Nature-inspired discontinuous calcium coatings on polyglycolic acid for orthopaedic applications

Abstract

Non-union in spinal fusion surgeries (SF) is a key cause of failure. Demineralized bone matrix is used in SFs to facilitate bone growth throughout the segment, and polyglycolic acid (PGA) meshes are used for their containment. A discontinuous calcium mineral coating could transform the function of PGA meshes from passive to active, where dissolved calcium ions could act as a chemoattractant for bone cells or it could form a barrier to prevent hydrolytic degradation of the mesh to better align its degradation profile with the fusion process. Challenges to depositing a mineral coating on PGA include its low glass transition temperature (~ 35 °C) and hydrolytic degradation.Inspired by calcite rafts in limestone cave pools, calcite grains were deposited on PGA meshes at the air–solution interface of supersaturated Ca(HCO3)2 (33 °C 6 h). X-ray diffraction (XRD) and 3D confocal microscopy were performed to assess phase composition and coating morphology. Durability was qualitatively assessed by mechanical tests. In vitro incubation was performed to elucidate the dynamic interactions between coating dissolution and PGA degradation; pH and calcium concentration of the solution were measured.XRD confirmed that coated PGA meshes were comprised of PGA and crystalline calcite. 3D confocal microscopy showed that the coatings were discontinuous and comprised of rhombohedral microcrystals. Retention of the particles following ultrasonic treatment and flexure/tensile testing indicates durability. Notably, the grains were compliant as the mesh was contorted. The interaction effect between the incubation time and pH for the uncoated and coated samples was statistically significant (p < 0.05).Graphical