Development of Novel Adhesives for Sternal and Radial Fixation
Authors: Mehrvar Cina 
Published: June 2024

Wrist fractures can be difficult to treat due to advanced age of the patient, medical co-morbidities, and comminution of bone. In addition, cerclage wires remain the current standard of care following median sternotomy, despite significant complications including dehiscence and infection. Glass polyalkenoate cements (GPCs) have been widely used in dentistry and ear, nose, and throat (ENT) applications but have yet to be indicated for orthopaedic applications. This dissertation focuses on the development of novel GPCs to improve on current treatments for distal
radial fixation and sternal fixation.
Two injectable GPCs, derived from either glass A (mole fraction: SiO2:0.48, ZnO:0.36, CaO0.12, SrO: 0.04), Glass B (mole fraction: SiO2:0.48, ZnO:0.355, CaO:0.06, SrO:0.08, P2O5:0.02, Ta2O5:0.005), or Glass C (mole fraction: SiO2:0.48, ZnO:0.351, CaO:0.073, SrO:0.143, P2O5:0.027) were investigated using both sternal and radial cadaveric models. Radii fixated with a GPC were ~60% as strong as their intact biological pair when tested to failure. Radii fixated with a GPC were found to be significantly stiffer than their biological pairs fixated with a volar locking plate when tested under fatigue. Further, midline sternal displacement for adhesive-enhanced sternal closures were significantly less than standard wire cerclage.
Novel GPCs were investigated in a sheep model by filling a non-critical defect. The GPCs were derived from either Glass A or Glass B at a particle size of <45 m, with a cement formulation consisting of [10g glass : 4g (poly)acrylic acid : 6ml water : 0.75g Trisodium Citrate]. The GPCs demonstrated significant bone resorption surrounding the material and were deemed non-viable in-vivo formulations. The cause of the resorption was believed to be the persistent inflammatory reaction surrounding numerous degraded GPC fragments given that debris release has been observed to cause bone resorption in studies related to polyethylene biomaterials. As a result, the GPC formulation derived from Glass A was improved by increasing the PAA molecular weight from 50k to 210k Mw,
increasing the glass particle size from 20-45 m to 45-63 m and reducing the P:L ratio from 1:1 to 1:0.6.
The improved GPC (GPC+) was investigated in a rabbit model, followed by a sheep model, by filling a non-critical defect. MicroCT images from all three GPC+ samples in the rabbit model did not show any bone resorption, while histology slides showed normal bone turnover. In the sheep model, five of seven GPC+ samples were associated with mild bone resorption, occurring because of increased osteoclast activity. However, two samples in sheep exhibited no resorption and appeared to stimulate increased bone density at the implant site. The in-vivo response with regards to GPC+ was more favorable than in the previous in-vivo trial.
To the best knowledge of the candidate, this dissertation is the first to report a GPC formulated using a glass particle size of 45–63 m, a GPC investigated for sternal and distal radial fixation using a cadaveric model, as well as the biocompatibility of a GPC using a sheep model.