42] observed the formation of micro-tubes through the degradation of glass fibre with composition 50P 2 O 5 -0.30 CaO-(0.17-0.15)Na 2 O-(0.03-0.05)Fe 2 O 3 (mol.%) after 3 months in deionized water.…”

Degradation and Characterization of Resorbable Phosphate-Based Glass Thin-Film Coatings Applied by Radio-Frequency Magnetron Sputtering

“…Degradation rates are influenced by processing routes, such that thermally annealed glasses degrade at slower rates compared to their melt quenched counterparts 47,[52][53] . Magnetron sputtering produces instantaneously quenched coatings upon a substrate, forming residual tensile stresses within the atomic layers, which may therefore account for higher degradation rates within the glass.…”

“…Magnetron sputtering produces instantaneously quenched coatings upon a substrate, forming residual tensile stresses within the atomic layers, which may therefore account for higher degradation rates within the glass. Cozien-Cazuc et al showed annealing at 5 °C below the Tg for fibres, allowing the structure to reorientate to its more thermodynamically stable position and relieving internal stresses reduced dissolution by half [52][53] .…”