Title: Sol-gel CaP deposition on magnesium alloy skeletal fixation devices for time certain commencement of bioresorption. INTRODUCTION: Resorbable magnesium alloys have been explored for skeletal fixation applications in order to remove the risk of device failure due to stress shielding, a phenomenon associated with the current standard-of-care, inert fixation device material, Ti-6Al-4V (aka Ti64). Ti64 has a bulk stiffness of 116 GPa whereas most biomedical Mg alloys have a stiffness of less than half that value. The stiffness of cortical bone is usually in the range of 18-25 GPa. Once resorbed, Mg alloys that serve in the role of skeletal fixation pose no risk of interrupting the normal loading of the newly healed bone. However, the bone will not heal if the Mg alloy resorbs too quickly or is not strong enough. Different strategies to produce devices with sufficient resistance to corrosion have been investigated with limited success [1]. We have explored the use of surface coatings to delay Mg alloy degradation until surgically repaired bone has healed. Here we present work on the deposition of a CaP ceramic coating via a sol-gel process on a novel magnesium alloy. METHODS: Cast and heat-treated Mg-1.2Zn-0.5Ca0.5Mn (wt%) cylindrical coupons, polished with grit size up to 2000, were sonicated in absolute ethanol. Next, the coating procedure involves the sequential immersion and air drying of substrates using: 0.1 M titanium(IV) butoxide solution in 1–1(v/v) toluene-ethanol solvent, 1–1(v/v) toluene-ethanol solution, distilled water, a solution of 50 wt% HA and 50 wt% β-TCP nanoparticles dispersed in ethanol (0.9 mg/ml). The procedure, well detailed in [2], was performed for 5, 10, 15, 20 and 25 times to obtain different numbers of layers (i.e., coating thickness). The samples were cross-sectioned and analyzed through SEM to assess the thickness and homogeneity of the coatings and the presence of defects. Immersion tests in Hank's balanced salt solution at 36.5 ± 1 °C were performed based on [1, 3] and according to ASTM G31-72, in triplicates. The coated substrates are weighed before and after immersion tests after removing the corrosion products to estimate the weight loss. Uncoated coupons of the same magnesium alloy are used as a control. RESULTS: Figure 1 shows an SEM image of a coated coupon and the presence of CaP microflakes typical of the deposited coating. As in our prior work, increasing the number of layers in the coating is expected to improve the corrosion resistance of the coupon. Our goal is to delay the commencement of corrosion for 3 months. Fig. 1: SEM image of a sol-gel coated magnesium alloy coupon. DISCUSSION & CONCLUSIONS: The introduction of a surface coating with varying thickness allows modulation of the degradation speed of the studied magnesium alloy, paving the way to proper deployment of stiffness-matched, resorbable skeletal fixation devices. We anticipate titrating coating thickness will allow us to modulate resorption so that the Mg alloy is not exposed to body fluid, and thus degradation does not occur, for 3 months. REFERENCES: 1 D. Cho, T. Avey, K. H. Nam, D. Dean, and A. A. Luo. (2022) Acta Biomater. 150:442–455. 2 A. Chmielewska, T. MacDonald, H. Ibrahim et al. (2020) MRS Commun. 10:467– 474. 3 J. Gonzalez, R. Q. Hou, E. P. S. Nidadavolu, R. Willumeit-Römer and F. Feyerabend, (2018) Bioact. Mater. 3:174–185.
Sol-gel CaP deposition on magnesium alloy skeletal fixation devices for time-certain commencement of bioresorption
M Sanguedolce
;
2023-01-01
Abstract
Title: Sol-gel CaP deposition on magnesium alloy skeletal fixation devices for time certain commencement of bioresorption. INTRODUCTION: Resorbable magnesium alloys have been explored for skeletal fixation applications in order to remove the risk of device failure due to stress shielding, a phenomenon associated with the current standard-of-care, inert fixation device material, Ti-6Al-4V (aka Ti64). Ti64 has a bulk stiffness of 116 GPa whereas most biomedical Mg alloys have a stiffness of less than half that value. The stiffness of cortical bone is usually in the range of 18-25 GPa. Once resorbed, Mg alloys that serve in the role of skeletal fixation pose no risk of interrupting the normal loading of the newly healed bone. However, the bone will not heal if the Mg alloy resorbs too quickly or is not strong enough. Different strategies to produce devices with sufficient resistance to corrosion have been investigated with limited success [1]. We have explored the use of surface coatings to delay Mg alloy degradation until surgically repaired bone has healed. Here we present work on the deposition of a CaP ceramic coating via a sol-gel process on a novel magnesium alloy. METHODS: Cast and heat-treated Mg-1.2Zn-0.5Ca0.5Mn (wt%) cylindrical coupons, polished with grit size up to 2000, were sonicated in absolute ethanol. Next, the coating procedure involves the sequential immersion and air drying of substrates using: 0.1 M titanium(IV) butoxide solution in 1–1(v/v) toluene-ethanol solvent, 1–1(v/v) toluene-ethanol solution, distilled water, a solution of 50 wt% HA and 50 wt% β-TCP nanoparticles dispersed in ethanol (0.9 mg/ml). The procedure, well detailed in [2], was performed for 5, 10, 15, 20 and 25 times to obtain different numbers of layers (i.e., coating thickness). The samples were cross-sectioned and analyzed through SEM to assess the thickness and homogeneity of the coatings and the presence of defects. Immersion tests in Hank's balanced salt solution at 36.5 ± 1 °C were performed based on [1, 3] and according to ASTM G31-72, in triplicates. The coated substrates are weighed before and after immersion tests after removing the corrosion products to estimate the weight loss. Uncoated coupons of the same magnesium alloy are used as a control. RESULTS: Figure 1 shows an SEM image of a coated coupon and the presence of CaP microflakes typical of the deposited coating. As in our prior work, increasing the number of layers in the coating is expected to improve the corrosion resistance of the coupon. Our goal is to delay the commencement of corrosion for 3 months. Fig. 1: SEM image of a sol-gel coated magnesium alloy coupon. DISCUSSION & CONCLUSIONS: The introduction of a surface coating with varying thickness allows modulation of the degradation speed of the studied magnesium alloy, paving the way to proper deployment of stiffness-matched, resorbable skeletal fixation devices. We anticipate titrating coating thickness will allow us to modulate resorption so that the Mg alloy is not exposed to body fluid, and thus degradation does not occur, for 3 months. REFERENCES: 1 D. Cho, T. Avey, K. H. Nam, D. Dean, and A. A. Luo. (2022) Acta Biomater. 150:442–455. 2 A. Chmielewska, T. MacDonald, H. Ibrahim et al. (2020) MRS Commun. 10:467– 474. 3 J. Gonzalez, R. Q. Hou, E. P. S. Nidadavolu, R. Willumeit-Römer and F. Feyerabend, (2018) Bioact. Mater. 3:174–185.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
